Measuring temperature with neutrons

Researchers from Osaka University, National Institutes for Quantum Science and Technology, Hokkaido University, Japan Atomic Energy Agency, and Tokamak Energy developed a way to rapidly measure the temperature of electronic components inside a device using neutrons.

The technique, called ‘neutron resonance absorption’ (NRA), examines neutrons being absorbed by atomic nuclei at certain energy levels to determine the properties of the material. After being generated using high-intensity laser beans, the neutrons were then decelerated to a very low energy level before being passed through the sample, in this case plates of tantalum and silver. The temporal signal of the NRA was altered in a predictable manner when the sample material’s temperature was changed.

“This technology makes it possible to instantaneously and accurately measure temperature,” said Zechen Lan of Osaka University, in a statement. “As our method is non-destructive, it can be used to monitor devices like batteries and semiconductor devices.”

The technique can acquire temperature data in a window of 100 nanoseconds, and the measurement device itself is about a tenth of the size of similar equipment.

“Using lasers to generate and accelerate ions and neutrons is nothing new, but the techniques we’ve developed in this study represent an exciting advance,” added Akifumi Yogo of Osaka University, in a statement. “We expect that the high temporal resolution will allow electronics to be examined in greater detail, help us to understand normal operating conditions, and pinpoint abnormalities.” [1]

Mapping heat transfer

Researchers from the University of Rochester applied optical super-resolution fluorescence microscopy techniques used in biological imaging to map heat transfer in electronic devices using luminescent nanoparticles.

By applying highly doped upconverting nanoparticles to the surface of a device, the researchers were able to achieve super-high resolution thermometry at the nanoscale level from up to 10 millimeters away.

Rochester researchers demonstrated their super-high resolution thermometry techniques on an electrical heater structure that the team designed to produce sharp temperature gradients. (Credit: University of Rochester / J. Adam Fenster)

“The building blocks of our modern electronics are transistors with nanoscale features, so to understand which parts of overheating, the first step is to get a detailed temperature map,” said Andrea Pickel, an assistant professor from the University of Rochester’s Department of Mechanical Engineering, in a release. “But you need something with nanoscale resolution to do that.”

The researchers demonstrated the technique using an electrical heater structure designed to produce sharp temperature gradients. To improve the process, the team hopes to lower the laser power used and refine the methods for applying layers of nanoparticles to the devices. [2]

ML for predicting thermal properties

Researchers from MIT, Argonne National Laboratory, Harvard University, the University of South Carolina, Emory University, the University of California at Santa Barbara, and Oak Ridge National Laboratory propose a new machine learning framework that provides much faster prediction of phonon dispersion relations, an important measurement for determining the thermal properties of a material and how heat moves through semiconductors and insulators.

Heat-carrying phonons have an extremely wide frequency range, and the particles interact and travel at different speeds. “Phonons are the culprit for the thermal loss, yet obtaining their properties is notoriously challenging, either computationally or experimentally,” said Mingda Li, associate professor of nuclear science and engineering at MIT, in a release.

The researchers started with a graph neural network (GNN) that converts a material’s atomic structure into a crystal graph comprising multiple nodes, which represent atoms, connected by edges, which represent the interatomic bonding between atoms.

To make it suitable for predicting phonon dispersion relations, they created a virtual node graph neural network (VGNN) by adding a series of flexible virtual nodes to the fixed crystal structure to represent phonons. This enabled the VGNN to skip many complex calculations when estimating phonon dispersion relations, making it a more efficient method than a standard GNN.

