Purpose and principle of operation of the ultrasonic sensor. Common modes of operation are described: uni-/bi-directional systems and systems with reflectors.

Purpose and principle of operation of the ultrasonic sensor

Physics and technology

The main purpose of the ultrasonic sensor is to measure the distance to the controlled object or to register the appearance of an object in the "field of view" of the sensor.
Ultrasonic sensors use ultrasonic waves as an information carrier. The transducer sends out a pulse of sound and converts the received reflected signal into a voltage. By measuring the time until the arrival of the reflected signal from the sound speed factor, the controller integrated into the sensor calculates the distance to the object.
Ultrasonic sensors use ultrasonic waves as an information carrier.

Depending on the operating conditions and the features of the controlled object, it is advisable to use a one-/bidirectional or reflective control method.

Unidirectional systems

The transmitter and receiver are mounted opposite. If the ultrasound signal path is interrupted by an object, the transducer output will become active.

Advantage: High range.

Reflective systems

The transmitter and receiver are in the same housing. Ultrasound is reflected from the nearest reflector.

Advantage: Non-reflective or only slightly reflective objects can also be recognized.

Object reflection mode

There are 2 main functional types:

Unidirectional mode

The transmitter and receiver are in the same housing. Ultrasound is directly reflected by the registered object to the receiver.

Advantages: Simple, compact sensor, the most commonly used principle.

Bidirectional mode

The transmitter and receiver are separated, the transmit/receive sectors (transmitter/receiver) intersect.

Advantages: 3D registration area - Recognizes very small objects.

Like the optical one, the ultrasonic sensor is widely used for automation in factories and at home. The principle of its operation is based on determining the distance to an object using acoustic radiation.

Measurements are stable and highly accurate. Their range is within 2-400 cm. Neither electromagnetic noise nor solar radiation affects the readings.

In everyday life, they are used to automatically turn on ventilation and lighting. These ultrasonic devices respond to movement both inside and outside the room. When a person approaches, they work, turning on the light, which goes out when there is no movement. This simplifies the life of users and saves energy.

As already mentioned, an ultrasonic sensor is a high accuracy, stability of readings, independence from external influences, as well as:

• low sensitivity to air pollution;
• independence from the color of objects to which the distance is determined;
• wide temperature range of operation;
• compact dimensions;
• no need for special experience to work with them;
• high-quality assembly, since there are no moving parts.

In addition to these advantages, such ultrasonic sensors do not require maintenance.

Kinds

Ultrasonic devices are internal and external.

The first are divided into:

• wall;
• corner;
• ceiling.

When choosing such ultrasonic devices, it is important to understand that they differ in the type of installation and design. To control external lighting, outdoor models are selected, equipped with a protective casing necessary to protect against physical impact and weather conditions. Household ultrasonic devices do not have such protection.

They are also conditionally divided into:

• ultrasonic distance sensor;

• movement;

• level.

Principle of operation

It is based on two methods - diffuse and oppositional:

• if the time interval necessary for the sound to overcome the distance from the device to the object and back is measured, this is a diffuse mode;
• when they check whether a specific object received a signal sent by the device, the mode is called oppositional.

Application

Ultrasonic position sensors are used for:

• determining the location and presence of various mechanisms;
• counting the number of specific objects.

The device can act as a signaling device that informs about the achievement of liquids or bulk substances of an acceptable level.

In this case, two separate devices are required - the receiver and transmitter should be installed opposite. In this case, the activation of the switch output will occur when the ultrasonic beam reaches the object.

Features include:

• greater range;
• instant switching;
• resistance to interference, allowing it to be used in particularly difficult cases.

Among the disadvantages, rather high installation costs can be noted, since two sensors must be installed.

They are used in industries and at home to automatically turn on and off the light. But, it’s not at all necessary to buy a sensor - it’s easy to make it yourself by finding step-by-step instructions on the Internet.

If the receiver and transmitter are placed in the same housing, they speak of a diffuse mode. The main advantage of the method is the low cost of installation, since a single device is installed.

Its disadvantages are the following:

• longer response time compared to devices operating in opposition mode.

The operation of ultrasonic motion and distance sensors is similar to that described above. The difference is only in the output signal, i.e. instead of discrete, there is an analog one.

These devices are capable of converting signals to a specific object linear, into electrical, corresponding to 1-10 Volt or 4-20 mA standards.

