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-6 dB Directivity (deg)
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People can hear the sound is due to the vibration of the object, its frequency in the 20HZ-20KHZ range, more than 20KHZ called ultrasound, less than 20HZ called infrasound. Commonly used ultrasound frequency of dozens of KHZ-dozens of MHZ.
Ultrasound is a type of mechanical oscillation in elastic media in two forms: transverse (transverse) and longitudinal (longitudinal). In industrial applications, the main use of longitudinal oscillation. Ultrasound can be in the gas, liquid and solid in the spread of its spread at different speeds. In addition, it also has refraction and reflection phenomena, and attenuation in the propagation process. In the air to transmit ultrasound, the frequency is low, usually tens of KHZ, and in solid, liquid, the frequency is higher available. Decay faster in the air, but in the liquid and solid spread, attenuation smaller, spread further. The use of ultrasonic properties, can be made of various ultrasonic sensors, coupled with different circuits, made of various ultrasonic measuring instruments and devices, and communications, medical appliances and other aspects are widely used.
Ultrasonic sensors are the main material piezoelectric crystal (electrostriction) and nickel-iron alloy (magnetostrictive) two categories. Electrostrictive materials are lead zirconate titanate (PZT) and so on. Piezoelectric crystal ultrasonic sensor composed of a reversible sensor, it can be converted into mechanical oscillations of electricity to produce ultrasonic waves, while it receives ultrasonic waves, but also into electrical energy, so it can be divided into transmitters or receivers. Some ultrasonic sensors for sending, but also for receiving. Here only describes the small ultrasonic sensor, send and receive slightly different, it is suitable for propagation in the air, the operating frequency is generally 23-25KHZ and 40-45KHZ. This type of sensor is suitable for ranging, remote control, anti-theft and other purposes. Such as T / R-40-60, T / R-40-12, etc. (where T said to send, R said to receive, 40 said the frequency of 40KHZ, 16 and 12 that its diameter size, in millimeters). Another kind of sealed ultrasonic sensor (MA40EI type). It is characterized by a waterproof (but can not be placed in water), can be used for material level and proximity switches, its better performance. There are three basic types of ultrasonic applications, the transmission type for remote control, burglar alarm, automatic doors, proximity switches, etc .; separate reflective type for distance measurement, level or material level; reflective type for material testing, thickness measurement .
By the sending sensor (or wave transmitter), the receiving sensor (or wave receiver), the control part and the power supply part. Transmitter sensor and the use of a diameter of about 15mm ceramic oscillator transducer composition, the role of the transducer is to vibrate the electrical vibration energy of the ceramic oscillator into super energy and radiation to the air; and receive the sensor from the ceramic oscillator transducer And the amplifier circuit, the transducer receives the wave to produce mechanical vibration, it is converted into electrical energy, as the output of the sensor receiver, so as to send the detection. In actual use, the ceramic transducer used to send the sensor can As a receiver sensor company's ceramic oscillator. The control part mainly controls the pulse train frequency, duty cycle, sparse modulation, counting and detection distance sent by the transmitter.