Ultrasonic sensors are transducers that convert ultrasonic signals into other energy signals (usually electrical).Ultrasonic waves are mechanical waves with a vibration frequency higher than 20kHz.It has a high frequency, short wavelength, small bypass phenomenon, especially good directionality, can become a ray and directional propagation and other characteristics.Ultrasonic waves on the liquid, solid penetration ability is great, especially in the sun opaque solids.Ultrasound encounters impurities or interfaces will produce significant reflections to form reflection echoes, and can produce the Doppler effect when it encounters moving objects.Ultrasonic sensors are widely used in industry, defense, biomedical and other aspects.、
Component
Commonly used ultrasonic sensors are composed of piezoelectric wafers, which can transmit ultrasonic waves and receive ultrasonic waves. The small power ultrasonic probe is used for more 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 transmits, one probe receives) and so on.
Performance indicators
The heart of an ultrasound probe is a piezoelectric wafer in its plastic or metal jacket.There are many different materials that make up the wafer.The size of the wafer, such as diameter and thickness, also varies, so the performance of each probe is different, and we must know its performance in advance before use.The main performance indicators of ultrasonic transducers include:
Operating Frequency
The operating frequency is the resonant frequency of the piezoelectric wafer.When the frequency of the AC voltage applied to both ends of the piezoelectric wafer is equal to the resonance frequency of the wafer, the output energy is the greatest and the sensitivity is also the highest.
Operating Temperature
Ultrasonic Transducers Because the Curie point of piezoelectric materials is generally high, and because ultrasonic probes for diagnostic purposes in particular use low power, the operating temperature is relatively low and they can be operated for long periods of time without failing.Medical ultrasound probes have higher temperatures and require separate refrigeration equipment.
Sensitivity
Depends mainly on the manufacturing wafer itself.A high electromechanical coupling coefficient results in high sensitivity; vice versa, low sensitivity.
Directivity
Range of ultrasonic sensor detection
Main Applications
Ultrasonic Sensors Ultrasonic sensing technology is used in different aspects of production and practice, and the medical application is one of its most important applications, the following medicine as an example of the application of ultrasonic sensing technology.Ultrasound in medicine is mainly used to diagnose diseases, it has become an indispensable diagnostic method in clinical medicine.The advantages of ultrasonic diagnosis are: no pain and no damage to the examinee, simple method, clear image, high diagnostic accuracy.Therefore, it is easy to promote and welcomed by medical workers and patients.Ultrasound diagnosis can be based on different medical principles, let's take a look at a representative one of them, the so-called type A method.This method utilizes the reflection of ultrasound waves.When ultrasound propagating through human tissue encounters two interfaces 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 the oscilloscope screen, and the difference in impedance between the two interfaces determines the amplitude of the echo.
In industry, two typical applications of ultrasound are non-destructive testing of metals and ultrasonic thickness measurement.In the past, many technologies have been hampered by the inability to detect the inside of an object's tissue, which has changed with the advent of ultrasonic sensing technology.Of course, more ultrasonic sensors are fixed installed in different devices, "silent" to detect the signals people need.In future applications, ultrasound will be combined with information technology, new materials technology, there will be more intelligent, highly sensitive ultrasonic sensors.
Ultrasonic Distance Sensor Technology Applications
Ultrasonic penetration of liquids, solids, especially in opaque solids, it can penetrate tens of meters in depth.
Ultrasound encounters impurities or sub-interfaces will produce significant reflections to form reflections into echoes, and can produce the Doppler effect when it encounters moving objects.Therefore, ultrasonic detection is widely used in industry, defense, biomedical and other aspects.
Ultrasonic distance sensors can be widely used in level monitoring, robot collision avoidance, various ultrasonic proximity switches, as well as anti-theft alarms and other related fields, reliable, easy to install, waterproof, small transmitter angle, high sensitivity, easy to connect with industrial display instrumentation, but also provides a larger transmitter angle probe.
Specific applications
1. Ultrasonic sensors can detect the state of containers.The ultrasonic sensor will be installed on the top of the plastic melt tank or plastic granule room, and when sound waves are sent to the inside of the container, the status of the container can be analyzed accordingly, such as full, empty, or half-full, and so on.
2. Ultrasonic sensors can be used to detect transparent objects, liquids, any table rough, smooth, light dense material and irregular objects.But not for outdoor, hot environment or pressure tanks and foam objects.
3. Ultrasonic sensors can be used in food processing plants, the realization of closed-loop control system for plastic packaging detection.With the new technology can be detected in the wet ring such as bottle washer, noise environment, temperature extremely drastic changes in the environment.
