A Human Body Heat Driven High Throughput Thermal Energy Harvesting Single Stage Regulator for Wearable Biomedical IoT Nodes

A human body heat driven thermal energy harvesting regulator with high output power at low input voltages and small form factor, suitable to power compact and feature-packed wearable biomedical Internet of Things (IoT) nodes, is developed in this paper. The system demonstrates <inline-formula> <tex-math notation="LaTeX">$2.3{\times }$ </tex-math></inline-formula> higher throughput than prior art at low input voltages with a maximum conversion ratio of <inline-formula> <tex-math notation="LaTeX">$83 \times $ </tex-math></inline-formula>, in order to support complex and power hungry IoT operations like onboard processing and data transmission. The peak load supportable by the system is extended by utilizing maximum power extraction and minimizing converter losses in a single-stage compact power management unit. A fixed-frequency technique, independent of input voltage variation is proposed to maximize output power when load demands. A digital switch controller with ultra low power digitally controllable delay circuit is implemented to perform zero current switching to improve efficiency. The system, fabricated in 180-nm standard CMOS process, operates from open circuit input voltages ranging from 25 to 210 mV while supplying a regulated 1 V output. The functionality of the system is demonstrated in real-time by integrating the regulator with an emulated cardiac monitoring IoT node. The system delivers a peak power of 1.03 mW at open circuit voltage of the transducer, <inline-formula> <tex-math notation="LaTeX">${V} _{\text {TEG}}$ </tex-math></inline-formula>, of 210 mV, generated at body to ambient temperature difference of ~8 °C. The total area occupied by the system is 0.13 mm² and has an end-to-end peak efficiency of 65% at <inline-formula> <tex-math notation="LaTeX">${V} _{\text {TEG}}$ </tex-math></inline-formula> of 50 mV in measurement.