Tissue temperature measurement and heat transfer mechanisms for inductively powered implantable microsystems

In this paper, we report on the tissue temperature measurement and heat transfer mechanisms for inductively powered microsystems. It is shown that heat transfer from the transmitter coil can be the dominant mechanism in tissue heating for applications that require continuous operation (e.g., neural and visual prosthetics). For long-term operation, this thermal effect shouldn´t be overlooked or underestimated for tissue safety. Tissue temperature measurements in open and thermally isolated environments are used to verify the above hypothesis. A high-efficiency class-E transmitter is used as the main power source. Heat is generated within the transmitter coil and is transferred to the tissue by conduction, convection, and radiation. Open-air temperature measurements in fat and muscle tissue show a net increase of 0.8 and 0.7°C respectively. However, thermally isolated sample show a lower temperature increase (fat: 0.6°C, muscle: 0.5°C).