Reflection Coefficient Research Articles

A low-cost reflection mode operated microwave resonator sensor for angular displacement detection

A low-cost microwave resonator sensor for angular displacement detection is proposed. The sensor uses a strip-loaded dielectric resonator (SLDR) as the key element. The sensor operates in the reflection mode, i.e. by producing a variation in the reflection coefficient (S11) according to the angular position of the SLDR relative to a microstrip transmission line. The primary advantage of the proposed strategy is its fixed-frequency operation enabling the S11 measurement with a low-cost reflectometer, thereby avoiding the costly vector network analyzer (VNA). Design modelling and initial analysis of the sensor are performed with ANSYS HFSS software. To demonstrate proof of concept, a sensor prototype is fabricated and experimentally characterized with a custom-made reflectometer. Results are compared against VNA-based measurements to be in decent agreement. The proposed sensor exhibits 0.43 dB/0 sensitivity over the dynamic range of 00–900.

Active differential reflection coefficient analysis of differentially-fed antenna array

Active differential reflection coefficient analysis of differentially-fed antenna array

Novel brittleness index construction and pre‐stack seismic prediction for gas hydrate reservoirs

AbstractReservoir transformation is essential for developing gas hydrate reservoirs. Predicting sediment brittleness is key to optimizing drilling design and evaluating engineering sweet spots. Constructing a brittleness index reflecting the brittle mineral content of a rock based on elastic parameters and predicting it using seismic data is a feasible solution for assessing reservoir brittleness. In addition, the elastic brittleness index can characterize the effect of complex pore types, fractures and pore fillings on rock brittleness. With the shallow hydrate reservoir in the sea as the research target. First, a novel brittleness index characterized by multiplying the Lamé parameter () by Poisson's ratio () is proposed. Its superiority in indicating brittle mineral content is verified by a rock‐physics model. Second, a reflection coefficient approximation equation including the novel brittleness index is derived, enabling direct estimation of reservoir brittleness from seismic data. The new brittleness index has proven to better reflect brittle mineral content and effectively indicate the high brittleness characteristics of hydrate reservoirs. The accuracy of the proposed approximate equation is verified by a layered medium model, and the viability of predicting the new brittleness index using seismic data is also theoretically supported by the model test. Finally, the proposed method has obtained favourable results in the application of hydrate work area data collected at the South China Sea, confirming its availability and practicality.

Seismic scattering inversion for multiple parameters of overburden-stressed isotropic media

Subsurface reservoirs are compressed by overburden stress resulting from the gravity of overlying masses, and the resulting stress changes significantly affect the seismic reflection responses generated at the reservoir interfaces. Several exact reflection coefficient equations have been well established to delineate the role that in situ stress plays in altering the energy transition and amplitude of seismic reflection responses. These exact equations, however, cannot be effectively used in practice due to their intricate formulations and the difficult geophysical estimation for the third-order elastic constants (3oECs) embedded in reflection coefficients. Based on the theories of nonlinear elasticity and elastic wave inverse scattering, we derive an approximate seismic reflection coefficient equation for overburden-stressed isotropic media in terms of the P-wave modulus, shear modulus, density, and a defined stress-related parameter (SRP). The SRP is a combined quantity of elastic moduli, 3oECs, and overburden stress, which can be naturally treated as a dimensionless stress-induced anisotropy parameter. Its inclusion effectively eliminates the need for 3oECs information when using our equation to estimate the desired reservoir properties from seismic observations. By comparing our equation to the exact one, we confirm its validity within the moderate-stress range. Then, we introduce a Bayesian inversion approach incorporating the new reflection coefficient equation to estimate four model parameters. In our approach, the Cauchy and Gaussian distribution functions are used for the a priori probability and the likelihood distributions, respectively. The synthetic tests from two well-log data sets and a field example demonstrate that four parameters can be reasonably inverted using our approach with rather smooth initial models, which illustrates the feasibility of our inversion approach.

Design and architecting of a broadband bullet-diamond shaped integrated frequency selective meta-surface absorber for aero-stealth platform.

