Reflection Amplitude Research Articles

Assessment of Ground Penetrating Radar for Pyrite Swelling Detection in Soils

Pyrite swelling in soils below buildings is a major issue. It leads to severe deformations in floor foundations. A survey is carried out at a selected site in the city of Laval, Quebec, to assess the usefulness of ground-penetrating radar (GPR) to detect deformations that may be indicative of the presence of pyrite. Four soil samples are taken from the aforementioned site to determine the soil type below the concrete slab. The results indicate the presence of limestone, moor clay, and shale sediments, which are prone to pyrite swelling. The GPR data were collected using the GSSI SIR 4000 with a high frequency antenna and processed using RADAN software. The GPR data indicate the presence of severe deformation in many locations of the concrete slab. The most important wave reflections indicative of pyrite swelling are the rebar reflections, showing interesting pushed-up and dropped-down reflections. These reflections appear in two forms. The first is the attenuated reflections that may occur due to pyrite-rich materials. The second is the high amplitude reflections that occur because of the air void, which can be formed due to heaving the concrete slab because of pyrite swelling. As a result, GPR appears to be an effective method for assessing and mapping the effect of pyrite swelling below concrete slabs. Doi: 10.28991/CEJ-2024-010-03-05 Full Text: PDF

Unlocking the Mysteries of the Mishrif Formation: Seismic Data Reinterpretation and Structural Analysis for Reservoir Performance Optimization in the Garraf Oil Field, Southern Iraq

The seismic survey is based on the reflected wave’s inherent nature from the interface among layers, which depends on the layer's density and velocity. This is called acoustic impedance and is used to resolve the confusion associated with the stratigraphic structure of the Mishrif formations in the Garraf oil field. The seismic section of the Garraf oil field in Thi-Qar Province, south of Iraq, was analyzed and interpreted. Considering the most important petroleum accumulation reservoir in the Garraf oil field, to update the structural images of the Mishrif Formation. A seismic study of the actual amplitude reflections, temporal maps, and three-dimensional depositional models demonstrated that the Mishrif Formation generate hydrocarbon from an individual structural trap in the presence of oil. Numerous abrupt discontinuities were observed in the seismic reflectors of the reservoir units of the Mishrif Formation, suggesting either a reef or a fault. The correct probability can be shown by establishing a historical match between the reservoir model and the actual behavior of the reservoir or by running a 3D vertical seismic profile log (VSP), which is more precise than the seismic survey previously used to explore faults.

Tunable Microwave Absorbing Devices Enabled by Reversible Metal Electrodeposition.

Tunable microwave absorbers have gained significant interest due to their capability to actively control microwaves. However, the existing architecture-change-based approach lacks flexibility, and the active-element-based approach is constrained by a narrowband operation or small dynamic modulation range. Here, a novel electrically tunable microwave absorbing device (TMAD) is demonstrated that can achieve dynamic tuning of the average reflection amplitude between -13.0 and -1.2 dB over a broadband range of 8-18 GHz enabled by reversible metal electrodeposition. This reversible tunability is achieved by electrodepositing silver (Ag) layers with controlled morphology on nanoscopic platinum (Pt) films in a device structure similar to a tunable Salisbury screen, employing Ag electrodeposited on Pt films as the modifiable resistive layer. Furthermore, this TMAD possesses a simple device architecture, excellent bistability, and multispectral compatibility. Our approach offers a new strategy for dynamically manipulating microwaves, which has potential utility in intelligent camouflage and communication systems.

Propagation Behavior of P1-Wave Passing through Fluid-Saturated Porous Continuous Barrier in Layered Saturated Soil

