Design, Construction, and Evaluation of Liquid and Solid Ultrasonic Lenses
NAVAL COASTAL SYSTEMS LAB PANAMA CITY FL
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The sound velocity, thermal coefficient of sound velocity, and attenuation coefficients of 20 common plastics were measured and used as a basis for the design of several lenses. Materials selected were polyethylene, nylon, polystyrene, polyphenylene oxide, and a low sound velocity silicone rubber compound. Using common geometrical optical techniques, lenses were designed to minimize off-axis aberrations for focal-length-to-aperture ratios ranging from one to three and aperture to wavelength ratios up to 150. Using methods analogous to chromatic aberration correction in optics, lenses were designed for constant focal length over a temperature range of 0 to 30 C. Two-and four-element lens systems with apertures up to 30 cm were fabricated. Measurements were made in the frequency range 600 kHz to 1.2 MHz. The theoretical model used to evaluate lens performance was based on the numerical evaluation of the Fresnel-Kirchoff diffraction integral.
- Acoustic Detection and Detectors