Ultrasonic sensor

An ultrasonic sensor comprising:

• a microphone that is comprised of a piezoelectric vibration element converting an electrical signal into a vibration and converting a vibration into an electrical signal;
• a microphone housing that accommodates the microphone, the microphone housing being formed in a bottomed tubular shape having a bottom constituting a vibration portion to which the microphone is attached and a side wall;
• and
• an adhesion sensor that detects adhesion of a foreign substance to a first surface of the bottom, wherein
• the adhesion sensor includes:
• a plurality of variable capacitances defined between a plurality of sensor electrodes disposed on the first surface of the bottom, each of the plurality of variable capacitances having a capacitance value which changes in response to adhesion of a foreign substance to the first surface;
• and
• an adhesion detection unit configured to measure an individual capacitance value which is a capacitance value of each of the plurality of variable capacitances and a total capacitance value which is a total of the capacitance values of all the plurality of variable capacitances to determine, based on the individual capacitance value and the total capacitance value, whether a foreign substance adheres to the first surface, and, when it is determined that a foreign substance adheres, specify a type of the foreign substance.