Characterization Of Dielectric Materials Research Articles

Aging characterization of dielectric materials using microstrip spiral resonator sensor: application in high frequency range, up to 18 GHz

This current work aims to propose a complete microwave procedure for dielectric materials aging characterization. To achieve this aim, a microstrip spiral resonator sensor, based on printed circuit board (PCB) technology, is designed to attend polyvinyl chloride (PVC) aging behavior through microwave measurements. The resonator is composed of a spiral microstrip, excited by coupling 50-Ohm transmission line on the top layer of the substrate; meanwhile a rectangular slot is etched in the bottom layer, behind the spiral shape to achieve high inductive effect. Structure optimization was conducted using high-frequency structure simulator (HFSS). The sensor is then used as a holder of the UV-aged PVC material while reflection (S11) and transmission (S21) coefficients are measured by vector network analyzer (VNA) in high frequency range, up to 18 GHz. The aging effect is finally perceived by observing the frequency shift of the resonance frequency between the empty and the aged-PVC loaded sensor, together with a variation in the S21 parameter amplitude. It is then found that for 864 h of UV-exposure is provided more than 0.45% frequency shift and about 4.67% decrease in electromagnetic energy transmission. Moreover, comparison between S11 and S21 results reveals that using S11 parameter is more practical to investigate material aging as it allows for simple visual checking of the frequency shift.

Innovate, insulate, integrate: Embracing circular economy in innovative insulations for reduced air conditioning expenses and carbon mitigation in fly ash brick buildings

Global demand for energy in the construction sector has increased drastically. A substantial portion of this energy belongs to fulfilling the heating, ventilation, and air-conditioning requirements of buildings, which are essential for maintaining the well-being of people. The development of zero-energy or environmentally friendly structures is required to attain a sustainable future. Strategic design of the building’s envelopes in green energy buildings can reduce air conditioning expenses. This article focuses on several insulation-integrated fly ash brick wall envelopes that have been designed to reduce CO2 emissions, reduce air conditioning expenses, and figure out payback times in warm-temperate and hot-arid regions. The degree-hour technique for heating and cooling, as well as unsteady heat transfer characteristics, are taken into consideration in this research. This is achieved by incorporating thirteen innovative insulation materials into fly ash bricks in three distinct configurations, (i.e., insulation layer near to the outer end of the fly ash block, on the middle of the fly ash block, and near to the inside end of the fly ash block). Experimental measurements were carried out to determine the thermo-physical characteristics of insulation materials. The analytical findings are confirmed through experimental validation. In hot-arid and composite climatic zones, placing an insulation layer (cloth-40/foam-60) near the outer end of the fly ash block resulted in the highest savings on air-conditioning costs of 0.89 $/m2 and 0.90 $/m2, respectively. They also achieved the highest carbon mitigation values at 17.2 and 16.8 kg/kWh. Insulation-integrated wall envelopes represent the pinnacle of energy efficiency in green building design, seamlessly combining advanced insulation materials with cutting-edge construction techniques to minimise energy consumption and maximise sustainability.

Insulation performance and harmonic characteristics of insulation materials of the cable under moisture conditions

Insulation performance and harmonic characteristics of insulation materials of the cable under moisture conditions

Varactor-Based Tunable Sensor for Dielectric Measurements of Solid and Liquid Materials

In this article, a tunable RF sensor is presented for the measurement of dielectric materials (liquids and solids) based on a metamaterial resonator. The proposed novel configuration sensor has a microstrip line-loaded metamaterial resonator with tunable characteristics by utilizing a single varactor diode in the series of the resonator. CST Microwave studio is employed for 3D simulations of the tunable sensor, and the desired performance is attained by optimizing various structural parameters to enhance the transmission coefficient (S21 magnitude) notch depth performance. The proposed RF sensor can be tuned in L and S-bands using the varactor diode biasing voltage range of 0–20 V. To validate the performance of the sensor, the proposed design has been simulated, fabricated, and tested for the dielectric characterization of different solid and liquid materials. Material testing is performed in the bandwidth of 1354 MHz by incorporating a single metamaterial resonator-based sensor. Agilent’s Network Analyzer is used for measuring the S-parameters of the proposed sensor topology under loaded and unloaded conditions. Simulated and measured S-parameter results correspond substantially in the 1.79 to 3.15 GHz frequency band during the testing of the fabricated sensor. This novel tunable resonator design has various applications in modulators, phase shifters, and filters as well as in biosensors for liquid materials.

