Nicolson-Ross-Weir Research Articles

Errors in Broadband Permittivity Determination Due to Liquid Surface Distortions in Semi-Open Test Cell

We study how surface distortions of liquid samples due to a meniscus and a tilt of a semi-open coaxial test cell affect errors in a broadband permittivity determination. The study is based on the scattering parameters, obtained using the electromagnetic simulations of samples with flat and distorted surfaces in a broad frequency range up to 18 GHz. The parameters are processed with the classic Nicolson–Ross–Weir (NRW) method and our new meniscus removal technique. We analyze the errors for several samples of different properties, such as distilled water and propan-2-ol. The results show that the meniscus removal technique is more robust and provides smaller errors in the permittivity determination compared to the classic NRW method. The effect of the cell tilt, to our best knowledge, has not been considered in the literature yet.

Extraction of Stable Complex Permittivity and Permeability of Low-Loss Materials From Transmission/Reflection Measurements

In this article, a technique based on artificial neural networks (ANNs) is proposed to extract stable complex permittivity and permeability of low-loss materials from transmission/reflection (T/R) measurements. The equations of attenuation constant $\alpha $ and phase constant $\beta $ of $a$ sample-filled transmission line are derived. The calculated $\alpha $ and $\beta $ are put into an ANN model. The outputs of the ANN model are stable complex permittivity and permeability over the whole measurement frequency range, while the values extracted by other techniques are resonant at the frequencies corresponding to integer multiples of one-half wavelength in the sample materials. Two low-loss materials with substantial thickness are measured in X-band to validate the proposed technique. Compared with the Nicolson–Ross–Weir (NRW) technique, the short-circuited technique, and an ANN technique without the derived equations, the proposed technique provides stable results for the two samples. In addition, the extracted values are compared with the “true values” measured from the thinner samples to further present the advantages of the proposed technique.

Retrieving the Effective Parameters of an Electromagnetic Metamaterial Using the Nicolson-Ross-Weir Method: An Analytic Continuation Problem Along the Path Determined by Scattering Parameters

Electromagnetic metamaterials (MMs) are composite structures that allow one to potentially develop unique and innovative microwave, millimetre wave, and optical devices due to their unusual physical properties. In this process, their electromagnetic characterization plays a fundamental role. Various procedures have been proposed to accomplish this task, but the Nicolson-Ross-Weir (NRW) method still appears to be the most commonly adopted one even though it is afflicted by the severe issue of branch ambiguity. In this paper, we have demonstrated that rigorously, as the branch ambiguity can be entirely overcome through the analytic continuation of a specific analytic logarithm element along the path determined in the complex plane by the scattering parameters of an MM under analysis. Furthermore, the underlying relationship between analytic continuation, phase unwrapping approach, implemented through a procedure devised by Oppenheim and Schafer for the homomorphic treatment of signals (hereafter named PUNWOS), and the Kronig-Kramers relation has been discussed and enlightened, demonstrating the full equivalence among the methods. To clarify this aspect, a couple of numerical examples is presented. The results discussed in this study open the possibility of employing the vast theoretical equipment developed in the phase unwrapping field to achieve the retrieval of MMs’ effective parameters when the NRW method is applicable.

Conductive layer-based multifunctional structural composites for electromagnetic interference shielding

The doped polyaniline (PANI) mixed with divinylbenzene (DVB) as a crosslinking thermoset polymer has been presented to exemplify as a structural electromagnetic interference (EMI) shielding material. Both theoretical and experimental analysis was conducted to analyze the shielding mechanisms. The effects of shielding layer thickness were studied to optimize the EMI shield properties. Preliminary studies reveal that the maximum EMI shielding effectiveness (SE) and electrical conductivity values of ~20 dB in the X-band (8.2–12.4 GHz) and 100 S/m, respectively, have been reached in the case of 1 mm thick PANI-based thermoset. It is also found from the experimental results that; absorption mechanism was the primary shielding mechanism for this material due to high conductivity. Further, both dielectric constant and permeability were estimated using Nicolson-Ross-Weir (NRW) algorithm and the S-parameters obtain from the vector network analyzer (VNA) to understand and correlate the shielding mechanisms. Finally, the PANI-based conductive layer successfully installs on structural fiber-reinforced composites to demonstrate its application as a self-EMI shielding structural composite materials. Both glass fiber reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites were able to shield the EMI radiation with a maximum SE value of 17 and 45 dB, while keeping the layer thickness of 1 mm.