The calculation error is:

• 0.5 mm at a distance of the object under study up to one meter;
• 1 mm - more than a meter.

Connection

For home safe use, it is important to connect the circuit breaker correctly, as well as take into account the nuances that exist for installing types of equipment, evaluate the operation of the machines in different situations, before proceeding to connect to the shield.

How successful the wiring in the house and installation will be will be determined by a well-designed ultrasonic sensor circuit and strict adherence to the installation steps. For instruments with an analog input and an upper limit value, the upper limit must be specified.

The slots of the potentiometer brought to the body help to realize this.

For devices with an analog input that memorize the operating range, fixed settings for both limits are important, which is explained by their volatile memory and programming method.

How to set up a work range

To do this, place an object in front of the sensor at the first boundary of the indication, press the save key, then, moving it to another boundary, use the button again.

Device with two digital outputs

A device with two digital outputs with a switching threshold, in that for threshold regulation it is important that the value of the liquid level or sag is not more than one value or less than the other.

With this regulator, the wire is connected to one device. On the panel, to adjust the threshold, there is a key, using which both outputs are configured.

Both sensors must be installed in close proximity, since they work alternately. This makes it possible to implement a synchronization input, which in turn helps to create a four-threshold controller that measures the threshold values ​​of both pairs.

Level instruments

The ultrasonic level sensor is a multifunctional device. It can measure the liquid filling of tanks, serve as a flow meter.

The use of a competent circuit diagram allows the liquid in the containers to be regulated by two values.

One of the sensors is used to measure control levels, the other - emergency. Synchronization of devices excludes not interfering with each other's work.

With the help of modern level sensors, the amount of liquid in the media is controlled without direct contact:

• aggressive;
• contaminated;
• corrosive.

This is important for areas such as:

• food, pharmaceutical and chemical industries;
• water treatment.

The operation of the level gauge is based on the propagation of an ultrasonic signal sent by the sensor, its reception and calculation of the fullness of the tank.

Video

Video: Working with ultrasonic distance sensor HC-SR04 in BASCOM-AVR

Price

Depending on the manufacturer's brand and functionality, you can buy ultrasonic sensors at a price from 2300 to 6000 rubles.

Profitable ultrasonic sensors to buy offer online stores:

Video: Ultrasonic sensor

New Articles

● Project 23: Ultrasonic Distance Sensor HC-SR04. Principle of operation, connection, example

In this experiment, we will consider an ultrasonic distance sensor and create a project to display the sensor readings on the WH1602 LCD screen.

Required components:

The ultrasonic range finder HC-SR04 (Fig. 23.1) is a receiver and transmitter of an ultrasonic signal placed on the same board. The emitter generates a signal, which, reflected from the obstacle, falls on the receiver. By measuring the time it takes a signal to travel to an object and back, you can estimate the distance. In addition to the receiver and transmitter themselves, the board also contains the necessary harness to make working with this sensor simple and convenient.

Specifications of ultrasonic range finder HC-SR04:

The measured range - from 2 to 500 cm;
. accuracy - 0.3 cm;
. viewing angle -< 15°;
. supply voltage - 5 V.

The sensor has 4 outputs of the 2.54 mm standard:

VCC - power supply +5 V;
. Trig (T) - input signal output;
. Echo (R) - output signal output;
. GND is ground.

The sequence of actions for obtaining data is as follows:

We apply a pulse with a duration of 10 μs to the Trig output;
. inside the rangefinder, the input pulse is converted into 8 pulses with a frequency of 40 kHz and sent forward through the emitter T;
. having reached the obstacle, the sent pulses are reflected and received by the receiver R, as a result, we obtain an output signal at the Echo pin;
. directly on the side of the controller, we translate the received signal into a distance according to the formula:

Pulse width (µs) / 58 = distance (cm);
-- pulse width (µs) / 148 = distance (inch).

In our experiment, we will create an audible alarm that will sound when you approach the Arduino board at a distance of less than 1 m. The sensor is located on the arm of the rotating servo and monitors the area with a 180° viewing angle. If the sensor detects an object within a radius of 1 m, an audible signal is given to the piezoelectric emitter, the rotation of the servo stops. The connection diagram of the elements is shown in fig. 23.2.

