Electromagnetic Wave Penetration Research Articles

Estimation of relative permittivity for measuring soil texture-dependent water content by GNSS-IR

Techniques for measuring the soil moisture content (SMC) using global navigation satellite system-interferometric reflectometry (GNSS-IR) with a positioning antenna have been reported. However, conventional methods are limited to evaluating the relative change in volumetric water content in a dry range for certain soil textures. In this study, we proposed a method to measure relative permittivity using GNSS-IR and evaluated its applicability at two sites with different soil textures and moisture content. The true multipath penetration depth was obtained from the tangent dielectric suitable for the soil textures, and the apparent penetration depth affected by the relative permittivity of the soil was calculated from the signal-to-noise ratio measured by GNSS. The relative permittivity of the soil was obtained from the ratio of these values and compared with the relative permittivity of the SMC sensor. As a result, we could measure soil permittivity according to soil textures from dry to wet conditions from GNSS-IR, except when the true multipath wave penetration depth was less than 1.5 cm, at which only surface reflection occurred. Sandy soils with a low dielectric loss tangent and wet areas with small changes in the depth of penetration of electromagnetic waves are particularly suitable environments for this method.

Coupled and radiated microwave sensors for vital signs and lung water level monitoring

This paper presents a novel approach for non-invasive monitoring of vital signs (heart rate (HR), respiration rate (RR)) and lung water levels using ultra-wideband (UWB) microwave sensors. The primary contribution of this study is the development and testing of two different sensor technologies to enhance the penetration and monitoring capabilities of electromagnetic waves within the human body. The first sensor technology employs a radiated UWB microwave that can be integrated into textiles, operating within a frequency range of 1.5 to 10 GHz, providing flexibility and comfort for wearable health monitoring. The second sensor technology involves using body-coupled UWB non-radiating sensors with a wide operational bandwidth from 1.3 to 10 GHz and a stable feeding structure, ensuring efficient reflection and transmission of waves for accurate monitoring. The shapes of flexible and textile UWB electromagnetic microwave sensor radiators and couplers, along with the measurement procedure, are tested in human clinical studies. The sensor-specific absorption rate (SAR) is evaluated at two distinct resonant frequencies on tissue masses of 1 g and 10 g, aligning with the IEEE C95.3 standard to ensure adherence to standard thresholds of 1.6 W/kg and 2 W/kg, respectively. Additionally, a denoising scheme utilizing deep learning techniques is proposed to filter Base Line Wander (BLW) noise attributable to misplaced electrodes, skin impedance, poor skin preparation, patient movement, and breathing within the frequency range of 0.05 to 3 Hz. The postprocessing outcome demonstrates the superiority of couplers over radiating sensors.

Enhancement of penetration of electromagnetic waves by field focusing applied to GPR detection

Ground penetrating radar (GPR) is limited by challenges such as signal attenuation and inadequate target detection in lossy dielectrics, prompting research on data processing algorithms to enhance detection capability. In this study, we propose a method for enhancing GPR detection capability based on electromagnetic field focusing (FF). The method involves calculating the phase difference attributable to the range difference between each antenna element and the focal point and compensating its feed phase accordingly. This approach effectively concentrates the energy of electromagnetic waves at the target area. Tapered slot antennas operating within the 2.5–8 GHz frequency band were employed for transmitting and receiving, thus facilitating algorithm verification and target detection. The synthetic aperture radar algorithm executed pulse compression and range migration on the received data, thereby intensifying the signal at the target object’s position and achieving double focusing. Notably, this study uniquely employs FF to enhance the penetrability of electromagnetic waves and augment the detection capability of GPR. Both simulation and experimental results demonstrated the effectiveness of the proposed method in improving the GPR imaging quality.

Effect of Carbon Fiber Paper with Thickness Gradient on Electromagnetic Shielding Performance of X-Band.

