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Ultrasonic Sensor : Working Principle and Applications

Updated: Mar 29

What is ultrasonic sensor ?

An ultrasonic sensor is an instrument or an electronic device that measures the distance to target object using ultrasonic sound waves. It ultrasonic sensor uses a transducer for sending and receiving the ultrasonic pulses which delivers us information about proximity of an object. An ultrasonic sensor transforms the sound reflected to an electric signal. Ultrasonic waves would travel faster compared to the speed of sound which is audible to humans.

Ultrasonic distance sensor
Ultrasonic distance sensor

The ultrasonic sensor has two components namely,

  • transmitter

  • receiver

Transmitter uses piezoelectric crystals, the transmitter emits the sound. Receiver finds the sound after it is traveled to and from the target.

For calculating the distance between the sensor and object, sensor measures the time it takes for the transmitter to emit the sound and to its contact with receiver.

D = (T*C)/2

where D = distance, T = time, C = speed of the sound

Ultrasonic sensors are used mainly as proximity sensors. Ultrasonic sensors are primarily found in anti-collision safety systems, automobile self-parking technology, robotic obstacle detection system and manufacturing system.

Ultrasonic distance measurement module
Ultrasonic distance measurement module

Level sensors to detect, monitor and regulate the liquid levels in closed containers. It highly helps the medical industry to produce the internal organ images, to identify tumors, make sure the babies health in womb. Upto 4.5m away ultrasonic sensors can measure the short distance and long distance accurately without contacting the item that is targeted. This is mainly useful in apps such as obstacle avoidance systems in robotics or autonomous vehicles. This is highly suitable in projects finding solutions using ultrasonic sensors technology with budget constraints.

Principle of ultrasonic sensors

The fundamental working principle of ultrasonic sensor is to measure the time it takes for the signal sent by a transmitter and sent back or propagated back to the receiver. It is evident from the name ultrasonic sensor that it operates on the ultrasonic frequencies. Ultrasonic frequencies ranges is beyond our audible sound to humans and these frequencies are greater than 20 kilo Hertz. Ultrasonic sensor is versatile in sensor technology and are used significantly in many industrial applications. There re various types of objects that can detected such as solids, liquids, granules and powder. They detect the transparent objects or shiny objects, as well as objects for which the color changes.

How does ultrasonic sensor work ?

Ultrasonic sensor is an electronic instrument which measures the distance to a targeted object by the emission of ultrasonic sound waves and converting the reflected sound into the electrical signals. A separate sound emitters and receivers used by some kind of senors, it is viable to combine both the functions into single device by using an ultrasonic element to switch between sending the signals and receiving the signals in a continuous cycle. The transmitter module transmits an ultrasonic sound. If an object is present in-front of the ultrasonic sensor, then this transmitted ultrasonic sound will be propagated or reflected back.

The sound reflected will be received by the receiver of the same module. Ultrasonic signal is reproduced by a wave at an angle of 30 degree. To achieve the maximum accuracy, external objects which come under this measurement angle will interfere to determine the distance to the object targeted.

The sensing sound reflection varies with respect to the configuration namely,

  • Flat objects - Liquids, sheets of plastic and box

  • Column objects - bottle, human body and can

  • Granular objects - rock, coke, ores, coal, plastic pellet

Usage of ultrasonic sensors

With micro-controllers like ARM, PIC, Beagle board, Arduino, Raspberry Pi, Ultrasonic sensor proximity level sensors and distance sensors are employed. Ultrasonic sensors send sound waves in the target direction and calculate its distance by measuring the time it takes for the waves to bounce back to the ultrasonic sensors.

Pins in ultrasonic sensor

  • Vcc - Power supply +5V

  • Gnd - Common ground

  • Trigger Pin - to start the sensor

  • Echo pin - to receive the signal

4 pins of ultrasonic sensor
4 pins of ultrasonic sensor

How to avoid interference ?

In an application, when multiple sensors are employed, it is necessary to connect them in such a way that problems such as cross-talk and other interference are avoided. It is vital keep front-side of the ultrasonic transducer clear to avoid interference with ultrasonic signal from sensor.

Advantage of ultrasonic sensors

  • Ultrasonic sensors are perfect way for measuring distance, speed, and position of the target objects. They provide great accuracy compared to the technologies that were used traditionally such as laser of infrared sensors.

  • Ultrasonic waves are generated from a transducer which emits high frequency sound waves that travels faster than the speed of light due to their high frequency range(kilo Hz - frequency range of ultrasonics).

  • These kind of sensors enable manufacturing engineers to detect the objects over wide ranges with minimum amount of complexity. While setting up certain systems, objects greater than 200m away distance can also be detected accurately.

  • Ultrasonic sensor do not depend on visible light like other types of technology so that can be used either indoors or outdoors without worrying about the environmental conditions and situations that affect the perfect levels - it can be perfect to be used in dark areas or low-light areas or conditions where visibility would otherwise be compromised by the techniques using regular sensing.

  • Ultrasonic sensors have self- diagnostics capabilities that allows user to quickly access the status of the system by checking the faults, error codes, and reading calibration parameters thus facilitates the easy maintenance.

  • Without the need of the external power source, these type of tools operate more reliably with less downtime which leads to improved levels of productivity for applications depending more on it usage from robotics automation industrial monitoring security surveillance activities.

Applications of ultrasonic sensors

Ultrasonic sensors are versatile devices that use sound waves with frequencies above the range of human hearing to measure distance, detect objects, or monitor various parameters. The following are some typical uses of ultrasonic sensors:

Distance Measurement

  • Ultrasonic sensors are frequently used for non-contact distance measurement. Ultrasonic waves are emitted by the sensor, and the sensor measures the duration it takes for these waves to bounce off an object and come back to the sensor. After obtaining this information, it is then utilized to determine the distance between the sensor and the object.

