A passive video-rate terahertz human body imager with real-time calibration for security applications

Real-time video-rate passive terahertz imaging systems are highly demanded for practical applications, especially in security checking. Here, we demonstrate a passive video-rate terahertz human body imaging system, which was mainly consisted of a scanning module, a quasi-optical lens, a calibration module and a one-dimensional terahertz detector array. The terahertz waves radiated from human bodies in front of the imager can transmit through a terahertz window into the imager, and were reflected by the scanning module, and then focused on the detector array by the quasi-optical lens. A calibration module was also designed to calibrate the terahertz detectors in real-time without disturbing the imaging process. In combination of the scanning module with the detector array, the imager can obtain a full image of a human body standing at a distance of 1.5 m in front of the imager with a resolution of 1.5 cm and a frame rate of 10 fps. The imaging system can discover suspected dangerous items carried on the human body such as metals, ceramics, powders and liquids. Furthermore, an intelligent terahertz imaging algorithm employing convolutional neural network was also successfully realized based on the terahertz images produced by this system to improve the image quality and mark the detected items automatically. We believe our real-time video-rate terahertz imaging techniques and systems not only have great values for further inspiring developing terahertz imaging systems but also can accelerate the terahertz technology towards more practical applications.