Rice. 23.2. Scheme of connection of elements for sound signaling

When writing a sketch, we will use the Servo library for working with a servo drive and the Ultrasonic library.
For Arduino to work with the HC-SR04 sensor, there is a ready-made library - Ultrasonic.
The Ultrasonic constructor takes two parameters: the numbers of the pins to which the Trig and Echo pins are connected, respectively:

ultrasonic ultrasonic(12,13);

The content of the sketch is shown in Listing 23.1.

#include // connecting the Servo library Servoservo1; const int pinServo=8 ; // pin to connect the servo int pos = 0 ; // variable to store the position of the servo int dir =1 ; // direction of movement of the servo // Pins for connecting HC-SR04 Trig - 12, Echo - 13 Ultrasonic ultrasonic ( 12 , 13 ) ; float dist_cm; // variable for distance, cm // connect speaker to pin 9 int speakerPin = 9 ; void setup(){ // connect servo1 variable to pinServo1 pin servo1.attach(pinServo1); pinMode(speakerPin, OUTPUT); ) void loop()(servo1.write(pos); // turn the servos to the received angle delay(15); // pause to wait for servos to turn float dist_cm = ultrasonic.Ranging(CM); if (dist_cm<100 && dist_cm>20) tone(speakerPin,); // turn on the piezo buzzer else (tone(speakerPin,0); // disable piezo buzzer pos=pos+dir; // change servo position variable if (pos==0 || pos==180 ) dir=dir*(-1 ); // change direction } }
Connection order:

1. We fix the distance sensor HC-SR04 on the servo.
2. We connect the HC-SR04 sensor, piezo buzzer and servo drive to the Arduino board according to the diagram in fig. 23.2.
3. Load the sketch from Listing 23.1 into the Arduino board.
4. We observe the cyclic movement of the servo, when an object enters the field of view of the HC-SR04 sensor, the piezo buzzer emits a signal, the servo stops, when the object disappears from the field of view of the sensor, the servo resumes movement.

Program listings

The ultrasonic sensor measures the distance to targets through the air using non-contact technology. It is easy to operate, reliable and economical. The principle of operation of this device is based on the technique used by various animals. The gadget provides accurate measurements in many difficult environments and unusual materials.

Features of work and history of invention

The ultrasonic transducer emits short high-frequency sound pulses at regular intervals. They travel through the air at the speed of sound. If the pulses collide with an object, they are reflected back to the sensor in the form of echo signals. The device independently calculates the distance to the target based on the time interval between the emission of a signal and the receipt of an echo.

Since the distance to an object is determined by the measurement of the time of flight, and not by the intensity of the sound, ultrasonic sensors are ideal for suppressing background noise. Almost all objects that reflect sound can be detected regardless of their color. Transparent materials or thin foils are also not a problem for ultrasonic waves, as the device is able to see through dust, air and ink mists. Even thin deposits on the sensory membrane do not impair its function.

The history of the invention of the ultrasonic sensor dates back to 1790, when Lazzaro Spallanzani first discovered that bats maneuver in flight using hearing rather than sight. Spallanzani conducted a series of experiments on bats, after which he came to the conclusion that they use sound and ears to navigate in complete darkness. He pioneered the original study of echolocation, although his research was limited to observation only.

Later, scientists moved on to research on sensory mechanisms. In the 1930s, researcher Donald Griffin was the first to confirm that bats navigate using sound to navigate, and unlocked the secret behind their remarkable ability to navigate in the dark. As it turned out, the animals emitted ultrasonic sounds and heard reflected sound waves in order to pinpoint objects in their flight path. Griffin called the sensory-acoustic form of bats navigational echolocation.

Echolocation is the use of sound waves and echoes to determine where and how far away objects are.

The ability to detect and emit ultrasonic frequencies above the human hearing range is an important survival tool, not only in bats. Nocturnal and marine animals rely on sensory systems to navigate and find prey, while some insects use ultrasonic hearing to detect predators. This ability is important for many animals.

Ultrasonic sensor module consists of transmitter and receiver. Any sound above 20 kilohertz (20,000 hertz) is considered ultrasound. For this reason, all sounds above the range of human hearing are called ultrasonic. The transmitter emits 40 kHz ultrasonic radiation, while the receiver is designed to receive 40 kHz sound waves only. A receiver sensor close to the transmitter can pick up reflected sound waves when the module hits any obstacle ahead.

