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Ultrasonic wave is a frequency higher than 20KHz (Hertz) of sound waves, its good directionality, strong reflection ability,
easy to obtain a more concentrated sound energy, in the water distance than the air, can be used for ranging, speed
measurement, cleaning, welding, gravel, sterilization and so on. It has many applications in medicine, military, industry
and agriculture. Ultrasound gets its name because its lower frequency exceeds the upper limit of human hearing.
The principle of ultrasonic ranging is to use the propagation speed of ultrasonic wave in the air as known, measure the
time when the sound wave is reflected back to the obstacle after launch, and calculate the actual distance from the
transmitting point to the obstacle according to the time difference between transmission and reception. First, the
ultrasonic transmitter emits ultrasonic waves in a certain direction, starts timing at the same time of transmission,
ultrasonic waves propagate in the air, encounter obstacles on the way to immediately return, and the ultrasonic receiver
receives the reflected waves immediately stop timing. Ultrasonic propagation speed in the air is C=340m/s, according
to the time recorded by the timer T seconds, you can calculate the distance between the launching point and the obstacle
L, that is: L= C×T /2. This is called the time difference method.
Since ultrasound is also a kind of sound wave, its sound speed C is related to temperature, Table 1 lists the sound speed
at several different temperatures. When in use, if the temperature changes little, it can be considered that the speed of
sound is basically unchanged. If the range accuracy is very high, it should be corrected by means of temperature compensation.
Ultrasonic and radar are very similar, is through the way of reflection for accurate ranging, although the ranging accuracy
is worse than radar, but the ranging accuracy of ultrasonic is very high, can reach the centimeter level.
The use of ultrasound to do the target location is not many, there are two typical applications
1. Ultrasonic beacon, establish a scheme similar to beacon, broadcast, listen to the radio through the headset of the
mobile phone to achieve positioning, the accuracy can reach the centimeter level;
2, ultrasonic robot positioning, on the robot jacket
https://www.seeedstudio.com/Marvelmind-Indoor-Navigation-System-Starter-Set-HW-915-868MHz-p-4296.html
High precise(±2cm) indoor tracking system for robot and human positioning.
Ultrasonic, ToF, and trilateration technology to measure the distance.
Station beacon installed on the walls or ceilings and mobile beacon installed on the human body and robots.
Beacons coverage radius up to 50 meters. beacons coverage radius up to 50 meters.
4 station beacons, 1 mobile beacon and 1 modem. The modem can support up to 250 beacons.
