Reducing aberration by inverse filtering in Fresnel zone plate transducers

Abstract

Transducers employing a spatial electrode pattern in the form of a Fresnel zone plate (FZP) are useful in acoustic imaging systems for focusing an ultrasonic beam. A technique has been developed to predict the spatial acoustic output of such a transducer from a knowledge of the spatial electrode pattern. It has been shown that, due to mechanical aberration, sharp edges in the electrode pattern are not reproduced in the output pattern. The mechanism producing the aberration can be modeled as a low-pass spatial filter. A desired acoustic spatial pattern may be generated by a synthesized electrode pattern obtained through inverse filtering. The approach is to assume that the desired acoustic pattern is the output of a linear spatial system and then to synthesize the electrode pattern that would produce it by multiplying it with the inverse of the aberrating low-pass filter. The synthesized electrode pattern will then generate an acoustic pattern which replicates the desired acoustic pattern very closely.