Piezoelectric Generation and Damping of Extensional Waves in Bars
Sammanfattning: This thesis focuses on the electromechanical processes of generation and damping of transient waves in bars with attached piezoelectric members. In particular, the influence of amplifier and electrical circuitry on the mechanical waves is of interest.A straight bar element containing piezoelectric members is viewed as a linear system with one electrical and two mechanical ports where it interacts with external electrical and mechanical devices through voltage, current, forces and velocities. For the modelling of the piezoelectric bar element (PBE) and its environment, coupled piezoelectric theory is used with allowance for the dynamics of the PBE and attached electrical and mechanical devices.Two applications are considered for a PBE that constitutes a part of a long bar, viz. generation and damping of extensional waves. In the first, simulations and experiments were performed when the PBE was driven by a power amplifier. In the second, simulations and experiments were performed when the PBE supplied an output voltage to an external load.In the case of wave generation, the influence of amplifier characteristics in terms of DC voltage gain, 3 dB cut-off frequency, output impedance and current constraints on the output voltage and current of the amplifier and the waves generated are studied. Further, generation of waves of prescribed shapes are studied for a specific amplifier. In general, good agreement between simulated and experimental results was obtained.In the case of wave damping, the influence of external electrical loads and incident waveforms on reflected and transmitted waves, and on gener-ated voltage, current, electrical power and dissipated energy, are studied. In general, fair agreement between simulated and experimental results was obtained. The fractions of a few percent of wave energy dissipated in the exter-nal load were well below the 50 percent achievable for a harmonic wave under condition of electrical impedance matching.
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