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Ultrasonic solid coupling inspection is a non-destructive testing technique that employs solid materials as coupling mediums. In this study, we investigated the propagation characteristics of ultrasonic waves at interfaces in solid coupling. Additionally, we established a dry coupling interface model based on interface total load and roughness, from which we derived the reflection coefficient. Using the solid coupling material selected as per our optimization, solid coupling ultrasonic testing experiments were conducted. The experimental results demonstrate that the roughness of the solid j/coupling interface significantly reduces coupling efficiency, and increasing the pressure between solid interfaces enhances coupling performance. Through the developed stochastic rough interface model, we quantitatively analyzed the influence of rough interfaces and interface pressure, offering new insights into ultrasonic solid coupling inspection. [ABSTRACT FROM AUTHOR]

The demand for high-performance antennas tailored for 5G applications has stimulated research into novel designs and optimization techniques. This study focuses on the design, development, and optimization of microstrip patch antennas (MPAs) integrated with slots to enhance their performance in 5G communication systems. Various slot configurations, including rectangular and T-shaped slots, are incorporated into the ground plane of the patch antennas to investigate their impact on antenna characteristics such as gain, bandwidth, and radiation pattern. Simulation results demonstrate that the introduction of slots effectively increases the antenna's effective aperture, modifies current distribution, and enhances radiation efficiency. Furthermore, the strategic placement of slots improves antenna directivity and suppresses surface waves, leading to a notable improvement in antenna gain. Experimental validation corroborates the simulation findings, showcasing the practical feasibility and efficiency of the proposed slot-integrated antenna designs. Overall, this research contributes to the advancement of antenna technology tailored for the evolving requirements of 5G communication systems. [ABSTRACT FROM AUTHOR]

In this paper, we designed, analyzed, and simulated a 32-element antenna array for the sub-6 GHz band. Each radiating element is a square patch on a Rogers RT5880 substrate, featuring a relative dielectric permittivity of 2.2, a low-loss tangent of 0.0009, and a thickness of 0.508 mm, measuring 28.1×28.1 mm². Simulations were conducted using two electromagnetic solvers, advanced design system (ADS) and CST Microwave Studio, providing a comprehensive comparison of the results. To achieve a high balance between performance and antenna size, two 4×8 array antenna structures were designed. The simulations demonstrated excellent input impedance matching around 3.5 GHz for both configurations, with high gains of 20.5 dBi for the first and 18 dBi for the second configuration, along with directional radiation patterns. The dimensions were 315×576×0.578 mm² for the first configuration and 170×961×0.578 mm² for the second. These performance metrics make the proposed antenna arrays highly suitable for wireless communication technologies operating below 6 GHz, particularly for 5G mobile communications. [ABSTRACT FROM AUTHOR]

This research problem is an investigation of reflection amplitude in a nonlocal porous-thermo-micropolar diffusion half-space under memory dependent derivative (MDD) thermo-elasticity subjected to impedance boundary reflecting surface. The governing equations for nonlocal porous-thermo-micropolar diffusion medium in MDD theory are formulated. This research challenge is solved analytically for a two-dimensional model in order to demonstrate the presence of four coupled longitudinal waves and two paired transverse waves denoted as coupled longitudinal displacement wave ( cLDW − I ), coupled longitudinal thermal wave ( cLDW − II ), coupled longitudinal mass diffusion wave ( cLDW − III ), coupled longitudinal void volume fraction wave ( cLDW − IV ), and coupled transverse displacement wave ( cTDW ) and coupled transverse micro-rotational wave ( cTMW ). When there is nonlocality, diffusion, and porous characteristics in the medium, it is discovered to have an impact on these coupled longitudinal waves, making them dispersive and attenuating. The transverse wave is non-attenuating but dispersive, it is unaffected by diffusion and porous characteristics. To find the expression for the reflection coefficients of reflected waves, the plane wave reflection from a thermally insulated surface subjected to an impedance boundary is explored. For a specific material, the reflection coefficients of the reflected waves are calculated, and graphic representations of the fluctuations of the reflection coefficients versus the incidence angle, nonlocality, diffusion and porous constants are provided. For further investigation, energy ratio can be studied in future. [ABSTRACT FROM AUTHOR]

Liquid-based absorbers using frequency selective surfaces (FSSs) rely on 2D periodic lattices. Each unit cell contains one or more resonators filled with liquids, which dissipate electromagnetic energy. Water is preferred because of its wide availability and its high real and imaginary permittivity components. In this paper, we propose and optimize an all-dielectric unit cell structure placed on a metallic plane to function as an absorber when filled with water. A sharp and deep absorption resonance is obtained at 2 GHz, with a relative bandwidth of 14.5%. When optimized to work with methanol as absorbing liquid, the structure presents a resonance frequency of 1.25 GHz, with a relative bandwidth of 36.9%, and a second wide absorption band between 3.56 and 5 GHz. Field images are used to gain insight into the operation of the absorber. The sensitivity of the design to polarization, angle of incidence and temperature has been investigated. The proposed absorber has potential applications in scattering reduction, electromagnetic compatibility and energy harvesting. [ABSTRACT FROM AUTHOR]