A New Planar Microwave Sensor for Building Materials Complex Permittivity Characterization.

A new microwave sensor is proposed to characterize the complex relative permittivity of building non-magnetic materials and used in the characterization of three concrete samples. The proposed sensor structure consists of a log-periodic planar antenna with microstrip elements tilted forward by an angle β and printed, alternately, on the top and bottom sides of a dielectric layer. The operation principle is based on the measurement of the scattering parameters S11 and S21 in a free space propagation transmitter-receiver setup, for both cases with the material under test (MUT) sample (non-line-of-sight, NLOS) and without it (line-of-sight, LOS). A prototype is fabricated and measured to determine the scattering parameters of concrete samples. After measurements, the obtained results are used in the efficient and accurate Nicolson–Ross–Weir (NRW) method, making it possible to estimate the values of the complex relative permittivity of the concrete blocks. The sensor design is demonstrated from initial simulations to measurements for validation of the developed prototype. The obtained results for the complex relative permittivity of concrete are in agreement with those available in the literature and the difference between the simulated and measurement results for the sensor antenna resonant frequency is 4.71%. The used measurement setup can be applied to characterize different types of solid or liquid dielectric materials.

A Position-Independent Approach to Accurate Measurement of Broadband Electromagnetic Constitutive Parameters of Magnetodielectric Materials

Magnetodielectric materials have been recently attracting great attention owing to their significant advantages for miniaturization and wide bandwidth of antennas. A precise measurement of broadband permeability and permittivity is crucial to develop and evaluate advanced magnetodielectric materials. The Nicolson-Ross-Weir (NRW) method is widely used to extract electromagnetic constitutive parameters from measured scattering parameters. One of the drawbacks of this method is requiring direct measurement of the actual sample position in the measurement fixture, which leads to uncertainties in the measured permeability and permittivity. In this article, we improve the standard NRW method by removing the need for prior knowledge of sample position. For any isotropic material, the sample position in the measurement fixture can be precisely determined by matching the phasor angles of the reflection coefficients at the sample surfaces. Due to eliminating the error from the direct measurement of sample position, the improved NRW method effectively reduces the uncertainties in the calculated permeability and permittivity. Based on the results from two kinds of magnetodielectric materials measured in two sets of test fixtures of different geometries, this straightforward, explicit, and noniterative method is theoretically and experimentally proven to have a high and position-independent accuracy over a wide frequency range.

Investigations into the microwave shielding behavior of oriented Polycaprolactone/Carbonyl iron particles composites fabricated using magnetic field assisted extrusion 3D printing

In the present study, development of a novel oriented polymeric composite comprising of Polycaprolactone (PCL) polymer and carbonyl iron filler particles (CIP) is presented. Incorporation of permanent magnets into solvent based extrusion 3 D printing set up produced the oriented polymeric composites. The microwave absorption properties of the oriented composite were investigated and compared with non-oriented composite and pristine PCL by utilizing vector network analyzer (VNA) and Nicolson-Ross-Weir (NRW) methodology. Higher values of permeability, permittivity, dielectric loss and magnetic loss of the oriented composite indicated the micro capacitor behaviour and domain wall motion of the parallel aligned CIP chains in the PCL matrix. The reflection and transmission loss values for the oriented composite were found to be -34 dB and -26 dB respectively. The microwave absorption of the oriented PCL/CIP composite was found to be approximately 93% suggesting the efficacy of the 3 D printed oriented composite as an excellent microwave absorber.

An improved technique for low-loss material complex permittivity and permeability determination from transmission-only measurements

Abstract In this paper, a novel technique based on transmission-only measurements is proposed to determine complex permittivity and permeability of low-loss materials. The proposed method removes the influences of the sample thickness and avoids the resonances in the extracted parameters. Both the experiment and simulation are applied to present the advantages of the proposed method. Compared with the well-known Nicolson–Ross–Weir (NRW) method, the proposed method shows a good performance in resonance avoidance. Compared with the conventional method based on the transmission-only measurements, the proposed method shows a good performance in accuracy.

