Power/Performance Bits: Sept. 14

Thermal management material
Engineers at the University of California Los Angeles integrated a new thermal management material, boron arsenide, with a HEMT chip to demonstrate the material’s potential.

The team developed boron arsenide as a thermal management material in 2018 and found it to be very effective at drawing and dissipating heat.

In the latest experiments, they used wide bandgap transistors made of gallium nitride called high-electron-mobility transistors (HEMTs). When running the processors at near maximum capacity, chips that used boron arsenide as a heat spreader showed a maximum heat increase from room temperatures to nearly 188 degrees Fahrenheit. This is significantly lower than chips using diamond to spread heat, with temperatures rising to approximately 278 degrees Fahrenheit, or the ones with silicon carbide showing a heat increase to about 332 degrees Fahrenheit.

An electron microscopy image of a gallium nitride-boron arsenide heterostructure interface at atomic resolution (Credit: The H-Lab / UCLA)

“These results clearly show that boron-arsenide devices can sustain much higher operation power than processors using traditional thermal-management materials,” said Yongjie Hu, an associate professor of mechanical and aerospace engineering at the UCLA Samueli School of Engineering. “And our experiments were done under conditions where most current technologies would fail. This development represents a new benchmark performance and shows great potential for applications in high-power electronics and future electronics packaging.”

In addition to excellent thermal conductivity, boron arsenide displays low heat-transport resistance.

“When heat crosses a boundary from one material to another, there’s typically some slowdown to get into the next material,” Hu said. “The key feature in our boron arsenide material is its very low thermal- boundary resistance. This is sort of like if the heat just needs to step over a curb, versus jumping a hurdle.”

The researchers said that the demonstration opens a path for industry adoption of boron arsenide. They also plan to investigate boron phosphide as a heat-spreader candidate.

Colorful electronic paper
Researchers at Chalmers University of Technology and Linköping University are working on a type of screen that can display colors in outdoor and bright light settings with low power consumption. Instead of a backlight, reflective screens, also called electronic paper or e-paper, use ambient light. Ones in use today are typically only in black and white.

“For reflective screens to compete with the energy-intensive digital screens that we use today, images and colors must be reproduced with the same high quality. That will be the real breakthrough. Our research now shows how the technology can be optimized, making it attractive for commercial use,” says Marika Gugole, a doctoral student at the Department of Chemistry and Chemical Engineering at Chalmers University of Technology.

Electronic paper using ambient light. A new design from Chalmers University of Technology could help produce e-readers, advertising signs and other digital screens with optimal color display and minimal energy consumption. ​​​​​​​​​​​(Credit: Marika Gugole/Chalmers​)

The team previously developed a porous and nanostructured material, containing tungsten trioxide, gold, and platinum, that could produce a wide range of colors. However, the ultra-thin, flexible screen did not have optimal color quality. To address the shortcoming, they tried inverting the design. In the previous screen, the component that makes it electrically conductive was placed above the pixelated nanostructure. In flipping the design so it is underneath, the colors showed up much more clearly.

Reflective screens consume minimal energy and are less tiring on the eyes. “Our main goal when developing these reflective screens, or ‘electronic paper’ as it is sometimes termed, is to find sustainable, energy-saving solutions. And in this case, energy consumption is almost zero because we simply use the ambient light of the surroundings,” explained Andreas Dahlin, a professor at the Department of Chemistry and Chemical Engineering at Chalmers.

The researchers plan to work on reducing the amount of rare metals needed to construct the display. Applications include e-readers, tablets, and outdoor advertising, and they are optimistic about commercialization possibilities. “A large industrial player with the right technical competence could, in principle, start developing a product with the new technology within a couple of months,” said Dahlin.

Charging wearables through skin
Researchers at the University of Massachusetts Amherst propose a way to charge low-power wearables such as fitness bands without having to take them off. The proposed method uses human skin as a conductor to transfer power to the device.

“Why can’t we instrument daily objects, such as the office desk, chair, and car steering wheel, so they can seamlessly transfer power through human skin to charge up a watch or any wearable sensor while the users interact with them? Like, using human skin as a wire,” said Sunghoon Ivan Lee, assistant professor in the University of Massachusetts Amherst College of Information and Computer Sciences and director of the Advanced Human Health Analytics Laboratory. “Then we can motivate people to do things like sleep tracking because they never have to take their watch off to charge it.”

“In this device we have an electrode that couples to the human body, which you could think of as the red wire, if you’re thinking of a traditional battery with a pair of red and black wires,” explained Jeremy Gummeson, an assistant professor of electrical and computer engineering at UMass Amherst. The conventional black wire is established between two metal plates that are embedded on the wearable device and an instrumented everyday object, which becomes coupled via the surrounding environment when the frequency of the energy carrier signal is sufficiently high – in the hundreds of megahertz range.

The researchers tested a prototype of their technology with 10 people in three scenarios during which the individuals’ arm or hand made contact with the power transmitter, either as they worked on a desktop keyboard or a laptop, or as they were holding the steering wheel of a car.

Their research showed that approximately 0.5 – 1 milliwatt of direct current (DC) power was transferred to the wrist-worn device using the skin as the transfer medium. This small amount of electricity conforms to safety regulations established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and Federal Communications Commission (FCC).

“You can think of the amount of power that gets transmitted by our technology as roughly comparable to what’s transmitted through the human body when you stand on a body composition scale, hence poses minimal health risks,” Gummeson said.

There is no sensation to the person who comes into contact with the power transmitter. “This is way beyond the frequency range that the human can actually perceive,” Lee added.

The team said that while the prototype currently doesn’t produce enough power to continuously operate a sophisticated device such as an Apple Watch, it could support ultra-low-power fitness trackers like Fitbit Flex and Xiaomi Mi-Bands. They aim to improve the power transfer rate in subsequent studies.