Is it possible to transmit and receive an electrical signal SAFELY using the human body as a medium? For example, I would have a transmitter of some sorts in my left hand, and a receiver in my right. And if it is, are there any commercially available transmitters, if not, any home made assemblies that can be made. Unlike this question: Data transmission through the human body, I'm looking for an actual module that I will be able to use. And if data is too much to be transferred, can I make it so that at least I can transmit 1 bit across (on or off), much like a switch?

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    \$\begingroup\$ What are you actually trying to achieve, and can you do it with normal radio transceivers? If radio transceivers are not a good solution - what are your reasons for excluding them? \$\endgroup\$ – Li-aung Yip Mar 23 '15 at 11:38
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    \$\begingroup\$ Microchip has their "BodyCom Technology" microchip.com/pagehandler/en-us/technology/embeddedsecurity/… \$\endgroup\$ – brhans Mar 23 '15 at 13:08
  • \$\begingroup\$ Sure... The resistance of your body is in the 1k to 100k ohm range. You can use your body to complete the circuit with a 9V battery and high brightness LED and blink the LED on and off... best in a dark room, or two 9V's.. lick your fingers first. \$\endgroup\$ – George Herold Mar 23 '15 at 13:42

Why does it have to use the body? Bluetooth LE works just fine from one side of the body to the other, even at minimum power, say -12 to -18dBm. I'm guessing it mainly uses reflection off whatever is nearby, it would get attenuated stongly on the direct path.

Now, to try to design what you're talking about: assume the two devices each touch the body with some conducive part. At audio to low mhz the body is a largeish capacitor (roughly nF), but you need to complete a circuit around that somehow. Assume the devices each have a metal case isolated from the body acting as antenna. The cases are small capactors to free space in the pF range, assuming a device which is at least a few inches in size (parasitics, basically). This gives you an ac circuit, but the free space side of it is very weakly connected. Also you are limited to very, very small currents through the body: I believe 50 microamp is one safety standard. If you can design a circuit that sends data through two wires with 1pf and 1nf capacitors in series on them while limited to 50uA, you can use that :) because that is equivalent to what you have through and around the body.

The described scenario is related to having ordinary rf antennas in each device: part of the signal is still transmitted as an electromagnetic field around the body, but instead of using dipole to dipole coupling (in approximately the far field), this can be monopole to monopole (and near field).

EDIT Also there are parasitic capacitances body to free space and each case to body, which form a capacitive divider. The result is maybe a picofarad across the two wires in the equivalent circuit described above.


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