List price is for 1 sensor Sensor knowledge: (for learning only) In order to study and use ultrasonic waves, many ultrasonic generators have been designed and made. Ultrasonic sensors, reversing radar sensors, Ultrasonic hair sensors can be divided into two categories 1: The first type is to generate ultrasonic waves electrically, 2: Ultrasonic waves are generated mechanically At present, the piezoelectric ultrasonic generator is more commonly used. It has two piezoelectric wafers and a resonance plate. When the pulse signal is applied at its two poles and its frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonance plate to vibrate to produce ultrasonic wave. On the contrary, if no voltage is applied between the two electrodes, when the resonance plate receives ultrasonic wave, The piezoelectric wafer will be compressed for vibration and the mechanical energy will be converted into electrical signals. At this time, it will become an ultrasonic sensor Reversing radar ranging: the reversing radar sensor sends out an ultrasonic signal at a certain time, reflects it back when it meets the measured object, and is received by the reversing radar. As long as the time from transmitting to receiving the echo signal of the ultrasonic signal is calculated, and the propagation speed in the medium is known, the distance from the measured object can be calculated: