An Improved System for Visualizing and Measuring Ultrasonic Wavefronts
At the previous Symposium we described an instrument to visualize and measure ultrasonic wavefronts [l]. In that system, a very thin, flexible, optically reflective membrane, called a pellicle, is immersed in a tank of water. The pellicle is so thin and so-wellcoupled to the water that an ultrasonic wave moves the pellicle at every point with almost exactly (>99.95%) the same motion as the water. This motion is detected by a scanning Michelson interferometer, and the changes in interference so caused are converted to an electronic signal by a photodiode. As indicated schematically in Fig. I, this signal is used to modulate the intensity of a spot on a CRT that is raster scanned synchronously with the laser beam rasterscanning the pellicle; in this way a map of the displacement amplitude on the pellicle is formed on the CRT. The electronic signal also is displayed for exact measurement of the displacement of a particular point or of a scan line on the pellicle. As shown in Fig. 1, acoustical lenses may be used to form an acoustic image on the pellicle that is made visible on the CRT.
KeywordsMichelson Interferometer Optical Path Difference Reference Mirror Pulse Arrival Time Acoustical Lens
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- 1.R. S. Mezrich, K. F. Etzold, D. H. R. Vilkomerson, “System for Visualizing and Measuring Ultrasonic Wavefronts;” Acoustical Holography, Vol. 6, N. Booth, Ed., Plenum Press, N. Y. (1975).Google Scholar
- 3.A peak-detector can consist of a diode in series with a capacitor; the highest positive voltage charges up the capacitor to that value and it remains at the peak value until reset.Google Scholar
- 5.M. Born and E Wolf, “Principles of Optics,” 3rd Ed. Pergamon Press, IvT, Y. (1965), page 691.Google Scholar
- 6.C. Calderon, D. Vilkomerson, R. Mezrich, K. F. Etzold, B. Kingsley, H. Haskin, “Differences in the Attenuation of Ultrasound by Normal, Benign, and Malignant Breast Tissue,” Journal Clinical Ultrasound 4,’ 249 (1976).Google Scholar
- 7.See reference 1, pages 168–170.Google Scholar
- 8.R, Mezrich and D. Vilkomerson, “Ultrasonic Phase-Contrast Imaging,” Appl. Phys. Lett. 27, 177 (1975).Google Scholar
- 9.To be published. See j. W. Goodman, “Introduction to Fourier Optics,” I. Wiley Sons, N. Y. (1968), Chapter 5, for a discussion of the Fourier transforming properties of lenses.Google Scholar