Flexible coil assembly for reflectance-mode nondestructive eddy-current examination

• US 5,047,719 A
• Filed: 05/25/1990
• Issued: 09/10/1991
• Est. Priority Date: 05/25/1990
• Status: Expired due to Term

• Current Assignee: Failure Group, Inc. (Exponent Incorporated)
• Original Assignee: Failure Group, Inc. (Exponent Incorporated)
• Inventors: Johnson, Duane, Krampfner, Yehuda
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US07/528,753
• Time in Patent Office: 473 Days
• Field of Search: 324/234, 324/236, 324/239-243, 324/262, 324/263, 336/20, 336/200
• US Class Current: 324/242
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01N 27/904 with two or more sensors

Abstract

An improved flexible coil array for nondestructive reflective-mode eddy-current testing of conductive members is disclosed. The assembly comprises a flexible substrate having a first array of coils formed on one side thereof. The first array of coils are connected in series in parallel columns. One end of each of the rows is connected to a common ground connection, while the other ends of each row are successively connected to a source of excitation energy. A second array of series-connected rows of coils, orthogonal to the columns, is formed on the opposite side of the substrate. Again, one end of each of the rows is connected to a common point while the other end of each of the rows is successively connected to means for detecting a voltage induced on the coils of the row. The voltage will vary if one of the coils is disposed in juxtaposition to a discontinuity of the member to be inspected. Comparison of voltages induced on the various rows of coils, together with indication of the column of driver coils which is being driven at the time of detection of a variation in the voltage, locates any discontinuity in the member to be inspected. The coils may be made up of pairs of half-coils connected in series to form the rows and columns.

Claims

1. A flexible coil assembly for non-destructive eddy-current examination of electrically conductive members, comprising:

a flexible planar substrate;

a first array of driver coils disposed on one side of said flexible substrate, said first array comprising a plurality of parallel columns of pairs of coils connected in series to one another, each of said parallel columns of pairs of coils comprising parallel outgoing and return lines, each line consisting of a plurality of series-connected coils, the lines having terminal and opposite ends, the terminal ends of said lines being connected to means for controllably connecting said columns to a source of excitation energy and the opposite ends of said lines being connected to one another, whereby current flows in opposite directions in the outgoing and return lines of each column; and

a second array of detector coils disposed on the opposite side of said flexible substrate, said second array comprising a plurality of parallel rows of coils connected in series to one another, said rows extending in a direction other than parallel to said columns, each of said parallel rows of pairs of coils comprising parallel outgoing and return lines, each consisting of a plurality of series-connected coils, the lines having terminal and opposite ends, the terminal ends of said outgoing and return lines being connected to means for controllably connecting said rows to means for processing signals detected by one or more of the coils of the corresponding row, and the opposite ends of said lines being connected to one another, whereby current flows in opposite directions in the outgoing and return lines of each row.

2. The assembly of claim 1, wherein each of the pairs of coils of said rows of detector coils comprises an upper and a lower half-coil, the upper half-coils being connected in series to the lower half-coils.

3. The assembly of claim 1, wherein each of the pairs of coils of said columns of driver coils comprises an upper and a lower half-coil, the upper half-coils being connected in series to the lower half-coils.

4. The assembly of claim 1, further comprising switch means mounted on said substrate for controllably connecting said rows to said means for processing.

5. The assembly of claim 4, wherein said switch means are responsive to control signals provided by control means external to said assembly.

6. The assembly of claim 4, in combination with computer means, and with means for connecting said computer means by a plurality of control lines to said switch means.

7. The assembly of claim 1, further comprising a plurality of controllable switch means mounted on said first substrate, each of said switches being connected to one of said parallel rows of coils, for controlling connection of the corresponding row to a source of excitation energy, and means for supplying control signals to said controllable switch means.

8. The assembly of claim 7, wherein said means for supplying control signals to said controllable switch means is a plurality of control lines connected to control means external to said assembly.

9. The assembly of claim 7, in combination with computer means for providing control signals to said switch means.

10. The assembly of claim 1, wherein said coils and conductors connecting them to form said rows and columns are printed on said flexible substrate.

11. The assembly of claim 10, wherein each of said coils comprises a loop.

12. The assembly of claim 11, wherein said loops are generally circular in outline.

13. The assembly of claim 1, wherein said rows and columns are substantially orthogonal to one another, and said driver coils and detector coils of said arrays are substantially coaxial.

