Patent attributes
An ultrasonic sensor includes an ultrasonic element and an element accommodation case. A side wall portion of the element accommodation case has a tubular shape surrounding a directional central axis. A bottom wall portion and a top wall portion of the element accommodation case cover ends of the side wall portion in a direction along the directional central axis. The top wall portion has a diaphragm portion. The bottom wall portion supports the ultrasonic element. For example, the ultrasonic element is opposed to the diaphragm portion across a gap defining an interval corresponding to an integral multiple of half of a wavelength of ultrasonic vibration. Alternatively, the diaphragm portion is formed of a material having an acoustic impedance of 50×105 Pa·s/m or more and 5000×105 Pa·s/m or less, and has a thickness of 1 mm or less.
