Abstract: A method and apparatus for determining a position of an external transceiver (24) relative to an implanted transceiver (23) comprising means (30) for measuring the strength of a magnetic field proximal to the external transceiver (24) and means for determining a position of the external transceiver (24) relative to the implanted transceiver (23) from said measured magnetic field strength. Furthermore there is disclosed is a method and apparatus for determining a skin flap thickness of a recipient of a prosthesis including a transcutaneous link between the external transceiver (24) and the implanted transceiver (23). A skin-flap thickness meter is also provided.

Abstract: An implantable device for treating a malfunctioning heart is disclosed. The device includes a high voltage circuit having a tank capacitor for storing therein during a charging mode of operation thereof high voltage DC electrical energy and for delivering such energy to a malfunctioning heart in the form of an electrical shock during a discharging mode of operation thereof.

Abstract: A magnetic field sensor including a resonant circuit having a coil. The resonant frequency varies with the strength of the magnetic field which passes through the coil. The resonant circuit is energized for approximately one-half cycle of the resonant frequency which characterizes the circuit in the absence of a magnetic field. During a sensing window of predetermined duration which then immediately follows, the voltage across the coil is examined for a zero crossing. A zero crossing will occur only in the presence of a magnetic field whose amplitude exceeds a threshold value.

Abstract: A combined telemetry system and magnetic field sensor for use in an implantable medical device. The telemetry system includes a conventional resonant circuit for transmitting and receiving data. The resonant circuit has a coil which is also used to sense the presence of a magnetic field exceeding a threshold value. The resonant frequency varies with the strength of the magnetic field which passes through the coil. Periodically, the resonant circuit is energized, and during a sensing window of predetermined duration which then immediately follows the voltage across the coil is examined for a predetermined number of zero crossings. That number of zero crossings will occur only in the presence of a magnetic field whose amplitude exceeds the threshold value. It is possible to achieve a sensitivity in such a system which is comparable to that of conventional miniature reed switches.