Using passively shunted electromechanical transducers to control the boundary impedance of dynamic test fixtures

One of the most basic problems with testing components in the vibration laboratory involves the discrepancy in boundary conditions between the laboratory and field environments. Boundary impedances that a component experiences when mounted in the field are usually quite different from those of traditional vibration test fixtures. These discrepancies can have dramatic effects on component response and therefore, the outcome of the vibration test. Simulation of field boundary conditions can be difficult because of the stochastic and time varying nature of some boundary impedances. A test fixture whose impedance can be continuously varied would be valuable in both qualification and modal-type testing. Similarly, a device that could mimic component impedance for purposes of test machine calibration would be of significant value. This paper develops the concepts necessary to implement variable impedance devices using electrically shunted piezoelectric and magnetostrictive transducers. Linear transducer models are developed and validated through experimentation. Practical considerations such as nonlinear transducer behavior are discussed.