This paper discusses the development and testing of a renewable energy source for powering wireless sensors used to monitor the structural health of bridges. Traditional power cables or battery replacement are excessively expensive or infeasible in this type of application. An inertial power generator has been developed that can harvest traffic-induced bridge vibrations. Vibrations on bridges have very low acceleration (0.1-0.5 m s −2 ), low frequency (2-30 Hz), and they are non-periodic. A novel parametric frequency-increased generator (PFIG) is developed to address these challenges. The fabricated device can generate a peak power of 57 μW and an average power of 2.3 μW from an input acceleration of 0.54 m s −2 at only 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration (0.54-9.8 m s −2 ) and frequency range (up to 30 Hz) without any modifications or tuning. Its performance was tested along the length of a suspension bridge and it generated 0.5-0.75 μW of average power without manipulation during installation or tuning at each bridge location. A preliminary power conversion system has also been developed.

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This paper reviews the state of the art in miniature microsystems for harvesting energy from external environmental vibration, and describes two specific microsystems developed at the University of Michigan. One of these microsystems allows broadband harvesting of mechanical energy from extremely low frequency (1-5 Hz) random vibrations abundant in civil infrastructure, such as bridges. These parametric frequency increased generators have a combined operating range covering two orders of magnitude in acceleration (0.54-19.6 m/s 2 ) and a frequency range spanning up to 60Hz, making them some of the most versatile harvesters in existence. The second of these systems is an integrated microsystem for harvesting energy from periodic vibrations at moderate frequencies (50-400 Hz) typically present in devices such as motors or transportation systems. This harvester utilizes a thinned-PZT structure to produce 2.74 µW at 0.1 g (167 Hz) and 205 µW at 1.5 g (154 Hz) at resonance. Challenges in the design of electronic circuitry (integrated or hybrid) for regulating the scavenged energy are briefly discussed.

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