Surface Permittivity Research Articles

Flexible, wearable triboelectric rubber with tunable surface charge density enabled by regulation of surface functional group density and permittivity

Flexible wearable triboelectric nanogenerator (TENG) has attracted immense interest in various application scenarios due to its intrinsic self-powered characteristics. Recently, rubbers with high elasticity are frequently reported to be favored substrates for wearable smart devices to enhance body comfort and contact effects. However, most commercial rubbers are nonpolar and lack of enough polar functional groups even after physical and chemical modification to earn satisfactory surface charge density for high triboelectric performance. Moreover, the combination of high triboelectric and mechanical properties is still a significant challenge for flexible TENG material. In this work, a flexible triboelectric rubber with tunable surface charge density and excellent mechanical properties is demonstrated via a natural polymer assisted dispersion of perovskite nanofiller strategy. The designed rubber-based TENG shows an excellent 310 V triboelectric output, 106 nC transferred charge and 6.14 W·m−2 power density, as well as a favorable mechanical property of 10.69 MPa Young’s modulus and 211 % strain. The material can harvest mechanical energy and charge 1 μF commercial capacitors to 1.8 V in 60 s from nature. When serves as flexible device, it can also self-powered to real-time monition various human behavior and distinguish different speed of vehicle driving conditions. We expect our works will provide a feasible strategy to significantly improve the comprehensive performance of flexible wearable rubber-based TENG and advance the potential application of rubber.

Surface Permittivity Estimation of Southern Utopia Planitia by High-Frequency RoPeR in Tianwen-1 Mars Exploration

Surface Permittivity Estimation of Southern Utopia Planitia by High-Frequency RoPeR in Tianwen-1 Mars Exploration

Wi-Painter

WiFi has gradually developed into one of the main candidate technologies for indoor environment sensing. In this paper, we are interested in using COTS WiFi devices to identify material details, including location, material type, and shape, of stationary objects in the surrounding environment, which may open up new opportunities for many applications. Specifically, we present Wi-Painter, a model-driven system that can accurately detects smooth-surfaced material types and their edges using COTS WiFi devices without modification. Different from previous arts for material identification, Wi-Painter subdivides the target into individual 2D pixels, and simultaneously forms a 2D image based on identifying the material type of each pixel. The key idea of Wi-Painter is to exploit the complex permittivity of the object surface which can be estimated by the different reflectivity of signals with different polarization directions. In particular, we construct the multi-incident angle model to characterize the material, using only the power ratios of the vertically and horizontally polarized signals measured at several different incident angles, which avoids the use of inaccurate WiFi signal phases. We implement and evaluate Wi-Painter in the real world, showing an average classification accuracy of 93.4% for different material types including metal, wood, rubber and plastic of different sizes and thicknesses, and across different environments. In addition, Wi-Painter can accurately detect the material type and edge of the word "LOVE" spliced with different materials, with an average size of 60cm × 80cm, and material edges with different orientations.

SHARAD observations for layered ejecta deposits formed by late-Amazonian-aged impact craters at low latitudes of Mars

Frequent changes of the rotational inclination of Mars have driven global transitions of the cryosphere. Although glaciers of water ice may have extended to the equatorial region, current observations of surface deposits at latitudes lower than 30° show relative depletion in hydrogen. Thermal stability models predict that at these low latitudes, ancient water ice may be preserved below a desiccated regolith layer that is meters to hundreds of meters thick. However, confirmed detections of massive water ice and/or water ice remain sparse at low latitudes. Here we use sounding radar observations of late-Amazonian-aged impact craters with layered ejecta deposits at low latitudes to search for subsurface layering and interface properties to investigate the possible existence of subsurface water/water ice. Such craters are widespread at low latitudes, including the landing area of the Zhurong rover, Tianwen-1 mission. The layered ejecta deposits of selected craters have lateral sizes and thickness suitable for investigation by sounding radar. Compared to previously-reported, but rare, cases that contained obvious reflectors between the layered ejecta deposits and underlying materials, we detect no clear reflections in neither the layered ejecta deposits nor deeper materials, suggesting that these materials have similar dielectric properties across their interfaces. Referring to the surface permittivity of background terrains of the investigated craters, we derive a broad range of relative permittivity of ∼2–10 for materials in the layered ejecta deposits. We discuss the implications of these results in the context of past and present water ice at low latitudes of Mars.

