Stanford researchers wirelessly transmit electricity to a nearby moving object

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Stanford Wireless Electricity Experiment

Wireless charging of moving objects is still a thing in distant future, but a recent study by researchers at Stanford wherein they wirelessly transmitted electricity to a nearby moving object is a firm step in that direction.

While the experiment involved transmitting electricity wirelessly to a moving LED lightbulb, it nonetheless paves way for wireless charging of moving devices. The experiment demonstrated only involved a 1-milliwatt charge, but in real-life scenarios, moving objects will most probably be electric cars that would require tens of kilowatts to operate. Stanford scientists have said they are now working on greatly increasing the amount of electricity that can be transferred, and tweaking the system to extend the transfer distance and improve efficiency.

More and more studies are being carried out in the field of wireless charging to address a major drawback of plug-in electric cars – their limited driving range. More and more electric car manufacturers are achieving greater single-charge distances, but considering that there is no on-the-go mechanism for charging the batteries, their adoption on a large scale is still facing issues.

Further, charging a depleted battery takes several hours to fully recharge and that’s another problem as the vehicle will be completely unavailable during this time. A charge-as-you-drive system would overcome these limitations.

Mid-range wireless power transfer, as developed at Stanford and other research universities, is based on magnetic resonance coupling. Just as major power plants generate alternating currents by rotating coils of wire between magnets, electricity moving through wires creates an oscillating magnetic field. This field also causes electrons in a nearby coil of wires to oscillate, thereby transferring power wirelessly. The transfer efficiency is further enhanced if both coils are tuned to the same magnetic resonance frequency and are positioned at the correct angle.

However, the continuous flow of electricity can only be maintained if some aspects of the circuits, such as the frequency, are manually tuned as the object moves. So, either the energy transmitting coil and receiver coil must remain nearly stationary, or the device must be tuned automatically and continuously – a significantly complex process.

To address the challenge, the Stanford team eliminated the radio-frequency source in the transmitter and replaced it with a commercially available voltage amplifier and feedback resistor. This system automatically figures out the right frequency for different distances without the need for human interference.

Graduate student Sid Assawaworrarit, the study’s lead author tested the approach by placing an LED bulb on the receiving coil. In a conventional setup without active tuning, LED brightness would diminish with distance. In the new setup, the brightness remained constant as the receiver moved away from the source by a distance of about three feet. Fan’s team recently filed a patent application for the latest advance.

He and his team used an off-the-shelf, general-purpose amplifier with a relatively low efficiency of about 10 percent. They say custom-made amplifiers can improve that efficiency to more than 90 percent.

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