Will it Heat my Pets, my Plants or my Plate of Pasta?

26 September 2018

Long-range wireless power sends energy through the air. This is true regardless of the technology used. Some of that energy hits the wireless power receiver. Energy that does not hit the receiver is “stray energy” that is absorbed by the environment.

But the “environment” is not necessarily as innocent as it sounds. It might include people, pets, plants and yes, even a plate of pasta.

The amount of power sent by the energy transmitter is limited by safety regulations. In the US, the FCC sets the regulations that govern how much power an RF-based product can emit, while the FDA does this for light-based products. Outside the US, every country has its own set of similar safety regulations. These safety regulations are focused on allowable human exposure to RF radiation or IR light. Depending on the desired level of energy that the receiving device (e.g. phone) needs and the efficiency of the power transmission, there is sometimes an incentive for the manufacturer of the transmission device to increase the transmission level up to (but not beyond) the regulatory safety limit.

I am not personally aware of the safe exposure limits for pets, but I think it’s safe to assume that less radiation is better than more radiation. Thus, it’s very desirable to minimize or even eliminate the “stray energy”, the amount of energy that does not hit the receiver.

That’s one of the beautiful things about using IR to deliver long-range power. You can think about the IR light beam coming out of the Wi-Charge transmitter as an invisible laser pointer. The beam remains tight and focused to the point that practically 100% of the energy reaches the Wi-Charge receiver. 100% on the receiver, means that 0% is “stray energy” that has the potential of impacting people, animals or plants in the environment.

In contrast, under any reasonable assumptions of transmitter size, receiver size and distance, a significant portion of RF radiation is not captured by the receiver. The reason for this problem is a physical phenomena called diffraction that causes RF beams to widen as they get farther from the energy source.

There are many good reasons to prefer IR light to RF radiation as they related to long-range wireless power. The desire not to bathe the environment in unhelpful energy is an additional reason.

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