Calibration and Performance Evaluation of Miniature Ultrasonic Hydrophones Using Time Delay Spectrometry

P.A. Lewin
1981 1981 Ultrasonics Symposium  
The authors recently presented a theory for a new inverse scattering technique for cross-sectional and three-dimensional imaging'. This technique was based upon the Born approximation to the wave equation and its primary highlight was that it eliminated the need for planewave insonification from the diffraction theory based approaches developed so far. In the present paper we will describe further theoretical analyses that approximately take into account the medium attenuation. A parallel
more » ... based on Rytov approximation will also be presented. The authors will also show some new computer simulation results that are a confirmation of the theories. Finally, we will show experimental results on tissue equivalent phantoms obtained with the data collected in the transmission mode. D. Nahamoo and A. C. Kak, "A new technique for reconstruction fromscattering fields,"presented at Sixth Int. We have carried out careful computer and analytical treatment of errors in digital imaging systems. The effect of digitization on sidelobe levels can be predicted accurately, as well as the amplitude level of grating lobes and the effects of apodization and use of short pulses. Improvements in a three sample per wavelength digital system obtained by interpolation will be shown and demonstrations of images obtained with surface wave array transducers, a contacting longitudinal wave transducer, and a contacting shear wave transducer placed on metal blocks with internal defects present, will be given. In all cases the center frequency of operation is at 3. The scanning laser acoustic camera (SLAC) is an ultrasonic imaging system which operates over the frequency range 0.8-25.0 MHz. Acoustic energy is detected by measuring the displacement of a solid plastic block surface with a stabilized Michelson interferometer. Unlike interferometer schemes previously reported, this detector is made stable against vibration and beam path instability by means of an ultrasonic pilot signal and AGC loop. A CRT is employed to display the spatial distribution of ultrasound as a two-dimensional image. The raster of information is produced by scanning the laser. One of the primary SLAC applications is ultrasonic transducer characterization in which pulsed, gated rf or CW operation may be employed. Applications to the testing of encapsulated electronic components and flaw detection in metals are also described. The ordinary (second-order) elastic constants determine the velocity of ultrasonic waves in solids, and hence have been evaluated from velocity measurements in many solids under a wide range of conditions. They are ubiquitous, appearing in virtually any theory or experiment which quantitatively describes the (linear) elastic behavior of solids. The third-order elastic (TOE) constants are equally fundamental, equally ubiquitous recently, and are being measured for similar reasons: to form a basis for describing the n o n h e a r (elastic) behavior of solids. The TOE constants are discussed, with emphasis on cubic symmetry, with the intention of relating them to other nonlinear observables (anharmonicity, nonlinear stress-strain relationships, thermal expansion, etc.). Recent results for cubic crystals, both at room temperature and at cryogenic temperatures, are discussed as examples of current trends in solid state physics. A new nonlinear FM function has been applied to the design of pulse compression EMAT's used in surface crack detection and SAW velocity variation measurements. The experimentally obtained compressed pulse S/N ratio is 10 dB and the time resolution is 500 ns. ' This work supported by the Air Force Office of Scientific Research. P-6 Low-Temperature Growth of the Piezoelectric AIN Film and its Optical and Acoustical Properties
doi:10.1109/ultsym.1981.197704 fatcat:hqap7ioh55dn5ilt2y4nojqnbi