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This work reports on the investigation of the element beam pattern of a 2D CMUT spiral array by finite element analysis, aiming at assessing the effect of the transducer integration with the ASIC on the fluid-coupled transmission performance. The array element acoustic directivity is computed for the clamped substrate condition and compared with that obtained by coupling the transducer with a Benzocyclobutene (BCB) layer, used as an underfill between the CMUT and the ASIC. Different packaging solutions are considered and their effect on the element directivity is compared. The CMUT spiral array element is experimentally characterized in water-coupled transmission operation using a hydrophone to validate the finite element simulation.

This paper explains how the measured directivity of antenna elements can be taken into account during shaped pattern synthesis. The method that is presented is based on the Orchard Elliott synthesis procedure. Important features of this classical way of synthesizing shaped antenna patterns are its high degree of control over the pattern's shape, and the flexible way in which the array excitations can be chosen. However, because it operates on the array factor, the directivity (i.e., element factor) of the antenna elements is neglected. Once synthesis is complete, and the element factor is reintroduced to evaluate the actual beam pattern, one often finds that the overall shape is not as it was specified. In particular when the shaped region of the pattern is placed further away from broadside, the differences become substantial. In those cases it may be necessary to take the element factor into account during synthesis.