Millimetre-Wave Detection Device for Discriminating Between Different Materials

Abstract

The detection device that can be used for detecting objects behind clothing etc including a dielectric lens and a receive element sensitive to millimetre wave radiation. Prior art systems produce an image of a scene usually using scanning optics. This can be large and expensive. The present invention instead takes spot readings from different parts of a scene without building up an image. The spot readings are processed, and an indication given to a user if certain characteristics of the readings are observed. Typical characteristics used are the differences in absolute received power level, and the power level at different polarisations. Such characteristics are typically present is an object of interest is in the scene. Also disclosed are various methods of altering the received beam to get readings from different areas from the scene, such as changing the beam width, or beam angle.

1 - 27 . (canceled) 
   
   
       28 . A detection device for discriminating between different materials comprising an antenna system and a receiver wherein the receiver is sensitive to millimetre-wave radiation, the antenna system is arranged provide incident energy from a scene to the receiver, and the device is adapted to measure the power of a received signal at different times and further adapted to include a system for changing an incoming direction of the incident energy to allow measurements from different parts of the scene, and to provide an indication based on the measurements without using said measurements in the formation of an image of the scene. 
   
   
       29 . The detection device of  claim 28  wherein the device is adapted to measure radiation at a plurality of polarisations from the scene. 
   
   
       30 . The detection device of  claim 29  wherein a means for altering the polarisation of the radiation within the device is incorporated into the antenna. 
   
   
       31 . The detection device of  claim 30  wherein the receive element is sensitive to a first polarisation state, and the means for altering the polarisation periodically alters the polarisation of radiation orthogonal to the first polarisation state such that it is in the first polarisation state. 
   
   
       32 . The detection device of  claim 31  wherein the polarity changing means incorporates a fixed quarter-wave plate and at least one moveable quarter-wave plate arranged such that the position of the (at least one) moveable quarter-wave plate determines which polarisation of the radiation incident upon the optical system will be detectable by the receive element. 
   
   
       33 . The detection device of  claim 32  wherein the quarter-wave plates are fitted with polarising elements. 
   
   
       34 . The detection device of  claim 32  wherein the at least one moveable quarter-wave plate is rotatably mounted such that radiation incident upon the optical system may be directed through the at least one moveable quarter-wave plate, and at different angular positions the radiation passing through the at least one quarter wave plate sees orthogonal fast axes. 
   
   
       35 . The detection device of  claim 32  wherein the quarter-wave plates comprise meanderline structures. 
   
   
       36 . The detection device of  claim 28  wherein the device includes an internal millimetre-wave source arranged to periodically provide a reference signal to the receive element, the reference signal being used in calibration of the device. 
   
   
       37 . The detection device of  claim 36  wherein the antenna comprises an optical system, and the internal millimetre-wave source comprises a radiation absorbent material rotatably mounted such that it periodically interrupts the path of the radiation received by the optical system. 
   
   
       38 . The detection device of  claims 28  wherein the device is arranged to change the direction of arrival of the incoming radiation with time. 
   
   
       39 . The detection device of  claim 38  wherein the device is arranged to male successive measurements at orthogonal polarisations. 
   
   
       40 . The detection device of  claim 39  wherein the device is arranged to measure successive measurements in a particular direction at orthogonal polarisations. 
   
   
       41 . The detection device of  claim 38  wherein a refractive element is mounted in the path of the received radiation, the refractive element being rotatable such that different rotational positions result in energy from differing directions being passed to the receive element. 
   
   
       42 . The detection device of  claim 41  wherein the refractive element comprises a prism. 
   
   
       43 . The detection device of  claim 41  wherein the refractive element comprises at least one segment of a cone. 
   
   
       44 . The detection device of  claim 41  wherein the refractive element comprises a parallel faced slab rotatably mounted such that a normal to a parallel face does not lie on the axis of the antenna. 
   
   
       45 . The detection device of  claim 28  wherein the device is arranged to change the beamwidth of a receive beam with time. 
   
   
       46 . The detection device of  claim 45  wherein the antenna comprises an optical system incorporating at least one dielectric lens, the beamwidth of which is arranged to be changed by means of changing the focal length of one or more lens elements making up the optical system. 
   
   
       47 . The detection device of  claim 46  wherein the means for changing the focal length of one or more of the lens elements comprises apparatus for switching different lenses into the path of the received radiation. 
   
   
       48 . The detection device of  claim 28  wherein the antenna comprises an optical system incorporating an afocal telescope. 
   
   
       49 . A method of detecting objects present in a scene by means of receiving millimetre wave radiation from the scene through a redirector for redirecting an incoming direction of the radiation, wherein:
 a first measurement is made of radiation from a first part of the scene using the redirector;   a further measurement is made of radiation from a second part of the scene using the redirector wherein the second part of the scene may overlap with the first part of the scene; and   an indication is provided if characteristics of the first measurement are different to characteristics of the further measurement without using said measurements to form an image of the scene.   
   
   
       50 . The method of  claim 49  wherein an observed characteristic is the received power level. 
   
   
       51 . The method of  claim 50  wherein power levels at orthogonal polarisations are used as an observed characteristic. 
   
   
       52 . The method of  claim 49  wherein the incoming radiation is focused onto a receive element by means of an optical system. 
   
   
       53 . The method of  claim 52  wherein the optical system incorporates scanning means to change with time the direction of arrival of the incoming radiation such that measurements from different parts of the scene are taken. 
   
   
       54 . The method of  claim 52  wherein the receive element is sensitive to the polarisation of the incoming radiation, and means is incorporated for altering the polarisation of incoming radiation. 
   
   
       55 . A detection device for discriminating between different materials comprising an antenna element and a receive element characterized in that the receive element is sensitive to millimeter-wave radiation, the antenna element is arranged to provide incident energy from a scene to the receive element, and the device is adapted to measure the power of a received signal at different times and further adapted to include optics for changing the beamwidth of the antenna to allow measurements from different sized parts of the scene, and provide an indication based on the measurements, without using said measurements in the formation of an image of the scene.