The fluid-saturated porous continuous barrier has a better vibration isolation effect than the single-phase solid continuous barrier, and layer-forming saturated soils will have an impact on the vibration isolation effect of the barriers due to their irregular layer-forming distribution. Based on Biot’s theory of saturated porous media and Snell’s law, a dynamic model of a fluid-saturated porous continuous barrier in layered saturated soil is established in this study. By introducing the potential function and using the continuous boundary condition of the interface between the saturated soil and the barrier, the analytical solution of the inverse transmission amplitude ratio of a P1-wave passing through the fluid-saturated porous continuous barrier in stratified saturated soil is obtained. The rationality of the proposed method is verified by comparing the solution of the P-wave model at the interface between the elastic medium and the saturated coarse particle interlayer. The differences in the propagation characteristics of fluid-saturated porous continuous barriers in layered saturated soils, homogeneous saturated soils, and layered single-phase soils are analyzed via numerical examples, and the influence of changes in the physical and mechanical parameters of the fluid-saturated porous continuous barriers on the reflectance amplitude ratios under the conditions of a layered saturated soil foundation are also analyzed. The results show that the presence of fluid in the stratified saturated soil model changes the trend of the reflection amplitude ratio with the incidence angle. The reflection amplitude ratio of the P2-wave and the SV-wave increases first and then decreases with the increase in the incident angle, while the reflection amplitude ratio of P1-wave decreases first and then increases. Barrier thickness and porosity change the energy distribution relationship at the interface; a relatively thicker barrier thickness and a higher porosity would result in a higher amplitude of barrier reflections.

Graphene‐Based Flexible Optically Transparent Dual‐Tunable Metasurface

AbstractDynamically tunable flexible metasurfaces with optical transparency are essentially useful in stealth, electromagnetic sensing, and camouflage while keeping continuous optical observation and communication. In this paper, a dual‐tunable graphene‐based metasurface is designed based on patterned graphene sandwich structures, showing independent dynamic control of reflection amplitude and resonance frequency, excellent optical transparency, and outstanding flexibility. Both the simulated and measured results demonstrate that the transition from dual band absorption at 12 and 24.8 GHz to broad band absorption from 10 to 25.7 GHz, and the absorption amplitude can be tuned between −5 and −15 dB on average in each case dynamically and independently by applying bias voltage to graphene layers. Lastly, the distributions of the induced electric field and surface currents, as well as an equivalent circuit model, are provided to illustrate the tunable electromagnetic absorption mechanism. The designed metasurface has potential applications that are speculated in the fields of electromagnetic tune and electromagnetic stealth.

Delineation of Nickel Laterite Deposits in “DCV” Block Southeast Sulawesi Based on Data Analysis of Ground Penetrating Radar (GPR) Method

The need for nickel is very intensive in the development of upstream to downstream industries so that domestic consumption of nickel ore will increase in the coming years, therefore domestic downstream is increasingly being improved. Overcoming the problem of the high demand for nickel in Indonesia can be done by conducting exploration and exploitation to support the downstream of nickel. Exploration of nickel laterite can be accomplished with geophysical methods that aim to obtain subsurface data from nickel laterite deposits. The Ground Penetrating Radar (GPR) geophysical method is one of the non-destructive methods that can be applied to determine the subsurface conditions of nickel laterite deposits based on physical properties in the form of dielectric constants and reflection patterns and amplitude contrasts produced on radargrams. The nickel laterite deposits can be separated into 4 layers based on Ground Penetrating Radar (GPR) data analysis: bedrock, saprolite, limonite, and topsoil. Based on GPR measurements, the average dielectric constant value of topsoil is 6.8 mS/m, the limonite layer is 10.87 mS/m, the saprolite layer is 12.37 mS/m, and bedrock is 7.87 mS/m. It can be seen that the saprolite layer has a high conductivity so that the dielectric constant value is also high, this is influenced by the very high nickel content in this layer. The depth of bedrock in the research area varies from 20 - 40 meters, the thickness of topsoil is dominated in the value range of 3.6 - 5 meters, while the thickness of the laterite layer which is the main target of nickel laterite mining includes saprolite and limonite layers which have varying values of 15 - 40 meters where the distribution of the thickness of this layer is in the eastern and central parts of the research area.

Polarization-insensitive, frequency- and amplitude-tunable transparent microwave absorber based on graphene metasurface

Transparent and flexible metamaterial absorbers can provide solutions for electromagnetic compatibility and electromagnetic radiation pollution. They also play key roles in platforms with optical windows that require low detectability and immunity to electromagnetic interference. Due to the lack of active adaptability to complex electromagnetic environments, early metamaterial absorbers need to be redesigned and manufactured once the application scenarios change. The new two-dimensional material graphene provides a practical technical approach for the realization of transparent tunable absorbers. In this work, we propose a polarization-insensitive dual-tunable microwave absorber based on graphene metasurface. By controlling two separate bias voltages applied to patterned graphene or continuous graphene, independent dynamic regulation of electromagnetic wave absorption frequency and amplitude is achieved. It also possesses the features of optical transparency and flexibility. The measurement results show that the absorption frequency can be shifted from 9.8 to 11.3 GHz, the peak absorption rate at each absorption frequency remains above 99.6%, and the reflection amplitude modulation can be achieved simultaneously at each absorption frequency. The proposed absorber integrates multiple modulation functions for electromagnetic waves, and the overall structure is optically transparent and flexible. Therefore, it can contribute to many practical wave absorbing applications.

