  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.
