Indoor passive sensing for detecting hidden objects under clothing

The physical security of government buildings, banks, schools, higher education institutions, train stations, airports and lastly but not least the people within them has been the key for the sustainability of our society. Day after day, technologies have been invented to improve the physical security of buildings. In this paper a Thru-Vision passive imager having a centre frequency of 250 GHz and a bandwidth of 36 GHz was used to scan images and detect different types of hidden objects under clothing. The clothing materials used in the experimental images were made of cotton, wool and leather. Experimental images show that millimetre-wave (MMW) radiations over the band (232-268) GHz can penetrate these materials and detect hidden objects. Experimental results indicate that the transmission over the MMW band is dependent on the clothing material, thickness and moisture content. The images obtained from the Thru-Vision passive imager provide information about the shape, the size and the dimensions of the hidden objects. These objects were a metal plate and a wax plate. Experimental images show that spraying water on textiles increases the loss over the MMW band and makes the objects less visible, but at the same time they remain detectable. Furthermore, the experimental measurements indicate that textiles made of cotton and wool have higher transmissions of MMW radiation and enabling more reliable object detection compared with leather. These findings indicate the potential of the MMW band of the electromagnetic spectrum for offering a non-contact method of screening people, a touchless pat-down security search for use in scenarios where harmful viruses and bacteria may prevail. This capability will increase the detection probabilities and reduce the false positives rates in security screening.