Beam characteristics of a transducer play a major role in defining the resolution of any ultrasound imaging system. Direct experimental estimation of the beam profile is often desirable, however, one has to carefully correct for effects that are attributed to the measurement process itself. We report here our experience of using a measurement technique developed for circular disk focused transducers. When the anticipated beam size is much smaller than 0.5 mm the use of a hydrophone to scan the monochromatic beam is not adequate. A more suitable approach is to make a measurement in pulse-echo mode using a thin (125 micron or less) wire target. In this case, a short pulse excitation is used from which the monochromatic information is derived via Fourier transform. However, two measurement artifacts need to be corrected. Multiple reflections due to the finite wire size show up as periodic spikes in the spectrum. These were corrected for using Cepstrum domain filtering method. Second, the wire target measurement essentially represents a one-dimensional projection of the two-dimensional beam pattern in a plane perpendicular to the beam axis. Smoothing effects were investigated by comparing experimental results and theoretical predictions based on Lommel diffraction formulation. The apodization of the transducer to remove the side-lobes would have also caused an increase in width of the main lobe. Line Spread Function and Modulation Transfer Function, with respect to frequency and distance from the target to the transducer, were characterized and reported.
Library of Congress Subject Headings
Ultrasonic transducers; Ultrasonic imaging; Lommel functions
Imaging Science (MS)
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Blair, Laura, "Development of a technique to measure the MTF of a transducer used in an ultrasonic fingerprint scanner" (2003). Thesis. Rochester Institute of Technology. Accessed from
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