The ultrasonic sensor is a sensor that converts ultrasonic signals into other energy signals. It consists of 4 parts: a transmitter, a receiver, a control part, and a power supply. For ultrasonic probes that can be made from different materials, we should learn about their performances before usage, which includes the working principle, working process, sensitivity, and directivity. Based on the properties of ultrasonic waves, ultrasonic sensors are widely used in communication, medical, and home appliance.
Catalog
I Ultrasonic Sensors Construction | 1.Transmitter |
2.Receiver | |
3.Control Part | |
4. Power Supply | |
II Performance Indicators | 1. Working Frequency |
2. Operating Temperature | |
3. Sensitivity | |
4. Directivity | |
III Working of Ultrasonic Sensors | 1. Ultrasonic Sound Wave |
2. How Ultrasonic Sensor Works | |
IV Ultrasonic Sensor Application | 1. Main Applications |
2. Specific Applications | |
V Problems and Precautions During Operation | 1. Reflection Problem |
2. Noise | |
3. Cross Interference | |
4. Precautions | |
VI Ultrasonic Sensors Working | 1. Detection Modes |
2. Detection Range | |
3. Detection Methods | |
VII Ultrasonic Sensors VS. Sonar Sensors | |
I Ultrasonic Sensor Construction
Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electric signals). They are widely used in industry, national defense, and biomedicine.
The ultrasonic sensor is mainly composed of the following four parts:
1. Transmitter
Ultrasonic wave is generated through the vibration of the oscillator (generally ceramic products, with a diameter of about 15 mm) and radiates into the air.
2. Receiver
When the ultrasonic oscillator receives the ultrasonic wave, corresponding mechanical vibration will occur and convert the ultrasonic wave into electrical energy as the output of the receiver.
3. Control Part
it uses an integrated ultrasonic sensor circuit to control the ultrasonic transmission of the transmitter and determines the size of the received signal and whether the receiver has received the signal (ultrasonic).
4. Power Supply
The ultrasonic sensor is usually powered by an external DC power supply of 12V±10% or 24V±10%, which is supplied to the sensor by an internal voltage stabilizing circuit.
Ultrasonic SensorsConstruction
II Performance Indicators
The core of the ultrasonic probe is a piezoelectric chip in its plastic or metal package. A chip can be made from many kinds of materials, and the size of the chip, such as diameter and thickness is also different, so the performance of each probe is different. Therefore, we must know its performance in advance before using it. The main performance indicators of ultrasonic sensors include:
1. Working Frequency
The operating frequency is the resonant frequency of the piezoelectric chip. When the ultrasonic sensor frequency of the AC voltage is equal to the resonance frequency of the chip, the energy output is maximum and the sensitivity is the highest.
2. Operating Temperature
Generally, because the Curie point of piezoelectric materials is high, especially for the ultrasonic probe with low service power used for diagnosis. So the working temperature is relatively low, and the probe can work for a long time without failure. Medical ultrasonic probes have higher temperatures and require a separate refrigeration unit.
3. Sensitivity
It mainly depends on the manufacture of the chip. If the electro-mechanical coupling coefficient is high, the sensitivity is high, otherwise, the sensitivity is low.
4. Directivity
The detection range of ultrasonic sensors
Directivity Type for Ultrasonic Sensors
III Ultrasonic Sensors Working
1. Ultrasonic Sound Wave
What is Ultrasonic Sound?
First, we should pay attention to the ultrasonic frequency range. The sound we hear is produced by the vibration of objects, whose frequency is in the range of 20Hz-20KHz. The sound with a frequency of more than 20KHz is called the ultrasonic wave or the ultrasonic sound, of less than 20Hz is called the infrasonic wave. The commonly used ultrasonic frequency is from tens of KHz to tens of MHz.
The ultrasonic wave is a kind of mechanical oscillation in the elastic medium, which has two forms: the transverse wave and longitudinal wave. It can travel in gases, liquids, and solids at different ultrasonic speeds. In addition, it also has refraction and reflection phenomena, and has attenuation in the propagation process.
If the ultrasonic is transmitted in the air, its frequency is low, generally tens of KHz, and in solid and liquid, the frequency is higher. Moreover, in the air, the attenuation is fast, but in the liquid and solid, the attenuation is small and the propagation distance is long.
Based on the properties of ultrasonic, the ultrasonic measuring device can be made with ultrasonic sensors and widely used in communication, medical and home appliance.
The main materials of ultrasonic sensors are piezoelectric crystals (electrostrictive) and Nickel-ferric aluminum alloy (magnetostrictive). A piezoelectric ultrasonic sensor is a reversible sensor that converts electrical energy into mechanical oscillations to produce ultrasonic waves. At the same time, when receiving ultrasonic waves, it can also convert them into electric energy.
