Remote detection and measurement of objects

• US 9,182,481 B2
• Filed: 03/18/2009
• Issued: 11/10/2015
• Est. Priority Date: 03/18/2008
• Status: Active Grant

• Current Assignee: Radio Physics Solutions Ltd.
• Original Assignee: Radio Physics Solutions Ltd.
• Inventors: Bowring, Nicholas, Andrews, David, Rezgui, Nacer Ddine, Harmer, Stuart
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): BOOSALIS, FANI POLYZOS
• Application Number:
  US12/519,903
• Publication Number:
  US 20110181300A1
• Time in Patent Office: 2,428 Days
• Field of Search: 250/221, 250/267
• US Class Current: 1/1
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 13/08 Systems for measuring distance only indirect measurement G01S13/46
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• 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 7/411 Identification of targets based on measurements of radar reflectivity G01S7/415 takes precedence
• CPC Class Codes: G01S 7/417 involving the use of neural networks

Abstract

Provided are methods of using electromagnetic waves for detecting metal and/or dielectric objects. Methods include directing microwave and/or mm wave radiation in a predetermined direction using a transmission apparatus, including a transmission element; receiving radiation from an entity resulting from the transmitted radiation using a detection apparatus; and generating one or more detection signals in the frequency domain using the detection apparatus. Methods may include operating a controller, wherein operating the controller includes causing the transmitted radiation to be swept over a predetermined range of frequencies, performing a transform operation on the detection signal(s) to generate one or more transformed signals in the time domain, and determining, from one or more features of the transformed signal, one or more dimensions of a metallic or dielectric object upon which the transmitted radiation is incident. A system and method for remote detection and/or identification of a metallic threat object using late time response (LTR) signals is also disclosed.

Claims

1. A system for remote detection and/or identification of a metallic threat object, comprising:

a transmission apparatus, including a transmission element, configured to direct microwave and/or mm wave radiation in a predetermined direction,

a detection apparatus configured to receive radiation from an entity resulting from the transmitted radiation and to generate one or more detection signals in the frequency domain, and

control circuitry, the control circuitry being operable to

(i) cause the transmitted radiation to be swept over a predetermined range of frequencies,

(ii) perform a transform operation on the detection signal(s) to generate one or more transformed signals in the time domain,

(iii) extract, from one or more features of the transformed signal, a late time response (LTR) signal of the metallic threat object upon which the transmitted radiation is incident, the metallic threat object being carried by or associated with the entity; and

(iv) from the LTR signal, determine the presence and/or identity of the metallic threat object.

2. The system of claim 1, wherein said one or more detection signals in the frequency domain comprise a target signal in the presence of the entity and a background signal;

and the control circuitry is operable, after an operation to cause the transmitted radiation to be swept over a predetermine range of frequencies, to subtract background signal from the target signal to provide a corrected detection signal.

3. The system of claim 1, wherein an operation to extract from one or more features of the transformed signal, a late time response (LTR) signal of the metallic threat object upon which the transmitted radiation is incident, the metallic threat object being carried by or associated with the entity includes time gating the transformed signal to derive the LTR signal.

4. The system of claim 3, wherein an operation to determine the presence and/or identity of the metallic threat object from the LTR signal includes applying a pole extraction technique to the LTR signal to obtain a set of poles.

5. The system of claim 3, wherein an operation to determine the presence and/or identity of the metallic threat object from the LTR signal includes filtering the set of poles obtained from time gating the transferred signal to derive the LTR signal to remove unwanted poles and leave remaining poles.

6. The system claim 3, wherein time gating the transformed signal to derive the LTR signal includes using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal.

7. The system of claim 6, using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes analyzing both amplitude and frequency content of the spectral data for each windowed portion.

8. The system of claim 7, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes for each window, applying thresholds (T_A, T_v) to both amplitude change and frequency change compared to previous windowed portion.

9. The system of claim 8, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes deriving the position of the start of an Early Time Response (ETR) from that where amplitude change >

T_A and frequency change >

T_f.

10. The system of claim 9, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes deriving the position of the end of the ETR and start of the LTR from that where amplitude change <

T_A and frequency change >

T_v.

