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Application of RF and Microwave Technology in Security Field
Source:Original | Author:C&T RF Antennas Inc | Publish time: 2018-11-13 | 2154 Views | Share:


The urgent demand for the construction of safe cities has promoted the rapid development of the security industry, and the words such as smart cities and intelligent security have also become popular, including multi-technology integration management including video surveillance, identification, hidden object detection, electronic maps, and linkage alarms. The system has begun to gradually replace the previous single security model. This new security system requires a variety of sensors to cooperate with each other, and RF-based and microwave-based sensors constitute an indispensable part of it because of its unique advantages.


1. Advantages of RF and Microwave Technology

Radiofrequency and microwave refer to electromagnetic waves with a frequency of 300 MHz to 300 GHz, which is a limited frequency band in radio waves. Microwave millimeter wave sensors have a series of unique features. First of all, electromagnetic waves of most frequencies in this frequency band are attenuated very little in the atmosphere, and they are almost negligible due to smoke or bad weather. For materials such as glass, plastics, and porcelain, they are transmitted with very little loss, and water Foods, etc., absorb microwaves and heat themselves. For metal materials, they reflect. The characteristics such as high carrier frequency, short wavelength, and easy implementation of large bandwidth also make this type of sensor highly adaptable in size and resolution. The above characteristics make it ideal for detecting and imaging human bodies or concealed objects through walls, shelters, or clothes, plus the almost all-weather detection capability and the ability to measure the Doppler frequency to promote its presence. Human body detection and behavior identification applications.


2.Main application scenarios in the field of security

RF and microwave sensors acquire information about an object or scene by transmitting an electromagnetic signal and then receiving and analyzing the signal reflected from the object, or according to the signal emitted by the object itself. Combining the characteristics of microwave millimeter wave and the requirements of security applications mentioned above, the application scenarios of such sensors are mainly divided into the following categories.


2.1. Entrance and Exit Human Security

It is of great significance to carry out human safety inspections on important places and key units (such as airports, train stations, and entrances and exits of large conferences) to carry out human safety inspections for people who may carry hazardous products. The existing imaging-based security inspection technologies mainly include X-ray backscatter imaging, infrared imaging, and millimeter wave imaging. X-ray backscatter technology has clear images and high resolution, but it has potential radiation damage to the human body and is suitable for fine inspection of carry-on baggage. Infrared imaging technology uses target temperature difference to form two-dimensional images, but cannot penetrate clothes. Suitable for long-term monitoring and identification in specific areas; while millimeter-wave can penetrate human body clothing to detect various metal hazardous items concealed under human clothes, as well as non-metallic hazardous items such as ceramic pistols and liquid explosives. Solve the first two kinds of undetectable hidden detections of carry-on items.


According to the imaging system, millimeter-wave human body security inspection technologies are mainly divided into active and passive imaging technologies. The active millimeter wave generally uses a millimeter wave source for illumination, and the image signal to noise ratio and contrast ratio are relatively high, and the image resolution can reach millimeters. However, due to the existence of the transceiving process, the imaging time is long, and the person to be inspected cooperates to raise hands. , Turning and other movements, slowing the passage of personnel, is suitable for occasions that require detailed inspections and relatively small personnel movements, including airports. Some airports in the United States and other countries have adopted a cooperative millimeter-wave human body security inspection system to conduct detailed inspections of passengers in the security inspection area. For people-intensive and fluid places, such as subways and railway stations, this type of security inspection will inevitably affect the public order. Therefore, we need to introduce more rapid and efficient human security inspection equipment, namely passive millimeter wave imaging technology. This technology determines the presence or absence of contraband by measuring the millimeter wave of radiation emitted by the human body and the objects it carries. The biggest advantage is that the imaging speed is fast, and the video speed can theoretically be achieved without affecting the normal behavior of the person being examined, but due to radiation signals. Generally weaker, corresponding radiometer temperature sensitivity is not high, the image signal to noise ratio is not high, the resolution is low.


Since the 90s of last century, some countries in the United States and Europe have begun to devote themselves to the study of millimeter-wave imaging systems for human body security. So far, a series of cooperative security target millimeter wave systems for airports have been developed abroad, mainly including the United States L-3 Communications' Safeview millimeter-wave human body security instrument and Germany's Smiths Heimann's Eqo millimeter wave imaging human body security. In 2012, Rohde & Schwarz GmbH of Germany, together with Infineon and Nuremberg University, successfully developed the QPS series millimeter-wave human body security instrument using active multi-station sparse array imaging technology. Its operating frequency is from 70 GHz to 80 GHz, and the imaging time of each image is about 4 s. The most important feature of these systems is that the inspected personnel must cooperate with the actions such as erecting and raising their hands. Although the resolution is high, the imaging speed is slow. It is mainly used in airport low-speed inspection of human body security applications, and it cannot meet the demand for large passenger flow and rapid security.


In terms of passive imaging, in 2011, QinetiQ of the United Kingdom and the University of Manchester in the United Kingdom jointly developed a prototype of the TRL-4 microwave human body security instrument. The array-based signal processing technology can achieve an imaging speed of 24 frames/s. Currently, due to application requirements Weak, insufficient investment, the prototype is still in the experimental research stage.


At the same time, several domestic research institutes, including Fangwei, CLP-38, etc., have developed multiple sets of millimeter-wave human body security inspection instruments by referring to active-active millimeter-wave scanning imaging security inspection technology. According to the detection of civil aviation application department, its imaging performance index is equivalent to that of foreign security inspection equipment.


