Why do you always have to go through a \”door\” when going through security check?

I believe everyone is familiar with security checks. You need to go through security checks when taking the subway, you need to go through security when taking the train, and you also need to go through security when taking the plane. No matter what kind of transportation you take, you always have to go through a door during security check. When passing through, you are often accompanied by a \”beep\” sound. After entering, security personnel will also check the passengers. People have long been accustomed to this, but this What exactly are the series of actions detecting? This article will clear up your doubts.

This door is called a security inspection door, also known as a metal detection door. It is a device specially used to detect whether metal objects are hidden on people. We see this type of product in airports, stations and other places, and the setting of security gates greatly improves their safety. The principle used by the security door to detect metal is magnetic field induction technology. When it works, a stable magnetic field distribution will be formed inside the security door. If a metal substance passes through the door, it will destroy the door\’s own magnetic field and be sensed by the metal detection door. , and an alarm sounds. At the same time, the security gate is divided into different areas, the more common ones are six and eight, and there are even higher ones such as twelve and twenty-eight. When the human body carries metal through the security gate, where is the metal? The alarm in the corresponding area will sound, so that security personnel can find metal objects carried by people\’s bodies more quickly and accurately.

After passing through the security gate, the security personnel will use a handheld metal detector to scan the passing people. The metal detector uses a rectangular detection head with a detection area of ​​12 centimeters. When checking the human body, it is scanned from top to bottom. Complete the inspection work. The working principle of metal detectors is similar to that of security gates, also using the principle of electromagnetic induction. Inside the detector are coils carrying alternating current, which produce a rapidly changing magnetic field. When a metal object is in this magnetic field, eddy currents will be induced and a magnetic field will be generated. The magnetic field generated by the metal object will affect the original magnetic field. The alarm device of the metal detector will activate, make a buzzing sound, and continue to vibrate. , informing you that there is a metal object nearby. Security personnel generally use handheld metal detectors in conjunction with metal detection doors. When the \”security door\” alarms and detects metal items, the handheld metal detector can be used to find the exact location where the metal items are hidden.

In crowded places such as stations and airports, X-ray baggage inspection machines are also used in conjunction with security gates and metal detectors to check passengers\’ baggage. It is precisely because of these security inspection facilities and The presence of security personnel greatly improves the safety of these places.

This article was scientifically reviewed by Zhang Zhongbao, associate professor of Computer Science and Technology Research at Beijing University of Posts and Telecommunications.

(Editors: Wang Shaoshao, Wang Yanhua)