The work report on architecture of integrated frequency selective meta-surface (IFSMS) absorbers for aerospace stealth applications. Fabricated IFSMS comprised of a pattern metasurface integrated with dielectric interlayer and conducting ground. Initially, a supercell (2 × 2-unit cell: 24 × 24 mm2) was designed with a fourfold topological symmetry. Supercell produces impedances (R), inductances (L), and capacitances (C) in tune with design on its interaction with microwave. RC performance was tested at variable incident transverse electric/magnetic (TE/TM) modes over, Θ, 0°-60° and at the normal incidence (TE), against a planer, clockwise rotation over, Φ, 0°-90°. The mode stability and rotational invariance was analyzed for displacement current- and power-density distributions. The impedance behavior and phase reversal S11 reflection coefficient studies revealed the emergence of mid-band Fabry-Perot mode distinguishing LC behavior of the circuit. The meta-pattern was manufactured by mask lithography using a customized resistive micro-carbon ink and imprinted onto dielectric/ground tile (dimension: 30 × 30 cm2). Structure-property relationship of the ink material was investigated using SEM, XRD, FTIR, UV-visible spectroscopy to reveled surface properties of imprinted material. The absorber was subjected to the free space measurements over C (4-8), X (8-12), and Ku (12-18GHz) bands, including pristine interlayer dielectrics. The simulated and experimental RC data was found to be in excellent agreement. The proposed IFSMS design is a potential candidate for the stealth application.

Shock Waves in Nonlinear Transmission Lines

In the first half of the article, interaction between the small amplitude travelling waves (“sound”) and the shock waves in the transmission line containing both nonlinear capacitors and nonlinear inductors is considered. Herein, the “sound” wave coefficient of reflection from (coefficient of transmission through) the shock wave is calculated. These coefficients are expressed in terms of the speeds of the “sound” waves relative to the shock and the wave impedances. In the second half of the article, the dissipation in the system is explicitly included into consideration, introducing Ohmic resistors shunting the inductors and also in series with the capacitors. This allows us to justify the conditions on the shocks, postulated in the first half of the article. This also allows us to describe the shocks as physical objects of finite width and study their profiles, same as the profiles of the waves closely connected with the shocks—the kinks. The profiles of the latter, and in some particular cases, the profiles of the former are obtained in terms of elementary functions.

Design and analysis of low-profile quad element wide band MIMO antenna with efficient isolation for C and X-band applications

ABSTRACT A low-profile, quad-element multiple-input/multiple-output (MIMO) antenna of 0.69 λ 0 λ 0 is presented in this study. The proposed design consists of a stub and slot-loaded partial ground plane with a quad rectangular-shaped radiator on top. The four elements are placed orthogonally to one another to reduce mutual coupling and envelope correlation coefficient (ECC). The maximum isolation of the proposed MIMO antenna is 61.5 dB at 9.94 GHz frequency. It achieved impedance bandwidth 5.56 GHz, ranging from 5.74–11.30 GHz. The peak gain of the proposed MIMO antenna is 6.18 dB at 7.3 GHz, with a maximum efficiency of 89.21% at 7.1 GHz. The minimum ECC between ports 1 and 2 over the operating band are observed as 0.0001. To achieve the best outcome, a parametric analysis of the proposed antenna is also performed. Various diversity characteristic metrics, including diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), channel capacity loss (CCL), and ergodic channel capacity (CC), are thoroughly analysed to determine how well the MIMO antenna performs in terms of diversity. Over the operating band, the measured values provide good agreement with respect to simulated and equivalent circuit model results, indicating a strong candidacy for operation in the investigated bands. The proposed MIMO antenna have the potential for C and X band applications such as WLAN, radio astronomy, satellite communication, and automotive radar.

