Dense and sparse 2-D array radiation patterns in lossy media

摘要

Two-dimensional (2-D) transducer arrays are potentially able tongenerate real-time volumetric images of internal organs of the humannbody, and much work has been done on the subject in recent years. A 2-Dnarray with high resolution and low grating lobe level requires anprohibitively large number of elements for existing technology. Ansuccessful solution to reduce the number of elements, withoutnsacrificing the above mentioned characteristics, is to select a limitednnumber of elements in a random way or combining transmitting andnreceiving apertures with element spacing greater than one-half of anwavelength. In this work, the effect of the human body attenuation onnthe performances of these so-called sparse arrays is investigated. Wenanalytically demonstrate that, for continuous wave excitation and undernparaxial approximation, the medium losses can be modeled as a Gaussiannweighting function, acting off-axis in the observation plane. Thenvariance of this weighting function decreases with the covered distance.nRadiation patterns computed with both this simple model and with a morenexact expression, are presented for sparse and dense 2-D arrays underncontinuous and pulsed wave operation. Comparisons between the resultsnobtained with and without attenuation also are shown