Surface mounted and scanning spatially periodic eddy-current sensor arrays

• US 20060082366A1
• Filed: 03/02/2005
• Published: 04/20/2006
• Est. Priority Date: 09/20/1999
• Status: Active Grant

• Current Assignee: Jentek Sensors, Inc.
• Original Assignee: Jentek Sensors, Inc.
• Inventors: Goldfine, Neil J., Schlicker, Darrell E., Washabaugh, Andrew P., Zilberstein, Vladimir A., Walrath, Karen E., Weiss, Volker
• Granted Patent: US 7,230,421 B2
• Time in Patent Office: Days
• US Class Current: 324/240
• CPC Class Codes: G01B 7/24 using change in magnetic properties
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G01N 27/72 by investigating magnetic variables
• CPC Class Codes: G01N 27/90 using eddy currents
• CPC Class Codes: G01N 27/902 by moving the sensors
• CPC Class Codes: G01R 33/12 Measuring magnetic properties of articles or specimens of solids or fluids involving magnetic resonance G01R33/20

Abstract

Inductive sensors measure the near surface properties of conducting and magnetic material. A sensor may have primary windings with parallel extended winding segments to impose a spatially periodic magnetic field in a test material. Those extended portions may be formed by adjacent portions of individual drive coils. Sensing elements provided every other half wavelength may be connected together in series while the sensing elements in adjacent half wavelengths are spatially offset. Certain sensors include circular segments which create a circularly symmetric magnetic field that is periodic in the radial direction. Such sensors are particularly adapted to surround fasteners to detect cracks and can be mounted beneath a fastener head. In another sensor, sensing windings are offset along the length of parallel winding segments to provide material measurements over different locations when the circuit is scanned over the test material. The distance from the sensing elements to the ends of the primary winding may be kept constant as the offset space in between sensing elements is varied. An image of the material properties can be provided as the sensor is scanned across the material.

Claims

1. A method of fabricating a damage standard comprising:

attaching an electromagnetic sensor to a critical surface of test material;

mechanically loading the test material and measuring a change in the electrical properties under the surface of the sensor; and

removing the mechanical load when the change in electrical properties indicates a prescribed level of damage.

2. A method as claimed in claim 1 where the damage is a fatigue crack.

3. A method as claimed in claim 1 where the sensor is a spatially periodic field eddy-current sensor and the test material is a metal.

4. A method as claimed in claim 3 where the sensor is flexible for conforming to the shape of the surface of the test material.

5. A method as claimed in claim 4 where the sensor is an array with multiple sensing elements for producing a spatial image of the damage.

6. A method as claimed in claim 1 where the sensor is a dielectrometer and the test material is a dielectric material.

7. A method as claimed in claim 1 further comprising the use of a temperature measurement sensor to correct for electrical property variations with temperature.

8. A method as claimed in claim 1 further comprising the use of multiple sensors to monitor multiple regions.

9. A method as claimed in claim 8 where the sensors include arrays with multiple sensing elements for producing spatial images of the damage.

10. A method as claimed in claim 2 further comprising the use of a sensor to monitor the change in crack length with the number of fatigue cycles.

11. A method as claimed in claim 2 further comprising the use of multiple frequency measurements to monitor crack depth.

12. A method as claimed in claim 2 where the damage is pre-crack damage.

13. A method as claimed in claim 2 further comprising mounting the sensor between layers of the test material.

14. A method as claimed in claim 3 further comprising the use of a sealant to provide mechanical support.

15. A method as claimed in claim 1 further comprising shaping the test material to create a stress distribution so that fatigue damage initiates under the sensor.

16. A method as claimed in claim 15 where the test material is formed into a dogbone shape and the center section is thinned to localize fatigue damage.

17. A method as claimed in claim 16 where the test material further comprises reinforcement ribs on the edges.

18. A method as claimed in claim 17 where the test material further comprises radius cutouts on both sides of the thinned section.

19. A method as claimed in claim 15 where the test material further comprises radius cutouts on both sides of the thinned section.