Modal parameter prediction for structures with resistive loaded piezoelectric devices

Natural frequencies and damping ratios of a structure, with piezo devices bonded on it and shunted with a resistive load, depend on the electrical load itself. Therefore, several tests (experimental or numerical) ought to be carried out in order to determine the resistor which provides the maximum damping ratio for a mode of interest, and in turn the natural frequency of the whole structure. In this paper we present relationships which allow us to predict the modal parameters mentioned above, by using the natural frequencies of the structure when the external electrical circuit of the piezo device is in short or open conditions. Thus, only two tests would be necessary in order to obtain both the maximum damping ratio, introduced by the piezo device, and the natural frequency of the whole system. Besides, under an acceptable approximation, the resistive load, which should be used to obtain the maximum damping, can be obtained from the natural angular frequencies previously derived.