physicsworld--2020-11-13--Ultrafast camera breaks 3D speed record - Physics World

A new camera that takes videos at record-breaking speeds of up to 100 billion frames per second in 3D has been demonstrated by researchers at the California Institute of Technology in the US .
The feat was made possible by a technique known as single-shot stereo-polarimetric compressed ultrafast photography ( SP-CUP ) , and it builds on the group ’ s earlier work – including a camera that takes images at 70 trillion frames per second , which is fast enough to see light travel .
The latest device could prove important for biomedicine , agriculture , electronics and other @ @ @ @ @ @ @ optical imaging .
In order to image processes that take place at the speed of light , researchers need frame rates at the level of one billion frames-per-second ( Gfps ) .
This is way beyond the readout speed of even the most advanced charge-coupled ( CCD ) devices and complementary metal oxide semiconductor ( CMOS ) sensors used in most modern ultrafast photography .
While sub-nanosecond frame interval devices have been developed , their low sequence depth ( that is , a low number of frames captured per acquisition ) means that @ @ @ @ @ @ @ luminescent and colour-selective objects such as distant stars and bioluminescent molecules .
Imaging high-speed processes in multiple dimensions poses additional challenges .
Most high-dimensional optical imaging systems acquire data by scanning – that is , they capture either a one-dimensional ( 1D ) column or a two-dimensional ( 2D ) slice of an object in separate measurements .
By combining a series of such measurements , these systems can build up higher-dimensional images of the object .
This approach has its drawbacks , however , with the main one being that successive measurements @ @ @ @ @ @ @ precise for the multidimensional picture to “ stitch together ” properly .
To overcome this ( and other inherent problems ) , imaging specialists have turned instead to single-shot high-dimensional CUP optical imaging techniques .
This form of image acquisition operates in parallel , and it has improved the efficiency of CUP to such an extent that an offshoot known as single-shot temporal imaging is creating a flurry of interest in the optical imaging community .
Using this technique , it is possible to capture a photon ’ s time of arrival without @ @ @ @ @ @ @ that could help scientists better understand fleeting phenomena in physics , chemistry and biology that are difficult or impossible to reproduce .
The single-shot stereo-polarimetric compressed ultrafast photography ( SP-CUP ) technique developed by Lihong Wang and colleagues combines many of these previous techniques into a single device .
The combination of compressed sensing , streak imaging ( a traditional 1D ultrafast imaging approach ) , spectroscopy and polarimetry produces a single-shot passive ultrafast imaging device that can capture non-repeatable phenomena evolving in 5D ( three spatial dimensions , plus time and ψ @ @ @ @ @ @ @ of reflected light ) with picosecond temporal resolution .
In Wang ’ s view , his team ’ s new camera “ sees ” more like humans do .
“ When we look at the world around us , we perceive that some objects are closer to us and some further away , ” he explains .
“ This depth perception is possible because our two eyes each observe objects and their surroundings from a slightly different angle .
The information from these two images is combined by the brain into a single @ @ @ @ @ @ @ in essentially the same way , and like humans , it sees in stereo .
“ While the camera does only have one lens , it functions as two halves that provide two views with an offset , ” Wang says .
“ Two channels in the device mimic our eyes.
” In addition , he notes that his group ’ s camera has an ability that no human possesses : it can sense the polarization of light waves .
Wang believes that the SP-CUP ’ s combination of high-speed three-dimensional imagery and @ @ @ @ @ @ @ a powerful tool that may be applicable to a wide variety of scientific problems .
One area of particular interest is the physics of sonoluminescence , a phenomenon in which sound waves create tiny bubbles in water or other liquids .
As the bubbles rapidly collapse after forming , they emit a burst of light .
“ Some people consider this one of the greatest mysteries in physics , ” Wang says .
“ When a bubble collapses , its interior reaches such a high temperature that it generates light .
The process @ @ @ @ @ @ @ because it all happens so fast , and we ’ re wondering if our camera can help us figure it out.
” Full details of the research are reported in Nature Communications .

A pulse of laser light passing through a laser-scattering medium and bouncing off reflective surfaces. Credit: Caltech
A new camera that takes videos at record-breaking speeds of up to 100 billion frames per second in 3D has been demonstrated by researchers at the California Institute of Technology in the US. The feat was made possible by a technique known as single-shot stereo-polarimetric compressed ultrafast photography (SP-CUP), and it builds on the group’s earlier work – including a camera that takes images at 70 trillion frames per second, which is fast enough to see light travel. The latest device could prove important for biomedicine, agriculture, electronics and other fields that rely on fast, high-dimensional optical imaging.
In order to image processes that take place at the speed of light, researchers need frame rates at the level of one billion frames-per-second (Gfps). This is way beyond the readout speed of even the most advanced charge-coupled (CCD) devices and complementary metal oxide semiconductor (CMOS) sensors used in most modern ultrafast photography. While sub-nanosecond frame interval devices have been developed, their low sequence depth (that is, a low number of frames captured per acquisition) means that they cannot be used to image luminescent and colour-selective objects such as distant stars and bioluminescent molecules.
Imaging high-speed processes in multiple dimensions poses additional challenges. Most high-dimensional optical imaging systems acquire data by scanning – that is, they capture either a one-dimensional (1D) column or a two-dimensional (2D) slice of an object in separate measurements. By combining a series of such measurements, these systems can build up higher-dimensional images of the object. This approach has its drawbacks, however, with the main one being that successive measurements in the series need to be very precise for the multidimensional picture to “stitch together” properly.
Combining previous techniques
To overcome this (and other inherent problems), imaging specialists have turned instead to single-shot high-dimensional CUP optical imaging techniques. This form of image acquisition operates in parallel, and it has improved the efficiency of CUP to such an extent that an offshoot known as single-shot temporal imaging is creating a flurry of interest in the optical imaging community. Using this technique, it is possible to capture a photon’s time of arrival without repeated measurements – a hitherto hard-to-achieve feat that could help scientists better understand fleeting phenomena in physics, chemistry and biology that are difficult or impossible to reproduce.
The single-shot stereo-polarimetric compressed ultrafast photography (SP-CUP) technique developed by Lihong Wang and colleagues combines many of these previous techniques into a single device. The combination of compressed sensing, streak imaging (a traditional 1D ultrafast imaging approach), spectroscopy and polarimetry produces a single-shot passive ultrafast imaging device that can capture non-repeatable phenomena evolving in 5D (three spatial dimensions, plus time and ψ, the angle of the linear polarization of reflected light) with picosecond temporal resolution.
Like human vision
In Wang’s view, his team’s new camera “sees” more like humans do. “When we look at the world around us, we perceive that some objects are closer to us and some further away,” he explains. “This depth perception is possible because our two eyes each observe objects and their surroundings from a slightly different angle. The information from these two images is combined by the brain into a single 3D image.”
The SP-CUP device works in essentially the same way, and like humans, it sees in stereo. “While the camera does only have one lens, it functions as two halves that provide two views with an offset,” Wang says. “Two channels in the device mimic our eyes.” In addition, he notes that his group’s camera has an ability that no human possesses: it can sense the polarization of light waves.
Powerful tool
Wang believes that the SP-CUP’s combination of high-speed three-dimensional imagery and the use of polarization information makes it a powerful tool that may be applicable to a wide variety of scientific problems. One area of particular interest is the physics of sonoluminescence, a phenomenon in which sound waves create tiny bubbles in water or other liquids. As the bubbles rapidly collapse after forming, they emit a burst of light.
“Some people consider this one of the greatest mysteries in physics,” Wang says. “When a bubble collapses, its interior reaches such a high temperature that it generates light. The process that makes this happen is very mysterious because it all happens so fast, and we’re wondering if our camera can help us figure it out.”
Full details of the research are reported in Nature Communications.


physicsworld--2020-11-13--Quantum technology: why the future is already on its way - Physics World

