An analytical Mason equivalent circuit is derived for a circular, clamped plate piezoelectric micro-machined ultrasonic transducer (pMUT) design in 31 mode considering an arbitrary electrode configuration at any axisymmetric vibration mode. The explicit definition of lumped parameters based entirely on geometry, material properties and defined constants enables straightforward and wide ranging model implementation for future pMUT design and optimization. Beyond pMUTs, the acoustic impedance model is developed for universal application to any clamped, circular plate system and operating regimes including relevant simplifications are identified via the wave number-radius product ka. For the single electrode fundamental vibration mode case, sol-gel P b (Zr0.52) T i0.48O3 (PZT) pMUT cells are micro-fabricated with varying electrode size to confirm the derived circuit model with electrical impedance measurements. For the first time, experiment and finite element simulation results are successfully applied to validate extensive electrical, mechanical and acoustic analytical modeling of a pMUT cell for wide ranging applications including medical ultrasound, non-destructive testing, and range finding.
Two-dimensional arrays of micro-cavities effectively control photon motion and selectively emit radiation tailored to the preferred bandgap of photovoltaic (PV) cells, thus enhancing the efficiency of thermophotovoltaic energy conversion. At the high operating temperatures, however, the microand nano-patterned structures of the selective emitters quickly lose their integrity-obliterating the tight tolerances required for precise spectral control. Even if oxidation, recrystallization, and grain growth could be avoided with single-crystal tungsten (W) selective emitters with vacuum packaging, surface diffusion, evaporation, and re-condensation are not avoidable in long-term operation at high temperatures. The concept of a planar array of plugged micro-cavities to suppress the curvaturedependent thermal degradation modes is proposed and tested. Based on scale-accelerated failure tests of silicon devices, the lifetime of W selective emitters operating at 1100 K is estimated to be at least 30 yr. V
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