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A Detector for Stationary Gas Bubbles: Feasibility Studies

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Technical rept. Aug 1989-Jan 1991

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Work progresses on developing operating procedures for a system intended to detect stationary gas bubbles of diameters 0.9 to 6 micron using ultrasonic interrogation. The original system has been redesigned and is now configured for menu-driven remote control from a PC. Signal averaging and subtraction of measured background noise are available for the signalnoise SN ratio. The output signal is now a spectrum consisting of the amplitude of the 2nd harmonic distortion component of the output signal versus the frequency of the input signal. For well-characterized physical systems, it should be possible to deduce bubble sizes from this spectrum. Calibration standards, consisting of stable bubbles in the 0.9 to 6 micron size range, have proven difficult to prepare. The reason for this difficulty is that size changes in such small spherical bubbles usually are fast relative to the measurement time, as has been studied using a mathematical simulation. Nonetheless, work will now proceed without calibration, using less well-defined bubble populations to test the systems ability to detect bubbles categorically i.e., bubbles or no bubbles. To predict the SN ratio for single bubbles in water, we have been used mathematical simulations of vibrating bubbles in conjunction with measurements of the system noise. Solutions have been obtained for the equation of motion outside of a bubble vibrating in a liquid or in an elastic solid using both an approximate analytic technique namely, the Method of Perturbation and a more accurate numerical technique a Galerkin method. Bubble detection, ultrasound, Doppler, bubble oscillation, noninvasive testing, decompression sickness.

Subject Categories:

  • Stress Physiology
  • Acoustics

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