Ambient ‘T-rays’ could help power IoT devices

Most things with a measurable temperature – human beings going about their daily routines, inert objects – generate terahertz waves, radiation that is sandwiched between infrared and microwave on the electromagnetic spectrum.

So far, these waves haven’t proved very useful, but now scientists at MIT are trying to harness them with devices that use them to generate electricity that could charge the batteries of cellphones, laptops, even medical implants.

If successful, the charging devices would passively gather the waves and generate DC current at room temperature, something that hasn’t been accomplished before. Previous devices that can turn terahertz waves – T-rays – to electricity only work in ultracold environments, according to an MIT News article about the project.

Called a terahertz rectifier, the device would collect T-rays on a layer of graphene laid on top of a layer of boron nitride. If the rays were to hit the graphene by itself, their effect on electrons in the graphene molecules would be scattered symmetrically in all directions rather than in a single direction that would create the desired electric current.

The proximity of boron nitride, however, affects how the graphene electrons respond to the T-rays. Rather than scattering in all directions, they moved in one direction (what is known as skew scattering), creating a DC current. Earlier rectifiers required electronics to steer waves through them in order to create a current.

Wi-Fi signals generate T-rays as a biproduct, and these, too, could be harvested by the rectifier in addition to ambient rays created by animals and objects.

The researchers have designed such a rectifier that would wrap the graphene-boron nitride layers within an antenna that would gather T-rays and boost their signal, and they have enlisted the help of experimental physicists at MIT to create a prototype. They have also filed for a patent on the design

“This would work very much like a solar cell, except for a different frequency range, to passively collect and convert ambient energy,” Liang Fu, one of the co-authors says in the MIT News article.

The researchers published their results Science Advances.

Others have been trying to generate electricity from ambient electromagnetic waves, including some at MIT and at Ohio State University.