Highly Sensitive Microwave Sensor Based on Planar Resonator Arrangement for Dielectric Material Characterization

Highly Sensitive Microwave Sensor Based on Planar Resonator Arrangement for Dielectric Material Characterization

Synthesis and characterization of new doped dielectric materials based on CaCu3Ti4O12 (CCTO) applied at high temperature

In this study, we explored the impact of La3+/Nd3+ substitutions on the microstructure and dielectric characteristics of Ca0.9(La1-yNdy)0.066Cu3Ti4O12 ceramics (with varying y values: 0.25, 0.5, and 0.75). The X-ray diffraction (XRD) analysis confirmed that the synthesized samples exhibited a cubic perovskite structure (Im-3 space group) without any discernible impurities. Examination of the samples using scanning electron microscopy (SEM) unveiled that the introduction of small amounts of La3+/Nd3+ during sintering led to a reduction in the grain size of CCTO. Dielectric assessments demonstrated that all the solid-state samples containing dopants displayed remarkable dielectric permittivity (ε'>3 × 103) across a wide spectrum of frequencies up to 1 MHz and various temperatures (Δε'/ε′20< ±15 %). This study lays the groundwork for the development of novel dielectric materials based on CCTO, specifically suited for applications at temperatures exceeding room temperature. Furthermore, the ceramic doped with y = 0.5 also exhibited low dielectric loss, with a tanδ value of approximately 0.02 at 60 °C and 1 kHz.

Determination of dielectric properties of plaster blocks for sealing masonry using non-destructive frequency scanning methods

With the increasing use of traditional and new models of wireless communication systems, the study and determination of the electrical characteristics of materials used in civil construction is an important topic to establish an understanding of how the radio frequency signal behaves inside built environments. This study presents an extensive process of characterization of electrical parameters of plaster blocks used in the construction of walls. Different from the literature where a prior estimation of the data occurs to enable sampling parameters to be obtained, this work proposes an innovative way of obtaining them entirely based on the analysis of the material through frequency measurements, which results in a greater level of precision of the data results. Analyses are made in the frequency range from 0.7 to 5.2 GHz, which has been used for several wireless communication standards. To carry out the electrical characterization of dielectric materials, a non-invasive methodology is proposed based on an innovative combination of the Nicolson–Ross–Weir Method (NRW) and the Ray Tracing Method. Through the proposed methodology and an extensive campaign of measurements using frequency scanning equipment, calculated and experimental data of Shielding Effectiveness (SE), complex relative electrical permittivity, loss tangent, attenuation coefficient and conductivity were obtained for a wide range of frequency, considering different samples of plaster blocks. The obtained results are compared to those available in the related literature, confirming the accuracy of the proposed analysis.

Efficient Calculation of the 3-D Rectangular Waveguide Green’s Functions Derivatives by the Ewald Method

In this contribution, the Ewald method has efficiently been applied to accelerate the computation of the rectangular waveguide Green’s functions (GFs) derivatives. Based on previous works, we have outlined new approximation formulae that avoid the evaluation of computationally expensive complementary error functions of complex argument, needed by the Ewald method. This is possible when the internal medium of the rectangular waveguide is homogeneous and lossless. On the other hand, different convergence numerical studies have been carried out, showing a similar convergence rate for computing the original GFs and their derivatives. Moreover, we have checked that the computational time is only slightly increased for obtaining the derivatives as compared to the original GFs, after the application of these new techniques. The newly derived expressions are useful for the evaluation of electromagnetic fields, the characterization of dielectric materials and step discontinuities between rectangular waveguides, and the analysis of rectangular cavities using integral equation formulations. For validation, the electric field produced by a surface electric current density with a rectangular pulse distribution has been evaluated, using the new proposed expressions. These results have been compared to simulations provided by full-wave finite elements commercial software to verify their correctness, exhibiting a good agreement.

