Variation Of Dielectric Research Articles

Impact of Aluminum Modification on the Dielectric Properties of Graphene Oxide Membrane: Different Al Source

The high dielectric constant and low dielectric loss of Graphene oxide (GO) membranes made them good dielectric separator membranes for developing high performance energy storage and transfer devices. Better understanding and be able to tailor the dielectric properties of the GO membrane is crucial for its dielectric applications. The interaction variation of Al3+ from different source with the functional group on the GO sheets could lead to different modification effects on the dielectric properties of GO membranes. Here, the Al3+-modification, where aluminum metal foil, chloride salt, and alumina serve as different Al3+ source, are applied to tailor the dielectric properties of GO membranes. The dielectric constant and dielectric loss of GO and Al3+ modified GO(AGO) in the frequency range from 0.01 Hz to 105 Hz is studied. The capacitance of a simple dielectric capacitor fabricated by sandwich the GO and AGO membrane in between carbon paper are evaluated to estimate the effect of dielectric separator membrane variation on the electrochemical performance of the capacitor. This study provides a facile and effective strategy to tailor the dielectric property of GO membrane and demonstrate the possibility of designing dielectric GO membrane with controllable dielectric performance.

Ethylcellulose-stabilized fat-tissue phantom for quality assurance in clinical hyperthermia

Background Phantoms accurately mimicking the electromagnetic and thermal properties of human tissues are essential for the development, characterization, and quality assurance (QA) of clinically used equipment for Hyperthermia Treatment (HT). Currently, a viable recipe for a fat equivalent phantom is not available, mainly due to challenges in the fabrication process and fast deterioration. Materials and methods We propose to employ a glycerol-in-oil emulsion stabilized with ethylcellulose to develop a fat-mimicking material. The dielectric, rheological, and thermal properties of the phantom have been assessed by state-of-the-art measurement techniques. The full-size phantom was then verified in compliance with QA guidelines for superficial HT, both numerically and experimentally, considering the properties variability. Results Dielectric and thermal properties were proven equivalent to fat tissue, with an acceptable variability, in the 8 MHz to 1 GHz range. The rheology measurements highlighted enhanced mechanical stability over a large temperature range. Both numerical and experimental evaluations proved the suitability of the phantom for QA procedures. The impact of the dielectric property variations on the temperature distribution has been numerically proven to be limited (around 5%), even if higher for capacitive devices (up to 20%). Conclusions The proposed fat-mimicking phantom is a good candidate for hyperthermia technology assessment processes, adequately representing both dielectric and thermal properties of the human fat tissue while maintaining structural stability even at elevated temperatures. However, further experimental investigations on capacitive heating devices are necessary to better assess the impact of the low electrical conductivity values on the thermal distribution.

Eco-Friendly Thermoplastic Alternatives to Epoxy Resin for Support Insulators

Epoxy/alumina composite materials are widely used in support insulators in air/SF6 switchgear. However, epoxy resin is difficult to be recycled or repro- cessed because of its cross-linked structure. With the worldwide promotion of net-zero strategy, it is necess- ary to investigate suitable replacement for the epoxy resin. For this purpose, this article investigates the applicability of several thermoplastic alternatives in support insulators and selects an optimal material for future research. The first study is the comparison of basic electrical and mechanical properties among several typical thermoplastics, in which the standardized material requirements for solid insulators were used as a reference. Subsequently, polycarbonate (PC), polyoxymethylene (POM), and polyamide 66 (PA66) were selected for the detailed evaluation on dielectric properties, i.e., electrical conductivity and broadband dielectric spectra (BDS). Electrical conductivity was measured in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 40\,\,^{\circ }\text{C}$ </tex-math></inline-formula> to 125 °C temperature range and 1 to 8 kV/mm electric field range. BDS were tested under the identical temperature range. Results on electrical conductivity indicate that the PC has the lowest value among three studied materials, which varies slightly with electric field. An Arrhenius study was carried out to understand the variation mechanism of the conduction process. For dielectric spectra, the results of PC show little temperature dependence, whereas the other material has significantly increased dielectric loss when operating under high temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt; 65~^{\circ }\text{C}$ </tex-math></inline-formula> ). The fitting results of the Havriliak–Negami (HN) model reveal the mechanism of dielectric spectra variation for the investigated thermoplastics. These results suggest that the PC has lower conductivity, lower dielectric loss, and less temperature and field dependence than the other thermoplastics, making it a potential, environmental-friendly replacement for epoxy resin in support insulators.