Effect of dielectric target properties on plasma surface ionization wave propagation

Surface ionization waves (SIWs) propagating along dielectric covered, grounded surfaces have been studied for various dielectric bulk and surface conditions; a dependence on the propagation velocity with respect to dielectric electrical thickness and near surface permittivity profiles are observed. SIWs generated by an atmospheric pressure plasma source are imaged interacting with planar dielectric surface. Surface wave velocity is obtained by tracking emission intensity as a function of time. Target dielectric thickness is varied from mm and dielectric constant is varied from . The propagation of SIWs can be generally predicted by relating their velocity to the RC time constant of the circuit generated between the plasma and the dielectric surface, but it is found that this approximation breaks down for dielectric substrates of sufficient thickness and wave velocity becomes constant. The results show that wave velocity is stable and predictable for target thicknesses beyond a certain point determined by the permittivity of the target material. It is also shown that SIW propagation is strongly driven by the dielectric material near to the surface of the target in addition to the bulk material. The possible mechanisms driving these thickness dependent behaviors is discussed.

Nano optical temperature sensor based on fiber Bragg grating using graphene

In this paper, a novel Graphene-Assisted Microfiber based temperature sensor is proposed that changing the surrounding temperature has a severe effect on the refractive index of the graphene, so these changes result in the transmission power of microfiber. In the proposed structure, the position of the graphene sheet affects the interaction of light and graphene, effectively. Simply, by examining the change in transmission power, the temperature sensitivity of 0.1038 dBC in the heating process and 0.1072 dBC in the high-resolution cooling process of 0.0098 ℃ is obtained, which is 16 times more than bare fiber. Moreover, in this paper, both MgF2 layer and the graphene ribbon affect fiber refractive index so a high sensitivity, compact size, low cost, linear operation and suitable transmission coefficient temperature sensor is achieved. This sensor has great potential in the field of measurement, especially surrounding temperature measurement. Also, a comprehensive and detailed study of the properties of surface conductivity, electric dispersion, refractive index and permittivity for graphene with sensitivity simulation is accomplished.

Retrieving Freeze/Thaw Surface State From CYGNSS Measurements

Freeze/Thaw (F/T) surface state retrieval is important to further understand hydrological patterns and climate change. This article investigates the use of Earth-reflected Global Positioning System (GPS) L-band signals as collected by the National Aeronautics and Space Administration NASA’s Cyclone Global Navigation Satellite System (CYGNSS) mission for F/T surface state retrieval over a target area in South America, covering the Andes Mountains and the Argentinian Pampas. In the study, CYGNSS responsiveness to changes in surface permittivity is leveraged to detect transitions of F/T surface state, at an improved spatio-temporal sampling as compared to traditional Remote Sensing missions. A Seasonal-Threshold Algorithm (STA) is developed and validated using surface temperature data as provided by the European Centre for Medium-Range Weather Forecast (ECMWF) ERA5-Land numerical reanalysis model. Then, the monthly evolution of CYGNSS-derived F/T surface state maps is evaluated and an inter-comparison with the Soil Moisture Active Passive (SMAP) F/T data product is performed.