A photonic crystal was created using a magnetic fluid–epoxy resin composite. The amplitude–frequency characteristics of the reflection coefficient of electromagnetic radiation in the microwave range from the resulting structure were experimentally studied. The possibility of using magnetic composites to create controlled photonic crystals was demonstrated. [ABSTRACT FROM AUTHOR]

This work presents the two port ultra-wide band MIMO antenna with novel isolation structure and dual band RF Rectifier for 3.3 GHz and 4.65 GHz frequencies for RF energy harvesting applications. The anticipated antenna is systematically examined within the ultra-wideband (UWB) range from 3.1 GHz to 10.6 GHz design frequency with four different steps: Antenna 1, Antenna 2, Antenna 3 and Antenna 4 (optimal design) are chosen for comprehensive study. A unique isolation structure was developed between two identical elements separated by 10 mm, resulting in an enhanced isolation of −23.5 dB at 3.15 GHz, −27 dB at 5.8 GHz, −28 dB at 9.26 GHz and greater than −34 dB at 7.5 GHz. The suggested antenna resonates at UWB band and have fractional bandwidth of 118.66 % and a peak gain of 4.1 dB at 3.15 GHz, 3.68 dB at 5.8 GHz, 6.4 dB at 7.5 GHz and 3.2 dB at 9.26 GHz has been obtained. Radiation efficiencies of 92.5 %, 95 %, 90 % and 84.5 % at 3.15 GHz, 5.8 GHz, 7.5 GHz and 9.26 GHz were obtained respectively. The recommended MIMO performance is simulated using HFSS in terms of ECC, DG, MEG and CCL. The results adhere to specified requirements and confirmed by experimentation. An HFSS simulated dataset of reflection coefficient is used as input for the various ML algorithms namely, Support Vector Machine (SVM), Ensemble, k-nearest neighbors' algorithm (KNN) and Gaussian Process Regression (GPR) models are trained with 80 % of the data and testing with 20 % of the data. The test results are compared and corresponding performance values of MAE, RMSE, MSE & R2 are 0.00029, 0.00197, 3.87e−6 and 1.0 validation results and corresponding test results are 0.00031, 0.00229, 5.20e−6 and 0.999. Finally, the proposed dual band rectifier with a shorted stub is tested for harvesting applications at 3.3 GHz and 4.65 GHz frequency and it attained RF to DC conversion efficiencies of 69 % and 55.40 % respectively. [ABSTRACT FROM AUTHOR]

Background. The using of mirror asymmetric chemical compounds for doping quartz makes it possible to metamaterial creation that has the chirality property. In such a compositional structure, unusual effects may arise when interacting with an optical wave. Aim. We calculate the transmission and reflection of a linearly polarized optical wave through a multilayer structure consisting of two doped quartz glasses separated by two air gaps. Methods. Based on a homogeneous mathematical model of a chiral metamaterial, taking into account the dispersion of the dielectric constant and the chirality parameter based on the matrix method, a system of linear algebraic equations is obtained for the complex reflection and transmission coefficients of an electromagnetic wave of linear polarization. Results. An analysis of the frequency and angular characteristics of the modules of the reflection and transmission coefficients was carried out at various values of the quartz doping level. It is theoretically predicted that at some wavelengths, most of the incident optical energy can be concentrated in the air gaps of the multilayer structure. Conclusion. The data obtained as a result of calculations can be used in the development of planar structures for frequency-selective concentration of energy in the visible and infrared spectrum based on quartz glasses doped with chiral chemical compounds.

Background. Plasma density variations caused by infrasonic wave can significantly affect conditions of propagation and reflection of whistler electromagnetic wave incident on the ionosphere from above. Aim. In that work, relationship between the coefficient of wave energy reflection from ionosphere, electromagnetic wave field near the ground surface and parameters of infrasonic wave are studied. Methods. The collocation method for solving the boundary problem for a plane-layered ionosphere and the perturbation theory method are used to find the electromagnetic wave field. Results. The greatest modulation of the reflection coefficient is associated with density perturbations at altitudes 80–110 km where whistler decay increases by an order of magnitude at the local altitude region (less than 15–20 km). In that case, the reflection coefficient variation can achieve 40 %. Conclusion. The results obtained are important for understanding the interconnection of magnetosphere radiation processes of different nature. The study of the modulation of coefficient of whistler reflection from the ionosphere is relevant for explaining the operation modes of a plasma magnetospheric maser.

