Millimeter wave spectroscopy of rocks and fluids
  One region of the electromagnetic spectrum that is relatively unexploited for materials characterization is the millimeter wave band (frequencies roughly between 40 and 300 GHz). Millimeter wave techniques involve free-space (non-contacting) measurements which have a length scale that makes them ideal for characterizing bulk properties of multicomponent composites where the scale of homogeneity is on the order of millimeters. Such composites include granular materials such as rocks, fluid mixtures, suspensions and emulsions. Here we show measurements on partially saturated rocks and an oil/water mixture, demonstrating that millimeter wave spectroscopy is sensitive yet rapid measure of changing composition. 
John A. Scales and Michael Batzle