A new three-dimensional (3D) model of a high-power composite ultrasonic transducer is proposed and evaluated in this paper. This transducer comprises two active layers, each with at least two mechanically series-connected piezoelectric elements. A metal mass element is clamped between active layers with two bolts to create a sandwich structure comprising back and front metal radiation masses. The electromechanical equivalent circuit of the transducer, representing a general one-dimensional (1D) model, is first derived and presented in this paper. The general 1D model takes into account all existing transducer components, including both central bolts, in addition to the proposed 3D model. Additionally, when effects of the bolts are excluded, the resonance frequency equation was analytically derived based on the general 1D model. The composite transducer is designed and manufactured. For a large number of electrical connection combinations, transducer resonance frequencies are measured and compared with the results obtained from 3D and 1D models. The results indicate that the resonance frequencies obtained from 1D model are in line with the measured frequencies for the first thickness mode only. However, for all thickness and radial oscillation modes and their mutual coupling the analytically obtained frequencies from 3D model correspond well to the measured frequencies. In addition, the presented results in this paper contribute to a better understanding of the geometry and material properties of the composite piezoelectric transducer parts impact on transducer behavior.

The results obtained after extensive research on the influence of the magnitude and phase approximation error on the output of the low-pass filter in the time domain are presented in this paper. The ideal filter does not exist, and real ones are usually obtained by approximating either the ideal magnitude or phase characteristics. If the obtained solution is not good enough, the issue can be addressed by designing a magnitude or phase corrector which will be connected in cascade with the low-pass filter. Of course, design methods can also be based on trade-offs between magnitude and phase error. This study offers valuable guidelines for determining the optimal maximum magnitude and phase error to ensure a balanced influence on the time domain error of the output signal.