Flexible paper-based materials play a crucial role in the field of flexible electromagnetic shielding due to their thinness and controllable shape. In this study, we employed the wet paper forming technique to prepare carbon fiber paper with a thickness gradient. The electromagnetic shielding performance of the carbon fiber paper varies with the ladder-like thickness distribution. Specifically, an increase in thickness gradient leads to higher reflectance of the carbon fiber paper. Within the X-band frequency range (8.2-12.4 GHz), reflectivity decreases as electromagnetic wave frequency increases, indicating enhanced penetration of electromagnetic waves into the interior of the carbon fiber paper. This enhancement is attributed to an increased fiber content per unit area resulting from a greater thickness gradient, which further enhances reflection loss and promotes internal multiple reflections and scattering effects, leading to increased absorption loss. Notably, at a 5 mm thickness, our carbon fiber paper exhibits an impressive average overall shielding performance, reaching 63.46 dB. Moreover, it exhibits notable air permeability and mechanical properties, thereby assuming a pivotal role in the realm of flexible wearable devices in the foreseeable future.

Near-field Focusing in Ground Penetrating Radar Based on Phase Compensation Algorithm

Underground energy intensity and electromagnetic wave penetration depth are important parameters to characterize the detection performance of Ground Penetrating Radar (GPR). Near-field focusing (NFF) is an effective means to improve the electromagnetic energy fed into the ground by the antennas. In this paper, the phase compensation algorithm considering underground media is derived. In order to verify the effectiveness of the algorithm, the NFF antenna array is proposed. By changing the phase of the NFF array, the focus distance can be adjusted in the range of 400 mm – 800 mm. The maximum field enhancement coefficient in the focal region can achieve 19.2 dB. This shows that NFF array based on phase compensation algorithm has potential application prospects in increasing GPR detection performance.

Evaluation of the Accuracy of the Remote Determination of the Brewster Angle When Measuring Physicochemical Parameters of Soil

In precision farming technology, the moisture of the soil, its granulometric composition, specific conductivity and a number of other physical and chemical parameters are determined using remote radar sensing. The most important parameters are those measured in the area of the plant root system located well below the “air-surface” boundary. In order to create conditions for the penetration of electromagnetic waves through the “air-surface” interface with a minimum reflection coefficient, the irradiation of the Earth’s surface is carried out obliquely with an angle of incidence close to the Brewster angle. The reflection coefficient, and, consequently, the Brewster angle, depend on the complex dielectric permittivity of the surface soil layer and are not known a priori. To determine the Brewster angle, the usual method is to search for the minimum amplitude of the vertically polarized signal reflected from the surface. Another approach is when the first derivative of the dependence of the modulus of the complex amplitude of a vertically polarized interference wave, taken with respect to the angle of incidence, is set equal to zero. In turn, in real dielectrics such as agricultural soils, the amplitude of the vertically polarized signal reflected from the surface is directly proportional to the reflection coefficient and does not have a pronounced minimum, which reduces the accuracy of the measurements. Based on the solution of the Helmholtz wave equation for a three-layered structure of the propagation medium (air, upper fertile soil layer, soil layer below the groundwater level), a model of the process of forming an interference wave under oblique irradiation of a planar layered dielectric with losses has been developed. Using the developed model, factors influencing the accuracy of determining the Brewster angle have been identified. For the first time, it is proposed to use the phase shift between the oscillations of the interference waves with vertical and horizontal polarization to measure the Brewster angle. A comparative assessment of the accuracy of determining the Brewster angle using known amplitude methods and the proposed phase method has been carried out. The adequacy of the method was experimentally confirmed. Recommendations have been developed for the practical application of the phase method of finding the Brewster angle for assessing the dielectric permittivity of soil and its moisture content.

Characterizing the Sensitivity of Dielectric Response in Reservoirs with Varying Lithology and Fluid Saturation