EM Radiation Thermal Effects Simulation Study on a Realistic Female Model at Some Frequencies

The purpose of research is to develop a computer simulation based mobile phone safety testing scheme that is well suited for testing any mobile phone antenna at different communication frequencies and various realistic scenarios. It has been shown how feasible the study of realistic models is, what difficulties may occur, what effects, moments appear in the modeling process. The aim of the study is also to show the need for changes in the standard of mobile phone safety testing and to investigate the possibilities of implementing these changes. It is preferable for manufacturers to perform testing using human realistic models through numerical calculations and conduct safety compliance testing under realistic conditions to produce more realistic picture. Computer modeling gives the possibility to consider various realistic models, realistic scenarios and different tissue dielectric properties according to the frequency. It was investigated how mobile phone antenna radiation parameters (S11 reflection coefficient) change according to the various positions of the hand and fingers at standard communication 2100 MHz and 3700 MHz frequencies; were estimated Specific Absorption Rate (SAR) values in the human head and their dependence on S11 parameters were studied. Based on the obtained results, it has been shown that the preferred S11 behavior should be one of the indicators in the phone safety standards. For this, manufacturers should carry out mobile phone antenna matching/S11 parameter testing with free space.

Interaction of a UWB impulse with a layer of sandy soil, having a rough upper boundary

ABSTRACT In this paper, the changes in the character of time shapes, amplitudes, frequency spectra, and time delay of ultra-wideband (UWB) impulses (duration of 0.33 ns) reflected from the layer of wet sand with a rough upper boundary were investigated. It was shown that the attenuation of UWB impulse amplitude, which is reflected from the upper rough boundary of the sand layer, can be described by the model of Fresnel reflection coefficient for a smooth surface using the Gaussian correction factor (FRGC). At this root-mean-square (RMS), height of soil surface roughness was in the range of ~0–21 mm, but the determination coefficient and RMS error (RMSE) were found to be equal to 0.94 and 0.02, respectively. An experiment close to linear increase/decrease in the propagation time of impulses reflected from the upper/lower boundary of the layer, respectively, was found with increasing the RMS heights of upper boundary. It is shown that the propagation time of such impulses can be described by the modified FRGC model with an error from RMSE = 0.09 ns to RMSE = 0.15 ns. The results of these findings are of practical importance for the interpretation of remote sensing data for precise soil moisture measurements from unmanned aerial vehicle platforms using UWB impulses.

Experimental characterization of the effective acoustic properties of anisotropic porous materials via free-field measurements

Porous media are commonly described as effective isotropic fluid materials, such that their acoustic properties can be adequately determined from their bulk modulus and dynamic density. Most acoustic absorbents, however, possess a marked anisotropy, which influences their acoustical behavior and the parameters necessary to deduce it. Specifically, the influence of anisotropy translates into a full symmetric density tensor (in place of a scalar). This study presents a method for retrieving the bulk modulus and all six components of the density tensor of a layer of porous material from reflection coefficients measured in free field with an array of microphones. The procedure consists in expressing the sound field measured in the vicinity of the layer as a superposition of plane waves, from which the surface impedance and the reflection coefficient are reconstructed. The reflection properties, as well as the pressure at the rigid backing interface, are estimated for various source positions (i.e., various angles of incidence) and an inverse problem is formulated to infer the effective fluid parameters. The validity of the method is examined experimentally on a manufactured porous material, and the resulting fluid parameters compared with experimental results obtained from reflection and transmission coefficients measured in an impedance tube.

Estimation of the surface impedance based on the discrete complex image source method and array processing

This paper introduces a method for estimating the sound absorption coefficient of a large panel of absorbing material from measurements using a microphone array. The method relies upon describing the pressure field as the set of monopoles obtained when the reflection coefficient is represented as the Laplace Transform of an image source distribution. This formulation results in a well-behaved integral equation, which is discretized using Gaussian quadrature to yield an inverse problem. It is possible to determine the regularized solution to the inverse problem and reconstruct the surface impedance of the sample by conducting measurements of the sound pressure at multiple points of observation. This sound field representation is adequate for sound sources in the close range of the material and the array. The paper presents simulated and experimental investigations to delineate the efficacy of the proposed measurement technique against the well-known image source method, thereby highlighting its significant potential to advance acoustic characterization methodologies.

