Power/Performance Bits: June 25

Improving IGBTs; carbon nanotube antenna; efficient drone swarms.


Improving IGBTs
Researchers at the University of Tokyo developed a power switching device that surpasses previous performance limits, showing that there may still be gains ahead for the silicon-based devices, which have been thought to be approaching their limits.

The team’s improved insulated gate bipolar transistor (IGBT) used a scaling approach, and simulations showed that downscaling part of an IGBT to a third of its original size could lower its operating voltage from 15 V to just 5 V and substantially decrease its driving power.

“Our IGBT scaling approach was based on a similar concept to that used in traditional microelectronics and indicated that an IGBT with an operating voltage of 5 V should be feasible,” said Takuya Saraya, a research assistant and the University of Tokyo. “However, we thought that a driving voltage of 5 V might be too low to surpass the unexpected noise level and ensure reliable operation.”

The researchers fabricated their IGBT with a rated voltage of 3300 V in a specialized clean room at The University of Tokyo and then assessed its performance. The IGBT achieved stable switching at an operating voltage of just 5 V while the power consumption of the drive circuit is only around 10% of that of a conventional IGBT operating at 15 V. Power conversion efficiency was also improved despite the lowered operation voltage.

“IGBTs are important power electronics components,” said Toshiro Hiramoto, a professor at the University of Tokyo. “Our miniaturized IGBT could lead to the further development of advanced power electronics that are smaller and have higher power conversion efficiency.”

Carbon nanotube antenna
Researchers at Rice University and NIST created antennas made of carbon nanotube films which they say are just as efficient for wireless applications as copper. They are also flexible, thinner, lighter, and could be easily applied to devices.

The antennas were made of “shear-aligned” nanotube films created by dissolving nanotubes in an acid-based solution. When spread onto a surface, the shear force produced prompts the nanotubes to self-align. This fluid-phase processing method lends itself to more scalable, continuous antenna manufacturing than gas-phase deposition, according to the researchers.

At the target frequencies of 5, 10 and 14 gigahertz, the antennas easily held their own with their metal counterparts, said Amram Bengio, formerly a graduate student at Rice who has now founded a company to further develop the material. “We were going up to frequencies that aren’t even used in Wi-Fi and Bluetooth networks today, but will be used in the upcoming 5G generation of antennas,” he said.

Metal-free antennas made of thin, strong, flexible carbon nanotube films are as efficient as common copper antennas, according to a new study by Rice University researchers. (Source: Jeff Fitlow/Rice University)

The test films were about the size of a glass slide, and between 1 and 7 microns thick. The nanotubes are held together by strongly attractive van der Waals forces, which gives the material mechanical properties far better than those of copper.

The researchers said the new antennas could be suitable for 5G networks as well as unmanned aerial vehicles, wireless telemetry portals for downhole oil and gas exploration, and IoT applications.

“There are limits because of the physics of how an electromagnetic wave propagates through space,” Bengio said. “We’re not changing anything in that regard. What we are changing is the fact that the material from which all these antennas will be made is substantially lighter, stronger and more resistant to a wider variety of adverse environmental conditions than copper.”

Efficient drone swarms
Researchers at Sun Yat-Sen University, University of Aizu, and University of Ontario Institute of Technology propose an energy-efficient data routing algorithm to improve the flying time of unmanned aerial vehicle (UAV) swarms.

Cooperative groups of UAVs can be used for civilian and military applications, such as surveying area after a natural disaster. However, they have limitations. “The battery capacity of UAVs is a critical shortcoming that limits their usage in extended search and rescue missions,” said Wuhui Chen, a researcher at China’s Sun Yat-Sen University.

To lower the UAV’s power consumption, the team developed a UAV swarm data routing algorithm that uses the strength of the group to maximize real-time transmission rates and minimize individual UAV battery challenges. Their new hybrid computational approach combines linear programming and a genetic algorithm to create a “multi-hop” data routing algorithm. A genetic algorithm solves chaotic optimization problems using an analogue of natural selection, the process that drives biological evolution.

The new adaptive LP-based genetic algorithm (ALPBGA) identifies the lowest communications energy route within a swarm in real time and simultaneously balances out individual UAV power use by determining which UAV will beam information to a base station.

Simulations showed that ALPBGA reduces the number of UAVs that stop communicating by 30% to 75% compared to existing leading UAV swarm communication algorithms and gets better as swarm size increases from tens to hundreds of UAVs.

“By balancing power consumption among the UAVs, we significantly enhance the ability of the whole system,” said Patrick Hung, of the University of Ontario Institute of Technology. “Our simulations show that our approach can outperform the existing state of the art methods.”

The team plans to extend the ALPBGA research to optimize it within the context of different swarm flying trajectories.

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