Reflected Wave Energy Research Articles

Influence of density variations of ionosphere plasma on the conditions of electromagnetic whistler waves propagation in the ionosphere

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.

Wave trapping by porous breakwater near a rigid wall under the influence of ocean current

The present work investigates the water wave interaction with bottom-standing thick porous trapezoidal-shaped structures and shore-side vertical rigid wall in the presence of uniform ocean currents. This study has been done to understand the impact of different physical parameters like friction, porosity, and ocean currents along with different structural parameters (width and height) on different phenomena like wave energy reflection, wave forces, wave energy dissipation, etc. The quadratic boundary element method-based numerical technique has been used to solve the boundary value problem. The structural porosity is modeled using Sollitt and Cross’s model of water wave interaction with thick porous structures. Several results associated with the wave energy reflection and energy dissipation have been analyzed. Also, the wave force exerted by the incoming waves has been investigated to check the stability and sustainability of the right vertical rigid wall and porous structure. The Doppler-shift effect is observed in wave transformation characteristics due to the presence of ocean currents. The impact of following and opposing ocean currents can be seen in the graph of wave energy reflection, dissipation, and wave forces. The periodic patterns can be observed clearly in wave characteristics like wave energy reflection, dissipation, and wave forces when plotted against the non-dimensional separation gap between the porous breakwater and shore-side rigid seawall.

ON THE PECULIARITIES OF REFLECTION OF SHEAR WAVES WITH LINEAR POLARIZATION FROM THE ROUGH SURFACE OF A CRACK

The reflection coefficient of shear waves with SV- and SH-linear polarization from a statistically inhomogeneous surface consisting of scattering linear elements with a feature of their height distribution according to the normal law in a two-dimensional approximation is estimated. The estimation of the reflection coefficients in the reverse and forward directions is based on the calculation of the reflected wave energy flow propagating from an inhomogeneous surface averaged over the possible values of the height of the reflecting elements. It is theoretically shown and confirmed experimentally that the ratio of the coefficients of the reverse reflection of SH- and SV-polarization waves is significantly greater than 1, which provides better detection of cracks by SH-waves. The peculiarity of the behavior of the dependence of the coefficients of the reverse and direct reflected signal of the SV-polarization waves on the mean square deviation corresponds to the results of theoretical estimates. The coefficient of variation of the ratio of reflection coefficients shows the statistical stability of the direct reflected signal, which determines the feasibility of using such a signal to measure the equivalent area of the reflector.

Flexural-gravity wave interaction with undulating bottom topography in the presence of uniform current: An asymptotic approach

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.

Crystal structure and peculiarities of microwave parameters of Mg1-xZnxFe2O4 nanospinel ferrites

Employing an advanced citrate precursor methodology, we successfully synthesized nanoscale spinel ferrites, denoted as Mg1-xZnxFe2O4 (where x ranges between 0.0 and 1.0) or MZFO. Comprehensive analysis, utilizing state-of-the-art X-ray diffraction (XRD) techniques, demonstrated the defining attributes of the crystal structure. All examined specimens consistently exhibited a singular phase, adopting a cubic crystalline architecture. XRD pattern analysis allowed us to deduce the average particle dimensions of these ferrite specimens, which span between 17.2 nm and 31.5 nm. This observed size distribution corroborates well with transmission electron microscopy (TEM) imagery estimations. Delving into the Fourier-transform infrared (FTIR) spectra, two distinctive absorption bands of ferrites emerged: the first between 540 and 570 cm−1 and the subsequent between 339 and 435 cm−1. To glean insight into the electromagnetic attributes of MZFO, we meticulously assessed the experimentally ascertained S-parameters. This scrutiny spanned a frequency spectrum of 8–18 GHz. It was inferred that electromagnetic wave energy dissipation arises chiefly from a combination of electrical and magnetic phenomena. The underlying mechanisms of electrical dissipation can be attributed to polarization processes. Concurrently, the magnetic energy losses predominantly stem from magnetization reversal dynamics. Notably, a substantial attenuation observed in the reflected wave energy, ranging between −10 and −18.5 dB, augments the potential for this material's integration into practical applications.

