Imaging apparatus and method
First Claim
1. A millimeter wave imaging apparatus comprising:
- at least one detector arranged to produce a plurality of images of a scene;
a frequency selector providing a plurality of different predominant frequencies of radiation for detection wherein each of said plurality of images corresponds to said different predominant frequency;
an image processor for processing the plurality of images by detecting changes in intensity occurring in corresponding objects across the plurality of images;
an indicator for indicating the presence of any frequency dependent changes in intensity detected by said image processor, andmeans for normalizing at least one of an output of the detector and an associated illuminator at each of the plurality of different frequencies.
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Abstract
A millimeter wave imaging apparatus and method capable of identifying the presence of relatively thin dielectric materials is disclosed. The method involves taking a plurality of millimeter wave images of a scene at different frequencies and analyzing the images at different frequencies to look for frequency dependent effects in the scene. Relatively thin dielectric materials can lead to interference effects which can be detected. In one embodiment the imaging apparatus comprises a millimeter wave imager (2) connected to a processor (16) and at least one variable frequency illumination source (22a . . . d, 24a . . . d). The or each illumination source sweeps the illumination frequency across a reasonably wide bandwidth and the imager captures radiation returned from the scene at a number of different illuminating frequencies.
22 Citations
22 Claims
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1. A millimeter wave imaging apparatus comprising:
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at least one detector arranged to produce a plurality of images of a scene; a frequency selector providing a plurality of different predominant frequencies of radiation for detection wherein each of said plurality of images corresponds to said different predominant frequency; an image processor for processing the plurality of images by detecting changes in intensity occurring in corresponding objects across the plurality of images; an indicator for indicating the presence of any frequency dependent changes in intensity detected by said image processor, and means for normalizing at least one of an output of the detector and an associated illuminator at each of the plurality of different frequencies. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of screening an object for a concealed item comprising the steps of:
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arranging a millimeter wave imaging detector relative to an object to be screened so as to be able to form a plurality of images of at least part of the object on said detector, wherein each of said images corresponds to a different predominant frequency and produces an output; determining a detector calibration factor at each of said different predominant frequencies; applying said calibration factor to said detector outputs at respective different predominant frequencies so as to normalize said detector outputs; detecting changes in intensity occurring in the object across said plurality of images; and analysing the images for any frequency dependent variation from the object. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A method of screening an object for a concealed item comprising the steps of:
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arranging a millimeter wave imaging detector array relative to an object to be screened so as to be able to form a plurality of images of at least part of the object; successively illuminating the object with millimeter wave radiation from an illuminator at a plurality of different frequencies; recording the output images from the detector array at each frequency; analyzing the outputs of the detector array for any frequency dependent variation in the scene, normalizing one of an output of the detector and the illuminator at each of the plurality of different frequencies; and indicating the presence of any frequency dependent changes in intensity detected.
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Specification