Airports and other public places require security measures for the screening of human subjects for illicit objects and materials concealed from view beneath clothing. However, at present most of such screening processes involve only metal detectors, which are inherently incapable of detecting non-metallic illicit objects and materials. For this reason, there remains a strong need for novel systems and methods that can detect all types of materials. The present invention provides for a portal detection system that is configured for safe, rapid, and non-invasive scanning of human subjects. For this purpose, the portal detection system utilizes acoustic technology to achieve this end. The portal detection systems of the present invention may optionally be used in conjunction with conventional metal detection means. The invention encompasses portal detection systems, their use in scanning human subjects, and corresponding methods of scanning human subjects for illicit objects and substances.