11. The system of claim 10, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes deriving the position of the end of the LTR from that where amplitude change >

T_A and frequency change <

T_v.

12. The system of claim 3, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes locating the position of the absolute maximum value in the transformed signal.

13. The system of claim 12, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes using absolute maximum value to indicate the position of the start and end of the ETR.

14. The system of claim 13, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes retrieving from a database two user set time delays (d1 and d2).

15. The system of claim 14, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes sampling the transformed signal starting from time delay d1 after time position of absolute maximum value and for a time length equal to time delay d2.

16. The system of claim 12, wherein using sliding time windows to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal includes using and/or storing sampled data as the LTR.

17. The system of claim 1, wherein an operation to determine the presence and/or identity of the metallic threat object from the LTR signal includes accessing a library of poles for known threat objects.

18. The system of claim 1, wherein, an operation to determine the presence and/or identity of the metallic threat object from the LTR signal includes using predetermined criteria, comparing the remaining poles with the library of poles;

and thereby making a determination of a level of certainty (between 0 and

     1) of the presence of the metallic threat object, and/or the identity of the metallic threat object.

19. The system of claim 18, wherein said identity comprises a specific identity of threat object or a class of threat object.

20. The system of claim 1, wherein:

an operation to cause the transmitted radiation to be swept over a predetermined range of frequencies includes stepwise sweeping by predetermined steps in frequency; and

an operation to perform a transform operation on the detection signal(s) to generate one or more transformed signals in the time domain includes performing a transform operation after each step to produce a time domain or optical depth domain trace, and storing each time domain or optical depth domain trace in a respective sweep channel, said time domain or optical depth domain traces thereby comprising said transformed signals.

21. The system of claim 1, further including a neural network for making a determination of level of certainty (between 0 and 1) of a presence of the metallic threat object, and/or an identity of the metallic threat object.

22. The system of claim 1, wherein the transmission element comprises a dual polarized transmission antenna.

23. The system of claim 1, wherein the detection apparatus comprises a dual polarized detection antenna.

24. A threat object detection system, for remote detection and/or identification of a metallic threat object being carried by or associated with the entity, comprising:

a plurality of detection systems, each detection system being in accordance with claim 1, the detection systems being arranged spaced apart in relation to a closed path defined by walls and to be traversed by the entity, whereby, in use, transmitted radiation from at least one of the detection systems is incident upon the entity.

25. The system of claim 24, wherein the walls comprise microwave transparent panels.

26. The system of claim 24, wherein the detection systems are disposed on the side of the panels opposite the path.

27. The system of claim 24, wherein adjacent the transmission elements and detection elements of the detection systems are provided anechoic elements.

28. The system of claim 24, wherein the anechoic elements comprise microwave absorbing foam blocks.

29. The system of claim 24, wherein the anechoic elements are substantially aligned with respective walls.

30. The system of claim 1, wherein extracting the LTR signal from one or more features of the transformed signal comprises removing an early time response from the transformed signal.

31. A method that uses control circuitry for remote detection and/or identification of a metallic threat object,

the method comprising

(i) causing transmitted radiation to be swept over a predetermined range of frequencies, wherein the transmitted radiation corresponds to microwave and/or mm wave radiation that is directed in a predetermined direction by a transmission apparatus including a transmission element;

(ii) performing a transform operation on detection signal(s) to generate one or more transformed signals in the time domain, wherein the detection signal(s) correspond to one or more detection signals generated in the frequency domain by a detection apparatus that is configured to receive radiation from an entity resulting from the transmitted radiation;

(iii) extracting, from one or more features of the transformed signal, a late time response (LTR) signal of the metallic threat object upon which the transmitted radiation is incident, the metallic threat object being carried by or associated with the entity; and

(iv) from the LTR signal, determining the presence and/or identity of the metallic threat object.

32. The method of claim 31, wherein said one or more detection signals in the frequency domain comprise a target signal in the presence of the entity and a background signal;

and the method comprises, after causing the transmitted radiation to be swept over a predetermined range of frequencies, subtracting background signal from the target signal to provide a corrected detection signal.

