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To accurately predict the relative permittivity of cement-stabilized base materials, a study on the dielectric mixing model for cracked base materials was conducted. Based on the electromagnetic mixing theory of multiphase composites, a comprehensive dielectric mixing model of cement-stabilized base materials was derived. The volume ratios and relative permittivity values of the specimen constituents in different cracking states of the cement-stabilized base were determined using industrial CT and a Percometer relative permittivity meter, with comprehensive consideration given to the effects of different initial porosities and crack widths on the dielectric properties. Based on the volumetric and dielectric properties of the base material specimens in both intact and cracked states, as well as the error analysis between the predicted and measured values of the relative permittivity constant, the u-optimal solution of the dielectric mixing model for cement-stabilized base material was determined to be 1. Consequently, an optimization dielectric mixing model for semi-rigid base course materials in a cracked state was developed. The optimization model proposed is suitable for predicting the dielectric properties of cement-stabilized base material with crack widths generally greater than 3 mm during the service life of semi-rigid base course in engineering practice. [ABSTRACT FROM AUTHOR]

To accurately predict the relative permittivity of cement-stabilized base materials, a study on the dielectric mixing model for cracked base materials was conducted. Based on the electromagnetic mixing theory of multiphase composites, a comprehensive dielectric mixing model of cement-stabilized base materials was derived. The volume ratios and relative permittivity values of the specimen constituents in different cracking states of the cement-stabilized base were determined using industrial CT and a Percometer relative permittivity meter, with comprehensive consideration given to the effects of different initial porosities and crack widths on the dielectric properties. Based on the volumetric and dielectric properties of the base material specimens in both intact and cracked states, as well as the error analysis between the predicted and measured values of the relative permittivity constant, the u-optimal solution of the dielectric mixing model for cement-stabilized base material was determined to be 1. Consequently, an optimization dielectric mixing model for semi-rigid base course materials in a cracked state was developed. The optimization model proposed is suitable for predicting the dielectric properties of cement-stabilized base material with crack widths generally greater than 3 mm during the service life of semi-rigid base course in engineering practice.

The advancement of high-power microwave technology has indeed brought about the possibility of E-bombs, also known as electromagnetic pulse (EMP) bombs. These weapons emit an electromagnetic pulse that can disable electrical circuitry within a specific radius. As the frequency spectrum becomes more congested with various technologies operating in similar frequency bands, the need for shielding against interference becomes crucial. One promising solution is the use of conductive concrete, which is created by incorporating conductive components into a traditional concrete mixture. This conductive concrete has shown excellent shielding properties and improved electrical characteristics. To assess and quantify its effectiveness, the relative complex permittivity of the concrete mixture needs to be estimated. In this paper, the authors propose a method for estimating the relative complex permittivity of the concrete mixture. This was achieved by measuring the scattering parameters of concrete samples using a rectangular waveguide within the C-band frequency range. The scattering parameters provide valuable information about how electromagnetic waves interact with the concrete. A dielectric mixing model was developed to determine the relative complex permittivity. This model takes into account the volume percentage and the dielectric properties of the individual constituents present in the concrete mixture. By applying this model and obtaining the complex permittivity of the mixture, it becomes possible to calculate the required thickness of the conductive concrete mix needed to achieve the desired levels of electromagnetic attenuation and shielding.

Complex dielectric constant (CDC) of bound water determines the accuracy of the complex dielectric constant of wet soil. According to electrical double-layer structure and dielectric properties, the bound water on clay particle surface is divided into strongly bound water and weakly bound water. Based on this classification, models for the complex dielectric constants of bound water and soil are established taking into consideration factors such as temperature, moisture, texture, and microwave frequency. The results show that the fundamental reason why the complex dielectric constant of bound water is between that of ice and free water is the adsorption force which forms the electrical double-layer structure on the surface of clay particles. Low-concentration cationic solution could exist in free soil water and was found as the reason for the higher salinity and conductivity of free soil water, as compared to the measured soil solution. Results of soil CDC model are in good agreement with measured data across a wide range of microwave frequencies and soil temperature, moisture, and texture. The absolute root mean square error analysis also shows that the soil CDC model in this paper compared to the other models is more accurate.

