Highly-Efficient Energy Harvesting Interfaces for Implantable Biosensors

University dissertation from KTH Royal Institute of Technology

Abstract: Energy harvesting is identified as an alternative solution for powering implantable biosensors. It can potentially enable the development of self-powered implants if the harvested energy is properly handled. This development implies that batteries, which impose many limitations, are replaced by miniature harvesting devices. Customized interface circuits are necessary to correct for differences in the voltage and power levels provided by harvesting devices from one side, and required by biosensor circuits from another. This thesis investigates the available harvesting sources within the human body, proposes various methods and techniques for designing power-efficient interfaces, and presents two CMOS implementations of such interfaces.Based on the investigation of suitable sources, this thesis focuses on glucose biofuel cells and thermoelectric harvesters, which provide appropriate performance in terms of power density and lifetime. In order to maximize the efficiency of the power transfer, this thesis undertakes the following steps. First, it performs a detailed analysis of all potential losses within the converter. Second, in relation to the performed analysis, it proposes a design methodology that aims to minimize the sum of losses and the power consumption of the control circuit. Finally, it presents multiple design techniques to further improve the overall efficiency.The combination of the proposed methods and techniques are validated by two highly efficient energy harvesting interfaces. The first implementation, a thermoelectric energy harvesting interface, is based on a single-inductor dual-output boost converter. The measurement results show that it achieves a peak efficiency of 86.6% at 30 μW. The second implementation combines the energy from two sources, glucose biofuel cell and thermoelectric harvester, to accomplish reliable multi-source harvesting. The measurements show that it achieves a peak efficiency of 89.5% when the combined input power is 66 μW.