Influence of Spread Gap Height on Piezoelectric Transducer Coupled via Pressureless Sintering of Nano-Ag

Spread gap height has a significant impact on the performance of piezoelectric transducers coupled by pressureless sintering of nano-Ag paste, but the specific mechanism of the effect has been lacking of systematic investigation. In this work, the effect of spread gap height on the preparation process and post-preparation performance of the nano-Ag coupled transducer is experimentally explored. Surface mount technology (SMT) stencils with various thicknesses are used to simulate different gap heights. The results show that mechanical jamming and cohesion-induced jamming coexist during the paste spreading process. Gap height is positively correlated with layer spreadability. When the spread gap height is narrow, limited spreadability and coupling layer flatness lead to suboptimal performance in transducer with the thinnest coupling layer. Conversely, a larger gap height results in a thicker coupling layer, which increases scattering and attenuation coefficients, thereby weakening the signal. Excellent transducer performance is obtained at a moderate gap height (about $50~\mu $ m).