What’s the ultrasonic transducer sensors

Ultrasonic transducer sensors developed using the characteristics of ultrasonic waves. Ultrasonic is a mechanical wave with a higher vibration frequency than sound waves. It is generated by the vibration of the transducer chip under the excitation of voltage. It has high frequency, short wavelength, small diffraction phenomenon, especially good directionality, and can be directed into rays. Dissemination and other characteristics. Ultrasonic waves have a great ability to penetrate liquids and solids, especially in solids that are opaque to sunlight. It can penetrate to a depth of tens of meters. When the ultrasonic wave hits the impurity or the interface, it will produce a significant reflection to form an echo, and it can produce a Doppler effect when it hits a moving object. Sensors developed based on ultrasonic characteristics are called "ultrasonic sensors" and are widely used in industry, national defense, and biomedicine.

component

Ultrasonic transducers are mainly composed of piezoelectric wafers, ultrasonic range transducer 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), Lamb wave probe (Lamb wave), dual probe (one probe is transmitted, one probe is received) Wait.

Performance

The core of the ultrasonic probe is a piezoelectric ultrasonic sensor chip in its plastic or metal jacket. There can be many kinds of materials that make up the wafer. The size of the wafer, such as diameter and thickness are also different, so the performance of each probe is different, we must know its performance before use. The main performance indicators of ultrasonic sensors include:

working frequency

The working frequency is the resonance frequency of the piezoelectric wafer. When the frequency of the AC voltage applied to both ends of it is equal to the resonance frequency of the chip, the output energy will be the highest, and the sensitivity will be the highest.

Operating temperature

Since the Curie point of piezoelectric materials is generally relatively high, especially for ultrasonic probes for diagnosis

Ultrasonic sensor

The power is small, so the working temperature is relatively low, and it can work for a long time without failure. The temperature of medical ultrasound probes is relatively high and requires separate refrigeration equipment.

Sensitivity

Mainly depends on the manufacturing wafer itself. The electromechanical coupling coefficient is large and the sensitivity is high; on the contrary, the sensitivity is low.

Directivity

Ultrasonic sensor detection range

main application

Ultrasonic sensing technology is applied in different aspects of production practice, and medical application is its one of the main applications of ultrasonic sensors, the following uses medicine as an example to illustrate the application of ultrasonic sensing technology. The application of piezoelectric ultrasonic transducer in medicine is mainly to diagnose diseases, and it has become an indispensable diagnostic method in clinical medicine. The advantages of ultrasound diagnosis are: no pain, no damage to the examinee, simple method, clear imaging, high diagnostic accuracy, etc. Therefore, it is easy to promote and is welcomed by medical workers and patients. Ultrasound diagnosis can be based on different medical principles. Let's take a look at one of the representative so-called A-type methods. This method uses the reflection of ultrasonic waves. When ultrasonic waves propagate in human tissue and encounter two media interfaces with different acoustic impedances, reflected echoes are generated at the interface. Every time a reflecting surface is encountered, the echo is displayed on the oscilloscope screen, and the impedance difference between the two interfaces also determines the amplitude of the echo. In industry, the typical applications of ultrasonic are non-destructive testing of metals and ultrasonic thickness measurement. In the past, many technologies were hindered because they were unable to detect the inside of the object's tissues. The emergence of ultrasonic sensing technology changed this situation. Of course, more ultrasonic sensors are fixedly installed on different devices to "quietly" detect the signals that people need. In the application of ultrasonic sensors in the future, ultrasound will be combined with information technology and new material technology, and more intelligent and highly sensitive ultrasonic sensors will appear.

Technology application of ultrasonic distance sensor 

Ultrasonic waves have a great ability to penetrate liquids and solids, especially in opaque solids, where they can penetrate to a depth of tens of meters. When the ultrasonic wave hits the impurity or the interface, it will produce a significant reflection to form an echo, and it can produce a doppler effect when it hits a moving object. Therefore, ultrasonic testing is widely used in industry, national defense, biomedicine, etc. Ultrasonic distance sensors can be widely used in level (liquid level) monitoring, robot anti-collision, various ultrasonic proximity switches, and anti-theft alarms and other related fields. They are reliable in work, easy to install, waterproof, small launch angle, high sensitivity, It is convenient to connect with industrial display instruments, and probes with larger launch angles are also provided.

