Ultrasonic sensor

An ultrasonic sensor attached to a certain object for sensing an ultrasonic wave that is reflected by a detected body, the sensor comprising:

• an acoustic matching member that has a receiving surface that is adapted on a side of the certain object to face toward the detected body, the receiving surface receiving the ultrasonic wave reflected by the detected body, the acoustic matching member transmitting the ultrasonic wave received by the receiving surface and being adapted such that a standing wave is generated inside of the acoustic matching member due to the ultrasonic wave received by the receiving surface;
• an ultrasonic detecting element that is attached to an opposing surface of the acoustic matching member opposite the receiving surface, the ultrasonic detecting element detecting the ultrasonic wave that is transmitted by the acoustic matching member, the acoustic matching member being made of a material having an acoustic impedance larger that that of air and smaller than that of the ultrasonic detecting element;
• and
• a reflection limiting member that is disposed to a side portion of the acoustic matching member between the receiving surface and the opposing surface, the reflection limiting member limiting the ultrasonic wave, which is transmitted inside the acoustic matching member, from being reflected by the side portion.