Characterization Of Dielectric Materials Research Articles

Investigation of the dielectric characteristics of materials manufactured using additive technologies

Based on the existing methods of measuring the dielectric characteristics of materials, the most optimal method for performing calculations in the electrodynamic computer-aided design system is selected by the finite integration method. Based on the calculated values of the scattering matrix, the permittivity and the tangent of the dielectric loss angle of the printed polymer samples are calculated according to a given algorithm. When evaluating the accuracy of the calculation of the dielectric characteristics, validation was performed for a sample with the specified characteristics. For a sample printed using the technology of fused filament fabrication, the influence of the filling parameters on the dielectric characteristics of the printed model in the X-band of wavelengths was estimated. The description of the model implemented in the computer-aided design system is given. By processing the simulation results, approximating dependences for the permittivity and losses on the degree of filling with the dielectric are obtained. It follows from the calculated angular diagrams that the decrease in the degree of filling of the dielectric directly affects the degree of anisotropy of the polymer obtained during printing in the plane of the extruded layers. This also increases the depth of the extremes observed at angles of 0°, 90° and 180°. The presence of these extremes is directly related to the fact that the force lines of the main wave type in the waveguide are located perpendicular to the wide wall and in a situation where the volumes of air gaps between the cylinders are parallel to the force lines of tension, there is a general decrease in the dielectric constant. For a printed sample consisting of two layers of crossed cylinders, the air volumes are parallel to the lines of force with a period of ninety degrees, which is confirmed by the results obtained. An increase in the depth of the extremes with a decrease in the degree of filling is associated with a corresponding increase in the air space between the cylinders in the layer of the printed polymer.

W-Band Sensor for Complex Permittivity Measurements of Rod Shaped Samples

A novel W-band sensor for complex permittivity measurements of rod shaped samples based on reflectometer method is described. Characterization of dielectric materials around 100 GHz is quite a challenge. The main limitation is the requirements for the accuracy of the dimensions of the test sample and ensuring good contact with conductive surfaces. From this point of view, it seems interesting to use a cylindrical waveguide with the TE01 mode. The four linearly-polarized H10 fields of rectangular waveguides with equal amplitude and phase circumnavigate the cylindrical waveguide to jointly excite its TEnm circular modes with four-fold symmetry. This precludes the excitation of lower-order modes of the metallic cylindrical waveguide. TE01 mode is unique in that its field leads to zero on the surface of the walls of a metallic cylindrical waveguide. The main field interaction takes place on the sample surface. The calibration method uses calibration curves obtained by simulation for known values of complex permittivity of the samples. This eliminates the requirement for a precision calibration standards, which is the problematic to realize at millimeter wavelengths. Moreover, the complex field structure in the sensor makes it impossible to apply a standard calibration method. Simulation and measurements using these method have been performed in W-band (70–114 GHz). Measurement results demonstrate the robustness of this new sensor for characterizing rod shaped dielectric samples.

Multi-band microwave sensor based on Hilbert’s fractal for dielectric solid material characterization

A planar sensor designed using the fourth Hilbert fractal curve iteration for solid material characterization at multiple frequencies is reported in this paper. The fractal curve is self-similar with space-filling properties. The Hilbert fractal geometry is used to form a compact resonator, with a multiband frequency response where miniaturization is achieved since a large transmission line length is effectively confined in a limited area. The sensor provides five resonances in the frequency range from 0 to 5 GHz. The resonant frequencies are 0.56, 1.68, 2.72, 3.69 and 4.72 GHz, all used to measure the real permittivity of known samples with a sensitivity of 7, 20, 27, 43 and 50 MHz/permittivity, respectively. The sensor is used to measure dielectric samples with 20 × 20 mm2 areas with several thicknesses. Simulations and measurements demonstrate that the Hilbert fractal geometry can be used to design a multiband planar sensor for solid dielectric material characterization.

