Patent ID: 7522475

Claim:
An ultrasonic sensor comprising: a first piezoelectric vibrator for transmitting an ultrasonic wave as a transmission wave toward an outside of a mobile body, wherein the transmission wave is reflected by an object of the outside of the mobile body so that a reflection wave is generated; a plurality of second piezoelectric vibrators for receiving the reflection wave and for outputting a reception signal corresponding to strength of the reflection wave; a casing for accommodating the first piezoelectric vibrator and the plurality of second piezoelectric vibrators, wherein the casing includes a bottom, wherein each of the first piezoelectric vibrator and the plurality of second piezoelectric vibrators contacts and is fixed to an inner surface of the bottom of the casing, and wherein an outer surface of the bottom of the casing opposite to the inner surface provides a vibrating surface; and a plurality of waveguide tubes for guiding the ultrasonic wave between the outside of the mobile body and the vibrating surface of the casing, wherein each waveguide tube has a first opening, which is coupled with a through hole of an outer member of the mobile body so that the waveguide tube communicates with the outside of the mobile body, each waveguide tube corresponds to one of the first piezoelectric vibrator and the plurality of second piezoelectric vibrators, an area of the first opening of each waveguide tube is smaller than an area of the vibrating surface of the casing, a distance between two adjacent first openings of waveguide tubes is smaller than a distance between two adjacent vibrating surfaces, and each waveguide tube has a length, which is set in such a manner that a phase difference of the reflection waves at the first openings between one waveguide tube and another waveguide tube is equal to a phase difference of the reflection waves at the vibrating surfaces between the one waveguide tube and the another waveguide tube.