Finite flange correction for microwave and millimeter-wave nondestructive material characterization

Open-ended waveguide material characterization is an effective nondestructive testing (NDT) technique for evaluating the dielectric constant and thickness of individual layers in a multilayered composite structure. A limitation of this technique is that the finite flange contributes to the estimation error, depending on the thickness and dielectric loss factor of the layers. Its effects are non-negligible in particular when measuring the dielectric constant of low-loss and thin materials. This paper studies the effect of using a common finite-flanged open-ended waveguide on the error in estimating the permittivity and loss-tangent of a dielectric sheet. This paper also presents a proposed modification to the flange geometry in order to markedly reduce this undesired effect.