Pressure Enhancing and Operating Frequency Tunable Pmut with Compressible Parylene Helmholtz Resonanting Chamber and Active Backing Plate

This paper presents an innovative piezoelectric ultrasonic transducer (PMUT) with sound pressure enhancement and operating frequency tunability. The device consists of three major parts (Fig. 1): (1) the upper master-driving element, fabricated with a micromachined PZT-based foil and SU-8 frame to form the ultrasound exciting source, the open hole and neck of Helmholtz resonator. (2) the lower slave-driving element, constructed with the PZT foil and SU-8 frame to serve as the active backing plate of the PMUT. (3) parylene-film fabricated bellow structure functions as the compressible chamber of Helmholtz resonator. Experimental results show that adjusting the volume of parylene compressible chamber of the PMUT, the operating frequency shift can be tuned 10% and sound pressure can increase by 100%, compared with the open-chamber PMUT. Activating the backplate of the PMUT, the sound pressure can be further increased.