Why do you need a quantum computer ?
Well , you don ’ t – unless someone else has one .
And if they have a quantum computer , you ’ ll want one too .
Driven by the promise of new technologies that will deliver benefits for all of society , nations around the world are investing heavily in the field .
When it comes to quantum computing , no-one wants to miss out – and that desire is triggering a kind of global arms race .
While a standard computer handles digital bits of 0s and 1s , @ @ @ @ @ @ @ , which can take any value between 0 and 1 .
And if you entangle the qubits , you can solve problems that classical computers can not .
A future quantum computer could , for example , crack any of today ’ s common security systems – such as 128-bit AES encryption – in seconds .
Even the best supercomputer today would take millions of years to do the same job .
The US National Institute of Standards and Technology has already said that quantum computers will be able to crack the existing @ @ @ @ @ @ @ 2029 .
That prospect means businesses and governments are scrambling to improve the security of conventional networks , for example by using quantum-key cryptography .
That ’ s a new market for quantum technology that ’ s expected to be worth anything from $ 214m to $ 1.3bn by 2024 ( depending on which market survey you read ) .
With all that in mind , I ’ m delighted that here in the UK , construction of the new National Quantum Computing Centre ( NQCC ) will start this year .
Thanks @ @ @ @ @ @ @ Research and Innovation ( UKRI ) , the centre is being built at the Harwell lab of the Science and Technology Facilities Council in Oxfordshire .
When it opens in late 2022 , the NQCC will bring together academia , business and government with the aim of delivering 100+ qubit user platforms by 2025 , thereby allowing UK firms to tap fully into this technology ’ s potential .
The NQCC is part of a £1bn , 10-year investment by the UK ’ s National Quantum Technologies Programme , which was launched by @ @ @ @ @ @ @ has already created a national network of quantum technology hubs in quantum sensors and metrology ( Birmingham ) , quantum communications ( York ) , quantum enhanced imaging ( Glasgow ) , and quantum IT ( Oxford ) .
Seeking to develop and commercialize new technology , the hubs are part of a growing quantum industry in the UK that saw more than 30 quantum start-ups founded by the end of 2019 .
The visionaries behind the programme were none other than Peter Knight – a former president of the Institute of Physics @ @ @ @ @ @ @ ( the IOP ’ s current honorary treasurer ) .
The potential benefits of quantum technology to the UK economy were discussed at an online seminar run by the IOP ’ s Business Innovation and Growth group , which featured the IOP ’ s current president elect , Sheila Rowan , as well as Knight and the UKRI ’ s “ challenge director ” , Roger McKinley .
Last year , researchers at Google claimed that their Sycamore processor , which has 53 superconducting qubits , was able to verify in just 200 @ @ @ @ @ @ @ randomly distributed .
The same calculation , the firm said , would take 10,000 years on IBM ’ s Summit machine , which was the world ’ s most powerful supercomputer at the time .
IBM hit back , insisting that , with some clever classical programming , its machine can solve the problem in 2.5 days .
Either way , Google had reached a significant milestone towards realizing the immense promise of quantum computers – “ a wonderful achievement ” as Knight put it .
“ It shows that quantum computing is @ @ @ @ @ @ @ he added .
However , to do something really useful with quantum computers will require significantly more than 50 qubits .
And given that a single qubit will set you back $ 10,000 or more , quantum computers will become commercially viable only when the cost per qubit has dropped dramatically .
What ’ s more , we ’ ll have to get round the fact that current qubit devices are super-sensitive to external disturbances , so they have to be enclosed in sealed , cryogenically cooled boxes to maintain their quantum behaviour @ @ @ @ @ @ @ when ENIAC – the first general purpose digital computer – was released in 1945 , it could do in 30 seconds what a human could do in 20 hours .
But with its vacuum tubes and vast size , ENIAC was as far removed from today ’ s super-advanced classical devices as today ’ s quantum computers will be from those in 50 years ’ time .
That ’ s why the race is on to scale and deliver a practical quantum computer , with many competing platforms , technologies and companies in @ @ @ @ @ @ @ be replaced by something cheaper , more practical and scalable .
Proper quantum computers will also require operating systems , programming languages , algorithms , input and output hardware , as well as the all-important storage and memory .
That ’ s why I was particularly pleased to see ORCA – a UK firm – win one of the IOP ’ s business awards this year for developing a promising new approach to quantum computing memory , which allows single and entangled photons to be stored and synchronized .
Another key commercial milestone @ @ @ @ @ @ @ firm Cambridge Quantum Computing ( CQC ) launched the world ’ s first cloud-based Quantum Random Number Generation ( QRNG ) service using an IBM quantum computer .
CQC offers true maximal randomness or entropy , which is impossible with a classical device and vital for accurate modelling and security applications .
It ’ s taken us 75 years to get from ENIAC to today ’ s integrated microprocessors , data centres , cloud-computing derived from “ quantum 1.0 ” devices ( semiconductor junctions , lasers and so on ) .
Imagine a @ @ @ @ @ @ @ devices and computers 75 years from now .
It ’ s great to see such a co-ordinated and visionary programme here in the UK right now .
• None An industry panel featuring members of the UK quantum-computing sector formed part of the IOP ’ s recent Quantum2020 conference

Physics World, where it appeared under the headline "A quantum future". Members of the Institute of Physics can enjoy the full issue Taken from the November 2020 issue of, where it appeared under the headline "A quantum future". Members of the Institute of Physics can enjoy the full issue via the Physics World app
With a new era of quantum technology beckoning, James McKenzie reflects on recent milestones in the quantum computing “arms race”
Little wonder Potential technological benefits are driving advances in quantum computing. (Courtesy: iStock/johnason)
Why do you need a quantum computer? Well, you don’t – unless someone else has one. And if they have a quantum computer, you’ll want one too. Driven by the promise of new technologies that will deliver benefits for all of society, nations around the world are investing heavily in the field. When it comes to quantum computing, no-one wants to miss out – and that desire is triggering a kind of global arms race.
While a standard computer handles digital bits of 0s and 1s, quantum computers use quantum bits or qubits, which can take any value between 0 and 1. And if you entangle the qubits, you can solve problems that classical computers cannot. A future quantum computer could, for example, crack any of today’s common security systems – such as 128-bit AES encryption – in seconds. Even the best supercomputer today would take millions of years to do the same job.
I’m delighted that here in the UK, construction of the new National Quantum Computing Centre will start this year
The US National Institute of Standards and Technology has already said that quantum computers will be able to crack the existing public-key infrastructure like 128-bit AES encryption by 2029. That prospect means businesses and governments are scrambling to improve the security of conventional networks, for example by using quantum-key cryptography. That’s a new market for quantum technology that’s expected to be worth anything from $214m to $1.3bn by 2024 (depending on which market survey you read).
Important investments
With all that in mind, I’m delighted that here in the UK, construction of the new National Quantum Computing Centre (NQCC) will start this year. Thanks entirely to a £93m investment from UK Research and Innovation (UKRI), the centre is being built at the Harwell lab of the Science and Technology Facilities Council in Oxfordshire. When it opens in late 2022, the NQCC will bring together academia, business and government with the aim of delivering 100+ qubit user platforms by 2025, thereby allowing UK firms to tap fully into this technology’s potential.
The NQCC is part of a £1bn, 10-year investment by the UK’s National Quantum Technologies Programme, which was launched by the UK government in 2013. It has already created a national network of quantum technology hubs in quantum sensors and metrology (Birmingham), quantum communications (York), quantum enhanced imaging (Glasgow), and quantum IT (Oxford). Seeking to develop and commercialize new technology, the hubs are part of a growing quantum industry in the UK that saw more than 30 quantum start-ups founded by the end of 2019.
The visionaries behind the programme were none other than Peter Knight – a former president of the Institute of Physics (IOP) – and David Delpy (the IOP’s current honorary treasurer). The potential benefits of quantum technology to the UK economy were discussed at an online seminar run by the IOP’s Business Innovation and Growth group, which featured the IOP’s current president elect, Sheila Rowan, as well as Knight and the UKRI’s “challenge director”, Roger McKinley.
To do something really useful with quantum computers will require significantly more than 50 qubits
Last year, researchers at Google claimed that their Sycamore processor, which has 53 superconducting qubits, was able to verify in just 200 seconds that a set of numbers was randomly distributed. The same calculation, the firm said, would take 10,000 years on IBM’s Summit machine, which was the world’s most powerful supercomputer at the time. IBM hit back, insisting that, with some clever classical programming, its machine can solve the problem in 2.5 days. Either way, Google had reached a significant milestone towards realizing the immense promise of quantum computers – “a wonderful achievement” as Knight put it. “It shows that quantum computing is really hard but not impossible,” he added.
However, to do something really useful with quantum computers will require significantly more than 50 qubits. And given that a single qubit will set you back $10,000 or more, quantum computers will become commercially viable only when the cost per qubit has dropped dramatically. What’s more, we’ll have to get round the fact that current qubit devices are super-sensitive to external disturbances, so they have to be enclosed in sealed, cryogenically cooled boxes to maintain their quantum behaviour.
It’s worth recalling that when ENIAC – the first general purpose digital computer – was released in 1945, it could do in 30 seconds what a human could do in 20 hours. But with its vacuum tubes and vast size, ENIAC was as far removed from today’s super-advanced classical devices as today’s quantum computers will be from those in 50 years’ time. That’s why the race is on to scale and deliver a practical quantum computer, with many competing platforms, technologies and companies in the running.
Towards quantum 2.0
Superconducting qubits might ultimately be replaced by something cheaper, more practical and scalable. Proper quantum computers will also require operating systems, programming languages, algorithms, input and output hardware, as well as the all-important storage and memory. That’s why I was particularly pleased to see ORCA – a UK firm – win one of the IOP’s business awards this year for developing a promising new approach to quantum computing memory, which allows single and entangled photons to be stored and synchronized.
Read more Inside the quantum bubble
Another key commercial milestone took place in September, when UK firm Cambridge Quantum Computing (CQC) launched the world’s first cloud-based Quantum Random Number Generation (QRNG) service using an IBM quantum computer. CQC offers true maximal randomness or entropy, which is impossible with a classical device and vital for accurate modelling and security applications.
It’s taken us 75 years to get from ENIAC to today’s integrated microprocessors, data centres, cloud-computing derived from “quantum 1.0” devices (semiconductor junctions, lasers and so on). Imagine a world with advanced “quantum 2.0” devices and computers 75 years from now. It’s great to see such a co-ordinated and visionary programme here in the UK right now.
An industry panel featuring members of the UK quantum-computing sector formed part of the IOP’s recent Quantum2020 conference


physicsworld--2020-11-13--Jupiter’s moon Europa could glow in the dark - Physics World

Ice on the night-side surface of Jupiter ’ s moon Europa could emit a unique glow , according to US-based scientists Murthy Gudipati , Bryana Henderson at NASA ’ s Jet Propulsion Laboratory and Fred Bateman at the National Institute of Standards and Technology .
The researchers did lab-based experiments that suggest that the ice emits visible light as a result of being bombarded by high-energy particles .
Their research provides important information for NASA ’ s upcoming Europa Clipper mission – which could offer an unprecedented glimpse of the composition of Europa ’ s subsurface ocean .
Europa is @ @ @ @ @ @ @ as it passes through the strong magnetic field of its host planet , its surface is bombarded by high-energy protons , electrons , and ions .
As these particles interact with the moon ’ s salt- and ice-rich crust , they could trigger complex physical and chemical processes that have important consequences for Europa ’ s chemical composition .
On geological timescales , the energy-rich products of these reactions could be transported through Europa ’ s crust , before entering the vast ocean of liquid water beneath .
Warmed by tidal forces , @ @ @ @ @ @ @ promising candidate locations for extraterrestrial life in the solar system .
Determining the composition of salt on Europa ’ s surface should therefore provide important clues about whether life could exist in its ocean .
In their study , the trio fired high-energy electrons at water ice containing different types of salt and analysed the light emitted by their samples .
They discovered that the samples emitted characteristic light spectra at visible wavelengths .
They also found that emission was enhanced in ice containing magnesium-sulphate based epsomite , and that ice containing sodium @ @ @ @ @ @ @ less light .
On Europa ’ s surface , this light emission would create a unique nighttime glow , not likely to be found elsewhere in the solar system .
By mapping variations in this glow on Europa ’ s surface , the trio believe that scientists could determine what salts are present within Europa ’ s ice , and in what concentrations .
While dark regions could indicate the presence of sodium- and chloride-rich surfaces , while brighter areas may give away magnesium- and sulphate- dominated surfaces .
Comparing these variations with @ @ @ @ @ @ @ would then enable astronomers to identify specific geological features by their chemical compositions .
Gudipati and colleagues now hope that through future missions , spacecraft flying low over Europa ’ s night-side surface could observe this light directly .
This will soon be soon be possible through visible instruments aboard NASA ’ s Europa Clipper mission , which due for launch in 2025 .
These observations could be key to determining whether life could exist beneath Europa ’ s surface , and may also pave the way for analyses of other Jovian moons @ @ @ @ @ @ @ and Ganymede .
The research is described in Nature Astronomy .

