[Keywords:] ultrasonic sensor liquid level measurement disease diagnosis and ranging system
I. Overview of Ultrasonic Sensors
1. Ultrasonic
Sound wave is the propagation form of the mechanical vibration state of an object. Ultrasonic wave refers to sound wave with vibration frequency greater than 20000Hz, and its vibration frequency per second is very high, which exceeds the upper limit of human hearing. People call this inaudible sound wave ultrasonic. Ultrasonic wave is a kind of mechanical vibration in elastic medium, which has two forms: transverse vibration (transverse wave) and longitudinal vibration (longitudinal wave). Longitudinal oscillation is mainly used in industrial applications. Ultrasonic wave can propagate in gas, liquid and solid at different speeds. In addition, it also has refraction and reflection phenomena, which are attenuated in the process of propagation. There is no essential difference between the propagation law of reflection, refraction, diffraction and scattering of ultrasonic waves in media and audible sound waves. Compared with audible sound waves, ultrasonic waves have many strange characteristics: propagation characteristics-ultrasonic waves have poor diffraction ability and can travel in a straight line in a uniform medium. The shorter the wavelength of ultrasonic wave, the more remarkable this characteristic is. Power characteristics-when sound propagates in the air, it pushes the particles in the air to vibrate back and forth and do work on them. At the same intensity, the higher the frequency of sound wave, the greater its power. Because the frequency of ultrasonic wave is very high, its power is very large compared with ordinary sound wave. Cavitation-when ultrasonic waves propagate in liquid, tiny cavities will be generated in liquid due to the violent vibration of liquid particles. The rapid expansion and closure of these small cavities will cause violent collisions between liquid particles, thus generating pressures of thousands to tens of thousands of atmospheres. This strong interaction between particles will suddenly increase the temperature of the liquid, thus emulsifying two immiscible liquids (such as water and oil), accelerating the dissolution of solute and accelerating the chemical reaction. This effect produced by the action of ultrasound in liquid is called ultrasonic cavitation.
Characteristics of ultrasonic wave: (1) When ultrasonic wave propagates, it has strong directivity and easy energy concentration; (2) Ultrasonic wave can propagate in different media and far enough; (3) The interaction between ultrasonic wave and sound transmission medium is moderate, and it is easy to carry information about the state of sound transmission medium (diagnosis or function of sound transmission medium).
2. Ultrasonic sensor
Ultrasonic sensor is a sensor developed by using the characteristics of ultrasonic. Using ultrasound as a detection means requires generating and receiving ultrasound. The device to realize this function is an ultrasonic sensor, usually called an ultrasonic transducer or an ultrasonic probe.
The ultrasonic probe is mainly composed of piezoelectric wafers, which can transmit and receive ultrasonic waves. The core of ultrasonic probe is piezoelectric chip in plastic or metal shell. There are many kinds of materials that make up the wafer. The main materials of ultrasonic sensor are piezoelectric crystal (electrostriction) and nickel-iron-aluminum alloy (magnetostriction). The electrostrictive material includes lead zirconate titanate (PZT). Ultrasonic sensor composed of piezoelectric crystal is a reversible sensor, which can convert electrical energy into mechanical oscillation to generate ultrasonic waves. When it receives ultrasonic waves, it can also be converted into electrical energy, so it is divided into transmitter or receiver. Some ultrasonic sensors can both send and receive. Ultrasonic sensor consists of transmitting sensor (or wave transmitter), receiving sensor (or wave receiver), control part and power supply part. The transmitter sensor consists of a transmitter and a ceramic vibrator transducer with a diameter of about15 mm. The function of the transducer is to convert the electric vibration energy of the ceramic vibrator into super energy and radiate it into the air. The receiving sensor consists of a ceramic vibration sensor and an amplifier circuit. The transducer receives waves and generates mechanical vibration, which is converted into electrical energy as the output of the sensor receiver, thus detecting the emitted ultrasonic waves. The control part mainly controls the pulse chain frequency, duty ratio, sparse modulation, counting and detection distance sent by the transmitter. Second, the application of ultrasonic sensors
Application of ultrasonic distance sensor technology
Ultrasonic sensor includes three parts: ultrasonic transducer, processing unit and output stage. First, the processing unit applies voltage excitation to the ultrasonic transducer, and the ultrasonic transducer emits ultrasonic waves in the form of pulses after being excited, and then the ultrasonic transducer turns into a receiving state, and the processing unit analyzes the received ultrasonic pulses to judge whether the received signal is an echo of transmitting ultrasonic waves. If yes, measure the propagation time of the ultrasonic wave, and divide it by 2 according to the measured conversion of time, which is the distance that the object reflects the ultrasonic wave. The distance between the surface of the object and the sensor can be measured by installing an ultrasonic sensor at a suitable position and emitting ultrasonic waves according to the changing direction of the measured object. Ultrasonic sensors have transmitters and receivers, but ultrasonic sensors can also have dual functions of sending and receiving sound waves. Ultrasonic sensor uses the principle of piezoelectric effect to convert electric energy and ultrasonic waves, that is, when transmitting ultrasonic waves, it converts electric energy and emits ultrasonic waves; When the echo is received, the ultrasonic vibration is converted into an electrical signal.
2. Application of ultrasonic sensor in medicine.
The application of ultrasound in medicine is mainly to diagnose diseases, which has become an indispensable diagnostic means in clinical medicine. The advantages of ultrasonic diagnosis are: no pain, no damage, simple method, clear imaging and high diagnostic accuracy.
3. Application of ultrasonic sensor in liquid level measurement.
The basic principle of ultrasonic liquid level measurement is that the ultrasonic pulse signal sent by ultrasonic probe propagates in gas and is reflected when it meets the interface between air and liquid. After receiving the echo signal, the distance or liquid level height can be converted by calculating the time of ultrasonic wave traveling back and forth. Ultrasonic measurement has many incomparable advantages over other methods: (1) It has no mechanical transmission parts, does not touch the measured liquid, belongs to non-contact measurement, and is not afraid of electromagnetic interference, acid and alkali and other highly corrosive liquids, so it has stable performance, high reliability and long service life; (2) The response time is short, and the real-time measurement without lag can be conveniently realized.
4. Application of ultrasonic sensor in ranging system.
There are roughly the following methods for ultrasonic ranging: ① Take the average voltage of the output pulse, and the voltage (whose amplitude is basically fixed) is directly proportional to the distance, and the distance can be measured by measuring the voltage; ② Measure the width of the output pulse, that is, the time interval t between transmitting and receiving ultrasonic waves, so the measured distance is S= 1/2vt. If the ranging accuracy is high, it is necessary to carry out temperature compensation and correction. Ultrasonic ranging is suitable for high-precision middle and long distance measurement.
Three. abstract
Based on the characteristics of ultrasonic waves relative to audible sound waves, this paper expounds the principles and characteristics of ultrasonic sensors, and sums up the extensive applications of ultrasonic sensors in various aspects of production and life. However, ultrasonic sensors also have their own shortcomings, such as reflection problems, noise problems and so on. Therefore, the further research and discussion of ultrasonic sensor is still of great value.
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