Contraband detection system

• US 5,073,782 A
• Filed: 12/19/1988
• Issued: 12/17/1991
• Est. Priority Date: 04/19/1988
• Status: Expired due to Term

• Current Assignee: MVT Equity LLC
• Original Assignee: Millitech Corporation (Proxim Wireless Corporation)
• Inventors: Huguenin, G. Richard, Walker, David K., Goldsmith, Paul F., Deo, Naresh C.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/286,210
• Time in Patent Office: 1,093 Days
• Field of Search: 342/179, 342/351, 342/53, 250/330-332, 250/334
• US Class Current: 342/179
• CPC Class Codes: G01S 13/06 Systems determining position data of a target
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves
• CPC Class Codes: G01S 7/032 Constructional details for solid-state radar subsystems
• CPC Class Codes: G01S 7/41 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01V 8/005 operating with millimetre waves, e.g. measuring the black losey radiation
• CPC Class Codes: H01Q 1/247 with frequency mixer, e.g. for direct satellite reception or Doppler radar
• CPC Class Codes: H01Q 13/085 Slot-line radiating ends
• CPC Class Codes: H01Q 15/248 using a reflecting surface, e.g. twist reflector combination with a polarisation filter in dual reflector antennas H01Q19/195
• CPC Class Codes: H01Q 3/46 Active lenses or reflecting arrays

Abstract

A contraband detection system especially suited for detecting concealed non-metallic contraband such as ceramic or plastic weapons or illegal drugs carried by a person is disclosed. Plural sources of quasi-coherent millimeter wave radiation are disposed so as to uniformly illuminate a field of view. In the preferred embodiment, the radiation emitted by the sources is linearly polarized in a single plane such that the polarization of the radiation with respect to the plane in which linearly polarized radiation is preferentially received by the detectors can be controlled. For detection of dielectric objects, such as ceramic weapons or narcotics, these planes of polarization should be orthogonal to one another. The detector is a staring array which does not require scanning to generate an image of the entire field of view; the signal provided by each element of the detector array corresponds to the illumination reflected from objects in a single portion of the field of view. Real-time imaging of concealed dielectric and metallic objects is thus made possible.

Claims

1. A source of radiation for illuminating a field of view with millimeter-wave radiation for contraband detection purposes, comprising:

a two-dimensional array of point sources of polarized radiation, each comprising a millimeter-wave oscillator coupled to radiative antenna elements for emitting polarized millimeter-wave energy toward a field of view, wherein the radiation emitted by all of said sources exhibits a first characteristic polarization, and wherein the oscillators are not constrained to emit radiation in phase with one another, or at the identical frequency, such that the radiation emitted by the array is quasi-coherent.

2. The source of claim 1, in combination with detector means, said detector means being preferentially sensitive to millimeter wave radiation polarized orthogonal to said first characteristic polarization.

3. The combination of claim 2, further comprising means for focusing radiation from the field of view onto said detector means.

4. The combination of claim 3, further comprising a second substantially similar two-dimensional array of point sources of radiation aligned such that the radiation from both said sources exhibits said first characteristic polarization, and such that said sources illuminate the field of view in a substantially uniform manner.

5. The combination of claim 2, wherein said first characteristic polarization is linear polarization, and said detector means comprises an array of detectors, each detector comprising a pair of planar antenna elements formed on a substrate defining a plane of preferential sensitivity to linearly polarized radiation, and a non-linear circuit element connected across said pair of antenna elements.

6. A method of detecting contraband, comprising the steps of:

uniformly illuminating a field of view, within which are disposed objects or persons to be examined, with millimeter-wave radiation,

wherein said illumination radiation is quasi-coherent, exhibiting a first characteristic polarization;

disposing a two-dimensional array of detectors sensitive to millimeter-wave radiation in a position such that radiation reflected from objects or persons in the field of view is incident thereon, each of said detectors providing an output signal responsive to said radiation reflected from objects or persons in a corresponding portion of the field of view; and

forming a real time image of the objects or persons within said field of view, responsive to illumination radiation reflected therefrom detected by the elements of the array,

wherein the pixels of the image correspond to radiation from particular portions of the field of view.

7. The method of claim 6, wherein said elements of said array are preferentially responsive to radiation polarized orthogonally to said first characteristic polarization.

8. The method of claim 7, wherein said first characteristic polarization is linear polarization.

9. Apparatus for detection of contraband, comprising:

at least one two-dimensional array of spatially distributed point sources of millimeter wave radiation arranged to illuminate a field of view, wherein said point sources comprising oscillators that are not constrained to oscillate at the same frequency,

means for focusing millimeter wave radiation from the field of view onto a focal plane, and

a two-dimensional array of detectors disposed in said focal plane, each of said detectors generating an output signal responsive to millimeter-wave radiation from a particular portion of the field of view,

whereby said output signals may be provided to means for displaying an image of the field of view, the pixels of the displayed image corresponding to the output signals generated by the elements of the array.

10. The apparatus of claim 9, wherein said sources of radiation all emit radiation with a particular polarization, and said detectors are preferentially sensitive to radiation polarized orthogonally to said radiation emitted by said sources.

11. Apparatus for detection of contraband, comprising:

at least one two-dimensional array of spatially distributed point sources of millimeter wave radiation arranged to illuminate a field of view;

means for focusing millimeter wave radiation from the field of view onto a focal plane; and

a two-dimensional array of detectors disposed in said focal plane, each of said detectors generating an output signal responsive to millimeter-wave radiation from a particular portion of the field of view,

whereby said output signals may be provided to means for displaying an image of the field of view, the pixels of the displayed image corresponding to the output signals generated by the elements of the array,

wherein said sources of radiation all emit radiation with a particular polarization, and said detectors are preferentially sensitive to radiation polarized orthogonally to said radiation emitted by said sources.

