Growing demand for battery-free or self-powered designs of electronics facilitates the development of energy harvesting from mechanical vibrations or impacts using piezoelectric materials. Piezoelectric materials used to date are featured in high elastic moduli and with high resonant frequency (kHz range), and thereby their performances are diminished in low frequency (0.1~100 Hz), which is, however, the frequency range of the majority of mechanical energy source from environment.ud This thesis reviews the techniques and interface circuits that have been developed to improve the power outputs of the piezoelectric energy harvesters for low frequency applications. Inspired by the Synchronized-switch harvester (SSH) circuit, this thesis brought up a concept of Synchronized-mechanical-switch harvester (SMSH) by taking advantage of large-deformation piezoelectric material to overcome the current issues of SSH, which includes the requirement of external power supply and displacement sensor. Thus, current piezoelectric materials and their mechanism of improving piezo-property are also reviewed. Two materials with low elastic modulus are selected as candidates for evaluation of SMSH.ud Up to 55% increase of output power was obtained by SMSH comparing to traditional interface circuit Full-Wave Rectifier (FWR) in the frequency range of 4Hz to 65Hz when a 390kOhm resistor load is connected. The influential factors of output power of SMSH are studied and discussed.
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