Damping of elastic strain waves by means of a piezoelectric bar element feeding an external RL circuit

Damping of elastic strain waves in an aluminum bar by means of a pair of piezoelectric members bonded to the bar and loaded by an external RL circuit is studied. Experimental results are compared with theoretical results based on a three-port impedance model for the laminated piezoelectric bar element (PBE). According to this model, the PBE is viewed as a linear system with one electrical and two mechanical ports at which interactions with external devices, e.g., the external parts of the aluminum bar, can take place. The two constitutive equations of the piezoelectric material, the dynamics of the piezoelectric members and the bar, and the dynamics of the resistive-inductive load are taken into account. The experimental results are below the theoretical ones by a few percent for the reflected and transmitted strain waves, by 6–11% for the voltage and current generated, and by 12–19% for the power and energy delivered to the load. This indicates that there are energy losses in the PBE and the external parts of the bars that have not been accounted for in the model. Such losses may be due to, e.g., viscoelastic shear, dielectric losses and generation of bending waves.