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What is an ultrasonic sensor?

What is an ultrasonic sensor, how does it work and what are its varied applications today?

Ultrasonic sensors are used to send and get ultrasonic pulses that in turn share information about an object’s proximity

Dec 24, 2021    By Team YoungWonks *

What is an ultrasonic sensor? In a previous blog post (https://www.youngwonks.com/blog/What-is-a-sensor), we briefly looked at the different types of sensors. In this blog post, we shall focus on one of them - the ultrasonic sensor. So what is an ultrasonic sensor, how does it work, where is it used and what are its advantages and disadvantages? Read on to know more…

 

What is an ultrasonic sensor?

An ultrasonic sensor is an electronic device that can measure the distance of a target object by sending out ultrasonic sound waves, and converting the reflected sound into an electrical signal. Basically, such a sensor uses a transducer to send and get ultrasonic pulses that in turn send back information about an object’s proximity. It is important to note that these ultrasonic waves travel faster than audible sound; i.e. these sensors send out sound waves at frequencies above the range of human hearing. 

Ultrasonic sensors have two key components: one is the transmitter that emits the sound using piezoelectric crystals and the other is the receiver that receives the sound after it has traveled to and from the target.

 

 How does an ultrasonic sensor work?

As mentioned earlier, an ultrasonic sensor sends out a high-frequency sound wave to begin with; here the transducer acts as a microphone to send the ultrasonic pulse / sound and receive the echo. The sensor then deduces the distance to the object by measuring time lapses between the sending and receiving of the ultrasonic pulse. 

In other words, it calculates the distance by measuring the time it takes between the emission of the sound by the transmitter to its contact with the receiver. The formula for this calculation is D = ½ T x C (where D is the distance, T is the time, and C is the speed of sound ~ 343 meters/second). For example, if an  ultrasonic sensor is aimed at a toy and it takes 0.025 seconds for the sound to bounce back, the distance between the ultrasonic sensor and the toy would be:

D = 0.5 x 0.025 x 343 or about 4.2875 meters.

Ultrasonic sensors are thus of great use when it comes to detecting objects. In fact, ultrasonic sensors can detect objects irrespective of their color, surface, or material, unless the material is very soft like wool in which case the sensor could fail to detect it as wool can absorb sound. Even for detecting transparent and not easily visible objects, ultrasonic sensors can be relied upon. 

However, to ensure the smooth functioning of a sensor, it is important to steer clear of anything that can interfere. For instance, if one is using multiple sensors in an application, one needs to connect them in such a way that crosstalk or any other interference is avoided. It is also important to keep the face of the ultrasonic transducer clear of any obstructions; this will prevent the disruption of the ultrasonic signals coming from the sensor. Some of the common obstructions to watch out for include dirt/ dust, snow/ ice and any other condensation. 

 

Applications of ultrasonic sensors 

Ultrasonic sensors used today in several industrial and consumer applications. Their low cost, simple functioning and sturdy build make them a good bet for new products or services that need presence detection or distance measurement. Plus, the fact that they also allow for changes in both their hardware and software configurations makes them even more useful and versatile. 

The most common of ultrasonic sensor applications would be object detection or person detection. As proximity sensors,  ultrasonic sensors are very useful in anti-collision detection for vehicles, presence detection, box sorting, etc. IoT ultrasonic sensors are used for non-contact detection of solid and liquid objects. Another popular use is as level sensors; they are often used for liquid level sensing, as these sensors can detect liquids of any color or opacity in a non-contact fashion (without even coming in contact with them).

A more creative way of using ultrasonic sensors would be to use the one-way functionality of ultrasonic transmitters and receivers separately. So an ultrasonic transmitter could use its emitters to transmit / send out sounds and, say, scare off birds, and the ultrasonic receiver could be used for noise detection.

 

Shared below are some major uses of ultrasonic sensors:

  • Presence detection
  • Sorting boxes using a ultrasonic monitoring system powered by multiple transducers
  • Bottle counting on drink filling machines
  • Pallet detection with forklifts
  • People detection
  • Profiling using ultrasonic systems
  • Vehicle detection for car wash and automotive assembly
  • Liquid level control / tank level control
  • Loop control
  • Tension control
  • Robotic sensing
  • Stacking height control
  • Detecting thread or wire breaks

 

 Strengths of ultrasonic sensors

Not affected by object color

The color of the object being detected has no impact on the functioning of an ultrasonic sensor. So the object could be any color, even translucent or transparent - think water or glass - and an ultrasonic sensor would be able to detect it efficiently.

Greater flexibility

Ultrasonic sensors come with minimum and maximum ranges that are quite flexible. Today, most ultrasonic sensors can detect as near as a few centimeters and go up to as far as five meters (approx). Specially configured modules can even detect up to nearly 20 meters.

Highly reliable

Ultrasonic sensors have been around for decades and over the years, this ultrasonic technology has matured well. Today, it is very reliable and can be trusted to produce consistent results.

Higher precision

Ultrasonic sensors offer relatively precise measurements, within 1% typically and even more precision if desired.

Better capabilities 

Ultrasonic sensors can take many measurements per second, thus affording quick refresh rates.

Low on cost

With not many raw materials required, they are usually easy on the pocket.

Resistance to noise 

Ultrasonic sensors are resistant to electrically noisy environments and most acoustic noise, especially when they use modules fitted with encoded chirps.

 

Limitations of ultrasonic sensors

Not immune to temperature changes in the environment 

Since the speed of sound can change with changes in temperature and humidity, environmental conditions can interfere with the measurements taken by ultrasonic sensors.

No additional info other object detection

Ultrasonic sensors only detect the object and the distance but do not share more information on the features of the object - be it shape, color or even its location in the sensing area. 

Not ideal for small, embedded projects

Ultrasonic sensors may be small enough to be easily integrated into cars or industrial applications, but they are still too big for tiny, embedded projects.

Need regular maintenance

Ultrasonic sensors can get dirty, wet, or frozen, which can in turn affect their functioning. So regular maintenance is essential to avoid erratic or non-functional behavior.

Cannot be used in a vacuum 

Since ultrasonic sensors rely on emitting sounds and their bouncing back, they do not work in a vacuum (since sound in turn needs a medium of some type to travel).

 

*Contributors: Written by Vidya Prabhu; Lead image by: Abhishek Aggarwal

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