Effect of Radar Incident Angle on Full-Wave Inversion for the Retrieval of Medium Surface Permittivity for Drone-Borne Applications

Drone-borne ground-penetrating radar (GPR) has proven to be efficient and promising for high-resolution topsoil moisture mapping at the field scale. However, in practice, the radar incident angle may change as a function of the terrain slope and unstable flying conditions. In this respect, we analyzed the effect of radar incident angle on full-wave inversion for soil permittivity characterization. Specifically, using the frequency-domain radar equation, antenna characteristic functions with different incident angles were determined for a horn antenna as an example. Then, numerical analyses and field measurements were performed to quantify the errors on the retrieved permittivity resulting from incident angle drifts. In agreement with the radar equation concept, we observed that the angle- and frequency-dependent global transmission functions of the antenna correspond well to its radiation pattern. Numerical and field results show that errors in the permittivity estimation can be very significant as a function of the antenna radiation pattern and the incident angle. Nevertheless, if the incident angle is known and the characteristic antenna functions are determined as a function of the incident angle, full-wave modeling and inversion remain accurate, provided that the signal-to-noise ratio remains sufficient.

Solketal as a renewable fuel component in ternary blends with biodiesel and diesel fuel or HVO and the impact on physical and chemical properties

The need for new bio based drop-in components for combustion engine fuels and the availability of sustainable glycerol from biodiesel production has focused attention on isopropylidene glycerol (solketal). The present study investigates the physical and chemical behavior of solketal in ternary blends with diesel fuel/biodiesel. Hydrotreated vegetable oil (HVO) was used as renewable non-polar aliphatic diesel fuel substitute in biodiesel/solketal blends. HVO can be considered a prototype for other non-polar fuel components such as paraffinic fuel streams from Fischer-Tropsch or BtL processes. Surface tension, permittivity and aging behavior were analyzed. Furthermore, the cetane number (CN) and the viscosity was determined. Permittivity reflects the polarity of blends and their components with its change being an indicator of loss of physical and chemical stability. The antioxidant triphenyl phosphorothioate (TPPT) was also tested in some blends. The biodiesel blends B20, B30 and B40 enables single phased diesel fuel or HVO with varied solketal content (2 and 10%) at a constant biodiesel amount. No effect of solketal on fuel aging was observed. However, HVO-containing blends tend to lower the thermo-chemical stability relative to diesel fuel.

High-absorption grating-insulator-metal structures.

A thin grating-insulator-metal (GIM) structure consisting of a top metal grating layer on a dielectric layer and a bottom metal layer is proposed, which shows a broadband high absorption at a small thickness. This phenomenon is attributed to the appropriate effective surface permittivity of the top grating layer and the cavity resonance of the middle insulator layer. By optimizing the structural and material parameters, the materials of the GIM structure from top to bottom are Mn, Al2O3, and Mn with thicknesses of 10, 70, and 70 nm, respectively. The structure with these optimum parameters is fabricated and characterized, and an improved performance with absorption exceeding 90% in the visible region is obtained using Mn as the metal layers. The experimental results are in good agreement with the numerical values, depicting an ultrabroad absorption bandwidth. The conclusions presented here could have potential applications in optical devices used for optical displacement detection and visible light absorption.

Properties of Lunar Regolith on the Moon's Farside Unveiled by Chang'E‐4 Lunar Penetrating Radar

AbstractThe complex thermal history of the Moon leads to an unequal distribution of volcanic products between the lunar nearside and the farside. So far, no lunar materials have been sampled from the Moon's farside and no detailed properties of lunar regolith on the farside have been detected before. On January 3, 2019, Chang'E‐4 (CE‐4) touched down onto the Von Kármán crater on the Moon's farside. CE‐4 Lunar Penetrating Radar (LPR) onboard the Yutu‐2 rover is the first surface radar on the Moon's farside. Here we show the subsurface structure and properties of regolith materials at the landing region with LPR data during the first five lunar days. The thickness of lunar regolith is constrained as ∼12 m, much thicker than that at Chang'E‐3 (CE‐3) landing site, which is expected since CE‐3 landed on lunar maria. The relative permittivity of lunar surface (<30 cm) at CE‐4 landing region is identified to be 2.35 0.20. The loss tangent and TiO2 + FeO content of the regolith materials layer (0–∼12 m) are constrained to be and wt.%, respectively, much lower than those at CE‐3 landing site. It indicates that local surface materials possess less attenuation for radiowave, in accordance with the greater penetrating depth of CE‐4 LPR than that of CE‐3 LPR. Furthermore, the results also prove that the growth rate of lunar weathered regolith successively declines over time and the growth rate of lunar regolith on the Moon's farside may well be higher than that on the nearside due to the more frequent meteorite impacts.

