Imagine powering all your devices without a plug.

Researchers at the University of Michigan and University of Tokyo are using magnetic fields to effectively develop a new kind of "charging room." The team's test space safely delivers electricity over the air, potentially turning entire buildings into wireless power zones.

"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 study author and U-M professor of computer science and engineering Alanson Sample in a recent news release .

In addition to untethering phones and laptops, the wireless-power system could also support implanted medical devices.

“Today’s heart implants, for example, require a wire that runs from the pump through the body to an external power supply," said Prof. Sample. "This could eliminate that, reducing the risk of infection and improving patients’ quality of life.”

Detailed in a new study published in Nature Electronics, the technology uses magnetic fields to deliver 50 watts of power — enough to wirelessly charge up lamps, fans, and cell phones in the purpose-built, 10' x 10' aluminum test area. The devices drew current, regardless of their placement in the room.

"The first time we turned on the system and got the LED receiver to glow was kind of magical," Sample told Tech Briefs. "It was like pulling electricity out of thin air."

Lumped capacitors set into wall cavities in the wireless charging room.
Lumped capacitors set into wall cavities in the wireless charging room. (Image credit: The University of Tokyo)

How the System Works

To generate magnetic fields, the room requires both a conductive pole and a conductive surface on the walls. Each device in the room is equipped with wire coils that harness the magnetic field.

The magnetic field in the room passes through the coil on the receiving device. The transmission induces an AC current in the wire which is then rectified and regulated into DC power for the device.

The design called for a crucial safeguard: a resonant structure that could deliver a room-size magnetic field while confining harmful electric fields, which can heat biological tissues.

The team added components known as capacitors, which pull in the harmful electric fields.

Placed in wall cavities, the capacitors help to control magnetic field that resonates throughout the room while trapping any electric fields.

The system avoids "dead spots," or power-less places in the room, by generating two separate, 3D magnetic fields. One travels in a circle around the room’s central pole, while the other swirls in the corners, moving between adjacent walls.

The team is also working on a smaller-scale idea: a toolbox that charges tools placed inside it.

In a Q&A with Tech Briefs below, Prof. Sample discusses how much power can be delivered now with magnetic fields, and how much power can be delivered with further refinement of the system.

Tech Briefs: What are the components of a “Charging Room?"

Prof. Alanson Sample: Currently, the wireless charging room consists of metalized walls, ceilings, and floors — with an optional central pole that helps control the distribution of the magnetic fields. The room can have large openings for windows and doors. All surfaces can be covered with drywall or other building materials, and the central pole can be hidden in a dividing wall, thus creating two wireless charging rooms.

Tech Briefs: How do you retrofit a “regular room” (and its devices) for something like this?

Prof. Alanson Sample: The current state of the QSCR, or quasistatic cavity resonance, technology is best suited for new construction, but we are investigating ways to easily retrofit existing rooms. Wireless power receivers also have to be incorporated into the electronic devices that need the be charged. This can be done with wireless charging cases, which were popular in early phone-based inductive charging solutions.

The finished charging room, located at The University of Tokyo.
The finished charging room, located at The University of Tokyo. (Image credit: The University of Tokyo)

Tech Briefs: What needs to happen before we can see a charging room in commercial and residential settings? Where do you see the first applications for this?

Prof. Sample: It is still early days for this type of wireless power system, and research needs to make it practical for consumer use. We envision the first application will be related to medical and or robotic applications.

Tech Briefs: How do you limit electromagnetic energy exposure?

Prof. Sample: The FCC, along with consultation with the NIH and IEEE, has set strict exposure limits for the amount of energy that humans can be exposed to. We use these standards to evaluate the wireless power room for safety using both simulation and direct measurements of the fields. We are encouraged that our initial safety analysis shows that it is possible to transfer useful amounts of power safely and efficiently. We will continue to explore and evolve this technology to meet or exceed all regulatory safety standards.

Tech Briefs: How much power is achieved, and how do you envision increasing that power in the future?

Prof. Sample: In this study, we showed that it is possible to transmit up to 50 watts of power which is enough to simultaneously charge 10 smartphones. Future work will focus on creating new resonator designs that increase safety by storing more of the harmful electric field in capacitors, thus allowing the system to transmit more power while meeting the established exposure limits.

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