Power Conversion Circuits for Low Power, Low Voltage and Non-Periodic Vibration Harvester Outputs
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According to the US Department of Transportation, more than 10% of the nation's bridges are structurally deficient. Wireless sensor technology is a superior solution for monitoring this deteriorating infrastructure as it eliminates the need for expensive wiring and permits easy relocation of sensors nodes. As these Structural Health Monitoring sensors (SHM) must operate continuously for many years without human intervention, battery replacement is a significant concern since the sensors are typically located in hard-to-reach and dangerous locations. The low frequency vibrations present on a bridge can be up-converted with an energy harvester. These up-converted outputs are ultra-low power (~10 Â µW), low voltage (100 to 450 mV), and non-periodic. This thesis develops circuit techniques capable of cold start, boosting, rectifying and storing the harvested energy of mechanical vibration harvesters that have outputs that are low power, low voltage and non-periodic. Techniques are developed to overcome the diode drops inherent in rectification of these harvester signals. New techniques for high efficiency low voltage functioning and active IC-based sub-threshold start-up are introduced. This thesis includes: 1) The development of innovative IC harvesting circuits for electromagnetic vibration harvesters capable of enabling active diode charge pumps to record high boosting, high power harvesting efficiency, low power functioning, and record low input voltage functioning in a boosting circuit; 2) The use of sub-threshold functioning to enable a boosting low voltage active diode cold start-up on an IC-based energy harvesting circuit utilizing the unique start-up properties of charge pumps; 3) The use and study of discrete passive circuit solutions for vibration harvesters with record low voltage and low power outputs; and 4) The testing of these circuits under bridge-like conditions or on a real suspension bridge.