4. Ultrasonic sensors can be used to detect the level of liquid, detecting transparent objects and materials, controlling tension and measuring distance, mainly for packaging, bottle making, material handling and inspection of coal equipment transportation, plastics processing and automotive industry.Ultrasonic sensors can be used for process monitoring to improve product quality, detect defects, determine the presence or absence and other aspects.
Ultrasonic Sensor Technology Prevents Pedal Mistakes
Nissan Motor has developed a function that prevents the vehicle from accelerating if the gas pedal is mistakenly pressed when the brakes are to be pressed, using a camera and ultrasonic sensors to infer "parking in a parking lot," and then forcing the brakes to be applied if the gas pedal is pressed by the driver.This technology is scheduled to be put into practice in two to three years. The ultrasonic sensor technology was developed to prevent accidents caused by stepping on the wrong brake or gas pedal while parking in a parking lot.
The technology is realized by using four cameras, one in the front, back, left and right side of the vehicle, and eight ultrasonic sensors, four in the front bumper and four in the rear bumper, which are similar to those used in the "surround view monitor" that displays an overhead image of the surrounding area of the vehicle.The cameras recognize white lines to infer that the car is in a parking lot, and ultrasonic sensors measure the distance between the car and surrounding obstacles to determine when to apply the brakes.
Preventing accidents caused by stepping on the wrong brake and gas pedal is implemented in two steps.When a driver tries to stop in a parking lot and steps on the gas pedal instead, he or she first reduces the speed of the vehicle to creeping speed, uses an icon on the dashboard to indicate danger, and sounds an alarm.If the driver continues to press the gas pedal and is about to hit an object such as a wall, the brakes are forced.The timing of braking is to ensure that the car can stop when it is about 20-30cm away from the obstacle.
Job-related
Working Principle
People can hear the sound is generated by the vibration of the object, its frequency in the range of 20HZ-20KHZ, more than 20KHZ known as ultrasound, less than 20HZ known as infrasound.Commonly used ultrasonic frequency of tens of KHZ - tens of MHZ.
Ultrasound is a mechanical oscillation in an elastic medium, which can take two forms: transverse oscillation (transverse wave) and longitudinal oscillation (longitudinal wave).Longitudinal oscillation is mainly used in industrial applications.Ultrasound can propagate in gases, liquids and solids at different speeds.In addition, it also has refraction and reflection phenomena, and there is attenuation in the propagation process.Propagation of ultrasound in the air, its frequency is low, generally tens of KHZ, while in solids and liquids, the frequency can be higher.In the air attenuation is faster, while in the liquid and solid propagation, attenuation is smaller, spread farther.Using the characteristics of ultrasound, can be made into a variety of ultrasonic sensors, with different circuits, made of a variety of ultrasonic measuring instruments and devices, and in communications, medical home appliances and other aspects of a wide range of applications.
The main materials of ultrasonic sensors are piezoelectric crystal (electrostrictive) and nickel-iron aluminum alloy (magnetostrictive).Electrostrictive materials such as lead zirconate titanate (PZT).The ultrasonic transducer composed of piezoelectric crystal is a reversible transducer, which can convert electrical energy into mechanical oscillation and generate ultrasonic waves, and at the same time, when it receives ultrasonic waves, it can also be converted into electrical energy, so it can be divided into 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.The kind of T / R-40-16, T / R-40-12, etc. (which T said to send, R said to receive, 40 said the frequency of 40KHZ, 16 and 12 said the size of its outer diameter, in millimeters).There is another sealed ultrasonic sensor (MA40EI type).It is characterized by its waterproof function (but cannot be put into water) and can be used as material level and proximity switch.There are three basic types of ultrasonic applications, transmissive type for remote control, burglar alarms, automatic doors, proximity switches, etc.; separate reflective type for distance measurement, liquid level or material level; reflective type for material flaw detection, thickness measurement and so on.
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 with a diameter of 15mm or so, the role of the transducer is the ceramic vibrator electrical vibration energy into super energy and radiation into the air; and receive the sensor by the ceramic vibrator transducer and amplifier circuitry, the transducer receives the wave to produce mechanical vibration, which will be converted into electrical energy, as the sensor receiver's output, so as to send the ultrasonic signalDetection.In practice, the ceramic oscillator used as the transmitter sensor can also be used as the ceramic oscillator of the receiver sensor.The control section mainly controls the frequency, duty cycle and sparse modulation of the pulse chain sent from the transmitter and counts and detects the distance.
