New WPT Prototype “Charging Room” Aims to Power Your Living Room Without Wires
Research on UTokyo and U-M's "charging room" could help power your cell phone and other items from anywhere in the room using up to 50 watts of magnetoquasistatic wireless power transfer.
Wireless power transfer (WPT) has been an enduring dream for electrical engineers, dating back nearly a century to Nikola Tesla's experiments. Many companies have tried to tackle WPT applications across a broad spectrum of products and research (including Disney, believe it or not), but the technology has yet to reach a level of scalability that would enable mass adoption.
Recently researchers from the University of Michigan and the University of Tokyo, led by U-M Associate Professor Alonson Sample, have demonstrated the "charging room," a system that claims to power small electronics without wires by providing magnetically coupled power up to 50 watts.
The completed charging room powering cell phones, lights, and fans. Screenshot used courtesy of the University of Tokyo
Today, this article will look at the construction of the charging room, its theory of operation, and consider the technology's viability from a safety and practical standpoint.
Constructing the Charging Room
The charging room is based upon research that dates back to 2014 by M. Chabalko and A. Sample. Despite how long this research has been around, the technology behind this breakthrough has gone through several iterations in power levels (from 1900 watts in modeling) and resonant frequencies (from 191.65 MHz down to 1.32 MHz).
Ultimately, the power has been narrowed down to 50 watts in a 3 m x 3 m x 2 m room. The room itself is resonant, based upon a principle the researchers call quasistatic cavity resonance (QSCR).
The QSCR near-field magnetic chamber's inner room. Screenshot used courtesy of the University of Tokyo
The room is constructed with a center copper pole which is capacitively coupled. Said to be a key element in the room's safety, the capacitors reduce the electric field (E-field) emanations within the room and store some of the electric energy.
The room is designed to generate widely spread currents on the conductive aluminum surfaces which make up the walls. According to the research, the room is capable of multiple eigenmodes with a power efficiency of 37.1%.
Now that the basics of the room's design are understood, let's dive into the theory aspect.
Charging Room's Theory of Operation
The generation of magnetic fields has evolved over the years of research. The current design operates in the near-field or sub-wavelength region, with irregular and changing E-fields and magnetic fields (H-fields), which are not orthogonally aligned to each other.
The design of a QSCR showing (a) the geometric setup, reference geometry, and coordinate systems, with (b) a depiction of the magnetic fields. Screenshot used courtesy of Sample et al
The central pole, shown above in (a) contains one set of capacitors with additional lumped capacitors placed within the wall cavities of the aluminum room. Basically, to reduce the possibility of dead zones, especially in the corners of the room or behind objects, the system generates two separate magnetic fields, as seen above in (b).
An example of how the room uses magnetic fields with a loop-coupled light source. Screenshot used courtesy of the University of Tokyo
These swirling magnetic fields fill the volume of space in the room both in the horizontal and vertical planes. The electronic and electrical products in the QSCR room have been outfitted with power systems designed to capture ambient energy.
Though these magnetic fields sound like a resourceful way to provide wireless charging and electricity, it is important to consider the overall safety of this system.
RF Safety in the Charging Room
The FCC has set limits based on time-averaged exposure to RF energy that is considered safe levels. In their recent research (circa 2017 onwards), Sample and his team acknowledge the importance of ensuring that the QSCR room meets the requirements for an uncontrolled RF environment.
Uncontrolled radiation limits are mandated by the FCC. Screenshot used courtesy of the FCC
Although far from a simplistic analysis, the data generated from the QSCR room seems to demonstrate potentially limit exceeding values (at 1.32 MHz) in the 2017 paper.
Data from the H-field & E-field results were gathered by the researchers. Screenshot (modified) used courtesy of Sample et al
However, the researchers produced modeling data showing the concentration of energy on a human male frame of approximately 1.78 m to ascertain the maximum potential exposure.
They stated that there were safe loading conditions while producing 100 watts at that time (2017), as long as there was a physical barrier (a keep-out zone) around the central pole.
Life Cycle Conditions for a Charging Room
WPT appears to be alive and kicking in the minds of engineers, and the charging room certainly appears to be an interesting application of WPT technology.
However, beyond the electrical engineer's role, considerations related to the room's full life cycle must be considered a total engineering problem.
There are many questions we can ask, such as:
- How do we source enough raw materials to build large-scale aluminum rooms to facilitate the charging room?
- What are the environmental considerations related to the production of these rooms?
In balancing the ultimate engineering question, are the benefits worth the trade-offs? Although that is a big if, this designer hopes so.
What are your thoughts on a wireless "charging room"? Let us know in the comments down below.