Non-contact millimeter wave security detector, a powerful weapon for new coronavirus detection

As the new crown pneumonia epidemic is becoming more and more stable, all units across the country are facing safe resumption of work and transportation of reworked personnel. For the security inspection department, how to ensure the security inspection work of the transportation industry and key units after the resumption of work while avoiding the risk of infection at work has become the focus of prevention.

The new coronavirus is usually spread through coughing and sneezing, close contact with an infected person or contact with an infected surface, and secondly through the mouth, nose or eyes. In order to reduce the risk of infection, when people go to public places, in addition to wearing masks, they should minimize exposure to public goods and parts in public places, reduce contact with others, and keep a certain distance from others as much as possible. As security check personnel are in daily contact with many people and the risk of infection is greater than that of the general population, they must pay more attention to the protection of new coronavirus infection. In addition to wearing masks and other protective equipment during the period of duty, daily cleaning and disinfection must be done. Because of the possibility of contact with passengers or their belongings, security personnel must pay special attention to hand hygiene. They usually wash their hands with hand sanitizer or running water, and measure their body temperature at least twice a day. If there are suspicious symptoms such as fever, cough, dyspnea, diarrhea, vomiting, muscle aches, etc., you should stop working immediately, seek medical treatment in time, and not bring sickness to work.

In order to prevent the carrying of prohibited objects that endanger public safety, the current security check method widely used in airports and stations is to allow passengers to pass through the metal detection security gate first. If the security gate calls the police, manual inspection is required. The metal detection security gate can detect metal objects carried by passengers. However, the disadvantages of this method are also obvious: on the one hand, it can only detect metal objects, and it has no ability to identify objects such as ceramics, plastics, liquids, etc., and it will leak. To remove non-metallic prohibited objects, manual inspection may be required as a supplement; on the other hand, the metal detection security gate will alarm but cannot Display the shape of the object and the accurate hiding position, and does not have the identification of objects-such as harmless coins or prohibited items. Blade-the possibility, only through subsequent manual inspection to locate and identify the object. In fact, almost every passenger will have belt buckles and other portable metal objects. The N95 masks worn by passengers also contain aluminum-plastic strips, and some passengers have metal implants in their bodies. The existence of various carry-on metal objects makes the metal detection security gates basically alarm, and then almost 100% of them still need to be manually inspected. In manual security inspections, security personnel need to be in close contact with passengers, which increases the risk of infection due to droplets and close contact. The millimeter wave human body security inspection device introduced in this article can detect metal and non-metallic contrabands and accurately display their shape and hiding location, which facilitates the identification of objects, which can greatly reduce the frequency of hand inspections, reduce the risk of infection, and protect the health of security personnel .

There are two types of millimeter-wave human security detectors: active and passive. The working principle of the former is similar to that of radar. The device first radiates millimeter waves to the human body, and then detects the millimeter waves reflected by the human body through a receiver to image the human body. The latter does not actively radiate, but realizes imaging by detecting the millimeter wave radiation of the target itself. In comparison, the active millimeter wave system has higher resolution, better imaging effect, and stronger environmental adaptability. It is not affected by temperature, sunlight, and surrounding radiation sources, so it is widely used in the security inspection industry. What is introduced later in this article are all active millimeter wave human body security inspection devices.

The resolution of the millimeter wave human body screening device is related to the working frequency. The higher the working frequency, the shorter the wavelength and the higher the resolution, but the cost of the device will also increase. Rohde & Schwarz’s R&S? QPS201 millimeter wave human body security detector uses electromagnetic wave signals in the 70-80GHz frequency band, with a resolution of 2mm. The detection resolution of devices that use low-frequency signals will be limited by wavelength. For example, a 38GHz signal can only detect objects of 5mm. The safety of electromagnetic radiation to the human body is an important consideration in the design of radio frequency and microwave equipment. The millimeter wave body security device is very safe for the human body. First of all, the millimeter wave signal can only be reflected by the body surface, but will not penetrate the human body. Second, the transmission power of the millimeter wave human body security device is very low, so it is very safe. Take R&S? QPS201 as an example, its transmit power intensity is less than one thousandth of that of a mobile phone, and the duration is only tens of milliseconds. Therefore, its electromagnetic radiation is very low and fully meets the electromagnetic environment standards of all countries in the world.

