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Boosting the Transfer Efficiency of Wireless Power Transfer Systems

Wireless power transfer is less efficient over distances, but there are remedies

2 min read
Boosting the Transfer Efficiency of Wireless Power Transfer Systems
Image: David Ricketts

The wireless transfer of electric current that charges your electric toothbrush is highly efficient: The receiver coil in the handle of the toothbrush fits tightly around the transmitter coil in the charger, making the process about as lossless the operation of the ubiquitous transformer. 

However, using wireless power transfer for electric cars by charging them with transmitter coils embedded in the pavement is more problematic.  The receiver coil in the car has to be placed as close as possible to the ground; still, only a part of the transmitted energy reaches the receiver coil. 

Now researchers from North Carolina State University and Carnegie Mellon University say they have hit upon a way to boost the efficiency of the energy transfer in that situation. They reported, in a paper published in the online edition of the journal IEEE Antennas and Wireless Propagation Letters, that by placing a magnetic resonance field enhancer (MRFE)—a loop of copper wire resonating at the same frequency as the AC current feeding the transmitter coil—between the transmitter and receiver coil, they could boost the transmission efficiency by at least 100 percent. “Our experimental results show double the efficiency using the MRFE in comparison to air alone,” David Ricketts of NC State, said in a press release. The MRFE increases the strength of the magnetic field that reaches the receiver coil, resulting in an increase of the transmission efficiency.

Previously, the team had investigated the use of metamaterials to enhance the magnetic field. “We performed a comprehensive analysis using computer models of wireless power systems and found that MRFE could ultimately be five times as efficient as using metamaterials and offer 50 times the efficiency of transmitting through air alone,” Ricketts says.  

For their experimental setup, the team used two coils of 4.25-centimeter- diameter copper wire with six turns for the transmitter and receiver coils.  The coils were separated by 12.2 cm and the transmitter coil was powered with a 2.94-megahertz signal. They measured the transmission efficiency by placing a metamaterial between the transmitter and receiver coil and comparing it with a setup where a single, 12-cm-diameter copper-wire loop replaced the metamaterial. They found that the copper wire version improved the efficiency by a factor of almost two.

These laboratory experiments, though much smaller systems than would be used in the future applications the researchers envision, clearly indicate how transmission efficiency could be tweaked. “This [research] could help advance efforts to develop wireless power transfer technologies for use with electric vehicles, in buildings, or in any other application where enhanced efficiency or greater distances are important considerations,” Ricketts says.

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Chinese Joint Venture Will Begin Mass-Producing an Autonomous Electric Car

With the Robo-01, Baidu and Chinese carmaker Geely aim for a fully self-driving car

4 min read
A black car sits against a white backdrop decorated with Chinese writing. The car’s doors are open, like a butterfly’s wings. Two charging stations are on the car’s left; two men stand on the right.

The Robo-01 autonomous electric car shows off its butterfly doors at a reveal to the media in Beijing, in June 2022.

Tingshu Wang/Reuters/Alamy
Purple

In October, a startup called Jidu Automotive, backed by Chinese AI giant Baidu and Chinese carmaker Geely, officially released an autonomous electric car, the Robo-01 Lunar Edition. In 2023, the car will go on sale.

At roughly US $55,000, the Robo-01 Lunar Edition is a limited edition, cobranded with China’s Lunar Exploration Project. It has two lidars, a 5-millimeter-wave radars, 12 ultrasonic sensors, and 12 high-definition cameras. It is the first vehicle to offer on-board, AI-assisted voice recognition, with voice response speeds within 700 milliseconds, thanks to the Qualcomm Snapdragon 8295 chip.

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