12. The apparatus of claim 11, wherein said point sources of radiation each emit radiation at substantially a single frequency.

13. The apparatus of claim 11, wherein the radiation emitted by said sources of radiation is linearly polarized in a first plane, and the detectors of said array are preferentially sensitive to radiation linearly polarized in a second plane.

14. The apparatus of claim 13, wherein said first plane is orthogonal to said second plane.

15. The apparatus of claim 13, further comprising means for varying the relative orientation of said first and second planes responsive to the nature of the contraband to be detected.

16. The apparatus of claim 13, wherein each of the detectors of said array comprises paired antenna elements adapted to detect millimeter-wave radiation, and means for rectifying the radiation thus detected.

17. The apparatus of claim 16, wherein the paired antenna elements each comprise planar conductors formed on a substrate, and the means for rectifying comprises a non-linear circuit element connected across said pair of planar conductors.

18. The apparatus of claim 17 wherein said non-linear circuit elements are diodes.

19. The apparatus of claim 17 wherein said detectors are preferentially sensitive to radiation linearly polarized parallel to the plane of said substrate.

20. The apparatus of claim 11, wherein said sources of said at least one two-dimensional array comprise oscillators which are not constrained to operate at the same frequency.

21. The apparatus of claim 20, wherein said oscillators comprise solid state oscillators.

22. The apparatus of claim 21, wherein said solid state oscillators are Gunn diode oscillators.

23. The apparatus of claim 11, further comprising local oscillator means for providing a local oscillator signal to the array of detectors, whereby said detectors individually mix said local oscillator signal with the radiation received from the corresponding portion of the field of view.

24. The apparatus of claim 23, wherein one of said sources of radiation provides said local oscillator signal.

25. Apparatus for detection of contraband, comprising:

plural two-dimensional arrays of spatially distributed point sources of millimeter wave radiation disposed to uniformly illuminate a field of view;

means for focusing millimeter wave radiation from the field of view onto a focal plane; and

a two-dimensional array of detectors disposed in said focal plane, each of said detectors generating an output signal responsive to millimeter-wave radiation from a particular portion of the field of view,

whereby said output signals may be provided to means for displaying an image of the field of view, the pixels of the displayed image corresponding to the output signals generated by the elements of the array.

26. Apparatus for detection of contraband, comprising:

at least one two-dimensional array of spatially distributed point sources of millimeter wave radiation arranged to illuminate a field of view;

means for focusing millimeter wave radiation from the field of view onto a focal plane;

a two-dimensional array of detectors disposed in said focal plane, each of said detectors generating an output signal responsive to millimeter-wave radiation from a particular portion of the field of view;

display means for displaying an image of the field of view, the pixels of the displayed image corresponding to the output signals, generated by the elements of the array and provided to said display means; and

image signal processing means for enhancing the image displayed on said display means.

27. Apparatus for the detection of contraband, comprising:

at least one source of polarized radiation, said source being arranged to substantially uniformly illuminate a field of view with radiation exhibiting a first characteristic polarization;

means for focusing radiation from the field of view onto a focal plane; and

an array of detectors disposed in said focal plane, each detector generating an output signal responsive to radiation reflected from objects in a particular portion of the field of view, said detectors being preferentially sensitive to radiation exhibiting a polarization different from said first characteristic polarization, such that the relative amplitude of the output signals is indicative of the material of the objects in the field of view;

whereby said output signals may be provided to means for displaying an image of the field of view, and in which the pixels of the displayed image correspond to the output signals generated by the detectors of the array.

28. The apparatus of claim 27, wherein said source of polarized radiation comprises a two-dimensional array of point sources of radiation, all of which is similarly polarized.

29. The apparatus of claim 28, wherein said sources of said array each emit radiation at a single frequency, but are not constrained to emit at the same frequency, whereby said radiation illuminating the field of view is quasi-coherent.

30. The apparatus of claim 28, wherein said sources each comprise oscillator means.

31. The apparatus of claim 30, wherein said oscillator means each comprise solid-state oscillators.

32. The apparatus of claim 31, wherein said solid state oscillators are Gunn diode oscillators.

33. The apparatus of claim 27, wherein said first characteristic polarization is linear polarization in a first plane.

34. The apparatus of claim 33, wherein said detectors are preferentially selective to radiation linearly polarized in a second plane.

35. The apparatus of claim 34, wherein each of the detectors of said array comprises paired antenna elements adapted to detect millimeter-wave radiation, and means for rectifying the radiation thus detected.

36. The apparatus of claim 35, wherein the paired antenna elements each comprise planar conductors formed on a substrate, and said means for rectifying comprises a non-linear circuit element connected across said paired planar conductors.

37. The apparatus of claim 36, wherein said non-linear circuit elements are diodes.

38. The apparatus of claim 36, wherein said detectors are preferentially sensitive to radiation linearly polarized in a plane substantially parallel to the plane of said substrate.

39. The apparatus of claim 34, further comprising means for controlling the first plane of polarization of the radiation relative to the second plane of radiation to which the detectors are preferentially sensitive, in accordance with the material of the contraband to be detected.

40. The apparatus of claim 39, wherein said second plane is orthogonal to said first plane.

41. The apparatus of claim 27, wherein plural sources are provided and are disposed to uniformly illuminate the field of view.

42. The apparatus of claim 27, wherein said radiation emitted by said sources is of millimeter-wave frequency.