Graphene-based tunable multi-band metamaterial polarization-insensitive absorber for terahertz applications

This paper presents a graphene-based tunable polarization-insensitive metamaterial absorber (MMA) at terahertz (THz) frequencies. The absorber consists of top patterned gold (Au) layer followed by single layer of graphene, dielectric spacer, and Au layer at bottom. The proposed MMA demonstrates multi-band absorption with the characteristics of both broad- and dual-band absorption by optimizing dimensions (parametric analysis). Broad-band absorption reaches over 90% for the range of 4.57–6.45 THz with the relative absorption bandwidth of 34%, and the absorption peak at 6.86 and 7.20 THz having 98.9 and 95.2% absorption. The normalized impedance and constitutive electromagnetic parameters of the MMA are calculated using the Nicolson–Ross–Weir (NRW) method to validate the absorption rate. Furthermore, proposed absorber is polarization-insensitive upto 90° for transverse electric wave. The tunable characteristic of MMA is achieved by tuning the Fermi energy of graphene with the application of bias voltage. Accordingly, the proposed multi- and broad-band absorbers find its potential applications in spectroscopy detection, imaging, and sensing.

An electromagnetic parameter retrieval method based on deep learning

The electromagnetic parameter retrieval method based on scattering (S) parameters is widely used because S parameters are easy to obtain. As a classic S parameters retrieval method, the Nicolson–Ross–Weir (NRW) algorithm has problems such as half-wave resonance, phase angle jump, and multivaluedness. In this work, an electromagnetic parameter retrieval method based on deep learning is proposed, which aims to solve the multivaluedness problem in the traditional NRW method. The method we proposed is suitable for retrieval of inhomogeneous medium that satisfies the theory of effective medium. The simulation shows that the electromagnetic parameter retrieval method based on deep learning has high calculation accuracy without the multivaluedness problem.

A Combined WU-shaped NRI Metamaterial for Dual Band Microwave Application

In the field of electromagnetism, artificially constructed metamaterial has opened a new hope for the researchers. Metamaterial is developed artificially and not found available in nature. This composite material shows more irregular properties than the natural materials. Negative refractive index (NRI) is one of the exceptional properties of it. Therefore, many researchers have started investigation with this material. Some metamaterials found in literature have NRI properties but very few of them are found operating simultaneously in C-and X-band. In this study, a new combined WU-shaped NRI metamaterial unit cell is presented. Here, three different substrate materials have been adopted for sensitivity analysis. The used substrate materials are FR-4, Rogers RT6006 and Rogers RT6010 and their permittivity are 4.3, 6.15 and 10.2 respectively. Finite integration technique based numerical tool is adopted for all analyses. The electromagnetic properties are determined by Nicolson-Ross-Weir (NRW) method. Perfect electric-magnetic boundary condition is applied for simulation. The metamaterial unit cell exhibits negative refractive index (NRI) within C-band and X-band for all these substrate materials. C-and X-band are widely used for satellite and long distance communication. Moreover, the proposed material shows better effective medium ratio with increasing relative permittivity which ensures the materials proper operation and sensitivity for any applications.

A Position-Independent Reflection-Only Method for Complex Permittivity and Permeability Determination with One Sample

AbstractThis paper presents a position-independent reflection-only method for determining complex permittivity and permeability of a sample. In this method, both the short and match calibration kits are used to measure the reflection coefficients. Only one sample positioned arbitrarily is measured using a one-port vector network analyzer (VNA), while the complex permittivity and permeability of the sample are determined simultaneously. Experimental results in X-band for the Acrylonitrile Butadiene Styrene plastic (ABS) are included to exhibit the validity of the proposed method. The results show that the complex permittivity and permeability determined by the proposed method have a good agreement with the parameters determined by the well-known Nicolson–Ross–Weir (NRW) method. In addition, a magnetic material is simulated to further validate the proposed method.

