Hybrid wound/etched winding constructs for scanning and monitoring

Abstract

Combined wound and micro-fabricated winding constructs are described for the inspection of materials and the detection and characterization of hidden features or flaws. These constructs can be configured as sensors or sensor arrays that are surface mounted or scanned over conducting and/or magnetizable test materials. The well-defined geometry obtained micro-fabricated windings and from carefully wound coils with known winding positions permits the use of model based inversions of sensed responses into material properties. In a preferred embodiment, the primary winding is a wound coil and the sense elements are etched or printed. The drive or sense windings can also be mounted under fasteners to improve sensitivity to hidden flaws. Ferrites and other means may be used to guide the magnetic flux and enhance the magnetic field in the test material.

1 . A test circuit comprising: 
 a drive coil having at least two conducting wire windings to impose a magnetic field in a test material when driven by an electric current; and    at least one micro-fabricated sense element proximate to the drive coil for sensing the response of the test material to the imposed magnetic field.    
   
   
       2 . The test circuit as claimed in  claim 1  wherein the at least one sense element is etched.  
   
   
       3 . The test circuit as claimed in  claim 1  wherein the at least one sense element is printed.  
   
   
       4 . The test circuit as claimed in  claim 1  wherein a sense element is an inductive coil.  
   
   
       5 . The test circuit as claimed in  claim 4 , further comprising at least one micro-fabricated magnetoresistive sensor.  
   
   
       6 . The test circuit as claimed in  claim 1  wherein the at least one sense element is a magnetoresistive sensor.  
   
   
       7 . The test circuit as claimed in  claim 1  wherein the at least one sense element is a giant magnetoresistive sensor.  
   
   
       8 . The test circuit as claimed in  claim 1  wherein the at least one sense element responds to a different component of the magnetic field than another sense element.  
   
   
       9 . The test circuit as claimed in  claim 1  wherein the at least one sense element is further from the drive coil than a second sense element.  
   
   
       10 . The test circuit as claimed in  claim 1  wherein the at least one sense element is mounted onto a flexible substrate.  
   
   
       11 . The test circuit as claimed in  claim 10  wherein the drive coil is mounted to the same substrate as the at least one sense element.  
   
   
       12 . The test circuit as claimed in  claim 1 , wherein location of each wire winding is shown with sufficient precision to model the magnetic field.  
   
   
       13 . A method for characterizing a material comprising: 
 disposing a drive coil proximate to a test material surface, the drive coil having at least two conducting wire windings to impose a magnetic field in a test material when driven by an electric current; and    measuring output of each sense element to sense response of the test material to the imposed magnetic field.    
   
   
       14 . The method as claimed in  claim 13  wherein the at least one sense element is etched.  
   
   
       15 . The method as claimed in  claim 13  wherein the at least one sense element is printed.  
   
   
       16 . The method as claimed in  claim 13  wherein the at least one sense element is an inductive coil.  
   
   
       17 . The method as claimed in  claim 11  wherein a sense element is a magnetoresistive sensor.  
   
   
       18 . The method as claimed in  claim 17  wherein there are two or more sense elements and at least one sense element is an inductive coil.  
   
   
       19 . The method as claimed in  claim 13  wherein the at least one sense element is a giant magnetoresistive sensor.  
   
   
       20 . The method as claimed in  claim 13  wherein the at least one sense element responds to a different component of the magnetic field than another sense element.  
   
   
       21 . The test circuit as claimed in  claim 13  wherein the at least one sense element is further from the drive coil than another sense element.  
   
   
       22 . The method as claimed in  claim 13  wherein the at least one sense element is mounted onto a flexible substrate.  
   
   
       23 . The method as claimed in  claim 22  wherein the drive coil is mounted to the same substrate as the sense elements.  
   
   
       24 . The method as claimed in  claim 13  further comprising measuring the response at multiple proximities to the test material surface.  
   
   
       25 . The method as claimed in  claim 13  wherein the location of each wire winding known with sufficient precision so that the magnetic field can be accurately modeled.  
   
   
       26 . The method as claimed in  claim 13  wherein the drive coil is mounted under a fastener  
   
   
       27 . A method for monitoring damage at a fastener comprising: 
 mounting a drive coil having at least two conducting wire windings with a support material shaped in the form of a washer;    placing the washer on a test substrate under the fastener;    placing at least one microfabricated sense element proximate to the drive coil; and    measuring a response from each sense element as a magnetic field is imposed in the test substrate by an electric current driven through the drive coil.    
   