The current paper reports on the crystal structure, microwave dielectric properties as well as the antenna parameters of (1-x)MgTiO 3 - xSrTiO 3 (abbreviated as (1-x)MT-xST) for x = 0.025, 0.05, 0.075, 0.1 ceramic based dielectric resonator antennas (DRAs). The (1-x) MT - xST samples have been prepared with the help of a solid-state reaction route. The SrTiO 3 was introduced to MgTiO 3 as a τ f compensator for developing a tunable τ f material. Rietveld refinement results of X-ray diffraction data suggest that all the samples exhibit a combination of two crystallographic phases i.e., rhombohedral (R-3) + cubic (Pm-3m). The SEM micrographs show clear and well-defined grains for (1-x)MT - xST (for x = 0.025–0.1) ceramics. The modes of vibration of the crystal structures of the materials have been identified by the Raman spectroscopy method. The bond strength, bond valency, bond energy, and tolerance factor have been determined for (1-x)MT - xST (for x = 0.025–0.1) materials. The microwave dielectric performances of ceramics have been analyzed over a frequency band of 1–10 GHz. It has been found that the dielectric constant is almost constant along the microwave frequency range. The behavioral change of tuned temperature coefficient of resonant frequency (τ f) along with quality factor have been reported. Besides, DRAs have been formed using all ceramic compositions, and simulations were performed to determine the various antenna properties, such as efficiency, input impedance, radiation properties, gain, and reflection coefficient. This study supports the use of microwave dielectric ceramics in antenna fields and highlights the enormous potential of (1-x)MT - xST for (x = 0.05) materials in communication systems. [ABSTRACT FROM AUTHOR]

Adhesive bonds, including car putty coatings, are used in the construction of modern motor vehicles. Therefore, it is important to improve methods that allow nondestructive evaluation of the properties of these joints. The main objective of this study was to evaluate selected properties of putty coatings such as the width of the applied coating and adhesion to the substrate based on changes in ultrasonic wave parameters. The research was carried out in two stages. In the first, the values of the surface wave amplitude were determined as a function of the width of the coating to the substrate. It was found that as the width of the coating increases, the amplitude of the surface wave pulse decreases. The second stage involved correlation studies to relate the reflection coefficient |r| to the adhesion of the coating to the substrate. Based on the results, it was found that as the value of the reflection coefficient decreases, the value of the coating's adhesion to the substrate increases. The determined values of this parameter range from 0.30 to 0.86, which correspond to the adhesion of the range 1.51 to 18.97 MPa. The obtained test results have practical significance and can be used in evaluating the condition of coatings in vehicle body repair shops. [ABSTRACT FROM AUTHOR]

We study the bistatic scattering properties of the samples of radio-absorbing composite materials and analyze the impact of diffraction effects at the edges of flat samples of small sizes (2–4 wavelengths of the incident wave) on the results of measurements of the reflection coefficient for a sample material, i.e., a bistatic characteristic that depends on the frequency of radiation in a broad range of the angles of incidence (10–85°). To reduce the influence of diffraction effects, we designed samples of various configurations made of magnetodielectric materials with frequency dispersions of dielectric and magnetic permeability. The samples have the form of metal plates one side of which is covered with the investigated material, while the other surfaces of the plate are covered with radiation-absorbent material. The scattering characteristics of the developed samples are numerically evaluated and experimentally measured on a bistatic installation in the anechoic chamber. The experimental data correspond to the numerical results. We observe a noticeable weakening of the influence of diffraction effects on the values of reflectivity in broad angular and frequency ranges. By using the numerical methods from the FEKO software package, we studied the influence of the configuration of samples on the systematic error of measuring of the reflection coefficients. It is also shown that this error can be reduced by using substrates of elongated shape in the plane of incidence (samples of hybrid configurations). The accumulated results can be used to measure the scattering characteristics of the materials in the free space, e.g., in refining the characteristics of the material. [ABSTRACT FROM AUTHOR]

This study deals with an oblique wave interaction by a floating rigid rectangular structure in the presence of a porous barrier which is placed in front of the floating structure. By considering the bottom topography as an elevated-type and a trench-type bottom, it is assumed that the train of water waves interacts with the porous barrier and the floating structure due to which it undergoes partial reflection. The boundary value problem in the fluid domain, which is split into five sub-regions, is solved by the utilization of separation of variables technique and eigenfunction expansion. The impact of the porous barrier and bottom topography on the reflection coefficient and hydrodynamic forces acting on the floating structure is discussed. As the distance of the porous barrier from the floating structure increases, an oscillatory pattern in the reflection coefficient is observed. Further, when the height of the elevated bottom or trench-bottom increases, the reflection coefficient increases in both cases; the reflection is higher in the presence of a trench than that due to the elevated sea-bed. The obtained results are validated against an established result which shows a very close match. • Water wave scattering by a rigid rectangular floating structure in the presence of a thin porous barrier is studied. • An elevated-type and a trench-type bottom topography are considered to represent the sea-bed. • The study aims to examine the variation of reflection and mitigation of forces acting on the rigid structure. • Significant variations in wave reflection and forces occur with changes in the porous-effect parameter of the barrier. • The effect of the various parameters on the reflection coefficient and hydrodynamic forces is also investigated. [ABSTRACT FROM AUTHOR]

