Built Environment Sensing

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A Vibration Harvesting System and Electronics for Bridge Health Monitoring Applications
James McCullagh, Rebecca L. Peterson, and Khalil Najafi
(Left) A schematic of PFIG function. A large inertial mass snaps between two FIGs as the acceleration from a bridge releases the mass from magnets on the FIG springs.  Once the inertial mass is released, the FIG spring vibrates at a mechanically up-converted frequency.  A magnet sitting on top of the FIG spring generates current through an electromagnetic coil.  (Center) The circuit block diagram. (Right) Charge and discharge cycles on a storage capacitor using an LED load.
(Left) A schematic of PFIG function. A large inertial mass snaps between two FIGs as the acceleration from a bridge releases the mass from magnets on the FIG springs. Once the inertial mass is released, the FIG spring vibrates at a mechanically up-converted frequency. A magnet sitting on top of the FIG spring generates current through an electromagnetic coil. (Center) The circuit block diagram. (Right) Charge and discharge cycles on a storage capacitor using an LED load.

The goal of this project is to convert non-periodic, low-frequency ambient bridge vibrations into electrical energy that can be used to power wireless sensors which can monitor the structural health of a bridge. We previously developed a novel parametric frequency-increased generator (PFIG) to harvest these bridge vibrations. The PFIG converts the < 10 Hz ambient vibrations on bridges into decaying sinusoidal voltages at a frequency 10 times greater than the original bridge vibrations, in order to improve mechanical-to-electrical energy conversion efficiency. The fabricated PFIG can generate a peak power of 57 µW and an average power of 2.3 µW from an input acceleration of 0.54 m/s2 at 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration range (0.54-9.8 m/s2) and frequency range (up to 30 Hz) without any modifications or tuning. A circuit system is built to convert the PFIG output into usable stored power. The electronics system consists of two cascaded six-stage Cockcroft multipliers used to boost and rectify the outputs of the two PFIG transducers. The boosted voltage is stored on a capacitor. To demonstrate system functionality, an LED, buzzer, or ring oscillator is used as a load. This work was supported by the National Institute of Standards and Technology (NIST) Technology Innovation Program (TIP) under cooperative agreement number 70NANB9H9008.

Updated 05/01/2012