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This article compares two systems for wireless energy transfer - one is by WiTricity and another is Bombardier PRIMOVE. I've read their descriptions thoroughly - to me they both look like resonant inductive coupling systems.

Yet the article says that WiTricity system uses resonance rather than electromagnetic induction and is more efficient because of that.

Is such comparison valid? Are there indeed "induction" and "resonance" wireless transfer systems or is it just the same thing being marketed differently?

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  • \$\begingroup\$ The difference is one has a better marketing department. \$\endgroup\$ – Connor Wolf May 16 '13 at 10:00
  • \$\begingroup\$ resonant is just like antennas, induction is just like transformers. its that simple \$\endgroup\$ – hassan789 Jul 12 '15 at 6:43
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In my opinion, for the last thirty years, nearly all magnetic induction energy transfer systems place a capacitor to put the secondary coil in resonance. This achieves better power transfer efficiency and everybody knows this. We have been doing this in the medical device industry for [at least] the last two decades. This is just obvious.

Witricity and others have invented this term magnetic resonance to make it sound like they are doing something nobody else has. Don't believe them.

You also hear A4WP using this term to differentiate themselves from Qi. The fact is that Qi standard allows the designer to use either resonant circuits or not. So plenty of Qi systems will use what Witricity and others call "magnetic resonance" to provide more efficiency transfer. Some will opt for a cheaper design that gives shorter range.

In conclusion, Witricity didn't invent anything. Using resonant circuits in magnetic induction is well known and is used all the time.

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I think we can classify two kinds of wireless power transfer system using magnetic field:

  1. Using non-resonant inductive coupling, like the principle of electric transformers.
  2. Using resonant inductive coupling, like what Witricity did.

They both used a magnetic field for power exchange, based on induction principle. The difference is resonance and non-resonance.

The terms "induction WPT" and "Resonance WPT" look not clear to differentiate them.

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I didn't follow the links, but inductive power transfer systems work like transformers. However, since the sender and receiver usually need to able to be disconnected by end users, serious compromises were made in the magnetic coupling. This means the transformer needs to be considerably larger than a dedicated fixed transformer where both sides can be wound around the same core of some convenient material. As a result, these inductive power coupling system genrally use high frequencies.

Another trick they can use is to resonance. If the whole system resonates at a particular frequency and it is driven at that frequency, it is possible that the power can be tranferred a bit more efficiently. Resonance by itself does not guarantee higher efficiency, but if exploited properly I can imagine that it could.

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  • \$\begingroup\$ I had the impression that such systems (some distance and very high power) can have decent efficiency only when resonance is used. Also does using resonance cancel out use of induction or is it used in addition to induction? \$\endgroup\$ – sharptooth Jan 17 '12 at 13:30
  • \$\begingroup\$ @sharptooth: Like I said, exploiting resonance should allow for better efficiency if done right. It should also allow for smaller physical size, which is probably a more important issue. Look at the specs and you'll find these systems are often not that efficient. Resonant is one mode that a inductive coupling system can be run in. \$\endgroup\$ – Olin Lathrop Jan 17 '12 at 13:36

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