| An experimental study of the natural sampling of trace signals from the human body was performed. Although this sampling technology can conceivably be used for the non-intrusive detection of diseases, this research has focussed on its application to the detection of explosives (RDX & TNT) concealed upon the human body. The knowledge thus gained has been applied to the preliminary design and development of an explosives detection portal for aviation security screening.; The sampling problem was addressed by taking proper account of the human microenvironment, especially the thermal behavior of the air surrounding the human body and the particles therein. The present experiments were conducted in a dispersal chamber to identify some of the variables affecting the detectibility of concealed explosives. "Agitation" was found to enhance the available traces. Clothing was found to block some of the trace signals released by agitation, which are then subject to release over time, and made available for detection. Additionally, the detected signal levels were found to vary significantly from volunteer-to-volunteer, emphasizing the importance of human-body aerodynamics and heat/mass transfer.; These dispersal chamber experiments were also used to identify the nature of the sampled explosive traces. Under the conditions studied here, the detectibility of both RDX and TNT was found to be primarily dependent upon the efficient sampling of contaminated particulate matter.; Flow visualization studies were performed to identify the added challenges of sampling in an open portal. The schlieren method was used to visualize the airflow in a preliminary portal design. These experiments revealed the importance of sufficient suction at the hood outlet for complete capture and containment of the human thermal plume, which carries the critical trace signals. Numerical analysis and modeling were used to elucidate and confirm all experimental results.; These results proved that the human boundary layer is capable of removing and transporting a detectable explosive trace signal from the body. Moreover, it is both possible and advantageous to detect concealed explosives using natural sampling only. Thus, this research contributed fundamental knowledge of the sampling of trace signals associated with the human body. |