Design and experimental verification of phase-reversal Fresnel lens for contact stress characterization

The accurate characterization of the contact stress on the mating surfaces of assembly components is a key means to ensure the assembly accuracy and operational safety of aero-engines. In this paper, a phase-reversal Fresnel lens for contact stress characterization is designed to solve the problem of low spatial resolution of contact stress characterization by the non water immersion ultrasonic method. The phase-reversal Fresnel lens is used to focus the ultrasonic wave on the mating surface of the assembly components to improve the spatial resolution of the contact stress characterization. The finite element simulation method is used to analyze the influence of the number of lens rings, the piezoelectric plate's diameter, the lens's thickness, and the groove depth on the focusing characteristics of Fresnel lenses. The power spectrum peak is used to analyze the residual reflected wave energy of the mating surface. According to the correlation between the residual reflected wave energy and the contact stress, a correlation model between the two is built to realize the characterization of the contact stress. This study provides a promising method for the characterization of contact stress on the mating surface of aero-engine assembly components by non water immersion focused ultrasound.

Quantitative monitoring of tensile force in post-tensioning systems using piezoelectric wave method

ABSTRACT The tensile force of a post-tensioning system is essential in prestressed concrete structures. Since the tensile force is related to the contact pressure at the interface between the anchor head and the bearing plate, this study utilizes the piezoelectric wave method to quantitatively monitor the reflected wave energy at the interface. A 3D solid element model was developed to simulate the propagation of stress waves in a simplified anchorage system across different contact areas. Three independent tests were conducted on a simplified 2-strand anchorage system, using the reception coefficient as a monitoring index. The empirical fitting formula between the reception coefficient and the load is derived from the loading data and verified using the unloading data. The experimental results demonstrate good monotonicity and stability within the test range. The study also conducted two temperature-based tests to investigate the effect of small temperature variations on the proposed method. The results indicate that temperature fluctuations of less than 20°C have little effect on the test method. Then, the proposed method is applied to a real 2-strand anchorage system in a concrete beam. The proposed method serves as a reference for quantitatively monitoring the prestressing force of a post-tensioning system.

Modulating microwave attributes of Ba1−xSrxTiO3 nanoparticles: Insights into strontium concentration, structural intricacies and electromagnetic dynamics

In this pioneering investigation, we meticulously synthesized Ba1−xSrxTiO3 nanoparticles, with Sr concentrations varying between 0.0 and 0.4 at intervals of 0.1, via a refined chemical approach. The crux of our study lies in establishing the intricate correlations between the chemical constitution (primarily Sr concentration), salient structural attributes (encompassing lattice and microstructural parameters), electrical dynamics and consequential microwave characteristics. X-ray diffraction (XRD) analyses reinforced the unity between the average ionic radii of the Ba/Sr ions and the lattice constants. Scanning electron spectroscopy (SEM) furnished insights into the microstructural intricacies, while the nominal chemical composition was ascertained via energy-dispersive X-ray (EDX) spectroscopy. A deep dive into the electrical realm revealed the temperature and field-dependent behaviors of permittivity, tangent losses and polarization. The electromagnetic traits of Ba1−xSrxTiO3 (where 0.0 < x < 0.4) were meticulously delineated by analyzing the experimentally determined S-parameters across a frequency spectrum of 6 to 18 GHz. Our findings elucidate that the predominant losses of electromagnetic wave energy are attributable to aggregated electrical losses, predominantly steered by polarization processes. Our findings demonstrate a significant attenuation in the reflected wave energy, with values spanning from − 14.3 to − 17.1 dB, highlighting the potential of these nanoparticles for cutting-edge applications in electromagnetic interference mitigation.

