Phase-matched air ultrasonic transducers using corrugated PVDF filmwith half wavelength depth

摘要

A new type of large area PVDF film air transducer is proposed. Thentransducer features a high power output and a sharp beam angle.nConventionally known curved length mode resonators with two clamps atnboth ends have a resonance frequency determined by the curvature. In thenpresent work, PVDF was formed into alternating concave and convexnmultiple curved sections, eliminating clamps, i.e., a periodicncorrugation structure using a single PVDF film. Each convex and concavensection has a common resonance frequency. A common excitation voltageninduces vibration for each section, and the vibration direction isnnormal to the film surface. The vibration phase of convex section isnshifted 180 degrees from the concave section. These waves addnconstructively to form a strong acoustic beam when corrugation height isnapproximately one-half of the wavelength. The corrugation heightncontrols propagation path difference, canceling excitation phasendifference. The design principle based on a uniform vibration mode isnpresented. Experimental investigations using 8.8×2.5-,n10×5-, and 20×20-cm2 transducers are presented.nSide lobes unique to this corrugation structure have been observed. Antheoretical analysis of the side lobes is also presented. According tonthe theory, choosing the corrugation height appropriately will reducenside lobes to -15 dB with regard to the main lobe, and the observed sidenlobe height agreed with the theoretical result