Inductive subdermal power supply
edited May 2011 in Prosthetics, wearables, and haptics
got started on inductive power supplies today. it is only a very basic test but it worked somewhat ok so here is the thing.
i started with some old rfid components i had around. that means between 120 and 130 khz operating frequency.
build the following circuit. in my case i used square signal from my function generator, it is 20Vpp with 50 Ohm output resistance.
transmitter coil is 60x30mm. so there is no need for ultra accurate positioning. used a led symbol as "load".
forgive me my ktechlab circuit sketch but i figured it still looks better than my hand drawing (ok there aint one but who cares anyway)
the right half is the receiver side, used a small compact coil on a ferit core, 12mm long, 8 in diameter.
the coil surfaces are 15mm apart, putting the hand in between has no real noticeable effect.
the rectified output delivered a constant 1mA at 4V (used a zener diode to limit the voltage). free running voltage goes up to 20 and more volts.
So this simple setup makes 4mW. i am rathar happy with it. it lights up an led quite nicely.
•Using anohter 60x30mm coil for the receiver increases current to about 4mA, i got 0.8mA with a random one i found a switching power supply. so it is not all to critical to have a huge coil implanted, smaller ones seems to work reasonably well.
•frequency tuning can be performed on the transmitter, a multimeter is enough to do so. so no need for tuning the subdermal parts nor a need for expensive equipment.
•simple and cheap to build. no expensive or rare parts used so far. the square wave input can be done with a ne555 or some 74hc14, all standard parts.
•not maximized for range (i think there is no real need for now is 15mm between surfaces seems to be plenty)
•not very powerful (yet)
Opportunities here would be to swap the 1n4001 diodes (they have 1V drop voltage) with some lower voltage ones to increase the range to 2cm or maybe even a tad more.
next things to try:
• using higher frequencies to get higher currents
• try low Vf diodes
• try out a variety of receiver coils. especially flat ones.
• more powerful transmitter
ultimate goal: charging a li-po cell with 10mA. that means, about 5 V and 10mA. that would allow for the southpaw battery to be charged in one night to run a week. i am confident.