People can hear voices because of the vibration of the object, its frequency in 20HZ-20KHZ
In the range, more than 20KHZ is called ultrasound, less than 20HZ called infrasound. Commonly used ultrasound frequencies are dozens of KHZ-dozens of MHz.
Ultrasound is a mechanical oscillation in elastic media, there are two forms: transverse oscillation (shear wave) and longitudinal oscillation (longitudinal wave). The application of vertical oscillation in industry is mainly used. Ultrasonic waves can be transmitted in gases, liquids and solids, and their propagation speeds differ. In addition, it also has refraction and reflection phenomena, and has attenuation in the propagation process. Ultrasonic waves in the air, the frequency of low, generally dozens of khz, while in solids, liquids, the frequency can be higher. In the air decay faster, while in liquids and solids spread, less attenuation, spreading farther. Using ultrasonic characteristics, can be made into a variety of ultrasonic sensors, with different circuits, to make a variety of ultrasonic measurement instruments and devices, and in communication, medical appliances and other aspects are widely used.
The main materials of ultrasonic sensors are piezoelectric crystals (magnetostrictive) and nickel-iron aluminium alloys (magnetostrictive). Electro-telescopic materials have lead zirconate titanate (PZT). The ultrasonic sensor consisting of piezoelectric crystals is a reversible sensor that converts electrical energy into mechanical oscillations and generates ultrasonic waves, which can also be converted into electrical energy when it receives ultrasound, so it can be divided into a transmitter or receiver. Some ultrasonic sensors are both sent and received. Here only the small ultrasonic sensors, sending and receiving slightly different, it is suitable for spreading in the air, the working frequency is generally 23-25KHZ and 40-45KHZ. Such sensors are suitable for ranging, remote control, anti-theft and so on. The species has a T/R-40-60,T/R-40-12, such as T, which is sent, R is received, and 40 represents the frequency for 40KHZ,16 and 12 to denote its outer diameter size, in millimeters. Another sealed ultrasonic sensor (MA40EI type). It is characterized by a waterproof function (but not in the water), can be condiments and proximity switches, its performance is better. Ultrasonic application has three basic types, transmission type for remote control, anti-theft alarm, automatic doors, proximity switches, etc. separated reflective type for ranging, liquid level or material position; reflective type for material flaw detection, thickness measurement, etc.
Consists of a sending sensor (or a wave transmitter), a receiving sensor (or a wave receiver), a control part, and a power supply part. The transmitter sensor consists of a transmitter and a ceramic oscillator with a diameter of 15mm or so, the transducer function is to convert the electrical vibration energy of the ceramic oscillator into ultra-energy and radiate to the air; The receiver sensor is composed of a ceramic vibrator transducer and a amplifying circuit, the transducer receives the wave generating mechanical vibration, transforming it into electrical energy, as the output of the sensor receiver. Thereby detecting the sent ultra. In practice, the ceramic oscillator of the transmitter transducer can also be used as the receiver of the transducer. The control part mainly carries on the control of the pulse chain frequency, the duty ratio and the sparse modulation and counting and detecting distance of the transmitter.