Advanced Modelling Techniques for Resonator Based Dielectric and Semiconductor Materials Characterization

This article reports recent developments in modelling based on Finite Difference Time Domain (FDTD) and Finite Element Method (FEM) for dielectric resonator material measurement setups. In contrast to the methods of the dielectric resonator design, where analytical expansion into Bessel functions is used to solve the Maxwell equations, here the analytical information is used only to ensure the fixed angular variation of the fields, while in the longitudinal and radial direction space discretization is applied, that reduced the problem to 2D. Moreover, when the discretization is performed in time domain, full-wave electromagnetic solvers can be directly coupled to semiconductor drift-diffusion solvers to better understand and predict the behavior of the resonator with semiconductor-based samples. Herein, FDTD and frequency domain FEM approaches are applied to the modelling of dielectric samples and validated against the measurements within the 0.3% margin dictated by the IEC norm. Then a coupled in-house developed multiphysics time-domain FEM solver is employed in order to take the local conductivity changes under electromagnetic illumination into account. New methodologies are thereby demonstrated that open the way to new applications of the dielectric resonator measurements.

Enhanced Performance of Spiral Co-planar Inter-Digital Capacitive Structures for Sensing Applications

In this work we consider a Spiral Inter-Digital Capacitive (SIDC) structure for its optimum design and performance analysis based on finite element simulation, for possible application as sensors. The effects of relevant geometrical parameters like sensor electrode width, inter-electrode gap, number of electrode pairs and electrode height on sensor output capacitance are evaluated and analyzed. In addition, influence of a test sample over the designed sensor for varying lift-off distances from the top of the sensor surface and for various material permittivity values are investigated. Results of the studies show that a spiral structure has about 25% higher sensitivity for its capacitance value compared to a corresponding Rectangular Inter-Digital Capacitive (RIDC) structure of comparable dimensions. The simulation results have been verified experimentally by fabricating and testing SIDC and RIDC structures for dielectric characterization of materials and proximity measurement applications. The results point to the possibility of designing and fabricating spiral inter-digital capacitive sensors with higher sensitivity for a multitude of applications.

Design of highly sensitive complementary metamaterial‐based microwave sensor for characterisation of dielectric materials

Metamaterial-based double-slit complementary split rectangular resonator sensor is proposed for the characterisation of dielectric properties of the materials under test (MUTs). The proposed sensor is designed and simulated on the CST microwave studio software using a low-cost substrate FR4. An array of three identical resonators is etched in the ground plane of the sensor to achieve a single and deep notch of −58.7 dB in the transmission coefficient (S 21) at the resonant frequency of 7.01 GHz, which is the novelty of the proposed sensor. A deep and single resonant frequency band has a significant role in the precise measurement of the dielectric properties of the MUTs. The effective constitutive parameters are extracted from the S-parameters. An equivalent circuit model is suggested that describes the overall behaviour of the sensor. The sensor is fabricated on the FR4 substrate and measured through the vector network analyser (N5224B) by placing the standard materials. The parabolic equation for the proposed sensor is formulated to approximate the permittivity of the MUTs. A very small percentage of error, 0.77, is found which shows high accuracy of the sensor. This methodology is efficient, simple in fabrication, and reduces cost and computational time also.

Characterization of Dielectric Materials by Sparse Signal Processing With Iterative Dictionary Updates

Estimating parameters and properties of various materials without causing damage to the material under test (MUT) is important in many applications. Thus, in this letter, we address this by wireless sensing. Here, the accuracy of the estimation depends on the accurate estimation of the properties of the reflected signal from the MUT (e.g., number of reflections, their amplitudes and time delays). For a layered MUT, there are multiple reflections and, due to the limited bandwidth at the receiver, these reflections superimpose each other. Since the number of reflections coming from the MUT is limited, we propose sparse signal processing (SSP) to decompose the reflected signal. In SSP, a so called dictionary is required to obtain a sparse representation of the signal. Here, instead of a fixed dictionary, a dictionary update technique is proposed to improve the estimation of the reflected signal. To validate the proposed method, a vector network analyzer (VNA) based measurement setup is used. It turns out that the estimated dielectric constants are in close agreement with the dielectric constants of the MUTs reported in literature. Further, the proposed approach outperforms the state-of-the-art model-based curve-fitting approach in thickness estimation.

