Fresnel Zone Plate and Fresnel Phase Plate Patterns for Acoustic Transducers

Abstract

An ultrasonic transducer with an electrode pattern in the shape of a Fresnel zone plate (FZP) is useful in acoustic imaging. However a major problem in focusing with an FZP is that the final image will have a large zero-order component and this will restrict the dynamic range of the system. One way to solve this problem is to use a Fresnel phase plate pattern (FPP). We employ a linear spatial system model to determine the transducer aberrations caused by wave generation and propagation inside the tranducer. The focal-plane intensity distribution is calculated for both the FZP and FPP, assuming similar parameters. The low-pass filtering effect of aberrations in the transducers using the FZP and the FPP are studied in the spatial-frequency domain and are compared. The analysis predicts that, due to these aberrations, the FPP can give better resolution than the FZP by a factor of almost two. Experimental results that support the linear model are presented.