Super sensitive eddy-current electromagnetic probe system and method for inspecting anomalies in conducting plates

• US 6,636,037 B1
• Filed: 03/31/2000
• Issued: 10/21/2003
• Est. Priority Date: 03/31/2000
• Status: Expired due to Term

• Current Assignee: Innovative Materials Technologies Incorporated
• Original Assignee: Innovative Materials Technologies Incorporated
• Inventors: Ou-Yang, Tian-He
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/540,370
• Time in Patent Office: 1,299 Days
• Field of Search: 324/240, 324/239, 324/229, 324/228, 324/232, 324/236, 324/237, 324/238, 324/242, 324/243, 324/217, 324/235, 324/262, 324/233, 324/234, 174/35.R, 174/35.CE
• US Class Current: 324/240
• CPC Class Codes: G01N 27/902 by moving the sensors
• CPC Class Codes: G01N 27/904 with two or more sensors

Abstract

Devices and methods for improved inspections of conducting structures of different shapes. An eddy-current probe includes an excitation coil unit, a magnetic detector within the probe, a signal-conditioning/preamplifier circuit within the probe, and a signal channel. The excitation coil unit is shielded on substantially all sides except an emission face that transmits an alternating magnetic signal to a conducting (e.g., metal) object, such that the metal object modifies the alternating magnetic signal. The magnetic detector within the probe is also shielded on substantially all sides except a reception face, such that the alternating magnetic signal as modified by the metal object is received into the shielded magnetic detector and converted into a first electrical signal. The signal-conditioning/preamplifier circuit within the probe is shielded on substantially all sides and provided with electrical power. The shielded preamplifier provides detection for very small signals, such as from magnetic probing of aircraft skin metals. Other embodiments include a traveling-wave excitation structure and a multiple-phase driving circuit, some of which include the shielded pre-amplifier, and others of which are not shielded. An eddy scope is described that provides a multiple-phase excitation signal to various different probes.

Claims

1. A method of transducing magnetic signals indicative of a flaw in a conducting object, comprising:

shielding an excitation coil on substantially all sides except an emission face;

transmitting an alternating magnetic signal to the conducting object from the shielded excitation coil, such that the alternating magnetic signal is modified by the conducting object;

shielding a magnetic detector within a probe on substantially all sides except a reception face;

receiving the alternating magnetic signal as modified by the conducting object into the shielded magnetic detector;

converting the received alternating magnetic signal into a first electrical signal within the shielded magnetic detector;

shielding a signal-conditioning circuit within the probe on substantially all sides;

providing electrical power to the shielded signal-conditioning circuit within the probe;

amplifying the first electrical signal with the signal-conditioning circuit to create a second electrical signal; and

analyzing phase and amplitude components of the second electrical signal to provide an indication of the flaw.

2. The method of claim 1, wherein the shielding the excitation coil comprises providing a cup-shaped copper shield that surrounds a ring-shaped steel shield that in turn surrounds an excitation coil having a ferromagnetic core.

3. The method of claim 1, wherein the shielding the magnetic detector comprises providing a cup-shaped copper shield that surrounds a steel flux-bypass shield that in turn surrounds a receiver coil having a ferromagnetic core.

4. The method of claim 3, wherein the ferromagnetic core of the magnetic detector is E-shaped, and the receiver coil is mounted on a central prong of the E-shaped ferromagnetic core.

5. The method of claim 1, wherein the shielding the signal-conditioning circuit comprises providing an aluminum shield that surrounds the signal-conditioning circuit on substantially all sides.

6. The method of claim 1, wherein the transmitting the alternating magnetic signal comprises transmitting a rotating magnetic field.

7. The method of claim 6, wherein the receiving and the converting the received alternating magnetic signal provides a differential first electrical signal.

8. The method of claim 1, wherein the transmitting the alternating magnetic signal comprises transmitting a traveling magnetic field.

9. The method of claim 8, wherein the receiving and the converting the received alternating magnetic signal provides a differential first electrical signal.

10. The method of claim 1, wherein the receiving and the converting the received alternating magnetic signal provides a differential first electrical signal.

11. The method of claim 1, wherein the shielding the signal-conditioning circuit includes shielding between the signal conditioning circuit and the magnetic detector.

12. The method of claim 1, wherein the amplifying the first electrical signal to create a second electrical signal also includes low-pass filtering.

13. An eddy-current probe system for detecting a flaw in a conducting object, the probe comprising:

an excitation coil unit shielded on substantially all sides except an emission face that transmits an alternating magnetic signal to the conducting object, such that the alternating magnetic signal is modified by the conducting object;

a magnetic detector within the probe shielded on substantially all sides except a reception face, such that the alternating magnetic signal as modified by the conducting object is received into the shielded magnetic detector and converted into a first electrical signal;

a signal-conditioning circuit within the probe, shielded on substantially all sides and provided with electrical power, which amplifies the first electrical signal to create a second electrical signal; and

a signal channel that transmits the second electrical signal to an instrument for analyzing phase and amplitude components of the second electrical signal to provide an indication of the flaw.