Measurement Errors and Uncertainties in the Complex Permittivity Extraction With a Fabry–Perot Open Resonator

A Fabry–Perot open resonator (FPOR) has recently become one of the most popular fixtures dedicated to the characterization of dielectric materials in the microwave and millimeter-wave range, mainly due to its quasi-broadband operation combined with large accuracy typical for resonant methods. However, to become a widely recognized measurement standard, an error budget of this approach has to be evaluated, accounting for systematic and random errors in the extraction of the dielectric constant (Dk) and loss tangent. It will be shown in this article that the main sources of the systematic and random Dk errors are the choice of the electromagnetic (EM) model and variation of the thickness of the dielectric sheet, respectively. The first one can be controlled to some extent by the developer of the measurement system, however, thickness variation cannot be easily controlled. Therefore, it has to be accounted for in the form of uncertainty bars. In the case of the loss tangent, systematic and random errors are mainly due to the electric energy filling factor error and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor variation, respectively. Moreover, it is shown in this article that the loss tangent uncertainty (LTU) is the lowest when the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor with the sample is 40%–50% of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor of the empty cavity. In addition to that, it is shown that the noise floor of the measurement is much less important when the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor is estimated with the aid of curve-fitting algorithms instead of the 3-dB-point method. However, complete knowledge on the LTU cannot be acquired from just one measurement as it does not account for the finite repeatability of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor measurement. It is, therefore, proposed in this article how to practically evaluate and suppress this error. Although the main attention has been focused on the FPOR, many conclusions presented in this study are not limited to a particular type of resonant technique.

A Novel Fractal Hilbert Curve-Based Low-Cost and Highly Sensitive Microwave Sensor for Dielectric Characterization of Liquid Materials

A Novel Fractal Hilbert Curve-Based Low-Cost and Highly Sensitive Microwave Sensor for Dielectric Characterization of Liquid Materials

Microwave Heating for the Conservation of Cultural Heritage Assets: A Review of Main Approaches and Challenges

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objectives:</i> The cultural heritage (CH) represents the proof of human achievements from the past in terms of historical and technological progress. One of the main issues regarding CH preservation is the bio-deterioration phenomenon which arises from biological colonization of artistic materials with consequent aesthetic, chemical and structural damage. The most common disinfestation methods are based on mechanical, chemical, biological or physical treatments. Among the physical methods, microwave heating has high potentialities, but its application is not a standard. Here we reviewed relevant literature on the use of microwave heating for the disinfestation of artworks from biodeteriogens. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Method:</i> We performed a systematic literature search, identified twenty relevant publications, and extracted relevant information. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results:</i> Microwave heating resulted effective for total disinfestation of various infesting agents on several materials, rapid, safe for operators and the environment. However, we highlighted the lack of a systematic approach to the planning of artworks treatment with microwave heating and developed operative guidelines that include dielectric characterization of materials, prediction and control of electric field distribution in the artwork, identification of lethal doses for infesting agents. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Impact:</i> The proposed approach might contribute to boost the use of this promising, non-invasive, and safe technology for artworks conservation.

High-entropy design for dielectric materials: Status, challenges, and beyond

Dielectric materials featured with polarization at an applied electric field have been demonstrated with a wide range of applications such as energy storage and conversion, thus triggering tremendous efforts in scientific and industrial research. To date, numerous strategies have been explored to improve the performance of dielectric materials; especially, the recently reported high-entropy design enabling flexible composition configuration and tunable functional properties has attracted increasing attention. In this contribution, we review the very recent investigations and applications of high-entropy design for dielectric materials, including dielectric energy storage, electrocalorics, piezoelectrics, and ferroelectrics, and address the challenges and remaining concerns. Finally, we suggest future research directions for the preparation and in-depth structure characterization of high-entropy dielectric materials. This review will provide a holistic view of the most state-of-the-art high-entropy dielectric materials and envision prospects of high-entropy design for dielectrics.

Miniaturized multi-modality field-ready sensing system for defect detection of CFRP materials

