Dielectric Detection Using Resonant Radio-Frequency Waves in an Electromagnetic Cavity Device

摘要

We describe the construction and testing of a prototype device designed to detect materials in glass and plastic containers using electrical measurement. The technique makes use of an electromagnetic cavity. A signal generator radiates a radio signal of variable frequency into the cavity, and a detector measures the response of the cavity as a function of frequency. Strong electromagnetic responses occur at certain well-defined 'resonant' frequencies. Using our device, we can detect how the electromagnetic resonances shift in their frequencies when a filled container is placed inside the cavity. This response depends on the electrical permittivity, or dielectric constant, of the filler material. Because the dielectric constant is a physical property that varies widely among materials, this electrical measurement is a useful discriminate for identification. A potential use of this device is to screen for explosives or flammable materials.