Powering Smart Jewelry Using An Energy Harvesting Necklace PDF Download

The development of low-power integrated circuits for the Internet of Things and wearable devices leads to the attraction of energy harvesting, a process that converts different types of energy into electrical energy to power autonomous wireless sensor systems and electronic circuits. The miniaturization of wearable, implantable, and wireless sensor devices is constrained due to bulkybatteries. Furthermore, battery maintenance cost and replacement time have become big challenges in large sensor networks. Hence, energy harvesting has been developed and improved to overcome battery drawbacks. In this project, an energy harvesting system in the form factor of a necklace was designed to scavenge radio frequency (RF) and vibration energy to power smart health tracking monitors integrated into a necklace pendant. The research contributions include the design of energy harvesting transducers (i.e., RF antennas and vibration piezoelectric thin films) to power management circuits including an RF to DC converter, an AC to DC bias flip rectifier, and a DC to DC buck-boost converter. The first part of the project developed, simulated, and tested different antenna configurations (including straight, Vee-, and U-shaped dipole antennas) and piezoelectric thin films embedded in the necklace and used as harvesters for RF and vibration energy harvesting. From theoretical calculations, simulations, and measurements of antenna radiation patterns, this thesis demonstrates the advantages of Vee- and U-shape dipoles to increase the received power omnidirectionality over the straight dipole. Simulated and physical human body phantoms were built to test the effects of the human head and chest on the antenna radiation pattern. Moreover, a flexible silver-ink RF dipole antenna integrated with a piezoelectric thin film is also presented and tested to not only provide the necklace flexibility to improve user comfort but also simultaneously harvest low-frequency vibration and RF energy. To convert the periodic electrical energy from the RF antenna and vibration transducer into usable DC energy to power the electronic loads, this work designed and tested different off-chip RF-DC converters and an on-chip AC to DC bias-flip rectifier. Various experimental comparisons between multistage Cockcroft-Walton and Dickson RF-DC converters show that the Dickson topology offers higher efficiency at high input power, whereas the Cockcroft-Walton converter performs better for low input power. For vibration piezoelectric energy harvesting, an implemented state-of-the-art bias-flip interface, which is a hybrid configuration between synchronized switch harvesting on inductor (SSHI) and on capacitor (SSHC), is proposed in this work to achieve high voltage flip efficiency from 90.2% to 95.6% with a small inductor of 100 [mu]H. The proposed rectifier interface increases the vibration power extraction capability by 7.43X compared to a full-bridge rectifier and 2.2X compared to a conventional SSHI circuit driven by a 117 Hz vibration excitation of 1.12 g. The approach minimizes the inductor and series resistor effects on the bias-flip efficiency and therefore allows 4X power improvement even with a very small inductor valueof 1 [mu]H. Finally, a dual-input buck-boost DC to DC converter that simultaneously scavenges the piezoelectric high-voltage input and a low-voltage input from an RF energy harvesting source was designed and tested with an off-chip circuit and then integrated with the bias-flip rectifier in a chip. The multiple-input converter not only increases the output power and environmental adaptability but also reduces the component volume by sharing the same inductor with the bias-flip rectifier circuit. The complete and optimized system from embedded vibration transducers and antennas to the power management circuit solution, demonstrated in this thesis, improves the performance of energy harvesting in future smart jewelry.