Through-window wireless power supply: The key to the next generation communication

5G, the hottest topic in the industry in the past few years, is deemed the revolutionary technology that can shape our world. Numerous articles are addressing what 5G can bring to us. If you are interested, you can refer to https://www.qualcomm.com/research/5g to get a comprehensive idea.

To completely release the 5G technology potential, you need a higher carrier frequency such as millimeter-wave frequencies like 28GHz and 37GHz. However, millimeter-wave frequencies have the drawback of a weaker signal penetration capability. The operators need to deploy more base stations than they did in the 4G era. And even though consumers are still suffering the poor signal issue while using the 5G service at home, millimeter-wave signals are blocked by walls.

Thus, a start-up company called PivotalCommware that Verizon and Bill Gates invest in, deploying the so-called 5G repeater in the market since January 2020 (https://olv.duke.edu/news/pivotal-commware-announces-commercial-launch-of-echo-5g/). This product is installed on the exterior side of the window to receive the millimeter-wave signals from the base stations well. Then it re-amplifies the millimeter-wave signal and floods it into the home, and consumers can enjoy the full signal in their 5G mobile phone even at home.

There is a crucial factor in achieving this magic, and PivotalCommware doesn’t mention it in the early 2020 announcement. In 2021 May, they finally reveal this at EETimes (https://www.eetimes.com/wireless-power-boosts-5g-deployment/#). The through-window wireless power supply is used to power the 5G repeater attached on the exterior side of the window. The whole idea is shown in the figure below. This approach
makes the entire system self-installable.

It’s worthy to notice that there are many types of glasses used in the window. Low-E (emissivity) glasses are widely applied worldwide to make the indoor environment more comfortable. Low-E glass has a microscopically thin, transparent coating, which is much thinner than human hair. It reflects long-wave infrared energy (or heat). Some also reflect significant amounts of short-wave solar infrared energy. When the internal heat energy tries to escape the colder outside during the winter, the Low-E coating reflects the heat inside, reducing the radiant heat loss through the glass. The reverse happens during the summer.

The ultra-thin silver coating in Low-E glass, which can be one layer to 3 layers, becomes a problem in wireless power transfer. The below figure explains the issue. What happens is that the magnetic field from the wireless power transmitter generates eddy current on the thin sliver coating, and the eddy current generates heat across the silver layer. The heat can be pretty high to damage the glass. Therefore, for the through-window wireless power supply, the major challenge is how to make it works across all types of Low-E glasses.

A formula below is derived to address the power loss on the silver coating of Low-E glasses (https://ieeexplore.ieee.org/document/9055631). We can find that the power loss is proportional to the square of the magnetic field frequency. The lower the magnetic field frequency applied in the wireless power system, the lower the heat generated in the Low-E glasses.

Tseetech wireless power module uses 79KHz~90KHz, which is the lowest wireless power transfer frequency approved by MIIT, China. Therefore, Tseetech wireless power module can achieve ~90% end-to-end efficiency even across a 3cm thick three silver-layers Low-E glass, which is the worst case of all types of windows. We believe this is the best performance for
a through-window wireless power supply in the whole world.

In addition to 5G, the 6G development is on the way and is expected to launch in early 2028. 6G will use a much higher frequency above 95GHz, resulting in a more severe signal penetration problem into the home. Therefore, we can see that the through-window wireless power supply approach will be more and more important as the next generation of communication moves forward.

We, Tseetech, own the best through-window wireless power supply solution. Want to get a place in the next generation communication industry? Contact us now and begin your product development!