In this study, we address the variations of bare soil surface microwave brightness temperatures and evaluate the performance of a dielectric mixing model over the desert of Kuwait. We use data collected in a field survey and data obtained from NASA Soil Moisture Active Passive (SMAP), European Space Agency Soil Moisture and Ocean Salinity (SMOS), Advanced Microwave Scanning Radiometer 2 (AMSR2), and Special Sensor Microwave/Imager (SSM/I). In situ measurements are collected during two intensive field campaigns over bare, flat, and homogeneous soil terrains in the desert of Kuwait. Despite the prevailing dry desert environment, a large range of soil moisture values was monitored, due to precedent rain events and subsequent dry down. The mean relative difference (MRD) is within the range of ±0.005 m3·m−3 during the two sampling days. This reflects consistency of soil moisture in space and time. As predicted by the model, the higher frequency channels (18 to 19 GHz) demonstrate reduced sensitivity to surface soil moisture even in the absence of vegetation, topography and heterogeneity. In the 6.9 to 10.7 GHz range, only the horizontal polarization is sensitive to surface soil moisture. Instead, at the frequency of 1.4 GHz, both polarizations are sensitive to soil moisture and span a large dynamic range as predicted by the model. The error statistics of the difference between observed satellite brightness temperature (Tb) (excluding SMOS data due to radio frequency interference, RFI) and simulated brightness temperatures (Tbs) show values of Root Mean Square Deviation (RMSD) of 5.05 K at vertical polarization and 4.88 K at horizontal polarization. Such error could be due to the performance of the dielectric mixing model, soil moisture sampling depth and the impact of parametrization of effective temperature and roughness.

Alkali-silica reaction (ASR) is a common cause of concrete deterioration. Water (either in free or bound form), in the presence of reactive aggregates, plays a major role in the reaction itself and in the formation and expansion of the deleterious gel produced. Since microwave signals are sensitive to the presence of water in dielectric materials, microwave materials characterization techniques have the potential to detect and monitor ASR gel in concrete structures. Dielectric mixing models are physics-based models that relate the macroscopic (i.e., effective) dielectric constant of a material to the dielectric constant of its constituents and their respective volumetric contents. In this investigation, an empirical multiphase dielectric mixing model is developed in conjunction with measured dielectric constants of two sets of mortar samples with ASR-reactive and nonreactive aggregates at R-band (1.7–2.6 GHz). The proposed model is capable of closely predicting the effective (temporal) dielectric constant of the samples. The modeling results are validated by a comparison with the measured temporal dielectric constant of the samples, showing good agreement. Through this investigation, quantitative information on the influence of constituents of ASR-reactive mortar samples (including ASR gel) are obtained, and the pertinent results indicate significant potential for microwave materials characterization techniques for ASR detection and evaluation. [ABSTRACT FROM PUBLISHER]

Accurate estimation of unfrozen/liquid water content (θ l ) of soils with time domain reflectometry (TDR) is important for understanding freezing and thawing processes and hydrology in cold regions. Empirical equations and composite dielectric mixing models are the two most commonly used methods to estimate water content in unfrozen soils from TDR-measured soil effective permittivity (ε eff ). However, empirical equations derived from unfrozen soil data always overestimate θ l in frozen soils and few studies were found to examine the validity of composite dielectric mixing models for measuring θ l . Therefore, the objective of this study was to evaluate the sensitivities and applicability of composite dielectric mixing models for modeling the ε eff (θ l ) relationship. Five multi-phase, composite dielectric mixing models (i.e., power law model, de Loor model, Sihvola discrete model, Sihvola confocal model, and Sphere model) were evaluated with published dataset consisting of independently measured ε eff and θ l on the same samples. The results show that: (1) the power law model and de Loor models are independent of configurations of dielectric mixtures; (2) the Sihvola discrete model depends on the host medium and independent on the configurations of the other components; (3) different dielectric mixing models may end up with the similar ε eff (θ l ) relationships by parameter adjusting to represent the same problem; and (4) the de Loor model, and Sihvola discrete and confocal models are most appropriate for modeling the ε eff (θ l ) relationship of frozen soils based on the published dataset. This study will significantly contribute to the application of TDR method for liquid water measurement in frozen soils and facilitate the understanding of freezing/thawing processes. [ABSTRACT FROM AUTHOR]