Random ferroelectric and dielectric phase distribution-induced device variation of negative capacitance field-effect transistors

Negative-capacitance field-effect transistors (NC-FETs) are significantly affected by their ferroelectric (FE)/dielectric (DE) phase configurations owing to the uncertainty of their crystalline phases. This study presents an analysis of random FE/DE grain distribution-induced variations from multiple perspectives using a seed random number generator in a technology computer-aided design (TCAD) simulation. The results obtained for the NC fully depleted silicon-on-insulator (NC-FDSOI) FETs indicate that device variations can be effectively reduced by increasing the probability of FE grains which improves the switching characteristics. Additionally, the FE distribution at the source presents a larger ON-state current (Ion), while the complete DE path from the source to the drain presents a larger OFF-state current (Ioff). The simulation results also demonstrate that reducing the lateral grain size reduces the device variations while improving the switching current ratio. Increasing the ferroelectric layer thickness of the NC-FDSOI FET can improve its switching performance; however, this also increases its variations. The random FE/DE distribution-induced variations can be reduced by adequately increasing the gate width through device scaling.

Coupling Dielectric Functionality with Magnetic Properties in Coordination Metal Complexes.

Significant research has been conducted on molecular ferroelectric materials, including pure organic and inorganic compounds; however, studies on ferroelectric materials based on coordination metal complexes are scarce. Ferroelectric materials based on coordination metal complexes have tunable structures and designs, with coexistence or synergy between the ferroelectric behavior and magnetic properties. Compared to inorganic compounds, few coordination metal complexes exhibit coupling between the magnetic and dielectric properties. Coordination metal complexes with strong coupling between the magnetic and dielectric properties exhibit dielectric permittivity variations under external magnetic fields. Therefore, they have attracted substantial interest for their potential use in magnetoelectric devices. In this review, we discuss recent advances in coordination metal complexes, that exhibit coupled magnetic functionalities and ferroelectricity or dielectric properties, including single-molecule magnets, electron delocalization systems, and external stimuli responsive compounds.

Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks.

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

Electrical and Magnetoelectric Properties of Particulate Composites and Laminated Trilayered Thick‐Film Composites

Hydraulic pressing and screen printing methods are used to create particulate magnetoelectric composites and laminated trilayered thick‐film composites. X‐ray diffraction studies reveal the presence of cubic spinel and tetragonal perovskite structures for individual powders of ferrite CuFe2O4 and ferroelectric‐phase PbZr0.58Ti0.42O3. The dielectric constant of particulate composites decreases with increasing frequency around 1 MHz and beyond that frequency, a saturation state is attained. However, for laminated films, the dielectric constant decreases up to 1 MHz and then increases. The maximum dielectric constant at low frequency for particulate CuFe2O4/PZT composites is around 72.2, whereas for laminated CuFe2O4/PZT/CuFe2O4 composites it is 4.97 and for PZT/CuFe2O4/PZT composites is 5.24. Loss tangent exhibits the same trend as dielectric constant with frequency, which is explained by space charge polarization and is consistent with Koop's phenomenological theory. The dielectric constant's variation with temperature describes the contribution of electric dipoles to polarization and both composites exhibit absorption peaks. The semiconducting nature of both particulate and laminated composites can be seen in the DC resistivity graph with frequency and as frequency increases, DC resistivity decreases for both composites, which is explained by the small polaron‐hopping phenomenon. The magnetoelectric coupling effect for particulate composites (44 mV Oe−1cm−1) is also found to be small when compared to laminated trilayered composites (CuFe2O4/PZT/CuFe2O4—105 mV Oe−1cm−1 and PZT/CuFe2O4/PZT—68 mV Oe−1cm−1).