Glowing orb: artist’s impression of how the night-side of Europa could appear. (Courtesy: NASA/JPL-Caltech)
Ice on the night-side surface of Jupiter’s moon Europa could emit a unique glow, according to US-based scientists Murthy Gudipati, Bryana Henderson at NASA’s Jet Propulsion Laboratory and Fred Bateman at the National Institute of Standards and Technology. The researchers did lab-based experiments that suggest that the ice emits visible light as a result of being bombarded by high-energy particles. Their research provides important information for NASA’s upcoming Europa Clipper mission – which could offer an unprecedented glimpse of the composition of Europa’s subsurface ocean.
Europa is Jupiter’s fourth largest moon and as it passes through the strong magnetic field of its host planet, its surface is bombarded by high-energy protons, electrons, and ions. As these particles interact with the moon’s salt- and ice-rich crust, they could trigger complex physical and chemical processes that have important consequences for Europa’s chemical composition.
On geological timescales, the energy-rich products of these reactions could be transported through Europa’s crust, before entering the vast ocean of liquid water beneath. Warmed by tidal forces, this ocean is one of the most promising candidate locations for extraterrestrial life in the solar system. Determining the composition of salt on Europa’s surface should therefore provide important clues about whether life could exist in its ocean.
High-energy electrons
In their study, the trio fired high-energy electrons at water ice containing different types of salt and analysed the light emitted by their samples. They discovered that the samples emitted characteristic light spectra at visible wavelengths. They also found that emission was enhanced in ice containing magnesium-sulphate based epsomite, and that ice containing sodium chloride and sodium carbonate gives off much less light. On Europa’s surface, this light emission would create a unique nighttime glow, not likely to be found elsewhere in the solar system.
By mapping variations in this glow on Europa’s surface, the trio believe that scientists could determine what salts are present within Europa’s ice, and in what concentrations. While dark regions could indicate the presence of sodium- and chloride-rich surfaces, while brighter areas may give away magnesium- and sulphate- dominated surfaces. Comparing these variations with observations of Europa’s daytime side would then enable astronomers to identify specific geological features by their chemical compositions.
Gudipati and colleagues now hope that through future missions, spacecraft flying low over Europa’s night-side surface could observe this light directly. This will soon be soon be possible through visible instruments aboard NASA’s Europa Clipper mission, which due for launch in 2025. These observations could be key to determining whether life could exist beneath Europa’s surface, and may also pave the way for analyses of other Jovian moons subjected to particle bombardment, including Io and Ganymede.
The research is described in Nature Astronomy.


physicsworld--2020-11-16--Graphene-based memristor is ideal for artificial neural networks, say researchers - Physics World

A graphene-based memory resistor ( memristor ) that can exist in many different states has been designed and demonstrated by Thomas Schranghamer , Aaryan Oberoi and Saptarshi Das at Pennsylvania State University in the US .
Using simulations and experiments , the team showed how the device can be used to substantially improve the performance of artificial neural networks – systems that could someday rival and even replace conventional computers .
Despite decades of relentless growth , advances in the semiconductor technologies used in digital computing are showing clear signs of slowing down .
To keep up with a growing @ @ @ @ @ @ @ developing new technologies that mimic the operation of neurons the human brain – which perform both the storage and processing of information .
This has the potential of being much more efficient than current computer architectures , which require both time and energy to shuttle data between separate storage and processing components .
In principle , this could be achieve using artificial neural networks ( ANNs ) , which learn to do tasks by being given examples .
ANNs are networks of artificial neurons that influence each other via synapses .
The strength @ @ @ @ @ @ @ the synaptic weight , which can change during the learning process .
One way of adjusting synaptic weight is to use memristors , which are nascent electronic devices that exist in conductance/resistance states that depend on the amount of charge that has flowed through them .
Ideally , memristors used in ANNs would have large numbers of conductance/resistance states , but current memristor designs tend to be binary — meaning they can only operate with two states .
Now Das and colleagues have created a graphene-based memristor that has 16 conductive states that @ @ @ @ @ @ @ .
“ What we have shown is that we can control a large number of memory states with precision using simple graphene field effect transistors , ” Das says .
The team also showed that unlike the fixed states in conventional memristors , those in graphene-based devices can be easily programmed to have arbitrary conductance values .
This flexibility could make them even more valuable for creating ANNs .
Finally , the team demonstrated a computational technique for assigning synaptic weight values in a smart way , enabling the levels of accuracy required @ @ @ @ @ @ @ that their design will lead to new developments of space-efficient , high-speed , and low-power neural networks , which could be scaled up for commercial applications in the future .
If achieved , these efforts could soon see the widespread use of graphene-based memristors , in emerging technologies ranging from self-driving cars to the Internet of things .
The research is described in Nature Communications .

Firing synapse artistic conception of a graphene-based memristor. (Courtesy: Jennifer M McCann/Penn State)
A graphene-based memory resistor (memristor) that can exist in many different states has been designed and demonstrated by Thomas Schranghamer, Aaryan Oberoi and Saptarshi Das at Pennsylvania State University in the US.
Using simulations and experiments, the team showed how the device can be used to substantially improve the performance of artificial neural networks – systems that could someday rival and even replace conventional computers.
Despite decades of relentless growth, advances in the semiconductor technologies used in digital computing are showing clear signs of slowing down. To keep up with a growing demand for computing power, researchers are developing new technologies that mimic the operation of neurons the human brain – which perform both the storage and processing of information. This has the potential of being much more efficient than current computer architectures, which require both time and energy to shuttle data between separate storage and processing components.
Synaptic weight
In principle, this could be achieve using artificial neural networks (ANNs), which learn to do tasks by being given examples. ANNs are networks of artificial neurons that influence each other via synapses. The strength of the influence between neurons is called the synaptic weight, which can change during the learning process.
One way of adjusting synaptic weight is to use memristors, which are nascent electronic devices that exist in conductance/resistance states that depend on the amount of charge that has flowed through them. Ideally, memristors used in ANNs would have large numbers of conductance/resistance states, but current memristor designs tend to be binary – meaning they can only operate with two states.
Now Das and colleagues have created a graphene-based memristor that has 16 conductive states that can be reliably stored and read out. “What we have shown is that we can control a large number of memory states with precision using simple graphene field effect transistors,” Das says.
Arbitrary conductance values
The team also showed that unlike the fixed states in conventional memristors, those in graphene-based devices can be easily programmed to have arbitrary conductance values. This flexibility could make them even more valuable for creating ANNs. Finally, the team demonstrated a computational technique for assigning synaptic weight values in a smart way, enabling the levels of accuracy required by complex ANNs.
The trio hopes that their design will lead to new developments of space-efficient, high-speed, and low-power neural networks, which could be scaled up for commercial applications in the future. If achieved, these efforts could soon see the widespread use of graphene-based memristors, in emerging technologies ranging from self-driving cars to the Internet of things.
The research is described in Nature Communications.


physicsworld--2020-11-16--Second cable failure puts iconic Arecibo Observatory at risk of collapse - Physics World

A second cable has failed at the iconic Arecibo Observatory in Puerto Rico – and engineering teams have been brought in to assess the remaining cables , which are holding up the telescope ’ s metal platform suspended above the 305 m-wide reflecting radio dish .
According to a statement from the University of Central Florida , two of the remaining main cables seem to have wire breaks , increasing the likelihood of the tower platform falling and destroying the telescope .
Since it opened in 1963 , the Arecibo Observatory has been crucial for radio astronomy and is currently @ @ @ @ @ @ @ .
On 10 August , however , one of the six 8 cm-wide auxiliary steel cables that support the telescope ’ s platform failed and crashed down , tearing a 30m gash through the main reflector dish .
The six auxiliary cables had been added in the 1990s to help balance the increased weight when the reflecting system was upgraded .
According to Arecibo director Francisco Cordova , the cable appears to have failed due to a manufacturing process error , adding that Hurricane Maria in 2017 and recent earthquake tremors have accelerated @ @ @ @ @ @ @ , the remaining cables should have held the additional load , but for a still-unknown reason , that did not happen .
Compounding the issue , on 6 November one of four main cables snapped , transferring the load onto the remaining cables and so making them more likely to fail .
Indeed , there are concerns that further auxiliary cables from the same manufacturer may be faulty , with two replacement cables due to arrive in Puerto Rico in December .
The Arecibo Observatory is working with three engineering firms to assess @ @ @ @ @ @ @ .
They will look at ways to reduce that load by temporarily repairing the August failure by either adding a new cable or relieving some of the load from the tower .
But these options will take several weeks and any temporary or permanent fix must be proposed to , approved by , and funded by the National Science Foundation – one of the organizations that manages the observatory together with the University of Central Florida , Universidad Ana G. Méndez and Yang Enterprises Inc. “ It ’ s a crisis , ” @ @ @ @ @ @ @ Arizona and a former Arecibo director .
“ But I ’ m cautiously optimistic that they will find a way to take that tension off [ the remaining cables ] .
” Laura Spitler from the Max Planck Institute for Radio Astronomy in Bonn , Germany , who has used the instrument to study transient radio sources , says losing the telescope would be a devastating blow to astronomy .
“ It would mean that one of the most important telescopes is gone , ” she says .
“ It is not an @ @ @ @ @ @ @

