Vanderbilt University

University of Alaska

Yu P Ma

John P Wikswo

Gour S Choudhury

Christopher G Bublitz

William G Jenks

A sheet inducer carrying a uniformly distributed ac current induces a sheet eddy current generally parallel to a generally smooth surface of an electrically conductive object. A magnetometer, preferably a superconducting quantum interference device (SQUID) magnetometer, detects the component of a magnetic field generally perpendicular to the generally smooth surface resulting from disturbances in the sheet eddy current caused by a flaw. Through appropriate selection of the phase angle between the detector signal and the applied current, the response can be adjusted to suppress surface flaws and enhance detection of flaws below the surface. The sheet eddy current is induced in multiple directions to detect flaws of all orientations and at multiple frequencies to refine determination of the size, shape, and depth of a flaw. An elongated solenoid is used to induce a circumferential sheet eddy current in elongated objects such as tubes and rods, and a current-carrying rod is used to induce a longitudinal sheet eddy current in an elongated tubular object.

Method and apparatus for detecting flaws below the surface of an

Inclusions such as encysted parasites and spoilage in food products such as fish fillets are detected by immersing the food products in a bath of an electrolyte, such as a saline solution, having substantially the same electrical conductivity as the uncontaminated food product. An electrical current passed through the electrolyte also passes through the food product. Perturbations in the resulting magnetic field produced by the discontinuities in conductivity at the boundaries of the inclusions or of the spoiled article which have substantially different conductivities from that of the electrolyte and unspoiled food products, provide an indication of the presence of the contamination. Production line inspection rates are achieved by conveying the food products through a container filled with electrolyte and past an array of stationary magnetometers. Perturbations in the magnetic field at the edges of the container are cancelled by directing the current which flows through the electrolyte in a first direction back over the container in the opposite direction through a cancelling conductor, while fields produced by the supply leads are cancelled by using coaxial cable.

Growing community of inventors

Nashville, TN, United States of America

Yu P Ma