Geophysical and chemical characteristics of peatland in coastal wetland, southern Thailand

Peatlands, as an important carbon sink, store a large amount of atmospheric carbon that is vulnerable to becoming a carbon emission source due to the disturbance of the peat layer by natural and anthropogenic processes. The Kuan Kreng peat swamp forest is the second largest peatland in Thailand and is in coastal wetland serving for carbon stock in the subsurface. To assess carbon stock in peatland, the thickness and distribution of the peat layer are necessary. This study determines physical and chemical characteristics of the peatlands in the coastal wetland, southern Thailand by conventional core study and geophysical surveys, including ground penetrating radar (GPR) and electrical resistivity imaging (ERI). There is a significant relationship between chemical and physical properties from the peat layer, which is useful to approximately predict the physical properties and peat layers in the geophysical profiles. The resistivity profiles exhibit high resistivity response, peat between 21.9 and 145.0 ohm-m, interpreted as the peat layers in the shallow subsurface. The high resolution GPR profiles provide an average GPR velocity in peat of 0.040 m/ns and a relative dielectric constant of 54.9 for the peat layers. The peat layer is characterized by a high amplitude of reflection in the GPR profiles. The thickness of the peat layers was estimated from the geophysical surveys and the drilling cores having an average thickness of 18 cm. Average values of bulk density (0.19 g/cm3) and TOC (31.18 wt. %) from the drilling core samples are used to calculate the carbon density in the peat layers giving a result of 59.24 Kg C/m3. Hence, the carbon stock at the Kuan Kreng peat swamp forest is estimated at least 7.53 megaton carbon, which is much higher than aboveground biomass carbon in this area. The innumerably high amount of carbon stock could raise awareness of peatland disturbances.

Bragg scattering by an irregular versatile seabed in the presence of current

The Bragg scattering due to an undulated elastic bottom in the presence of a uniform current is discussed in the present paper. The conditions of Bragg resonance are derived analytically and discussed numerically for various values of physical parameters. The mathematical techniques used for discussing the analysis are the perturbation and Fourier transform methods. It is seen that the amplitude of the Bragg reflection increases with the increase in the flexibility factor in the versatile floor of the sea, and there is a significant impact of the current speed on Bragg reflection and transmission coefficients. The maximum value of the amplitude of Bragg reflection is observed to decrease as the Froude number increases. Again, it is seen that the transmitted energy produced in the presence of uniform current does not fluctuate considerably when the nature of an elastic bottom gets closer to that of a stiff floor. The blocking resonance in the presence of current and elastic bottom is analyzed by neglecting the small bottom undulation. A significant effect of blocking resonance on Bragg reflection and transmission is observed.

Frequency-multiplexed multifunctional coding metasurface based on transmission and reflection modes

In this work, a frequency-multiplexed multifunctional coding metasurface is proposed, which can realize focusing lens at the lower frequency and multiple scattering beams at the higher frequency. The two functions can be manipulated independently. The proposed metasurface is composed of the top metal patch with a circular ring, two fan rings and two rectangle patches (CFRP), the bottom metal patch with C-shaped and rectangular metal slots (CRS) and a dielectric substrate. By changing the opening direction and size of CRS and the tilt direction and fan ring size of CFRP, the amplitude and phase of transmission and reflection can be modulated, respectively. The transmission mode works at 7 GHz, which can form focal points in different focal planes. The reflection mode works at 17.5 GHz, which can form multiple scattered beams in different directions in the far field. To further verify its practical feasibility, the proposed metasurface is fabricated and measured, the experimental results are in good agreement with the numerical simulation results. The proposed metasurface provides new possibilities to develop multifunctional devices.

