This SBIR Phase I proposal will investigate a new methodology known as electromagnetic induction spectroscopy (EMIS) as a means of detecting and characterizing hidden corrosion in multi-layered airframe structures. This technique, in contrast to traditional single-frequency eddy current methods, records the in-phase and quadrature response of a specimen over a broad range of frequencies. The method then exploits a relationship between the loss of conducting material under the probe and the peak frequency of the quadrature component of the scattered magnetic field. This relationship provides a quantitative measure of the loss (or change) in conducting material under the sensor, which is indicative of corrosion. The proposed EMIS instrument will also incorporate a bucking scheme which eliminates the primary flux linking the sensing coil; this innovation greatly enhances sensitivity and dynamic range compared to conventional impedance-based eddy-current systems. This technique can result in scattered field measurements on the order of parts per million of the source field. The EMIS methodology will be tested in the Phase I effort by performing experimental tests on metallic samples with layers of varying thicknesses and conductivities to simulate metal depletion due to corrosion.
Keywords: Aircraft, Airframe, Corrosion, Eddy-Current Inspection, Electromagnetic Induction, Electrical Conductivity, Flaw Detection, Nondestructive Evaluation
