Diffractive limited acoustic field of an apodized ultrasound transducer

The diffraction in the acoustic held of an ultrasound transducer can be modeled as the result of the interference of edge and plane waves generated from the periphery and the center of the piezoelectric element, respectively. Our objective in developing ultrasound transducers with apodized piezoelectric ceramic discs was to generate acoustical fields with reduced edge waves interference. Transducers were built with apodized ceramic discs (polarized more intensively in the central region than in the edges) and their mapped acoustic fields showed a distinct pattern when compared to those of conventional transducers. A polynomial equation describing the nonlinear poling held intensity, was used with the Rayleigh equation to simulate the nonuniform vibration amplitude distribution generated by the apodized transducers. Simulated acoustic fields were compared to experimental held mappings. The results of simulations and experimental tests showed reduction in the lateral spreading of acoustic fields produced by apodized transducers, compared to those produced by conventional transducers. The reduced presence of the lateral lobes in the apodized acoustic held is due to the minimized vibration of the disc periphery. The numerical and experimental results were in good agreement and showed that it was possible to reduce acoustic held diffraction through nonlinear polarization of the piezoelectric element.