Multi-Source Energy Harvesting Interface Circuits for Biomedical Wearable Electronics

Abstract

Emerging technology in semiconductor devices and circuits has enabled ultra-low power systems in medical applications, and hard to reach places which fueled the energy scavenging research and the interface circuits. State-of-the-art researches have reported self- powered systems using ambient sources such as vibration, wireless, thermal and solar. Such sources need special interface circuits that have low power consumption for suitable energy conversion, such as DC-DC converters and rectifiers. The main goal of this work is to design, implement and verify a complete energy harvesting system from human body thermal and vibration targeting wearable electronics in biomedical applications. This includes an efficient interface circuit and control for thermoelectric generators, energy combiner for multi-source energy harvesting and power manager for self-powered systems. First, characterization of thermal and vibration energy harvesting from a human body is presented. This includes using on-the-shelf harvesters placed on human hand to characterize the power density from each harvester in a controlled environment. The experimental ii results showed a power density of 2.2 W/cm2 and 7.4 W/cm3 for thermoelectric generator and piezo electric harvester, respectively. The following chapters focus more on the interface circuits for the energy harvesting system, especially for the thermoelectric generator. In Chapter 3, a comprehensive literature review is carried out for different power converter topologies used in thermal energy harvesting applications. In particular case, inductor-based DC-DC converters are explained in details, including the losses associated with different parameters and the digital control circuits needed for proper operation. Finally, prior work on reported power conversion architectures are discussed and compared. Chapter 4 proposes a zero current switching control that is designed for inductor-based boost converters which has an all-digital implementation in 65 nm CMOS. The proposed control circuit achieves 56 delay steps using 3 control bits. Measured results confirm 81% effciency at 55 W output power. In Chapter 5, a new method for detecting and reversing the polarity of a thermoelectric generator is presented for inductor-based DC-DC converters. The method is based on an all-digital technique with small area and power overhead compared to literature. The circuit is implemented in 65nm CMOS and measured results show an overall effciency of 70% at 50 mV input voltage and 40 A output current. In Chapter 6, recent work of multi source energy harvesting system is compared. This includes different energy combining techniques used to deliver the energy from multiple energy sources to the load. In addition, three different energy combiner circuits are designed for energy harvesting from multiple sources with measurement results. Further, a power manager is presented to manage multi-source energy harvesting sources to power an ECG processor. iii Finally, Chapter 7 provides conclusions for the work done as part of this thesis, and presents possible directions for future work in this area of research. Finally, it discusses limitations of the conducted research. Indexing Terms: thermoelectric generator, auto polarity, zero current switching, energy mixer, power manager.

Date of Award	May 2016
Original language	American English
Supervisor	Mohammed Ismail (Supervisor)