A study was made on echogram distortion based on the refraction of an acoustic ray behind a cylinder that was large compared with ultrasonic beam width. It was observed from the results of the experiment and was simulated by computer that the image of a reflector behind a cylinder is reduced and shifted to the transducer when the sound velocity of the cylinder is faster than that of water. When a cylinder with a sound velocity lower than its surroundings was used, the distorted image around the focal point appeared enlarged and farther from the transducer. The image reduction in a direction lateral to the ultrasonic beam was estimated by a lateral reduction rate.
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