Summary This research delivers a comprehensive analysis of complex permittivity’s sensitivity—a key parameter in characterizing electromagnetic (EM) wave absorption and penetration dynamics within oil reservoirs—to various reservoir properties including temperature, pressure, mineralogy (limestone, quartz, and clays), and water saturation. Contemporary estimation techniques, primarily grounded in simplistic mixing rule models, often fail to capture the intricacy inherent to heavy oil reservoirs. Thus, this study, buttressed by extensive experimental data, introduces a distinctive, intrinsically multivariable regression model that better delineates the relationships between dielectric properties and reservoir conditions. Our investigation uncovers water saturation as a pivotal factor in the sensitivity of the regression model, largely due to water’s inherently polar nature. We note that the complex permittivity of the sample diminishes with increasing quartz content and decreasing limestone content—despite limestone possessing a higher individual dielectric constant. Moreover, the presence of clays, primarily found within the pore space delineated by the quartz and limestone sand’s grain boundaries, accentuates the expansive sensitivity of the dielectric constant to water volume, overshadowing the polarizability induced by the double-layer effect of water-sensitive clays. The study additionally uncovers temperature-dependent behavior, characterized by an increase in both components of complex permittivity with rising temperatures, particularly for composite materials comprising diverse rock minerals and hydrocarbons. We also explore pressure as a variable and find no discernible impact on complex permittivity due to pressure fluctuations, although samples with high quartz content exhibit dynamic polarization under pressure. Our multivariable regression model, responsive to all identified parameters, offers a more accurate and realistic interpretation of complex permittivity within the reservoir. The model’s validation on assorted unconsolidated and consolidated core samples underpins its reliability, paving the way for its implementation in any model estimating absorption and penetration dynamics within the reservoir. In summation, the results of this study hold significant implications for reservoir simulation. The regressed models can be directly integrated to bridge the gap between numerical simulation and experimentally obtained relationships. These findings offer insights into the behavior of complex permittivity and its sensitivity to various reservoir properties. The regression model developed herein provides a more nuanced approach to estimating complex permittivity in oil reservoirs, enhancing our comprehension of EM wave absorption dynamics, and contributing to the advancement of more efficient and sustainable oil extraction methodologies.

Unpaved road characterization during rainfall scenario: Electromagnetic wave and cone penetration assessment

This study aims to examine the effect of rainfall on integrity assessment on unpaved roads using electromagnetic waves and cone penetration. An unpaved road testbed is prepared with sandy soil in densely- and loosely-packed conditions. Site investigations using a time domain reflectometry (TDR), ground penetrating radar (GPR), and dynamic cone penetrometer (DCP) are performed on the testbed under before and after rainfall scenarios, and an additional laboratory compaction test using the soil samples is conducted. The results show that the spatially scaled GPR signal converted by the TDR signal can accurately estimate the interface depth. In addition, rainfall may reduce the accuracy of GPR signal polarity-based analyses for anomaly detection on unpaved roads. This study reveals that TDR, GPR, and DCP with simple laboratory compaction tests and physics-inspired effective stress-depth models can be a powerful tool for underground mapping when subjected to rainfall season.

High-Sensitivity RFID Sensor for Structural Health Monitoring.

Structural health monitoring (SHM) is crucial for ensuring operational safety in applications like pipelines, tanks, aircraft, ships, and vehicles. Traditional embedded sensors have limitations due to expense and potential structural damage. A novel technology using radio frequency identification devices (RFID) offers wireless transmission of highly sensitive strain measurement data. The system features a thin, flexible sensor based on an inductance-capacitance (LC) circuit with a parallel-plate capacitance sensing unit. By incorporating tailored cracks in the capacitor electrodes, the sensor's capacitor electrodes become highly piezoresistive, modifying electromagnetic wave penetration. This unconventional change in capacitance shifts the resonance frequency, resulting in a wireless strain sensor with a gauge factor of 50 for strains under 1%. The frequency shift is passively detected through an external readout system using simple frequency sweeping. This wire-free, power-free design allows easy integration into composites without compromising structural integrity. Experimental results demonstrate the cracked wireless strain sensor's ability to detect small strains within composites. This technology offers a cost-effective, non-destructive solution for accurate structural health monitoring.

On Possible Mechanism of Enhancement of Absorption of Powerful Laser Radiation by Metals

In this work, it is shown that the dependence of the mass of conductive band electrons in a metal on their energy can be a reason of enhancement of the absorption of powerful laser radiation by the metal. To do this, a problem of response (current) of the electron placed in one-dimension periodic potential (lattice) to an electric field periodic in time (electromagnetic wave) is solved. The solution shows that for sufficiently large amplitude of the wave the dependence of the electron current on the wave amplitude becomes non-linear. Within a certain rangе of parameters, this dependence can be described by a simple formula that corresponds to the dependence of the electron mass on its energy. The formula was used for solving the problem of penetration of electromagnetic wave into a metal with the approach of modified Drude model. The non-linearity results in the enhancement of the wave absorption and generation of wave with frequencies close to those of plasma penetrating deep into the metal. The discussed effects manifest themselves in electric fields about. 1 V/Angstrom. The obtained results can be used in the interpretation of experiments data and in the creation of mathematical modeling of the interaction of powerful laser radiation with metal.

