What is ultrasound?
    People can hear the sound vibrations generated due to the object, its frequency in the range of 20HZ-20KHZ, more than 20KHZ called ultrasound, less than 20HZ called infrasound. The ultrasonic frequency used dozens of KHZ-scores MHZ.
     Ultrasound is an elastic medium in the mechanical oscillation, there are two forms: horizontal oscillation (wave) and longitudinal and vibration (longitudinal wave). Used in industry mainly vertical oscillations. Ultrasound can be gas, liquid and solid spread, its propagation speed difference. In addition, it also has the phenomenon of refraction and reflection, and communication in the process of decay. Airborne ultrasound, the frequency of low, typically tens of KHZ, but in solid, liquid is much higher frequencies available. Attenuation in the air faster, and in the liquid and solid in the spread of small attenuation, spread far. And ultrasonic properties, can be made into a variety of ultrasonic sensors, coupled with the different circuits, made of a variety of ultrasonic measuring instruments and devices, and Communication, medical appliances and other areas has been widely used.
    Ultrasonic sensors are piezoelectric crystal material are (electrostriction) and nickel-iron alloy (magnetostriction) categories. Electrostrictive materials are lead zirconate titanate (PZT) and so on. Piezoelectric crystals of the ultrasonic sensor is a reversible sensors, it Keyi into electrical energy to mechanical vibration caused by ultrasound, 同时 when it receives the ultrasound, Ye energy into electrical energy, so it can be divided into Fasong device Huo receiving device. Some ultrasonic sensors not only for transmission, but also for receiving. Here only on the small sensor, the structure shown in Figure 1, send and receive slightly different, it applies to spread in the air, the working frequency is generally 23-25KHZ and 40-45KHZ. Such sensors are suitable for distance measurement, remote control, anti-theft purposes. The species has T/R-40-60, T/R-40-12, etc. (where T that sends, R said the receiver, 40, said frequency 40KHZ, 16 and 12 that the external diameter size, in millimeters). Another kind of sealed ultrasonic transducer (MA40EI type), its appearance in Figure 2. It features a waterproof effect (but not into the water), seasoning spaces and proximity switches can be used, its performance is better. T/R40 series and MA40EI features such as Table 1 and Table 2 below. There are three basic types of ultrasonic applications, shown in Figure 3, the transmission type for the remote control, burglar alarm, automatic doors, proximity switches, etc.; separate reflective for distance, level or material level; reflective for material flaw detection, thickness, etc.