Microwave sensors are  playing an  increasingly vital  role  in  modern technology, particularly those  operating  at the  24GHz frequency  band.  These  devices  have garnered significant attention due to their unique performance characteristics and broad application scope. This article will provide a comprehensive analysis of the working principles, primary applications, and selection criteria for 24GHz microw- ave sensors.

(1) Working Principle of Microwave Sensor

24GHz microwave sensors are mainly based on the following two technologies:

(1)  Continuous Wave Doppler Radar (CW Doppler Radar)

(A) Suitable for motion detection (e.g., human body sensing, speed measurement).

(b) Principle: The fixed frequency (24GHz) microwave is emitted. When the moving object is encountered, the reflected wave frequency will have Doppler shift (Doppler Shift). (c) The sensor calculates the velocity of the object through the frequency shift.

(d)  Typical  applications:   intelligent  lighting  (human  body  induction),  automatic  door, security alarm.

(2)  Frequency Modulated Continuous Wave Radar (FMCW Radar)

(a) Suitable for distance measurement (e.g., liquid level detection, UAV obstacle avoidance).

(b) Principle: The microwave with linear variation of transmission frequency over time (e.g.,  24GHz ~ 24.5GHz) calculates the distance by calculating the frequency difference between the echo and the transmitted wave.

(c)   Typical   applications:   industrial   ranging,   intelligent   parking,   autonomous   driving assistance

（3） Key Components

Transmitter: Responsible for transmitting microwave signals.

Receiver: receives microwave signals reflected from a target object.

Signal processor: Analyze the difference between the transmitted signal and the received signal, so as to extract the motion information of the object.

（4） Working Mechanisms

When a microwave sensor emits a signal that encounters an object, part of the signal is reflected back. The sensor's receiver captures these reflected signals and uses a signal  processor to analyze the time difference, frequency difference, or phase  difference  between  the  transmitted  and   received  signals.  This  analysis calculates information such as the object's distance, speed, and direction.

(2) Application Fields

24GHz  microwave sensors are widely used in  many fields  because of their  high accuracy and reliability:

（1） Automatic Door Control

In the automatic door system, 24GHz microwave sensor can detect whether there is a person or object in front of the door, so as to control the opening and closing of the door.

（2） Vehicle Inspection

In traffic monitoring and vehicle management systems, microwave sensors can be used to detect the presence, speed and flow of vehicles, providing data support for traffic control.

（3） Security and Protection Monitoring

Microwave sensors can be used in intrusion detection systems that trigger alarms by detecting small movements of the human body.

（4） Industrial Automation

In the field of industrial automation, 24GHz microwave sensors can be used for material detection, speed measurement and position control.

(3) Selection Guide

The following key factors need to be considered when selecting an appropriate 24 GHz microwave sensor:

（1） Scope of Testing

Select the detection range of the sensor according to the application requirements to ensure that the sensor can cover t he area to be detected.

（2） Accuracy and Resolution

Accuracy and resolution determine the accuracy of sensor detection results. Select appropriate accuracy and resolution according to specific applications.

（3） Output Type

Common output types include analog output, digital output, and serial commun- ication interfaces. Select the appropriate output type based on system compatibil- ity and data processing requirements.

（4） Environmental Suitability

Consider  the  environmental  conditions  that  the  sensor  will  work  in,  such  as temperature,  humidity, dust, etc., and select the sensor with the corresponding protection class.

（5） Power Supply and Power Consumption

Select  the  appropriate  sensor   power  type  and   power  level  according  to  the application's power supply conditions and power requirements.

(IV) Conclusion

24GHz microwave sensors play a vital role in modern technology with their unique performance   and   broad   application   fields.   By   understanding   their   working principles, application areas, and selection guidelines, you can better choose and utilize this advanced  sensor technology to add  more value to your  projects  or products.