Sub‐THz complex dielectric constants of smectite clay thin samples with Na + /Ca ++ ions

We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm −1 to 4.95 cm −1 ) of oriented smectite samples using an open cavity resonator connected to a submillimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na + ion and Ca ++ ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (∼30 μm) than the glass substrate (∼2.18 mm). The real part of dielectric constant, ϵ r e , is essentially constant over this frequency range but is larger in Na + ion than in Ca ++ ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ϵ i m ) of both samples increases monotonically at lower frequencies (<110 GHz) but shows rapid increase for Na + ions in the regime > 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., ζ potential in the Stern layers.