Microwaves are the electro -magnetic radiations whose frequency ranges from 0.3 GHz to 300 GHz.  These waves are mostly use for the non- broadcasting issues. Unlike other waves, these waves have narrow beam which imparts it with the characteristic features like broad bandwith and high data transmission rate. These waves are used in space crafts, communication satellites and various other fields like TV, telephone communications and security systems. 

Microwave motion detector- introduction 

One of the most unique use of these waves are in the operation of various security devices. These days, the security and surveillance concerns have risen and so has the tools to deal with such menaces. Microwave motion detectors are one of the motion sensors which detect the intruder’s motion into a specific portion and triggers alarm as a consequence. These detectors emit microwaves into the specific region and detect any intrusion by analyzing the frequency of the received microwaves after the reflection from the intruder.

The main guiding principle for almost all of these sensors has been the Doppler’s Effect. A microwave motion detector circuit mainly comprises of components- the transmitter, receiver and the alarm/related circuit. The transmitter sends off microwaves into the area. These waves have a specific frequency. However, as they strike with an intruder moving with a velocity, the frequency and consequently, the phase of the wave signal gets altered. Once these reflected waves are received by the receiver, its phase analysis is done and consequently, an alarm is triggered on if the analysis depicts some change in the phase of the wave signals. It is worth mentioning here that the change in phase of the signal wave is directly proportional to the velocity of the intruder .  Today, with an advancement in technology, we are endowed with a variety of microwave motion detectors. Let us have a look over them:

Detector combating false alarms : Most of the microwave motion detectors work upon the principle discussed in the previous section. However, there is a kind of disadvantages which these kind of sensors suffer from. The problem is related to the cases of false alarms which occur even due to slight vibrations of objects like curtain and swinging signs. To combat this problem, an improved detector has been designed which contains all the components of a normal sensor along with two receiver/mixer diodes.  These diodes emit surveying signals which mix up with the transmitted microwave signal. These altered phase signals when received by the receiver, trigger the alarm only when the shift in phase has been upto the threshold frequency change pre-fed into the sensor.

Once, this pre-fed threshold frequency is over-crossed, the alarm is triggered on. 

In an other kind of detector , the sensor device consists of field transceivers which have microwave oscillator and antennae so that continuous wave energy is transmitted into the specified area.  These antennae contain certain devices which can easily recognize the human intrusion by analyzing the phase shift occurred in the received wave. Thus, in this way, it is ensured that the cases of false alarm do not arise easily. 

Detector based upon random motion : Some of the detectors contain diodes which enable the detector to sense whether the intruder is moving towards or away from the detector. These detectors are helpful in sensing and differentiating between the ordinary movement and intruder movement. This feature of such  sensors  make them  highly reliable.

Uses of microwave motion detector

  • The microwave motion detectors have a wide array of application. Some of them are enlisted below:
  • These detectors, apart from addressing security problems, are also used in door openings .
  • These detectors are used to detect the heartbeat and breathing rate of a human.  
  • These detectors are used in the elevator shaftway where they are used to display the information regarding the parking of a car in an elevated parking system
  • These sensors are used in security issues and traffic law enforcement.  
  • They are used in monitoring the light system of a house or a building. 

Benefits and Limitations of microwave motion detector

Some key benefits are:

  • Unlike  other detectors, the microwave motion detectors can be used in harsh environment where the heat cycles are not regular. 
  • Since, the microwave radiations can easily penetrate through the walls and holes, so, they can be used to impart security across the boundary/closings. 
  • These detectors when combines with passive infrared detectors can become much reluctant to false alarms.