Coupled vibrations in the vibration system of high-power ultrasonic transducers lead to extremely complex vibration characteristics, which seriously degrade their operational performance. Therefore, optimizing the coupled vibration system and improving its dynamic performance to meet engineering application requirements have become urgent issue.

Currently, phononic crystal structures with hole and pillar configurations have been widely investigated to optimize the coupled vibrations of ultrasonic transducers. Nevertheless, studies have demonstrated that the hybrid pillar-hole phononic crystal structure offers distinct advantages in broadening the bandgap width. Accordingly, this paper adopts the pillar-hole structure to optimize the coupled vibration system of high-power ultrasonic transducers. Considering that diverse performance demands of different operating environments, this work focuses on the optimal design of coupled vibration systems for high-power, large-scale ultrasonic transducers in plastic welding, guided by practical application in requirements.

This paper applies a quasi-periodic phononic crystal structure, which incorporates combined cylindrical holes with transverse bandgaps (capable of suppressing lateral vibrations in both the length and width directions), topological defects, and acoustic surface structures, to the optimal design of high-power ultrasonic vibration systems. Specifically, five structural types are studied: cylindrical holes, pipe column holes, square column holes, three-fan column holes, and four-fan column holes. Data analysis techniques were employed to quantify the optimization effects of these different structures on system performance.

Simulation and calculation results demonstrate that the amplitude distribution uniformity of the system's radiation surface is excellent for pipe, square, three-fan, and four-fan column hole shapes. The displacement amplitude is relatively large for square, three-fan, and four-fan column holes. Considering both the amplitude distribution uniformity and displacement amplitude, the system performance reaches an ideal state with square, three-fan, or four-fan column hole designs. A system with a square column hole structure was fabricated and experimentally tested. The results show that the square column hole structure effectively improves the displacement amplitude and amplitude distribution uniformity of the system’s welding surface, enhances the design efficiency and reliability of the coupled vibration system for high-power ultrasonic transducers, fully verifying the feasibility of the proposed optimization scheme.