Effect of Focal Zone on a Curved Array Transducer

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Abstract
This study investigates the effect of electronic focusing of a linear array transducer on received ultrasound signal. Two tissue-mimicking phantoms of known attenuation were imaged with a focal distance that was varied from 2 to 12 cm. Received signal was processed by Fourier analysis to compute average frequency and power as functions of depth within the phantom. Average received frequency increases dramatically over the first centimeter from the transducer and then decreases linearly to 8 to 11 cm with a slope proportional to the phantom's attenuation. Average frequency from greater depths decreases more rapidly and is dependent on the focal zone. Received power peaks at approximately the focal depth and decays exponentially beyond that level; the decay constant is proportional to the phantom's attenuation but independent of focusing. The frequency and power of received ultrasound signal are altered by electronic focusing in ways that may significantly influence both tissue characterization and clinical imaging applications.

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