What is an acoustic sensor What is the principle of operation

Definition of ultrasonic sensor is the use of ultrasonic characteristics of the sensor developed. Ultrasonic is a vibration frequency higher than the sound wave mechanical waves, vibration generated by the transducer chip in the voltage excitation, it has a high frequency, short wavelength, small bypass phenomenon, especially the direction of good, can become a ray and directional propagation and other characteristics. Ultrasonic penetration of liquids, solids, especially in the sun opaque solids, it can penetrate the depth of tens of meters. Ultrasound encounters impurities or interfaces will produce significant reflections to form reflections into echoes, and can produce the Doppler effect when it encounters moving objects. Therefore, ultrasonic testing is widely used in industry, defense, biomedical and other aspects. Principle of operation people can hear the sound is due to object vibration, its frequency in the range of 20HZ-20KHZ, more than 20KHZ called ultrasound, less than 20HZ called infrasound. Commonly used ultrasonic frequency of tens of KHZ - tens of MHZ. Ultrasound is a kind of mechanical oscillation in an elastic medium, there are two forms: transverse oscillation (transverse) and longitudinal and oscillation (longitudinal). In industrial applications mainly use longitudinal oscillation. Ultrasonic waves can propagate in gases, liquids and solids with different propagation speeds. In addition, it also has refraction and reflection phenomena, and there is attenuation in the propagation process. Ultrasonic propagation in the air, its frequency is low, generally tens of KHZ, while in the solid, liquid is available in higher frequency. Faster attenuation in the air, while in the liquid and solid propagation, attenuation is smaller, spread farther. The use of ultrasonic characteristics, can be made into a variety of ultrasonic sensors, with different circuits, made of a variety of ultrasonic measuring instruments and devices, and in communication, medical home appliances and other aspects of a wide range of applications. Ultrasonic transducer main materials are piezoelectric crystal (electrostrictive) and nickel-iron aluminum alloy (magnetostrictive) two types. Electrostrictive materials such as lead zirconate titanate (PZT). Piezoelectric crystal ultrasonic transducer is a reversible sensor, it can be converted into mechanical oscillation of electrical energy to produce ultrasonic waves, at the same time it receives ultrasonic waves, can also be converted into electrical energy, so it can be divided into a transmitter or receiver. Some ultrasonic sensors can be used as both transmitter and receiver. Here only introduce small ultrasonic sensors, send and receive a slight difference, it is suitable for propagation in the air, the working frequency is generally 23-25KHZ and 40-45KHZ. these sensors are suitable for distance measurement, remote control, anti-theft and other purposes. This kind of T / R-40-60, T / R-40-12, etc. (which T said to send, R said to receive, 40 said that the frequency of 40KHZ, 16 and 12 said that the size of its outer diameter, in millimeters). There is another sealed ultrasonic sensor (MA40EI type). It is characterized by waterproof (but can not be put into the water), can be used as a material level and proximity switch, its performance is better. There are three basic types of ultrasonic applications, transmissive for remote control, burglar alarms, automatic doors, proximity switches, etc.; separate reflective for distance measurement, liquid level or material level; reflective for material flaw detection, thickness measurement, etc.. By the sending sensor (or wave transmitter), receiving sensor (or wave receiver), control part and power supply part. Transmitter sensor by the transmitter and the use of ceramic vibrator transducer diameter of 15mm or so, the role of the transducer is the ceramic vibration of the electrical energy into super-energy and radiation into the air; and receive the sensor by the ceramic vibrator transducer and amplifier circuit, the transducer receives the wave mechanical vibration, which will be converted into electrical energy as the sensor receiver's output, so as to send the super for detection. The transducer receives the wave to generate mechanical vibration and transforms it into electrical energy as the output of the sensor receiver, thus detecting the sent super. And in practice, the use of ceramic vibrators with sending sensors can also be used as a receiver sensor society's ceramic vibrators. Control part of the main sender issued by the pulse chain frequency, duty cycle and sparse modulation and counting and detection distance and so on. Performance indicators 1, operating frequency. Operating frequency is the piezoelectric wafer *** vibration frequency. When the frequency of the AC voltage added to its ends and the chip's *** vibration frequency is equal, the output energy is the largest, the highest sensitivity. 