When ac power is applied, a piezo-ceramic actuator exerts a force to the structure under testing. Because of the electromechanical interaction taking place in the actuator, the input electrical impedance of the actuator can be utilized to detect the mechanical impedance of the structure at the excitation point. In this sensor-less technique for measuring mechanical impedance, the system behavior of the sensor cum actuator should be identified first analytically or experimentally. In this paper, a new method for identifying the system behavior is presented to overcome the commonly met experimental difficulties. A two-port model can be built to relate the input and output variables of a piezoceramic actuator.
V are the force and velocity at the output mechanical port.
To evaluate ZM from Ze, impedances ZMO, Zec and Zef should be made known by calibrating the device in advance under various mechanical boundary conditions and electrical terminal conditions. In this formula, Zef can be easily calibrated by letting the output port free mechanically, while ZMO and Zec are much more difficult to calibrate. This is because mechanical clamp conditions and electrical open-circuit conditions are difficult to be realized in a laboratory. To overcome these problems, ZMO and Zec are indirectly identified from the measured Zef and a set of Ze of the actuator when various known masses are applied to its output port. It is demonstrated by experiments that the proposed identification technique can correctly identify ZMO and Zec and significantly improve the accuracy and convenience of using the sensor-less technique for measuring mechanical impedance using only an actuator.