Field patterns of pulsed, focused, ultrasonic radiators in attenuating and nonattenuating media

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Abstract
A theoretical method which can be used to calculate the pressure field patterns of pulsed, focused, ultrasonic radiators in attenuating and nonattenuating media is discussed. The underlying principle involved is the superposition of continuous wave beams to form pressure pulses. The method is adapted to the circumstances associated with using a hydrophone to measure field patterns. Experimentally obtained hydrophone signals are then compared to theoretical predictions. The field patterns of 4 transducer-pulser combinations are investigated. A medium with tissue-mimicking acoustical properties is used to attenuate the ultrasonic beam in these studies. The theory compares favorably with experiment whether an attenuating medium is present or not. However, the theory fails at positions very close to the transducer face (.apprx. 1 cm) and when significantly nonlinear effects occur during the transmission of the pulse through the medium. This work may have significant applications in research devoted to designing ultrasonic transducers for particular studies, determining dose profiles of medical ultrasonic machines [for human organ imaging], and analyzing the ultrasonic signals backscattered from within patients.

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