Why have power supply via induction?

In the very small amount of projects about implanting actual electronical components, I've only seen charging via induction.
Induction requires a rather big area of wire spool, which makes the implants huge, also the power supply is very unstable and needs to be converted to DC, right?

Why not have two transdermal piercings (maybe even made of non-conductive material with a conductive core) and a DC power supply through these?


  • Because transdermals have an incredibly high rejection rate. And would likely be sped up because of constantly moving it and connecting things to it. It's just not feasible, the jewelry would eventually reject, and that's not even taking into account that they would have to be connected to the implant under the skin. I'd anticipate the whole thing rejecting, or the body trying to pull the transdermals under. There is potentially a way have a "plug" in the same fashion that Warwick did, but even if that happened there is a much higher chance for infection because of a basically perpetually open wound. Induction is the best option for the average grinder because it's simple, it's wireless so no protrusions above the skin, and it's for more unlikely for something completely under the skin to reject.
  • edited March 2014
    The assumption that inductive power supplies are big is a misconception. The bigger they are, and the better the magnetic coupling, the more power you can transmit. But since most implants are reasonably low power you can get away with very small inductors. The smallest one i tried was about 3x3x2 millimeters. It was enough to power a small Atmega. 8x8 mm can give you 10mW and more.
    A well designed implant requires about 5 to 10mW while active, and driving an output electrode. image
    This thing is a home-made RFID tag (with LED as debug output) next to a AAA battery. And that's using DIP parts and the biggest coil I have around. I have plans for a device similar to this one, but with an output electrode.

    The AC/DC conversion can be done with a simple rectifier circuit. If you have any kind of IC on your implant, you can even use the internal protection diodes like this guy did:

    it's a bit of a hack and isn't exactly within the circuit's specifications for strong fields, but it works. a proper circuit with filtering takes about 4 tiny additional parts, or 6, if you want a stable, regulated output (no need for digital circuits only).

    So the reason why you've only seen inductive charging is, because it's simple, small, robust, easy to use, and the best thing we have at the moment.
  • Surely inductive power can handle more? After all, it's the same basis as a transformer.
    Mount a transformer secondary winding underneath the skin around, say, the top of your arm, and the primary winding in a wearable arm band. Use a reasonably high frequency and a surprisingly large amount of power could be transferred.
    Rectify and condition the power with diodes and ceramic capacitors (not electrolytics or tantalums or anything else- just simple, safe ceramics) as mentioned above.

    This means that you can remain entirely skin-breach free, getting rid of the worries transdermals bring. And it could be relatively flat, removing the "block under the skin" look that some powered implants have had in the past.
    For comms with the outside world, IR or visible spectrum optical transmission through skin wouldn't be much of an issue. Gigabit non-fibre optical links have been about for years now, so even transferring large amounts of data from sensors shouldn't be an issue.

    Coat it in implant-grade silicone and I can't see it being too impossible...
  • Bit of an old thread to revive, but the inductive charging standard is that way because of the heat and methods used for charging. Sure you could push more power, but that means more loss and more heat dissipation subdermally, as well as having to use custom hardware over the common and well developed Qi standard.
Sign In or Register to comment.