Measurement of Complex Permittivity of Lossy Materials in Free Space Using Matched THz Power Meter

Abstract

The complex permittivity of lossy materials is measured at 330 GHz by matched THz power meter. Such a power meter operates near the Brewster's angle of its absorbing film resulting in an own reflection coefficient close to zero. It permits to reduce an uncertainty associated with parasitic reflections created by conventional power meters. The measured power transmission coefficient of the dielectric slab as a function of the incident angle is used for estimating the dielectric constant. Its evaluation is based on the rootfinding procedure applied to the proper formulated system of two non-linear equations. Convergence and sensitivity of this system in the space of " 0 r ; " 00 r f g are investigated in order to formulate recommendations how guess values providing the unique solution must be chosen. The results are useful for estimating sheilding effects caused by dielectric losses in the sub-mm range with application to detecting hidden objects as well as other homeland security purposes.

Complex Permittivity Measurements of Textiles and Leather in a Free Space: An Angular-Invariant Approach

“…The reconstructing procedure needed to restore complex permittivity from the transmittance measurements has been described in [9]. The solution of the system of nonlinear equations ( 5) requires knowledge of the two independent transmittances for corresponding incidence angles.…”

“…This parameter has statistical nature and should be characterized by standard deviation of the measured material characteristics in angular domain. In the present study, the matched THz power meter (MPM) has been used in the transmittance measurements at 330 GHz resulting in a minimization of destructive role of the parasitic standing wave interference [9]. High directivity Gaussian beam hornlens antenna was employed in order to suppress undesirable spillover effect during variations of the sample's position.…”

Using Millimeter and Terahertz Frequencies for Complex Permittivity Retrieval of Low-Loss Materials

“…The same fact is also shared with scattering parameter measurements [21]. In recent studies, amplitudeonly transmittance measurements for ε retrieval of lossy dielectrics are investigated [19,22]. Although these approaches are promising, they are not applicable to electrical characterization of low-loss dielectrics.…”

Differential uncertainty analysis for evaluating the accuracy of S-parameter retrieval methods for electromagnetic properties of metamaterial slabs

“…The methods in [42][43][44][45][46][47][48][49][50][51] can be employed for different purposes to remove this disadvantage. The final drawback of electromagnetic retrieval of MM slabs by methods based on S-parameters is the unfeasible measurement of the phase of S-parameters at very high frequencies [29,[52][53][54][55][56][57]. As a solution to this problem, amplitude-only Fresnel measurements at multiple frequencies could be utilized [29,[52][53][54][55][56].…”

“…The final drawback of electromagnetic retrieval of MM slabs by methods based on S-parameters is the unfeasible measurement of the phase of S-parameters at very high frequencies [29,[52][53][54][55][56][57]. As a solution to this problem, amplitude-only Fresnel measurements at multiple frequencies could be utilized [29,[52][53][54][55][56]. Because, in the region of negative refraction, real parts of both relative complex permittivity ( r  ) and relative complex permeability ( r  ) depend mainly on the phase measurements, as another solution, complex S-parameter measurements based on an interferometric approach are more appealing for sensitive measurements [57].…”