Radar Backscattering Over Sea Surface Oil Emulsions: Simulation and Observation

Oils floating on the sea surface can be observed as “dark” patches on radar images since the backscattered signals from the contaminated area are reduced in two dominant ways. First, oil slicks could damp short gravity and capillary waves on the sea surface responsible for backscattering energy. Second, the oil-covered sea surface permittivity decreases significantly if the oil film is sufficiently thick or mixed with seawater, i.e., oil emulsion. In this article, the geometry of the oil-covered sea surface is accounted for by the damping of sea waves, which is described by the model of local balance (MLB) combined with the sea wave spectrum. The radar backscattering is predicted by the advanced integral equation method (AIEM) model. The reflection coefficients are calculated based on a layered-medium model to analyze the impact of oil thickness and emulsions on the radar scattering. Numerical simulations demonstrate that: 1) the sensitivity to oil thickness and water content of the oil spills increases when the radar frequency increases; 2) the backscattering signals exhibit a nonlinear behavior with respect to oil thickness; and 3) high wind speed can generally narrow the difference between the radar backscattering from the clean and oil-covered sea surface, while the incidence angle has little effect. Numerical simulations are then compared with the multifrequency synthetic aperture radar observations acquired during the Gulf of Mexico Deepwater Horizon (DWH) oil spill accident and the 2011 Norwegian Clean Seas Association for Operating Companies (NOFO) oil-on-water exercise. Comparison results show that it is possible to estimate the oil thickness at reasonably good accuracy.

Lunar Surface and Buried Rock Abundance Retrieved from Chang’E-2 Microwave and Diviner Data

Abstract Microwave emission of the Moon, measured by the Chang’E-2 Microwave Radiometer (MRM), provides an effective way to understand the physical properties of lunar near-surface materials. The observed microwave brightness temperature is affected by near-surface temperatures, which are controlled by the surface albedo, roughness, regolith thermophysical properties, and the high thermal inertia and permittivity of both surface and buried rocks. In this study, we propose a rock model using thermal infrared measurements from the Lunar Reconnaissance Orbiter's (LRO) Diviner as surface temperature constraints. We then retrieve the volumetric rock abundance (RA) from nighttime MRM data at several rocky areas. Although our retrieved MRM RA cannot be compared to the rock concentration measured with LRO Camera images directly, there is a good agreement with Diviner-derived RA and radar observations. The extent of several geological units, including rocky craters, hummocky regions, and impact melts, agree well with the distribution of elevated rock concentration. Based on seven large craters with published model ages, we present an inverse correlation between rock concentration and crater age. The result shows that the rock concentration decreases with crater age rapidly within 1 Ga but declines slowly after that. These data are consistent with a short survival time for exposed rocks and a long lifetime for buried rocks that are shielded from lunar surface processes.

Design of a terahertz metamaterial sensor based on split ring resonator nested square ring resonator

A terahertz (THz) sensor based on the metamaterial structure, split ring resonator with four-gaps relied on centrosymmetric nested square ring resonator, is presented. The two resonant elements of the metamaterial structure generate a corresponding resonant valley on the transmission spectrum curve in the frequency range from 0.1 to 1.9 THz respectively, and both of these resonant valleys show different redshifts when the surface permittivity of the structure changes. This feature is very suitable for THz sensing, especially the quantum interference effect between the two resonant elements, which results in the formation of an electromagnetically induced transparency (EIT)-like resonance peak on the transmission spectrum curve. The sensing performances are simulated by using commercialized full-wave electromagnetic simulation software. The results demonstrated that the proposed sensor is polarization-insensitive and has a highly boosted sensitivity, which has a promising application prospect in the fields of biomedical science and drug industry.