2, operating temperature. Because the Curie point of piezoelectric materials is generally higher, especially when the diagnostic ultrasound probe with less power, so the working temperature is relatively low, can work for a long time without failure. Medical ultrasound probe temperature is higher, need a separate refrigeration equipment. 3, sensitivity. Depends mainly on the manufacturing wafer itself. Electromechanical coupling coefficient is large, high sensitivity; conversely, low sensitivity. Application technology ultrasonic sensing technology is used in different aspects of production and practice, and medical applications is one of its most important applications to medicine as an example of the application of ultrasonic sensing technology. The application of ultrasound in medicine is mainly to diagnose diseases, and it has become an indispensable diagnostic method in clinical medicine. The advantages of ultrasonic diagnosis are: no pain, no damage to the examinee, simple method, clear image, diagnostic accuracy and so on. Therefore, it is easy to popularize and welcomed by medical workers and patients. Ultrasonic diagnosis can be based on different medical principles, one of which is the so-called Type A method. This method utilizes the reflection of ultrasound waves. When ultrasound traveling through human tissue encounters an interface between two layers of media with different acoustic impedances, a reflected echo is generated at the interface. Each time a reflective surface is encountered, the echo is displayed on an oscilloscope screen, and the difference in impedance between the two interfaces determines the amplitude of the echo. In industry, the typical applications of ultrasound are both non-destructive testing of metals and ultrasonic thickness measurement. In the past, many technologies have been hindered by the inability to detect the inside of an object's tissue, and the advent of ultrasonic sensing technology has changed this situation. Of course, more ultrasonic sensors are fixed on different devices, "silent" to detect the signal people need. In future applications, ultrasound will be combined with information technology, new materials technology, there will be more intelligent, highly sensitive ultrasonic sensors. Remote control switch ultrasonic remote control switch can control household appliances and lighting. Using small ultrasonic sensors (Φ12-Φ16), the working frequency is 40KHZ, and the remote control distance is about 10 meters. The transmitter of the remote control, which is composed of 555 time base circuit oscillator, adjust the 10KΩ potentiometer, so that the oscillation frequency is 40KHZ, the sensor is connected to the ③ foot, when the button is connected, the ultrasonic wave is sent out, the receiving circuit. Power supply from 220V by capacitor step-down, rectifier, filtering, voltage regulator to obtain 12V operating voltage. As a result of non-isolated power supply, to the entire circuit with a plastic shell package to prevent electric shock (in the debugging should also be noted). Signal received by the ultrasonic receiver, by Q1, Q2 amplification (L, C resonant groove tuned at 40KHZ). Amplified signal to trigger the bistable circuit composed of Q3, Q4, Q5 and LED as a trigger isolation, and can light display. Due to the bistable in the power-on random, so add a zero button. q5 output trigger signal to make the bi-directional thyristor conduction, the load is connected. To disconnect the load, press the send button once. Liquid level indicator and controller due to ultrasonic attenuation in the air, then sent to the liquid surface and the size of the signal reflected back from the liquid surface and the liquid level related to the liquid level, the higher the liquid level position, the larger the signal; the lower the liquid level of the signal is small. The received signal is amplified by BG1 and BG2, and rectified into DC voltage by D1 and D2. When the voltage on 4.7KΩ exceeds the conduction voltage of BG3, a current flows through BG3 and the ammeter indicates that the current size is related to the liquid level. When the liquid level is lower than the set value, the comparator output is low, BG does not conduct, if the liquid level rises to the specified position, the comparator flip-flop, the output is high.