Relative Dielectric Permittivity Variations during Compaction as a Mean of Compaction Quality Control: Case Study on Laterite Samples from Senegal

This study explores an alternative to the classical use of direct methods, as water content and dry density measurements, for compaction quality control. For this purpose, the dielectric properties of lateritic materials are determined by radar method and are compared with the permittivity determined from the Topp formula and from the CRIM model. This approach allowed to establish a relationship between the geotechnical properties determined during compaction such as dry density, water content or porosity with dielectric permittivity. The obtained results made it possible to determine an optimum dielectric permittivity corresponding to the optimum dry density and the optimum water content that could be used for non-destructive in situ compaction testing. Such an approach should improve the implementation and effectiveness of in situ compaction quality control of geotechnical infrastructures.

An Improved Hyperbolic Method and Its Application to Property Inversion in Martian Tianwen-1 GPR Data

On 15th May 2021, the Tianwen-1 (TW-1) successfully landed on the surface of Mars within the southern Utopia Planitia. It delivered a rover named Zhurong equipped with ground penetrating radar (GPR), a device that can investigate the thickness and structure of the geological layers below the martian surface. The hyperbola method is commonly used for extracting dielectric property variations with depth from GPR data to aid the interpretation of the subsurface structure and material composition. This study analyzes the advantages and drawbacks of three hyperbola methods with different geometric models. Next, it proposes a new method aiming to use the highly precise, yet complex geometric model and address issues caused by its solving process. We also analyze the influencing factors contributing to measurement errors and design corresponding criteria for measurement point selection to mitigate errors. The average error of the proposed method is less than 5% for a depth of up to 9 m. We employed the proposed method to obtain the dielectric constant distribution in the shallow surface layer of the TW-1 landing zone to a depth of up to 16 m. The dielectric constant is mainly concentrated between 2 and 8 m and increases gradually with depth. Below 2 m, the dielectric constant is about 5.1 and the density is about 2.5 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The stratification and density variation can be inferred from the dielectric constant distribution diagram.

Loss Tangent Estimation From GPR Data in Complex Medium Scenarios Using Amplitude and Power Spectrum Centroid Frequency Shift Methods

Electromagnetic losses estimation in complex scenarios lacking subsurface continuous reflectors is challenging. We present here a robust approach based on the centroid frequency shift method and Ricker wavelet as the input signal, to compute intrinsic (absorption) losses. The centroid-frequency shift is calculated using the amplitude and power spectrum of records, leading to equations that relate the centroid frequency variation in time to the loss tangent (intrinsic losses). First, the approaches are evaluated and compared by implementation to synthetic Ground Penetrating Radar (GPR) data generated with the gprMax simulator, starting from an inhomogeneous material with spatially smooth dielectric variations. Then, they are applied to real GPR data collected on a fractured basaltic lava flow. The retrieved loss tangent values are compared to the total attenuation estimated from the signal amplitude decay, to evaluate the contribution due to scattering phenomena. The proposed analysis is particularly suitable for GPR data collected in planetary environments, since dielectric losses could be used to constrain the oxide composition of the material as well as scattering losses to determine the amount and distribution of subsurface inhomogeneities.

A Soil Semi-Empirical Dielectric Model Based on the Dielectric Variation Characteristics of an Electrical Double-Layer Solution

The complex permittivity of bound water are uncertain factors in the modeling of soil permittivity. Based on the electrical double-layer theory, this study divides soil bound water into strongly and weakly bound components. These strongly and weakly bound water are assumed to be cation solutions in the adsorption and diffuse layers, respectively. Characteristic functions of the permittivity of weakly bound water were proposed to describe the variation in the complex permittivity of weakly bound water with changes in moisture, and a soil semi-empirical dielectric model (SEM) was established based on these characteristic functions. Through further fitting, this SEM only requires the soil temperature, moisture, clay content, and microwave frequency to obtain the soil complex permittivity. Measured data from 20 soils and four SEMs were used for model validation. The results show that this SEM can accurately calculate the complex permittivity of sand, silt, clay, and soils with low organic matter and low salinity in the range of 0 to 0.5 volume moisture content at 1.4–18 GHz. The characteristic functions link the electrical properties of clay with the complex permittivity of bound water. The two constituent formulas of the characteristic functions (the cation concentration and electric field strength) are almost independent of soil texture. Soil texture affects the soil complex permittivity by changing the contents of strongly and weakly bound water. This phenomenon suggests that the dielectric algorithm of bound water is minimally affected by soil texture. The dielectric algorithms of bound water utilized in existing SEMs are reasonable.