Study on electromagnetic wave absorbing properties of nanocrystalline Fe81.5Si3B9P3C1Cu1Ti1.5/Graphene oxide composite

To prevent and control electromagnetic pollution problems, there is an urgent need to develop better wave-absorbing materials. In this study, nanocrystalline alloy/graphene oxide(GO) composite modified powder was obtained on the basis of Fe81.5Si3B9P3C1Cu1Ti1.5 nanocrystalline alloy powder with different weight percentages of GO, which was mechanically mixed by high-energy ball milling treatment, and the microstructure and morphology of the materials and the electromagnetic wave absorption properties were characterized. The results show that the Fe81.5Si3B9P3C1Cu1Ti1.5/GO composite powder has excellent wave absorption performance, and the loss mechanism is magnetic loss including eddy current loss and natural resonance. Defects and groups in GO not only improve the impedance matching characteristics, but also introduce defect polarization relaxation and electron dipole polarization relaxation of the groups, which are beneficial to the penetration and absorption of electromagnetic waves. The minimum reflection loss (RLmin) of the nanocrystalline alloy powder can reach −37.55 dB and the maximum effective absorption bandwidth (ΔfRL<-10dB) can reach 5.95 GHz; the RLmin of the composite powder is as high as −52.55 dB when the GO content is 1.5 wt%, and the widest bandwidth can reach 6.12 GHz at 2.00 mm when the GO content is 0.5 wt%. With the addition of GO, its RLmin increased by 40%. This indicates that the composite material have superior absorption performance compared to a single absorber.

Mathematical Channel Modeling of Electromagnetic Waves in Biological Tissues for Wireless Body Communication

In the wireless body area network (WBAN), radio propagations from devices that communicate with the human body are very complex and distinctive compared to other environments. As we know, the human body is a lossy channel that significantly attenuates the propagation of electromagnetic waves (EMW). Therefore, channel models are critical in evaluating the communication link. One of the most predominant models is the path loss channel model, which is used to cover a wide range of communication channels and frequency bands in WBAN. This paper investigates the EMW in a human model irradiated by an incident electromagnetic plane wave. A planar multilayer structure is used for modeling human tissue. Moreover, the steady-state electromagnetic distribution is calculated by solving the differential and integral equations (DIE) by using the method of moments (MoM). The obtained results demonstrate the great use of performing a theoretical analysis for path loss (PL) and power loss density (PLD) estimation. The magnitude of the electric field inside muscle tissue at various depths, and with the most important frequencies in medical applications, is evaluated. This investigation provides evidence that the penetration of EMW in biological tissue strongly depends on the frequency and thickness of the tissue involved. Thus, for different examined conditions, an excellent agreement between recent results that were obtained by an analytical method, finite element (FEM), and the proposed MoM method is verified to be valid in this investigation, and it is found that the distribution of the field, PL, and PLD for different communication scenarios is very promising to determine the quality of communication for WBAN technology.

Assessment of Transmitted Power Density in the Planar Multilayer Tissue Model due to Radiation from Dipole Antenna

Recent relevant safety guidelines IEEE-Std C95.1- 2019 and ICNIRP-RF Guidelines 2020 have converged towards 6 GHz as a transition frequency from specific absorption rate (SAR), as basic restriction quantity, to absorbed power density (APD). Namely, the penetration of electromagnetic waves into the human tissue rapidly decreases as frequency increases, therefore, tissue heating can be considered as superficial above 6 GHz. However, besides the APD, an alternative internal dosimetric quantity transmitted power density or TPD is sometimes computed since its relation to SAR is more obvious and is easier to obtain. This paper deals with an analytical/numerical approach to determine TPD in planar multi-layered model of the human tissue exposed to the dipole antenna radiation. Analytical approach deals with assumed sinusoidal current distribution, while numerical approach pertains to the determination of current by solving the corresponding Pocklington integro-differential equation via Galerkin-Bubnov Indirect Boundary Element Method. The novelty presented in this paper with respect to previous work is a multilayer geometry whose effects are considered via the corresponding Fresnel plane wave reflection/transmission approximation. Some illustrative results for current distribution, transmitted field, volume power density (VPD) and TPD at various frequencies and distances of the antenna from the interface are given.

