Sonar Sensors - Basics

Ultrasonic references the frequencies of sound that are above the range that the human can hear. A sonar uses these ultrasonic sounds to find the place of the robot in the environment, using a technique called echolocation. Echolocation works in this way: a sonar has an emitter and a receiver. The emitter sends the ultrasonic sounds, which bounces on the surface of the objects in the environment and comes back to the receiver. The amount of time since the emission (time-of-flight) and reception of the sounds is used to calculate the distance.

There are, however, many things that have to be considered when working with sonar. The key point that has to be addressed is that the direction of the bounce depends on many variables, (angle of incidence on the surface, surface smoothness, etc), and some sounds that bounce from a surface can never come back to the sonar even or come after bouncing from many different surfaces (specular reflection). To deal with this, some solutions that can be used are:

  • Smooth the surfaces of the objects of the environment
  • Use multiple sonar sensors sensing at different directions
  • Use more processing power

Other problems include:

  • Foreshorting: sonars work on a certain cone, and the reflection on a non-perpendicular surface may create an error where one side of the cone receives measurements earlier than the other.
  • Cross-talk: when dealing with rig configurations of sonars, some of the waves reflected because of the specular reflection may arrive to another sonar receiver, causing false readings.

In order to deal with specular reflection easily, one can use instead laser sensors at the cost of more power and money 20210602191021.

Notes References

20210523205908 Robotics Complex Sensors - Basics

20210514183815 INDEX - Robotics

20210602191021 Laser Sensors - Basics

References

(Matariâc 2007) (Murphy 2000)

Matariâc, Maja J. 2007. The Robotics Primer. Intelligent Robotics and Autonomous Agents Series. Cambridge, Mass: The MIT Press.

Murphy, Robin. 2000. Introduction to AI Robotics. Intelligent Robotics and Autonomous Agents. Cambridge, Mass: MIT Press.