Working program
If the resonant frequency of 40KHz piezoelectric ceramic chip (double crystal oscillator) to send the sensor within the 40KHz high-frequency voltage is applied, the piezoelectric ceramic chip according to the added high-frequency voltage polarity elongation and shortening, and then send 40KHz frequency ultrasonic sound, the ultrasonic sound wave in the form of sparse-dense propagation (sparse-dense degree of modulation can be controlled by the circuit), and transmitted to the wave receiver.Receiver is the use of pressure sensors used by the principle of the piezoelectric effect, that is, in the piezoelectric element on the pressure, so that the piezoelectric element strain, then produce a side of the "+" pole, the other side of the "-" pole of the 40KHz sinusoidal voltage.Because of the small amplitude of this high-frequency voltage, it must be amplified. Ultrasonic sensors make it possible for the driver to reverse safely by utilizing the principle of detecting any obstacle present in or near the reversing path and providing a timely warning.The designed detection system provides both audible and visual warnings with sound and light, and the warnings indicate that the distance and direction of an obstacle in the blind spot has been detected.In this way, with the aid of the reversing obstacle warning detection system, the driver will be less psychologically stressed and will be able to take the necessary action with ease, whether parking or driving in a narrow place.
Operating mode
Ultrasonic sensors utilize an acoustic medium for non-contact, wear-free detection of the object being detected.Ultrasonic sensors detect transparent or colored objects, metallic or non-metallic objects, solids, liquids, and powders.Their detection performance is virtually unaffected by any environmental conditions, including smoky environments and rainy days.
1. Detection Mode
Ultrasonic Sensors mainly use the direct reflection detection mode.The object to be detected, which is located in front of the sensor, is detected by the sensor by partially transmitting the emitted sound waves back to the receiver of the sensor.There are also some ultrasonic sensors that utilize an opposed mode of detection.An opposed ultrasonic sensor consists of a transmitter and a receiver that are constantly "listening" to each other.A detected object located between the receiver and the transmitter will block the receiver from receiving the transmitted sound waves, and the sensor will generate a switching signal.
2. Detection Range
Ultrasonic Sensors The detection range of ultrasonic sensors depends on the wavelength and frequency used.The longer the wavelength and the smaller the frequency, the greater the detection range, such as compact sensors with millimeter wavelengths have a detection range of 300 to 500 mm and sensors with wavelengths greater than 5 mm have a detection range of up to 8 m. Some sensors have a narrower acoustic emission angle of 6º, which makes them more suited to accurately detecting relatively small objects.Other sensors with acoustic emission angles of 12º to 15º are capable of detecting objects with large inclination angles.In addition, there are ultrasonic sensors with an external probe, where the corresponding electronics are located inside the conventional sensor housing.This type of construction is more suitable for inspections where installation space is limited.
3. Adjustment
Almost all ultrasonic sensors have the ability to adjust the near and far points of the switching output or the measuring range.Objects outside the set range can be detected but will not trigger a change in the output state.Some sensors have different adjustment parameters, such as the response time of the sensor, the return loss performance, and the set adjustment of the working direction when the sensor is used in connection with a pump device.
4. Repeat Accuracy
Ultrasonic Transducers Factors such as wavelength affect the accuracy of ultrasonic transducers, with the most significant affecting factor being the temperature-dependent acoustic velocity, and thus many ultrasonic transducers have a temperature-compensated feature.This feature enables the analog output type ultrasonic sensors in a wide temperature range of up to 0.6mm repeatability.
5. Output Functions
All series of ultrasonic sensors are available in switching output versions.Some products also have 2 switching outputs (e.g. minimum and maximum level control).Most product lines are available with analog current or analog voltage outputs.
6. Noise Suppression
Noise such as metallic knocks, booms, etc. do not affect the parameter assignment of the ultrasonic sensors, mainly due to the preferred frequency range and the patented noise suppression circuitry.
7. Synchronization Function
Ultrasonic Sensors The synchronization function of ultrasonic sensors prevents interference.They are synchronized by simply connecting their respective synchronizing wires.They emit acoustic pulses at the same time and work as a single sensor with an extended detection angle.
8. Work in turn
Ultrasonic sensors operating in an alternating mode are independent of each other and do not affect each other.The more sensors working in an alternating mode, the lower the switching frequency of the response.
9. Detection conditions
Ultrasonic sensors are particularly suitable for operation in the medium "air".These sensors can also work in other gaseous media, but sensitivity adjustment is required.
