One of the challenges for wearable Health Tech devices is coming up with a long-lasting, reliable energy source. Various energy harvesting approaches offer some appealing solutions because they eliminate the need to recharge from some electrical source. They can pull energy out of thin air, relying on motion, temperature differentials, or electromagnetic emissions as the power source. Researchers at the University of Waterloo have come up with a new approach that could lead to more efficient harvesting of electromagnetic radio waves.
Making electricity from electromagnetic emissions is not new; this is exactly what solar cells do. And the venerable crystal radios drew their power from broadcast radio waves. The problem is that most systems that collect energy from longer wavelength sources — such as radio waves — can only produce a small amount of power. This is due to the fact that the antenna in such a device is optimized for a certain wavelength signal.
The Waterloo engineers have come up with a way to etch “metasurfaces” that are made up of patterned shapes. These can be tuned to provide “near-unity” energy absorption, which means that almost all power from the waves hitting the surface are collected and channeled to an electrical circuit. In terms of visible light, imagine a pure black material; it absorbs all the light and does not reflect any back, so the material looks black. In a similar way, this new material would “look black” to radio waves.
The researchers have already extended their technology to infrared wavelengths, and are working on higher frequency emissions such as light in the visible spectrum.