Detection of Scatterers Inside Metal Containers via VLF Signals of Opportunity

Radio frequencies at or below the VLF range (3-30 kHz) are uniquely capable of penetrating highly conductive materials. This can be exploited to detect objects hidden within metal containers. In this paper, we present observations of VLF scattering in such a situation, using VLF transmitters as signals of opportunity. Scattering is detected in the near field from an object inside an aluminum enclosure, and a gradiometric method is presented to differentiate the scattered signal from the plane wave that is incident onto the system.