Counting the cost The, Arecibo Observatory is a crucial instrument in radio astronomy, but the failure of two supporting cables, the first of which broke in August (pictured). is putting the telescope in peril. (Courtesy: Univeristy of Central Florida)
Update: 19 November 2020
Officials at the US National Science Foundation have decided to decommission the Arecibo Observatory as a result of the cable failure.
A second cable has failed at the iconic Arecibo Observatory in Puerto Rico – and engineering teams have been brought in to assess the remaining cables, which are holding up the telescope’s metal platform suspended above the 305 m-wide reflecting radio dish. According to a statement from the University of Central Florida, two of the remaining main cables seem to have wire breaks, increasing the likelihood of the tower platform falling and destroying the telescope.
It is not an end that this telescope deserves Laura Spitler
Since it opened in 1963, the Arecibo Observatory has been crucial for radio astronomy and is currently the world’s second-largest single-dish telescope. On 10 August, however, one of the six 8 cm-wide auxiliary steel cables that support the telescope’s platform failed and crashed down, tearing a 30m gash through the main reflector dish.
The six auxiliary cables had been added in the 1990s to help balance the increased weight when the reflecting system was upgraded.
According to Arecibo director Francisco Cordova, the cable appears to have failed due to a manufacturing process error, adding that Hurricane Maria in 2017 and recent earthquake tremors have accelerated the degradation.
Following the first failure, the remaining cables should have held the additional load, but for a still-unknown reason, that did not happen. Compounding the issue, on 6 November one of four main cables snapped, transferring the load onto the remaining cables and so making them more likely to fail. Indeed, there are concerns that further auxiliary cables from the same manufacturer may be faulty, with two replacement cables due to arrive in Puerto Rico in December.
Crisis time
The Arecibo Observatory is working with three engineering firms to assess the situation using drones and remote cameras. They will look at ways to reduce that load by temporarily repairing the August failure by either adding a new cable or relieving some of the load from the tower.
But these options will take several weeks and any temporary or permanent fix must be proposed to, approved by, and funded by the National Science Foundation – one of the organizations that manages the observatory together with the University of Central Florida, Universidad Ana G. Méndez and Yang Enterprises Inc.
“It’s a crisis,” says Michael Nolan of the University of Arizona and a former Arecibo director. “But I’m cautiously optimistic that they will find a way to take that tension off [the remaining cables].”
Laura Spitler from the Max Planck Institute for Radio Astronomy in Bonn, Germany, who has used the instrument to study transient radio sources, says losing the telescope would be a devastating blow to astronomy. “It would mean that one of the most important telescopes is gone,” she says. “It is not an end that this telescope deserves.”


physicsworld--2020-11-17--Modularity, flexibility and scalability: S-Cube vacuum chambers have it all - Physics World

Vacuum technology is a ubiquitous presence in all manner of fundamental and applied physics research endeavours – from synchrotron light sources to semiconductor fabrication , from electron microscopy to quantum computing , and plenty more besides .
Yet as any vacuum end-user knows all too well , cutting-edge research projects rarely stick to the script .
As such , the process of designing , developing and manufacturing a turnkey vacuum chamber to support a diverse set of scientific applications is tricky at best and , when extrapolated over an extended timeframe , vanishingly hard to get right – not least @ @ @ @ @ @ @ ’ s technical specifications versus research priorities that are , by definition , always fluid and always evolving .
Now , however , the Czech vacuum equipment manufacturer STREICHER Pilsen appears to have come up with an elegant and potentially game-changing concept that has the potential to both simplify and future-proof the design of scientific vacuum systems .
In short : STREICHER Pilsen ’ s S-Cube modular vacuum chamber system offers researchers a controlled vacuum space where modification is the norm rather than the exception – an “ evolve-as-you-grow ” technology model that @ @ @ @ @ @ @ as a result , many more design degrees of freedom versus conventional vacuum equipment .
There ’ s an environmental upside as well , with the modular S-Cube approach enabling vacuum users to extend the lifetime of their vacuum chambers ( rather than making cyclical investments in new hardware as research priorities change ) .
“ Our S-Cube modular vacuum concept enables modification of the existing vacuum chamber by replacing only some of the walls or by adding another extension module , ” explains Jiří Lopata , CEO of STREICHER Pilsen .
“ @ @ @ @ @ @ @ new chamber as the scientists ’ research requirements change – a feature that ultimately translates into significantly lower capital outlay over time .
Put simply : if you can adapt your existing vacuum system , you don ’ t need to invest in a new one.
” The new rules of vacuum Near term , the priority for Lopata and colleagues is to raise awareness of the S-Cube product concept within STREICHER Pilsen ’ s established customer base – far from straightforward in the grips of a global pandemic .
For context , @ @ @ @ @ @ @ and components for more than 25 years , serving OEMs and technology start-ups across a range of industries – chemical and pharmaceutical , semiconductor , food processing , heat treatment and steel manufacturing .
Big science is another core market segment , with activities to date spanning high-profile projects for the Extreme Light Infrastructure ( ELI ) beamlines in central Europe ; the Joint Institute for Nuclear Research ( Dubna , Russia ) ; and the Fusion for Energy project ( which coordinates the European Union ’ s contribution to the ITER experimental @ @ @ @ @ @ @ to Lopata , this diverse customer base – spanning industry and R & D – provides the foundation for STREICHER Pilsen ’ s core competency .
“ Our design and engineering teams have first-hand experience and deep domain knowledge about the production of custom vacuum equipment , ” he explains .
“ S-Cube is a logical progression of that collective know-how .
For us , it ’ s all about supporting the complex applications and ever-changing vacuum requirements of our customers , whether they ’ re in a research or an industry setting.
@ @ @ @ @ @ @ , what ’ s particularly attractive about the S-Cube concept is its combination of simplicity , modularity and ease of customization – features that would be otherwise unthinkable with a conventional welded vacuum chamber .
In effect , S-Cube users are able to design their own complex vacuum system by connecting – via standardized interfaces – a mix of basic building blocks comprising cubic , hexagonal and cuboid vacuum chamber modules ( all available in a range of custom sizes , with wall lengths from 450 mm up to 2 m ) .
@ @ @ @ @ @ @ a given , there ’ s also a broader emphasis on system-level S-Cube solutions ( see “ Two heads are better than one ” , below ) .
“ We always support our customers –not only with the design and production of the vacuum chamber , but with the entire vacuum system , ” says Emil Černy , head of engineering at STREICHER Pilsen .
“ That means expert guidance regarding the optimum choice of vacuum pumps , valves , electrical feedthroughs and vacuum gauges , as well as easy-to-use systems for vacuum @ @ @ @ @ @ @ also have a range of more granular options in terms of S-Cube functionality – for example , direct integration of an optical table on independent supports ; specification of aluminium chamber walls within a stainless-steel system frame ; as well as polished or sand-blasted internal surfaces .
For now , all S-Cube chambers are compatible with low , medium and high-vacuum applications , though a planned option for metal sealing will ensure future support for ultrahigh-vacuum ( UHV ) systems .
Your vacuum , your way When it comes to market-facing activity , @ @ @ @ @ @ @ also extends to the online presentation of the product offering .
A case in point is the Configurator , a dedicated website that allows customers to design and optimize their own S-Cube vacuum chamber via an intuitive and easy-to-use interface .
“ Think collaborative product design , ” says Černy .
“ The Configurator is our shop window – a great way for new customers to get to know the basic features of the S-Cube system.
” With the help of the online tools , for example , the user is able to @ @ @ @ @ @ @ of built-in accessories ( hinges , flanges , locks and viewports ) , integrate an optical table , as well as define key pressure and temperature cycles .
What ’ s more , all system variants are displayed immediately in a preview that can be exported to PDF for proofing and discussion with the STREICHER Pilsen design team .
“ Ultimately , our goal is to make the interface with S-Cube technology as easy to use and as accessible as possible , ” concludes Černy .
“ The Configurator puts the design capability @ @ @ @ @ @ @ while our in-house technical team provides the specialist support to move them rapidly from a v1.0 specification to a finalized S-Cube chamber configuration.
” • For further information , see the S-Cube video presentation .
Two heads are better than one To fast-track the commercial roll-out of the S-Cube product portfolio , STREICHER Pilsen has teamed up with fellow vacuum manufacturer Edwards in what , the vendors hope , will be a win-win for vacuum customers in research and industry .
The formal collaboration kicked off earlier this year and sees STREICHER Pilsen @ @ @ @ @ @ @ – pumps , sensors , leak detectors and control systems – to end-users interested in purchasing not just a vacuum chamber , but a turnkey S-Cube vacuum system .
This approach to the market will open up wider commercial opportunities for STREICHER Pilsen , while Edwards stands to gain new sales channels for its diverse product portfolio as well as its after-sales support and field-service teams .
“ Our two companies have complementary rather than competing technology portfolios , ” explains Radim Hlavaty , Edwards ’ regional account manager ( Czech Republic and @ @ @ @ @ @ @ also a logical collaboration in terms of proximity , given that Edwards has a large manufacturing facility in the Czech Republic.
” Notwithstanding the commercial drivers , there are other significant upsides to consider , notes Emil Černy , head of engineering at STREICHER Pilsen .
“ We can see real synergies for our respective design teams and application engineers , ” he explains .
“ On our side , we ’ re benefiting directly from Edwards ’ specialist capabilities in areas like vacuum simulation and system-level optimization , as well as gaining @ @ @ @ @ @ @ next-generation vacuum pumps .
”

