| Popis: |
Imaging capability of an active acoustic imaging system in an incoherent homogeneous medium is characterized by a Contrast Figure of Merit (CFM) defined as the incoherent energy entering the mainlobe of the beampattern over the incoherent energy entering the sidelobes over all space. If this contrast is negative, the intensity at beam output is governed by the sidelobes and is not related to the steering direction, meaning that imaging capability is lost. This contrast is also related to the quality of the shadow formed behind an object of angular size larger than the mainlobe. The effect of spatial sampling on the CFM is analyzed in the case of 2D probes assumed to be oversampled in one dimension and undersampled in the other.First, the expression for the total incoherent intensity at beam output is derived for directive transmission and reception on a continuous rectangular focused array. Correction term due to undersampling is evaluated.In the following section, the expression for the incoherent intensity entering the mailobe is derived, for a rectangular array, in the same conditions. Corrections due to sampling and defocusing are given.The last section shows the behavior of the CFM on a specific example. |