Ultra-broad band plasma–graphene absorber at millimeter-wave frequency bands

This paper introduces a new absorber that can effectively absorb millimeter wave frequencies. The design involves stacking foam, plasma, and laminated graphene sheets on a perfect electric conductor substrate. The absorber can generate a wideband effect on electromagnetic waves by combining graphene layers and a plasma medium. The absorption and bandwidth of the plasma slab depend on various parameters like plasma frequency, collisional rate, and thickness. By tuning the plasma frequency ωp (rad/s), average collision frequency υp(Hz), Fermi energy of graphene sheets, and thickness of the foam and plasma layers, the benefit of wideband and good absorption considering reflection amplitude lower than −15 dB, an ultra-bandwidth from 32 to 150 GHz can be achieved. This structure has multiple layers that have bandgap and band-stop regions. These regions are associated with the cavities of dielectric slabs that have graphene sheets. These regions are identified as coupled Fabry–Pérot resonances, which can induce multiple interference effects in multi-reflection for the incident electromagnetic waves, resulting in high-level absorption. Understanding and controlling these resonances is crucial for optimizing the performance of such systems. An equivalent circuit model has been used to predict the absorber's performance. The proposed absorber has a symmetrical structure that reacts similarly to transverse-electric and transverse-magnetic waves. The frequency range of the absorber has been studied to determine the effects of the graphene sheets' relaxation time and voltage biasing. The absorber offers advantages such as being thin, having a wide bandwidth, and being insensitive to polarization.

Tuning effects of a thin layer with triclinic anisotropy

Tuning effects, induced by the interference between scattering waves at the top and bottom interfaces, characterize the dependence of thin-layer seismic responses on wave frequencies, thin-layer thicknesses, and medium elastic properties. The characteristics of tuning effects are frequently used to infer thin-layer properties. We analyze the tuning effects of a thin triclinic layer between two varying triclinic half-spaces. Exact thin-layer reflection and transmission (R/T) coefficients are developed to characterize the prestack thin-layer tuning effects of P, S1, and S2 waves. The thin-layer R/T coefficient approximations are developed to build concise relationships between tuning effect characteristics and medium parameters. The relationships give insights when estimating thin-layer properties from interpreting tuning effect characteristics. As inferred from the approximations, the tuning effect of a thin triclinic layer is composed of two fundamental tuning effects that make sense for two particular thin-layer models wherein one has identical enclosing half-spaces and the other has identical elastic parameter discontinuities at the bottom and top interfaces. The combined influence of wave frequencies, thin-layer thicknesses, and incidence angles on the two fundamental tuning effects can be assessed by a unique factor for each wave mode. For a general thin triclinic layer, this factor characterizes the periodic variations of reflection amplitudes versus wave frequencies. The maximum and minimum thin-layer reflection amplitudes are determined by the reflectivities at the top and bottom interfaces. With wave frequencies or thin-layer thicknesses increasing from zero, thin-layer reflections have smaller or larger amplitudes when the two single-interface reflectivities have equal or opposite polarities, respectively. We develop a method to evaluate the sensitivity of thin-layer reflection amplitudes to thin-layer elastic parameters. The sensitivity is higher when the two single-interface reflectivities have opposite polarities compared with the equal-polarity case. Numerical tests are used to demonstrate our approximation accuracy and the characteristics of tuning effects.

Zn2+-Enhanced Lithium Magnesium Molybdate Ultralow Temperature Cofired Ceramics for Terahertz Wavefront Modulation Applications.

High efficiency, high frequency, low error, and low latency of wavefront modulation are challenges that must be addressed simultaneously in 5G/6G communication systems. In order to cope with these challenges, novel Li2Mg2-xZnxMo3O12 (x = 0.00-0.08) ceramics are prepared by a solid-state reaction method. The microwave dielectric properties (εr = 8.7, Q × f = 61,312 GHz, τf = -59.1 ppm/°C) and terahertz transmission properties (εr1 = 8.3, tanδ1 = 0.00908, Tamplitude = 0.673, Δphase = 27.65°) of this ceramic (x = 0.06, 625 °C) are effectively enhanced by Zn2+. The chemical compatibility between this ceramic and the Al electrode is demonstrated. The reflection amplitude of this ceramic combined with the Al electrode at 0.5 THz is revealed, and the error between simulation and experiment is only 0.06. A terahertz reflective device for wavefront modulation is designed and demonstrated by using this ceramic and Al electrode. This device can deflect the wavefront of cross-polarized waves and has a certain isolation effect on co-polarized waves. This work accelerates the development of dielectric ceramics and ultralow temperature cofired ceramics technology in the terahertz field.

