A theoretical approach for a low diffraction ultrasonic tranducer

Abstract

Abstract The finite aperture of a piezoelectric ultrasonic focusing monotransducer leads to some alteration in the pulse shape depending upon the location of the observation point in the field. This is a diffraction problem which is of great importance in some applications such as the attenuation measurement in biological soft tissues. The aim of this study is to develop a special kind of ultrasonic transducer such that the pulse shape is spatially invariant in the main part of the field. It is shown that the pulse shape is spatially independent in the main lobe of the field if, for each frequency, the emitting aperture of the piezoelectric element varies as the inverse of this frequency. Such an aperture can be achieved with the help of a special focusing annular array such as described in this paper. A simulation program applied on the whole field confirms its low diffraction property and shows that its other acoustical characteristics suffer little deterioration.