As infrastructure decays rapidly due to structural and material aging and failures, the development of new improved, and efficient nondestructive evaluation (NDE) techniques is vital for system health monitoring and preventive maintenance. Composite material, such as carbon fiber reinforced polymer (CFRP) plays a significant role in energy and transportation infrastructure due to the advantages of corrosion resistance, durability, and lightweight, which contributes to minimal maintenance and long service life. However, due to their unique anisotropic dielectric and mechanical characteristics, detecting composite material defects by NDE techniques is still challenging. This paper presents a novel, low-cost miniaturized multi-modality imaging system combining low-frequency capacitive shortwave and high-frequency microwave NDE technologies to detect various types of defects in CFRP materials. Based on the governing electromagnetic theory behind multi-modality electromagnetic NDE methods, the merit of combining low-frequency shortwave and near-field microwave imaging for dielectric characterization of composite materials is thoroughly investigated and demonstrated. Then, a miniaturized imaging system is developed to operate at ultra-wide bands: 10 kHz to 200 MHz for the capacitive shortwave probes and 1 GHz to 9 GHz for the microwave probes. Customized multi-material joining samples of CFRP and steel with different defect types, locations, depths, and sizes are tested by the developed imaging system, and the experimental results of the miniaturized system are compared with the existing table-top systems, which demonstrates comparatively accurate results for the developed multi-modality imaging system. The compact and practical nature of the presented imaging system makes it an optimal tool that can be utilized in field conditions with constrained operational spaces and NDE uncertainties.

A new technique for 3D printing dielectric structures using aerosol-jettable photopolymers

In this article, we report the development of a new method for the 3D printing of dielectrics. An aerosol-jet printer is used to deposit overlapping layers of photopolymer material under ultraviolet floodlight in the assembly of ramping microstructures in situ without the need for supporting structures. Printing is conducted using an in-house photodielectric ink, the development of which is presented with an emphasis on dielectric and mechanical bulk material characterization. Low dielectric loss at the X-band and structural strength are demonstrated, followed by print characterization wherein the driving mechanisms of the new method are explored, tied to print conditions, and related to specific material properties. Finally, a complex structure in the form of a 3D flower is printed to demonstrate the controlled and repeatable performance of the proposed technique.

A Study on the Estimation of RIC (Radiation-Induced Conductivity) of Proton Irradiated Polyimide

The recent expansion of the application environment of power electronics to high-radiation environments will cause the deterioration of insulation materials used in power electronics due to charging caused by cosmic ray irradiation. The charging phenomena should induce malfunctions in power electronics. Therefore, it is important to understand the insulation characteristics of insulation materials irradiated with protons, electrons, etc., to improve the reliability of power electronics. With respect to the above, there are few reports on the RIC (radiation-induced conductivity) of insulation materials irradiated with proton beams. In this paper, we experimentally evaluated the RIC of PI (polyimide) films irradiated with proton beams under various irradiation conditions. We also studied a calculation method to estimate the measured RIC of the PI. As a result, we clarified that the total conductivity of the PI increased under non-penetrating irradiation conditions and saturated under penetrating irradiation conditions. The reason for this is that the higher the irradiation energy, the deeper the maximum proton penetration depth under non-penetrating irradiation conditions. On the other hand, the conductivity characteristics did not change under penetrating conditions because the penetration depth was the same as the sample thickness. We also developed a calculation method to estimate the conductivity of the entire PI irradiated with proton beams. The estimated data calculated by the above method were analytically fitted with the measured data for most irradiation energy conditions. It is suggested that the above calculation method can estimate the conductivity of the entire PI irradiated with proton beams, regardless of penetrating or non-penetrating irradiation, based on the relationship between the RIC and dose rate of the PI irradiated under penetrating conditions. In the future, we will incorporate the results of this study into a computational model of space charge accumulation inside insulation materials to verify the influence of the RIC caused by proton irradiation on space charge accumulation.

Design and Test of a New Dielectric-Loaded Resonator for the Accurate Characterization of Conductive and Dielectric Materials.

The spread of additive manufacturing techniques in the prototyping and realization of high-frequency applications renewed the interest in the characterization of the electromagnetic properties of both dielectric and conductive materials, as well as the design of new versatile measurement techniques. In this framework, a new configuration of a dielectric-loaded resonator is presented. Its optimization, realization, and use are presented. A measurement repeatability of about one order of magnitude lower than the commonly found values (10-3 on the Q-factor and 15×10-6 on the resonance frequency, given in terms of the relative standard deviations of repeated measurements) was reached thanks to the design of a closed resonator in which the samples can be loaded without disassembling the whole measurement fixture. The uncertainty levels, the ease of use, and the versatility of the realized system make its use of potential interest in numerous scenarios.