Structural, magnetic, and microwave features of Sc3+ ions substituted Sr0.5Ba0.5Fe12O19 nanohexaferrites

In this study, magnetic, structural, and hyperfine interactions of Sc3+ ion substituted Sr0.5Ba0.5Fe12O19 (Sr0.5Ba0.5ScxFe12−xO19 (x ≤ 0.1)) nanohexaferrites (Sc→SrBa NHFs) have synthesized through the sonochemical approach. The structure and morphology were studied by XRD, SEM, HR-TEM, and TEM along with EDX. XRD analysis confirmed the hexaferrite formation having crystallite within the range of 45 to 79 nm. Both TEM, HR-TEM, and SEM analyses proved the hexagonal morphology of all products. All products show ferrimagnetic hysteresis loops at both Ts. The evaluation of M(H) hysteresis loops indicated that the Ms (saturation magnetization), Mr (remanence), Hc (coercivity), and nB(Bohr magneton number) gradually decline with the incorporation of Sc3+ ion. Higher doping contents (x ≥ 0.08) revealed a considerable decline in Mr and Hc, showing significant changes from hard to soft magnetic behavior at higher contents. Mössbauer spectra show that Sc3+ ions are located at commonly octahedral (Oh) 4 f2 site. It was also determined that a small amount of Sc3+ occupied the 2b site. The microwave features of the products were determined by measuring S-parameters within the 2–10 GHz range. It was presumed that the energy losses resulting from reflection encompass both electrical and magnetic loss components. The average value of the reflection coefficient is − 14.48–14.24 dB. A noteworthy attenuation of the reflected wave energy opens up broad prospects for practical applications as coatings for providing electromagnetic compatibility.

Impact of the Sc3+/In3+ co-substitution on the structural, magnetic, and microwave characteristics of Co0.5Ni0.5Fe2O4 nanospinel ferrites

In this article, In3+ and Sc3+ ions dual-substituted NiCo nanospinel ferrites (ScIn→CoNiFe2O4 NSFs) have been synthesized through citrate-gel auto combustion method to investigate the effect of In3+ and Sc3+ ions on magnetic, and microwave characteristics. The following techniques TEM, SEM, EDX, and XRD were applied to characterize surface morphology, chemical composition, phase identification, and crystallinity of products, respectively. The XRD verified a phase formation of spinel structure with a minor amount of Sc2O3 was observed for products having x ≥ 0.04. The average crystal size (DXRD) of the products was estimated within the 33–68 nm range using the Scherrer equation. SEM and HR-TEM analyses exhibited accumulating sphere-shaped particles. By fitting the room-temperature spectra obtained from Mössbauer spectroscopy (Moss), Hyperfine interactions were determined. The cation distribution shows that there is a migration of In3+ ions in the lattice in an A→B direction with increasing concentrations while the B site is preferred by the larger Sc+3. M−H plots for 300 and 10 K illustrated all products carried out with a ferrimagnetic character. An enhancement in saturation magnetization (Ms) was remarked with Sc–In doping ratio up to 0.04 and thereafter a drop as the Sc–In concentration increased. The tendency in Ms values might be described by correlating it to the cation distribution amongst Oh and Td (octahedral and tetrahedral, respectively) sublattices. Temperature-dependent magnetization measurements were also investigated, which further confirmed the maintenance of the ferrimagnetic character throughout the temperature range 10–300 K. The peculiarities of the microwave properties have been analyzed by the measured S-parameters in the range of 6–18 GHz. It was assumed that the energy losses due to reflection are a combination of electrical and magnetic losses due to polarization processes and magnetization reversal processes in the region of inter-resonant processes. The average value of the reflection coefficient is −14.48 … −14.24 dB. A significant attenuation of the reflected wave energy opens up broad prospects for practical applications as coatings for providing electromagnetic compatibility.

