Ultrasonic sensor

The sensor device that converts electrical energy into ultrasonic waves (mechanical vibration with a frequency greater than 20 kHz), is called the ultrasound transducer. The principle of operation of the ultrasonic sensor is similar to radar and assesses whether objectives based on the interpretation of the signal reflected from it. Taking the speed of sound for a constant value by using an ultrasonic sensor is determined by the distance to the object corresponding to the time interval between sending the signal and the return of its echo.



Ultrasonic sensor
The ultrasonic sensor has a number of features that define the scope of this unit. Among them expressed orientation signals a small range, low speed of wave propagation. The main advantage of ultrasonic sensors – a relatively low price.
The basis of the ultrasonic sensor is a transducer that combines the active element and the diaphragm. The converter operates as a transmitter and as a receiver. Active element generates a short pulse and receives its echo from the obstacle. It is made of a piezoelectric material. Aluminum diaphragm is the contact surface of the sensor and determine its acoustic characteristics. The transmitter has an elastic base, which absorbs vibrations.
Upon receipt of an external signal causes the active element to vibrate the diaphragm, which sends ultrasonic pulses into the space. When meeting an obstacle pulses are reflected back to the transducer and create vibrations of the active element, which is removed from the electrical signal.
The main technical characteristics of the ultrasonic sensor is the detection range of obstacles, signal frequency, speed (the speed of the definition of obstruction).
Manufacturers do not indicate the value of such an important figure as the viewing angle. In the ultrasonic sensor angle is determined by the frequency of the pulses, as well as the size and shape of the converter. Thus, the higher the pulse frequency, the narrower the angle sensor. Ultrasonic sensor with a pulse frequency of 40 kHz has a sufficiently large viewing angle.
Despite the obvious advantages, the ultrasonic sensor has severe functional limitations. Operation of the sensor and thus the accuracy of the decrease in bad weather conditions (rain, snow, ice) and pollution. The sensor may miss small items (rack enclosures), the surface having a low reflectivity. The sensor may not work correctly when driving on steep slope, when the surface of the earth is seen as a hindrance. Errors in the readings observed at a meeting with a smooth inclined surface.

hs-sr04-001
Figure 1 – The ultrasonic distance sensor HC-SR04



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