That Elephant in the Room is your Wireless Power Transmitter

4
Feb. 2019

In wireless power, small is beautiful. This is certainly true as it relates to wireless power transmitters.

A wireless power system – regardless of what wireless technology is used – has two parts: a transmitter that sends the energy in some form and a receiver that converts that energy back to electricity.

For home use, one can imagine many practical limitations to the size of the transmitter. Would you be willing to install a transmitter in your living room if the transmitter was the size of an elephant? a grand piano? an upright piano? a refrigerator? a 40″ TV screen? For most people, I think the answer would be “no”. The transmitter needs to be as small as possible, practically invisible.

How large does the transmitter need to be? That does depend on the technology being used and is related to physical phenomena called ‘diffraction’. Diffraction causes waves to spread out when passing through a narrow aperture. The more the waves spread out, the more difficult it is to focus these energy waves on the object to be powered. The degree of diffraction depends on the ratio between the size of the aperture (and thus the size of the device) and the wavelength of the type of energy being sent. If the aperture is similar to the wavelength of the energy, the wave will spread out. If the aperture is much larger than the wavelength of the energy, the wave will remain focused and directed. Diffraction is one reason why radio telescopes are so large – they want to energy beam to remain focused when sending it into space. 

The Wi-Charge energy transmitter as shown at CES 2019

When light is used for power transfer, the wavelength is extremely short and thus the transmitter can be very small while still generating a very tight, focused energy beam. With other technologies, that is not the case and thus engineers need to choose between a beam that becomes very wide and a transmitter that is large or even impractically large.