3- ULTRASONIC DETECTOR
Ultrasonic waves are waves of frequencies which are above the range of normal human hearing, though dogs and certain other animals are sensitive to it. Ultrasound is usually generated by using crystal, in which both the surfaces ground so that it vibrated at a frequency 40Khz, To make the crystal vibrate we apply an oscillating potential across it, if the frequency of the oscillator is exactly
40KHz, the crystal resonate with the applied oscillating potential, and ultrasonic is generated.
The reverse process detects ultra sound, the detector is a crystal similar to the generator crystal. Its surface are ground so that it vibrate at a frequency of 40KHz, When ultrasonic of the correct frequency falls on this crystal, the crystal resonates and begin to vibrate at the same frequency, its vibrations generate the oscillating potential, and to detect the oscillation of the receiver crystal, are simple to construct and operate, System using ultra sound is good one for the beginner to construct as an introduction to object detection and security systems.
The circuit consist of the following main parts:
Accuracy of the ultrasound based measuring system is basically limited by the inherent characteristics of the ultrasound. Depending on the frequency and the propagation speed of the ultrasound, the wavelength determines the minimum duration of an ultrasound pulse and the thickness of the ultrasound beam.