Radiation pattern distortion caused by the interelement coupling in linear array transducers

It is well known that the performances of the acoustic imaging arrays are degraded by the interelement coupling. In this work the effect on the radiation pattern of the array of the cross-coupling due to the filling material is investigated. A hybrid experimental-numerical technique is used. We built an array with three different filling materials, without matching layers, and using a classical backing material. On every piezoelectric element we built in a probe of small dimensions, in order to capture the waveform on its emitting surfaces. The cross-coupling waveforms were recorded for the three groups of elements when: only the central element of the group was driven; all the elements were driven with the same pulse applied at the same time; the array was driven by an echograph. Fourier transforming the temporal signals, the cross-coupling transfer function of each element was computed and the radiation pattern simulated by means of a numerical model based on the Rayleigh-Sommerfeld integral. A comparison among the radiation patterns for all the groups of elements, for the above mentioned excitations is presented.