Thin layer terahertz sensing using two-channel parallel-plate waveguides.

We report on the highly sensitive terahertz measurement of a thin, dielectric layer using two channels formed by inserting a single slit sheet in the parallel-plate waveguides (PPWGs). When a thin layer is applied to coat the upper surface of the channel, the single resonance frequency caused by the two-channel PPWGs is shifted as a result of the layer's properties, including length, thickness, and refractive index. The measured frequency tuning sensitivities (FTS) throughout the 20-mm layer length are 2.41 and -1.95 GHz/mm at the open upper and lower channels, respectively. The experimental results agree with those of theoretical simulations performed using the finite-difference time-domain (FDTD) method.