Ultrasonic sensors are developed by using the characteristics of ultrasonic wave. Ultrasonic wave is a mechanical wave with higher vibration frequency than sound wave, which is produced by vibration of transducer chip under excitation of voltage, it has the characteristics of high frequency, wave length, small diffraction phenomenon, especially directional good, can become ray and directional propagation.
Ultrasonic penetration of liquids and solids is great, especially in opaque solids, which can penetrate dozens of of meters in depth. The ultrasonic wave encounters the impurity or the interface will produce the remarkable reflection to form the echo, the movement object can produce the Doppler effect. Therefore, ultrasonic testing is widely used in industry, national defense, biomedicine and so on.
The ultrasonic wave and the receiving ultrasonic wave must be produced by means of ultrasound. The device that accomplishes this function is the ultrasonic transducer, which is customarily called the ultrasonic transducer, or the ultrasonic probe.
Ultrasonic probes are mainly composed of piezoelectric wafers, which can emit both ultrasonic and ultrasonic. The small power ultrasonic probe is used for detecting more. It has many different structures, which can be divided into direct probes (longitudinal wave), oblique probes (shear wave), surface wave probes (surface waves), lamb waves probes (lamb waves), dual probes (one probe reflex, one probe receiving), etc.