Exploring the optical properties of naphdiyne sheet: First-principles study

Naphdiyne sheet is a two-dimensional carbon-based structure composed of naphthyl rings and acetylenic linkages. The optical characteristics of naphdiyne sheets are investigated using density functional theory. The results showed that this sheet is suitable for energy storage systems due to its high dielectric constant. The dielectric constant of naphdiyne is higher than that of graphene. The refractive index, absorption, reflection, and transmission coefficients are calculated based on the dielectric function. A notable optical absorption is observed across a wide energy range for parallel polarization. The transparency of this material is evident in its reflection and transmission constants, particularly in high-energy regions. The findings suggest that the naphdiyne sheets hold promise for use in nanoelectronics and optoelectronics.

Comparison of standard Bayesian methods and PINNs for the reconstruction of acoustic fields in 'in situ' combustion chambers

Acoustic measurements, utilizing sensors such as microphones strategically placed, are commonly employed to monitor acoustic systems and extract quantities of interest, such as acoustic reflection coefficients. Typically, a specialized test rig must be constructed to allow for external harmonic acoustic forcing via loudspeakers. In this study, we propose two different methods: physics-informed neural networks (PINNs) and the extended Kalman filter, to reconstruct the acoustic field of a system and assess the acoustic reflection coefficient at a defined boundary. We demonstrate numerically that a single external broadband forcing signal suffices for these methods. This implies that these methods can be applied to 'in situ' configurations, such as industrial combustion chambers, where the broadband nature of combustion noise serves as the acoustic forcing element. Furthermore, we investigate the performance of the two aforementioned methods in reconstructing the acoustic systems and corresponding acoustic boundaries.

Optimizing acoustic black hole structures for vibration control in beams: a comprehensive analysis

Acoustic black holes (ABH) have caught the attention of researchers because of their potential to absorb sound and control vibrations. This study presents an analytical framework that determines reflection coefficients in ABH structures. It focuses on implementing an acoustic black hole with a power-law tapered profile on beams. Moreover, this research investigates how various geometric shapes affect Damping Loss Factor (DLF) coefficients. This helps identify optimal approaches to optimize ABH structures based on specific requirements. The finite element method and a topology optimization solver were used to optimize various parameters systematically. The aim is to reduce weight and response, thereby improving the efficiency of ABH designs, especially in low-frequency insulation applications. The results demonstrate that ABH exhibits excellent performance in suppressing vibrations.

Numerical modeling of acoustic scattering characteristic with wavenumber domain admittance

A conversion from the wavenumber domain acoustic reflection coefficient to the wavenumber domain acoustic admittance is formulated to deal with the acoustic reflection properties of arbitrary materials in numerical simulation. This method, which can represent arbitrary reflection directional properties, is an extended reactive boundary condition modelling method based on a spatial Fourier transform over the boundary surface. The advantages are that it is computationally inexpensive because it does not need to consider the interior of the material in the analysis, and that it can handle reflection characteristics obtained from actual measurements, etc. From the results of applying the wavenumber domain acoustic admittance to the numerical analysis, it has been confirmed that the proposed method can handle not only the specular reflection component, but also when arbitrary scattering components are included, or when the main reflection direction is changed from the specular reflection direction.

Revisiting reverberation formulae

In 1992, the author proposed a generalization of Sabine's formula that develops reverberation time over a series of powers of the reflection coefficient on the boundaries. Some years later, he reduced the development to just two terms that made it possible to monitor reverberation times up to large absorptions. The present paper revisits this development and justifies it with the help of free path statistics in 3D rectangular enclosures. It proves that Kuttruff's reverberation formula is a special case of the general formula, but diverges for large absorption. Reverting to Kuttruff's original integration process leads to a formula that does not diverge. The paper further explains the difference between Eyring-type reverberation times that vanish for total absorption, and Sabine-type reverberation times that never vanish even for total absorption, and proposes a simple scheme for evaluating the asymptotic free path statistics and thus improving reverberation time prediction. Lastly, the approach is extended to non-ergodic enclosures.