Penetration of a plane electromagnetic wave into a moving ferromagnetic medium

The article is devoted to mathematical modeling of the penetration of the electromagnetic field into a moving ferromagnetic conducting medium. It is shown that the depth of penetration of a plane electromagnetic field depends both on the speed of movement and on the direction of movement of the medium. The movement of the medium "towards" the field reduces the depth of its penetration into the material, which is equivalent to an increase in the frequency of the field. At certain speeds of movement of the medium in the direction of the field, the penetration depth increases so much that the medium becomes "transparent" and there is no attenuation of the field. It is shown that the vibration of a thin ferromagnetic plate in the electromagnetic field, even in the case of a linear medium, leads to nonlinear oscillations of the field in the substance. The nonlinearity of the medium affects the value of the field attenuation but the nature of the field does not change significantly. It is shown that the vibration of a thin ferromagnetic plate increases the field penetration depth compared to the case of a stationary medium.

Electromagnetic Heating for Heavy-Oil and Bitumen Recovery: Experimental, Numerical, and Pilot Studies

Summary This study provides an extensive critical review of electromagnetic heating (EMH) methods [inductive heating (IH), low-frequency heating (LFH), and high-frequency heating (HFH)] to highlight their existing challenges in enhanced heavy-oil and oil sands recovery. In general, IH is considered to be less practicable than LFH and HFH. The resistance (ohmic or conduction) heating prevails in LFH while dielectric heating prevails in HFH. Thus, the effectiveness of LFH decreases if reservoir water is overheated to generate steam. Also, the intensity of the energy released and the temperature rise in LFH are not as significant as those in HFH. LFH also fails in penetrating the media with breaks, heterogeneities, and in partially saturated media (e.g., when some oil saturation has been produced). These challenges might somewhat be remedied by HFH at the expense of reducing the electromagnetic (EM) wave penetration depth. The advantages of HFH include remote heating through a desiccated reservoir region around the EM energy source, higher intensity of the energy released and greater temperature rise, and better EM wave penetration through partially saturated media with breaks and heterogeneities. The caveat, however, is that the practical application of HFH could be more expensive than LFH. Besides, the lower depth of EM wave penetration in HFH remains a challenge. During HFH, the temperature increase occurs as a result of the induced molecular rotation in the dielectric material, in particular if the material contains more polar compounds. The polar molecules follow the EM field. This increases the internal molecular friction within the material and generates heat, leading to the rise of temperature. Because the heat generated is a function of the stored (absorbed) energy in the reservoir, the dielectric constant or the real permittivity of the reservoir should be enhanced to enhance the performance of HFH. This ensures that the temperature has risen reasonably in a reasonable amount of time with a reasonable amount of electricity consumption. However, to generate a uniform rise in temperature on a large scale away from the wellbore, the imaginary permittivity of the material should be reasonably lowered, too, for maximizing the penetration of the EM wave (while the real permittivity is an indication of the degree of polarization, the imaginary permittivity is associated with dielectric losses). Lowering the imaginary permittivity away from the wellbore helps minimize the effects of steam condensation (condensate formation retards the EM wave propagation) or delay steam condensation because the reservoir temperature is reduced during the later stages of oil production. The thermal conductivity of the formation should also be enhanced, especially away from the wellbore to generate a more uniform rise in temperature. These three reservoir improvements (enhancing real permittivity, lowering imaginary permittivity, and enhancing thermal conductivity) in an attempt to enhance EMH underpin the rationale behind proposing future optimizations of EMH, and in particular, HFH.