STREICHER Pilsen’s S-Cube modular vacuum chamber system can help scientific users to maximize research productivity while simplifying and future-proofing their vacuum infrastructure requirements
Vacuum management the S-Cube modular vacuum chamber system comes with an easy-to-use interface for vacuum process control and data visualization. (Courtesy: STREICHER Pilsen)
Vacuum technology is a ubiquitous presence in all manner of fundamental and applied physics research endeavours – from synchrotron light sources to semiconductor fabrication, from electron microscopy to quantum computing, and plenty more besides. Yet as any vacuum end-user knows all too well, cutting-edge research projects rarely stick to the script. As such, the process of designing, developing and manufacturing a turnkey vacuum chamber to support a diverse set of scientific applications is tricky at best and, when extrapolated over an extended timeframe, vanishingly hard to get right – not least when it comes to matching the chamber’s technical specifications versus research priorities that are, by definition, always fluid and always evolving.
Now, however, the Czech vacuum equipment manufacturer STREICHER Pilsen appears to have come up with an elegant and potentially game-changing concept that has the potential to both simplify and future-proof the design of scientific vacuum systems. In short: STREICHER Pilsen’s S-Cube modular vacuum chamber system offers researchers a controlled vacuum space where modification is the norm rather than the exception – an “evolve-as-you-grow” technology model that offers built-in flexibility, scalability and, as a result, many more design degrees of freedom versus conventional vacuum equipment. There’s an environmental upside as well, with the modular S-Cube approach enabling vacuum users to extend the lifetime of their vacuum chambers (rather than making cyclical investments in new hardware as research priorities change).
“Our S-Cube modular vacuum concept enables modification of the existing vacuum chamber by replacing only some of the walls or by adding another extension module,” explains Jiří Lopata, CEO of STREICHER Pilsen. “There is no need to manufacture a new chamber as the scientists’ research requirements change – a feature that ultimately translates into significantly lower capital outlay over time. Put simply: if you can adapt your existing vacuum system, you don’t need to invest in a new one.”
The new rules of vacuum
Near term, the priority for Lopata and colleagues is to raise awareness of the S-Cube product concept within STREICHER Pilsen’s established customer base – far from straightforward in the grips of a global pandemic. For context, the company has been manufacturing vacuum equipment and components for more than 25 years, serving OEMs and technology start-ups across a range of industries – chemical and pharmaceutical, semiconductor, food processing, heat treatment and steel manufacturing. Big science is another core market segment, with activities to date spanning high-profile projects for the Extreme Light Infrastructure (ELI) beamlines in central Europe; the Joint Institute for Nuclear Research (Dubna, Russia); and the Fusion for Energy project (which coordinates the European Union’s contribution to the ITER experimental fusion reactor in France).
According to Lopata, this diverse customer base – spanning industry and R&D – provides the foundation for STREICHER Pilsen’s core competency. “Our design and engineering teams have first-hand experience and deep domain knowledge about the production of custom vacuum equipment,” he explains. “S-Cube is a logical progression of that collective know-how. For us, it’s all about supporting the complex applications and ever-changing vacuum requirements of our customers, whether they’re in a research or an industry setting.”
Make it easy S-Cube users are able to design their own complex vacuum system by connecting a mix of basic building blocks comprising cubic, hexagonal and cuboid chamber modules. (Courtesy: STREICHER Pilsen)
For scientific end-users of vacuum systems, what’s particularly attractive about the S-Cube concept is its combination of simplicity, modularity and ease of customization – features that would be otherwise unthinkable with a conventional welded vacuum chamber. In effect, S-Cube users are able to design their own complex vacuum system by connecting – via standardized interfaces – a mix of basic building blocks comprising cubic, hexagonal and cuboid vacuum chamber modules (all available in a range of custom sizes, with wall lengths from 450 mm up to 2 m).
Yet while flexibility and customer choice are a given, there’s also a broader emphasis on system-level S-Cube solutions (see “Two heads are better than one”, below). “We always support our customers –not only with the design and production of the vacuum chamber, but with the entire vacuum system,” says Emil Černy, head of engineering at STREICHER Pilsen. “That means expert guidance regarding the optimum choice of vacuum pumps, valves, electrical feedthroughs and vacuum gauges, as well as easy-to-use systems for vacuum process control and data visualization.”
Customers also have a range of more granular options in terms of S-Cube functionality – for example, direct integration of an optical table on independent supports; specification of aluminium chamber walls within a stainless-steel system frame; as well as polished or sand-blasted internal surfaces. For now, all S-Cube chambers are compatible with low, medium and high-vacuum applications, though a planned option for metal sealing will ensure future support for ultrahigh-vacuum (UHV) systems.
Your vacuum, your way
When it comes to market-facing activity, it’s clear that S-Cube innovation also extends to the online presentation of the product offering. A case in point is the Configurator, a dedicated website that allows customers to design and optimize their own S-Cube vacuum chamber via an intuitive and easy-to-use interface. “Think collaborative product design,” says Černy. “The Configurator is our shop window – a great way for new customers to get to know the basic features of the S-Cube system.”
With the help of the online tools, for example, the user is able to equip removable chamber walls with a range of built-in accessories (hinges, flanges, locks and viewports), integrate an optical table, as well as define key pressure and temperature cycles. What’s more, all system variants are displayed immediately in a preview that can be exported to PDF for proofing and discussion with the STREICHER Pilsen design team.
“Ultimately, our goal is to make the interface with S-Cube technology as easy to use and as accessible as possible,” concludes Černy. “The Configurator puts the design capability in the hands of the customer, while our in-house technical team provides the specialist support to move them rapidly from a v1.0 specification to a finalized S-Cube chamber configuration.”
For further information, see the S-Cube video presentation.
Two heads are better than one To fast-track the commercial roll-out of the S-Cube product portfolio, STREICHER Pilsen has teamed up with fellow vacuum manufacturer Edwards in what, the vendors hope, will be a win-win for vacuum customers in research and industry. The formal collaboration kicked off earlier this year and sees STREICHER Pilsen offering a range of Edwards’ technologies – pumps, sensors, leak detectors and control systems – to end-users interested in purchasing not just a vacuum chamber, but a turnkey S-Cube vacuum system. This approach to the market will open up wider commercial opportunities for STREICHER Pilsen, while Edwards stands to gain new sales channels for its diverse product portfolio as well as its after-sales support and field-service teams. “Our two companies have complementary rather than competing technology portfolios,” explains Radim Hlavaty, Edwards’ regional account manager (Czech Republic and Slovakia). “It’s also a logical collaboration in terms of proximity, given that Edwards has a large manufacturing facility in the Czech Republic.” Notwithstanding the commercial drivers, there are other significant upsides to consider, notes Emil Černy, head of engineering at STREICHER Pilsen. “We can see real synergies for our respective design teams and application engineers,” he explains. “On our side, we’re benefiting directly from Edwards’ specialist capabilities in areas like vacuum simulation and system-level optimization, as well as gaining insights from their product development roadmaps for next-generation vacuum pumps.”