Measurement of Electric and Magnetic Properties of ZnO Nanoparticles in the X-Band Using Nicolson–Ross–Weir Analysis

The electric and magnetic properties of zinc oxide (ZnO) nanoparticles (NPs) have been investigated through waveguide measurement in the x-band. Because of the advantages of the x-band, the application of the Nicolson–Ross–Weir (NRW) method was able to be used to extract the mentioned characteristics from the scattering parameters. The advantages of the NRW method are that it is fast and applicable to waveguides and coaxial lines, and it can also be used to determine both the permittivity and permeability. Therefore, the results show two main resonant frequencies at 9.279 GHz and 10.46 GHz. The response of the ZnO NPs for an incident electromagnetic wave implies that both capacitance and inductance behaviors can be observed. Finally, the obtained magnetic susceptibility characteristic confirms that the ZnO NPs are ferromagnetic over the frequency range from 8 GHz to 8.265 GHz and paramagnetic up to 12.5 GHz.

A Simplified Nicolson–Ross–Weir Method for Material Characterization Using Single-Port Measurements

We present a simplified Nicolson-Ross-Weir (NRW) material characterization procedure that employs only a single-port network analyzer for data collection. This approach is particularly attractive for mmW and THz applications, as it eliminates the need for costly two-port instrumentation required in the conventional NRW method. Akin to the well-known adapter removal techniques, we use two successive calibrations of the defined measurement ports and deduce the two-port response of the sample under test. Subsequently, the conventional NRW procedure can be employed to simultaneously determine permittivity and permeability of the material under test. We demonstrate our approach for the WR8.0 waveguide band (90-140 GHz) using a multioffset-short calibration method. Similar to the two-port through-reflect-line calibration, the multioffset-short process determines the propagation constant of the waveguide, which provides additional verification of the quality of the collected measurements and the validity of the NRW procedure. We demonstrate that the simplified one-port NRW method is as effective in performance as the conventional two-port procedure. To our knowledge, this is the first-time realization of the single-port NRW method for mmW and THz bands.

Split ring resonator loaded EF-structured left-handed metamaterial for modern electronic communications

A novel miniaturised EF-structured metamaterial loaded with split ring resonator (SRR) has been developed and investigated for multi-band frequency applications. Miniaturisation is achieved by increasing the metallic strips to form EF-structure resonator. Commercially available, the advanced electromagnetic simulator has been utilised for the layout design and elaborated analysis of this developed left-handed metamaterial. The unit cell structure is embedded in low-cost FR4 dielectric substrate and size of the metamaterial is 11.11 × 11.11 mm2. Due to the miniaturised size, a highly effective medium ratio of about 14.82 is obtained. The developed left-handed metamaterial exhibits negative permittivity, negative permeability, and negative refractive index over multiple frequency ranges. Nicolson-Ross-Weir (NRW) method has been utilised for the extraction of the effective parameters. Thus, a novel metamaterial has been presented where the miniaturised size and its performances makes it compatible to use for the applications of 1.82 GHz, 2.22 GHz, 4.82 GHz, 5.89 GHz, 10.54 GHz, i.e. for digital cellular system (DCS), earth exploration-satellite communications (EESC), lower band 5G mobile communications, WiMAX applications, and military satellite applications, respectively. Furthermore, the metamaterial has average SAR reduction of about 44%. These results proceed to a guideway of better SAR reduction of modern electronic communications.

Left-handed metamaterial bandpass filter for GPS, Earth Exploration-Satellite and WiMAX frequency sensing applications.

Interferences and accuracy problem are one of the most talked issues in today's world for sensor technology. To deal with this contention, a microstrip framework consisting of a dual mode double negative (DNG) metamaterial based bandpass filter is presented in this article. To obtain the ultimate noise reduction bandpass filter, the proposed structure has to go through a series of development process, where the characteristics of the structure are tested to the limit. This filter is built on Rogers RT-5880 substrate with a 50Ω microstrip line. To pursue the elementary mode of resonant frequency, the ground layer of the structure is kept partially filled and a gradual analysis is executed on the prospective metamaterial (resonator) unit cell. Depending on the developed unit cell, the filter is constructed and fabricated to verify the concept, concentrating on GPS (1.55GHz), Earth Exploration-Satellite (2.70GHz) and WiMAX (3.60GHz) bands of frequencies. Moreover, the structure is investigated using Nicolson-Ross-Weir (NRW) approach to justify the metamaterial characteristics, and also tested on S-parameters, current distribution, electric and magnetic fields and quality factor. Having a propitious architecture and DNG characteristics, the proposed structure is suitable for bandpass filter for GPS, Earth Exploration-Satellite and WiMAX frequency sensing applications.

