An Implanted Telemetry Unit for Ambulatory Animals

An implanted physiological-signal telemetry unit for an ambulatory animal is described. It uses a single 1.35 V mercury cell, is
1 \times 2.5 \times 4
cm in size, and weighs 15 g. Transcutaneous RF turn-on and magnetic turn-off are used to conserve battery power. The battery can operate 175 h before replacement. An integrated circuit amplifier supplies a voltage gain of 250 over a nominal band from 0.2 Hz to over 4 kHz. With 2 mV peak input, it yields 75 kHz peak deviation of a 20 MHz carrier. Relations between frequency,
Q
, receiving antenna voltage, and implant coil diameter are derived. Circuits are also given for a "turn-on" device, a 20 MHz converter, and the sequential gating of three mutually perpendicular antennas to avoid dropouts as the animal moves within the cage.