Differential Phase Contrast Imaging in the Electronically Focused Acoustic System
Phase contrast imaging which has been used in optical imaging for years, has recently been introduced into acoustic imaging, in systems using mechanical scanning. In this paper, a phase contrast imaging system is introduced which employs electronic scanning and focusing. Differential phase contrast imaging is used, which compares the phases at adjacent points on the object which are separated by a constant distance along the scan line. The advantage of differential phase contrast imaging, as compared to fixed reference phase contrast imaging, is that the reference and signal beams travel almost identical paths, suppressing,the effects of vibration, temperature, and other external influences. The present system consists of an acoustic receiver using a 100 element PZT array, which has two identical main beams separated slightly in space, focused at the same distance and scanned simultaneously. The relative phases between the two beams can be varied, and for “dark field” imaging they are set 180° out of phase. The output of the receiver then reproduces either the phase distribution across the object, or its spatial derivative. Two dimensional differential phase contrast images are obtained by adding a mechanical frame scan. The peripheral sensitivity of this system is presently 12° phase difference, and the ultimate objective is a few degrees.
KeywordsDelay Line Line Source Acoustic Velocity Acoustic Image Peripheral Sensitivity
Unable to display preview. Download preview PDF.
- 1.M. Francon, “Isotropic and Anisotropic Media. Application of Anisotropie Materials to Interferometry,” in Advanced Optical Techniques, Van Heel, Editor, ( North-Holland Publishing Co., Amsterdam, 1967 ), Chapter 2.Google Scholar
- 2.J. Fraser, J. Havlice, G. Kino, W. Leung, H. Shaw, K. Toda, T. Waugh, D. Winslow, and L. Zitelli, “An Electronically Focused Two-Dimensional Acoustic Imaging System,” in Acous- tical Holography, Vol. 6, edited by Newell Booth, Plenum Press, New York, 1975, P. 275.Google Scholar
- 3.J. F. Havlice, G. S. Kino, and C. F. Quate, “A New Acoustic imaging Device,” 1973 IEEE Ultrasonics Symposium, Monterey, California, December 1973.Google Scholar