Dielectric properties of alkali silicates ((Na,K) 2 (SiO 2 ) n O) or ‘water glasses’ are a critical input into the electromagnetic modeling of these materials, which have a broad range of applications. Recent increased interest in understanding geopolymerization of aluminosilicates with water glasses and the potential to improve understanding of the role of moisture in damage due to alkali–silica reaction (ASR) in concrete (where water glass is a suitable analogue for ASR gel) motivates this research. This investigation presents the results of microwave dielectric property measurement of twelve laboratory-produced (synthetic) water glass samples at X-band (8.2–12.4 GHz). Results show an exponential decay of loss factor as a function of increasing silica-to-alkali ratio, suggesting a correlation with increase in bound water in the samples and a decrease in the fluid ionic concentration. The results provide an insight into the temporal changes of the dielectric properties of ASR-affected materials, as well as geopolymers. [ABSTRACT FROM AUTHOR]

We consider the exploitation of dielectric properties of saline deposits for the detection and mapping of moisture in arid regions on both Earth and Mars. We present simulated and experimental study in order to assess the effect of salinity on the complex permittivity of geological materials and, therefore, on the radar backscattering coefficient in the [1-7 GHz] frequency range. Laboratory measurements are performed on sand/sodium chloride aqueous mixtures using a vectorial network analyzer coupled to an open-ended coaxial dielectric probe. We aim at calibrating and validating semiempirical dielectric mixing models. In particular, we evaluated the dependence of the real and imaginary parts of complex permittivity on the microwave frequency, water content, and salinity. Our results confirm that if the real part is mainly affected by the moisture content, the imaginary part is more sensitive to salinity. In addition to the classic formulas of mixing models, the ionic-conductivity losses, which are due to mobile ions in the saline solution, are taken into account in order to better assess the effect of salinity on the dielectric properties of mixtures. Dielectric mixing models are then used as input parameters for the simulation of the radar backscattering coefficients by means of an analytical model: the integral equation model. Simulation results show that salinity should have a significant impact on the radar backscattering recorded in synthetic aperture radar data in terms of the magnitude of the backscattering coefficient. Moreover, our results suggest that VV polarization provides a greater sensitivity to salinity than HH polarization. [ABSTRACT FROM AUTHOR]

Complex dielectric constant (CDC) of bound water determines the accuracy of the complex dielectric constant of wet soil. According to electrical double-layer structure and dielectric properties, the bound water on clay particle surface is divided into strongly bound water and weakly bound water. Based on this classification, models for the complex dielectric constants of bound water and soil are established taking into consideration factors such as temperature, moisture, texture, and microwave frequency. The results show that the fundamental reason why the complex dielectric constant of bound water is between that of ice and free water is the adsorption force which forms the electrical double-layer structure on the surface of clay particles. Low-concentration cationic solution could exist in free soil water and was found as the reason for the higher salinity and conductivity of free soil water, as compared to the measured soil solution. Results of soil CDC model are in good agreement with measured data across a wide range of microwave frequencies and soil temperature, moisture, and texture. The absolute root mean square error analysis also shows that the soil CDC model in this paper compared to the other models is more accurate. [ABSTRACT FROM AUTHOR]

In this study, we address the variations of bare soil surface microwave brightness temperatures and evaluate the performance of a dielectric mixing model over the desert of Kuwait. We use data collected in a field survey and data obtained from NASA Soil Moisture Active Passive (SMAP), European Space Agency Soil Moisture and Ocean Salinity (SMOS), Advanced Microwave Scanning Radiometer 2 (AMSR2), and Special Sensor Microwave/Imager (SSM/I). In situ measurements are collected during two intensive field campaigns over bare, flat, and homogeneous soil terrains in the desert of Kuwait. Despite the prevailing dry desert environment, a large range of soil moisture values was monitored, due to precedent rain events and subsequent dry down. The mean relative difference (MRD) is within the range of ±0.005 m3·m−3 during the two sampling days. This reflects consistency of soil moisture in space and time. As predicted by the model, the higher frequency channels (18 to 19 GHz) demonstrate reduced sensitivity to surface soil moisture even in the absence of vegetation, topography and heterogeneity. In the 6.9 to 10.7 GHz range, only the horizontal polarization is sensitive to surface soil moisture. Instead, at the frequency of 1.4 GHz, both polarizations are sensitive to soil moisture and span a large dynamic range as predicted by the model. The error statistics of the difference between observed satellite brightness temperature (Tb) (excluding SMOS data due to radio frequency interference, RFI) and simulated brightness temperatures (Tbs) show values of Root Mean Square Deviation (RMSD) of 5.05 K at vertical polarization and 4.88 K at horizontal polarization. Such error could be due to the performance of the dielectric mixing model, soil moisture sampling depth and the impact of parametrization of effective temperature and roughness. [ABSTRACT FROM AUTHOR]