A recent article in The New York Times looks at a number of new technologies that use ambient radio waves to provide power for wireless, low-power devices and sensors. Harnessing waves from everything in the air — cellphone antennas, radio stations, TV towers, WiFi transmitters — these new technologies are using otherwise wasted energy to power a wide range of low-power sensors.

At Intel, Dr. [Joshua] Smith, working with the researcher Alanson Sample of the University of Washington, created an electronic “harvester” of ambient radio waves. It collects enough energy from a TV station broadcasting about 2.5 miles from the lab to run a temperature and humidity sensor.

The device collects enough power to produce about 50 microwatts of DC power, Dr. Smith said. That is enough for many sensing and computing jobs…. The power consumption of a typical solar-powered calculator, for example, is only about 5 microwatts…and that of a typical digital thermometer with a liquid crystal display is one microwatt.

Dr. Smith and his colleagues have built a second device, powered by radio waves, that collects signals from an outdoor weather station and transmits them to an indoor display. The unit can accumulate enough energy to send an updated temperature every five seconds.

Thanks to the virtually endless supply of radio waves in the air, these technologies could soon create wireless devices that can run continuously on an endless power supply — battery-free.