Ultrasonic sensors are widely used for distance measurement, object detection, and ranging. They emit ultrasonic waves and measure the time taken for the waves to return after hitting an object or surface. The distance is then calculated using the speed of sound and the time taken. Ultrasonic sensors can detect colored, shiny, or transparent surfaces that can be challenging for optical sensor technologies.
Sensor Positioning and Orientation
When mounting ultrasonic sensors, there are several factors to consider. The sensors can be incorporated and operated in any position, but positions that could lead to severe soiling of the sensor surfaces should be avoided. Drops of water and severe deposits on the surface of the transducer can impair the function. However, small dust deposits and splashes of paint do not affect the function.
For scanning objects with flat and smooth surfaces, the sensors should be mounted at an angle of 90 ± 3° to the surface. This ensures that the ultrasonic waves are reflected back to the sensor at the optimal angle, maximizing the detection range and accuracy. On the other hand, rough surfaces can cope with much larger angular deviations, as the sound is reflected in a scattered fashion, which can lead to a shortening of the operating range. In the case of rough surfaces, the maximum permissible angular deviation and the maximum possible detection range should be determined by way of trials.
Environmental Factors and Interference
Sound-absorbent materials, such as cotton wool or soft foams, can reduce the operating range of ultrasonic sensors. These materials can dampen the ultrasonic waves, preventing them from being reflected back to the sensor. On the other hand, liquids and solid materials are very good reflectors of sound, which can enhance the sensor’s performance.
If two or more sensors are mounted too close to one another, they can influence each other, leading to interference and inaccurate measurements. To avoid this, either the mounting spacing must be sufficiently large, or the sensors must be synchronized with one another. The following table lists the minimum mounting distances between unsynchronized sensors:
| Operating Range | Minimum Mounting Distance |
|---|---|
| 0.07 m | ≥ 0.25 m |
| 0.15 m | ≥ 0.25 m |
| 0.24 m | ≥ 0.25 m |
| 0.25 m | ≥ 0.35 m |
| 0.35 m | ≥ 0.40 m |
| 0.7 m | ≥ 0.70 m |
| 1.0 m | ≥ 0.70 m |
| 1.3 m | ≥ 1.10 m |
| 3.4 m | ≥ 2.00 m |
| 6.0 m | ≥ 4.00 m |
Measurement Uncertainty
When using ultrasonic sensors for distance measurement, it is important to consider the uncertainty of the measurement system. This can be determined by taking multiple distance measurements and calculating the standard deviation of the measurements. For example, in one experiment, 334 distance measurements were taken with the panel staged 25 cm away from the sensor. The mean of the 334 samples was 25 cm, and the estimated uncertainty was ±0 cm, as 68% of the values were within that range.
The uncertainty of ultrasonic distance measurements can be affected by various factors, such as temperature, humidity, and the surface properties of the target object. To minimize the uncertainty, it is recommended to:
- Calibrate the sensors regularly to ensure accurate measurements.
- Maintain a stable environmental temperature and humidity, as changes in these factors can affect the speed of sound and the sensor’s performance.
- Use targets with consistent surface properties, as rough or irregular surfaces can scatter the ultrasonic waves and introduce measurement errors.
- Perform multiple measurements and calculate the average or median value to reduce the impact of random errors.
Advanced Techniques and Applications
Ultrasonic sensors can be used in a wide range of applications beyond simple distance measurement, such as:
- Obstacle Avoidance: Ultrasonic sensors can be used in robotic systems to detect and avoid obstacles, enabling autonomous navigation.
- Level Sensing: Ultrasonic sensors can be used to measure the level of liquids or granular materials in tanks or silos, providing valuable data for process control and inventory management.
- Structural Health Monitoring: Ultrasonic sensors can be used to detect changes in the structural integrity of buildings, bridges, and other infrastructure, enabling early detection of potential failures.
- Gesture Recognition: Ultrasonic sensors can be used to detect and interpret human gestures, enabling intuitive user interfaces for various applications, such as smart home control and gaming.
To further enhance the performance and capabilities of ultrasonic sensors, advanced techniques such as sensor fusion, signal processing, and machine learning can be employed. By combining ultrasonic sensors with other sensing modalities, such as vision or inertial measurement units, the accuracy and reliability of the overall system can be improved. Additionally, advanced signal processing algorithms and machine learning models can be used to extract more detailed information from the sensor data, enabling more sophisticated applications.
Conclusion
Ultrasonic sensors are versatile and can be used for a variety of applications, including distance measurement, object detection, and ranging. When mounting ultrasonic sensors, it is important to consider the surface properties of the objects being scanned, the mounting spacing and synchronization of the sensors, and the uncertainty of the measurement system. By following best practices and leveraging advanced techniques, ultrasonic sensors can be effectively integrated into a wide range of systems and applications.
References
- Ultrasonic Sensors Enabling Early Detection of Emergency Trends in Structural Health Monitoring of Bridges, Lukasz Oleszek, Pawel Piszczek, and Anna Oleszek, Sensors, 2021, 21, 2591.
- Product Detection and Ranging Using Ultrasonic Sensors, DigiKey, 2022-01-18.
- Installation instructions for ultrasonic sensors, microsonic, 2022-01-18.
- Lab 4 Ultrasonic Sensors, ISAT 300 Spring Semester, 2022 Section, James Madison University, 2022-01-18.
- Measuring within a range ultrasonic sensors, Arduino Forum, 2020-05-28.
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