Parking Assistance Systems

  • Ultrasonic sensors are integrated into parking assistance systems in automobiles. They help drivers by providing audible or visual alerts as they approach obstacles during parking.

Object Detection and Avoidance

  • In robotics and automation, ultrasonic sensors are used to detect the presence of objects in the path of a moving device. This is commonly seen in robots or automated guided vehicles (AGVs) to avoid collisions.

Level Measurement in Tanks

  • Ultrasonic sensors can be employed to measure the level of liquid in tanks. They calculate the distance from the sensor to the liquid surface and provide accurate level measurements.

Proximity Sensors

  • Ultrasonic sensors serve as proximity sensors in various applications, including touch-less faucets, automatic soap dispensers, and other hands-free devices. They detect the presence of a person or object and trigger the corresponding action.

Traffic Management

  • Ultrasonic sensors are used in traffic management systems to monitor vehicle and pedestrian movement at intersections. They can help optimize traffic signal timings based on real-time data.

Security Systems

  • Ultrasonic sensors are employed in security systems for intrusion detection. They can sense movement or the presence of an object in a protected area and trigger alarms.

Medical Imaging

  • In medical applications, ultrasonic sensors are used in ultrasound imaging devices to generate images of internal body structures. They are safe and widely used for diagnostic purposes.

Industrial Applications

  • Ultrasonic sensors find applications in industries for quality control, material inspection, and process monitoring. They can be used to detect flaws or irregularities in materials.

Animal Detection and Monitoring

  • Ultrasonic sensors are used in wildlife monitoring to detect the presence of animals. They are also employed in pest control systems to deter or repel animals.

Limitations of ultrasonic sensors

While ultrasonic sensors have a wide range of applications, they also come with certain limitations that should be considered in specific use cases. Here are some common limitations of ultrasonic sensors:

Limited Range

  • Ultrasonic sensors typically have a limited sensing range. Beyond a certain distance, the accuracy and reliability of measurements can decrease.

Interference from Ambient Noise

  • Ultrasonic sensors may be affected by ambient noise in the environment, such as other ultrasonic sources or loud machinery. This interference can impact the sensor's ability to accurately detect and measure objects.

Absorption and Reflection

  • Certain materials may absorb or reflect ultrasonic waves differently, affecting the sensor's performance. Soft and porous materials, for example, may absorb the waves, leading to inaccurate distance measurements.

Temperature and Humidity Effects

  • Extreme temperatures and humidity levels can impact the speed of sound, affecting the accuracy of distance measurements. Sensors may need compensation mechanisms to account for these environmental factors.

Limited Angular Coverage

  • Ultrasonic sensors typically have a narrow beam angle. This means they may not be able to detect objects outside of their specified angle, leading to blind spots.

Multiple Object Detection Challenges

  • When multiple objects are present within the sensor's detection range, it can be challenging to accurately distinguish between them. This can result in confusion, especially if the objects are close together.

Inability to Detect Transparent or Soft Objects

  • Ultrasonic sensors may struggle to detect transparent or soft objects that do not reflect or absorb ultrasonic waves effectively. This limitation can impact their effectiveness in certain applications.

Limited Resolution

  • The resolution of ultrasonic sensors may not be as high as some other sensing technologies. This limitation can affect their ability to detect small or closely spaced objects.

Limited Accuracy in Air

  • Ultrasonic sensors are most accurate in air, and their performance may vary when used in other mediums, such as water or liquids.

Power Consumption

  • Depending on the design and operation mode, ultrasonic sensors can consume more power compared to some other sensor types. This consideration is important in battery-powered or energy-efficient applications.

Despite these limitations, ultrasonic sensors remain valuable tools in many applications. Careful consideration of these constraints is necessary to ensure optimal performance and reliability in specific use cases. In some scenarios, a combination of different sensor types may be employed to overcome these limitations.

Exploring Sensor Technologies: Understanding Different Types

The relationship between ultrasonic sensors, thermistors, accelerometers, motion sensors, current transducers, and inductive sensors lies in their respective functionalities and applications within the realm of sensors and electronic instrumentation. These devices serve different purposes and are used in various fields for sensing and measuring different physical phenomena. Here's a brief overview of each sensor and how they relate:

Ultrasonic Sensor

  • Measures distance by emitting ultrasonic waves and calculating the time it takes for the waves to bounce back after hitting an object.

  • Often used in applications such as proximity detection, obstacle avoidance, and distance measurement.


  • A temperature sensor that exhibits a change in electrical resistance in response to temperature variations.

  • Used to measure and monitor temperature in a variety of applications, including climate control, industrial processes, and electronic devices.


  • Measuring acceleration is typically done in three axes: X, Y, and Z.

  • Used for detecting changes in velocity, orientation, and tilt in applications such as motion sensing, navigation systems, and impact detection.

Motion Sensor

  • Encompasses various sensors, including accelerometers, gyroscopes, and sometimes magnetometers.

  • Detects and measures motion in its different forms, such as acceleration, rotation, and magnetic field changes.

  • Used in applications like gaming controllers, security systems, and wearable devices.

Current Transducer

  • Measures the electric current flowing through a conductor and transforms it into an output signal.

  • Used in power monitoring, motor control, and energy management systems.

Inductive Sensor

  • Detects the presence or absence of an object based on changes in inductance.

  • Often used in industrial automation for proximity sensing, object detection, and position control.

In summary, while these sensors serve distinct purposes, they can also complement each other in certain applications. For example, a system might use an ultrasonic sensor for distance measurement, a thermistor for temperature monitoring, an accelerometer for motion detection, a current transducer for power monitoring, and an inductive sensor for proximity sensing. The specific combination and integration of these sensors depend on the requirements of the application or system being developed.


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