Ultrasonic sensors, also called ultrasonic rangefinders, are among the sensors to measure distances without contact. These sensors are particularly complementary infrared sensors, since, unlike them, they can monitor a wide conical. They are relatively well represented in the robotics community because of their good price / efficiency ratio. So, there are an increasing number of suppliers, with various models for various uses.
The ultrasonic range finder is based on measuring the time elapsed between emission and returning the echo. When the ultrasonic wave is emitted it spreads with speed of sound in the surrounding air, to 342 m / sec. Once an obstacle is encountered, the echo returns to the transducer which then calculates the elapsed time between transmission and receiving of the wave. These waves can not be heard by the human ear.
All rangefinders work the same way, regardless of the manufacturer. The differences will be within the frequencies transmitted, and the conical diffraction of the wave. Depending on the model, the ultrasonic sensors will be more or less accurate, and will have a greater or lesser extent. Their prices vary accordingly. Generally, the higher is the connical end, the sensor will be more precise, it will be more expensive. But as we shall see, some manufacturers have things differently