Any device that gives off a Wi-Fi signal also produces terahertz waves, which are electromagnetic waves with a frequency between microwaves and infrared light. These radiation waves are known as ‘T-rays’ and are also generated by almost anything that records a temperature, such as our own bodies, as well as objects around us.
A Useful Purpose for Terahertz Waves
Terahertz waves are widespread in our daily lives, and if controlled, their condensed power could probably be used as an alternative energy source; for instance, a smartphone add-on that could passively absorb surrounding T-rays and use their energy to charge the device.
Still, until now, terahertz waves are wasted energy because there was not found any practical method to capture and convert them into something useful. Now, physicists from MIT have created a blueprint for a device they suggest would be able to convert ambient terahertz waves into a direct current (DC), a type of energy that runs in numerous household electronics.
Their structure is benefiting from the quantum mechanics of the carbon material, graphene. The team discovered that by merging graphene with another material, more precisely, boron nitride, the electrons in graphene should tilt their motion toward a common trajectory. Any incoming terahertz waves should ‘shuttle’ graphene’s electrons to stream through the material in one direction, as a direct current.
“We are surrounded by electromagnetic waves in the terahertz range,” said 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.”
Altering Graphene’s Proportion
Throughout the last decade, researchers have searched for methods to harvest and transform ambient energy into usable electrical energy. They have tried this by using rectifiers, devices that are created to convert electromagnetic waves from their alternating current to direct current.
A few experimental studies have been capable of converting terahertz waves into DC, but they can only do so at extremely cold temperatures, environments that would be hard to use in practical applications.
Rather than turning electromagnetic waves into a DC by employing an external electric field in a device, Isobe tried making the material’s own electrons flow in one direction in order to drive the terahertz waves into direct current, following quantum mechanics.
To steer graphene’s electrons to take a single path, researchers would have to break the material’s natural proportion, or make a so-called ‘inversion.’ After numerous experiments, Isobe created a systematic theoretical study of all the methods electrons in graphene might disperse, as it would normally happen, in combination with a basic substrate, such as boron nitride, and the way electron scattering would impact any incoming electromagnetic waves, more so in the terahertz frequency extent.
He discovered that electrons were steered by incoming terahertz waves to flow in one direction, and this motion produces direct current if graphene materials were relatively pure.
“With many impurities, this skewed motion just ends up oscillating, and any incoming terahertz energy is lost through this oscillation,” Isobe explained. “So, we want a clean sample to effectively get a skewed motion.”
The team of scientists have published the paper detailing their results in the journal Science Advances, and are collaborating with researchers to turn their creation into a physical device.