10. Blind zone
Directly reflecting ultrasonic sensors cannot reliably detect objects located partially in front of the ultrasonic transducer.The resulting area between the ultrasonic transducer and the start of the detection range is known as the blind zone.The transducer must remain unobstructed in this area.
11. Temperature and Humidity
Ultrasonic Sensors Air temperature and humidity affect the travel time of sound waves.For every 20ºC increase in air temperature, the detection distance increases by up to 3.5%.In relatively dry air conditions, an increase in humidity will result in an increase in the speed of sound of up to 2%.
12. Air Pressure
Routinely atmospheric variations of ±5% (select a fixed reference point) will result in a ±0.6% change in detection range.In most cases the sensor can be used without problems at a pressure of 5 Bar.
13. Airflow
Changes in airflow will affect the speed of sound.However, the effects caused by air velocities of up to 10 m/s are negligible.Under conditions where the generation of air eddy currents is common, e.g. for hot metals, it is not recommended to use ultrasonic sensors for detection, as it is very difficult to calculate the echoes of distorted sound waves.
14. Standard detectors
A square acoustic reflector plate is used for the calibration of the nominal switching distance sn.
15. Protection class
The housing is resistant to solid particles and water.
IP65: Fully dustproof; intrusion by waterproof columns.
IP67: Fully dustproof; can be effectively protected by immersion in water up to a depth of 1m and left for 30 minutes at constant temperature.
IP69K: conforms to DIN 40050-9 based on EN 60529.
16. Pump function
Dual-position control, such as a pump-in/pump-out function for a level control system, can be implemented.When a measured object moves away from the sensor to the far point of the detection range, an action is output.When a measured object moves closer to the sensor and reaches the near point of the detection range setting, the opposite action is output.
System configuration
Ultrasonic sensors are composed of the following four parts:
1. Transmitter: Ultrasonic waves are generated by the vibration of a vibrator (generally ceramic, with a diameter of about 15 mm) and emitted into the air.
2. Receiver: the oscillator receives the ultrasonic waves, according to the ultrasonic waves generated by the corresponding mechanical vibration, and will be converted into electrical energy, as the output of the receiver.
3. Control section: By using an integrated circuit to control the ultrasonic transmission of the transmitter, and to determine whether the receiver receives the signal (ultrasonic), as well as the size of the received signal.
4. Power supply section: ultrasonic sensors are usually powered by an external DC power supply with a voltage of DC12V ± 10 % or 24V ± 10 %, which is supplied to the sensors via an internal voltage regulator circuit.
Detection method
According to the volume of the object to be detected, the material, and whether the characteristics of mobile, ultrasonic sensors using different detection methods, the common detection methods are as follows:
Penetration: the transmitter and receiver are located on both sides, when the object to be detected from the passage between them, according to the attenuation of ultrasonic waves (or blocking) to detect the situation.
Limited distance type: the transmitter and receiver are located on the same side, when the object to be detected passes within the limited distance, according to the reflected ultrasonic waves for detection.
Limited range type: The transmitter and receiver are located in the center of the limited range, and the reflector is located at the edge of the limited range, and the attenuation value of the reflected wave when there is no obstruction from the object to be detected is used as the reference value.When a detected object passes within the limited range, detection is performed based on the attenuation of the reflected wave (comparing the attenuation value with the reference value).
Retro-reflective type: The transmitter and receiver are located on the same side, and detection is performed based on the attenuation of the reflected wave with the detected object (flat object) as the reflective surface.
Other information
Differences between ultrasonic sensors and sonar sensors
Sonar sensor directly detects and recognizes the objects in the water and the contour of the bottom of the water, the sonar sensor sends out an acoustic signal, when it encounters the object it will be reflected back, based on the reflection time and the waveform to calculate its distance and position.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 good directionality, can become a ray and directional propagation and other characteristics.Sonar sensors are mainly used for detecting organisms, such as for detecting what organisms are under the water, and how big the organisms are.The devices you often ask about and hear about for detecting water monsters are sonar sensors.
Ultrasonic penetration of liquids, solids, especially in opaque solids, it can penetrate the depth of tens of meters.Ultrasound encounters impurities or sub-interface will produce a significant reflection of the formation of reflections into the echo, and can produce the Doppler effect when it encounters an active object.Therefore, ultrasonic detection is widely used in industry, defense, biomedical and other aspects.Ultrasonic sensors are sensors developed by utilizing the characteristics of ultrasonic waves.In industry, the typical application of ultrasound is the non-destructive flaw detection of metal and ultrasonic thickness measurement.Ultrasonic sensors in medicine is mainly used to diagnose diseases, it has become an indispensable diagnostic method in clinical medicine.