A tunable graphene-based phase-jump inversion plasmonic sensor for ultra-sensitive refractive index sensing over THz frequency

The surface plasmon resonance effect has been previously reported as an essential mechanism for terahertz wave sensing applications. However, due to its structural geometric parameters dependence, either the reconfiguration of the arrays or the realignment of the prism system is required, which always remains one of the challenges limiting practical applications. Here, a graphene-based phase-jump inversion plasmonic sensor (GPPS) operating at a fixed gap and incident angle is established. The optimal wave vector matching between specific analytes and the GPPS can be achieved by adjusting the Fermi level of graphene. On this basis, an ultrahigh sensitivity of 0.488 THz/RIU is achieved under the optimal Fermi level. Remarkably, the comparison between the phase spectra and the reflective amplitude spectra indicates that the phase-based FoM and Q-factor are two orders of magnitude larger than those calculated by amplitude spectra, which could reach 244RIU−1 and 218.5. The unique phase-jump responses on graphene surface plasmon resonance provide new ideas for ultra-sensitivity THz sensing methods.

Constrained nonlinear amplitude-variation-with-offset inversion for reservoir dynamic changes estimation from time-lapse seismic data

We develop a novel elastic amplitude-variation-with-offset (AVO) inversion process to estimate the fluid saturation and effective pressure or variations in these properties from time-lapse seismic data sets. These changes occur in oil and gas reservoirs caused by fluid injection or hydrocarbon production that leads to changes in the elastic wave properties, reflectivity, and seismic response. Our method is based on a seismic forward model that consists of a linearized AVO equation and a rock-physics model. The AVO equation links the elastic wave properties to seismic reflection amplitudes, whereas the rock-physics model maps the saturation and pressure into seismic velocities and density. The inversion approach relies on the gradient descent technique to estimate the unknown variables by searching for the minimum of the least-squares misfit between the observed and modeled data. The first-order gradient equations of the least-squares data misfit function with respect to effective pressure and water saturation are derived by using the adjoint-state method and the chain rule. The optimization method used to minimize the misfit function and obtain the best optimal solution is a limited-memory quasi-Newton algorithm. This inversion process allows us to incorporate prior constraints by using the logistic function to map the model variables to a bounded range. To achieve a stable solution to ill-posed inversion problems, optimal regularization weights are applied. The application of the developed workflow on 1D synthetic and real well-log data from the Edvard Grieg oil field simulating various saturation-pressure conditions during production demonstrates the validity of the approach with different noise levels. The inversion is then applied to a 2D synthetic data set modeled from the reservoir model of the Smeaheia field, a potential site for a large-scale offshore CO2 storage field located in the North Sea. Our results illustrate that our inversion method efficiently and accurately estimates reservoir saturation and pressure variations.

A Design Strategy for Surface Nanostructures to Realize Sensitive Refractive-Index Optical Sensors.

Refractive-index optical sensors have been extensively studied. Originally, they were surface plasmon resonance sensors using only a flat gold film. Currently, to develop practically useful label-free optical sensors, numerous proposals for refractive index sensors have been made using various nanostructures composed of metals and dielectrics. In this study, we explored a rational design strategy for sensors using surface nanostructures comprising metals or dielectrics. Optical responses, such as reflection and transmission, and resonant electromagnetic fields were computed using a numerical method of rigorous coupled-wave analysis combined with a scattering-matrix algorithm. As a result, good performance that almost reached the physical limit was achieved using a plasmonic surface lattice structure. Furthermore, to precisely trace the refractive-index change, a scheme using two physical quantities, resonant wavelength and reflection amplitude, was found to be valid for a 2D silicon metasurface.

Experimental Distributions of the Reflection Amplitude for Networks with Unitary and Symplectic Symmetries

Experimental Distributions of the Reflection Amplitude for Networks with Unitary and Symplectic Symmetries

Quantification of choroidal hyperreflective layer: A swept-source optical coherence tomography study.

