Magnetic resonance detection of water in composite sandwich structures

The results of a series of experiments to determine the sensitivity of magnetic resonance to water inside an aerospace–grade composite sandwich panel are presented. The measurements were performed with a purpose-built unilateral probe designed to overcome problems associated with attenuation of the radio frequency (RF) magnetic field used in magnetic resonance by the presence of conductive materials in the panel. The detection limit of the probe is 2–3 honeycomb core cells filled with water in 64 scans (measurement of approximately 1 min). Profiles of a water containing region of cells were generated by displacing the probe laterally across the panel's surface. By varying the amount of water in the cells, it was determined that the magnetic resonance signal is obtained from throughout the height of the cells, not just the region nearest the probe's coil.