Ultrasonic sensor

An ultrasonic sensor configured to be mounted to a vehicle by being attached to an outer plate of the vehicle, the ultrasonic sensor comprising:

• a magnetic substance;
• an electromagnetic transducer comprising a conversion function between an oscillating magnetic field and an electric signal and disposed opposing the magnetic substance across the outer plate, the oscillating magnetic field being between the magnetic substance and the electromagnetic transducer;
• and
• a diaphragm having the shape of a thin film with a film thickness direction along an axial direction parallel to a directional axis, the diaphragm being able to ultrasonically oscillate by being joined to an outer surface of the outer plate at an outer edge in a radial direction crossing the directional axis, wherein
• one of the magnetic substance and the electromagnetic transducer is fixed to the diaphragm in such a manner as to be able to ultrasonically oscillate and to reciprocate along the axial direction, and the other is disposed opposing an inner surface which is a back surface of the outer surface of the outer plate, causing ultrasonic oscillation corresponding to the oscillating magnetic field to be generated in the diaphragm, and
• with the outer edge of the diaphragm joined to the outer surface of the outer plate, an internal space that expands and contracts along the axial direction in response to ultrasonic oscillation of the diaphragm is formed between the diaphragm and the outer surface of the outer plate.