Patent ID: 8129684

Claim:
A method of detecting objects or substances concealed in or under a person's clothing comprising: scanning a first beam of THz-frequency radiation, said first beam having a frequency tunable over a predetermined range, from a first source thereof; modulating the frequency of said first beam through said predetermined range to create a modulated frequency chirp while scanning said first beam of THz-frequency radiation over the person whereby a portion of said first beam penetrates the person's clothing and is reflected by an object or substance concealed under the person's clothing; mixing the reflected portion of said first beam with THz-frequency radiation from a second source thereof wherein the frequency of the radiation from the second source is different from the frequency of the first source to provide a signal having an intermediate frequency (IF) including said frequency chirp; demodulating the intermediate frequency as a function of the frequency chirp and deriving phase and amplitude changes induced by the interaction of the beam with the person's clothing and any object or substance concealed under the clothing; processing the phase and amplitude changes to produce image data representative of the concealed object or substance said image data including both intensity and range information, said range information corresponding to individual scattering sites along the propagation axis of the first beam and associated with the object or substance concealed under the person's clothing.