Highly Resonant Wireless Power Transfer:
Safe, Efficient, and over Distance
Introduction
Driving home from the airport, Marin noticed his new smart phone was low on battery once again. Its HD display, and apps using GPS, Bluetooth, and LTE/4G data communications conspired to drain the battery quickly. Without looking, he dropped his phone into an open cup-holder in the center console. Hidden several centimeters below the console, a wireless power source sensed the presence of the phone, and queried the device to determine whether or not it was wireless power enabled. The phone gave a valid response and configured itself for resonant wireless power transfer. Under the console, the source electronics turned on and began charging the phone wirelessly—with no need for a charging cradle, power cord, or especially accurate placement of the phone. Marin relaxed when he heard the recharging chime and focused his attention on the road ahead.
After exiting the highway, Marin was surprised to see that the price of gasoline had climbed to over $4.00 per gallon, as it had been months since he had last filled his tank of his new car-- a wirelessly charged hybrid electric vehicle. Since installing a wireless 3.3 kW charger in his home and office garage, his car’s traction battery was fully charged every morning before work and every evening as he began his commute home. As Marin’s car silently pulled into his driveway, it communicated with the wireless charger in his garage. The wall mounted charger electronics ran through its diagnostics and sent a low-power pulse to the mat on the garage floor. Sensors in the mat confirmed it was safe to begin charging. As Marin drove into the garage, he simply parked his car as usual. The resonant charger had enough positioning tolerance that it would work without needing any special parking procedures.
WiTricity power transfer had succeeded to make these essential products more available, convenient, and reliable.
Although the story above is fictitious, the wireless power technology described is very real. This article explores the advances in wireless power technology enabled by the use of highly resonant wireless power transfer, how those advances are being applied across a broad spectrum of applications, and how they address the safety concerns in typical applications.
Background
The idea of transmitting power through the air has been around for over a century, with Nikola
Tesla’s pioneering ideas and experiments perhaps being the most well-known early attempts to do so [1]. He had a vision of wirelessly distributing power over large distances using the earth’s ionosphere. Most approaches to wireless power transfer use an electromagnetic (EM) field of some frequency as the means by which the energy is sent. At the high frequency end of the spectrum are optical techniques that use lasers to send power via a collimated beam of light to a remote detector where the received photons are converted to electrical energy. Efficient transmission over large distances is possible with this approach; however, complicated pointing and tracking mechanisms are needed to maintain proper alignment between moving transmitters and/or receivers. In addition, objects that get between the transmitter and receiver can block the beam, interrupting the power transmission and, depending on the power level, possibly causing harm. At microwave frequencies, a similar approach can be used to efficiently transmit power over large distances using the radiated EM field from