physicsworld--2020-11-17--Physics challenges for green aviation - Physics World

Once upon a time , air travel was risky , costly and highly polluting .
But these days modern airliners are the safest way to travel long distances , as well as being cheaper , quieter and more fuel-efficient than their predecessors .
If you need to cross the US , a seat on an Airbus will get you there on less than half the fuel of an average American car – and save you three days .
Unfortunately , this efficiency is a double-edged sword , encouraging more and more people to fly or send cargo by plane .
@ @ @ @ @ @ @ ’ s CO emissions has risen from zero to 2 % within the last century despite the fact that the litres of fuel burned per passenger-kilometre has plummeted – from 10.3 l/100 passenger-km for the De Havilland Comet 4 in 1958 , when commercial flight with jet engine aircraft was new , to 2.42 l/100 passenger-km with today ’ s Airbus A330neo-900 .
Furthermore , with around 107,000 commercial flights taking place every day prior to the COVID-19 pandemic , noise pollution from airports is a huge concern .
So , what can @ @ @ @ @ @ @ Well let ’ s consider Boeing ’ s 787 Dreamliner – a modern airliner that looks much like its noisier , less-efficient ancestor , the 707 .
Each has a cylindrical fuselage with a square-root-of-x nose profile , wings swept back about 35° , and jet engines sticking forward from under the wings .
This shape is set by the laws of mechanics and by compressible fluid flow .
Look closer , however , and differences emerge .
The Dreamliner ’ s engines are fatter in front , so they have a high @ @ @ @ @ @ @ less kinetic energy into the airstream for the same amount of thrust .
The engine exhaust nozzles are scalloped with a chevron shape , which creates vortices in the exhaust fumes .
When high-speed exhaust mixes with the slower-moving air , the vortices make less noise than the chaotic mixing of earlier engines .
More subtly , the leading edge of the 707 ’ s aluminium wing is straight but the Dreamliner ’ s is curved , which reduces fuel-wasting drag .
Although the shape is too complex to be affordably built with @ @ @ @ @ @ @ to a composite material – carbon-fibre-reinforced plastic ( CFRP ) .
Besides allowing aircraft components such as the wings , tail and fuselage to have a wide variety of shapes , CFRP is stiffer and has a higher strength-to-weight ratio than aluminium or steel .
These factors make the aeroplane lighter , so less fuel is needed to get it off the ground and keep it airborne .
One challenge of CFRP is in the factory , where it starts as a flexible fabric or tape infused with uncured epoxy resin .
This @ @ @ @ @ @ @ by automated tape-laying machines .
To make it rigid , it then has to be “ cured ” or baked in an autoclave at temperatures of up to 180 °C , depending on the blend of CFRP .
The problem is that ensuring that every region of the part stays at exactly the right temperature is tricky , calling for careful process control and sometimes for instruments embedded within the fabric .
To verify that every ply of material ( there can be as many as 100 layers ) lies smoothly on the @ @ @ @ @ @ @ voids or delaminations , aircraft manufacturers use inspection methods , such as machine-vision , for automatic checks while the tape is being applied , and X-ray and ultrasound to verify each part before it ’ s built into a larger structure .
A big issue for CFRP is that it has a very high resistance , which is a problem when a typical commercial airliner is struck by lightning at least once a year .
A bolt can carry as much as 200 kA of electrical current , which enters at one location @ @ @ @ @ @ @ exits at another , like the tail .
Aeroplanes that have skin and sub-structure of mostly aluminium easily handle the current and the heat it produces at the point of attachment : engineers only need to include good conductive paths between components , skins thick enough to prevent melt-through , and internal sealant over gaps or joints to prevent arcs and sparks .
Part of the problem is that CFRP conducts electricity anisotropically .
Current flows fairly easily along the fibres , which are 2000 times less conductive than copper but 30 times @ @ @ @ @ @ @ current flows poorly between the fibres or between ply layers .
Electrical potential from a lightning strike may therefore arc through the air to get around non-conductive zones , or the current may heat fibres and create a spark of vaporized material – either of which could cause a fire in a fuel tank .
Governments and manufacturers have therefore developed ways to avoid arcs and sparks .
Metal foils , for example , are used on the outside of a plane to guide lightning current and protect composite skins .
Other techniques @ @ @ @ @ @ @ and direct it away from sensitive components , and minimizing resistance in fastener installations .
There are also laboratory experiments and software that can simulate lightning current , allowing us to get a better theoretical and experimental understanding of lightning attachment , arc conditions and ignition processes .
Engineers can then use this knowledge to design aircraft with large margins of safety above the strongest lightning strike .
These efforts have paid off .
Aircraft built with CFRP wings and fuselages are routinely struck by lightning , just like their aluminium siblings , @ @ @ @ @ @ @ The challenge now is to reduce the weight of these solutions so fuel economy gets even better .
While heating and arcing are direct effects of a lightning strike , it can also cause indirect effects by inducing voltage , current or force in components where the lightning current doesn ’ t reach .
For example , a fast-changing lightning current can induce a voltage that flips a bit in nearby electronics , or it can induce eddy-current forces so strong they bend or break some components .
Designers use modelling and testing @ @ @ @ @ @ @ problems , or that counter-measures such as shunt diodes or shielded cables keep a current spike from reaching a sensitive component .
On an aeroplane , the wings ’ job is to lift the craft against gravity .
It does this by deflecting air downward , which imparts downward momentum to the air and an equal upward momentum to the wings .
The structure inside the wing transfers the force to the fuselage ( the body of the plane ) thereby allowing the aircraft to fly .
( a ) Early planes featured @ @ @ @ @ @ @ some modern small aircraft still do .
While these are structurally efficient , requiring little mass to safely transfer lifting force to the body , a tapered wing is even better .
The structure is lighter than for straight wings because most lift is produced by the thick region near the fuselage , meaning it only has to transfer that lift a short distance .
A plane can also be made more stable if there is slight sweep back on the leading edge .
For a plane flying straight , the wings have @ @ @ @ @ @ @ the craft twists to the right , perhaps from a gust of turbulence , a swept left-wing presents a larger cross-section to the wind than the right wing .
This helps the aeroplane quickly straighten out after small disturbances .
For planes with jet engines , the wings are swept back even further than for their slower , non-jet-engine counterparts – in some cases they can even be angled at more than 40° .
Jet engines allow planes to fly near the speed of sound , at transonic speeds .
Air flowing over @ @ @ @ @ @ @ must move even faster than the speed the plane is travelling , often meaning it reaches supersonic speeds ( faster than the speed of sound ) .
So when that supersonic airflow moving over those thicker parts of the wing collides with slower moving air , it creates shockwaves .
A shock irreversibly transforms the air ’ s kinetic energy into heat and that loss of energy creates lots of drag .
The engineers who built early jets solved the problem by sweeping the wings .
( b ) With a straight wing @ @ @ @ @ @ @ region , airflow is supersonic .
( c ) With a swept wing , the air follows a gentler path .
Its arrival at the thick part of the wing is delayed by a factor of 1/cos ( θ ) , where θ is the sweep angle .
Air farther from the wing has more time to shift out of the way , so air near the wing has a wider “ channel ” .
It needn ’ t go supersonic to get around the wing .
Though the shape of airliners has @ @ @ @ @ @ @ , the cantilevered swept-wing shape may , over the next decade or two , finally give way to a new design thanks to NASA and companies like Boeing , which are developing the “ transonic truss-braced wing ” that will exhibit little or no sweep .
Conventional truss-braced wings with no sweeping V-shape are an old idea and the design is still popular for small aeroplanes .
In fact , the world ’ s best-selling aircraft , the four-seat Cessna 172 , has a straight truss-braced wing .
Until now , however , @ @ @ @ @ @ @ wing , truss-braced or not , because it produces too much drag at transonic speeds , those that are near or at the speed of sound ( see box above ) .
Airliners usually travel at Mach 0.8–0.85 , where the Mach number is the fraction of the speed of sound in the local atmospheric condition ( 343 m/s in dry air at 20 °C ) – typically the actual speed is 246–271 m/s ( 885–974 km/h ) depending on air temperature .
New , thin airfoils made possible by CFRP , plus @ @ @ @ @ @ @ finally allow for wings with little or no sweep that can travel at these speeds without producing too much drag .
The advantages of an unswept wing include the fact that it is structurally more efficient than a swept-back wing .
To have a given wingspan , a swept wing must be longer than an unswept one .
The wing ’ s lift then acts with a longer moment arm , which increases the bending moment on the wing ’ s structure .
To resist this , the structure of the swept wing @ @ @ @ @ @ @ , than an unswept one .
The external truss also reduces stress on the wing ’ s internal structure so the wing can be thinner top-to-bottom , giving it a small frontal cross-section and thereby reducing drag .
To cut drag more , the wing is narrower front-to-back than a traditional wing , which lets laminar flow cover a larger fraction of the wing surface .
The wing is also longer relative to its front-to-back width , or “ chord ” , and this higher aspect ratio reduces the energy lost when high-pressure @ @ @ @ @ @ @ the wingtip to the low-pressure region above the wing .
An upward-folding tip allows this long-winged aircraft to fit into the small gates of regional airports .
Another way to make planes greener is to develop hybrid propulsion , rather like we now have hybrid cars .
The idea is that jet turbines would boost power for take-off while batteries or fuel cells would provide steady power for cruise .
Of course , it would be even better if aeroplanes could fly purely on renewable energy ( such as solar or hydro ) @ @ @ @ @ @ @ carbon .
Alas , an all-electric airliner to replace today ’ s planes is not on the cards .
Batteries have a specific energy ( measured in joules per kilogram ) that is orders of magnitude lower than the specific energy of hydrocarbon fuel .
This figure will improve , but not enough .
That ’ s because when weight matters , as it does in aeroplanes , batteries will always suffer from the fact that they have to carry their own oxidizer , whereas fuel-burning engines use oxygen from air .
Therefore @ @ @ @ @ @ @ only work over tens or perhaps hundreds of miles , not over the thousands of miles where an aeroplane ’ s speed makes it most useful .
There are a few prospects on the horizon for getting around the fundamental limits of batteries .
One option is to use lasers or microwaves to transmit energy from the ground to aircraft in flight .
The beam of photons creates voltage and current in dipole antenna elements or photovoltaic arrays on the aircraft , with diodes siphoning off the power to run motors or electronics @ @ @ @ @ @ @ small scale .
One of the best demonstrations was by the SHARP project in Canada back in 1987 using microwaves , but more recent efforts include Lockheed Martin and LaserMotive ( now PowerLight ) flying an unmanned aerial vehicle ( UAV ) using laser beams .
However , the method faces regulatory and cost challenges before it can scale up to commercial flight .
As for solar-powered aircraft , they do already exist , but because the sunlight is so weak , these fragile aircraft fly slowly and with little payload .
A @ @ @ @ @ @ @ flight , just as aerial tankers transfer fuel to military aircraft today .
It ’ s plausible for long-range all-electric flight , but technical challenges remain .
Another development that we could see over the next two or three decades is hypersonic travel , which means craft flying at Mach 5 ( 6126 km/h ) or faster .
This kind of speed could get you from Los Angeles to Beijing in no more than two hours .
Supersonic airliners – the Concorde and the Tupolev 144 – only flew at half that speed @ @ @ @ @ @ @ .
They were also horribly noisy at take-off and landing , and emitted sonic booms during cruise .
Both are now out of operation .
Hypersonic airliners will do better .
These new aircraft will likely use hydrogen – produced by electrolysis using non-fossil energy sources – or low-carbon fuel like methane .
With such light molecules , the fuel and air can rapidly mix , which is vital because air moves through the engine so fast it spends only a few milliseconds in the combustion zone .
Sonic boom is less of @ @ @ @ @ @ @ is already developing low-boom aircraft designs , which have a long , sharp nose that reduces the area over which air is compressed to form the leading shockwave .
They also keep protuberances , like the engine intake , on top of the fuselage so shockwaves produced there go up , not downward to bother people .
What ’ s more , thanks to a quirk of the atmosphere , most acoustic energy from hypersonic planes will never reach Earth .
If you imagine a sonic boom heading out diagonally down from an @ @ @ @ @ @ @ warmer air as it moves .
Given that sound and shockwaves travel faster in warm air , the sonic boom will refract – its path will curve and become more horizontal as it moves lower .
So apart from shockwaves that are heading almost straight down , the path eventually curves upward , avoiding the ground altogether .
And because hypersonic aircraft fly at 27,000 to 30,000 m – more than twice as high as today ’ s airliners , because higher altitudes mean thinner air and therefore less drag – nearly 100 @ @ @ @ @ @ @ from the Earth .
Despite these benefits , several challenges of hypersonic flight must be overcome .
One is the fact that air at the nose and leading edge of a hypersonic plane can get hotter than 1300 K because the air ’ s kinetic energy becomes heat energy when it runs into the perpendicular surface and stops .
At those temperatures , CFRP , which has revolutionized today ’ s airliners , simply doesn ’ t hold its strength .
Fortunately , titanium alloys and other advanced , lightweight materials – some @ @ @ @ @ @ @ – are being developed to solve this problem .
Another issue is ionizing radiation .
When a galactic cosmic-ray particle strikes a nucleus in the upper atmosphere , the nucleus shatters into a spray of secondary particles .
The trails of these secondaries create conductive paths in semiconductor electronics .
Today ’ s planes fly at altitudes of 9000–13,000 m , where the secondaries are spread out , so any one electronic device sees only a small effect .
But for a hypersonic plane flying at 30,000 m , the secondaries will be @ @ @ @ @ @ @ stronger radiation environment .
It wouldn ’ t be a problem for passengers ; a flight will be so short that the total dose would be lower than in today ’ s flights .
But electronics will have trouble .
A single chip may be hit by many secondaries at the same time , and such a sudden rise in conductivity can cause errors in a semiconductor chip , or even damage it permanently .
Costly solutions do exist for spacecraft , such as physical shielding or electronics made of expensive materials with @ @ @ @ @ @ @ to devise solutions for aircraft that are affordable and lightweight .
Sky taxi Aircraft like this helicopter developed by Volocopter could be roaming our city skies taxiing people and cargo .
( Courtesy : CC BY-SA 4.0 Matti Blume ) With towns and cities suffering from rising congestion on the roads , there is a growing demand for an aircraft that can land vertically in a small space , load one or two people or a van-sized cargo , and fly above the clogged highways to another spot in the same city .
@ @ @ @ @ @ @ be the answer .
With four or more rotors , these electric “ rotorcraft ” will soon be carrying cargo , and perhaps passengers , in cities .
Their short range – a few dozen miles – is a perfect match for urban flight .
This new family of aircraft has many environmental benefits .
Because they fly at about 320 km/h and use uncongested routes , each aircraft can make as many trips per day as , say , 10 cars or trucks .
If that happens , it gets 10 vehicles @ @ @ @ @ @ @ a little easier .
Each aircraft would also mean that 10 cars or trucks wouldn ’ t need to be built , saving energy and materials .
Of course , being electric-powered , the aircraft emit no CO in cities where electricity comes from non-fossil sources .
It also helps keep engine noise tolerable .
Challenges remain , however .
For a two-person taxi service , the aircraft would have to be recharged quickly .
The 15-minute charging time of today ’ s batteries would need to be shortened , or ways would @ @ @ @ @ @ @ depleted batteries for charged ones .
Batteries would go through up to 20 deep discharge cycles per day , so they would reach end-of-life in a few months as the electrochemical process involved in a rechargeable battery isn ’ t totally reversible .
That ’ s because with each charge–discharge cycle , some atoms from the electrodes or the electrolyte go to the wrong place , eventually weakening the battery and making it potentially develop too much leakage current to hold charge for long .
Discarding or refurbishing the batteries at the required @ @ @ @ @ @ @ Helicopters are also noisy , as is any vehicle with many small rotors .
There are ways to make them quieter , like ducts around the rotors , but these have costs and trade-offs .
Finally , the density of air traffic would be unprecedented ; a thousand aircraft simultaneously flying in an area the size of Los Angeles or London will require a new , and probably automated , approach to air traffic control .
Computers , not humans , would have to pilot these vehicles and co-ordinate with traffic control .
@ @ @ @ @ @ @ is continuing to refine and develop traditional aircraft as it has throughout its 100-year-old history , constantly seeking to reduce costs and lower their impact on the environment .
But there are now new directions for the industry too , in the form of super-efficient new airliners that will look quite different , electric-powered rotorcraft that revolutionize urban transport ( see box above ) , and hypersonic aeroplanes that protect the world ’ s environment while shrinking the distance between its people .
Within decades , air travel may look very different to @ @

