| CPC G01H 11/08 (2013.01) [G01S 7/521 (2013.01); H04R 17/00 (2013.01)] | 13 Claims |

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1. An ultrasonic sensor comprising:
a case including a cylindrical side wall and a bottom plate in one end portion of the side wall; and
a piezoelectric element on the bottom plate inside the case; wherein
the side wall includes a pair of thick wall portions facing each other and a pair of thin wall portions thinner than the thick wall portions facing each other;
an inner peripheral edge of another end portion of the side wall includes a chamfered portion; and
the chamfered portion of one of the pair of thin wall portions includes a recessed portion.
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