A Dual-Scale CSRRs-Based Sensor for Dielectric Characterization of Solid Materials

A compact planar sensor is presented in this letter, which could measure the dielectric constants of solid materials at microwave and sub-THz frequencies, simultaneously. The lower band resonator is based on a complementary split ring resonator (CSRR), fed by a coplanar waveguide line on the board operating at 4.76 GHz, and the upper band sensor is a 3 × 3 CSRR array, excited by a pair of WR-10 open-ended waveguide probes operating at 112 GHz. The upper band CSRR array is nested in the lower band CSRR resonator, but their sensing functions are independent of each other. A coincident sensing area is obtained that needs a testing sample with small volume. Dielectric films composed of polydimethylsiloxane and barium-titanate with different volume fractions are used to verify the performance of the sensor in both frequency scales. The advantages of the proposed design, including compact size, high sensitivity, low sample volume, and dual-scale operation, make it a competitive solution for detecting solid materials with similar dielectric properties in a single frequency band, for application such as the food industry, material quality control, and biomedical.

Correction to: Theoretical analysis for effects of nanoparticles on dielectric characterization of electrical industrial materials

Correction to: Theoretical analysis for effects of nanoparticles on dielectric characterization of electrical industrial materials

Optimization and demonstration of two types of spring-roll dielectric elastomer actuators for minimally invasive surgery.

Resulting from the restricted size of incisions and confined surgical space, the existing rigid and slender minimally invasive surgery (MIS) instruments are inefficient in providing an optimum articulation to handle certain minimally invasive surgery tasks. Thus, developments of novel articulating actuators are of urgent requirement. In this paper, with the aim to enhance the flexibility and maneuverability of surgical instruments in diverse minimally invasive surgery scenarios, two types of spring-roll dielectric elastomer (DE) actuators, namely linear-type and bending-type, are proposed. The actuators’ parameters were optimized and calibrated using a novel step-by-step procedure, based on the characterization and modeling of dielectric elastomer material (VHB 4905). Critical design factors including dimensions of the core spring, the pre-stretch ratio of the dielectric elastomer, and the excitation level of the actuator were identified, while the boundary conditions for the modeling of the actuator were derived from the requirements of minimally invasive surgery applications. The dielectric elastomer actuators’ deformation behavior and force response were analyzed both theoretically and experimentally, and the results from the two approaches were in good agreement. The linear-type actuator could achieve a maximum strain of 29% and a blocking force up to 5.05 N, while the bending-type actuator could achieve angulation over 70° and a blocking force of up to 0.22 N. The proposed actuators are lightweight, compact, and cost-effective, which could provide novel design inspiration for minimally invasive surgery instruments.

Dielectric and electrical properties of nematic liquid crystals 6CB doped with iron oxide nanoparticles. The combined effect of nanodopant concentration and cell thickness

Dispersing nanomaterials in liquid crystals has emerged as a very promising non-synthetic way to produce advanced multifunctional and tunable materials. As a rule, dielectric and electrical characterization of such materials is performed using cells of single thickness. As a result, the published reports vary even for similar systems. Confusion still exists as to the effects of nanodopants and cell thickness on the dielectric and electrical properties of liquid crystals. This factor hinders a widespread use of liquid crystals - nanoparticles systems in modern tech products. In this paper, we report systematic experimental studies of the combined effect of the cell thickness and iron oxide nanoparticle concentration on the electrical and dielectric properties of nematic liquid crystals 6CB. The measured dielectric spectra can be divided into three distinct regions corresponding to a low frequency (<10 Hz) dispersion, dispersion free range (102 – 104 Hz (electrical conductivity) and 102 – 105 (dielectric permittivity)), and high frequency dispersion (104 – 106 Hz (electrical conductivity) and 105-106 Hz (dielectric permittivity)). The real part of the dielectric permittivity is not affected by the cell thickness and its value can be tuned by changing the concentration of nanoparticles. At the same time, the electrical conductivity depends on both cell thickness and nanoparticle concentration. At intermediate frequencies (102 – 104 Hz) the electrical conductivity obeys the Jonscher power law and is dependent on the cell thickness because of ion-releasing and ion-capturing effects caused by nanoparticles and substrates of the cell. In addition, its value is affected by the electronic conductivity due to iron oxide nanoparticles and their nanoclusters. At higher frequencies (104 – 106 Hz) the electrical conductivity follows a super linear power law and is nearly independent of the cell thickness and nanoparticle concentration.