Ultrasonic sensor

An ultrasonic sensor that transmits an ultrasonic wave to a target object and receives the ultrasonic wave reflected by the target object, the ultrasonic sensor comprising:

• an ultrasonic array chip on which ultrasonic elements that transmit and receive the ultrasonic wave are arranged in an array shape, wherein
• each of the ultrasonic elements includes a vibrating section and a piezoelectric element provided in the vibrating section, vibrates the vibrating section to transmit the ultrasonic wave, and outputs a reception signal of the ultrasonic wave by the vibration of the vibrating section, and
• each of the ultrasonic elements is configured to selectably have one of the following properties:
• a first property in which:
• a resonance frequency is 600 kHz or more and less than 1000 kHz;
• a reverberation time is 60 us or less;
• a distance between the ultrasonic sensor and the target object is 10 mm;
• and
• a spot diameter of an ultrasonic beam is 10 mm or less;
• a second property in which:
• the resonance frequency is 1000 kHz or more and less than 1500 KHz;
• the reverberation time is 50 us or less;
• the distance between the ultrasonic sensor and the target object is in a range of 5 mm to 10 mm;
• and
• the spot diameter of the ultrasonic beam is 10 mm or less;
• and
• a third property in which:
• the resonance frequency is in a range of 1500 kHz to 2000 kHz;
• the reverberation time is 25 us or less;
• the distance between the ultrasonic sensor and the target object is 5 mm or less;
• and
• the spot diameter of the ultrasonic beam is 10 mm or less.