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Eddy-current test probe utilizing a combination of high and low reluctance materials to optimize probe sensitivity

  • US 4,088,953 A
  • Filed: 11/15/1976
  • Issued: 05/09/1978
  • Est. Priority Date: 01/06/1975
  • Status: Expired due to Term
First Claim
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1. An eddy-current generator type test probe for material testing use, said probe comprising:

  • a main body of low reluctance magnetic material defining an annular, internal chamber that is bounded on all sides by the low reluctance magnetic material except for in the region of an annular gap in said body which extends from said chamber to break an externally connected surface of said body,an axially wound exciting coil of electrically conductive wire within said annular chamber, said coil being the only coil within said annular chamber and including terminal means for use in connecting said coil to alternating current means for operating said coil at a suitable frequency for the particular material testing to be done,a sleeve of high reluctance material within said chamber, concentric with said coil and extending lengthwise of the body adjacent said coil for the full length of said coil, and high reluctance material extending through said gap in the low reluctance material from said concentric coil and sleeve of high reluctance material, terminating substantially even with surface portions of said body which immediately bound both sides of said surface break, and forming therewith an annular test gap region which in use is positioned contiguous a material to be tested,said low reluctance material including a core portion, said concentric coil and sleeve of high reluctance material immediately surrounding said core portion, and said low reluctance material including a surrounding portion which immediately surrounds said concentric coil and sleeve of high reluctance material, andsaid high reluctance material being selected to have a reluctance that is much higher than the reluctance of the material to be tested and being a material which at the operating frequency of the coil during material testing use has an electromagnetic skin depth which is substantially less than the thickness of said high reluctance material, so that said high reluctance material influences substantially all of the magnetic flux which is generated by the coil to flow outwardly of said body, across said gap and through the material being tested, resulting in the total reluctance of the magnetic circuit being concentrated within the material being tested.

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