Nanoscale probing of local dielectric changes at the interface between solids and aqueous saline solutions.

The mobility of dissolved ions and charged molecules at interfaces underpins countless processes in science and technology. Experimentally, this is typically measured from the averaged response of the charges to an electrical potential. High-resolution Atomic Force Microscopy (AFM) can image single adsorbed ions and molecules at solid-liquid interfaces, but probing the associated dynamics remains highly challenging. One possible strategy is to investigate the response of the species of interest to a highly localized AC electric field in an approach analogous to dielectric spectroscopy. The dielectric force experienced by the AFM tip apex is modulated by the dielectric properties of the sample probed, itself sensitive to the mobilities of solvated charges and dipoles. Previous work successfully used this approach to quantify the dielectric constant of thin samples, but with limited spatial resolution. Here we propose a strategy to simultaneously map the nanoscale topography and local dielectric variations across a range of interfaces by conducting high-resolution AFM imaging concomitantly with electrical AC measurements in a multifrequency approach. The strategy is tested over a 500 MHz bandwidth in pure liquids with different dielectric constants and in saline aqueous solutions. In liquids with higher dielectric constants, the system behaves as inductive-resistive-capacitive but the adjunction of ions removes the inductive resonances and precludes measurements at higher frequencies. High-resolution imaging is demonstrated over single graphene oxide (GrO) flakes with simultaneous but decoupled dielectric measurements. The dielectric constant is consistent and reproducible across liquids, except at higher salt concentrations where frequency-dependent effects occur. The results suggest the strategy is suitable for nanometre-level mapping of the dielectric properties of solid-liquid interfaces, but more work is needed to fully understand the different physical effects underpinning the measurements.

Assessing concrete strength loss at elevated temperatures as a function of dielectric variation measured by GPR: an empirical study

ABSTRACT Reinforced concrete (RC) parts, which are exposed to high temperatures for a certain period, undergo physical-chemical changes that deteriorate their mechanical properties. To this end, this study investigates the efficiency of using ground-penetrating radar (GPR) as a non-destructive testing (NDT) method in assessing the core compressive strength loss, elastic modulus decrease, and tensile strength loss of concrete under extreme temperatures. RC specimens are fabricated and exposed to elevated temperatures (300°C, 400°C, 500°C, 600°C, and 700°C). GPR measurements are performed to estimate the relative dielectric permittivity (RDP) of the specimens before fire exposure (BFE) and after fire exposure (AFE). The compressive strengths of the cores extracted from the specimens are obtained also for BFE and AFE cases. Attained RDP values are in conformance with the previous research results and contribute additional evidence to the published literature. As the temperature levels are increased, RDP and strength-related values of concrete specimens decrease. The strength-related parameters are more sensitive to elevated temperatures, whereas the change in the RDP values is rather gradual. Through multiple correlations within 95% confidence intervals, core compressive strength loss, elastic modulus decrease, and tensile strength loss are, individually, estimated as a function of relative RDP change and applied temperature levels. Empirical formulas are obtained with high coefficients of correlation. The relative effects of RDP change and temperature are more pronounced in elastic modulus decrease and tensile strength loss compared to compressive strength loss. Overall, the outcomes of this paper confirm the viability of using the GPR technique for concrete dielectric characterisation in estimating the strength-related properties of concrete exposed to high temperatures, which might reduce the need for destructive testing.