Interdigital capacitor loaded electric‐LC resonator for dielectric characterization

AbstractA high sensitivity microstrip line‐based sensor loaded with the electric‐LC (ELC) resonator is proposed in this work for the accurate characterization of dielectric materials. The high sensitivity in the present situation is achieved due to usage of novel interdigital capacitor in the ELC resonator topology, which actually provides enhanced electric field for dielectric testing. The proposed sensor is designed in the S band regime, and various standard dielectric samples are tested to validate the proposed design. For retrieving the dielectric constants of these samples, an empirical relationship is proposed relating the dielectric properties with the resonant frequency of the sensor. The proposed empirical model is further improved by introducing two error terms to take into consideration the effect of fabrication tolerance of the sensor and surface roughness of the test specimen. The normalized sensitivity of the proposed sensor using standard procedure is estimated to be 5.14%, which is reasonably higher than that of other sensors reported in literature.

Perforated serpentine membrane with AlN as dielectric material shunt capacitive RF MEMS switch fabrication and characterization

In this communication, we have designed, simulated, performance improved, fabricated and characterized a shunt capacitive RF MEMS switch with perforated serpentine membrane (Au). Fabrication is done using surface micromachining with four masks. AlN dielectric material of 50 nm thickness is offering high isolation of − 58.5 dB at 31.5 GHz, and incorporation of perforation to the membrane the switch insertion loss is very low i.e., − 0.4 dB. The perforated serpentine membrane with non-uniform meanders of 500 nm thickness using Au material is helped to reduce the actuation voltage, the fabricated switch is requiring 4.5 V actuation voltage. DC sputtering PVD is used to deposit metal (Au) and dielectric (AlN) thin Films. S1813 photoresist is used as a sacrificial layer and the membrane structure is released using piranha, IPA and critical point drying (Pressure 1260 Psi, Temperature 31 °C).

CSRR-Based Microwave Sensor for Dielectric Materials Characterization Applied to Soil Water Content Determination.

A new and compact sensor based on the complementary split-ring resonator (CSRR) structure is proposed to characterize the relative permittivity of various dielectric materials, enabling the determination of soil water content (SWC). The proposed sensor consists of a circular microstrip patch antenna supporting a 3D-printed small cylindrical container made out of Acrylonitrile-Butadiene-Styrene (ABS) filament. The principle of operation is based on the shifting of two of the antenna resonant frequencies caused by changing the relative permittivity of the material under test (MUT). Simulations are performed enabling the development of an empirical model of analysis. The sensitivity of the sensor is investigated and its effectiveness is analyzed by characterizing typical dielectric materials. The proposed sensor, which can be applied to characterize different types of dielectric materials, is used to determine the percentage of water contained in different soil types. Prototypes are fabricated and measured and the obtained results are compared with results from other research works, to validate the proposed sensor effectiveness. Moreover, the sensor was used to determine the percentage of water concentration in quartz sand and red clay samples.

Effect of low-energy electron irradiation on voltage-capacity curves of Al/SiO2/Si structure

Charging of dielectric targets by electron irradiation is a well-known phenomenon which should be taken into account in characterization of dielectric materials and coatings with electron microscopy, in electron beam lithography, in development of dielectric coatings for spacecrafts and other fields of science and engineering. Charging kinetics is strongly affected by spatial distribution of electrons and holes formed by irradiation. At the experimental electron beam energy electron penetration depth is smaller than dielectric thickness and this allows identifying the contribution of excess carrier transport to trap formation at the SiO2/Si interface. Low-energy electron beams have been shown to substantially affect C–V curve slope, i.e., to form traps at the interface. We have studied the effect of bias applied to the test structure before and after electron beam irradiation. The experiment has shown that bias of either polarity applied to the test MOS structure before low-energy electron beam irradiation practically does not affect the C–V curves of the test structure. Positive bias applied to the metallization layer during low-energy electron beam irradiation has a strong effect on the C–V curve pattern while negative bias affects the C–V curves but slightly. Study of the stability of the changes caused by electron beam irradiation has shown that the C–V curves of the test structure restore slowly even at room temperature. Application of negative bias decelerated charge relaxation.

Characterization of Dielectric Materials at WR-15 Band (50–75 GHz) Using VNA-Based Technique

This article presents an in-depth study of a new vector network analyzer (VNA)-based electromagnetic material measurement method relying on a commercially available material characterization kit (MCK). These MCKs provide effectively a guided free-space technique with less stringent requirement on alignment compared with conventional free-space techniques. Coupled with time gating, these MCKs employ a simple calibration, composed of reflect and thru standards only, prior to taking reflection and transmission S-parameter measurements. This MCK-based method complements other conventional measurement techniques, e.g., time-domain spectroscopy (TDS) and resonant cavity, allowing fast broadband dielectric material characterization over the millimeter- and submillimeter-wave frequency ranges. In this article, a WR-15 (50-75 GHz) MCK is utilized for the measurements of S-parameters for seven types of low-loss dielectric material. Their dielectric constant and loss tangent are extracted from S-parameters and are compared against literature values. A relatively good agreement is achieved. Moreover, an investigation into the uncertainties of the extracted dielectric constant and loss tangent is performed and reported.

