Eddy-current test probe utilizing a combination of high and low reluctance materials to optimize probe sensitivity
First Claim
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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Abstract
A coil of insulated wire surrounds a low reluctance core. A combination of low reluctance and high reluctance materials positioned adjacent said coil: (1) control the spatial extent of the magnetic flux and, (2) concentrate the total reluctance of the magnetic circuit of the exciting coil into a volume of controlled size and shape within the material being tested. The magnetic flux is controlled, and the reluctance is concentrated, in such a manner as to optimize the sensitivity of the eddy-current generator to variations in the material being tested; at the same time, the coil impedance is maintained at a value which is optimum for the performance of any selected precision electrical impedance measuring device.
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Citations
13 Claims
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1. An eddy-current generator type test probe for material testing use, said probe comprising:
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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, and said 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. - View Dependent Claims (2, 3, 4, 5)
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6. Eddy-current generator type apparatus for material testing use, comprising:
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a probe having 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, 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, alternating current means connected to the terminal means of said coil, for operating said coil at a suitable frequency for the particular material testing to be done, and said high reluctance material within said probe 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. - View Dependent Claims (7, 8, 9, 10)
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11. An eddy-current generator for material testing use, comprising:
an elongated composite probe having a probe end which in use is positioned on a surface of a material being tested, and an opposite end, said probe comprising; an exciting coil of electrically conductive wire having a first end directed towards the material being tested and a second opposite end, low reluctance magnetic material establishing a low reluctance magnetic path within said probe, comprising a core portion about which said coil extends and including an end surface at said probe end, an outer portion surrounding said coil in a spaced relationship with said core portion and also including an end surface at said probe end, and an end portion which is magnetically integral with both said core portion and said outer portion and which extends endwise therefrom towards said probe'"'"'s opposite end, said magnetic path of magnetic material extending uninterrupted from said core portion through said end part into said outer portion, only one electrically conductive sleeve of high reluctance material concentric with said coil and extending lengthwise of said probe adjacent said coil from the second end of said coil only to the probe end and including an end surface at said probe end, said concentric coil and sleeve of high reluctance material immediately surrounding said core portion, said coil being the only coil in said probe, said outer portion of said low reluctance material immediately surrounding said concentric coil and sleeve of high reluctance material, said outer portion of said low reluctance material and said core portion of said low reluctance material together defining a gap at said probe end, said high reluctance material occupying said gap, and said end surfaces of said high and low reluctance materials being substantially even with each other at said probe end, said 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 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 through the material being tested, resulting in the total reluctance of the magnetic circuit being concentrated within the material being tested. - View Dependent Claims (12, 13)
Specification