Ultrasonic sensors are an indispensable technology for manufacturing industries and give companies a competitive edge by streamlining processes. When selecting an ultrasonic sensor for, there are four main characteristics that must be considered: range, resolution, and selectivity. Range is the set of distances between which the sensor can make accurate measurements. This can vary from 30mm-8000mm. Resolution is the smallest measurable change in distance of the target body and background that the sensor can detect. Selectivity is the ability to distinguish between the target object and extraneous materials. This paper will examine the basic workings of an ultrasonic sensor that influence its range, resolution, and selectivity. We will explore how the sensor’s acoustical, electrical, and physical qualities determine the sensor’s capabilities.
The ultrasonic sensor is both a transmitter and receiver. It emits an ultrasound signal at about 40kHz, a frequency undetectable by the human ear. A CPU measures how long the signal takes to travel from the sensor, bounce off, and return. The CPU processes the data received, including how far away the object is from the sensor and its shape. Different types of sensors have differ in their methods of transmitting the ultrasonic signal, but are all founded on the same electrical mechanisms to work.
Inside an ultrasonic sensor are piezoelectric, quartz crystals. These crystals vibrate and create sound waves when an electrical current is applied. The crystals can also emit electrical currents when sound waves hit them, allowing the device to both absorb and emit sound waves. This form of sending and receiving acoustic signals is known as the piezoelectric effect.
For sound to be received by the sensor, the sound path must be perpendicular to the device. This reduces the chance that external noise sources will be picked up. The ultrasonic sensor is not completely insusceptible to noise disturbance, however. Strong winds or air currents can deflect or scatter the sound waves such that the sensor fails to receive an echo. Furthermore, the sensor is limited by the reflection of sound. For example, the side walls of a tank may interfere with a fill-level ultrasonic sensor placed too close to it. This makes the placement of the sensor very important for accurate readings.
The device is customizable for different ranges and sensitivities and can be connected to other sensors to accomplish a task. It can be programmed to accomplish varied tasks, from high speed object detection to liquid-level measurement. They have also proved advantageous in functions such as:
- distance measurement
- determining dimensions of an object (height, width, length)
- anti-collision detection
Ultrasonic sensors can work in temperatures as high as 80ºC. However, for each degree Kelvin change in temperature, the speed of sound changes by 0.17% and must be accounted for when processing the signal.
Some sensors are made with a steel housing that can withstand high pressure and steam jet cleaning. Steel head sensors are fully encapsulated, making them suitable for high pressure and rugged and environments like food processing.
An Indispensable Technology
The precision of this technology provides additional safety to manufacturing facilities. The sensor is not limited by dirt or fog that would limit a light-dependent sensor. It can emit and receive signals almost simultaneously, reducing the need for multiple sensors to accomplish the same task. Ultrasonic sensors function well even with sound-absorbing materials such as wadding or rubber foam. They can detect clear, shiny and non-reflective objects, and even minuscule targets like splices in i.e. paper, textiles, or sheet metal. But their capabilities spread far wider. The design and durability of the ultrasonic sensor makes it an in indispensable technology for precise manufacturing processes in the most difficult environmental conditions.
Ariadna is a junior at Cornell University studying Materials Science and Engineering. She is a staff writer for The Cornell Daily Sun and a member of the Nanoscale Materials for Energy Lab.