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Non-contact system for sensing and signalling by externally induced intra-body currents
| Details |
Inventors: Gersheneld, Neil; Zimmerman, Thomas; Allport, David;
Assignee: Massachusetts Institute of Technology (Cambridge, MA)
Primary Examiner: Peng; John K.
Assistant Examiner: Lo; Linus M.
Attorney, Agent or Firm: Cesari and McKenna, LLP
A wireless system includes one or more transmitters and one or more remote receivers that are respectively coupled through one or more users and room ground. The transmitters each produce low-frequency, low power signals that, through capacitive coupling, pass as displacement currents into and from the body of the user, which acts as a conductive node. A receiver that couples capacitively to the user responds to the displacement currents and reproduces the signals. The transmitter includes a signal generator and a pair of electrodes. The signal generator produces modulated signals that vary the voltage between the electrodes, a first one of which is closely coupled capacitively to the user's body such that the "quasi-electrostatic" field resulting from the electrode potential causes a displacement current to pass to the user's body. The second electrode is oriented so that its coupling to the room ground is stronger than that of the first electrode, such that room ground acts as a return path for the current from the receiver. The signal generator may modulate the information to be transmitted using, for example, a pseudorandom code, to produce spread spectrum signals. This increases noise immunity and allows multiple transmitters, each using a different modulation code, to operate at the same time. The receivers each include a detector/demodulator that acquires and tracks the signals from the one or more transmitters. |
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DETAILED DESCRIPTION The invention is a wireless system in which a transmitter and a receiver are coupled through a user and room ground, rather than by wire or by optical or high frequency transmitted signals.
The transmitter produces low-frequency, low power signals that, through capacitive coupling, pass as displacement currents into and from the body of the user.
The user's body acts as a conductive node and a receiver that is capacitively coupled to the user's body responds to the displacement currents passed to it from the body, to detect the low frequency signals.
The user's body thus becomes part of the system rather than an impediment to signal propagation.
Also, since the transmitter and receiver do not couple with one another directly, the shared room ground provides the return path for the current.
The transmitter includes a signal generator and a pair of electrodes, referred to hereinafter as inner and outer electrodes.
The signal generator produces modulated signals that vary the voltage between the electrodes.
The inner electrode is closely coupled capacitively to the user's body such that the "quasi-electrostatic" field resulting from the electrode potential causes a displacement current to pass to the user's body.
The outer electrode is oriented so that its coupling to the room ground is stronger than that of the inner electrode, such that room ground acts as a return path for the current from the receiver.
The signal generator may modulate the information to be transmitted using, for example, a pseudorandom code, to produce spread spectrum signals.
This increases noise immunity and allows multiple transmitters, each using a different modulation code, to operate at the same time.
The receiver includes a pair of electrodes and a detector/demodulator that acquires and tracks the spread spectrum signal.
One of the electrodes is closely coupled capacitively to the user's body such that displacement current that passes from the body passes to that electrode.
The current then flows through detector circuitry to the other electrode, which is asymmetrically coupled capacitively to room ground, to complete the path for the current
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Finance 