Salt weathering is a common deterioration phenomenon that affects outdoor cultural properties, and it is important to precisely predict the heat, moisture, and salt transfer in porous materials to suppress salt weathering. Osmosis and osmotic pressure were considered in the field of soil research, especially in clay research, but not in the field of outdoor cultural properties and building materials, which are the main target of salt weathering. Osmosis in clay is supposed to be caused by its surface charge. However, it has been suggested that sandstones and bricks that constitute cultural properties and buildings also have surface charge as clay. Thus, osmosis and osmotic pressure can occur in building materials, which may lead to materials degradation. In this study, we derive basic equations, based on nonequilibrium thermodynamics, for the simultaneous heat, dry air, water vapor, liquid water, cation, and anion transfer in building materials by considering osmosis. This equation was compared with existing model for heat and moisture transfer equations as well as models that considered the salt transfer. Based on the previous research for osmosis in clay, we summarized conditions under which osmosis occurs in building materials and presented an outlook for modeling the physical properties of materials related to osmosis. [ABSTRACT FROM AUTHOR]

In this article, a set of equations is derived to find incident and load power explicitly in terms of load and source reflection coefficients in a lossless transmission line mismatched to both source and load impedances. A transmission line can be mismatched as the frequency varies if the source and load impedances are frequency dependent. Unlike in a scenario, where the transmission line is either matched to the source or load, the incident and load power depends on the length of the transmission line when both the source and load impedances are not matched to the line. The equations derived show that the power varies with the line length with a period of half wavelength. The maximum and minimum incident and load power with the corresponding line lengths are derived. The use of the Smith chart to find these lengths and the ratio of maximum to minimum is also described. Finally, three applications of the results including an additional version of the Friis transmission equation and the bandwidth improvement of power transfer for frequency dependent source and load impedances are presented. [ABSTRACT FROM AUTHOR]

Using an asymptotic method, this article deals with flexural-gravity wave scattering with undulating bottom topography, including the effect of uniform currents. The interest in this problem lies in developing second-order solutions using the Fourier transform, which minimises the error gap between first and second-order solutions. The present method allows the physical processes involved in the sea-bed topography, uniform current, plate-covered surface, and wave interaction to be studied. Specifically, we observe Bragg resonance between the flexural-gravity waves and the bottom ripples, which are associated with the reflection of incident wave energy. We examine the effects of wave current and emphasise how crucial the asymptotic expansion method is to the emergence of the current response. We demonstrate that bottom topography dominates the effects of Bragg resonance for depth Froude numbers valued at 0.8 or less. Further, most reflected wave components have their frequencies shifted by the current, and wave action conservation causes reflected wave energy to be enhanced for following currents. Using the Joint North Sea Wave Observation Project spectrum and the discrete Fourier transform, the theory derived in the frequency domain is shown in the time domain to analyse wave propagation through the whole system. • A mathematical model to study flexural-gravity wave scattering with undulating bottom in the presence of uniform current. • The problem is studied using an asymptotic approach under linear water wave theory. • Develop the second-order solutions using the Fourier transform technique. • Identify the existence of Bragg resonance between the flexural-gravity waves and the bottom ripples. • The frequency domain analysis is illustrated in the time domain using JONSWAP. [ABSTRACT FROM AUTHOR]

Linear surface gravity wave scattering by a partial porous breakwater is studied in a two-layer ocean having an interface with bottom undulations. The partial breakwaters, namely surface-piercing breakwater (SPB) and bottom-standing breakwater (BSB), are considered. The continuity of fluid pressure and mass flux is applied at interface boundaries, while mass conserving conditions are employed to account for slope discontinuity in seabed geometry. Porous breakwaters' reflective and dissipative characteristics are studied under wave-wave interaction. The study reveals that when a mound bottom is present, more incident waves in interface mode are transmitted through BSB, while more waves in surface mode are dissipated. More incident waves in surface mode are transmitted through SPB, while more waves in interface mode are dissipated. In contrast, more transmission occurs in surface mode through both BSB and SPB for a slope-shelf bottom. However, the breakwater dissipates a substantial amount of incident-wave energy in interface mode. Further, a considerable reduction in wave transmission occurs due to higher reflection by the interface-piercing porous breakwaters, and the breakwaters experience high wave loads. Relatively, porous breakwater dissipates less wave energy in shallow depth. The study reveals that the dead water effect is weakened by the porous breakwater. [ABSTRACT FROM AUTHOR]

The research article deals with the reflection of plane waves in a micropolar thermoelastic diffusion solid half-space with voids in the context of Lord-Shulman theory of thermoelasticity. The governing equations are formulated to obtain two velocity equations. The plane wave solution of these velocity equations indicate the existence of six plane waves, a set of four coupled longitudinal displacement waves and a set of two coupled transverse displacement wave namely coupled longitudinal displacement wave $ (LD - 1) $ (LD − 1) , coupled thermal wave $ (LD - 2) $ (LD − 2) , coupled mass diffusion wave $ (LD - 3) $ (LD − 3) , coupled longitudinal void volume fraction wave $ (LD - 4) $ (LD − 4) and coupled transverse displacement wave $ (TD - 1) $ (TD − 1) , coupled transverse micro-rotational wave $ (TD - 2) $ (TD − 2). A reflection of the plane wave from a stress-free thermally insulated surface is studied to obtain the reflection coefficients and energy ratios of reflected waves. The reflection coefficients and energy ratios of the reflected waves are computed for a particular material and the variations of the reflection coefficients and energy ratios against the angle of incidence are shown graphically. [ABSTRACT FROM AUTHOR]

