A Free-Space Measurement Technique of Terahertz Dielectric Properties

The free-space method for material dielectric characterization in the microwave band is extended to terahertz frequencies. By analyzing the advantages and disadvantages of the relative permittivity of the transmission/reflection method for non-magnetic materials, a fast calculation method using a transmission-only method is proposed. Based on the convergence analysis of the algorithm, a method to estimate the initial value is also proposed. Finally, through measurements of the permittivity of high-density polyethylene, polystyrene, polypropylene, and polymethyl methacrylate in the 325-500 GHz band, we verify the rationality of the algorithm and demonstrate its applicability. Through the combination of the two methods, the terahertz dielectric properties of a majority of flat non-conducting solid materials and non-polar liquid materials can be measured.