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

Two-dimensional (2-D) transducer arrays are potentially able to generate re al-time volumetric images of internal organs of the human body, and much wo rk has been done on the subject in recent years. A 2-D array with high reso lution and low grating lobe level requires a prohibitively large number of elements for existing technology, A successful solution to reduce the numbe r of elements, without sacrificing the above mentioned characteristics, is to select a limited number of elements in a random way or combining transmi tting and receiving apertures with element spacing greater than one-half of a wavelength. In this work, the effect of the human body attenuation on the performances of these so-called sparse arrays is investigated. We analytically demonstra te that, for continuous wave excitation and under paraxial approximation, t he medium losses can be modeled as a Gaussian weighting function, acting of f-axis in the observation plane, The variance of this weighting function de creases with the covered distance. Radiation patterns computed with both th is simple model and with a more exact expression, are presented for sparse and dense 2-D arrays under continuous and pulsed wave operation. Comparison s between the results obtained with and without attenuation also are shown.