Physics Spotlight  
Terahertz waves are pervasive in our daily lives, and if harnessed, their concentrated power could potentially serve as an alternate energy source. Imagine, for instance, a cellphone add-on that passively soaks up ambient T-rays and uses their energy to charge your phone. Terahertz waves are pervasive in our daily lives, and if harnessed, their concentrated power could potentially serve as an alternate energy source. Imagine, for instance, a cellphone add-on that passively soaks up ambient T-rays and uses their energy to charge your phone. Credit: José-Luis Olivares, MIT

Energy-harvesting design aims to turn Wi-Fi signals into usable power

Device for harnessing terahertz radiation might enable self-powering implants, cellphones, other portable electronics.

Jennifer Chu | MIT News Office
March 27, 2020

Any device that sends out a Wi-Fi signal also emits terahertz waves —electromagnetic waves with a frequency somewhere between microwaves and infrared light. These high-frequency radiation waves, known as “T-rays,” are also produced by almost anything that registers a temperature, including our own bodies and the inanimate objects around us.

Terahertz waves are pervasive in our daily lives, and if harnessed, their concentrated power could potentially serve as an alternate energy source. Imagine, for instance, a cellphone add-on that passively soaks up ambient T-rays and uses their energy to charge your phone. However, to date, terahertz waves are wasted energy, as there has been no practical way to capture and convert them into any usable form.

Now physicists at MIT have come up with a blueprint for a device they believe would be able to convert ambient terahertz waves into a direct current, a form of electricity that powers many household electronics.

Their design takes advantage of the quantum mechanical, or atomic behavior of the carbon material graphene. They found that by combining graphene with another material, in this case, boron nitride, the electrons in graphene should skew their motion toward a common direction. Any incoming terahertz waves should “shuttle” graphene’s electrons, like so many tiny air traffic controllers, to flow through the material in a single direction, as a direct current.

The researchers have published their results today in the journal Science Advances, and are working with experimentalists to turn their design into a physical device.

“We are surrounded by electromagnetic waves in the terahertz range,” says lead author Hiroki Isobe, a postdoc in MIT’s Materials Research Laboratory. “If we can convert that energy into an energy source we can use for daily life, that would help to address the energy challenges we are facing right now.”

Isobe’s co-authors are Liang Fu, the Lawrence C. and Sarah W. Biedenharn Career Development Associate Professor of Physics at MIT; and Su-yang Xu, a former MIT postdoc who is now an assistant professor chemistry at Harvard University.

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