Wireless ‘charging room’ powers devices safely at up to 50W

According to Professor Alanson Sample, an author of the Nature Electronics study, the technology could not only untether phones and laptops but also power implanted medical devices and raise new possibilities for mobile robotics in domestic and industrial spaces.

“This really ups the power of the ubiquitous computing world; you could put a computer in anything without ever having to worry about charging or plugging in,” said Sample. “There are a lot of clinical applications as well. Today’s heart implants, for example, require a wire that runs from the pump through the body to an external power supply. This could eliminate that, reducing the risk of infection and improving patients’ quality of life.”

The researchers have demonstrated the technology in a purpose-built aluminium test room measuring approximately 3m by 3m. Lamps, fans and phones were wirelessly powered in the room, drawing current from anywhere in the room regardless of the placement of people and furniture.

Notably, the system is a significant improvement over previous attempts at wireless charging systems, which used potentially harmful microwave radiation or required devices to be placed on dedicated charging pads.

Instead, this system uses a conductive surface on the walls and a conductive pole to generate magnetic fields. Devices harness the magnetic field with coils of wire, which can be integrated into devices like phones. According to the researchers, the system could be easily scaled up to larger structures, such as warehouses, while still meeting current safety guidelines for radiation exposure.

Professor Takuya Sasatani, of the University of Tokyo, said: “Something like this would be easiest to implement in new construction, but I think retrofits will be possible as well. Some commercial buildings, for example, already have metal support poles and it should be possible to spray a conductive surface onto walls, perhaps similar to how textured ceilings are done.”

Sample said that a crucial step in making the system work was building a resonant structure that could deliver a room-size magnetic field while confining harmful electric fields, which could potentially heat tissues. Their solution was to place lumped capacitors in wall cavities; these generate a magnetic field throughout the room while containing electric fields within the capacitors themselves. This approach overcomes a restriction on previous wireless power systems, which are limited to either delivering high power over a few millimetres or low power over longer distances.

A second challenge was generating a magnetic field that reaches every part of the room without 'dead spots' and with the receivers aligned with the field such that they can draw power. Sample explained: “Drawing power over the air with a coil is a lot like catching butterflies with a net. The trick is to have as many butterflies as possible swirling around the room in as many directions as possible. That way, you’ll catch butterflies no matter where your net is or which way it’s pointed.”

The system generates two separate magnetic fields: one travelling in a circle around the room’s central pole and the other swirling in the corners, travelling between adjacent walls. This approach eliminates dead spots and enables devices to draw power from anywhere in the room.

Tests using anatomical dummies demonstrated that the system can deliver at least 50W to any location in the test room without exceeding US guidelines for electromagnetic radiation exposure. Sample commented that it is likely to be possible to deliver even higher levels of power with further refinements.

Although the implementation of the system in commercial or residential settings is certainly years away, the researchers are moving on to test their system in a building on the University of Michigan campus. They will experiment both with a retrofit and with new construction in a series of rooms built using standard construction techniques. They are also working on implementing the system in smaller spaces, such as a toolbox which charges power tools stored inside it.

In July, researchers from Aalto University reported that they have developed technology for charging multiple devices simultaneously, transferring energy with 90 per cent efficiency with a range of 20cm, in another step towards practical 'true wireless' charging for consumer electronics.