33. The method of claim 31, wherein extracting, from one or more features of the transformed signal, a late time response (LTR) signal of the metallic threat object upon which the transmitted radiation is incident, the metallic threat object being carried by or associated with the entity;

comprises time gating the transformed signal to derive the LTR signal.

34. The method of claim 33, wherein time gating the transformed signal to derive the LTR signal comprises using sliding time window to analyze (e.g. by FFT) spectral content of discrete windowed portions of the transformed signal.

35. The method of claim 34, wherein time gating the transformed signal to derive the LTR signal further comprises analyzing both amplitude and frequency content of the spectral data for each windowed portion.

36. The method of claim 35, wherein time gating the transformed signal to derive the LTR signal further comprises for each window, applying thresholds (T_A, T_v) to both amplitude change and frequency change compared to previous windowed portion.

37. The method of claim 36, wherein time gating the transformed signal to derive the LTR signal further comprises deriving the position of the start of an Early Time Response (ETR) from that where an amplitude change >

T_A and a frequency change >

T_f.

38. The method of claim 37, wherein time gating the transformed signal to derive the LTR signal further comprises deriving the position of the end of the ETR and start of the LTR from that where the amplitude change <

T_A and the frequency change >

T.

39. The method of claim 38, wherein time gating the transformed signal to derive the LTR signal further comprises deriving the position of the end of the LTR from that where the amplitude change >

T_A and the frequency change <

T.

40. The method of claim 33, wherein time gating the transformed signal to derive the LTR signal comprises locating a position of the absolute maximum value in the transformed signal.

41. The method of claim 40, wherein time gating the transformed signal to derive the LTR signal further comprises using absolute maximum value to indicate the positions of the start and end of an ETR.

42. The method of claim 41, wherein time gating the transformed signal to derive the LTR signal further comprises retrieving from a database two user set time delays (d1 and d2).

43. The method of claim 42, wherein time gating the transformed signal to derive the LTR signal further comprises sampling the transformed signal starting from time delay d1 after time position of absolute maximum value and for a time length equal to time delay d2.

44. The method of claim 40, wherein time gating the transformed signal to derive the LTR signal further comprises using and/or storing sampled data as the LTR.

45. The method of claim 31, wherein determining the presence and/or identity of the metallic threat object from the LTR signal comprises applying a pole extraction technique to the LTR signal to obtain a set of poles.

46. The method of claim 31, wherein determining the presence and/or identity of the metallic threat object from the LTR signal further comprises filtering the set of poles obtained by time gating the transformed signal to derive the LTR signal to remove unwanted poles and leave remaining poles.

47. The method of claim 31, wherein determining the presence and/or identity of the metallic threat object from the LTR signal further comprises accessing a library of poles for known threat objects.

48. The method of claim 47, wherein determining the presence and/or identity of the metallic threat object from the LTR signal further comprises using predetermined criteria, comparing the remaining poles with the library of poles;

and thereby making a determination of a level of certainty (between 0 and

     1) of the presence of the metallic threat object, and/or an identity of the metallic threat object.

49. The method of claim 48, wherein said identity comprises a specific identity of the metallic threat object or a class of threat object.

50. The method of claim 31, wherein:

causing the transmitted radiation to be swept over a predetermined range of frequencies comprises stepwise sweeping by predetermined steps in frequency; and

performing a transform operation on the detection signal(s) to generate one or more transformed signals in the time domain comprises performing a transform operation after each step to produce a time domain or optical depth domain trace, and storing each time domain or optical depth domain trace in a respective sweep channel, said time domain or optical depth domain traces thereby comprising said transformed signals.

51. The method of claim 31, further comprising determining, using a neural network, a level of certainty (between 0 and 1) of the presence of the metallic threat object, and/or the identity of the metallic threat object.

52. A computer program product for remote detection of one or more dimensions of a metallic or dielectric object, the computer program product comprising a non-transitory computer usable storage medium having computer readable program code embodied in the medium, the computer readable program code configured to carry out the method of claim 31.

53. The method of claim 31, wherein extracting the LTR signal from one or more features of the transformed signal comprises removing an early time response from the transformed signal.