전자파 흡수체를 이용한 대형 함체의 차폐효과 개선

This study analyzed that the penetration of electromagnetic waves through an unknown opening in a large enclosure generated standing waves within the enclosure, thereby reducing its shielding characteristics. A 3D numerical analysis confirmed that the shielding performance can be improved by using electromagnetic absorbers to reduce the standing wave. This was verified experimentally.

Justification of the parameters of a microwave installation with a metal-dielectric resonator for defrosting of colostrum of animals

The article is devoted to the substantiation of the structural performance of an ultra-high-frequency (UHF) installation of continuous flow action for defrosting and warming up animal colostrum. The dielectric parameters of colostrum in the frozen and liquid state were analyzed to determine the generated power and the depth of penetration of electromagnetic waves. For a given generator power, a threshold power that depends on the electric field strength (EF), and taking into account the change in the attenuation coefficient of electromagnetic waves during heating, a theoretical assessment of the optimal volume of raw materials in which animal colostrum is disinfected was carried out. These indicators are consistent with the design parameters of unconventional cavity resonators.

Flexible Microwave Biosensor for Skin Abnormality Detection Based on Spoof Surface Plasmon Polaritons

Point-of-care testing plays an important role in the detection of skin abnormalities. The detection of skin abnormalities requires sufficient depth and no harm. A flexible microwave biosensor based on spoof surface plasmon polaritons was designed to meet the requirements of skin abnormalities. The designed biosensor, which works at 11.3 GHz, is small and can be flexibly attached to the skin surface of any part of the human body for measurement. The health status of the skin can be evaluated by the resonant frequency and the magnitude of the reflection coefficient of the sensor. The sensor was tested on pork skin. The experiment results showed that the sensor can detect skin abnormalities such as skin burn, skin tumor, and others. Compared with other sensors, the sensor has sufficient penetration depth because of the strong penetration of microwave electromagnetic waves. It is the first flexible microwave biosensor used for skin, which involves point-of-care testing, and continuous monitoring of skin.

Antarctic snow-covered sea ice topography derivation from TanDEM-X using polarimetric SAR interferometry

Abstract. Single-pass interferometric synthetic aperture radar (InSAR) enables the possibility for sea ice topographic retrieval despite the inherent dynamics of sea ice. InSAR digital elevation models (DEMs) are measuring the radar scattering center height. The height bias induced by the penetration of electromagnetic waves into snow and ice leads to inaccuracies of the InSAR DEM, especially for thick and deformed sea ice with snow cover. In this study, an elevation difference between the satellite-measured InSAR DEM and the airborne-measured optical DEM is observed from a coordinated campaign over the western Weddell Sea in Antarctica. The objective is to correct the penetration bias and generate a precise sea ice topographic map from the single-pass InSAR data. With the potential of retrieving sea ice geophysical information by the polarimetric-interferometry (Pol-InSAR) technique, a two-layer-plus-volume model is proposed to represent the sea ice vertical structure and its scattering mechanisms. Furthermore, a simplified version of the model is derived, to allow its inversion with limited a priori knowledge, which is then applied to a topographic retrieval scheme. The experiments are performed across four polarizations: HH, VV, Pauli 1 (HH + VV), and Pauli 2 (HH − VV). The model-retrieved performance is validated with the optically derived DEM of the sea ice topography, showing an excellent performance with root-mean-square error as low as 0.26 m in Pauli-1 (HH + VV) polarization.

Verification of the electromagnetic deep-penetration effect in the real world

The deep penetration of electromagnetic waves into lossy media can be obtained by properly generating inhomogeneous waves. In this work, for the very first time, we demonstrate the physical implementation and the practical relevance of this phenomenon. A thorough numerical investigation of the deep-penetration effects has been performed by designing and comparing three distinct practical radiators, emitting either homogeneous or inhomogeneous waves. As concerns the latter kind, a typical Menzel microstrip antenna is first used to radiate improper leaky waves. Then, a completely new approach based on an optimized 3-D horn TEM antenna applied to a lossy prism is described, which may find applications even at optical frequencies. The effectiveness of the proposed radiators is measured using different algorithms to consider distinct aspects of the propagation in lossy media. We finally demonstrate that the deep penetration is possible, by extending the ideal and theoretical evidence to practical relevance, and discuss both achievements and limits obtained through numerical simulations on the designed antennas.