Implantable RF Power Converter for Small Animal In Vivo Biological Monitoring

A miniature, long-term, implantable radio frequency (RF) power converter for freely moving small animal in vivo biological monitoring is proposed. An environment consisting of a laboratory mouse inside a cage is used for a prototype monitoring system design. By employing an inductive coupling network, a prototype implant device with a dimension of approximately 6 mm times 6 mm times 1 mm and a weight of 100 mg including medical-grade silicone coating can wirelessly receive an input RF power from an array of external coils positioned underneath the cage. Each coil is designed to be 5 cm times 5 cm, comparable to a typical mouse size for minimizing power coupling variation. The received AC voltage is further rectified by a half-wave rectifier to supply DC current to a 3 kOmega load resistance, representing a typical bio-implant microsystem loading. The proposed RF power converter was implanted in the peritoneal cavity of a laboratory mouse for performance evaluation. With a 5-turn external coil loop separated from a 30-turn internal coil by 1 cm distance and centered to each other, an optimal voltage gain of 3.5 can be achieved with a 10 MHz operating frequency to provide a maximum rectified output DC voltage of 21 V. The DC voltage varies at different animal tilting angles and positions with a minimum voltage of 4 V at 60deg tilting angle near the corner of the external coil. This variation can be further minimized by overlapping the external loops layout. A voltage regulator can also be designed to provide a stable supply for an overall bio-implant system