Timing-Aware Fill Insertions With Design-Rule and Density Constraints

Metal fill insertion has become an essential step in reducing dielectric thickness variation and improving pattern uniformity, which is important in mitigating process variations, thereby achieving better manufacturing yield. However, metal fills could induce coupling capacitance, which is not often considered in existing works that typically focus more on pattern density uniformity, incurring significant problems in timing closure. However, it is a great challenge to consider three types of capacitances (i.e., area, fringe, and lateral capacitances) with design rules and density constraints at the fill insertion stage simultaneously. This article presents an efficient timing-aware fill insertion algorithm for minimizing the total capacitance and fill amount, considering the density constraints. First, we present an initial metal fill insertion and design-rule-aware legalization to obtain an initial fill insertion solution quickly. Second, from critical conductors to powers/grounds in a circuit, we divide conductors into different equivalent paths and then construct a capacitance graph to reduce the capacitance of each equivalent path globally. Third, we propose a density-aware coupling capacitance optimization method and a fast Monte Carlo-based fill selection to further reduce the coupling capacitance between any pair of conductors. Finally, we present a density-aware fill deletion method to reduce the fill amount. We evaluate the performance of our algorithm on the benchmarks of the 2018 CAD Contest at ICCAD and its official contest evaluator. Compared with the first-place team of the contest and the state-of-the-artwork, experimental results show that our algorithm achieves the lowest total capacitance and the least fill amount in a comparable runtime.

A Two-Dimensional Model for the Field-Plate Design of High-Voltage Transistor

The field plate (FP) is a widely adopted concept and has been commonly used for high-voltage (HV) transistors to increase the breakdown voltage without enlarging the device dimension. In this article, a 2-D mathematical equation is derived for the FP design of HV transistors which reveals the potential and the electric field distributions in the reduced-surface field (RESURF) region. From the derived mathematical model, the mechanism of the FP-induced electric field suppression for the HV transistors is completely explained as the FP can reduce the potential gradient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E} = -\nabla \varphi $ </tex-math></inline-formula> ) caused by the dielectric thickness differences above the RESURF region. The potential and the electric field distributions of the RESURF region will change as the FP is inserted due to the dielectric thickness variations. The derived equations also explained the capacitive behaviors and quantitatively described the potential and electric field distributions in different configurations of the FP-assisted RESURF devices. The results obtained by the derived equation are found to be very much accurate compared with technology computer-aided design (TCAD) simulation results.

Giant Near-Room-Temperature Pyroelectric Figures-of-Merit Originating from Unusual Dielectric Bistability of Two-Dimensional Perovskite Ferroelectric Crystals

Pyroelectric materials with the capability of converting temperature changes into electrical signals have been widely used as essential elements for assembling integrated smart electronic detectors. Regarding the conversion efficiency of the voltage output, however, it is significant but quite challenging to exploit new candidates with large pyroelectricity figures-of-merit (FOMs) at room temperature. Herein, we have acquired giant near-room-temperature pyroelectric FOMs in the two-dimensional (2D) perovskite-type improper ferroelectric crystals of (BA)2(EA)2Pb3I10 (1, where BA = n-butylammonium and EA = ethylammonium), for which the room-temperature voltage FOM (Fv = 1.06 × 10–2 cm2/μC) is about 10 times as large as that of the state-of-the-art inorganic oxides (often ∼0.1 × 10–2 cm2/μC), while the peak values near the Tc are almost 2–3 orders of magnitude higher than those of the typical oxide counterparts. Such ultrahigh FOMs are mainly due to their large pyroelectric coefficients and unusual bistability of dielectric behavior, that is, an extremely small-amplitude dielectric variation caused by dipole reorientations during the ferroelectric-to-antiferroelectric phase transition at ∼315 K. This achievement of ultrahigh pyroelectric FOMs in improper ferroelectrics is in sharp contrast to the proper counterparts. Moreover, the low-cost and facile integration of crystal-based devices favors their great potential as smart pyroelectric detectors. As far as we know, the findings of giant pyroelectricity FOMs are unprecedented in 2D hybrid perovskites, which probably recall their broader prospects toward high-performance electronic device application.

Single-slice microwave imaging of breast cancer by reverse time migration.

