Airport security checks typically include security checks for passengers and carry-on baggage, security checks for checked baggage, and perimeter security checks at the airport.

I briefly introduce several security technologies:
1. Technology used in X-ray security inspection of luggage items: X-ray transmission imaging technology
The X-ray transmission imaging technique measures the number of X-photons passing through the object to be detected, and the probability that X is absorbed reflects the density information of the substance to be detected. The transmissive detection method is performed by the staff's interpretation of the shape and density information of the substance to be detected.
The X-ray imaging products currently used at airports are basically dual-energy X-ray imaging technology, multi-view X-ray technology, and CT-ray imaging technology.
Compared with the single-energy X-ray inspection system, the double atomic X-ray can obtain the effective atomic number information of the test object, and improve the material resolving power of the system.
CT technology can form a three-dimensional image of an object, determine the thickness of the material, and distinguish explosives from other low-atomic similar substances.
2. Inspection of explosive trace detection technology: ion migration technology
In the case of a high level of security inspection, the “scratch test paper” method is used to detect the explosive traces of the person or the package.
The technical principle is that the sample to be tested is ionized to form ions in the atmosphere or in the moving gas, and then drifts in the applied electric field. Due to the different mobility of the different samples, the different components in the sample are separated within the migration tube, and in general the heavy molecules go slower than the light molecules. Thus, the composition of the sample can be known from the measured migration time.
Ion mobility spectrometry has been widely used in the fields of drug detection, explosives detection, chemical warfare agent detection, atmospheric and organic pollution detection, factory toxic gas monitoring, food testing, and wood species testing.
3. Human imaging technology currently used at US airports: backscatter imaging technology
Backscattering is a method of analyzing a substance to be detected based on Compton backscattering. The principle of this type of method is to image an object in two or three dimensions by measuring Compton scattered X-rays scattered from the substance being detected. It can obtain information on the distribution of the internal electron density of the substance to be detected.
Backscattering technology is suitable for detecting low Z organic materials.
4. Human Imaging Technology Currently Used in US Airports: Millimeter Wave Imaging Technology
Millimeter waves are generally defined as a frequency band from 30 GHz to 300 GHz, which is spectrally between infrared and microwave. Compared with visible light and infrared light, this spectrum has a certain penetration into most non-metallic objects, and at the same time has the resolution that microwaves do not have.
There are two main types of millimeter wave imaging methods: one is passive and the other is active. Passive imaging devices are devices that use millimeter-wave aggregation imaging of human radiation. The amount of millimeter-wave radiation radiated by an object depends on their physical properties and temperature. The human body radiates millimeter-waves more than metals, ceramics, plastic explosives, powdered explosives, clothing, and insulating materials. Millimeter waves can penetrate any insulating material, all clothing fabrics, and most building materials. Most of the active millimeter-wave imaging devices currently used on the market are more accurate than passive.
In the face of the millimeter wave imaging equipment, the clothes on the person are gone, and the coins, buttons, pens, keys, etc. on the person are clearly visible against the contours of the human body. If you hide hidden weapons such as pistols, bombs, drugs, etc., you will have a clear view.
5. Technology for the inspection of suspected dangerous liquids, explosive solid powders, drugs: laser Raman technology
Laser Raman technology is an analytical method based on the use of laser as a source of Raman scattering. When the material molecules are irradiated by light radiation, the wavelength of the Raman scattering is related to the structure of the material due to the vibration of the molecules or the transition of the rotating energy level. The Raman scattering can be used as a basis for qualitative analysis, Raman scattering. Strength can be used as a basis for quantitative analysis.
Laser Raman technology has a wide range of applications in security, environmental protection, food, pharmaceuticals and other fields.
6. Technology for checking suspected liquids: Dielectric constant measurement technique (microwave detection)
The relative dielectric constant indicates the physical quantity of the degree of polarization of the medium under the action of an external electric field, which is related to the polarity of the substance molecule. Molecular polarity refers to the non-uniformity of the charge distribution inside the molecule. According to the dielectric constant characteristics of liquid materials, flammable hazardous liquid products with a low dielectric constant can be distinguished from other liquid materials to some extent.
7. Techniques for inspecting metal carried by people: metal detection technology
Common products are metal security doors and hand-held metal detectors.
The security door can alarm the passing metal objects because the two side panels are equipped with sensors that can transmit and receive alternating electromagnetic fields. When the metal conductor is excited by the alternating electromagnetic field, an eddy current is generated in the metal conductor, and the current emits a magnetic field having the same frequency but opposite direction to the original magnetic field. The metal detector detects the presence or absence of the eddy current signal to find the vicinity. Whether there is metal. The excitation electromagnetic wave is emitted by the transmitter, and the receiving sensor receives the signal of the metal object, and the receiving sensor detects the signal generated by the eddy current, and then performs a series of amplification processing by the circuit, and when the signal quantity reaches the set value, the sound and light form is adopted. An alarm is generated.
Each technology has its applicability, so airport security is a combination of multiple technologies to ensure security. In addition, the equipment is auxiliary, and the operational skills and norms of the inspectors are also very important to improve the security level.