2. How Ultrasonic Sensor Works
If a high-frequency voltage is applied to the piezoelectric ceramic plate(double crystal oscillator) in the transmitter, the piezoelectric ceramic plate will be elongated or shortened based on the voltage polarity. The ultrasonic wave is propagated to the receiver in the form of density (density degree can be modulated by the control circuit).
The ultrasonic receiver uses the principle of the piezoelectric effect adopted by the pressure sensor. After we apply pressure on the piezoelectric element, strain occurs, and a sinusoidal voltage with a "+" pole on one side and a "-" pole on the other is generated. As the amplitude of the high frequency is small, it must be amplified.
IV Ultrasonic Sensor Application
1. Main Applications
Ultrasonic systems are applied in different aspects of production practice, and medical application is one of its main applications.
In the medical field, the ultrasonic sensor is mainly used to diagnose diseases, which has become an indispensable diagnostic method in clinical medicine.
Ultrasonic Sensor in Medical Field
The advantages of ultrasonic diagnosis are no pain, no damage, simple method, clear imaging, and high diagnostic accuracy. Therefore, it is easy to popularize and is welcomed by medical workers and patients.
In industries, the typical application of ultrasonic sensors is the nondestructive test of metal and ultrasonic measurements.
Ultrasonic Thickness Gauge
In the past, the development of many technologies has been hindered by their inability to detect the internals of objects. The advent of ultrasonic sensing technology has changed this situation. Many ultrasonic sensors are now installed on different devices, "silently" detecting the signals people need.
In future applications, combined with information technology and new material technology, a more intelligent ultrasonic sensor with higher sensitivity will appear.
2. Specific Applications
(1)Ultrasonic sensors can be used to detect the status of containers. They can be mounted on the top of the plastic melt tank or plastic granulating chamber. When a sound wave was sent to the container, we can analyze the status of the container, such as full, empty, or half full with the ultrasonic sensor.
(2)Ultrasonic sensors can be used to detect transparent objects, liquids, dense materials with rough, smooth or light surface and irregular objects. They're not suitable for outdoors, hot environment, pressure tanks and foam objects.
(3) Ultrasonic sensors can be used in food processing factories to realize the closed-loop control system of plastic packaging detection. With this new technology, the ultrasound detection can be performed in a wet environment such as a bottle washing machine, noise environment, and the environment where temperature varies greatly.
(4) Ultrasonic sensors can be used to detect liquid level, control tension and ultrasonic distance measuring like the distance sensor, mainly for packaging, bottle making, material transfer, coal inspection, plastic processing and automobile industry. They can also be used for process monitoring to detect defects and improve product quality.
V Problem and Precautions During Operation
The application of ultrasonic sensors is simple and convenient, and the cost of the sensor is very low. However, some problems will occur during the operation of ultrasonic sensors such as the reflection problem, noise and crossover interference.
1. Reflection Problem
If the object is always at the right angle, the ultrasonic sensor will obtain the right angle. Unfortunately, in practice, very few objects can be correctly detected. Several errors may occur:
(1) Triangular Error
When the object is at a certain angle to the sensor, there is a triangular error between the detected distance and the actual distance.
(2)Specular Reflection
At certain angles, the sound waves emitted are reflected away by a smooth object, so there are no echo and no reading of distance. In this situation, the ultrasonic sensor will “ignore” the object.
The Geometry of Ultrasound Sensor Reflection from a Wall
(3) Multiple Reflection
This phenomenon is more common when we detect corners or similar structures. The sound waves are bounced back and forth several times before they are received by the sensor, so the actual detected value is not the real distance value. This problem can be solved by using multiple ultrasonic rings arranged at certain angles. By detecting the returning value of multiple ultrasonic waves, we can screen out the correct reading.
2. Noise
Although most ultrasonic sensors operate between 40Khz and 45Khz, which are far higher than the frequency that humans can hear. But there is a noise of a similar frequency in the surrounding environment, like the high-frequency noise produced by the rotation of a motor or caused by the friction of wheels on the hard ground, and the shaking of the robot itself or even the sound waves emitted by ultrasonic sensors of other robots, all of which will cause the sensor to receive wrong signals.
To deal with this problem, we can encode the emitted ultrasound waves. For example, we can send sound waves with different lengths and calculate the distance only when the probe detects the same combination of sound waves. This can effectively avoid the misreading caused by ambient noise.
