Patent ID: 8098000

Claim:
An ultrasonic sensor for detecting an object, comprising: a piezoelectric element having a piezoelectric body and first and second electrodes for sandwiching the piezoelectric body, wherein the piezoelectric element detects an ultrasonic wave reflected by the object, the ultrasonic wave being initially transmitted from a transmitting element; an acoustic matching element having a reception surface, which faces the first electrode and receives the ultrasonic wave reflected by the object, wherein the acoustic matching element transmits the ultrasonic wave from the reception surface to the piezoelectric body via the first electrode; and a circuit electrically coupled with the piezoelectric element via a conductive element and processing a voltage signal output from the piezoelectric element, wherein the piezoelectric element is embedded in the acoustic matching element so that the acoustic matching element covers at least the first electrode and a part of the conductive element between the circuit and the piezoelectric element, a sidewall of the piezoelectric element is adjacent to the first electrode, the acoustic matching element covers a whole surface of the piezoelectric element, the acoustic matching element has symmetry with respect to the piezoelectric element, the acoustic matching element has a bottom surface, which faces the second electrode, a first distance between the reception surface and the first electrode is substantially equal to one-fourth of a wavelength of the ultrasonic wave transmitting through the acoustic matching element, and a second distance between the bottom surface and the second electrode is substantially equal to one-fourth of a wavelength of the ultrasonic wave transmitting through the acoustic matching element.