Inductively powered implantable microcoil temperature measurements: safety implications and operational guidelines

In this paper, we report on the temperature variations on the surface of a microcoil that is inductively powered by a strong magnetic field generated by a Class-E transmitter. It is shown that microcoil temperature increase cannot be neglected and can cause tissue damage in continuous mode operations if adequate cooling is not provided by a nearby blood vessel. The microcoil operated in the air shows a temperature increase of 4.5, 2.2, and 1/spl deg/C at the distances of 5, 10 and 20mm, respectively. Submerging the coil in saline resulted in 2, 1, and 0.2 /spl deg/C temperature increase at similar distances. We also measured the time to reach 1 /spl deg/C increase to provide an operational guideline in order to protect heat sensitive tissues from serious damage.