Within the framework of the impedance concept, approximate analytical formulas for the distributed surface impedance of the magnetodielectric layer with the inhomogeneous permeability and permittivity located on a perfectly conducting plane (PCP) for the cases of a quadratic law of changes in electrical parameters along the layer thickness are obtained. A comparative analysis of electromagnetic waves reflection coefficient from this structure for various laws of change of the permeability and permittivity is presented.

Background. Taking into account temperature, soil composition, surface roughness and the dependence of effective dielectric constant on frequency allows a more accurate assessment of soil moisture and other important parameters, which can be used in various fields such as agriculture, geology, ecology and hydrology. Aim. In this work, we calculate the reflection of a linearly polarized electromagnetic wave from wet soil, taking into account such physical factors as heterogeneity of soil structure, surface roughness and dispersion. Methods. Based on a heterogeneous mathematical model of wet soil, taking into account the dispersion of the dielectric constant of water and surface roughness, expressions are derived for the complex reflection coefficients of electromagnetic waves of vertical and horizontal polarization. Results. The model of loose wet soil with the standard deviation of roughness on the surface was chosen as the object of study. An analysis of the frequency and angular characteristics of the modules of the reflection coefficients was carried out at a fixed level of soil moisture. Conclusion. The data obtained as a result of the calculations is a valuable tool for further improving methods of remote sensing of the Earth and contributes to the development of new technologies for monitoring soil parameters using unmanned aerial vehicles, which opens up prospects for more accurate and efficient analysis of the state of land resources and ecosystems.

Subject and Purpose. The paper is aimed at suggesting ways for implementing electromagnetic devices that would involve a nonlinear dielectric inside the structure for concentrating electromagnetic field within it at relatively low intensities of the excitation field. A representative example is offered by a Fabry-Pérot resonator with semi-transparent mirrors and a nonlinear dielectric inside. Methods and Methodology. The paper presents a fundamentally new approach to controlling the frequency response of a metasurface, and a method for protecting electronic modules from high excitation powers. The method is based on the use of nonlinear properties of a Fabry-Pérot "resonator-capacitor" containing a nonlinear dielectric in its volume. Thus, we propose a method for creating spatial filters and antenna protecting fairings capable of active reconfiguration. Results. Analysis of the results has shown that by changing the voltage across the resonator-capacitor plates it is possible to control the degree of electromagnetic field localization in the resonator volume. The frequency response of the metasurface based on the Fabry-Pérot resonator with a nonlinear dielectric inside can be reconfigured by changing the voltage applied to the resonator mirrors. The advantages provided by electrical control of the frequency-selective characteristics include an increased efficiency and possibility of integrating digitally controllable systems into antennas. Conclusions. The use of a Fabry-Pérot "resonator-capacitor"model, with a nonlinear dielectric inside, in the capacity of a reconfigurable metasurface, else as a power limiter in a variety of devices, has sufficient prospects for application in microwave transmitting systems. A special area of application for the reconfigurable Fabry-Pérot resonators is creation of broadband receive antenna systems for direction- finding. In essence, the proposed Fabry-Pérot resonator is a reflective antenna array with an ability to exhibit, conceal or alter its electrodynamic properties according to a certain algorithm. This opens up prospects for its application in "friend-or-foe" recognition systems, reflective beacons, navigation systems, etc.

Different types of resonators are used to create acoustic metamaterials and metasurfaces. Recent studies focused on the use of multiple resonators of the dipole, quadrupole, octupole, and even hexadecapole types. This paper considers the theory of an acoustic metasurface, which is a flat surface with a periodic arrangement of multipole resonators. The sound field reflected by the metasurface is determined. If the distance between the resonators is less than half the wavelength of the incident plane wave, the far field can be described by a reflection coefficient that depends on the angle of incidence. This allows us to characterize the acoustic properties of the metasurface by a homogenized boundary condition, which is a high-order tangential impedance boundary condition. The tangential impedance depending on the multipole order of the resonators is introduced. In addition, we analyze the sound absorption properties of these metasurfaces, which are a critical factor in determining their performance. The paper presents a theoretical model for the subwavelength case that accounts for the multipole orders of resonators and their impact on sound absorption. The maximum absorption coefficient for a diffuse sound field, as well as the optimal value for the homogenized impedance, are calculated for arbitrary multipole orders. The examples of the multipole resonators, which can be made from a set of Helmholtz resonators or membrane resonators, are discussed as well.

