PowerbyProxi > Features > Resonance and Wireless Trickery

Resonance and Wireless Trickery

August 15, 2012 / 1 Comments / 385 / Features, Technical
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Over the last few years Wireless Power has made rapid advances towards becoming a mainstream technology and is often the case, marketing departments  become the source of many new inventions.  Perhaps the biggest  marketing “invention” to date is  something called “Magnetic Resonance” (related to Resonant Inductive Coupling) when everyone else is just doing  stone age “Inductive Power.”

It’s a term many have now adopted, as if it was some space-age technological leap from “Inductive Power.”  When in fact Magnetic Resonance and Inductive Power are EXACTLY the same thing.

Lets dig into this a little more …

I’m sure all EEE majors will remember that Inductive Power uses Magnetic Resonance.

Any Inductive Power system has to have resonance, even the WPC  which requires complete alignment between the transmitter and receiver coils uses resonance. Yes, tightly coupled systems, like loosely coupled systems, do use resonance! This is accepted science since The University of Auckland started researching modern day wireless power 20 years ago.

Originally, before induction, wireless power could be achieved by effectively taking a transformer and separating the primary and secondary coils (i.e. a split transformer).

To increase the power efficiency it was worked out a long time ago that we need to use resonant coupling. This is just a fancy way of saying that by adding capacitors on both coils, a resonant circuit is created between the inductance of coil and capacitor. At the resonance frequency, the reactance cancels out and you are left with only the parasitic effects of finite winding resistance, AC resistance (proximity effect) and dielectric losses.

If you had a perfect AC source and drive the resonant circuit you have no losses. Losses are solely limited by your parasitics.

“Magnetic Resonance” is just sticking some capacitors in place. It was great to see Marin Soljacic, the inventor of WiTricity confirm this in the IEEE publication, A Critical Look at Wireless Power. “Resonance enables efficient energy transfer…. …. it’s not a new idea: Tesla’s eponymous coils use that very same principle.”

To summarize in non-technical speak, all Inductive Power systems use magnetic resonance and its certainly not the difference between tightly coupled and loosely coupled systems.

Like most new technologies you need to get underneath the marketing spin to understand the features and benefits that each vendor can deliver to those who matter most – our customers!

Fady Mishriki is Co-Founder, EVP and Chief Tesla Officer at PowerbyProxi


Comments (1)

  1. Konstantin Lakirovich

    I agree with Fady Mishriki, that there is some not traditional terminology, which serves a marketing  puropose.At the same time there are a lot of interesting things, especially  IP section, which Witricity is offering. I anderstand the desire to get rid of resonance capacitor ( as a component), because for high power it will be very difficult to find capacitors with needed parameters, such as AC current capabilities and high voltage withstanding. Even for small applications where power is around hundreds of watts, it is a challange to find not expensive and not very big capacitor. They found a way to elliminate this problem by using capacitive properties of a coil, and this is why their frequency ( I may be wrong) is so high.

    Their use of resonator repeater looks very exotic and its implementation increases transmitting power. I have an explanation for this phenomena – I believe, this additional resonance loop is used as a “loosely coupled” transformer and it doesn’t amplify energy, but transforms from one level of current to another, as any regular transformer will do. Allowing tremendous currents flow in this repeater increases magnetic field and distance where it may be harvested.    

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