Concrete application

1. The ultrasonic sensor can detect the status of the container. When the ultrasonic sensor is installed on the top of the plastic melt tank or the plastic pellet chamber, when sound waves are emitted into the container, the status of the container can be analyzed accordingly, such as full, empty or half full.

2. Ultrasonic sensors can be used to detect transparent objects, liquids, any dense materials with rough, smooth and light surfaces, and irregular objects. But it is not suitable for outdoor, hot environment or pressure tank and foam objects.

3. Ultrasonic sensors can be used in food processing plants to realize a closed-loop control system for plastic packaging detection. With the new technology, it can detect in the humid ring, such as the bottle washing machine, the noise environment, and the environment with extreme temperature changes.

4.Ultrasonic sensors can be used to detect liquid level, detect transparent objects and materials, control tension and measure distances, mainly for packaging, bottle making, material handling, coal inspection, plastic processing, and automobile industries. Ultrasonic sensors can be used for process monitoring to improve product quality, detect defects, determine presence and other aspects. Using ultrasonic sensor technology to prevent wrong pedaling. Nissan has developed a function to prevent the vehicle from accelerating by accidentally stepping on the accelerator when the brake is about to be stepped on. When using cameras and ultrasonic sensors to infer the situation of “parking in the parking lot”, if The driver will force the brakes when stepping on the accelerator. This technology is scheduled to be put into practical use within 2 to 3 years. Ultrasonic sensor technology was developed to prevent accidents caused by stepping on the wrong brake and accelerator when parking in a parking lot.

The technology is realized by using four cameras equipped with one at the front, rear, left, and right of the vehicle, and eight ultrasonic sensors in the front bumper and the rear bumper. The four cameras use the "surround view display" camera that displays the bird's-eye view of the vehicle's surroundings. Use the camera to recognize white lines to infer that the car is in the parking lot, and use the ultrasonic sensor to measure the distance between the car and surrounding obstacles to determine the timing of braking. The prevention of accidents caused by stepping on the wrong brake and accelerator is implemented in two steps. When the driver wants to stop in the parking lot, if he steps on the accelerator, he first reduces the speed to creeping speed, uses the icon on the dashboard to indicate danger, and sounds an alarm. If the driver continues to step on the accelerator and is about to hit a wall or other objects, the brake will be forced. The timing of braking .The car can stop when it is about 20 to 30 cm away from the obstacle.

Working principle

People can hear the sound is produced by the vibration of the object, and its frequency is within the range of 20HZ-20KHZ ultrasonic sensor, more than 20KHZ is called ultrasonic, and below 20HZ is called infrasound. The commonly used ultrasonic frequency ranges from tens of KHZ to tens of MHZ. 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 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 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 ultrasonic waves, 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 communication, medical appliances and other aspects.

The main materials of ultrasonic distance transducer sensors 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 be used for both sending and receiving. Only small ultrasonic sensors are 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, ultrasonic sensor 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. Its characteristic is that it is waterproof (but cannot be put into the water), can be used as a material level and proximity switch, and 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, 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, converts it into electrical energy, as the output of the sensor receiver, so as to detect the transmitted 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 company. The control part mainly controls the pulse chain frequency, duty cycle, sparse modulation and counting, and detection distance sent by the transmitter.

Work program

If you send a piezoelectric ceramic crystal (double crystal oscillator) with a resonance frequency of 40KHz in the sensor.The ultrasonic sensor applies a high frequency voltage of 40KHz, and the piezoelectric ceramic sheet expands and contracts according to the polarity of the applied high-frequency voltage, and then sending 40KHz frequency ultrasonic waves, which propagate in the form of density (the degree of density can be modulated by the control circuit) , And pass it 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 Voltage. 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 of ultrasonic distance transducer can provide both sound and light 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.

Operating mode

The ultrasonic sensor uses the ultrasonic acoustic wave medium to carry out non-contact and wear-free detection of the detected object. The ultrasonic sensor can detect transparent or colored objects, metal or non-metal objects, solid, liquid, and powdery substances. Its detection performance is hardly affected by any environmental conditions, including smoke and dust environments and rainy days.