Production of a Diffractionless Ultrasonic Beam
The propagation of ultrasonic beams is a phenomenon of widespread interest to a variety of technologies including sonar, medical ultrasound, and nondestructive evaluation. One goal in most applications is the production of a narrow, highly collimated beam of sound. Rigid piston radiators have often been employed and have been thoroughly analyzed. This type of source has the generally undesirable attributes of a complicated near field interference structure as well as far field side lobes. Sources which produce a Gaussian amplitude distribution have been studied since, for this case, the previous disadvantages are eliminated. Unfortunately, Gaussian radiators are more difficult to manufacture [1,2]. Various types of focusing probes have also been analyzed for concentrating the sound in a narrow band over a short depth of field. Conically focussed, or axicon, probes have been examined for the purpose of extending the focal region for resolution over a greater depth of field. One disadvantage common to all of the above sources, and indeed to any physically realizable source, is the phenomenon of beam spread due to diffraction.
KeywordsQuartz Attenuation Polystyrene Sonar
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