A Method for Improving Acoustic Switching Ratio in Opto-Acoustic Transducers

  • B. Noorbehesht
  • V. Arat
Part of the Acoustical Imaging book series (ACIM, volume 12)

Abstract

Previous theoretical and experimental work on Opto-Acoustic Transducers (OATs) has shown their switching ratios to be lower than that necessary for most imaging applications. We will show that this problem can be overcome by applying intensity-modulated light to the OAT instead of constant intensity light, as suggested previously.

The conductivity of the photoconductive layer of the OAT follows the same time variations as the intensity of the light applied to it. Under these conditions the OAT may be considered as a linear system with a time-varying component. It will be shown, using an equivalent circuit, that sinusoidally intensity-modulated light applied to the OAT gives rise to sideband signals in the illuminated region which do not exist in the dark region. Therefore, in principle, infinite switching ratios may be realized by allowing one of these sidebands to occur at the resonant frequency of the OAT.

There is an additional advantage to using intensity-modulated light. When a Fresnel zone pattern is projected onto the OAT the acoustic signals from the illuminated and dark regions, being at different frequencies, focus at different depths thus improving the signal to noise ratio at the desired focal point.

Keywords

Sulphide 

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References

  1. 1.
    K. Wang and G. Wade, “A Scanning Focused Beam System for Real-Time Diagnostic Imaging”, Acoustical Holography, Vol. 6, N. Booth Ed., Plenum Press, New York, pp. 213–228, 1975.Google Scholar
  2. 2.
    S. Elliott, V. Domarkas and G. Wade, “Frequency Characteristics of Opto-Acoustic Transducers”, IEEE Trans. Sonics and Ultrasonics, SU-25, pp. 346–353, Nov. 1978.Google Scholar
  3. 3.
    B. Noorbehesht and G. Wade, “An Improved Equivalent Circuit for Opto-Acoustic Transducers”, 1979 Ultrasonics Symposium Proceedings, pp. 195–199.Google Scholar
  4. 4.
    B Noorbehesht, “A Modified Equivalent Circuit for Opto- Acoustic Transducers”, IEEE Trans. on Sonics and Ultrasonics, 1982. (In Press)Google Scholar
  5. 5.
    C. W. Turner, and S. O. Ishrak, “Comparison of Different Piezoelectric Transducer Materials for Optically Scanned Acoustic Imaging”, Acoustical Imaging, Vol. 10, P. Alais and A. F. Metherell Eds., Plenum Press, New York, pp. 761778, 1980.Google Scholar
  6. 6.
    B. Noorbehesht, and V. Arat, “Opto-Acoustic Transducers with Intensity Modulated Optical Input,” IEEE Trans. on Sonics and Ultrasonics, 1982. (Under Review)Google Scholar
  7. 7.
    V. Arat, M. S. Thesis, University of Houston, Houston, Texas, 1982.Google Scholar

Copyright information

© Plenum Press, New York 1982

Authors and Affiliations

  • B. Noorbehesht
    • 1
  • V. Arat
    • 1
  1. 1.Electrical Engineering DepartmentUniversity of HoustonHoustonUSA

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