Free-Space Materials Characterization by Reflection and Transmission Measurements using Frequency-by-Frequency and Multi-Frequency Algorithms

Fábio Gonçalves,Elson Silva,Adriana Brancaccio,Renato Mesquita,Alfred Pinto

doi:10.3390/electronics7100260

Fábio Gonçalves, Elson Silva + Show 3 more

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https://doi.org/10.3390/electronics7100260

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Abstract

The knowledge of the electromagnetic constitutive properties of materials is crucial in many applications. Free-space methods are widely used for this purpose, despite their inherent practical difficulties. This paper describes an affordable free-space experimental setup for the characterization of flat samples in 1–6 GHz in a non-anechoic environment. The extracted properties are obtained from the calibrated Scattering Parameters, using a frequency-by-frequency solution or a multi-frequency reconstruction. For the first, we describe how the Time-Domain Gating can be implemented and used for filtering the signals. For the latter, a weighting factor is introduced to balance the reflection and transmission data, allowing one to have a more favorable configuration. The different role of transmission and reflection measurements on the achievable results is analyzed with regard to experimental uncertainties and different noise scenarios. Results from the two strategies are analyzed and compared. Good agreement between simulation, measurement and literature is obtained. According to the reported results for dielectric materials, there is no need of filtering the data by a Time-Domain Gating in case of the multi-frequency approach. Experimental results for Polymethylmethacrylate (PMMA) and Polytetrafluorethylene (PTFE) samples validate both the setup and the processing.

Highlights

Characterization of the electric permittivity ε, the magnetic permeability μ and the electric conductivity σ is of fundamental importance in physics and engineering, since these constitutive properties determine the response of the Material Under Test (MUT) to the electromagnetic fields [1,2]
Such properties are extracted from the Scattering (S-) Parameters [1,2,3,4], which can be measured by a Vector Network Analyzer (VNA) [3]
Several measurement setups can be conceived for this purpose, including the Free-Space Method (FSM) [1]

Summary

Introduction

Characterization of the electric permittivity ε, the magnetic permeability μ and the electric conductivity σ is of fundamental importance in physics and engineering, since these constitutive properties determine the response of the Material Under Test (MUT) to the electromagnetic fields [1,2] Such properties are extracted from the Scattering (S-) Parameters [1,2,3,4], which can be measured by a Vector Network Analyzer (VNA) [3]. The FSM is contactless, requires little sample preparation and is suitable for heterogeneous samples It can be used for measuring large flat solids, materials under

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