Physics World. Members of the Institute of Physics can enjoy the full issue Taken from the November 2020 issue of. Members of the Institute of Physics can enjoy the full issue via the Physics World app
Commercial air travel has changed a lot since the first aeroplane took passengers around a century ago. Brian Tillotson explores the future challenges to make aviation greener
All shapes and sizes The popular Cessna 172 (top left) features a straight truss-braced wing (Courtesy: Adrian Pingstone, Public Domain), while commercial airliners, like the Boeing 707 (top right), have sweeping wings (Courtesy: Carlos Ponte, Public Domain). The Boeing 787 (bottom right) has succeeded the 707, and the design differences make it quieter and more efficient (Courtesy: CC BY-SA 2.0 pjs2005). Concorde (bottom left) was a commercial supersonic aircraft but was retired in 2003 (Courtesy: Adrian Pingstone, Public Domain).
Once upon a time, air travel was risky, costly and highly polluting. But these days modern airliners are the safest way to travel long distances, as well as being cheaper, quieter and more fuel-efficient than their predecessors. If you need to cross the US, a seat on an Airbus will get you there on less than half the fuel of an average American car – and save you three days.
Unfortunately, this efficiency is a double-edged sword, encouraging more and more people to fly or send cargo by plane. Aviation’s contribution to the world’s CO 2 emissions has risen from zero to 2% within the last century despite the fact that the litres of fuel burned per passenger-kilometre has plummeted – from 10.3 l/100 passenger-km for the De Havilland Comet 4 in 1958, when commercial flight with jet engine aircraft was new, to 2.42 l/100 passenger-km with today’s Airbus A330neo-900. Furthermore, with around 107,000 commercial flights taking place every day prior to the COVID-19 pandemic, noise pollution from airports is a huge concern.
Aviation’s contribution to the world’s CO 2 emissions has risen from zero to 2% within the last century despite the fact that the fuel burned per passenger-kilometre has plummeted
Green solutions
So, what can be done to make aviation greener? Well let’s consider Boeing’s 787 Dreamliner – a modern airliner that looks much like its noisier, less-efficient ancestor, the 707. Each has a cylindrical fuselage with a square-root-of-x nose profile, wings swept back about 35°, and jet engines sticking forward from under the wings. This shape is set by the laws of mechanics and by compressible fluid flow.
Look closer, however, and differences emerge. The Dreamliner’s engines are fatter in front, so they have a high “bypass ratio” – they put less kinetic energy into the airstream for the same amount of thrust. The engine exhaust nozzles are scalloped with a chevron shape, which creates vortices in the exhaust fumes. When high-speed exhaust mixes with the slower-moving air, the vortices make less noise than the chaotic mixing of earlier engines.
More subtly, the leading edge of the 707’s aluminium wing is straight but the Dreamliner’s is curved, which reduces fuel-wasting drag. Although the shape is too complex to be affordably built with aluminium, it is made possible thanks to a composite material – carbon-fibre-reinforced plastic (CFRP). Besides allowing aircraft components such as the wings, tail and fuselage to have a wide variety of shapes, CFRP is stiffer and has a higher strength-to-weight ratio than aluminium or steel. These factors make the aeroplane lighter, so less fuel is needed to get it off the ground and keep it airborne.
One challenge of CFRP is in the factory, where it starts as a flexible fabric or tape infused with uncured epoxy resin. This is laid on moulds by hand or by automated tape-laying machines. To make it rigid, it then has to be “cured” or baked in an autoclave at temperatures of up to 180 °C, depending on the blend of CFRP. The problem is that ensuring that every region of the part stays at exactly the right temperature is tricky, calling for careful process control and sometimes for instruments embedded within the fabric. To verify that every ply of material (there can be as many as 100 layers) lies smoothly on the one below it with no wrinkles, voids or delaminations, aircraft manufacturers use inspection methods, such as machine-vision, for automatic checks while the tape is being applied, and X-ray and ultrasound to verify each part before it’s built into a larger structure.
When lightning strikes
A big issue for CFRP is that it has a very high resistance, which is a problem when a typical commercial airliner is struck by lightning at least once a year. A bolt can carry as much as 200 kA of electrical current, which enters at one location, such as a wingtip, and exits at another, like the tail. Aeroplanes that have skin and sub-structure of mostly aluminium easily handle the current and the heat it produces at the point of attachment: engineers only need to include good conductive paths between components, skins thick enough to prevent melt-through, and internal sealant over gaps or joints to prevent arcs and sparks.
Part of the problem is that CFRP conducts electricity anisotropically. Current flows fairly easily along the fibres, which are 2000 times less conductive than copper but 30 times more conductive than silicon. However, current flows poorly between the fibres or between ply layers. Electrical potential from a lightning strike may therefore arc through the air to get around non-conductive zones, or the current may heat fibres and create a spark of vaporized material – either of which could cause a fire in a fuel tank.
Governments and manufacturers have therefore developed ways to avoid arcs and sparks. Metal foils, for example, are used on the outside of a plane to guide lightning current and protect composite skins. Other techniques include using dielectric material to isolate current and direct it away from sensitive components, and minimizing resistance in fastener installations. There are also laboratory experiments and software that can simulate lightning current, allowing us to get a better theoretical and experimental understanding of lightning attachment, arc conditions and ignition processes. Engineers can then use this knowledge to design aircraft with large margins of safety above the strongest lightning strike. These efforts have paid off. Aircraft built with CFRP wings and fuselages are routinely struck by lightning, just like their aluminium siblings, but none has had an ignition. The challenge now is to reduce the weight of these solutions so fuel economy gets even better.
While heating and arcing are direct effects of a lightning strike, it can also cause indirect effects by inducing voltage, current or force in components where the lightning current doesn’t reach. For example, a fast-changing lightning current can induce a voltage that flips a bit in nearby electronics, or it can induce eddy-current forces so strong they bend or break some components. Designers use modelling and testing to verify that indirect effects cause no problems, or that counter-measures such as shunt diodes or shielded cables keep a current spike from reaching a sensitive component.
Sweeping wings On an aeroplane, the wings’ job is to lift the craft against gravity. It does this by deflecting air downward, which imparts downward momentum to the air and an equal upward momentum to the wings. The structure inside the wing transfers the force to the fuselage (the body of the plane) thereby allowing the aircraft to fly. (a) Early planes featured straight, thick wings – indeed, some modern small aircraft still do. While these are structurally efficient, requiring little mass to safely transfer lifting force to the body, a tapered wing is even better. The structure is lighter than for straight wings because most lift is produced by the thick region near the fuselage, meaning it only has to transfer that lift a short distance. A plane can also be made more stable if there is slight sweep back on the leading edge. For a plane flying straight, the wings have equal cross-section to the airstream. When the craft twists to the right, perhaps from a gust of turbulence, a swept left-wing presents a larger cross-section to the wind than the right wing. This helps the aeroplane quickly straighten out after small disturbances. For planes with jet engines, the wings are swept back even further than for their slower, non-jet-engine counterparts – in some cases they can even be angled at more than 40°. Jet engines allow planes to fly near the speed of sound, at transonic speeds. Air flowing over curved or thick parts of the plane must move even faster than the speed the plane is travelling, often meaning it reaches supersonic speeds (faster than the speed of sound). So when that supersonic airflow moving over those thicker parts of the wing collides with slower moving air, it creates shockwaves. A shock irreversibly transforms the air’s kinetic energy into heat and that loss of energy creates lots of drag. The engineers who built early jets solved the problem by sweeping the wings. (b) With a straight wing’s profile, in the thick region, airflow is supersonic. (c) With a swept wing, the air follows a gentler path. Its arrival at the thick part of the wing is delayed by a factor of 1/cos(θ), where θ is the sweep angle. Air farther from the wing has more time to shift out of the way, so air near the wing has a wider “channel”. It needn’t go supersonic to get around the wing.
The next generation
Though the shape of airliners has changed little over the last 60 years, the cantilevered swept-wing shape may, over the next decade or two, finally give way to a new design thanks to NASA and companies like Boeing, which are developing the “transonic truss-braced wing” that will exhibit little or no sweep.
Conventional truss-braced wings with no sweeping V-shape are an old idea and the design is still popular for small aeroplanes. In fact, the world’s best-selling aircraft, the four-seat Cessna 172, has a straight truss-braced wing. Until now, however, no jet airliner has used an unswept wing, truss-braced or not, because it produces too much drag at transonic speeds, those that are near or at the speed of sound (see box above). Airliners usually travel at Mach 0.8–0.85, where the Mach number is the fraction of the speed of sound in the local atmospheric condition (343 m/s in dry air at 20 °C) – typically the actual speed is 246–271 m/s (885–974 km/h) depending on air temperature.
