WPT breaks all connections, Part 1: Page 11 of 12

March 16, 2015 //By Sanjaya Maniktala
WPT breaks all connections, Part 1
Sanjaya Maniktala offers the first part of a high-level review of the current state of wireless power transfer (WPT).
the coffee even within the relatively small confines of our kitchen microwave oven — we use waves inside it, not bare electric or magnetic fields. The latter would give us an induction cooker for example, not a microwave oven.

The moment we talk only in terms of pure electric or magnetic fields, we are implying near-field effects, and depending on the physical distances involved, we are indirectly making a statement about the rate of the time-variation involved, i.e. its frequency.

Let’s check the numbers for inductive WPT too. These methods use frequencies of about 200 kHz. At such a low frequency, the “near-field” extends up to 23,870 cm, or a quarter kilometer away from the source. The other modern inductive standard works at a higher frequency, of 6.78 MHz. For ~7 MHz, we see that its near-field region extends up to 682 cm, i.e. almost 7 meters (its wavelength being six times that).  In other words, considering the frequencies we use in modern inductive WPT (with a maximum of 6.78 MHz), we need to look upon all separations up to a minimum of 7 meters as near-fields.

Specifically, we are dealing with rapidly attenuating and varying magnetic fields within that distance, not electromagnetic waves. And that is Faraday’s Law in effect. So, at these small distances, if we wanted to create beams of energy, or waves, instead of just fields, we would need to go to much higher frequencies, as we do in MPT. Though at significant risk to our personal health and safety as mentioned.   That is why modern methods intended for homes have defaulted to safe (lower) frequencies of inductive WPT, and the consequent smaller distances for energy transfer, since fields attenuate rapidly. Remember: only waves propagate. Fields die out.

Lastly, keep in mind that our bodies accept powerful magnetic fields 24/7 with no ill-effects. After all, we live on a planet with a strong magnetic field. For

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