A parametric study of dynamic stress in acoustic black holes

Acoustic Black Holes (ABHs) make modifications to a structure that act to reduce the speed of a wave travelling through the ABH region. The reduced wavespeed has a corresponding reduced wavelength which increases the effectiveness of damping treatment applied to the ABH. A common way in which the reduction of wavespeed can be achieved is by gradually reducing the thickness of a structure. This is commonly implemented as a beam termination, which results in a thin tip. In this case, the energy focusing effect of the ABH causes high amplitude vibrations to occur in the thin section of the structure, raising concerns about high levels of dynamic stress that could result in fatigue failure. This paper presents an investigation into the effect of changing the ABH taper length, tip height and power law on the dynamic stress in an ABH terminated beam. This is achieved via numerical model of the structure, which enables a full parametric analysis to be carried out. For each ABH parameterisation, the performance is also quantified in terms of reflection coefficient so that trade-offs between performance and stress can be observed.

Compensation of staircase-induced boundary absorption errors in FDTD simulation

Finite-difference time-domain (FDTD) methods are popular for wave-based simulations because their regular grid enables highly efficient implementation, especially on parallel processing architectures. On the flip side, these methods exhibit errors caused by the staircase approximations that result when arbitrary boundary geometries are approximated on the fixed grid. Of particular concern in room acoustics is the staircasing of absorptive boundaries, as this has been shown to cause errors as large as 40% in computed reverberation times that do not reduce when the grid is refined. This paper analyses the effectiveness of a previously proposed compensation method that consists of modifying the admittance boundary conditions based on the staircased surface area. A theoretical analysis shows that for special boundary orientations the numerical reflection coefficient converges to the exact result at low frequencies. Numerical tests complement this analysis to show that the compensation yields accurate results at intermediate orientations as well. A spherical resonator case further demonstrates that a close match between numerically and analytically computed relaxation times is also obtained for curved boundaries.

Tunable optical properties of BAs/ZnO vdW heterostructure

Stacked heterostructures is an effective strategy for physical property modulation and application of novel two-dimensional materials. In this study, a heterostructure consisting of two-dimensional III-V group hexagonal BAs and monolayer of ZnO is presented. The minimum value of binding and cohesive energies screened the BB’ configuration. Phonon spectra and ab initio molecular dynamics (AIMD) simulations further demonstrated the kinetic and thermodynamic stability of the selected model. Most notably, the formation of the heterostructure greatly improves the optical absorption performance of the monolayer, especially in the infrared (IR) regions. At a compressive strain of −6%, the band alignment shifts from type I to type II, while the bandgap becomes dramatically smaller. Refraction and reflection coefficients in the IR region under compressive strain (−2% and −4%) modulation were enhanced significantly. Our results provide theoretical guidance for the design of high-performance photovoltaic devices and solar cells based on BAs/ZnO heterostructures.

Modeling of seismic wave scattering in poroelastic media

Understanding wave scattering in the earth is considered fundamental in describing seismic wave propagation and providing information on structural features of the earth’s interior. Petrophysical parameters (especially porosity and permeability) affect the reflection coefficients of subsurface interfaces, which can better explain the field data and infer the subsurface structure. However, the numerical solutions to the scattering problem for efficient modeling of wave propagation in poroelastic earth structures have limitations. We develop a numerical algorithm for solving the poroelastic scattering integral equations. Specifically, applying perturbation theory to Biot’s equations, the solutions are expressed by the Lippman-Schwinger integral equations, which can express the displacement and pressure fields. We derive the contrast-source integral equations of the decoupled poroelastic wave equations. We apply a conjugate-gradient fast Fourier transform method for fast solutions of the integral equations. We show that despite the complexity of the geologic structure, the numerical method enables the modeling of the displacement and pressure fields in the frequency and time domains. We determine that the wave scattering problem for the Biot model provides a good description to understand the earth’s interior.