Surface defect identification based on broadband laser-generated Rayleigh wave with wavenumber filtering

As a non-contact, couplant-free and nondestructive technique, the laser ultrasonic technology has great potential for detecting surface defects. In this paper, we propose a surface defect identification method based on broadband laser-generated Rayleigh wave with wavenumber filtering in an area scanning mode. Firstly, a particular lowpass filter is constructed in frequency-wavenumber domain to extract the scattered wave generated by the defects, and then a surface defect image can be reconstructed based on the broadband scattered wave wavenumbers. Secondly, a threshold denoising method is employed to enhance the signal-to-noise ratio and improve the image sharpness. Thirdly, the experimental validation is carried out, in which a laser ultrasonic detection system is used to detect the surface defects of aluminum alloy specimens and identify their different parameters. The experimental results verify that the proposed method can identify the location, size and orientation of surface defects effectively, meanwhile, its imaging effect shows significantly superior to that of the conventional reflected wave energy and standing wave energy methods. Furthermore, the correlation between maximum local scattered wave energy and the depth of defects is found, which can characterize the severity of the surface defects.

SPATIAL VARIABILITY IN BEACH-FACE SLOPES FROM SATELLITE REMOTE SENSING

The beach face is the most seaward region of the dry beach. This region is the primary interface between land and ocean, and therefore has a great influence on coastal processes such as the exchange of sediment between land and sea or the reflection of wave energy at the shoreline. In particular, the slope of the beach-face, is an important parameter in coastal engineering to calculate the vertical and horizontal excursion of wave run-up (Stockdon et al., 2006). Yet, despite the importance of the beach-face slope parameter in many formulations used by coastal engineers, this quantity remains poorly mapped along the world’s sandy coastlines and the absence of large-scale datasets of beach-face slope is presently limiting our ability to deploy coastal inundation forecasting systems (O’Grady et al., 2019). This work describes a novel methodology to estimate beach-face slopes with satellite remote sensing and presents large-scale datasets of beach-face slopes along open-coast sandy coastlines around the Pacific Rim.

Reflected wave energy by two collinear submerged wavy breakwaters

Under the assumption of a potential flow, we obtain an asymptotic solution up to the second order in a regular expansion, for the problem of the interaction between linear long waves and two submerged floating breakwaters of wavy surfaces, placed in a collinear manner. The hydrodynamics that results from the interaction between the waves and the structures is modeled with the aid of the well-known shallow water wave equations together with the Laplace equation. For this purpose, the domain perturbation method is used to obtain the solution of the governing equations and assume, as is common, small amplitudes of the breakwater's wavy surfaces. This solution is compared with classical analytical solutions reported in the specialized literature, and they adjust properly. Several geometrical configurations of the breakwaters are analyzed. As the breakwaters are near the free surface elevation, just at one-third of the total water depth, larger values of the reflection coefficients are obtained. The maximum wave reflection occurs for four undulations of the breakwater surfaces. In addition, the wave reflection increases as the amplitude of the surfaces of the breakwaters increases. The results of this study are expected to be used by coastal engineers for preliminary feasibility and desk design of submerged breakwaters with wavy surfaces.

Response of propagation of ELF electromagnetic waves through the morning ionosphere to small density variations caused by infrasonic wave

We consider the problem of the effect of small plasma density variations on the propagation and reflection of ELF (extremely-low-frequency) electromagnetic wave incident on the morning ionosphere from above. Modifications of the electromagnetic wave field near the Earth surface and coefficient of wave energy reflection from ionosphere caused by infrasonic wave are studied. The greatest modifications of the field on the Earth surface and reflection coefficient are related to the density perturbations at altitudes of strong electromagnetic wave attenuation (80–110 km). Reflection of electromagnetic waves is especially sensitive to the plasma density perturbations if the value of horizontal refractive index is close to a unit. In this case, modulation percentage of reflection coefficient can exceed the modulation percentage of density in the infrasonic wave by an order of magnitude. The parametric influence of plasma density perturbations in an infrasonic wave on the ELF electromagnetic field is analyzed. If the values of the horizontal wave numbers of the electromagnetic and infrasonic waves are close to each other, the field of the electromagnetic wave near the Earth surface can increase several times. The obtained results are important for understanding the interconnection of ionospheric wave processes of different nature. The study of the modulation of coefficient of ELF reflection from the ionosphere is relevant for explaining the operation modes of a plasma magnetospheric maser.