New, thin airfoils made possible by CFRP, plus structural bracing by thin CFRP trusses, finally allow for wings with little or no sweep that can travel at these speeds without producing too much drag. The advantages of an unswept wing include the fact that it is structurally more efficient than a swept-back wing. To have a given wingspan, a swept wing must be longer than an unswept one. The wing’s lift then acts with a longer moment arm, which increases the bending moment on the wing’s structure. To resist this, the structure of the swept wing must be stronger, and therefore heavier, than an unswept one.
The external truss also reduces stress on the wing’s internal structure so the wing can be thinner top-to-bottom, giving it a small frontal cross-section and thereby reducing drag. To cut drag more, the wing is narrower front-to-back than a traditional wing, which lets laminar flow cover a larger fraction of the wing surface. The wing is also longer relative to its front-to-back width, or “chord”, and this higher aspect ratio reduces the energy lost when high-pressure air from below the wing flows around the wingtip to the low-pressure region above the wing. An upward-folding tip allows this long-winged aircraft to fit into the small gates of regional airports.
Electric aeroplanes
Another way to make planes greener is to develop hybrid propulsion, rather like we now have hybrid cars. The idea is that jet turbines would boost power for take-off while batteries or fuel cells would provide steady power for cruise. Of course, it would be even better if aeroplanes could fly purely on renewable energy (such as solar or hydro) or nuclear power, which emit no carbon.
Alas, an all-electric airliner to replace today’s planes is not on the cards. Batteries have a specific energy (measured in joules per kilogram) that is orders of magnitude lower than the specific energy of hydrocarbon fuel. This figure will improve, but not enough. That’s because when weight matters, as it does in aeroplanes, batteries will always suffer from the fact that they have to carry their own oxidizer, whereas fuel-burning engines use oxygen from air. Therefore, a battery-powered aeroplane or helicopter can only work over tens or perhaps hundreds of miles, not over the thousands of miles where an aeroplane’s speed makes it most useful.
A battery-powered aeroplane or helicopter can only work over tens or perhaps hundreds of miles, not over the thousands of miles where an aeroplane’s speed makes it most useful
There are a few prospects on the horizon for getting around the fundamental limits of batteries. One option is to use lasers or microwaves to transmit energy from the ground to aircraft in flight. The beam of photons creates voltage and current in dipole antenna elements or photovoltaic arrays on the aircraft, with diodes siphoning off the power to run motors or electronics. This has been done at a small scale. One of the best demonstrations was by the SHARP project in Canada back in 1987 using microwaves, but more recent efforts include Lockheed Martin and LaserMotive (now PowerLight) flying an unmanned aerial vehicle (UAV) using laser beams. However, the method faces regulatory and cost challenges before it can scale up to commercial flight.
As for solar-powered aircraft, they do already exist, but because the sunlight is so weak, these fragile aircraft fly slowly and with little payload. A third option is to recharge aircraft in flight, just as aerial tankers transfer fuel to military aircraft today. It’s plausible for long-range all-electric flight, but technical challenges remain.
From super to hypersonic airliners
Another development that we could see over the next two or three decades is hypersonic travel, which means craft flying at Mach 5 (6126 km/h) or faster. This kind of speed could get you from Los Angeles to Beijing in no more than two hours. Supersonic airliners – the Concorde and the Tupolev 144 – only flew at half that speed and gave off huge amounts of CO 2 . They were also horribly noisy at take-off and landing, and emitted sonic booms during cruise. Both are now out of operation.
Hypersonic airliners will do better. These new aircraft will likely use hydrogen – produced by electrolysis using non-fossil energy sources – or low-carbon fuel like methane. With such light molecules, the fuel and air can rapidly mix, which is vital because air moves through the engine so fast it spends only a few milliseconds in the combustion zone.
The future of flight Concept images of a future commercial airliner with straight truss-braced wings (left, courtesy: NASA/The Boeing Company) and a low-sonic-boom hypersonic aircraft (right, courtesy: Lockheed Martin).
Sonic boom is less of a problem now, too. NASA is already developing low-boom aircraft designs, which have a long, sharp nose that reduces the area over which air is compressed to form the leading shockwave. They also keep protuberances, like the engine intake, on top of the fuselage so shockwaves produced there go up, not downward to bother people.
What’s more, thanks to a quirk of the atmosphere, most acoustic energy from hypersonic planes will never reach Earth. If you imagine a sonic boom heading out diagonally down from an aircraft, the sound will meet steadily warmer air as it moves. Given that sound and shockwaves travel faster in warm air, the sonic boom will refract – its path will curve and become more horizontal as it moves lower. So apart from shockwaves that are heading almost straight down, the path eventually curves upward, avoiding the ground altogether. And because hypersonic aircraft fly at 27,000 to 30,000 m – more than twice as high as today’s airliners, because higher altitudes mean thinner air and therefore less drag – nearly 100% of the sonic boom refracts away from the Earth.
Despite these benefits, several challenges of hypersonic flight must be overcome. One is the fact that air at the nose and leading edge of a hypersonic plane can get hotter than 1300 K because the air’s kinetic energy becomes heat energy when it runs into the perpendicular surface and stops. At those temperatures, CFRP, which has revolutionized today’s airliners, simply doesn’t hold its strength. Fortunately, titanium alloys and other advanced, lightweight materials – some with honeycomb structures to reduce heat transport – are being developed to solve this problem.
Another issue is ionizing radiation. When a galactic cosmic-ray particle strikes a nucleus in the upper atmosphere, the nucleus shatters into a spray of secondary particles. The trails of these secondaries create conductive paths in semiconductor electronics. Today’s planes fly at altitudes of 9000–13,000 m, where the secondaries are spread out, so any one electronic device sees only a small effect. But for a hypersonic plane flying at 30,000 m, the secondaries will be tightly clumped still, creating a much stronger radiation environment. It wouldn’t be a problem for passengers; a flight will be so short that the total dose would be lower than in today’s flights. But electronics will have trouble. A single chip may be hit by many secondaries at the same time, and such a sudden rise in conductivity can cause errors in a semiconductor chip, or even damage it permanently. Costly solutions do exist for spacecraft, such as physical shielding or electronics made of expensive materials with large band gaps. The challenge is to devise solutions for aircraft that are affordable and lightweight.
Urban aviation Sky taxi Aircraft like this helicopter developed by Volocopter could be roaming our city skies taxiing people and cargo. (Courtesy: CC BY-SA 4.0 Matti Blume) With towns and cities suffering from rising congestion on the roads, there is a growing demand for an aircraft that can land vertically in a small space, load one or two people or a van-sized cargo, and fly above the clogged highways to another spot in the same city. That’s where battery-powered helicopters could be the answer. With four or more rotors, these electric “rotorcraft” will soon be carrying cargo, and perhaps passengers, in cities. Their short range – a few dozen miles – is a perfect match for urban flight. This new family of aircraft has many environmental benefits. Because they fly at about 320 km/h and use uncongested routes, each aircraft can make as many trips per day as, say, 10 cars or trucks. If that happens, it gets 10 vehicles off the roads, making our commute a little easier. Each aircraft would also mean that 10 cars or trucks wouldn’t need to be built, saving energy and materials. Of course, being electric-powered, the aircraft emit no CO 2 in cities where electricity comes from non-fossil sources. It also helps keep engine noise tolerable. Challenges remain, however. For a two-person taxi service, the aircraft would have to be recharged quickly. The 15-minute charging time of today’s batteries would need to be shortened, or ways would have to be found to quickly swap depleted batteries for charged ones. Batteries would go through up to 20 deep discharge cycles per day, so they would reach end-of-life in a few months as the electrochemical process involved in a rechargeable battery isn’t totally reversible. That’s because with each charge–discharge cycle, some atoms from the electrodes or the electrolyte go to the wrong place, eventually weakening the battery and making it potentially develop too much leakage current to hold charge for long. Discarding or refurbishing the batteries at the required rate will therefore be a challenge. Helicopters are also noisy, as is any vehicle with many small rotors. There are ways to make them quieter, like ducts around the rotors, but these have costs and trade-offs. Finally, the density of air traffic would be unprecedented; a thousand aircraft simultaneously flying in an area the size of Los Angeles or London will require a new, and probably automated, approach to air traffic control. Computers, not humans, would have to pilot these vehicles and co-ordinate with traffic control.
In essence, the commercial aviation sector is continuing to refine and develop traditional aircraft as it has throughout its 100-year-old history, constantly seeking to reduce costs and lower their impact on the environment. But there are now new directions for the industry too, in the form of super-efficient new airliners that will look quite different, electric-powered rotorcraft that revolutionize urban transport (see box above), and hypersonic aeroplanes that protect the world’s environment while shrinking the distance between its people. Within decades, air travel may look very different to now.