Apparatus that invention detects and characterizes hard or metallic materials or objects, worn or carried by persons or concealed on their persons or in bags or luggage, using directed or propagated energy such as ultrasound or microwave, that is reflected or scattered by the materials and objects of interest and that has a wavelength or wavelengths such that the width and/or shape of the reflected beam can be measured at the desired detection distance or range of distances and has a measurable dependence on the size and/or shape of the object, utilizing diffraction methods. Also disclosed are a system and a method utilizing this apparatus.