Abstract: 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.

Abstract: 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.