Method for metal object identification using a three-dimensional steerable magnetic field antenna

• US 7,106,194 B2
• Filed: 11/13/2002
• Issued: 09/12/2006
• Est. Priority Date: 11/16/2001
• Status: Expired due to Fees

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Nelson, Carl V.
• Primary Examiner(s): NGUYEN, HUNG T
• Application Number:
  US10/484,155
• Publication Number:
  US 20040178794A1
• Time in Patent Office: 1,399 Days
• Field of Search: 340/551, 340/568.1, 340/686.6, 340/691, 340/331, 340/825.36, 340/825.49, 340/552, 340/561, 340/668.6, 324/329, 324/326, 324/332, 324/344, 324/345, 324/323, 600/117, 600/407
• US Class Current: 324/329
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence

Abstract

A method for identifying a buried metal object using a three-dimensional steerable magnetic field (3DSMF) system. The method comprises generating a magnetic field vector (MFV) at a first MFV position above the buried metal object; measuring a time decay response at the first MFV position; generating a MFV at a next MFV position above the buried metal object; measuring a time decay response at the next MFV position; repeating the above steps until a complete 360-degree measurement of time decay responses of the buried metal object is completed; processing all measured time decay responses with a target search algorithm to determine a magnetic polarizability tensor of the buried metal object; and identifying the buried metal object by matching the magnetic polarizability tensor of the buried metal object to a known magnetic polarizability tensor of an object.

Claims

1. A method for identifying a buried metal object using a three-dimensional steerable magnetic field (3DSMF) system, comprising:

(a) generating a magnetic field vector (MFV) at a first MFV position above the buried metal object;

(b) measuring a time decay response at the first MFV position;

(c) generating a MFV at a next MFV position above the buried metal object;

(d) measuring a time decay response at the next MFV position; and

(e) repeating steps (c) and (d) until a complete 360-degree measurement of time decay responses of the buried metal object is completed.

2. The method according to claim 1, further comprising processing all measured time decay responses with a target search algorithm to determine a magnetic polarizability tensor of the buried metal object.

3. The method according to claim 2, further comprising identifying the buried metal object by matching the magnetic polarizability tensor of the buried metal object to a known magnetic polarizability tensor of an object.

4. The method according to claim 3, wherein the known magnetic polarizability tensor of an object is stored in an object library including a plurality of known magnetic polarizability tensors of objects.

5. A method for identifying a buried metal object having a body of revolution (BOR) using a three-dimensional steerable magnetic field (3DSMF) system, comprising:

(a) generating a magnetic field vector (MFV) at a first MFV position above the buried metal object;

(b) measuring a time decay response at the first MFV position;

(c) generating a MFV at a next MFV position above the buried metal object;

(d) measuring a time decay response at the next MFV position; and

(e) repeating steps (c) and (d) until a predetermined range of measurements of time decay responses of the buried metal object is completed.

6. The method according to claim 5, further comprising (f) estimating a primary axis of the buried metal object from the predetermined range of measurements of time decay responses of the buried metal object.

7. The method according to claim 6, further comprising (g) refining the primary axis by generating and measuring additional MFVs and time decay responses, respectively, around the estimated primary axis.

8. The method according to claim 7, further comprising:

(h) generating a MFV at a first MFV position 90 degrees to the refined primary axis;

(i) measuring a time decay response at the first MFV position 90 degrees to the refined primary axis;

j) generating a MFV at a next MFV position 90 degrees to The refined primary axis;

(k) measuring a time decay response at the next MFV position; and

(l) repeating steps (j) and (k) until a predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object is completed.

9. The method according to claim 8, further comprising:

(m) testing the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object for symmetry; and

(n) if the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object are symmetrical, identifying the buried metal object by matching one of the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object to a known magnetic polarizability tensor of an object.

10. The method according to claim 9, wherein the known magnetic polarizability tensor of an object is stored in an object library including a plurality of known magnetic polarizability tensors of objects.

11. A method for identifying a buried metal object with a body of revolution (BOR) using a three-dimensional steerable magnetic field (3DSMF) system, comprising:

(a) generating a magnetic field vector (MFV) in an X-direction, a Y-direction, and a Z-direction above the buried metal object;

(b) measuring a time decay response in the X-direction, the Y-direction, and the Z-direction; and

(c) estimating a primary axis of the buried metal object from the measured time decay responses in the X-direction, the Y-direction, and the Z-direction.

12. The method according to claim 11, further comprising (d) refining the primary axis by generating and measuring additional MFVs and time decay responses, respectively, around the estimated primary axis.

13. The method according to claim 12, further comprising:

(e) generating a MFV at a first MFV position 90 degrees to the refined primary axis;

(f) measuring a time decay response at the first MFV position 90 degrees to the refined primary axis;

(g) generating a MFV at a next MFV position 90 degrees to the refined primary axis;

(h) measuring a time decay response at the next MFV position 90 degrees to the refined primary axis; and

(i) repeating steps (g) and (h) until a predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object is completed.

14. The method according to claim 13, further comprising:

(j) testing the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object for symmetry; and

(k) if the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object are symmetrical, identifying the buried metal object by matching one of the predetermined number of measurements of time decay responses 90 degrees to the refined primary axis of the buried metal object to a known magnetic polarizability tensor of an object.

15. The method according to claim 14, wherein the known magnetic polarizability tensor of an object is stored in an object library including a plurality of known magnetic polarizability tensors of objects.