Acoustic imaging

Nielsen, S.A. and Bj0rn0, L. (1997). Bistatic circular array imaging with gated ultrasonic signals. Acoustical Imaging, Vol. 23 (In press). 

Koshovy V. V. Methods of restoring of the acoustical images and their applications to nondestructive testing in civil engineering // Proc. Int. Symp. Non-Destructive Testing in Civil Engineering - Berlin, Sept. 26-28, 1995. - V.2. -P. 1153-1156. 

BE>3833 Two[Pg.935]

The development of active ceramic-polymer composites was undertaken for underwater hydrophones having hydrostatic piezoelectric coefficients larger than those of the commonly used lead zirconate titanate (PZT) ceramics (60—70). It has been demonstrated that certain composite hydrophone materials are two to three orders of magnitude more sensitive than PZT ceramics while satisfying such other requirements as pressure dependency of sensitivity. The idea of composite ferroelectrics has been extended to other appHcations such as ultrasonic transducers for acoustic imaging, thermistors having both negative and positive temperature coefficients of resistance, and active sound absorbers. 

In view of the formidable technical difficulties, the results that have been achieved are all the more impressive. Figure 3.3(a) (see colour plate section) is an acoustic image of a bipolar transistor on a silicon integrated circuit taken at 4.2 GHz. There is a very severe acoustic impedance mismatch between helium and a material such as silicon. Even for normally incident waves 99 per cent of the power is reflected straight off the surface, and for waves incident at an angle greater than 3° all the power is reflected. For a lens of N.A. = 0.5,... 

Figure 3.7 demonstrates the resolution that can be achieved using water-coupled acoustic microscopy. It represents a remarkable achievement in the development of the instrument. Never before had it been possible to obtain an acoustic image through water with such high resolution. Nevertheless,... 

As an example of the application of this result, the minimum aberration for acoustic imaging with a wavelength of 25 fan at a depth of 0.5 mm below the surface of a material of refractive index n = 0.25 would be given by h/sb = 0.7, so that the optimum lens angle would be 0opt = 8.3°. This result depends rather weakly on Sb, so that halving the depth would increase the optimum angle by less than 1 °. 

In general, the acoustic properties of biological tissue show much greater variation than their optical properties. This means that acoustic images can be obtained without the need for any staining. By itself this is not a decisive advantage, because sophisticated interference contrast and other techniques... 

Fig. 9.3. Fibroblast on glass (a) conventional acoustic image, 550 MHz (b) time-resolved S(t,y) along the vertical line in (a). In the S(t, y) picture, the horizontal axis is time t the vertical axis is y just as in (a), and the value of S(t, y) is indicated by the intensity, with mid-grey as zero and dark and light as negative and positive values of S (courtesy of Jun Wang).

Fig. 9.12. Acoustic images and V(z) curves for a specimen of human tooth enamel prepared with the left half slightly demineralized and the right half sound. V(z) curves ---- sound enamel - - - - slightly demineralized. Micrographs (a) z = 0 ...

Fig. 9.17. Horse bone section (a) acoustic image, z = 0 (b) V(z) 650 MHz (courtesy...

The specimen shown in Fig. 10.12 had been kept at 450°C in air for 500 hours after manufacture had been completed. In the first acoustic image (Fig. 10.12(a)), there is a layer thick surrounding the outer /3-SiC this... 

Bennett, S. D. (1982). Approximate materials characterization by coherent acoustic microscopy. IEEE Trans. SU-29,316-20. [Reprinted in Lee, H. and Wade, G. (1986). Modern acoustical imaging, pp. 389-93 IEEE, New York.] [110]... 

Cargill, G. S. (1988). Electron beam-acoustic imaging. In Physical acoustics XVIII (ed. W. P. Mason and R. N. Thurston) pp. 125-65. Academic Press, San Diego. [17]... 

---