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difference between NF wireless power transfer and theory of transformers/electrical machines?

Discussion in 'Power Electronics' started by max_torch, Nov 30, 2015.

  1. max_torch

    max_torch

    98
    1
    Feb 9, 2014
    I've been doing research into wireless power transfer theory and technologies, both the radiative and the resonant coupling types.
    Now I just want to clarify some things about the theory of near-field wireless power transfer and what sets it apart from the theory behind mere magnetic induction used in transformers and motors/generators. One of the research papers I've found on the topic is this: http://www.hindawi.com/journals/jece/2014/906537/

    So what I understand (or think I understand) is:

    In ordinary Magnetic Induction (MI) devices, most, if not all of the flux makes it into the second coil from the first coil, achieving around a high percent of coupling. That is why there is very little loss in transformer action, or in transfers between stators and rotors. The amount of power transferred is a direct result of the percentage of coupling, so if the second coil is offset or moved away then the power transfer is drastically reduced. If 50% of the flux makes it to the second coil then only 50 % of the power from the first coil has been transferred.

    What happens in MI:
    MI.png full power transfer because of 100% coupling

    MI offset.png small amount of power transfer because of offset coil


    In Magnetic Resonant Coupling (MR) the distance between the coils is several times the coil diameters, as a result the amount of flux that enters the second coil is only 1% (possibly even lower) of the total flux being generated by the first coil, hence the extremely small coupling coefficient. But this is compensated for by making the Quality Factor so high, and making the accuracy of the oscillation so precise in matching the resonant frequency, and the tuning of the two coils so precise, that all of the power is forced and squeezed through that small bit of flux that reaches the second coil.

    What happens in MR:
    MR.png large amount of power transferred despite low coupling

    I just want to confirm if everything I've said is correct and that my understanding is correct, even my visual interpretation.. And I would like to ask if there is anything that can be improved in the explanation, or anything that anyone can add. What really sets the theory involved in ordinary Magnetic Induction apart from the theory in Highly Resonant Magnetic Induction?

    By the way the images are edited versions of something originally derived from a website in stanford.edu.
     
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