Ultrasonic Polishing of Zirconia Ceramics Based on a Fresnel-Structured Transducer

Zirconia (ZrO2) ceramics are widely used in 5G-enabled devices owing to their excellent performance. However, their high hardness and brittleness during ultrasonic polishing lead to complex behavior that is influenced by the setup and abrasive size. This study presents Fresnel-structured transducer-based ultrasonic polishing (FSTUP), which employs a Fresnel-structured transducer into ultrasonic polishing to enhance the surface quality and material removal rate (MRR) of ZrO2 ceramics. The improved polishing performance is attributed to the combined effects of acoustic streaming, abrasive impact, and cavitation collapse. Cavitation collapse leads to surface erosion, thereby decreasing surface quality, unlike the other two methods. Therefore, it is essential to control this phenomenon. We investigated the effects of transducer structure, polishing distance, and abrasive particle size on the surface roughness (Ra) and MRR of ZrO2 ceramics. White light interferometry and laser confocal microscopy were used to characterize surface morphologies, and COMSOL simulations were performed to verify the sound field focusing capability of the FST. Under the optimized conditions (polishing distance D = 1.5 mm, abrasive size A = 2.5 µm, and polishing time T = 30 min), we obtained an Ra of 5.22 nm and an MRR of 6.45 nm/min. This research is applied to the polishing processing of 5G device back covers.