Aging monitoring of electrical machines using winding high frequency equivalent circuits

Abstract This study defines a monitoring method based on impedance analysis in the upper part of the spectrum. It focuses on the analysis of the high frequency behavior of electrical machines windings considering the turn-to-turn capacitance variations (delta-C) due to insulation aging. An equivalent circuit is automatically generated from the turn arrangements in coils; parameters are computed considering the coil shape and the characteristics of insulation materials. PSpice analysis of the equivalent circuit yields the resonance frequencies to be monitored. With this software and a database giving the relationship between the turn-to-turn capacitance variation delta-C and the reduction of insulation performances due to aging, it is possible to build a monitoring system able to produce an alert when the probability of failure becomes higher than a predetermined level.

Embroidered Rectangular Split-Ring Resonators for the Characterization of Dielectric Materials

In this paper, we report an embroidered rectangular split-ring resonator (SRR) operating at S band for material characterization based on the differences in dielectric parameters. We designed, fabricated and characterized SRR sensors on a conventional fabric that can be conformally attached over the surface of samples under investigation. The structures are made of conductive threads and can be embroidered on any dielectric fabric at low cost using conventional embroidery methods. We have demonstrated material characterization capability of the sensors using a specific design with a length of 60 mm and a width of 30 mm. We wrapped the sensors on low-density polyethylene (LDPE) bottles filled with deionized (DI) water and common solvents (ethanol, methanol, isopropanol and acetone) in our experiments. We measured the nominal resonant frequency of a specific sensor wrapped around an empty bottle as 2.07 GHz. The shifts in resonant frequencies when the bottle was filled with the solvents follow the dielectric constants of the solvents.

A Simplified Dielectric Material Characterization Algorithm for Both Liquids and Solids

A simplified dielectric material characterization technique that combines an equivalent impedance algorithm and a general “line–line” trace method is introduced. The technique is applicable to every type of transmission lines. Due to the convenient fabrication and the allowance of integration with various polymers, coplanar waveguide transmission lines integrated with an SU-8 microfluidic channel is primarily used in this study. The conformal mapping method, an efficient and straightforward way, is introduced to build the foundation of dielectric material characterization and to optimize the sensor design. A validation measurement of the proposed technique is performed on deionized water, and show valuable consistency with previous reliable data presented in the literature. Next, the technique is applied on solid SU-8 characterization with four groups of on-wafer measurements. SU-8 measurement results and the related uncertainty analysis are demonstrated subsequently.

Impact of Use Conditions on Dielectric and Conductor Material Models for High-Speed Package Interconnects

Use conditions based on temperature and humidity can have a significant impact on the package material properties and loss, which is required to be included in modeling assumptions to be able to set realistic specifications. The dielectric loss is affected by both temperature and humidity through material properties. The conductor loss, however, is affected by only temperature explicitly through conductivity and implicitly through skin depth and surface roughness modeling. This paper presents a systematic use condition-dependent methodology for package high-speed interconnects including a robust dielectric material characterization metrology. Correlation to high fidelity insertion loss measurements at different temperatures indicates that the roughness correction factor extracted at one temperature does not fit all and leads to underestimating the loss at higher temperatures. Without loss of generality due to a unified form of correction factors of the existing common roughness models, a modified version of Huray’s snowball model with an explicit temperature dependence is proposed to achieve high-quality on-package interconnect loss correlation at different temperatures.