Whenever there is an obstacle in front of the ultrasonic module, it calculates the time it takes to send signals and receive them, since time and distance are related to sound waves traveling through the air at a speed of 343.2 m/s. After receiving the signal, the display shows the data. In this way a wide range of materials can be measured, including:

• hard or soft;
• colored or transparent;
• flat or curved.

Device and specifications

These devices can determine the height, width and diameter of objects using one or more sensors. Items can be selected or rejected depending on their dimensions or profiles.

An ultrasonic distance sensor determines the distance to an object by measuring the time taken by sound to reflect it. The sound frequency is in the ultrasonic range, which provides a more accurate direction of the sound wave. This is due to the fact that the sound, which is at a higher frequency, is scattered in the environment.

The device contains two membranes. One of them produces sound, and the other receives the reflected echo. The membranes in the device are usually a speaker and a microphone. The sound generator generates short ultrasonic pulses and starts a timer. The second membrane registers the arrival of a sound pulse and stops the timer. From the time obtained, you can calculate the path that the sound has overcome. The distance to the object is half the path traveled by the sound wave.

Applications and benefits

Distance sensors are widely used in everyday life. Cars are equipped with parking sensors. In addition to measuring distances, they can simply register the presence of an object within the measurement range, for example, in hazardous areas of working machines. Such devices used in a wide range of industries, for example:

Distance sensors can be used to control or indicate the position of objects and materials. These instruments are so widely used that they can be implemented reliably in applications such as grain size measurement, water level detection, and more, as ultrasound reflects off almost any surface. The only exceptions are soft materials, such as wool. Its surface absorbs ultrasonic waves and does not reflect sound.

Ultrasonic distance meters are superior to infrared sensors because they are unaffected by smoke and other factors. Although this system is not completely perfect, it is a good, reliable and economical solution for determining distance and obstacles.

Gadgets connect to all common types of automation and telemetry tools. Applications range from simple analog connections to complex multi-sensor data networks.

• Work principles
• Operating modes
• Applications
• Installation rules
• Detection zones

Description of Microsonic Ultrasonic Sensors

Ultrasonic sensors emit short, high-frequency sound pulses at a certain interval. They travel through the air at the speed of sound. Upon encountering an object, the sound wave is reflected back from it as an echo. The sensor senses this signal and calculates the distance to the object based on the time interval between measuring the signal and receiving the signal echo.

Ultrasonic sensors are ideal for suppressing background noise, as the distance to an object is determined by measuring the flight time of the sound wave, not its intensity. Almost all materials that reflect sound can be used as detection targets, regardless of their color. Even transparent materials and thin films are no problem for ultrasonic sensors. Microsonic's ultrasonic sensors can detect targets at distances from 30 mm to 8 m, while measuring with very high accuracy. Some transducer models are capable of measuring to within 0.18 mm. Ultrasonic sensors can see through dusty air, fog, or toner particles. Even a small coating on the sensor membrane does not affect its operation. The blind zone of the sensor is only 20 mm, and the density of the emitted flux is very low, which makes it possible to use the sensors in completely new applications. Sensors measure the fill level of small bottles on the conveyor, and can even detect the presence of fine threads.

General description of ultrasonic sensors with analog and discrete output.

An ultrasonic sensor is a device consisting of an ultrasonic emitter, an electronic part and, on the opposite side, an output connector or cable. The sensor generates an analog signal proportional to the distance to the object or a discrete signal that changes when the object reaches a predetermined distance.

On the electronic part there is a piezoelectric element that emits ultrasound in the generation mode and converts the received vibrations into electric current in the receive mode. Inside the sensor are control circuits and converters. The electronic circuit measures the transit time of the ultrasound in the medium and converts it into an analog or digital output signal.

There are the following types of sensors:

• devices operating on the principle of signal reflection from an object;
• devices that detect an object located between the receiver and transmitter.

Measurement accuracy depends on the following factors:

• ambient temperature (in this regard, temperature compensation has been introduced);
• humidity of the air in which ultrasound propagates;
• medium pressure.

Since the reflected signal provides the main information about the distance to the object, the characteristics of the surface, along with the angle of incidence of the sound wave, significantly affect the operation of ultrasonic sensors. Sensors work best with highly reflective surfaces: glass, liquids, smooth metal, wood, and plastic. For stable operation of the sensor, it is recommended that surfaces with rough relief be located in a position close to perpendicular to the direction of the beam.
For smooth surfaces, a deviation from the perpendicular direction of the ultrasonic beam by no more than 3 degrees is permissible.

