Power gadgets with energy leaking from your microwave

Rather than have to replace the batteries in small gadgets like thermometers, cooking timers, and digital scales, now you can scavenge just enough power to run them using the electricity that leaks past your microwave's door.

New Scientist explains:

A microwave oven uses a device called a magnetron to generate electromagnetic waves with a wavelength of 12.5 centimeters and a frequency of 2.4 gigahertz - enough for vibrating water molecules to heat food.

Although a waveguide delivers the microwaves into the food chamber some still escape through the gap around the oven door and through the metal-meshed window.

For consumer safety, the U.S. Food And Drug Administration specifies that leakage can't exceed a power density of 5 milliwatts per square centimeter, at around 5 cm from the oven surface.

Now, Yoshihiro Kawahara at the University of Tokyo and colleagues have found a way to harness that escaped energy.

They began by studying the energy leakage from a range of ovens to see what useful power levels might be harvestable to replace button cell batteries. They conducted leakage tests on a range of popular commercial ovens, including those from Sharp, Panasonic, and Whirlpool. The average leakage is generally lower than the legal limit: around 0.5 milliwatts per square centimeter. That made around 1 milliwatt of power available in front of the oven. The team then designed a quarter-sized power harvester. Combined with a 1-cm-long microwave antenna, it generates an electric current that could charge a circuit.

"The energy accumulated over a two-minute run of the microwave oven was enough to operate some low-power kitchen tools for a few minutes," Kawahara says. They were able to power a digital cooking timer to count down for 3 minutes and beep for 2.5 seconds.

The small harvester could be embedded in most kitchen gadgets. So by leaving gadgets close to the microwave, they would gradually be charged up enough to operate.

The work was presented at UbiComp 2013 in Zurich earlier this month.

[ UbiComp via New Scientist]

Image: Geoffrey Fairchild via Flickr