Air-coupled ultrasound transduction improvement using vertical piezoelements’ array

Novel transducer construction is proposed: array of PVDF film strips placed parallel to each other with air gaps between. Films are oriented in such way that strip extension (31 mode) is aligned with emission direction. Transduction is improved by providing better acoustic impedance match to air and increased displacement of emitting surface. Two distinct operation modes are presented: i) emission from the gaps ii) emission from membrane attached to the edges at array top with lower edges backed. In gap emission mode, the transduction efficiency is increased because of two mechanisms. The pressure produced by the expansion of the individual films is concentrated into narrow gap. Also, emission of edges due to height extension. Height extension (31 mode) is much higher than thickness expansion (33 mode) if film height is larger than film thickness. Low, 500 Rayl, equivalent acoustic impedance of gap emission is achieved at film thickness 10 μm and gap with 50 μm. In membrane emission mode, only extension (31 mode) is used, pressure emitted is increased due to large membrane displacement and better match to air. Equivalent acoustic impedance is 500 kRayl at PVDF film thickness 40 μm and 200 μm air gap. Displacement is maximized if PVDF film with large transverse piezoelectric coefficient d 31 is used. Experimental measurements are presented. Transmission sensitivity peak for gap emission was 155 mPa/V, for membrane emission mode it was 320 mPa/V. Impressive, more than 270 % fractional bandwidth was confirmed experimentally. • Novel air-coupled transducer construction: array of parallel PVDF film strips with air gaps between. • Two operation modes: i) gap transmission ii) membrane transmission. • Better match to air than single PVDF film. • Higher transduction efficiency than single PVDF film. • Wide bandwidth.