At the place where the sensors are installed, air flow turbulence should be avoided, and the fact of the mutual influence of the sensors should be taken into account when they are located close to each other. Here you can rely on the data in the table given in the "Installation Rules" section.

Examples of using

	Ultrasonic sensors determine the distance to the surface of almost any liquid.			Ultrasonic sensors are great for working with transparent objects.
	Ultrasonic sensors can be used to measure the paint level.			Sensors detect almost all tissues.
	White on white, black on black? Ultrasonic sensors detect objects regardless of the background they are placed against.			Sawdust, gravel or fine sand In measuring the level of such materials, ultrasonic sensors have no competitors.

Operating modes of Microsonic ultrasonic sensors

Object presence sensor mode The ultrasonic sensor in this mode works like a classic proximity sensor (capacitive, optical, etc.). The sensor is triggered when an object approaches the sensor at a distance less than or equal to the specified triggering distance. This mode is used to count the number or determine the presence of an object.		Window mode In this mode, the sensor is triggered only when the object is in a certain zone, set by two values ​​- minimum and maximum. This mode can be used to control the dimensions of products or control the position of objects in various control systems.
In this mode, in contrast to the window mode, the sensor ignores sound waves reflected from objects located closer than the set sensing distance. This allows you to ignore small objects located in the foreground in front of the trigger zone (for example, the neck of a bottle when controlling the filling level of the product in a glass or pet container). In this case, the sensor works as a distance sensor.		To work in this mode, a reflector is required. Any object that reflects sound well (for example, a metal plate) can be used as a reflector. This mode is used to work with objects that reflect sound poorly or objects with complex geometry (when the reflected sound waves do not fall on the sensor surface). In this case, the sensor works as a distance sensor.
In this mode, the sensor generates a signal of 4...20 mA or 0...10 V, proportional to the distance to the object. The sensor can be set to the limits of the operating range, as well as the type of signal - directly or inversely proportional to the distance. Regardless of the operating range and sensor type, the resolution is always 0.025…0.36 mm. In this case, the sensor works as a distance sensor.		Some series of microsonic probes can be used to monitor 2 or more sheets that are accidentally stuck together. This system can be used to detect paper, film, board or foil. The sensor detects the presence of double sheets or no sheets at all. In this case, the sensor works as a position or proximity sensor.
Ultrasonic sensor with digital output (IO-Link) Performs continuous communication at all levels of the system architecture, from the sensor to the upper limit of the operating range. The measured distance is transmitted to the controller as a sequence of bits.		It works on the same principle as the double sheet sensor. Since the internal adhesion of the stickers to the substrate is a connection without a layer of air between them, the sticker sensors must be calibrated to the substrate and to the stickers themselves.
Designed in a fork shape and also works as a one-sided barrier. Used to control movement along a path and provides an analog signal of 0...10 V or 4...20 mA, proportional to the orientation of the edge of the path.

Areas of use

main parameters

Blind spot. Specifies the minimum detection distance. Objects or reflectors should not be placed in the blind zone, as this will lead to incorrect measurements.

Detection range. Represents the maximum detection distance under ideal reflection conditions.

This is a typical working area of ​​the sensor. The sensor can also work at distances up to the maximum range in case of good reflection.

Rules for installing and working with sensors

Ultrasonic sensors can work in any position. However, positions where severe contamination of the sensor surface occurs should be avoided. Drops of water and various deposits on the surface of the sensor may affect operation, but a small layer of dust or paint will not affect operation. To scan objects with a flat and smooth surface, the sensors should be installed at an angle of 90 ±3°. On the other hand, uneven surfaces can be swept at large angles. In terms of ultrasonic transducers, a surface is considered rough when the depth of its roughness is greater than or equal to the ultrasonic wavelength. The sound is then reflected in a diffused form, resulting in a reduced operating range. In the case of rough surfaces, the maximum allowable angle deviation and the maximum possible detection range must be determined empirically. Sound-absorbing materials such as wadding or soft foams will also reduce the operating range. On the other hand, liquid solid materials are very good sound reflectors.

