Electromagnetic target discriminator sensor system and method for detecting and identifying metal targets

• US 20030052684A1
• Filed: 07/17/2002
• Published: 03/20/2003
• Est. Priority Date: 03/22/2000
• Status: Active Grant

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Nelson, Carl V, Cooperman, Charles B, Smith, Dexter G
• Granted Patent: US 6,853,194 B2
• Time in Patent Office: Days
• US Class Current: 324/329
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence
• CPC Class Codes: G01V 3/105 forming directly coupled primary and secondary coils or loops
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat
• CPC Class Codes: G06V 10/255 Detecting or recognising potential candidate objects based on visual cues, e.g. shapes

Abstract

A time-domain electromagnetic target discriminator (ETD) sensor system and method are provided capable of measuring a metal target'"'"'s time decay response based on the physical parameters of the metal target and its environment and for identifying the metal target. The ETD sensor system includes a pulse transmitter connected to a receiver via a data acquisition and control system. The transmitter and receiver include coil configurations for placement in proximity to a visually obscured, e.g., buried, metal target (or underground void) for inducing eddy currents within the metal target. The ETD sensor system measures the eddy current time decay response of the metal target in order to perform target recognition and classification. The identification process entails comparing the metal target'"'"'s (or, underground void or other object'"'"'s) time decay response with a library of normalized object signatures, e.g., time decay responses and other characteristics.

Claims

1. A system for detecting a visually obscured object or an underground void, said system comprising:

means for generating a first signal and a second signal from induced eddy currents;

means for determining if the first signal is greater than the second signal, the first signal is less than the second signal, and if the first signal is approximately equal to the second signal; and

means for determining the detection of the visually obscured object if the first signal is greater than the second signal, the detection of the underground void if the first signal is less than the second signal, and the non-detection of the visually obscured object or the underground void if the first signal is approximately equal to the second signal.

2. The system according to claim 1, further comprising means for storing within a library of object signatures characteristics of a time decay response signal generated by subtracting the first signal from the second signal and a description of the detected visually obscured object or the underground void corresponding to the time decay response signal.

3. The system according to claim 1, further comprising at least one processor for executing programmable instructions for determining a time decay response corresponding to the visually obscured object or the underground void and identifying characteristics of said time decay response.

4. The system according to claim 3, wherein said at least one processor further executes programmable instructions for comparing the identified characteristics of said time decay response with a library of object signatures for identifying at least the type of visually obscured object or the configuration of the underground void.

5. The system according to claim 1, wherein said means for generating the first and second signals includes an antenna having a transmitter coil and two receiver coils, where the transmitter coil surrounds at least one of the two receiver coils.

6. The system according to claim 5, wherein the means for determining if the first signal is greater than the second signal, the first signal is less than the second signal, and if the first signal is approximately equal to the second signal includes a differential amplifier for subtracting the first signal from the second signal and outputting a time decay response signal.

7. The system according to claim 5, wherein the two receiver coils of the antenna are at least one receiver coil diameter apart.

8. The system according to claim 5, wherein the transmitter coil has a rectangular configuration having a length of approximately 60 cm and a width of approximately 20 cm, and each of the two receiver coils has a square-like configuration with each side measuring approximately 10 cm.

9. The system according to claim 5, wherein the transmitter coil has a rectangular configuration having a length of approximately 100 cm and a width of approximately 60 cm, and each of the two receiver coils has a square-like configuration with each side measuring approximately 30 cm.

10. The system according to claim 5, wherein the transmitter coil has at least six loop turns and each of the two receiver coils has 16 loop turns.

11. The system according to claim 6, wherein the differential amplifier begins outputting the time decay response signal approximately 3 to 5 μ

s after current flow to the transmitter coil is turned off.

12. The system according to claim 1, wherein said system includes means for measuring target decay time constants corresponding to the buried object or the underground void as short as 1.4 μ

s.

13. The system according to claim 5, wherein the two receiver coils cancel effects of electromagnetic noise and far-field metal object signals.

14. The system according to claim 6, further comprising an amplifier stage connected to the differential amplifier for receiving and amplifying the time decay response signal before transmitting the time decay signal to a computer control system.

15. A method for detecting a visually obscured object or underground void, said method comprising the steps of:

scanning a region with a sensor system having a transmitter coil, a first receiver coil and a second receiver coil for inducing eddy currents within the visually obscured object, the underground void, and/or soil;

converting the eddy currents received by the first receiver coil to a first signal and converting the eddy currents received by the second receiver coil to a second signal;

subtracting the first signal from the second signal to generate a time decay response signal;

determining whether the first signal is greater than the second signal, the first signal is less than the second signal, or if the first signal is approximately equal to the second signal; and

determining the detection of the visually obscured object if the first signal is greater than the second signal, the detection of the underground void if the first signal is less than the second signal, and the non-detection of the visually obscured object or the underground void if the first signal is approximately equal to the second signal.

16. The method according to claim 15, further comprising the step of storing within a library of object signatures characteristics of the time decay response signal generated by subtracting the first signal from the second signal and a description of the detected visually obscured object or the underground void corresponding to the time decay response signal.

17. The method according to claim 15, further comprising the step of comparing characteristics of the time decay response signal with a library of object signatures for identifying at least the type of visually obscured object or characteristics of the underground void.

18. The method according to claim 15, wherein the generation of the time decay response signal is initiated approximately 3 to 5 μ

s after current flow to the transmitter coil is turned off.