To investigate variation in reflectivity of choroidal layers in normal eyes. From the swept-source optical coherence tomography database, we retrospectively included eyes with a normal fundus. Choroidal reflectivity was measured on the horizontal and vertical B-scan optical coherence tomography images. The optical barrier of the choroid was defined as the first hill in the middle of the reflectance graph from the retinal pigment epithelium-Bruch's membrane complex to the chorioscleral junction. The optical barrier of the choroid was identified in 91 eyes of 91 individuals. The amplitude of peak reflectivity of the optical barrier of the choroid at macular center (142.85 ± 15.04) was greater than those in superior (136.12 ± 14.08) or inferior macula (135.30 ± 16.13) (P = 0.028, P = 0.008, respectively). Latency between the peak of the retinal pigment epithelium-Bruch's membrane complex and the optical barrier of the choroid at macular center (48.11 ± 13.78 μm) was shorter than those in nasal macula (55.58 ± 19.21 μm) (P = 0.021). The amplitude of the peak reflectivity of the optical barrier of the choroid in the center negatively correlated with the latency between the retinal pigment epithelium-Bruch's membrane complex and the optical barrier of the choroid (P < 0.001). An optical barrier exists in the inner choroid of the normal eye. Its depth depends on the location within the macula. Further studies are mandatory to evaluate variations in the barrier in the eyes with chorioretinal disease.

Maximising offset well information in unravelling onshore geohazards indicators: Case study of the Gale field

An attempt is made in this study towards maximising offset wells information in unravelling onshore geohazards indicators in the Gale field. The Gale field is located about 100km north-west of Port Harcourt, Nigeria. The field consists of a highly faulted and elongated rollover anticline, bounded to the north by a regional growth fault. The data used for this study integrates the quadrature and reflectivity amplitude attributes from seismic data, with offset well data. The conventional reflectivity seismic data was 90° phase rotated to derive the quadrature volume. The quadrature seismic was considered a more appropriate reflectivity seismic attribute for use in shallow geohazard analysis as it is known for its characteristic preservation of high frequency spectrum inherent in the data. Offset wells (GALE-01, GALE-03, GALE-04, GALE-05, GALE-06, and GALE-08) analysis revealed mud losses, stuck pipe, overpull and gas cut as gathered from the daily drilling reports. These could translate to potential triggers of some geohazards where poorly managed. Review of field geotechnical report did not reveal any geohazards issues. Based on the geohazards assessment carried out for these wells; chances of encountering shallow gas for all the units as shown in the well summary is rated low. Results from a geohazards analysis indicate the presence of possible shallow gas within the area of interest and particularly along the shallow section of planned well trajectory. This is further supported by the presence of faults within the vicinity of gas bearing reservoirs at deeper level and a potential for these faults extending to the shallower interval. These faults are likely to serve as migration pathways for gas to seep to the shallower section, hence forming a potential geohazard. In addition, some of the offset wells targeting deeper gas reservoirs penetrated pockets of gas at the shallower interval that stratigraphically correlates with the shallow section that would be penetrated by the planned wells. The results of this work were used to move the proposed drilling location of the Gale planned wells to a nearby area free of shallow gas signatures.

BRCA1 detection by porous silicon double-layer via reflectometric interference Fourier transform spectroscopy

Porous silicon double-layer (PSiDL) was fabricated to reduce noise for biosensing measurements via reflectometric interference Fourier transform spectroscopy (RIFTS). The design of the top layer was performed to trap the bio-analyte molecules by their larger diameter pores. However, by constructing the smaller diameter pores on the bottom layer, attempts were made to prevent these molecules from entering the pores as much as possible. Thus, the top layer acted as the sensing layer, whereas the bottom layer played a reference layer role. The Field emission scanning electron microscopy (FE-SEM) revealed that the top and bottom layers had pores with the highest diameter frequency of about 19 and 7 nm, respectively. Surface modification was performed for both layers and was confirmed by Fourier transform infra-red spectroscopy (FTIR) and RIFTS. Modified PSiDL nanostructure was then used to detect the high penetrance breast cancer susceptibility gene, BRCA1, via RIFTS. Examination of both the peaks' location in fast Fourier transform (FFT) of reflection graphs and amplitude value of these peaks was performed. Both analyses showed that the top layer noise could be reduced by using the bottom layer signal.