How do security machines find dangerous goods in the subway?

- Jul 29, 2019-

At present, the most used security equipment is X-ray security detector. When the passenger's luggage passes through the safety check door, X-rays are scanned in turn. X-ray is an electromagnetic wave with shorter wavelength than visible light. It has stronger penetration ability than visible light, and even can penetrate a certain thickness of steel plate. Because the density of various items in luggage is different, the degree of X-ray absorption is obviously different. Therefore, the depth of the image displayed on the fluorescent screen is also different. According to the different shadows of various items on the fluorescent screen, after objective comparative analysis, the correct inspection and judgment can be made.


Two sets of sensor arrays can detect high energy and low energy radiation signals, and compare high energy and low energy signals to obtain the atomic number of the detected items. After X-ray examination, the items in the luggage will show a general shape in the display, and show yellow, green, black and so on (the specific distinction is shown in the following figure). Safety inspectors can detect the presence of contraband in luggage from the screen. In addition, the X-ray signal projected through a certain intensity can be transformed into electrical signal by electronic instruments, and the alarm can be used to alarm. Because electronic components may interfere with X-rays, security checks often require items such as laptops to be taken out.


Another kind of equipment which is often used is arched metal detector gate, which works by using the principle of electromagnetic induction. There are rapidly changing magnetic fields on both sides of the walk through security gate. These magnetic fields do not have any effect on human body, but for metal exceptions, because the metal will produce eddy current under the rapidly changing magnetic field, and the eddy current will produce a magnetic field. When the security gate detects the new magnetic field, the security gate will automatically emit a sound or flashlight. 。 In addition, hand-held metal detectors are also used in similar devices. When the metal detection door alarms, hand-held metal detectors can be used to find the specific location of metal objects.

These two methods are currently the most commonly used security inspection methods, but with the rapid development of science and technology, more advanced security inspection methods with long-distance, non-contact and higher sensitivity are constantly being developed.