Simple analytical approach for measurement of the complex permittivity of resins and viscous liquids

An analytical method to determine the dielectric constant and the loss tangent of epoxy resins and other viscous liquids is presented. The method requires the injection of the liquid-under-test (LUT) into a disposable cuvette of rectangular or square cross-section, and measuring the reflection and transmission coefficient data in the S-band by positioning it at the center of a WR-340 rectangular waveguide. The complex relative permittivity of the LUT is reconstructed from the measured scattering data using the proposed analytical closed form relations. The analytical expression is based on the derivation of the transcendental equation using the transverse resonance method, which basically helps in analyzing the multi-layered partially filled waveguide structure. The proposed method is validated by reconstructing a number of known liquid specimen.