Abstract: Methods and apparatus for detecting objects are disclosed. In one embodiment of the invention, a person entering a secured or “Safe Zone™” is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected and measured. In a preferred embodiment of the invention, concealed weapons are detected by calculating the difference of a pair of differences between levels of different polarized reflected energy in the time domain, and by using signal processing methods and apparatus to improve the reliability of the detection process. Alternative embodiments of the invention may be used to detect a wide variety of objects other than concealed firearms. The invention may be used for inventory control or to thwart shoplifting.

Abstract: A projector (10) for creating electrohydraulic acoustic and pressure waves comprising an energy source (21) (such as a capacitor) within approximately one meter of an electrode array (23). Larger projectors may be formed by arraying the projectors, and still larger projectors by arraying them.