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After having read the introductions of the Wikipedia articles about "sonar" and "ultrasonic sensor", it is still not clear to me what the differences between the two are. In the context of robotics, is there any difference between these two sensors (terms)?

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Ultrasonic means above audible range, Sonar may be within the audible range In my opinion the ultrasonic being more precise also may come with higher price.

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    $\begingroup$ Welcome to Robotics Naguesh. Thanks for your answer but we are looking for comprehensive answers that provide some explanation and context. Very short answers cannot do this, so please edit your answer to explain why it is right, ideally with citations. Answers that don't include explanations may be removed. $\endgroup$
    – N. Staub
    Sep 3, 2018 at 10:21
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Sonar, as used in robotics means having an ultrasonic emitter and and ultrasonic receiver. There are also some sonar with a single emitter/receiver.

However, they all use ultrasonic sound waves to sense the distance to an object. Well, actually they really sense the time between the emission of the ultrasonic wave and the reception of it, which is proportional to the distance to the object.

I am sure that there are sensors that are true ultrasonic sensors in that they are used only to detect ultrasonic "sounds." For example, if you wanted to detect some of the sounds made by marine mammals, you need to be able to detect ultrasonic waves. I might call this an ultrasonic sensor.

However, since I don't study marine animals, I use "sonar" and "ultrasonic sensor" to mean the same thing.

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The main difference is, SONAR (originally an acronym for SOund Navigation And Ranging) is used underwater and uses low frequency sounds (100-500Hz) as well as high frequency sounds (ultrasound, etc).

Ultrasonic sensors are used mostly over the terrain and limited to high frequency sounds.

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In terms of functionality, an ultrasonic sensor performs a single distance measurement in a given direction (strictly speaking, such a sensor emits a sound cone, the angle of which depends on how the sensor is implemented).

A SONAR, on the other hand, seems to generally refer to a device that performs aggregated range measurements, i.e., a 360 degree scan combining many single distance measurements.

Similarly, a LIDAR combines many single laser distance measurements.

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SONAR was to find submarines under water. It used low frequency sound that was readily conducted by water. The sound was audible and could be heard. Similar to RADAR with SONAR the sound reflected from the submarine and the delay in the return allowed to determine the range or distance to the target. The emitter and microphones were directional and allow you to determine the bearing or direction to the target.

The low frequency sound did not work well in air and the emitter and microphones were not very directional. so newer versions where developed that used high frequency or ultrasonic sounds, beyond the frequencies humans can hear. These were more directional and worked better in air that older audible sonar.

More solid state emitters, microphones, and microprocessors have greatly lowered the cost making them common for small mobile robots to detect obstacles.

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