Method and apparatus for transbody transmission of power and information

DETAILED DESCRIPTION The present invention capacitively transmits not only data but power through a user's body.
In one implementation, a transmitter carried by the user transmits power and data to a receiver, which is also carried on the user's body; the return path for the current is provided by environmental ground.
The signal that the transmitter applies to the user's body not only contains a data component, but also powers the receiver and enables it to detect and decode the data.
Various strategies for simultaneous transmission of power and data may be employed.
In one approach, power and data are simply transmitted at different frequencies.
In another approach, the data is transmitted by modulating a carrier from which power is derived.
Virtually any modulation scheme can be adapted to the present invention.
For example, data may be encoded by frequency modulation of a carrier; the receiver recovers the data by detecting carrier modulations, and derives power from the frequency-varying carrier itself.
Alternatively, the data may be encoded by amplitude modulation or phase modulation of a carrier.
In still another approach, the data is modulated using, for example, a pseudorandom code to provide spread-spectrum encoding within a broadband carrier, with the carrier again supplying power.
And in yet another approach, the data is not actually "transmitted" at all, but is instead imparted to the transmitter by the receiver in the form of loading variations.
In the time domain, the temporal pattern of these variations can encode a sequence of bits.
In the frequency domain, multiple receivers resonating at different frequencies can impart information merely by their presence or absence, or can instead impart a continuous range of information through variation of resonant frequency (or frequencies).
Furthermore, the coupling of resonators to a transmitter (i.
e.
, a reader) can impart information about their proximity to the transmitter.
The coupling strength is inversely proportional to the square of the distance between transmitter and receiver