14. The system of claim 13, further comprising:

an eddy-scope, operatively coupled to the signal channel, that receives the transmitted second electrical signal, provides power the signal conditioning circuit and provides the analyzing phase and amplitude function for components of the second electrical signal, and that presents the indication of the flaw.

15. The system of claim 14, wherein the excitation coil unit comprises a coil having a ferromagnetic core, and is surrounded radially and axially by a cup-shaped first shield that surrounds substantially all sides except the emission face, wherein the ferromagnetic core of the excitation coil unit is surrounded radially by a ring-shaped second shield, located inside the cup of the first shield, wherein the first shield is substantially made of copper, and wherein the magnetic detector comprises an E-shaped ferromagnetic core having a coil mounted around a central prong of the E-shaped ferromagnetic core, a C-shaped steel flux bypass structure around and magnetically coupled to the E-shaped ferromagnetic core, and a copper shield surrounding C-shaped steel flux bypass structure and the E-shaped ferromagnetic core on substantially all sides except the reception face.

16. The system of claim 14, wherein the excitation coil unit comprises a multiple-phase coil configuration, and the eddy scope includes a multiple-phase excitation circuit that generates a plurality of phases of excitation signal to the excitation coil unit.

17. The system of claim 16, wherein the excitation coil unit comprises a traveling-wave multiple-phase coil configuration.

18. The system of claim 16, wherein the excitation coil unit comprises a rotating-wave multiple-phase coil configuration.

19. The system of claim 13, wherein the excitation coil unit comprises a coil having a ferromagnetic core, and is surrounded radially and axially by a cup-shaped first shield that surrounds substantially all sides except the emission face.

20. The system of claim 19, wherein the ferromagnetic core of the excitation coil unit is surrounded radially by a ring-shaped second shield, located inside the cup of the first shield.

21. The system of claim 19, wherein the first shield is substantially made of copper.

22. The system of claim 13, wherein the magnetic detector comprises a coil having a ferromagnetic core, and is surrounded radially and axially by a cup-shaped first shield that surrounds substantially all sides except the emission face.

23. The system of claim 22, wherein the first shield is substantially made of copper.

24. The system of claim 13, wherein the magnetic detector comprises an E-shaped ferromagnetic core having a coil mounted around a central prong of the E-shaped ferromagnetic core, a C-shaped steel flux bypass structure around and magnetically coupled to the E-shaped ferromagnetic core, and a copper shield surrounding C-shaped steel flux bypass structure and the E-shaped ferromagnetic core on substantially all sides except the reception face.

25. The system of claim 13, wherein the excitation coil unit comprises:

an E-shaped core having at least a first, second, third, fourth, and fifth pole portion all connected to a common back section;

a first coil positioned around the first, second and third pole portions;

a second coil positioned around the second, third, and fourth pole portions; and

a third coil positioned around the third, fourth, and fifth portions;

wherein the first, second, and third coils are driven by three different phases of an alternating electrical signal to generate a traveling magnetic field.

26. The system of claim 13, wherein the excitation coil unit comprises:

an E-shaped core having at least a first, second, third, fourth, and fifth pole portion all connected to a common circular back section;

a first coil positioned around the first, second and third pole portions;

a second coil positioned around the second, third, and fourth pole portions; and

a third coil positioned around the third, fourth, and fifth portions;

wherein the first, second, and third coils are driven by three different phases of an alternating electrical signal to generate a rotating magnetic field.

27. The system of claim 13, wherein the signal-conditioning circuit is further substantially shielded between the magnetic detector and the signal-conditioning circuit.

28. The system of claim 13, wherein the signal-conditioning circuit also includes a low-pass filter.

29. An eddy-current probe system for detecting a flaw in a conducting object, the probe comprising:

an excitation coil unit having a plurality of excitation coils that transmit a traveling magnetic signal to the conducting object, such that the alternating magnetic signal is modified by the conducting object;

an excitation driving circuit, operatively coupled to the excitation coil unit, that provides a multiple-phase electrical signal to the plurality of excitation coils to generate the traveling magnetic signal;

a magnetic detector within the probe shielded on substantially all sides except a reception face, such that the traveling magnetic signal as modified by the conducting object is received into the shielded magnetic detector and converted into a first electrical signal;

a signal-conditioning circuit within the probe, provided with electrical power, which amplifies the first electrical signal to create a second electrical signal; and

a signal channel from the probe that transmits the second electrical signal to be analyzed to provide an indication of the flaw.

30. The system of claim 29, further comprising:

shielding substantially surrounding the signal-conditioning circuit, wherein the shielding shields substantially all electrical and magnetic signals from affecting the signal-conditioning circuit.

31. The system of claim 29, further comprising:

an instrument, operatively coupled the signal channel, that analyzes phase and amplitude components of the second electrical signal to be analyzed to provide the indication of the flaw.

32. The system of claim 29, wherein the traveling magnetic signal is a rotating magnetic signal.

33. The system of claim 29, wherein the traveling magnetic signal is a linear magnetic signal.

34. The system of claim 29, wherein the signal-conditioning circuit is separated from the magnetic detector by shielding.