Related knowledge of ultrasonic transducer sensors

basic introduction:

Ultrasonic transducers sensor are developed by using the characteristics of ultrasound. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity, which can become rays and propagate directionally. Ultrasonic waves have a great ability to penetrate liquids and solids. Ultrasonic waves will cause significant reflections when they encounter impurities or interfaces, forming echoes, and they can produce doppler effects when they encounter moving objects. Therefore, ultrasonic testing is widely used in industry, national defense, biomedicine, etc. To use ultrasound as a detection method, ultrasound must be generated and received. The device that accomplishes this function is an ultrasonic sensor, which is habitually called an ultrasonic transducer or an ultrasonic probe.

 Component:

The acoustic wave probe is mainly composed of piezoelectric wafers, which can transmit and receive ultrasonic waves. Low-power ultrasound probes are mostly used for detection. It has many different structures, which can be divided into straight probe (longitudinal wave), oblique probe (transverse wave), surface wave probe (surface wave), probe (lamb wave), dual probe (one probe reflection, one probe reception), etc.

Working principle:

People can hear the sound because the object vibration is in the range of 20KHZ, more than 20KHZ is called ultrasonic, and less than 20HZ is called infrasound. 

Ultrasound is a kind of mechanical oscillation in elastic medium, which has two forms: transverse oscillation (transverse wave) and longitudinal oscillation (longitudinal wave). The application in the industry mainly adopts longitudinal oscillation. Ultrasonic waves can propagate in gases, liquids and solids, and their propagation speeds are different. In addition, it also has refraction and reflection phenomena, and attenuation during propagation. The frequency of ultrasonic waves non-contact ultrasonic level meter are propagating in the air is low, generally tens of KHZ, while in solids and liquids, the frequency can be higher. The attenuation is faster in the air, while it spreads in liquid and solid, the attenuation is small, and the spread is longer. Utilizing the characteristics of ultrasound, it can be made into various ultrasonic sensors, equipped with different circuits, and made into various ultrasonic measuring instruments and devices, and they are widely used in the communication, medical appliances and other aspects.

The main materials of 200KHz ultrasonic transducer are piezoelectric crystal (electrostriction) and nickel-iron-aluminum alloy (magnetostriction). Electrostrictive materials include lead zirconate titanate (PZT) and so on. The ultrasonic sensor composed of piezoelectric crystal is a reversible sensor. It can convert electrical energy into mechanical oscillation to generate ultrasonic waves. At the same time, when it receives ultrasonic waves, it can also be converted into electrical energy, so it can be divided into transmitters or receivers. Some ultrasonic sensors can both send and receive. Only the small ultrasonic sensor is introduced here. There is a slight difference between sending and receiving. It is suitable for transmission in the air, and the working frequency is generally 23-25KHZ and 40-45KHZ. This type of ultrasonic sensor is suitable for ranging, remote control, anti-theft and other purposes. There are T/R-40-60, T/R-40-12, etc. (where T means sending, R means receiving, 40 means the frequency is 40KHZ, 16 and 12 mean its outer diameter, in millimeters). There is also a sealed ultrasonic sensor (MA40EI type). It is characterized by being waterproof (but not in water), and can be used as a material level and proximity switch. Its performance is better. There are three basic types of ultrasonic applications, transmission type is used for remote control, anti-theft alarm, automatic door, proximity switch, etc.; separated reflection type is used for distance measurement, liquid level or material level; reflection type is used for material flaw detection, thickness measurement, etc. . It is composed of sending sensor (or wave transmitter), receiving sensor (or wave receiver), control part and power supply part. The transmitter sensor is composed of a transmitter and a ceramic vibrator transducer with a diameter of about 15mm. The function of the transducer is to convert the electrical vibration energy of the ceramic vibrator into super energy and radiate into the air; while the receiving sensor is composed of a ceramic vibrator transducer Composed with an amplifier circuit, the transducer receives the wave to produce mechanical vibration and converts it into electrical energy, which is used as the output of the ultrasonic sensor receiver to detect the transmitting super. In actual use, the ceramic vibrator used as the transmitting sensor can also be used. Used as a ceramic vibrator for the receiver sensor . The control part mainly controls the pulse chain frequency, duty cycle, sparse modulation, counting and detection distance sent by the transmitter.

Work program

If a 40KHz high-frequency voltage is applied to the piezoelectric ceramic sheet (dual crystal oscillator) with a resonance frequency of 40KHz in the transmitting sensor, the piezoelectric ceramic sheet will expand and contract according to the polarity of the applied high-frequency voltage, and then send 40KHz ultrasonic waves , The ultrasonic wave brass material ultrasonic transducer propagates in the form of density (the degree of density can be modulated by the control circuit) and is transmitted to the wave receiver. The receiver uses the principle of the piezoelectric effect used by the pressure sensor, that is, applying pressure on the piezoelectric element to cause the piezoelectric element to strain, then a 40KHz sine with a "+" pole on one side and a "-" pole on the other side . Because the amplitude of the high-frequency voltage is small, it must be amplified. Ultrasonic sensors allow the driver to back up safely. The principle is to detect any obstacles on or near the backing path and issue a warning in time. The designed detection system can provide both audible and visual audible and visual warnings at the same time. The warning indicates that the distance and direction of obstacles in the blind zone are detected. In this way, whether is parking or driving in a narrow place, with the help of the reversing obstacle alarm detection system, the driver's psychological pressure will be reduced, and the driver can take necessary actions with ease.

To

Note when using:

1. To ensure reliability and long service life, do not use the sensor outdoors or where the temperature is higher than the rated temperature.

2. The ultrasonic sensor uses air as the transmission medium, so when the local temperature is different, the reflection and refraction at the boundary may cause malfunction, and the detection distance will also change when the wind blows. Therefore,ultrasonic sensors should not be used next to equipment such as forced ventilators.

3. The jet from the air nozzle has multiple frequencies, so it will affect the ultrasonic sensor and should not be used near the sensor.

4. The water droplets on the surface of the sensor shorten the detection distance.

5. Materials such as powder and cotton yarn cannot be detected when they are absorb sound (reflective sensor).

6. The ultrasonic sensor can be used in vacuum area or explosion-proof area.

7. Do not use the ultrasonic sensor in an area with steam; the atmosphere in this area is uneven. A temperature gradient will be generated, which will cause measurement errors.