3. Cross Interference
The crossover interference occurs when multiple ultrasonic sensors are mounted on the robot at a certain Angle. After reflected by a mirror, the sound waves emitted by ultrasonic X are picked up by sensor Z and Y. The 2ultrasonic distance sensors will then calculate the distance based on this signal, thus failing to obtain the correct measurement result. The solution is to encode the ultrasonic signal from each sensor and let each ultrasonic sensor "hear” only its own sound.
Precautions
(1)To ensure reliability and long service life, do not use the ultrasonic sensor outdoors or above the rated temperature.
(2) Since the ultrasonic sensor uses air as the transmission medium, when the local temperatures are different, the reflection and refraction at the boundary may lead to malfunction. The ultrasonic detection distance will also change when the wind blows. Therefore, sensors should not be used next to devices such as forced draught fans.
A Forced Draught Fan
(3) The air injection from the nozzle has a variety of frequencies, so it will affect the sensor and should not be used near the sensor.
(4) Water droplets on the sensor surface will shorten the detection distance.
(5)Fine powders and materials such as cotton cannot be detected when the sound is absorbed (reflective sensor).
(6) Do not use sensors in vacuum or explosion-proof areas.
(7)Do not use the sensor in the area with steam. The atmosphere in such areas is uneven, which will cause a temperature gradient, resulting in a measurement error.
VI Detection of Ultrasonic Sensors
1. Detection Modes
Ultrasonic sensors mainly adopt the detection mode of direct reflection. The object in front of the sensor transmits the emitted sound wave partially back to the receiver, thereby being detected by the sensor.
There are also some ultrasonic sensors using the bijection mode. A bijection ultrasonic sensor consists of a transmitter and a receiver that continuously “keep in touch” with each other. The object between the receiver and the transmitter will block the transmitted sound waves and the sensor will produce the switching signal.
2. Detection Range
The detection range of ultrasonic sensors depends on the wavelength and frequency. The longer the wavelength, the smaller the frequency and the longer the detection distance. For example, the detection range of the compact sensor with millimeter-wavelength is from 300 to 500mm, and the detection ultrasonic range of the sensor with 5mm wavelength is up to 8m.
Some sensors have a narrow 6 sound wave emission angle and are therefore more suitable for accurate detection of relatively small objects. Other sensors with an sound wave emission angle of 12 to 15 can detect objects with large dip angles.
3. Detection Methods
Different detection methods are adopted according to the characteristics of the detected object such as volume, material, and whether it can be moved or not. There are four common detection methods:
(1) Penetration:the ultrasonic transmitter and receiver are located on both sides, and when the object passes between them, it can be detected according to the ultrasonic attenuation (or occlusion) is detected.
(2) Limited Distance Type: the transmitter and receiver are located on the same side. When the object passes within the limited distance, it will be detected according to the reflected ultrasonic wave.
(3) Limited Range Type: the transmitter and receiver are located in the center of the limited ultrasonic ranging, and the reflector is located at the edge of the limited range. The attenuation value of the reflected wave without blocking of the object is taken as the reference value.
When the object passes within the limited range, it is detected according to the attenuation of the reflected wave (compare the attenuation value with the reference value).
(4) Regression Reflection Type: the transmitter and receiver are located on the same side, and the detection object (plane object) is used as the reflection surface. The object is detected according to the attenuation of the reflected wave.
VII Ultrasonic Sensors VS. Sonar Sensors
The sonar sensor and ultrasonic sensor are 2 common detection devices, many people think that the two are the same, but it is not the truth.
The sonar sensor directly detects and identifies the object in the water and the wave outline of the underwater. It sends out a sound wave signal, which will be reflected when it meets an object. Its distance and position can be calculated according to the reflection time and wave pattern.
Sonor sensing is mainly for detecting living things, such as what is in the water, how big it is, and so on. The device used to detect water monsters is sonar sensors.
A Sonar Sensor
The ultrasonic wave is a kind of mechanical wave whose vibration frequency is higher than the sound wave, which is generated by the vibration of the transduction chip under the excitation of voltage. It has high frequency, short wavelength, small diffraction phenomenon, and good directivity, and can become ray for directional propagation.
Ultrasonic waves can penetrate liquid, solid and can even penetrate tens of meters depth in opaque solid. When the wave contacts with impurities or the interface, there will be a significant reflection to form a reflection echo, and the Doppler effect will occur when it touches the moving object. Therefore, ultrasonic detection is widely used in industry, national defense, and biomedicine.
The ultrasonic sensor is a sensor developed by utilizing the characteristics of ultrasonic waves.
In industry, the typical application of ultrasonic is the nondestructive inspection of metal and ultrasonic thickness measurement. The application of ultrasonic sensors in medicine is mainly to diagnose diseases, which has become an indispensable diagnostic method in clinical medicine
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