Stanford researchers demonstrate a new method to transmit electricity wirelessly

Engineers at Stanford have demonstrated a new method of transmitting electricity wirelessly to multiple devices. The wireless electricity transmission system they developed could send electricity to electric cars, robots, and drones as they move. The team says that the technology would need to be scaled up to be able to power electric cars as they drive on highways or to power robots on factory floors.Wireless power transmission also has the potential to be able to transmit power to drones as they fly through the skies. Stanford researchers Shanhui Fan and Sid Assawaworrarit have demonstrated the technology in the past that was able to charge objects that were in motion wirelessly, but the technology was too inefficient to be used outside the lab. The team says that their new research is a significant step towards a practical and efficient system for wirelessly recharging cars or robots.

Fan says that to be able to recharge a moving electric car would require their system to be scaled up. However, he doesn't believe scaling the technology up would present a significant roadblock. He says the technology is already within the range of practical usefulness recharging movie robots.

The first part of the breakthrough that allows this wireless recharging came three years ago when the researchers were able to develop a charger that can transmit electricity even as the distance to the receiver changes. This range improvement was made possible by incorporating an amplifier and feedback resistor allowing the system to adjust the operating frequency as distances changed automatically. The downside to that technology was that it was only able to transmit 10% of the power going through the system.

The new technology the researchers developed can transmit up to 92% of the power that flows through the system. That improvement was possible by switching the original amplifier to a more efficient "switch mode" amplifier. In the lab, the team can wirelessly transmit 10 W of electricity over a distance of two or three feet. Scaling of the system to transmit the tens or hundreds of kilowatts a car would require is possible. The system could transmit electricity quickly enough to power a vehicle traveling 70 mph through a four-foot charging zone. The team admits one limitation is how fast the car batteries can absorb power. The electricity can be transmitted through people without them feeling it, and without any health issues.