The effect of relative permittivity of surface supporting materials for high-speed rechargeable LiCoO2 cathode film

We previously reported that the BaTiO3(BTO)-LiCoO2(LCO)-electrolyte triple-phase interface (TPI) could play an important role in C-rate enhancement, however, why this supporting material is effective for high performance remains unknown. We focus on the relative permittivity of supporting materials using finite element method calculations and experiments. Calculations revealed that the electric field near the TPI was reinforced as the relative permittivity of supporting materials increased. Experimentally, we prepared nanodots and micropads deposited on LCO thin film using BTO and CeO2 as supporting materials to evaluate electrochemical properties and SEI formation mechanisms, respectively. High C-rate performance was improved by the introduction of CeO2 and BTO nanodots; however, only the BTO nanodots deposited on LCO could work at 100C. In addition, SEI around the TPI was quite thin around CeO2 and BTO pads, although 10 and 300 nm SEI were observed at the non-pad area of CeO2 and BTO, respectively. This indicated that the Li+ motion between electrolyte and electrode could be accelerated depending on the relative permittivity of supporting materials. The low SEI around the TPI of both the CeO2 and BTO pads suggested that the main reactions of Li+ insertion/de-insertion into/from LCO might be dominant around the TPI area.

Potential of multispectral reflectance for assessment of snow geophysical parameters in Solang valley in the lower Indian Himalayas

ABSTRACTSnow geophysical parameters such as wetness, density and permittivity are a significant input in hydrological models and water resource management. In this paper, we utilize the triangle method based on a feature space developed with the near-infrared (NIR) reflectance and the Normalized Differenced Snow Index (NDSI) for the estimation of surface snow wetness, permittivity and density. The triangular feature space based on NIR reflectance and NDSI is parameterized to yield a linear relationship between the snow wetness and the NIR reflectance. Snow density and permittivity are derived based on the least squares solution of empirical relations based on the observations of surface snow wetness. The proposed methodology was evaluated using Sentinel-2 data, and the modeled snow geophysical parameters were validated with respect to field measurements. Based on the results, it was inferred that the NIR reflectance varies linearly with the liquid water content in the snow. A good agreement was determined between the modeled and measured parameters for wet snow conditions as observed by the coefficient of determination of 0.968, 0.521 and 0.969 for the snow wetness, density and permittivity (real part), respectively. The proposed approach can be significantly utilized with unmanned aerial sensors for monitoring of physical properties of fresh or wet snow and is thus expected to contribute considerably in hydrological applications and avalanche studies.

Geometric quantization of localized surface plasmons

Abstract We consider the quasi-static problem governing the localized surface plasmon modes and permittivity eigenvalues $\epsilon $ of smooth, arbitrarily shaped, axisymmetric inclusions. We develop an asymptotic theory for the dense part of the spectrum, i.e. close to the accumulation value $\epsilon =-1$ at which a flat interface supports surface plasmons; in this regime, the field oscillates rapidly along the surface and decays exponentially away from it on a comparable scale. With $\tau =-(\epsilon +1)$ as the small parameter, we develop a surface-ray description of the eigenfunctions in a narrow boundary layer about the interface; the fast phase variation, as well as the slowly varying amplitude and geometric phase, along the rays are determined as functions of the local geometry. We focus on modes varying at most moderately in the azimuthal direction, in which case the surface rays are meridian arcs that focus at the two poles. Asymptotically matching the diverging ray solutions with expansions valid in inner regions in the vicinities of the poles yields the quantization rule \begin{equation*}\frac{1}{\tau} \sim \frac{\pi n }{\varTheta}+\frac{1}{2}\left(\frac{\pi}{\varTheta}-1\right)+o(1),\end{equation*}where $n\gg 1$ is an integer and $\varTheta $ a geometric parameter given by the product of the inclusion length and the reciprocal average of its cross-sectional radius along its symmetry axis. For a sphere, $\varTheta =\pi $, whereby the formula returns the exact eigenvalues $\epsilon =-1-1/n$. We also demonstrate good agreement with exact solutions in the case of prolate spheroids.