Li noted that a VGNN could be used to calculate phonon dispersion relations for a few thousand materials in a few seconds with a personal computer. The technique could also be used to predict challenging optical and magnetic properties. [3]

References

[1] Lan, Z., Arikawa, Y., Mirfayzi, S.R. et al. Single-shot laser-driven neutron resonance spectroscopy for temperature profiling. Nat Commun 15, 5365 (2024). https://doi.org/10.1038/s41467-024-49142-y

[2] Ziyang Ye et al., Optical super-resolution nanothermometry via stimulated emission depletion imaging of upconverting nanoparticles. Sci. Adv. 10, eado6268 (2024) https://doi.org/10.1126/sciadv.ado6268

[3] Okabe, R., Chotrattanapituk, A., Boonkird, A. et al. Virtual node graph neural network for full phonon prediction. Nat Comput Sci 4, 522–531 (2024). https://doi.org/10.1038/s43588-024-00661-0

The post Research Bits: Aug. 5 appeared first on Semiconductor Engineering.

This year, the sun will reach solar maximum, a period of peak magnetic activity that occurs approximately once every 11 years. That means more sunspots and more frequent intense solar storms. Here on Earth, these result in beautiful auroral activity, but also geomagnetic storms and the threat of electromagnetic pulses (EMPs), which can bring widespread damage to electronic equipment and communications systems.

Yilu Liu

Yilu Liu is a Governor’s Chair/Professor at the University of Tennessee, in Knoxville, and Oak Ridge National Laboratory.

And the sun isn’t the only source of EMPs. Human-made EMP generators mounted on trucks or aircraft can be used as tactical weapons to knock out drones, satellites, and infrastructure. More seriously, a nuclear weapon detonated at a high altitude could, among its more catastrophic effects, generate a wide-ranging EMP blast. IEEE Spectrum spoke with Yilu Liu, who has been researching EMPs at Oak Ridge National Laboratory, in Tennessee, about the potential effects of the phenomenon on power grids and other electronics.

What are the differences between various kinds of EMPs?

Yilu Liu: A nuclear explosion at an altitude higher than 30 kilometers would generate an EMP with a much broader spectrum than one from a ground-level weapon or a geomagnetic storm, and it would arrive in three phases. First comes E1, a powerful pulse that brings very fast high-frequency waves. The second phase, E2, produces current similar to that of a lightning strike. The third phase, E3, brings a slow, varying waveform, kind of like direct current [DC], that can last several minutes. A ground-level electromagnetic weapon would probably be designed for emitting high-frequency waves similar to those produced by an E1. Solar magnetic disturbances produce a slow, varying waveform similar to that of E3.

How do EMPs damage power grids and electronic equipment?

Liu: Phase E1 induces current in conductors that travels to sensitive electronic circuits, destroying them or causing malfunctions. We don’t worry about E2 much because it’s like lightning, and grids are protected against that. Phase E3 and solar magnetic EMPs inject a foreign, DC-like current into transmission lines, which saturates transformers, causing a lot of high-frequency currents that have led to blackouts.

How do you study the effects of an EMP without generating one?

Liu: We measured the propagation into a building of low-level electromagnetic waves from broadcast radio. We wanted to know if physical structures, like buildings, could act as a filter, so we took measurements of radio signals both inside and outside a hydropower station and other buildings to figure out how much gets inside. Our computer models then amplified the measurements to simulate how an EMP would affect equipment.

What did you learn about protecting buildings from damage by EMPs?

Liu: When constructing buildings, definitely use rebar in your concrete. It’s very effective as a shield against electromagnetic waves. Large windows are entry points, so don’t put unshielded control circuits near them. And if there are cables coming into the building carrying power or communication, make sure they are well-shielded; otherwise, they will act like antennas.

Have solar EMPs caused damage in the past?

Liu: The most destructive recent occurrence was in Quebec in 1989, which resulted in a blackout. Once a transformer is saturated, the current flowing into the grid is no longer just 60 hertz but multiples of 60 Hz, and it trips the capacitors, and then the voltage collapses and the grid experiences an outage. The industry is better prepared now. But you never know if the next solar storm will surpass those of the past.

This article appears in the June 2024 issues as “5 Questions for Yilu Liu.”

Over just the past couple of years, supercomputing has accelerated into the exascale era—with the world’s most massive machines capable of performing over a billion billion operations per second. But unless big efficiency improvements can intervene along its exponential growth curve, computing is also anticipated to require increasingly impractical and unsustainable amounts of energy—even, according to one widely cited study, by 2040 demanding more energy than the world’s total present-day output.