When the active millimeter wave human body security inspection device radiates millimeter waves to the human body, there are two implementation methods: full Electronic scanning and electronic plus mechanical scanning. The antenna array of the former is a two-dimensional large-scale antenna array composed of thousands of antennas. The scanning method Two-dimensional scanning is carried out in an all-electronic manner. The representative products are the German R&S? QPS series. The latter’s antenna array is composed of a small number of antennas to form a one-dimensional electrical scanning antenna array, and then mechanically moving the one-dimensional antenna array to achieve two-dimensional scanning, the representative product is the United States L3 ProVision. Due to the use of a two-dimensional large-scale antenna array, the cost of full electronic scanning is relatively high, but it brings three advantages: First, the response speed of the circuit far exceeds that of moving parts. For example, the scanning time of R&S? QPS201 is only 64 milliseconds, which is completed in an instant. Point and scan, no mechanical start-stop process; secondly, there are no mechanical moving parts, work stability can be greatly improved, greatly reducing the risk of failure, and does not require regular calibration; finally, maintenance is extremely simple and convenient. The antenna array is a module arrangement and mosaic structure. When a module fails, only a spare module needs to be replaced and inserted. It takes only a few minutes, and the local maintenance personnel can directly operate it after training. The working principle of the fully electronically scanned millimeter wave human body security detector is shown in Figure 1. The two-dimensional antenna array (QPS Panel in Figure 1) of the instrument sends out millimeter-wave signals to the human body in turn from the transmitting antenna, which is reflected back to the panel by the subject (PAX in Figure 1). All the receiving antennas of the antenna array measure the signal distribution at the same time, and the massive data obtained from all scans are transferred to the signal processing unit and computer to perform related imaging operations and restore the body surface characteristics of the examinee. Calculate the shape of the object and the intensity of the reflection according to the reflectance of the object. Recognition is assisted by artificial intelligence algorithms to find independent items that are not part of the human body. Finally, the location and shape of the suspicious object are marked on the schematic diagram of the human body (Figure 2). The image will not show the details of the human body to respect personal privacy. If remote manual discrimination is performed on the basis of machine artificial intelligence, further identification of suspicious objects can be carried out.

Figure 1. In a test, the transmitting antennas transmit one by one, while the receiving antennas all work at the same time each time.Ensure high efficiency and high precision detection

Figure 2. The detection result is displayed on the human body diagram to protect privacy

With the advancement of radio frequency technology and the improvement of computer system integration capabilities, the application and promotion of millimeter wave human body security inspection instruments has become a new trend in the industry. This instrument is suitable for security inspections in airports and key units. The advantage is a high effective detection rate, which can greatly reduce the frequency of manual inspections. First of all, the scope of detection items has been greatly increased. It can detect metal objects as well as non-metallic objects such as plastics, ceramics, and liquids. Secondly, it can accurately and meticulously display the shape of the object and the hidden location, and display the shape and location of the target on the screen in front of the security personnel in the form of a schematic diagram of the human body. If the passenger has not concealed prohibited items, they can be allowed to pass directly without hand inspection; if there are hidden items, the security personnel only need to check the hiding of the relevant body parts according to the schematic diagram without the need for a full-body inspection. Therefore, it can greatly reduce the chance of hand-check contact, and significantly reduce the risk of infection while improving the efficiency of security checks. This article takes Rohde & Schwarz’s QPS201 as an example to introduce the application of millimeter wave body security inspection devices in the field of security inspection. Rohde & Schwarz was founded in Munich, Germany in 1933. It specializes in RF microwave and millimeter wave products. It has a rich foundation in the communications, military, aviation, and airport industries, and has maintained an industry leading position in related fields. In the current frontiers of science and technology: microwave imaging and intelligent identification, Rohde & Schwarz has high-precision measurement scheme design experience, and unique and efficient algorithm software and hardware systems. R&S? QPS series products have been used in passenger security check areas in dozens of large and medium-sized airports in Europe and America, as well as security check posts in some key units. In China, R&S? QPS201 has passed the security inspection equipment certification of the Civil Aviation Administration of China, and has begun to deploy to domestic airports.

Figure 3 The R&S? QPS201 millimeter wave human security inspection device used at Munich Airport in Germany replaces the traditional metal detection security gate

The core component of the R&S? QPS201 millimeter wave human body security instrument is two measuring panels 2.3 meters high and 1.1 meters wide. The two panels are separated by 1.5 meters to form a spacious and open measurement channel, which is beneficial to people with claustrophobia. . Each panel contains thousands of transceiver units and miniature antennas to form a large-scale antenna array, and built-in fast data processing units and high-performance computers for control, processing and imaging. The overall design is highly integrated, stable and reliable. The system provides two display terminals: the main display terminal can be operated and displayed by the operator, and is generally placed near the security inspection instrument; the auxiliary terminal can be equipped with multiple options and can be flexibly placed, and is usually placed next to each hand inspection position. The inspector provides prompts, as shown in Figure 4.

Figure 4 R&S? QPS201 millimeter wave human body security inspection instrument

In terms of the space placement of the instrument, the operator and the passenger can keep a distance without close contact (as shown in Figure 3); the hand-inspected display terminal can be placed arbitrarily within the length of the network cable. Both the distance between passengers and the distance between passengers and security personnel are guaranteed. Working method: According to the portrait prompt on the instrument, the passenger stands naturally facing the main panel, with his feet and hands slightly separated. The operator clicks the start button, and the scan is completed in 64 milliseconds, accompanied by a “ding” prompt. Passengers under inspection can leave the detection area when they hear the sound. The instrument quickly showed the test results, including the number of suspicious objects and the hidden location. At this time, the operator guides the passengers according to the inspection results: if the security check passes, the passengers should go directly through the security check area; some passengers are reminded that there are suspicious objects, and the passengers are asked to go to the hand check station for inspection. In the hand-check area, the hand-checker will check the passenger’s corresponding body parts according to the terminal prompts. Because there are already site tips, the purpose of hand inspection is clearer and the contact time is shorter. It can be seen from the working mechanism of the instrument that during the security check:

●Passengers can wear masks to pass through the millimeter wave security device, even if there are metal aluminum strips on the mask;

●When the security checker detects, the operator should keep a sufficient distance from the passengers;

●The detection result of the security inspection instrument has extremely high accuracy, which can greatly reduce the probability of inspection by hand inspection;

●Hand inspection