A Pixelated Microwave Near-Field Sensor for Precise Characterization of Dielectric Materials

A highly sensitive microwave near-field sensor based on electrically-small planar resonators is proposed for highly accurate characterization of dielectric materials. The proposed sensor was developed in a robust complete-cycle topology optimization procedure wherein first the sensing area was pixelated. By maximizing the sensitivity as our goal, a binary particle swarm optimization algorithm was applied to determine whether each pixel is metalized or not. The outcome of the optimization is a pixelated pattern of the resonator yielding the maximum possible sensitivity. A curve fitting method was applied to the full-wave simulation results to derive a closed form expression for extracting the dielectric constant of a chemical material from the shift in the resonance frequency of the sensor. As a proof of concept, the sensor was fabricated and used to measure the permittivity of two known liquids (cyclohexane and chloroform) and their mixtures with different volume ratios. The experimentally extracted dielectric constants were in an excellent agreement with the reference data (for pure cyclohexane and chloroform) or those obtained by mixture formulas.

Electromechanical characterization of a 3D printed dielectric material for dielectric electroactive polymer actuators

Dielectric electroactive polymers (DEAPs) represent a subclass of smart materials that are capable of converting between electrical and mechanical energy. These materials can be used as energy harvesters, sensors, and actuators. However, current production and testing of these devices is limited and requires multiple step processes for fabrication. This paper presents an alternate production method via 3D printing using Thermoplastic Polyurethane (TPU) as a dielectric elastomer. This study provides electromechanical characterization of flexible dielectric films produced by additive manufacturing and demonstrates their use as DEAP actuators. The dielectric material characterization of TPU includes: measurement of the dielectric constant, percentage radial elongation, tensile properties, pre-strain effects on actuation, surface topography, and measured actuation under high voltage. The results demonstrated a high dielectric constant and ideal elongation performance for this material, making the material suitable for use as a DEAP actuator. In addition, it was experimentally determined that the tensile properties of the material depend on the printing angle and thickness of the samples thereby making these properties controllable using 3D printing. Using surface topography, it was possible to analyze how the printing path affects the roughness of the films and consequently affects the voltage breakdown of the structure and creates preferential deformation directions. Actuators produced with concentric circle paths produced an area expansion of 4.73% uniformly in all directions. Actuators produced with line paths produced an area expansion of 5.71% in the direction where the printed lines are parallel to the deformation direction, and 4.91% in the direction where the printed lines are perpendicular to the deformation direction.

Partially Filled Substrate Integrated Waveguide-Based Microwave Technique for Broadband Dielectric Characterization

A novel partially filled substrate integrated waveguide (PFSIW)-based generalized microwave technique for broadband characterization of dielectric materials is presented. The proposed technique is based on the newly derived closed-form analytical formulation to extract the complex permittivity of test specimens placed in the PFSIW structure. The analytical formulations are further improved by developing an empirical model, which especially helps in extracting the loss tangent of the low-loss test specimen in the specified frequency band. The PFSIW structure along with appropriate planar microstrip transition section operating in the X-band region is designed using the full-wave electromagnetic solver, the CST-MWS. The designed substrate integrated waveguide (SIW) structure is fabricated on the commercially available FR-4 substrate, and accordingly, the S-parameters are measured under the unloaded condition which is in close agreement with the corresponding simulated data. Finally, a robust calibration methodology for the PFSIW structure is proposed by designing and fabricating a set of SIW calibration standards, which basically helps to translate the measured S-parameters to the sample interface by removing the effect of microstrip feed section. A number of standard planar RF substrates and dielectric specimens are measured using the designed PFSIW structure, and a close agreement between the extracted permittivity of these samples with their reference values shows the applicability of the proposed SIW technique.

A compact planar cylindrical resonant RF sensor for the characterization of dielectric samples

ABSTRACTA conventional cavity-based planar cylindrical resonant sensor for the RF characterization of dielectric materials is proposed in this work. The designed planar cylindrical sensor is about 22% more compact providing 25% higher sensitivity as compared to its rectangular counterpart working at the same frequency. The proposed sensor is designed for the fundamental TM010 mode at 1.5 GHz resonant frequency and is excited using the coaxial probe instead of conventional microstrip feeding, which aids in obtaining further compactness. The sensor is designed on low-cost FR4 substrate and experimentally validated using various dielectric samples like Teflon, polyethylene, PVC and plexiglass yielding a good match between the retrieved dielectric constants and data available in the literature. For characterization of dielectrics, a slot is drilled at the center of the sensor having the maximum electric field for inserting the test sample and later optimized for higher sensitivity. For determining the loss tangent in terms of the transmission coefficient at the resonant frequency, a numerical model is derived using the curve fitting technique.