Mounting position and synchronization. Two or more sensors installed side by side can influence each other. To avoid this, the sensors must be installed at a sufficiently large distance or synchronized with each other. The following table shows the minimum mounting distances between non-synchronized sensors.

Mounting distances should be considered as standard values. If objects are placed at an angle, the sound may be reflected to the adjacent sensor. In this case, the minimum mounting distances must be determined empirically.

Some sensors can be synchronized with each other, which allows the use of smaller mounting distances than those indicated in the table. If the ultrasonic sensors are installed at a distance less than those indicated in the table, they should be synchronized with each other, which will allow them to take measurements at the same time.

Most microsonic sensors have built-in timing, which is activated by connecting Pin 5 on the connector. Other sensors require an external clock signal.

Sound redirection. The sound wave can be redirected without significant loss by using a reflective, smooth surface. With optional equipment, the sound can be deflected by 90°. This can be used in special applications.

Accuracy. Absolute accuracy is the discrepancy between the real distance between the sensor and the object and the distance measured by the sensor. Accuracy depends on the reflective properties of the object and the physical phenomena that affect the speed of sound in air. Objects with low reflectivity or with surface irregularities exceeding the ultrasonic wavelength have a negative effect on accuracy. This cannot be determined exactly, but as a rule, the error of several wavelengths of the supersonic frequency used is accepted.

Air temperature. The air temperature (0.17%/K) has the biggest influence on the speed of sound and accuracy, so most microsonic ultrasonic transducers are temperature compensated. It is even better to make a comparative measurement over a specific distance to determine the effect of temperature. For example, the pico series sensors are specially designed for such comparative measurements. The accuracy of temperature-compensated sensors is up to ±1%.

Atmosphere pressure. The speed of sound over a wide range is independent of air pressure. microsonic has developed special sensors for distance measurement under overpressure conditions up to 6 bar.

Relative Humidity. Unlike temperature, the relative humidity of the air has practically no effect on the measurement accuracy.

Positioning stability R. Positioning stability, or reproducibility, describes the deviation of the measured distance under the same conditions over a specific period. Positioning stability of microsonic sensors is less than ±0.15%.

Method for determining the detection zone of Microsonic ultrasonic sensors

The most important criterion when choosing an ultrasonic transducer is its detection range and associated 3D detection area. In ultrasonic measurement, various standard reflectors are introduced from the outside into the detection zone of the sensor at a distance at which these reflectors begin to be detected by the sensor. Objects can be entered into the detection zone from any direction.

red areas determine the dimensions of a thin round rod (10 or 27 mm, depending on the type of sensor), which characterizes the working range of the sensor.

To define blue areas: a plate (500×500 mm) is installed in the path of the ultrasound beam. This applies the optimal angle between the plate and the sensor. Thus, this indicates the maximum detection area of ​​the sensor. Outside the blue area, the object is no longer detectable.

A reflector with less reflective properties than a round rod may be detected in an area smaller than the red area. In turn, the reflector with the best properties will be determined in the area between the red and blue areas. The blind zone of a sensor determines its smallest acceptable detection range. Objects or reflectors should not be placed in the blind area as this will result in incorrect measurements.

Operating ranges shown in the diagram. In these ranges, the sensor will be guaranteed to detect the presence of conventional reflectors. Also, the diagram shows the areas of detection by the sensor of reflectors with good reflective properties. The maximum detection range is always greater than the operating range. The diagrams are based on 20 °C, 50% relative humidity and atmospheric pressure. Specific detection zones depend on the type of sensor, and they can be viewed by going to the section of the corresponding sensor, in the "Detection zones" tab.

These symbols in the technical parameters define
operating range of Microsonic ultrasonic sensors

Attenuation of sound in air depend on the temperature and pressure of the air, as well as its relative humidity. The physical parameters are related and have a different effect at different ultrasound frequencies. For simplicity, we can say that air attenuation increases with increasing temperature and increasing humidity. This reduces the operating range of the sensor.

At lower relative humidity and lower temperature, air attenuation decreases and the working area increases accordingly.

The reduction in operating range is mainly compensated for by the sensor settings. And at temperatures below 0 °C, some sensors can operate at distances up to twice the distances given here.

As the pressure increases, the attenuation in air decreases significantly. This aspect must be taken into account when using the sensor in a pressurized environment. Sound propagation is impossible in a vacuum.