A $Q$ -Band Free-Space Characterization of Carbon Nanotube Composites

Abstract

We present a free-space measurement technique for non-destructive non-contact electrical and dielectric characterization of nano-carbon composites in the Q-band frequency range of 30 GHz to 50 GHz. The experimental system and error correction model accurately reconstruct the conductivity of composite materials that are either thicker than the wave penetration depth, and therefore exhibit negligible microwave transmission (less than −40 dB), or thinner than the wave penetration depth and, therefore, exhibit significant microwave transmission. This error correction model implements a fixed wave propagation distance between antennas and corrects the complex scattering parameters of the specimen from two references, an air slab having geometrical propagation length equal to that of the specimen under test, and a metallic conductor, such as an aluminum plate. Experimental results were validated by reconstructing the relative dielectric permittivity of known dielectric materials and then used to determine the conductivity of nano-carbon composite laminates. This error correction model can simplify routine characterization of thin conducting laminates to just one measurement of scattering parameters, making the method attractive for research, development, and for quality control in the manufacturing environment.

Determination of Complex Conductivity of Thin Strips with a Transmission Method

“…To show the competency of the method, we compare our analytic method with modelling results. A general purpose programming tool [32] was used to find analytic results from Equations (18) and (22) or Equations (23) and (24). We used two commercial electromagnetic packages with a finite element method (FEM) solver [33] and method of moments (MoM) solver [34] to simulate the structures.…”

“…In reflection methods [13][14][15][16], SUT is placed as the termination of the transmission line, and the material is characterized through investigation of the reflection coefficient. Transmission methods [1,[17][18][19][20][21][22] are based on placing the object inside the transmission line, and both transmission and reflection coefficients are used. Cavity methods [3][4][5][6][7][8][9][10][11] are inherently narrowband, while reflection [13,15,16] and transimssion methods [18][19][20][21] are broadband methods.…”

Air-Gap Correction for High Power Microwave Measurements of Conductive Materials

“…Measurements are first made without a material placed in the coax airline. Empty measurements are used to eliminate power dependent properties of the coax airline and connectors, which are subsequently used to determine the electrical length of the airline for time gated algorithms [17]. The MUT is then placed in the coax airline to be measured, but its position within the cavity is unknown and needed to account for propagation through the airline.…”

“…The additional noise introduced by this process is mitigated by Fourier Transforming the frequency information from the VNA, placing a window at The upper half of the plot is for inner air-gaps, specified by "I 0.XX" followed by the normalized volume, and the outer gaps similarly labeled, "O 0.XX". a time associated with the electrical length of the transmission line which reduces the contribution from repeated reflections [17]. Time-Gate filtering for magnetic materials requires measurements of the MUT against a short standard, which was not considered for our study due to the complications of short standards that can withstand high power measurements, as short standards are low impedance and are not tolerant of the power levels needed, and the reflected power can be destructive to the VNA.…”

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

“…Moreover, the knowledge of the electromagnetic properties can be used to evaluate the physical conditions of materials in different areas, such as masonry structures in civil engineering [17,19,20], the characteristics of snow [21] or even agricultural materials [22]. There are also several works in millimeter wavelengths, for instance, for characterizing dielectrics [23], electromagnetic absorbers [24] and nanocomposites [25].…”