‘Folded-Line’ Left Handed Metamaterial for Efficient Architecture Implementation

The design of artificial metamaterial (MTM) has been proposed as an effective medium with extracted scattering parameter by applying Nicolson-Ross-Weir (NWR) equation to achieved negative permittivity and permeability. The novel architecture of ‘Folded-Line’ Left-handed metamaterial (FL-LHM) consist of split ring resonator SRR is designed and modified using LC lump elements analysis to extend bandwidth and operational frequency at 6 GHz to 12 GHz. In this study, we proposed metamaterial novel unit cell designs and simulate the performance in terms of the distribution of electric and magnetic fields, absorption, transmittance and reflectance. The unit cell of FL-LHM as medium allows controlling electromagnetic waves can cause backwave propagation is observed electromagnetic response that current induced in the closed FL-LHM unit cell. This design has its own advantage in term of FL-LHM parameter width, thickness, and absorption bandwidth and transmittance wavelength, might be severely important for particular purposes such as waveguiding or sensing application.

UWB Metamaterial-Loaded Antenna for C-Band Applications

A novel metamaterial-inspired patch antenna is proposed, wherein a 2-segment SRR Labyrinth metamaterial is embedded inside the antenna substrate. It is observed that upon incorporation, the bandwidth widens to around 600% and VSWR improves by approx. 1.5% and the antenna is miniaturized by 400%. The Nicolson-Ross-Weir (NRW) method has been used to retrieve the material parameters from transmission and reflection coefficients.

Microwave Characterization of Low-Loss FDM 3-D Printed ABS With Dielectric-Filled Metal-Pipe Rectangular Waveguide Spectroscopy

Over time, the accuracy and speed by which a material can be characterized should improve. Today, the Nicolson–Ross–Weir (NRW) methodology represents a well-established method for extracting complex dielectric properties at microwave frequencies, with the use of a modern vector network analyzer. However, as will be seen, this approach suffers from three fundamental limitations to accuracy. Challenging NRW methods requires a methodical and robust investigation. To this end, using a dielectric-filled metal-pipe rectangular waveguide, five independent approaches are employed to accurately characterize the sample at the Fabry–Perot resonance frequency (non-frequency dispersive modeling). In addition, manual Graphical and automated Renormalization spectroscopic approaches are introduced for the first time in the waveguide. The results from these various modeling strategies are then compared and contrasted to NRW approaches. As a timely exemplar, 3-D printed acrylonitrile–butadiene–styrene (ABS) samples are characterized and the results are compared with existing data available in the open literature. It is found that the various Fabry–Perot resonance model results all agree with one another and validate the two new spectroscopic approaches; in doing so, exposing three limitations of the NRW methods. It is also shown that extracted dielectric properties for ABS differ from previously reported results and reasons for this are discussed. From measurement noise resilience analysis, a methodology is presented for determining the upper bound signal-to-noise ratio for the vector network analyzer (not normally associated with such instrumentation). Finally, fused deposition modeling (FDM) 3-D printing can result in a non-homogeneous sample that excites open-box mode resonances. This phenomenon is investigated for the first time analytically and with various modeling strategies.

Determination of Complex Permittivity of Low-Loss Materials From Reference-Plane Invariant Transmission/Reflection Measurements

In this paper, a novel method is proposed to determine unique and stable relative complex permittivity of low-loss materials from the transmission/reflection (TR) measurements, though the positions of the materials under test are unknown. The proposed method systematically combines artificial neural network (ANN) models with the Nicolson-Ross-Weir (NRW) method. Firstly, an ANN model is established to estimate the position of the sample in the transmission line. Secondly, the NRW method is adapted to estimate the relative complex permittivity, and the unique solutions are selected with the help of dielectric properties. Thirdly, the noniterative technique in the literature is adapted to avoid the instabilities in the relative complex permittivity. Finally, the S-parameters of the amplitude-only or transmission-only measurements are used to accurately determine the relative complex permittivity. The proposed method is experimentally validated by two samples. The simulated data are used to further validate the accuracy of the proposed method. The results of the proposed method based on the transmission-only measurements are the most accurate.