█ Introduction 

Using ultrasonic sensor as  transmitter and receiver, transmitter emission amplitude ultrasound to area  being detected, the receiver receives the reflected ultrasound. When there is no  moving object is detected to enter the area, the reflected ultrasound is  amplitude. When there are active objects into the detection area, the magnitude  of the reflected ultrasonic ranging, and changing. Receiver circuit detect  changes in the signal control circuit and then alarm.

█ The principle of Ultrasonic  anti-theft alarm

 
According to the Installed  methods and its structure, we may divide into two types: One is to install two  ultrasonic transducers in the same case, that is the sending and receiving  co-set type, and its working principle is based on the acoustic Doppler effect,  also known as the Doppler-type. When there is no moving object is detected to  enter the area, the reflected ultrasound is amplitude. When there are active  objects into the detection area, the magnitude of the reflected ultrasonic  ranging, and changing. The emission of ultrasonic energy field distribution has  a certain direction, usually oval-shaped area for the direction to field  distribution. Another is the two transducers were placed in different locations,  namely the sending and receiving sub-set type, known as the acoustic detector,  its transmitter and receiver to use more non-directional type (ie,  omnidirectional) sensors or half the sensor. Non-directional sensors have  hemispherical energy field distribution pattern, and a half to the type of field  distribution patterns can produce tapered.

Principle of ultrasonic sensor continuous wave for moving object detection

█ The example of continuous wave  transmitting circuit

█ Applications field of Ultrasonic  anti-theft alarm

Because it can detect moving  objects, ultrasonic detectors have a wide range of applications. For example:  automatic door detection, controller; elevator automatic starter; burglar alarm  detectors. The detector characteristics can be detected to determine whether the  activities of people within the region or other moving objects, animals, control  around a large, high reliability.