A Century After Tesla, Wireless Power Transfer May Finally Be Delivering
At last week’s Sensors Converge in San Jose, Wireless Power Transfer was on display for applications from microWatt IoT to 0.5 kW 5G repeaters and ranges out to 15 m.
Naturally, as our industry looks toward a future with trillions of interconnected devices, supplying power for years or even decades is a significant area of concern. Wiring up all of these devices is often impractical. Batteries in small form factors typically cannot provide the energy needed to operate for the target lifetimes, and replacing the batteries is cost-prohibitive.
EE Power recently talked with two companies, Powermat and Energous, about their vastly different wireless power transfer (WPT) technologies at the 2022 Sensors Converge show in San Jose, California.
The basic idea of wireless power transfer is not new, as evidenced by Nikola Tesla’s 1907 patent application for an “apparatus for transmitting electrical energy.” But 115 years later, the technology may finally be reaching a mature enough level to find regular use in a variety of applications.
Powermat’s Award-Winning Tiny WPT Solution
While many companies in this space are focused on wireless power transfer of a few milliwatts, Powermat is looking to transmit picowatts to nearly 1 kW, all wirelessly. At this year's show, the Powermat PMT 100 Wireless Power Solution was a Best of Sensors Award winner in the Innovative Medical Product of the Year category.
EE Power met with Aya Kantor, Vice President of Products at Powermat, at the show to discuss their technology in more detail.
Block diagram demonstrating use of a Powermat WPT device in a medical application. Image used courtesty of Powermat
The PMT 100 does not require a microcontroller on the receiver side and has a low peripheral component count. Kantor explained this provides two significant benefits.
“One, it can be very small,” Kantor said. “The second is low cost.”
These features are important for cost-sensitive consumer electronics and ultra-small medical devices including hearing aids, EKG sensors, glucose monitors, and implantable products. The PMT 100 supports inductive power transfer of up to 40 W at maximums of 30 V and 2 A.
WPT for Drones, eMobility, and Communications
While ultra-small, low-power wireless power transfer may have won the award, Kantor also spoke to us about Powermat’s higher power products, including 300 W solutions that are available today and a platform “coming out this year” for 600 W.
Applications for their high-power wireless power systems include robots, electric scooters, and 5G repeaters for home and public installations with efficiencies “up to 95%.”
According to Kantor, Powermat’s advantages come from an advanced software-defined radio interface that “enables us not only to control power over longer distances but also drive both power and data over the wireless power link.” They support data rates to 100 Kbps without a separate radio and use that communication capability to improve system performance.
"One of the things we're talking about today is the charging of robotics in a bit more holistic way. So, not just beaconing or charging, but also managing battery health, using this (built-in) communication to improve the battery health of the robot."
By “microcharging” the battery during robot operation, Powermat aims to improve battery health and reduce charging-related downtime. They use software controls at the transmit side to support higher misalignment and angular charging with a reduced impact on the power transfer efficiency. This allows charging robots when loading, unloading or queuing without having to achieve precise docking alignment.
A second application Kantor discussed with EE Power was installing exterior 5G repeaters without “drilling through walls.” The wireless charging transmitter can be attached to the inside wall or window and the 5G system is then mounted on the exterior.
Demonstration of a Powermat wireless power transfer system on a window. Image used courtesy of Powermat
Kantor went on to discuss how the system automatically adapts to the distance between the transmitter and receiver, the alignment, and even the materials. She reflected on “one of our first challenges”—low-e glass with silver particles.
"Magnetic induction doesn't necessarily like silver particles, but we managed to actually charge with very high efficiencies."
Wireless Power Transfer at a Distance
But what if you are looking to transfer power at distances much further than the thickness of your office wall? Energous CEO Cesar Johnston also spoke with EE Power at Sensors Converge to detail their power-at-a-distance technology. Johnston was quick to highlight that their WPT solutions are different from most:
“Most people talking about wireless power today, they mean transmission right next to each other. The transmitter on top of the receiver or vice versa.”
Energous is providing WPT at ranges up to 15 m by transmitting 1 W in the 900 MHz frequency band. They also have products certified in the US to transmit 5 and 10 W, but that are currently limited to 1 m.
Johnston was quick to add that they have been “working with the FCC closely for a number of years” to hopefully soon support higher powers and ranges beyond 1 m. Energous is designing silicon ICs specifically “optimized for wireless at a distance; they’re not communication devices,” Johnston said.
When we asked Johnston to elaborate on how Energous’ ICs are optimized for power transfer, he explained the differences between power amplifiers (PA) designed for transmitting communication signals and those designed for transmitting power.
Energous Wireless Power Transfer transmits and receives ICs. Author image
In communication, the linearity of the PA is important to minimize signal distortion. Therefore, Class A and B amplifiers are typically used. However, in power transfer, “you really want your PAs to be extremely efficient,” which allows the use of a different class of amplifier.
Johnston went on to explain that they are using Class E amplifiers running at power saturation. This allows them to achieve power efficiencies up to 85% as opposed to communication PAs that are limited to 18-40% power efficiency.
On the receiver side, Energous uses silicon CMOS designs for powers up to 1 W and GaAs for receivers that can support up to 4 W of received power. The CMOS chips are 1.3 mm on a side and fabricated in older, low-cost fabs to keep production costs low.
Changing the Way the World Views Power
Energous is hoping to change how the world thinks about power devices that must operate for many years. Rather than thinking in terms of how much battery power capacity you need to design into a system, Johnston wants people to ask, “how much power do I need and when do I need it?”
To assist developers, Energous and Atmosic announced during the show the availability of their new Wirelessly Powered Sensor Evaluation Kit. The kit contains Energous’ FCC-certified 1 W WattUp PowerBridge transmitter and Atmosic’s ATM3 energy harvesting Bluetooth Low Energy (BLE) SoCs.
Energous and Atmosic Wirelessly Powered Sensor Evaluation Kit. Image used courtesy of Energous
Energous sees initial opportunities for their technology in RF tags and electronic shelf labels, with sensors as a potential third market. While the system can be paired with batteries to provide recharging capability, Johnston wants to “remove batteries as much as we can.” Not only does this provide potential system cost reductions, but it can support mobility in applications like asset tracking.
Wireless Power Transfer Is Still in its Infancy
One of the takeaways from the conference is that wireless power transfer is still in its infancy. Not only must the technologies continue to improve, but the infrastructure and regulations must continue to move forward if wireless power transfer is going to make significant inroads.