Scientists in Japan have discovered a way to run kitchen appliances using electromagnetic energy scavenged from microwave ovens.
While the majority of radiation generated by the common kitchen appliance is directed at the food inside the device, a portion of the energy can still escape through the gap around the door and through the metal-meshed window. So, for consumer reasons, the U.S. Food and Drug Administration placed limitations on the leakage, stipulating that it not exceed a power density of “1 milliwatt per square centimeter at any point 5 centimeters or more from the external surface of the oven, measured prior to acquisition by a purchaser, and, thereafter, 5 milliwatts per square centimeter at any such point.”
According to Yoshihiro Kawahara, an electronics engineer at the University of Tokyo, this leakage is enough to run low-power devices such as oven thermometers, cooking timers and digital scales. Kawahara, along with colleagues from the University of Tokyo and the Georgia Institute of Technology in Atlanta, designed and tested a tiny power harvester’s capability to absorb leakage from a nearby microwave oven. The power harvester was then used to power a digital cooking timer enough to count down for 3 min and beep for 2.5 seconds.
“Our experimental results showed that the leakage received by a dipole antenna was about 0 dBm (1 mW) at a point 5 cm in front of the door. A rectenna consisting of a dipole antenna and charge pump can convert the leaked microwave energy into a DC current. When a microwave oven is operated for 2 min, 9.98 mJ of energy was harvested,” Kawahara wrote in a paper published with the Association for Computing Machinery.
Approximately the size of a US quarter, the energy harvester can be embedded in most devices found in the kitchen, and could even eventually provide power to larger, energy-efficient devices. The technology could also be used in smart home sensor networks.
“As energy efficiency continues to improve, the energy requirements to power electronic devices will continue to drop,” Kawahara said. “This in turn means it is feasible to power more devices by a small amount of energy of about a few dozen microwatts.”