Technologies for the manufacture of microwave electromagnetic shields based on powdered carbon, foil and composite multilayer materials are presented. Technological methods for their manufacture and shielding properties are described, and the main mechanisms leading to increased shielding properties are considered depending on the manufacturing technology, composition and alternation of composite layers. It is shown that the values of the reflection coefficient of electromagnetic radiation in the frequency range 2–17 GHz for the shields considered reach a value of (–20) dB. Microwave absorbers with a reflection characteristic lower than (–10.0) dB (down to (–52.0) dB) in the frequency band 8.0–12.0 GHz are developed, and the electrophysical parameters, composition and concentration of components of the composite materials for such microwave absorbers are determined. The systems for active protection of speech information that use combined masking signals consisting of “white” noise and speech-like signals as masking signals, along with “white” noise are considered. Criteria have been developed for the approach to selecting speakers and audiences when assessing speech intelligibility to solve problems of protecting speech information and methods for experimental studies of speech intelligibility against a background of masking acoustic noise. Technologies for the formation of nanocomposites based on carbon nanotubes and nanoparticles of ferromagnetic materials are presented to increase the degree of coherence of the spin texture at macroscopic distances, increase the degree of security of electronic products to strong magnetic fields and noise immunity. It has been shown that at certain concentrations of ferromagnetic nanoparticles, micromagnetic parameters increase, ensuring high performance of active elements in magnetic fields. The role of carbon in this case turns out to be decisive. The presented results seem promising for use in the creation of anechoic chambers, partitions for separating indoor zones intended for the location of electronic devices, products for protecting humans from the effects of electromagnetic radiation in the microwave range, and the formation of combined masking signals in the form of “white” noise for devices protection of speech information, composite coatings to level out the effects of a constant magnetic field on electronic products.

Cyanobiphenyls (CBs) are a class of molecules with unique properties that make them highly versatile in various fields. Their anisotropic nature, low viscosity, and sensitivity to external stimuli make them ideal for applications in display technology, photonic devices, sensors, and in tunable antennas. In this article, we present the design and simulation of a 5CB LC antenna for tunable microwave frequency applications due to its fast response time and low dielectric loss than other CB materials. The proposed antenna contains two glass substrates with an air gap of 0.004 mm between them. The lower glass contains a size of 20 × 15 mm2, while the upper glass contains a size of 13 × 15 mm2. The proposed antenna produces two bands when there is an air gap between the glass plates; three bands when diodes are used for the radiating patch; and four bands when 5CB LC material is introduced between the glass plates as a dielectric medium. The same structure produces various frequency bands, which is a notable advantage compared to the existing state of the art. All the results shown in this manuscript were simulated and measured with the body of data available from the literature. [ABSTRACT FROM AUTHOR]

In recent studies, two‐dimensional propagation model of fast magnetosonic (MS) waves has been proposed to interpret the satellite observations of MS waves knocking into a density boundary. Although the theoretical model is able to capture the main properties of the two‐dimensional propagation of MS waves, quantitative description about the MS wave behaviors has not been given yet. Here, with the assumption of a parabolic function for the potential function near its minimum, we solve the wave equation only with a potential function to obtain the reflection coefficients. It is found that the wave equation with a potential function can describe the full reflection and full transmission of MS waves rather well. Furthermore, the first‐order derivative term in the wave equation is utilized to modify the reflection coefficient when the minimum of the potential function is near zero. Our result is helpful for further understanding the two‐dimensional propagation of MS waves. Plain Language Summary: Fast magnetosonic (MS) waves have been demonstrated to play an important role in the dynamical evolution of radiation belt electrons. As ray tracing simulations have shown that MS waves propagate around the magnetic equator, wave equation of the two‐dimensional propagation model is given to describe the behaviors of MS waves. In the wave equation, the potential function is the key factor to determine the wave behaviors (full reflections, full transmissions, or partial reflections). However, the first‐order derivative term in the wave equation should take effects, especially when the potential function is near zero. Here the reflection coefficients in the both cases where the first‐order derivative term is included or not have been given. Our results are also compared to the full wave simulation results. It is suggested that the first‐order derivative term is important to give a reasonable result when partial reflections occur. Otherwise, the potential function can describe the wave behavior rather well. Key Points: Analytical expression of reflection coefficient for two‐dimensional propagation of MS waves emerging density boundaries has been givenWe find that the behavior near the minimum potential function can be described by a Weber differential equationCorrection near the minimum potential function has been provided to give a more reliable physical solution [ABSTRACT FROM AUTHOR]

