Terahertz Characterization of Unique Thin Materials by Free-Space Transmission and Reflection Coefficients Without Thickness Information

Accurate material characterization is essential for designing high-performance electronic, optical, and sensing systems, particularly at terahertz (THz) frequencies. Conventional methods often require accurate thickness knowledge, identical reference samples, or complex calibration, which are impractical for unique thin materials, e.g., soft or fragile thin films. This work introduces a self-calibrated method to characterize thin films placed between two dielectric slabs using free-space transmission and reflection measurements at THz frequencies, while eliminating the need for thickness information of either the films or slabs, thereby reducing system complexity. The approach employs a time-gating technique and provides closed-form solutions for permittivity extraction from measured coefficients. It accommodates substrates of different thicknesses, requiring only their permittivity values. Simulations and measurements over 220–330 GHz validate the method’s accuracy, demonstrating its effectiveness for THz multilayer permittivity characterization.