Abstract: A system and method for relaying signals from a magneto-inductive system, which are normally used to communicate between magneto-inductive units using quasi-static magnetic fields, over a voice-band communication system. The magneto-inductive signals are modulated data signals having a carrier frequency typically between 300 Hz and 3 kHz. The voice-band communication system facilitates long distance communication of voice-band signals. By supplying the signals from one magneto-inductive unit to the voice-band communication system through an analog input port, the signals are transmitted through the voice-band communication system. They are output from the system through an analog audio output port to the other magneto-inductive unit.

Abstract: A system and method for relaying signals from a magneto-inductive system, which are normally used to communicate between magneto-inductive units using quasi-static magnetic fields, over a voice-band communication system. The magneto-inductive signals are modulated data signals having a carrier frequency typically between 300 Hz and 3 kHz. The voice-band communication system facilitates long distance communication of voice-band signals. By supplying the signals from one magneto-inductive unit to the voice-band communication system through an analog input port, the signals are transmitted through the voice-band communication system. They are output from the system through an analog audio output port to the other magneto-inductive unit.

Abstract: A passive inductive switch for coupling a battery to a load in a remotely deployed battery-powered electronic device. The switch operates in response to a transmitted magnetic field at a particular frequency. The switch includes an antenna for transforming the magnetic field into an induced voltage and a voltage detector for sensing the induced voltage and triggering a switching element. The switch operates in a standby mode until a sufficient voltage is induced in the antenna which causes the switch to couple the battery to the load. In the standby mode the switch draws a negligible amount of power, which permits the device to be deployed in the field for long periods of time without expending significant battery power.

Abstract: An amplifier circuit for efficiently driving a tuned resonant load where the amplifier circuit controls the continuously variable resonant frequency of the tuned resonant load so as to match step changes or slower changes in the frequency of the signal with which it is being driven. The circuit includes a tuned resonant load, a driver, a controller and a feedback loop. The driver is coupled to the load and drives it with a driving signal at a frequency under the control of the controller. The controller dynamically controls the resonant frequency of the tuned resonant load in response to an error signal received through the feedback loop. The error signal represents the mismatch in phase between the resonant phase of the load current and the phase of the driving signal, or between the resonant phase of the tuning capacitor voltage offset by 90 degrees and the phase of the driving signal.

Abstract: An amplifier circuit for efficiently driving a tuned resonant load where the amplifier circuit controls the continuously variable resonant frequency of the tuned resonant load so as to match step changes or slower changes in the frequency of the signal with which it is being driven. The circuit includes a tuned resonant load, a driver, a controller and a feedback loop. The driver is coupled to the load and drives it with a driving signal at a frequency under the control of the controller. The controller dynamically controls the resonant frequency of the tuned resonant load in response to an error signal received through the feedback loop. The error signal represents the mismatch in phase between the resonant phase of the load current and the phase of the driving signal, or between the resonant phase of the tuning capacitor voltage offset by 90 degrees and the phase of the driving signal.

Abstract: An apparatus and method for continuous variable reactive impedance control. The apparatus and method enable the continuous variation of the reactive impedance of an oscillating circuit. A reactive component, in one embodiment a capacitor, is switched into the oscillating circuit for a duration at the beginning and end of each half cycle of the oscillation frequency. Through varying the duration, the oscillation frequency is varied between the frequency that occurs without the reactive component in the circuit and the frequency with the reactive component permanently in the circuit. A controller determines the duration and controls a switch coupled to the reactive component. The apparatus and method may be used to adjust the oscillation frequency of a resonant circuit or to match the resonant frequency to a driving frequency in a driven oscillating circuit so as to improve efficiency.

Abstract: An apparatus and method for continuous variable reactive impedance control. The apparatus and method enable the continuous variation of the reactive impedance of an oscillating circuit. A reactive component, in one embodiment a capacitor, is switched into the oscillating circuit for a duration at the beginning and end of each half cycle of the oscillation frequency. Through varying the duration, the oscillation frequency is varied between the frequency that occurs without the reactive component in the circuit and the frequency with the reactive component permanently in the circuit. A controller determines the duration and controls a switch coupled to the reactive component. The apparatus and method may be used to adjust the oscillation frequency of a resonant circuit or to match the resonant frequency to a driving frequency in a driven oscillating circuit so as to improve efficiency.

Abstract: An antenna for a transceiver. The antenna is switchable between a receive and a transmit mode. In receive mode, the antenna is configured to provide increased sensitivity for improved inductive pickup of signals. In transmit mode, the antenna is configured to provide efficient power output without undue losses. The antenna coil comprises a plurality of conductor bundles. In receive mode, the conductor bundles in series to increase the number of effective turns in the antenna coil and thereby increase the inductive pickup of the coil for receiving signals. In transmit mode, the conductor bundles are configured in parallel. The parallel configuration of the conductor bundles reduces the AC and DC resistance of the antenna coil, and therefore the power loss, to allow the antenna to be driven efficiently to transmit signals.