   
       28 . The method as claimed in  claim 27  wherein the at least one sense element is etched.  
   
   
       29 . The method as claimed in  claim 27  wherein the at least one sense element is printed.  
   
   
       30 . The method as claimed in  claim 27  wherein the at least one sense element is an inductive coil.  
   
   
       31 . The method as claimed in  claim 27  wherein the at least one sense element is a magnetoresistive sensor.  
   
   
       32 . The method as claimed in  claim 27  wherein the at least one sense element is a giant magnetoresistive sensor.  
   
   
       33 . The method as claimed in  claim 27  wherein the at least one sense element responds to a different component of the magnetic field than another sense element.  
   
   
       34 . The test circuit as claimed in  claim 27  wherein the at least one sense element is at a different radial distance from the drive coil than another sense element.  
   
   
       35 . The method as claimed in  claim 27  wherein the support material has a lower electrical conductivity than the electrical conductivity of the test substrate.  
   
   
       36 . The method as claimed in  claim 35  wherein the support material is a composite.  
   
   
       37 . The method as claimed in  claim 27  wherein the support material is split to reduce induced eddy currents in the support material.  
   
   
       38 . The method as claimed in  claim 27  wherein the drive coil is enclosed by the support material.  
   
   
       39 . The method as claimed in  claim 27  wherein the support material includes a magnetizable material.  
   
   
       40 . The method as claimed in  claim 39  wherein the magnetizable material is a ferrite.  
   
   
       41 . The method as claimed in  claim 27  wherein the shaft of the fastener is coated with a magnetizable material.  
   
   
       42 . The method as claimed in  claim 27  wherein the fastener has a hollow shaft filled with a magnetizable material.  
   
   
       43 . The method as claimed in  claim 27  wherein the nut has an electrical conductivity lower than the electrical conductivity of the test substrate.  
   
   
       44 . The method as claimed in  claim 27  further comprising scanning a sense element around the fastener.  
   
   
       45 . The method as claimed in  claim 27  further comprising measuring the response at multiple proximities to the test material surface.  
   
   
       46 . The method as claimed in  claim 27  wherein the location of each wire winding known with sufficient precision so that the magnetic field can be accurately modeled.  
   
   
       47 . A method for monitoring damage at a fastener comprising: 
 placing a drive coil having at least two conducting wire windings proximate to a fastener;    mounting at least one microfabricated sense element to a test substrate under a fastener; and    measuring a response from each sense element as a magnetic field is imposed in the test substrate by an electric current driven through the drive coil.    
   
   
       48 . The method as claimed in  claim 47  wherein the at least one sense element is etched.  
   
   
       49 . The method as claimed in  claim 47  wherein the at least one sense element is printed.  
   
   
       50 . The method as claimed in  claim 47  wherein the at least one sense element is an inductive coil.  
   
   
       51 . The test circuit as claimed in  claim 47  wherein the at least one sense element is at a different radial distance from the drive coil than another sense element.  
   
   
       52 . The method as claimed in  claim 47  wherein the at least one sense element is mounted into a support material formed into a washer.  
   
   
       53 . The method as claimed in  claim 52  wherein the support material has a lower electrical conductivity than the electrical conductivity of the test substrate.  
   
   
       54 . The method as claimed in  claim 53  wherein the support material is a composite.  
   
   
       55 . The method as claimed in  claim 52  wherein the support material is split to reduce induced eddy currents in the support material.  
   
   
       56 . The method as claimed in  claim 52  wherein the support material includes a ferrite.  
   
   
       57 . The method as claimed in  claim 47  wherein the shaft of the fastener is coated with a magnetizable material.  
   
   
       58 . The method as claimed in  claim 47  wherein the fastener has a hollow shaft filled with a magnetizable material.  
   
   
       59 . The method as claimed in  claim 47  wherein the nut has an electrical conductivity lower than the electrical conductivity of the test substrate.  
   
   
       60 . The method as claimed in  claim 47  further comprising: 
 scanning the drive coil around the fastener.    
   
   
       61 . The method as claimed in  claim 47  further comprising: 
 measuring the response at multiple proximities to the test material surface.    
   
   
       62 . The method as claimed in  claim 47  wherein the location of each wire winding known with sufficient precision so that the magnetic field can be accurately modeled.