Permittivity measurement of cementitious materials and constituents with an open-ended coaxial probe: combination of experimental data, numerical modelling and a capacitive model

The study presents the development of a new two-dimensional FEM numerical model describing the operation of two large open-ended coaxial probes designed to investigate the permittivity of concrete, and its constituents. This numerical simulation, combined with a capacitive approach describing the behaviour of the probes, enabled to prove the suitability of such device to determine the permittivity of dispersive dielectrics. Finding back the permittivity of a specified material by calculation of the S parameters, change of the reference plane and use of the capacitive model is the key to the proof. Measurements performed onto different materials show good similarities with the numerical simulations. Special considerations are mentioned concerning the size of the probe and its ability to measure the permittivity of heterogeneous materials made of large inclusions. Combination of such numerical tool and measuring device can be used as a non-destructive testing technique to assess the near surface permittivity of concrete structures or as a calibration technique for GPR measurements.

A comparative analysis of the accuracy of Kubo formulations for graphene plasmonics

In recent years, there has been a growing need for the design and fabrication of smaller, faster, low-consumption and high-performance devices, as well as the technology approaches to the integration of electronics and photonics. This has led to the wide use of plasmonic structures. On the other hand, the excellent optical and electrical properties of graphene have made it a suitable material for plasmonic applications. The graphene properties can be manipulated by operation frequency and tuning its Fermi energy. Fermi energy of graphene can be tuned through electric gating or chemical doping. A phenomenon called Pauli blocking governs the interband transitions in graphene, and it is worth noting that since Pauli blocking is directly related to the Fermi energy of graphene, all parameters tuning the Fermi energy of graphene lead to variation of the imaginary parts of graphene’s permittivity and refractive index. Many applications of graphene in plasmonics rely on this property. Since the permittivity and refractive index formulas of graphene are extracted from its two-dimensional conductivity called the Kubo formulation, the accurate calculation of graphene’s two-dimensional conductivity is very important. In this paper, for the first time to our knowledge, the available Kubo formulations have been analyzed and compared so that the most accurate Kubo formulation could be chosen for plasmonic applications. Also, a comprehensive and detailed study about the properties of graphene including surface conductivity, permittivity, refractive index and plasma frequency, along with a sensitivity analysis for its refractive index and plasma frequency are accomplished.

A generalized dynamic model of nanoscale surface acoustic wave sensors and its applications in Love wave propagation and shear-horizontal vibration

• A generalized dynamic model based on the Hamilton's principle and variational approach is established. • The model is applied to depict the wave propagation in SAW nano-devices or vibration of piezoelectric nanoplates. • The surface effect is included with the aid of the surface elasticity , surface piezoelectricity and surface permittivity. • A critical thickness value of surface acoustic wave nano-devices or piezoelectric nanoplates can be obtained. • Below the critical thickness, the size-dependent properties will become evident and should be taken into account. A generalized dynamic model to depict the wave propagation properties in surface acoustic wave nano-devices is established based on the Hamilton's principle and variational approach. The surface effect, equivalent to additional thin films, is included with the aid of the surface elasticity, surface piezoelectricity and surface permittivity. It is demonstrated that this generalized dynamic model can be reduced into some classical cases, suitable for macro-scale and nano-scale, if some specific assumptions are utilized. In numerical simulations, Love wave propagation in a typical surface acoustic wave device composed of a piezoelectric ceramic transducer film and an aluminum substrate, as well as the shear-horizontal vibration of a piezoelectric plate, is investigated consequently to qualitatively and quantitatively analyze the surface effect. Correspondingly, a critical thickness that distinguishes surface effect from macro-mechanical behaviors is proposed, below which the size-dependent properties must be considered. Not limited as Love waves, the theoretical model will provide us a useful mathematical tool to analyze surface effect in nano-devices, which can be easily extended to other type of waves, such as Bleustein-Gulyaev waves and general Rayleigh waves.