Q-Factor Spectrum of a Piezoceramic Resonator and Method for Piezoelectric Loss Factor Determination.

The quality factor (Q) spectrum of a piezoceramic resonator, as a Q-factor frequency dependence for the specific resonator and its vibrational modes, was determined under baseline low-excitation level with a new approach proposed. The theoretical prediction was experimentally confirmed that the resonator Q-factor increases with frequency nearly linearly from the resonance reaching its maximum near the antiresonance. For the industrial PZT-5A piezoceramic the antiresonance-to-resonance quality factor ratio is 1.8 to 2.4 as much, depending on the type of vibration. As the theory states, this effect is directly related to the piezoelectric "losses" in piezoceramics, usually represented by the imaginary part of complex piezocoefficients, which have a unique property of lowering the total cumulative energy dissipation in a resonator in certain frequency intervals. Based on the electromechanical Q-factor (EMQ) concept, a new relatively simple method was proposed for the piezoelectric loss factor determination at just a single resonance frequency-it requires measurements of the resonance Q-factor and its frequency derivative at the resonance, or the first and second frequency derivatives of the immittance phase at the resonance. Experimentally determined is close to near 0.8 of its upper (positive) phenomenological limit in the conventional PZT-5A piezoceramic at the basic vibrational modes. The piezoelectric loss factor, theoretically reaching the upper limit, can provide extremely high value of the Q-factor (near the fundamental antiresonance) with possible an order of magnitude EMQ increase. That paradoxical fact for the piezoelectric "losses" is a novel possible way of improving the piezoceramic performance and operation.