19. The method according to claim 15, further comprising the step of measuring decay time constants corresponding to the visually obscured object or the underground void as short as 1.4 μ

s.

20. The method according to claim 15, further comprising the step of using the first and second receiver coils to cancel effects of electromagnetic noise and far-field metal objects.

21. A sensor system for detecting visually obscured objects and underground voids by inducing eddy currents in same, said antenna comprising:

a transmitter coil;

two receiver coils surrounded by the transmitter coil and being at least one receiver coil diameter apart, each of said two receiver coils configured for converting the eddy currents into a first signal and a second signal; and

a differential amplifier for subtracting the first signal from the second signal.

22. The system according to claim 21, wherein the transmitter coil has a rectangular configuration having a length of approximately 60 cm and a width of approximately 20 cm, and each of the two receiver coils has a square-like configuration with each side measuring approximately 10 cm.

23. The system according to claim 21, wherein the transmitter coil has a rectangular configuration having a length of approximately 100 cm and a width of approximately 60 cm, and each of the two receiver coils has a square-like configuration with each side measuring approximately 30 cm.

24. The system according to claim 21, wherein the transmitter coil has at least six loop turns and each of the two receiver coils has 16 loop turns.

25. An algorithm for optimizing target characterization of a visually obscured object upon detection of said visually obscured object by a metal detector sensor system having a transmitter and a receiver, said algorithm comprising the steps of:

a. adjusting a first parameter of said metal detector sensor system and collecting a data set using the receiver;

b. analyzing the collected data set to determine at least one measurement of a time decay response corresponding to the object; and

c. adjusting a second parameter of said metal detector sensor system, collecting a data set using the receiver, and returning to step (b), if the determined at least one measurement is outside a predetermined range.

26. The algorithm according to claim 25, further comprising the steps of:

d. estimating a decay time response constant corresponding to the object; and

e. adjusting at least the first parameter based on the estimated decay time response constant.

27. The algorithm according to claim 26, further comprising the steps of:

f. collecting a plurality of data sets, including an object data set corresponding to the object and background data sets corresponding to non-object areas, using the receiver;

g. averaging the background data sets to obtain an average background data set; and

h. subtracting the average background data set from the object data set.

28. The algorithm according to claim 27, further comprising the steps of:

i. determining a characteristic of the object'"'"'s time decay response;

j. adjusting at least the second parameter and returning to step (f), if the characteristic is less than a predetermined threshold; and

k. adjusting at least the second parameter and returning to step (f), if the characteristic is greater than the predetermined threshold.

29. The algorithm according to claim 28, further comprising the step of classifying the visually obscured object, said step comprising the steps of:

l. comparing the object'"'"'s time decay response with a library of normalized time decay responses each corresponding to an object;

m. identifying a time decay response from the library approximating the object'"'"'s time decay response; and

n. determining the visually obscured object to be the object corresponding to the identified time decay response.

30. The algorithm according to claim 29, further comprising the step of appending the library by storing the object'"'"'s time decay response within the library with a corresponding description of the object.

31. The algorithm according to claim 30, wherein the library is appended in real-time.

32. The algorithm according to claim 25, wherein the first parameter of said detector is a transmitter pulse rate.

33. The algorithm according to claim 32, wherein step (a) adjusts the transmitter pulse rate to approximately 5 kHz.

34. The algorithm according to claim 28, wherein the second parameter of said metal detector sensor system is a transmitter current of said sensor system.

35. The algorithm according to claim 25, further comprising the step of adjusting a data sample window of said detector to approximately 100 μ

s upon detection of said visually obscured object.

36. The algorithm according to claim 25, wherein step (e) includes adjusting a transmitter pulse rate, a data sample window, and a digitizer sample rate of said detector based on the estimated decay time response constant, where the transmitter pulse rate is the first parameter.

37. The algorithm according to claim 25, wherein the at least one measurement includes a saturation and a voltage measurement of the time decay response corresponding to the object.

38. The algorithm according to claim 28, wherein step (k) further includes adjusting at least the first parameter of said metal detector sensor system.

39. The algorithm according to claim 38, wherein step (k) includes adjusting a transmitter pulse rate, a data sample window, and a digitizer sample rate of said metal detector sensor system, where the transmitter pulse rate is the first parameter.

40. An algorithm for optimizing target characterization of a visually obscured object upon detection of said visually obscured object by a detector having a transmitter and a receiver, said algorithm comprising the steps of:

a. collecting a plurality of data sets from a plurality of respective receiver positions in proximity to the position of the visually obscured object using the detector; and

b. computing the plurality of data sets to derive a single data set.

41. The algorithm according to claim 40, further comprising the step of classifying the visually obscured object, said step comprising the steps of:

c. comparing the single data set with a library of data sets each corresponding to an object;

d. identifying a data set from the library approximating the single data set; and

e. determining the visually obscured object to be the object corresponding to the identified data set.

42. The algorithm according to claim 41, further comprising the step of appending the library by storing the single data set within the library with a corresponding description of the visually obscured object.

43. The algorithm according to claim 42, wherein the library is appended in real-time.

44. The algorithm according to claim 40, wherein the visually obscured object is one of an underground void, a low metal content target, and a medium to high metal content target.

45. The algorithm according to claim 40, wherein the step of computing entails averaging the plurality of data sets to obtain the single data set, wherein the single data set represents an average data set.