In the field of passive imaging security technology, the microwave engineering laboratory of Beihang University has begun the research of millimeter wave array imaging technology since 2003. It has successively broken through several key technologies and successfully developed a prototype and prototype system for multiple generations of millimeter wave imaging. The launch of the domestic first set of video-type millimeter-wave human body security inspection instrument has now developed two video-type millimeter-wave human body security engineering prototype. The first prototype is mainly used for outdoor checkpoint applications and can achieve speeds of 1,200 passengers per hour for customs clearance. It has completed testing and experimental verification of all types of dangerous items, but its system sensitivity is poor and it is only suitable for outdoor applications. For indoor applications such as subways and railway stations, Beihang Microwave Engineering Laboratory has launched the second engineering prototype, which increases the temperature sensitivity of the system by increasing the number of receiving channels, and enables fast security without changing the behavior of the persons under inspection under large passenger flow conditions.


2.2.Electromagnetic suppression and decoy capture of low-slow and small unmanned aerial vehicles

The rapid development of science and technology has made civilian small drones a well-known electronic product. However, this high-speed popularization has brought convenience to life and also caused various problems. A statistical result in 2015 showed that the total number of driver certifications for drones in China was only 2,142, while the number of unmanned drones was tens of thousands, and most of them were “black flying” without training or reporting. This will not only affect people's lives and property but also threaten public safety and air defense security. Therefore, the anti-drone technology equipment and market are also rapidly expanding.

At present, the anti-UAV technologies in various countries mainly include acoustic wave interference, signal interference, hacker technology, laser cannons, and “anti-UAV” drones. Various technologies have their unique advantages, and today’s defense systems are more In combination with the above two or more technologies, a regulatory system is established to capture or properly guide the use of small drones from multiple perspectives. The signal interference is a relatively central component of the capture system. It mainly uses the electromagnetic suppression function of the microwave millimeter wave band. According to the actual situation of the site, the remote control and GPS of the “black fly” drone are selectively controlled by the electromagnetic signal interference transmitter. Electromagnetic suppression of the signal transmitted by the map, capturing the control of the controller, and directly causing the “black fly” drone to land.


In America, Europe, and other countries, there have emerged a variety of drone capture systems that include electromagnetic suppression, such as the Drone Defender gun in the United States, the short- and medium-range "Giraffe" AMB multi-beam radar system in Sweden, and so on. The most prominent of these is the UK-based AIDS system developed jointly by several companies. The system integrates electronic scanning air-defense radars, photoelectric indicators, visible/infrared cameras and target tracking software, and directional RF suppression/interference systems. The drone within 8 km is used for detection, tracking, identification, interference, and suppression. The effective distance of this system to the micro-drone is 1 km, and the effective range of the small drone is up to several kilometers.


2.3.Millimeter Wave Radar in Perimeter Defense

Intelligent active regional security is an emerging security solution that integrates multiple security technologies and products and builds on the analysis of big data networks. Traditional perimeter security systems (physical fences, fences, and electronic fences, vibration sensors, video, etc.) may be affected by optical visibility or by bad weather (wind, rain, snow, fog, hail, dust, etc.) Or, it is affected by complicated environment (small animals, weeds, trees, etc.), resulting in high false alarm rate, high false alarm rate, and inaccurate detection of distance, angle, and speed of moving targets.


Regional intelligent active security alert Based on the traditional video monitoring equipment, the new regional type millimeter-wave phased array radar and the industry's fiery machine vision intelligent video analysis are two techniques, using multiple Sensor complex calibration, to achieve regional security alarm.


The implementation of regional phased array radar sensor security for a domestic enterprise. After the target enters the defensive zone, it performs detection and early warning. At the same time, the target's distance, angle, and speed are measured to determine the exact location of the target. The machine vision video analysis technology performs target review, determines whether it is human motion through algorithm filtering, and minimizes false alarms.


The regional security radar adopts a reliable integrated technology that can be widely used in military defense detection, prison area prevention, oil depot area monitoring, airport area security, and multi-sensor fusion. It is based on the mature technology of military radars. Detection distance, anti-jamming capability, monitoring area, accuracy, etc. are guaranteed. In addition, combined with the development of video analytics technology, multi-target tracking, target identification, etc. have also become the advantages of such products.


2.4.Electronic RF Identification

In addition to the detection and identification of target radiation or reflection, one of the more common applications of microwave and millimeter waves in security is the electronic radio frequency identification (RFID), which is a wireless communication technology that can identify specific targets and read and write related signals through radio signals. Data without having to identify mechanical or optical contact between the system and a specific target.


RFID technology itself is already very mature and widely used in a variety of security scenes. In public areas, such as entrances and exits of scenic spots, theaters, etc., this technology can be used to implement an open access control system. When visitors are equipped with electronic tags, the RFID system automatically senses whether the identity of the person is valid.

At the same time, RFID tags can solve short-distance, especially indoor object positioning, and can make up for GPS and other positioning systems can only be applied to outdoor large-scale deficiencies. GPS positioning, mobile phone positioning, together with RFID short-range positioning means and wireless communication means can achieve full tracking and monitoring of item positions. Therefore, in addition to personal identification, vehicle identification can also be performed in residential areas or unit entrances and exits, commonly referred to as radio frequency access control. The radio frequency identification technology applied to the access control system can realize the parking of vehicles with effective electronic tags, save the time for convenient access, improve the traffic efficiency of intersections, and more importantly, enable real-time monitoring of vehicles entering or leaving a residential area or parking lot. The identity of the vehicle and the owner of the vehicle and the maintenance of regional security will make the security management of the community or parking lot more user-friendly, informative, intelligent, and highly efficient.


3. Summary

As many of the threats to public safety have become increasingly complex, microwave millimeter-wave security-related technologies have gradually improved their position in security because of their advantages in penetrating smoke, various kinds of shelters, and the ability to identify people and things. With the continuous advancement of related technologies such as device design and manufacturing, signal processing methods, and multi-sensor fusion, this technology will become an indispensable part of the security field.