Fortunately, the high-performance computing community is shifting focus now toward not just increased performance (measured in raw petaflops or exaflops) but also higher efficiency, boosting the number of operations per watt.

The Green500 list saw newcomers enter into the top three spots, suggesting that some of the world’s newest high-performance systems may be chasing efficiency at least as much as sheer power.

The newest ranking of the Top500 supercomputers (a list of the world’s most powerful machines) and its cousin the Green500 (ranking instead the world’s highest-efficiency machines) came out last week. The leading 10 of the Top 500 largest supercomputers remains mostly unchanged, headed up by Oak Ridge National Laboratory’s Frontier exascale computer. There was only one new addition in the top 10, at No. 6: Swiss National Supercomputing Center’s Alps system. Meanwhile, Argonne National Laboratory’s Aurora doubled its size, but kept its second-tier ranking.

On the other hand, The Green500 list saw newcomers enter into the top three spots, suggesting that some of the world’s newest high-performance systems may be chasing efficiency at least as much as sheer power.

Heading up the new Green500 list was JEDI, Jülich Supercomputing Center’s prototype system for its impending JUPITER exascale computer. The No. 2 and No. 3 spots went to the University of Bristol’s Isambard AI, also the first phase of a larger planned system, and the Helios supercomputer from the Polish organization Cyfronet. In fourth place is the previous list’s leader, the Simons Foundation’s Henri.

A Hopper Runs Through It

The top three systems on the Green500 list have one thing in common—they are all built with Nvidia’s Grace Hopper superchips, a combination of the Hopper (H100) GPU and the Grace CPU. There are two main reasons why the Grace Hopper architecture is so efficient, says Dion Harris, director of accelerated data center go-to-market strategy at Nvidia. The first is the Grace CPU, which benefits from the ARM instruction set architecture’s superior power performance. Plus, he says, it incorporates a memory structure, called LPDDR5X, that’s commonly found in cellphones and is optimized for energy efficiency.

Nvidia’s GH200 Grace Hopper superchip, here deployed in Jülich’s JEDI machine, now powers the world’s top three most efficient HPC systems. Jülich Supercomputing Center

The second advantage of the Grace Hopper, Harris says, is a newly developed interconnect between the Hopper GPU and the Grace CPU. The connection takes advantage of the CPU and GPU’s proximity to each other on one board, and achieves a bandwidth of 900 gigabits per second, about 7 times as fast as the latest PCIe gen5 interconnects. This allows the GPU to access the CPU’s memory quickly, which is particularly important for highly parallel applications such as AI training or graph neural networks, Harris says.

All three top systems use Grace Hoppers, but Jülich’s JEDI still leads the pack by a noticeable margin—72.7 gigaflops per watt, as opposed to 68.8 gigaflops per watt for the runner-up (and 65.4 gigaflops per watt for the previous champion). The JEDI team attributes their added success to the way they’ve connected their chips together. Their interconnect fabric was also from Nvidia—Quantum-2 InfiniBand—rather than the HPE Slingshot used by the other two top systems.

The JEDI team also cites specific optimizations they did to accommodate the Green500 benchmark. In addition to using all the latest Nvidia gear, JEDI cuts energy costs with its cooling system. Instead of using air or chilled water, JEDI circulates hot water throughout its compute nodes to take care of the excess heat. “Under normal weather conditions, the excess heat can be taken care of by free cooling units without the need of additional cold-water cooling,” says Benedikt von St. Vieth, head of the division for high-performance computing at Jülich.

JUPITER will use the same architecture as its prototype, JEDI, and von St. Vieth says he aims for it to maintain much of the prototype’s energy efficiency—although with increased scale, he adds, more energy may be lost to interconnecting fabric.

