Terahertz is a kind of electromagnetic wave that exists in the natural world. The human body generates this electromagnetic wave all the time and emits and spreads outward. The clothes worn by people are "transparent" to terahertz and cannot block its spread. Therefore, the use of terahertz sensors can find "opaque" objects such as guns and knives hidden in people that are imperceptible to the naked eye, that is to say, the exact location of the hidden objects. The terahertz security detector developed by 50 can receive most of the terahertz waves emitted by the human body through the front and rear devices within tens of milliseconds. After the system calculation and processing, it is displayed in real time in the form of video. When there are "opaque" items on the body, shadows that are obviously different from other parts of the body will appear in this area of the image, the automatic identification algorithm can be prepared to obtain the accurate location of the area and give early warning in time.

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