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

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.

A multiband circular polarization selective metasurface for microwave applications

“…To measure cross-polarized transmission, the two antennas were placed orthogonal to each other, i.e., the transmitting antenna was vertically while the receiving antenna was placed horizontally. For the measurements of the transmission components, the free space method was used through the following expression 38 : where w , c and d represent the angular frequency, speed of light and thickness of the sample, respectively. Figure 8 c,d show that the simulated and experimental results are in good agreement.…”

Monitoring the Dielectric Properties and Propagation Conditions of Mortar for Modern Wireless Mobile Networks

“…When the period of curing increases, the amount of free water in mortar decreases attributed to the procedure of cement hydration and evaporation [15]. The water changes from free to an absorbed state, which reduces ionic polarization and conductivity due to decreases in ion production [16]. Additionally, the pore sizes become very small, in consequence making it difficult for the movement of free water remaining in mortar [13].…”

“…Additionally, the pore sizes become very small, in consequence making it difficult for the movement of free water remaining in mortar [13]. The reflection coefficient in Figure 5(a) is a strong function of the dielectric constant of water [16]. It can be clearly observed from the dielectric properties of water that the dielectric constant of water values was much higher at the lower frequencies [14].…”

A free space frequency‐time‐domain technique for electromagnetic characterization of materials using reflection‐based measurement

“…13 Some of the methods avoid these kinds of calibration procedure but they require the knowledge of both reflection and transmission coefficients for determining the dielectric properties of the material under test (MUT). [22][23][24][25][26][27] In a few real-life situations viz., defense applications, and through-wall imaging, the measurement of transmission coefficient is very hard to realize as it requires access from another side of the wall. In case of metal backed samples, the measurement of transmission coefficient is not possible.…”

“…The electrical and physical properties (surface roughness and conductivity) of these additional materials can affect the reconstruction procedure 13 . Some of the methods avoid these kinds of calibration procedure but they require the knowledge of both reflection and transmission coefficients for determining the dielectric properties of the material under test (MUT) 22‐27 . In a few real‐life situations viz., defense applications, and through‐wall imaging, the measurement of transmission coefficient is very hard to realize as it requires access from another side of the wall.…”