Equivalent phased array methods to predict acoustic fields of planar and focused ultrasound transducers

Acoustic fields generated by single‐source ultrasonic transducers were predicted accurately by combining phased array theory and the Rayleigh–Sommerfeld diffraction integral. Two methods were developed and experimentally tested. The first is the equivalent phased array method (EPAM), which treats any small transducer as a phased array composed of many square elements [Moros et al., J. Acoust. Soc. Am. 101, 1734–1741 (1997)]. The second method, called CREPAM for the concentric‐ring equivalent phased array method, was developed for larger axisymmetric transducers. The goal of both methods is to determine the excitation source of the equivalent phased array employing an inverse technique and data measured at a plane in the near field and perpendicular to the transducer’s axis. The determined excitation source and equivalent phase array can then be used to compute the acoustic field from the measurement plane to the far field. It was demonstrated that both methods accurately predict the location of major grating lobes and general patterns of the near and far pressure fields for several planar and focused transducers. These methods should be useful in diagnostic and therapeutic ultrasound applications where transducer‐specific field characteristics are important. [Supported by NCI Grant R29‐CA63121.]