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Near Field Magnetic Induction Circuit Design

Discussion in 'Radio and Communications' started by alex610, Feb 24, 2017.

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  1. alex610

    alex610 New Member

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    Hi, I'm completely new to NFMI and I can't find much material online about it. I'm currently designing a transmitter to communicate with the telecoil in a hearing aid. My understanding is that I need to achieve an inductance of around 1uH in my transmitter and the rest of the circuit is a simple LC circuit with the signal that is to be transmitted passing through an op amp. Am I correct in thinking this?
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Welcome,

    I worked on the original multi-channel auditory prosthesis based on direct cochlear stimulation back in the 1970s.

    Are you trying to power implanted circuits using induction, or are you just trying to send data through the skin? If the latter, what powers the implanted circuitry?
     
  3. alex610

    alex610 New Member

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    Hi Mike, I'm just trying to send audio from a device to the hearing aid using induction. The transmission distance only has to be half a metre and the hearing aid is powered by a 1.3V battery. Thanks
     
  4. dave

    Dave New Member

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  5. RadioRon

    RadioRon Well-Known Member

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    Induction is one way. You can also do it with electrostatic (capacitive) coupling if both pieces are against the body. I've seen this done and it is quite interesting. You have a modest plate in the transmitter and another in the receiver, both of which are well coupled to the body. The body is the capacitor's dielectric. It probably works best if the audio is modulated onto an RF carrier using FM. I'm not sure what carrier frequency would be best, but starting at 50 MHz might be a good choice. The working implementation that I saw was cool because the transmitter required very little power and there were virtually no electro-magnetic emissions. This was because only the electric field was used, and the transducers avoided generating any magnetic field. There was little power needed because no power is transmitted by electro-magnetic radiation, only electro-static field.
     
  6. alec_t

    alec_t Well-Known Member Most Helpful Member

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    If your transmitter is simply driving a conductor loop at audio frequencies I don't think the inductance is at all critical.
     

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