To increase the ultrasonic intensity and power of a piezoelectric transducer, a cascaded piezoelectric ultrasonic transducer with the three sets of piezoelectric ceramic stacks is analyzed. The cascaded piezoelectric ultrasonic transducer consists of four metal cylinders and three sets of piezoelectric ceramic stacks in the longitudinal direction. In analysis, the electromechanical equivalent circuit of the cascaded piezoelectric ultrasonic transducer is obtained, as well as the resonance/anti-resonance frequencies equations. By means of an analytical method, when the position of piezoelectric ceramic stacks PZT-2/PZT-3 changes, the resonance/anti-resonance frequencies and the effective electromechanical coupling coefficient of the cascaded piezoelectric ultrasonic transducer have certain characteristics. Several prototypes of the cascaded piezoelectric ultrasonic transducer are manufactured. The experimentally measured resonance frequencies are in good agreement with the theoretical and simulated results. The cascaded piezoelectric ultrasonic transducer with three sets of piezoelectric ceramic stacks presented in this paper is expected to be used in the field of high power ultrasound.

This Letter proposes an ultrasonic stress monitoring method utilizing the S1 zero group velocity (S1-ZGV) mode based on a PVDF comb transducer. Experimental investigations have revealed that under varying uniaxial stress conditions, both the measured S1-ZGV frequency and its corresponding amplitude exhibit appreciable variations. By adopting the relative change rate of the amplitude corresponding to the S1-ZGV frequency (denoted by RCA) as the characteristic parameter, it is evident that RCA demonstrates a monotonic and highly sensitive response to the applied uniaxial stress. Notably, RCA exhibits a significant increase as the applied uniaxial stress rises. This characteristic enables the use of RCA to predict the stress state, facilitating real-time stress monitoring. Experimental validation indicates that the predicted stress values align closely with the actual applied stress values, demonstrating a high level of accuracy in stress prediction. This method enables real-time and in situ monitoring of the stress state in thin plates subjected to uniaxial stresses, which holds paramount importance for a wide array of industrial applications in structural health monitoring.