New Wave Interference Technique Boosts Long‑Range Wireless Charging

• Researchers develop a unique system that can efficiently transfer power through free space. 
• The system could make it easy to wirelessly charge a mobile at some distance from the power socket. 
• It works by transferring the signal with specific amplitude and phase. 

We all know that antenna plays a major role in wireless technology, including information as well as power transfer. While wireless communication system is well developed, the wireless power transfer is still in its early phase.

It’s not that we haven’t tried; significant studies have been devoted to finding new ways of transferring power with higher efficiency, by optimizing the geometry of resonators and surrounding elements. In fact, we achieved a great progress recently.

An international team of researchers has demonstrated a new concept that increases the power transfer efficiency and might lead to feasible, long-distance wireless charging. If implemented, this will be beneficial for all phone consumer electronics, medical implants and even electric vehicles.

How Did They Do It?

It’s very hard to transfer enough amount of energy through electromagnetic waves over a long distance (without using wires). However, researchers have developed a new technique that relies on the wave impedance’s local control provided by interference mechanism.

They showed that it’s possible to increase the efficiency of a receiving antenna, using coherent excitation of the out coupling waveguide with a signal (propagating backward) of particular phase and amplitude. The signal forms a unique interference pattern, which offers optimal wave impedance at the receiving end, maximizing the amount of power transferred through free space.

What does it mean? 

In simple language, one of the major problems with wireless power transmission is, the antenna does not absorb radiation, in fact, it ejects small portion of impinging radiation. These two processes are usually associated with a coupling constant, and when the constants of these two processes are same, the maximum amount of energy is transferred.

To keep these coupling constants stable, researchers integrated a few configurable circuit modules, including inductors and capacitors. In addition, they transferred the signal with specific amplitude and phase, in order to suppress the imbalance of coupling constants. The signal can also be configured to improve wave transmission without any need to alter the load.

Demonstration

Image credit: Krasnok / University of Texas

The image shows a transmitting antenna (at the right hand side) radiating waves (radio frequency). The antenna on the receiving end sends energy (waves in blue color) via a coaxial cable to the battery. The red wave emitted from the circuit interferes in a manner that maximizes the amount of energy transmitted. 

The team developed a theoretical model to prove this principle with full wave numerical simulations. They used a signal generator and two antennas to transfer microwave power at 40 centimeter distance. A coaxial cable further connects the receiving antenna to circuit (like battery).

They demonstrated that their technique can restore maximum energy transfer, even with a large difference in coupling constants. According to the researchers, the technique can be used to developed efficient wireless energy transfer systems in drastically changing environments.

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However, Witricity, company that manufactures devices for wireless power transfer, says that the benefits of this concept have yet to be verified. They’re still not sure whether it’s worth trying to implement.