WiFi Signals Could Be Turned Into Usable Power to Charge Phones and Laptops

Household electronics may soon be powered with direct current converted from high-frequency terahertz waves, a typically wasted form of energy, U.S. scientists say.

The electromagnetic waves are produced by almost anything that registers a temperature, including human bodies and inanimate objects or signals, such as phones and WiFi. Now, research suggests these "T-waves" could soon be harnessed and concentrated into an alternate energy source.

Traditionally, terahertz waves have been considered wasted energy as there has been no practical way to capture and convert them into any usable form.

But physicists from the Massachusetts Institute of Technology (MIT) have now made a blueprint for a device they believe could convert ambient waves into direct current.

In theory, the energy could be used to power a cell phone by soaking up the ambient T-waves and using them to help charge the device via an add-on. The research was published this week in the journal Science Advances and the team is now working to turn the design into a physical device.

"We are surrounded by electromagnetic waves in the terahertz range," lead author Hiroki Isobe, a postdoc in MIT's Materials Research Laboratory, said in a recent media release.

"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," he added.

The researchers said the theoretical design was based on the behavior of the carbon material graphene at a quantum—or atomic—level. When they combined graphene with boron nitride, the team found the electrons in graphene should skew electron motion toward a common direction.

As a result, any incoming T-waves would cause graphene's electrons to flow through the material in a single direction, creating a direct current, the physicists said.

To date, scientists have harnessed ambient energy into usable electrical energy using rectifiers—devices that convert electromagnetic waves from alternating current to direct current. But the devices only work up to a certain frequency and that does not include the terahertz range.

Previous experiments that tried to convert terahertz waves into direct currents could only manage it in "ultracold" temperatures—which is not ideal for practical consumer use cases.

This led Isobe to theorize if a material's own electrons could ever be induced to flow in one direction at a quantum mechanical level, MIT said. Graphene was chosen as the starting material because it is clean and largely free of impurities—letting electrons flow through it within minimal disruption.

Isobe determined that electrons were driven by incoming terahertz waves to skew in one direction, and this skew motion could generate a direct current if graphene were relatively pure.

Using that initial finding, the team created a blueprint for a "terahertz rectifier."

The theoretical device consisted of a square of graphene sitting on top of a layer of boron nitride, and an antenna that could collect, concentrate and then convert the ambient terahertz radiation.

Researchers said terahertz rectifiers may be used in future to convert ambient WiFi signals to charge electronics, including phones and laptops, or to wirelessly power implants in a patient's body.

The team said it has already filed a patent for the "high-frequency rectification" design and is hoping to make a real device with MIT's experimental physicists that works at room temperature.

That will be crucial to it working for real-world portable devices, Isobe said.

The new research was funded in part by the U.S. Army Research Laboratory and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies (ISN), MIT confirmed.