Apparatus and methods for measuring permeability and conductivity in materials using multiple wavenumber magnetic interrogations

Abstract

Devices and analytical techniques are disclosed for measuring spatial profiles of complex permeability and conductivity of a material by multiple wavenumber interrogations. Coil array structures are disclosed which define a number of different fundamental wavelengths (or wavenumbers). Spatially periodic interrogation signals (of temporal frequency " omega ") from the coil array structures are attenuated by varying degrees in the material undergoing analysis, depending on the wavenumber ("k"), thereby permitting the derivation of composite complex permeability / conductivity profile.

Description

BACKGROUND OF THE INVENTIONThe technical field of this invention is magnetometry and, in particular, the spatial interrogation of materials to deduce their physical properties from measurements of complex permeability and conductivity.Magnetometers or arrays of coils have been used for noninvasive measurement of kinematic and physical properties of conducting materials. For example, eddy current sensors have been used to measure the thickness of conducting strips, as disclosed in Soviet Patents 573,609 and 502,205. Another use of such eddy current sensors has been in flaw detection, as disclosed in U.S. Pat. No. 3,939,404. However, the utility of these sensors typically is limited by their inability to provide enough information to resolve distributions of parameters.There exists a need for better permeability / conductivity measuring devices and methods. In particular, there exists a need for better devices and methods for conducting non-destructive interrogations of materials to det...

AI Technical Summary

Benefits of technology

The techniques described herein are referred to as an "imposed .omega.-k" approach to magnetometry. A spatially periodic field is imposed upon the material via a coil structure under the control of a wavenumber controller. The coil structure can be near the material surface or embedded. The properties of the material are reflected in the measurement of the current or voltage induced in the sensing coils in response to this field. By varying the wavenumber, k, a spatial distribution of complex permeability and conductivity is deduced

Problems solved by technology

However, the utility of these sensors typically is limited by their inability to provide enough information to resolve distributions of parameters.

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