The present work analyzes the interaction of oblique waves by a porous flexible breakwater in the presence of a step-type bottom. The physical models for both scattering and trapping cases are considered and developed within the framework of small amplitude water-wave theory. Darcy's law is used to model the wave interaction with the porous medium. It is assumed that the varying bottom extends over a finite interval, connected by a finite length of uniform bottom near an impermeable wall, and a semi-infinite length of bottom in the open water region. The boundary value problem is solved using the eigenfunction expansion method in the uniform bottom regions, while a modified mild-slope equation (MMSE) is used for the region with the varying bottom. Additionally, a mass-conserving jump condition is employed to handle the solution at slope discontinuities in the bottom. A system of equations is derived by matching the solutions at interfaces. The reflection coefficient and force on the breakwater and impermeable wall are plotted and analyzed for various parameters, such as the length of the varying bottom, depth ratio, angle of incidence, and flexural rigidity. It is observed that moderate values of flexural rigidity and depth ratio significantly contribute to an optimum reflection coefficient and reduce the wave force on the wall and breakwater. Remarkably, the outcomes of this study are assumed to be applicable in the construction of this type of breakwater in coastal regions. [ABSTRACT FROM AUTHOR]

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Different types of resonators are used to create acoustic metamaterials and metasurfaces. Recent studies focused on the use of multiple resonators of the dipole, quadrupole, octupole, and even hexadecapole types. This paper considers the theory of an acoustic metasurface, which is a flat surface with a periodic arrangement of multipole resonators. The sound field reflected by the metasurface is determined. If the distance between the resonators is less than half the wavelength of the incident plane wave, the far field can be described by a reflection coefficient that depends on the angle of incidence. This allows us to characterize the acoustic properties of the metasurface by a homogenized boundary condition, which is a high-order tangential impedance boundary condition. The tangential impedance depending on the multipole order of the resonators is introduced. In addition, we analyze the sound absorption properties of these metasurfaces, which are a critical factor in determining their performance. The paper presents a theoretical model for the subwavelength case that accounts for the multipole orders of resonators and their impact on sound absorption. The maximum absorption coefficient for a diffuse sound field, as well as the optimal value for the homogenized impedance, are calculated for arbitrary multipole orders. The examples of the multipole resonators, which can be made from a set of Helmholtz resonators or membrane resonators, are discussed as well. [ABSTRACT FROM AUTHOR]

The fifth-generation technology is popular and best as far as data rates are concerned for wireless applications. To meet the increased demand of the modern world for faithful communication, this research work is carried out. In this approach, a single patch, 1×2 array, and 2×2 array are designed using a low-cost FR4 dielectric substrate (Є𝑟=4.4) covering the 3.3-3.8 GHz frequency band. Due to the lack of gain from arrays in the present research, an attempt is made to achieve excellent gain from arrays with a minimum number of patches. First, the gain of a single inset-fed antenna is compared with another normal single patch of the same thickness but with an additional air dielectric medium. Next, the second single patch is extended to obtain a rectangular 1×2 array and a 2×2 array antenna. A second single patch measuring 50×32.5×0.8 mm is designed assuming an infinite ground plane. It has 3 mm air gap between the patch strip and the ground. Air acts as a second dielectric layer that reduces power loss. This allows a maximum gain of 15.2 dB with a return loss of -22 dB. Also, antenna efficiency and bandwidth are 91% and 267.69 MHz, respectively. [ABSTRACT FROM AUTHOR]

The paper investigates the possibility of fabricating a carbon nanotubes (CNT)-modified nanocomposite based on pyrolyzed polyacrylonitrile (PPAN). The layered structure of PPAN ensures the attachment of nanotubes (NT) to the polymer matrix, forming enhanced PPAN/CNT nanocomposites. We synthesized a PPAN/CNT polymer nanocomposite and investigated its mechanical, conductive, and electronic properties. Using the quantum chemical method density functional theory (DFT), we studied an interaction mechanism between PPAN and single-walled carbon nanotubes. We described the structural features and electron energy structure of the obtained systems. We found that the attachment of a CNT to the PPAN matrix increases tensile strength, electrical conductivity, and thermal stability in the complex. The obtained materials were exposed to electromagnetic radiation and the dielectric constant, reflection, transmission, and absorption coefficients were measured. The study demonstrates the possibility of using carbon nanotubes for reinforcing polyacrylonitrile polymer matrix, which can result in the development of an enhanced class of materials possessing the properties of both polymers and CNTs. [ABSTRACT FROM AUTHOR]

The incidence of electromagnetic H-wave on the thin metal layer at the angle of theta is considered, taking into account the dependence of the specularity coefficients on the surfaces of the thin layer q1 and q2 on the angle of incidence of electrons. The behavior of reflection, transmission and absorption coefficients depending on the thickness of the thin layer is analyzed. The obtained results are compared with experimental data. [ABSTRACT FROM AUTHOR]

