Toshikazu Nishida

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  1. Piezoelectric Transducers: Strain Sensing and Energy Harvesting (and Frequency Tuning)

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    15 Jun 2007 | Online Presentations | Contributor(s): Toshikazu Nishida

    Acoustic pressure or mechanical force sensing via piezoelectric coupling is closely related to the harvesting of electrical energy from acoustical and mechanical energy sources. In this talk, mesoscale and microscale piezoelectric transducers for acoustic and vibrational sensing and energy harvesting will be discussed. For example, a micromachined piezoelectric microphone has been developed for aeroacoustic applications with a demonstrated sensitivity of 0.75 µV/Pa, a dynamic range greater than six orders of magnitude (47.8 –169 dB, ref . 20 µ Pa), and a resonant frequency of 50.8 kHz. In addition, acoustic energy harvesting has been demonstrated using a mesoscale (~ 2 cm) Helmholtz resonator machined in aluminum, delivering 25 mW to a resistive load at a sound pressure level (SPL) of 152 dB (ref. 20 µPa. This acoustic energy may be used to locally power a wireless active liner for suppression of engine noise in turbofan engines, where acoustic levels typically reach up to 150 dB. For space-constrained applications, a micromachined acoustic energy harvester was also recently developed. It employed a silicon-micromachined, circular, piezoelectric composite diaphragm. Experimental results indicated a maximum output power density of 0.34 µW/cm2 at 149 dB (ref. 20 µPa) and a potential output power density of 250 µW/cm2 with an improved fabrication process. Similar examples will be given for cantilever-based vibrational energy harvesters. Finally, some system considerations will be discussed for energy harvesting- powered systems. As the volume of the energy harvester is reduced, as expected, the harvestable power decreases given a specific power density for the available ambient conditions and material parameters. For system designs, the power balance between average power dissipation and average power harvesting determines the maximum duty cycle possible under specific energy harvesting conditions.