Of course, most crucial is the performance of these systems on real scientific tasks, not just on the Green500 benchmark. “It was really exciting to see these systems come online,” Nvidia’s Harris says, “But more importantly, I think we’re really excited to see the science come out of these systems, because I think [the energy efficiency] will have more impact on the applications even than on the benchmark.”

Researchers at Oak Ridge National Laboratory in Tennessee recently announced that they have set a record for wireless EV charging. Their system’s magnetic coils have reached a 100-kilowatt power level. In tests in their lab, the researchers reported their system’s transmitter supplied enough energy to a receiver mounted on the underside of a Hyundai Kona EV to boost the state of charge in the car’s battery by 50 percent (enough for about 150 kilometers of range) in less than 20 minutes.

“Impressive,” says Duc Minh Nguyen, a research associate in the Communication Theory Lab at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. Nguyen is the lead author of several of papers on dynamic wireless charging, including some published when he was working toward his PhD at KAUST.

In 15 minutes, “the batteries could take on enough energy to drive for another two-and-a-half or three hours—just in time for another pit stop.”
–Omer Onar, Oak Ridge National Laboratory

The Oak Ridge announcement marks the latest milestone in work on wireless charging that stretches back more than a decade. As IEEE Spectrum reported in 2018, WiTricity, headquartered in Watertown, Mass., had announced a partnership with an unspecified automaker to install wireless charging receivers on its EVs. Then in 2021, the company revealed that it was working with Hyundai to outfit some of its Genesis GV60 EVs with Wireless charging. (In early 2023, Car Buzz reported that it had sniffed out paperwork pointing to Hyundai’s plans to equip its Ionic 5 EV with wireless charging capability.)

The plan, said WiTricity, was to equip EVs with magnetic resonance charging capability so that if such a vehicle were parked over a static charging pad installed in, say, the driver’s garage, the battery would reach full charge overnight. By 2020, we noted, a partnership had been worked out between Jaguar, Momentum Dynamics, Nordic taxi operator Cabonline, and charging company Fortam Recharge. That group set out to outfit 25 Jaguar I-Pace electric SUVs with Momentum Dynamics’ inductive charging receivers. The receivers and transmitters, rated at 50 to 75 kilowatts, were designed so that any of the specially equipped taxis would receive enough energy for 80 kilometers of range by spending 15 minutes above the energized coils embedded in the pavement as the vehicle works its way through a taxi queue. Now, according to Oak Ridge, roughly the same amount of charging time will yield about 1.5 times that range.

The Oak Ridge research team admits that installing wireless charging pads is expensive, but they say dynamic and static wireless charging can play an important role in expanding the EV charging infrastructure.

This magnetic resonance transmitter pad can wirelessly charge an EV outfitted with a corresponding receiver.Oak Ridge National Laboratory

Omad Onar, an R&D staffer in the Power Electronics and Electric Machinery Group at Oak Ridge and a member of the team that developed the newest version of the wireless charging system, envisions the static versions of these wireless charging systems being useful even for extended drives on highways. He imagines them being placed under a section of specially marked parking spaces that allow drivers to pull up and start charging without plugging in. “The usual routine—fueling up, using the restroom, and grabbing coffee or a snack usually takes about 15 minutes or more. In that amount of time, the batteries could take on enough energy to drive for another two-and-a-half or three hours—just in time for another pit stop.” What’s more, says Onar, he and his colleagues are still working to refine the system so it will transfer energy more efficiently than the one-off prototype they built in their lab.

Meanwhile, Israeli company Electreon has already installed electrified roads for pilot projects in Sweden, Norway, Italy, and other European countries, and has plans for similar projects in the United States. The company found that by installing a stationary wireless charging spot at one terminal end of a bus route near Tel Aviv University (its first real-world project), electric buses operating on that route were able to ferry passengers back and forth using batteries with one-tenth the storage capacity that was previously deemed necessary. Smaller batteries mean cheaper vehicles. What’s more, says Nguyen, charging a battery in short bursts throughout the day instead of depleting it and filling it with up with, say, an hour-long charge at a supercharging station extends the battery’s life.