14. A method for non-destructive eddy-current examination of a conductive member, comprising the steps of:

placing an assembly of driver coils and of detector coils in close physical juxtaposition to the member to be examined, said assembly comprising;

a planar substrate;

a first array of driver coils disposed on one side of said substrate, said first array comprising a plurality of parallel columns of coils connected in series to one another, each of said parallel columns of coils comprising parallel outgoing and return conductors, said outgoing and return conductors each being formed to comprise a number of series-connected coils, inner ends of said conductors being connected to means for controllably connecting said columns to a source of excitation energy, and outer ends of said outgoing and return conductors being connected to one another. whereby equal and opposite currents flow in the parallel conductors of each column; and

a second array of detector coils disposed on the opposite side of said flexible substrate, said second array comprising a plurality of parallel rows of coils connected in series to one another, said rows extending in a direction other than parallel to said columns, each of said parallel rows of coils comprising parallel outgoing and return conductors, each of said conductors being formed to comprise a number of series-connected coils, inner ends of said conductors being connected to means for controllably connecting said rows to means for processing induced voltage signals detected by one or more of the coils of the corresponding row and outer ends of said conductors being connected to one another, whereby equal and opposite currents flow in the conductors of each column;

sequentially connecting a source of excitation energy to the columns of coils of the first array;

sequentially detecting and measuring the induced voltage signals in the rows of coils of the second array; and

analyzing variations in the signals detected by the second array of coils to locate discontinuities in the member to be examined.

15. The method of claim 14 wherein the impedance of each of the rows of coils in the second array is sequentially measured while the source of excitation energy is connected to a single one of the columns of coils.

16. The method of claim 14 wherein said source of excitation energy provides a sinusoidal signal at between 1 Hz and 100 mHz.

17. A system for eddy-current nondestructive examination of conductive members, comprising:

a coil assembly, comprising;

a planar substrate;

a first array of driver coils disposed on one side of said substrate, said first array comprising a plurality of parallel columns of pairs of coils connected in series to one another, the coils of each column being provided as two parallel series-connected arrays, the arrays being connected to one another at a first end of each, and being connected to means for controllably connecting said columns to a source of excitation energy at their second ends; and

a second array of detector coils disposed on the opposite side of said substrate, said second array comprising a plurality of parallel rows of coils connected in series to one another, said rows extending in a direction other than parallel to said columns, the coils of each column being provided as two parallel series-connected arrays, the arrays being connected to one another at a first end of each, and being connected to means for controllably connecting said rows to means for processing signals detected by one or more of the coils of the corresponding row;

a source of excitation energy at a predetermined frequency;

first multiplexing means for applying said energy in sequence to the plurality of columns of driver coils comprised by the flexible coil assembly;

second multiplexing means for sequentially receiving and storing induced voltage signals detected by the plurality of rows of detector coils also comprised by said flexible coil assembly; and

means for comparing the signals detected by the rows of detector coils and for identifying variations therein, and for determining the row and column of coils with respect to which the signals exhibiting the variations were recorded.

18. The system of claim 17, wherein said second multiplexing means comprises control means providing switch control signals, and switch means, responsive to control signals provided by said control means, mounted on said substrate for multiplexing the induced voltage signals.

19. The system of claim 18, wherein said first multiplexing means comprises a plurality of controllable switch means mounted on said first substrate, each of said switches being connected to one of said parallel rows of coils for controlling connection of the corresponding row to said source of excitation energy, and control line means connected to said control means for supplying control signals to said controllable switch means.

20. The system of claim 17, wherein said coils and conductors connecting them to form said rows and columns are printed on said substrate.

21. The system of claim 20 wherein each of said coils comprises a loop which is not fully closed.

22. The system of claim 21 wherein said loops are generally circular in outline.

23. The system of claim 17 wherein said rows and columns are generally orthogonal to one another and said driver coils and detector coils of said arrays are substantially coaxial.

24. The system of claim 17 wherein said coil assembly is flexible.

25. A flexible coil assembly for non-destructive eddy-current examination of electrically conductive members, comprising:

a flexible planar substrate;

a first array of driver coils disposed on one side of said flexible substrate, said first array comprising a plurality of first groups of coils connected in series to one another, each of said first groups being connected to means for controllably connecting said first groups to a source of excitation energy; and

a second array of detector coils disposed on the opposite side of said flexible substrate, said second array comprising a second plurality of second groups of coils connected in series to one another, each of said second groups being connected to means for controllably connecting said second groups to means for processing signals detected by one or more of the coils of the corresponding group wherein each of the coils of said first and second groups of coils comprises a first and a second half-coil, the first half-coils being connected in series to the second half-coils.

26. The assembly of claim 25, further comprising switch means mounted on said substrate for controllably connecting said first and second groups of coils to said source of excitation energy and to said means for processing, respectively.