Characterization of the mechanical nonlinear behavior of piezoelectric ceramics

A characterization of the nonlinear behavior with high signal excitation in piezoceramic resonators was carried out. The behavior of power devices wor king at resonance, in which high strains are involved, is explained. A theo retical model previously described is used to explain the motional impedanc e variation proportional to the square of the motional current. This impeda nce increase PZ is independent of the frequency and explains: the nonlinear elasticity that produces the A-F effect, the nonlinear mechanical losses t hat increase greatly close to the resonance, and the hysteresis phenomenon produced with frequency sweeps. Different methods for measuring the mechani cal nonlinear coefficients of piezoceramics with high signal excitation are presented. An experimental method is proposed to measure the mechanical lo ss tangent and the compliance variations as a function of the mean square s train in the piezoceramic. This consists in measuring the maximum admittanc e and the series resonance frequency for downward frequencies. At this jump ing point, the phase angle remains zero whatever the amplitude of the excit ation. Two main coefficients characterizing the material mechanical nonline arity are deduced. Experimental measurements were carried out to compare th e nonlinearity of different ceramic materials in longitudinal and transvers e mode.