| 摘要 |
PROBLEM TO BE SOLVED: To provide the ultrasonic images of high image quality, to facilitate insertion by a narrow tip diameter and to reduce pains given to a patient. SOLUTION: A lens surface 35 for ultrasonic vibration convergence for converging ultrasonic vibration provided on a center part and a chamfer 36 provided on an otter periphery are formed at an acoustic lens 33 and the lens surface 35 for the ultrasonic vibration convergence is composed of a part of a spherical surface and forms a concave recessed toward a piezoelectric element 31. The outer diameter of the piezoelectric element 31 is denoted byϕp, the diameter of a circle formed by the crossing line of the chamfer 36 and the lens surface 35 for the ultrasonic vibration convergence is denoted byϕL and the outer diameter of a housing 32 is denoted byϕM further. The chamfer 36 is formed so as to beϕp<ϕL<ϕM.
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