Microwave imaging of breast cancer is considered and a new microwave imaging prototype including the imaging algorithm, the antenna array, and the measurement configuration is presented. The prototype aims to project the geometrical features of the anomalies inside the breast to a single-slice image at the coronal plane depending on the complex dielectric permittivity variation among the tissues to aid the diagnosis. The imaging prototype uses a solid cylindrical dielectric platform, where a total of 24 optimized Vivaldi antennas are embedded inside to form a uniform circular antenna array. The center of the platform is carved to create a hollow part for placement of the breast and the multistatic, microwave scattering parameters are collected with the antenna array around the hollow center. The dielectric platform further enhances the microwave impedance matching against the breast fat tissue and preserves the vertical polarization during the measurements. In the imaging phase, a computationally efficient inverse electromagnetic scattering method-reverse time migration (RTM)-is considered and adapted in terms of scattering parameters to comply with the actualmeasurements. The prototype system is experimentally tested against tissue-mimicking breast phantoms with realistic dielectric permittivity profiles. The reconstructed single-slice images accurately determined the locations and the geometrical extents of the tumor phantoms. These experiments not only verified the microwave imaging prototype but also provided the first experimental results of the imagingalgorithm. The presented prototype system implementing the RTM method is capable of reconstructing single-slice, nonanatomical images, where the hotspots correspond to the geometrical projections of the anomalies inside the breast.

Broad-temperature-span and improved piezoelectric/dielectric properties in potassium sodium niobate-based ceramics through diffusion phase transition

Continuous progress of piezoelectric coefficient (d33) and dielectric constant (εr) are obtained in (K, Na)NbO3 (KNN)-based lead-free piezoceramics by phase boundary formation, while usually accompanying by the poor temperature/thermal stability, which are not conductive to actual applications. In this work, the perovskite-type compound Bi(Ni2/3Nb1/3)O3 is designed and added into KNN ceramic. This additive can not only shift orthogonal-tetragonal (O-T) phase transition towards room temperature to enhance d33, but also make the O-T phase transition becoming diffusion in a broad temperature range. Furthermore, the piezoelectricity is further elevated by optimizing polarization via Ce3+ doping. Finally, the enhanced d33 is achieved with the excellent thermal stability from room temperature to> 350 °C. Besides, the high εr of ~ 1150 and low dielectric variation of ≤ ± 15 % can be obtained in a quite broad temperature span from room temperature to ~ 300 °C. These overall performances of this work show the potential multifunctional applications in high-temperature piezoelectric and dielectric devices.

Selective gas detection of titania nanoparticles via impedance spectroscopy and capacitive measurement

The present paper demonstrated the impedance analysis of Au/TiO2 nanoparticles/Si–Al capacitive sensor for selective detection of volatile organic compounds (VOCs) at different frequency regimes. TiO2 nanoparticles (NP) were synthesized through the solution process and characterized by field-emission scanning electron microscopy , x-ray diffraction analysis, photoluminescence spectroscopy, and atomic force microscopy. The gas sensitivity of Au/TiO2 -NP/Si–Al was investigated, with the effect of temperature modulation (25 °C–250 °C) and dielectric variation in the vicinity of nanoparticles. Impedance spectroscopy of TiO2 -NP was carried out to obtain resonant peaks over the frequency ranging from 0.05 to 225 kHz and fitted with a complex nonlinear least-squares method. The optimum sensor response of 136%, 63%, 152%, and 174% was found at resonant frequencies of 0.38 kHz, 0.22 kHz, 0.15 kHz, and 0.1 kHz for the exposure of 2-propanol, acetone, ethanol, and methanol, respectively. The fastest response time and recovery time were found to be 32/21 s, 31.2/8 s, 32.5/9 s, and 40/26 s for acetone, 2-propanol, ethanol, and methanol, respectively. Selective detection of different VOCs at various resonant frequencies has correlated with the dielectric variation of the NPs and their associated void region under gas exposure.

A frequency-independent inhomogeneous planar radome with high angular stability based on permittivity manipulating

In this paper, an inhomogeneous planar radome (IPR) has been thoroughly investigated from an electromagnetic perspective. The inhomogeneity is considered to be an exponential function. Closed-form expressions have been derived for the transmission and reflection coefficients. A radome with frequency-independent response and angular stability up to 53° is achieved by manipulating the dielectric Permittivity Profile Variation (PPV) function with definite curvature. Implementation has been done with the use of the equivalent material theory (EMT). The optimal radome wall is prototyped by perforating the host medium continuously (which eliminates losses due to the discretization). An ultra-wide-band (3–18 GHz) free space measurement setup is used to characterize the frequency response of this prototype. Measurements are performed for both polarizations of TE and TM and various angles of the incidence. The results are in good agreement with the unit-cell full-wave simulations. The design procedure is generally described, which can be implemented for various electromagnetic and mechanical requirements.