A Transcutaneous Implanted Battery Recharging and Biotelemeter Power Switching System

A system has been developed for extending the lifetime of an implantable biotelemeter (or potentially a variety of implantable electronic devices), first by recharging implanted nickel cadmium (NiCd) batteries via radio frequency power transmitted from an external portable source, and second by providing on/off electronic power switching which, when activated externally, allows for shutdown of the biotelemeter when not required and subsequent powering up when needed. The battery pack, which has been successfully evaluated in the dog, uses four sealed NiCd 100 mA ·h, 1.25 V dc cells which can be "quick charged" at 40 mA in 2.5 h. Higher or lower charge rates are available and the charging rate is telemetered for continuous battery status indication. The system has been designed to charge the implanted batteries through 13 mm tissue thickness, using 50 mm diameter transmitting and receiving coils. The on/off operation of the system is limited to a maximum 100 mm coil spacing. The switching circuitry has been implemented on a 28 ×43 mm ceramic substrate with reflow soldered integrated circuit leadless inverted devices (LID's®) and resistor and capacitor chips. It is expected that the reflow soldering can be duplicated easily by other investigators on either ceramic or glass-epoxy boards. The power transmitter and its battery pack are intended for placement in an animal jacket. The transmitter has a 2.5 W dc power input and will operate from a 1.2 A ·h, 12 V dc battery pack for the required recharging period.