Generation of prescribed strain waves in an elastic bar by use of piezoelectric actuators driven by a linear power amplifier

The problem of generating prescribed strain waves in an elastic bar by means of a pair of piezoelectric actuators driven in phase by a linear power amplifier was considered theoretically and experimentally. The power amplifier was characterized by its DC voltage gain and 3 dB cut-off frequency unloaded, and by its output resistance and inductance. With the assumption of one-dimensional (1D) wave propagation in the bar, including the actuator region, a linear difference equation was derived for the required input voltage to the power amplifier in terms of the strain associated with the prescribed wave. This difference equation was solved numerically for a bell-shaped strain wave and for a single-period sine strain wave. After identification of the linear power amplifier, two tests were carried out with the aim to generate the two strain waves in an aluminium bar instrumented with semi-conductor strain gauges. Very good agreement was obtained between the implemented and required input voltages, output voltages and output currents of the power amplifier, and good agreement was achieved between the implemented and prescribed strain waves.