The standard configuration of a sonic black hole (SBH) is a discrete set of rings with back cavities at a duct termination, whose inner radii decrease according to a power-law. Although several practical realizations of this type of slow-sound waveguide have been investigated, the continuous problem in which the number of ring/cavity sets goes to infinity has not been analyzed in depth. Understanding its performance is interesting in itself and could provide clues for new designs. For this purpose, we transform the generalized Webster equation for the acoustic pressure inside the ideal SBH into a spatially varying wavenumber Helmholtz equation for a new locally scaled pressure. We eliminate the singularity of the original problem at the SBH termination by considering a rigid residual surface that will be shown to play a role analogous to that of the acoustic black hole (ABH) residual thickness in beams and plates. The variational formulation of the Helmholtz equation is presented and solved by expanding the unknown scaled pressure in terms of a basis of Gaussian functions. The same framework is used to set up an eigenvalue problem that provides the SBH modes and thereby a modal decomposition for the pressure within the SBH. Once the theoretical foundations are established, the variation of the speed of sound and wavenumber in the SBH is presented. The dependence of the shape and distribution of the modes on the residual surface and damping helps to clarify the occurrence and disappearance of oscillations in the input admittance and reflection coefficient of the SBH at different frequencies. For the latter, a detailed parametric study is carried out. Alternative profiles to the power law are also investigated, some showing reflection coefficient values similar to those of the classical SBH. • Sonic black holes at the end of ducts provide minimal wave reflection. • A theoretical approach is proposed to solve the SBH governing equation. • The modal distribution in the SBH is strongly affected by the residual radius. • The modal distribution explains the oscillations in the reflection coefficient. • Alternative SBH profiles to the power law are studied. [ABSTRACT FROM AUTHOR]

BACKGROUND: Food adulteration has long been considered a major problem. It compromises the quality, safety, and nutritional value of food, posing significant risks to public health. Novel techniques are required to control it. RESULTS: A graphene‐based T‐shaped monopole antenna sensor was tested for its ability to detect adulteration in liquid foods. Mustard oil was the pure reference sample used for product quality analysis. Olive oil and rice bran oil were adulterants added to the pure sample. It was found that the sensor could be immersed easily in the liquid sample and provided precise results. CONCLUSION: The graphene‐based T‐shaped monopole antenna sensor can be used for the quality assessment of liquid food products and is suitable for real‐time monitoring. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Despite the increasing interest in acoustic silencer design for various noise control applications, the good matching performance duct design has not been getting much interest. The present work gives the theoretical study and the experimental verification of the matching performance to plane sound waves in a one-dimensional duct lined with a parabolic increasing microperforated area. The wave propagation inside the duct is modelled using the boundary element method (BEM), and its solution is derived using the modified Hankel function. The matching performance, namely the wave impedance, and the sound reflection coefficient at the duct inlet were computed when this duct is inserted between two similar hard ducts. Ducts lined with different duct parameters of length, cross-section diameter, graduality of the wall conductance of different micro-perforation characteristic parameters were considered. The wave impedance and the sound reflection coefficient of a single slit treatment, at the duct inlet were theoretically studied and discussed. Also, ducts of multiple treatments by equal and similar slit areas of micro-perforation were studied. The theoretical study of the proposed duct design shows that the matching performance can be improved by tuning both duct parameters and MPP liner physical characteristics, especially for liners in which the reactive part of its impedance is less or equal to its resistive part, and a reflection coefficient of less than 0.15 which is the reflection-free condition, is obtained in a wideband frequency from low frequency, from 200 Hz to the first high mode frequency in the duct. In comparing the theoretical and experimental measurement data, a reasonable agreement has been found for both the sound impedance and the sound reflection at the duct inlet [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the interaction of acoustic waves with a layer of multifractional vapor–gas–droplet mixture with polydispersed inclusions of different sizes and materials. A mathematical model that determines the oblique incidence of an acoustic wave on a layer of finite thickness is presented.The calculations results of acoustic wave reflection from a layer of multifractional vapor–gas–droplet mixture are presented. The influence of layer thickness, mass concentration, inclusion sizes, phase transitions, and the angle of wave incidence on the reflection of acoustic waves from the layer of multifractional polydispersed vapor–gas–droplet mixture has been analyzed. [ABSTRACT FROM AUTHOR]

The increasing need for high-speed telecommunications has motivated extensive research on fifth-generation (5G) technology. Many industries require quick data throughput, low latency, and consistent radiation patterns utilizing 5G techniques. This article proposes an antenna with two simulations and measurements for different 5G applications. It is tiny and operates at a wide frequency range of 1 to 9 GHz, making it suitable for various modern systems. The results obtained from this antenna were superior to those proposed in previous articles. It is observed that the reflection coefficient ratio is much less than -10 dB for both the simulation and measurement sides at all frequencies. In addition, the highest value of the reflection coefficient is -82 dB at 8 GHz. The antenna's maximum gain and efficiency are 9.8 dB and 98%, respectively. Thus, the best antenna performance when measuring the voltage standing wave ratio (VSWR) parameter at 8 GHz is up to 0.3. It has been discovered that the measured radiation pattern is nearly omnidirectional and matches the simulated radiation pattern exactly. The discrepancies between the design proposed and the authors' designs in other recent works are that it is based on a spatial and aperture technique for both the patch and ground layers. Therefore, the antenna achieved good results of wide bandwidth, high efficiency, gain, etc. Furthermore, it has been concluded that the antenna is well-suited for many applications within the 5G Internet of Things (IoT) ecosystem. [ABSTRACT FROM AUTHOR]