Power performance of an asymmetric wave energy converter near a partial reflection wall

Wave power absorption of a heaving-body wave energy converter (HBWEC) can be improved by making the device highly asymmetric and deploying it near a coastal wall, harbour pier, or breakwater. However, the coupling between the geometric asymmetry of the HBWEC and the partial reflecting boundaries of the various walls and the consequential influence on the power performance of the HBWEC are unclear. This research aims to fill this gap. A semi-analytical model based on the linear potential flow theory is proposed to deal with an HBWEC with an arbitrary bottom shape and a partial reflection wall. The degree of asymmetry (DoA) of the HBWEC and the reflection rate of the wall are mathematically defined. Results show that the wall increases the power performance of an HBWEC by increasing the reflected wave energy through an increase in the reflection rate. Practically, an HBWEC should have a larger DoA to make it more immune to the change of the reflection rate and therefore more adaptable to different situations. These findings could offer recommendations for the design and deployment of an HBWEC according to the properties of the wall, improving wave power absorption efficiency and avoiding unnecessary costs due to improper design.

Quantitative detection of surface defect using laser-generated Rayleigh wave with broadband local wavenumber estimation

Laser ultrasonic technology has been widely used in surface defect detection attribute to its non-contact, non-destructive and high spatial resolution characteristics. This paper proposes a surface defect quantitative detection method using laser-generated Rayleigh wave with broadband local wavenumber estimation. In this method, considering the broadband characteristics of laser-generated Rayleigh wave, the broadband local wavenumber estimation is presented to achieve the defect imaging accurately, and then the defect geometric parameters are estimated based on image segmentation. A surface defect detection experiment using the laser ultrasonic detection system is conducted to verify the effectiveness of the proposed method. The experimental results show that the proposed method has superior imaging effect for vertical and inclined defects than the standing wave energy method or reflected wave energy method. Besides, the geometric parameters such as length, width, and inclination angle of a surface defect can be accurately identified by the proposed method, the errors of vertical defects are 1.6% in length and 4.0% in width respectively, as well as the maximum and minimum error of inclined defects are 5.0% and 1.28% in inclination angle respectively. The research results provide a potential application for the fast and non-destructive surface defect detection of metal structures.

Crystal structure and peculiarities of microwave parameters of Co1-xNixFe2O4 nano spinel ferrites.

Nanosized spinel ferrites Co1-xNixFe2O4 (where x = 0.0-1.0) or CNFO have been produced using a chemical method. The crystal structure's characteristics have been determined through the utilization of X-ray diffraction (XRD). It has been demonstrated that all samples have a single phase with cubic syngony (space group Fd3̄m). The lattice parameter and unit cell volume behavior correlate well with the average ionic radii of Co2+ and Ni2+ ions and their coordination numbers. Thus, an increase in the Ni2+ content from x = 0.0 to x = 1.0 leads to a decrease in the lattice parameter (from 8.3805 to 8.3316 Å) and unit cell volume (from 58.86 to 57.83 Å3). Elastic properties have been investigated using Fourier transform infrared (FTIR) analysis. The peculiarities of the microwave properties have been analyzed by the measured S-parameters in the range of 8-18 GHz. It was assumed that the energy losses due to reflection are a combination of electrical and magnetic losses due to polarization processes (dipole polarization) and magnetization reversal processes in the region of inter-resonant processes. A significant attenuation of the reflected wave energy (-10 … -21.8 dB) opens broad prospects for practical applications.

A Novel BEM–FEM Scheme for the Interaction of Water Waves with Multiple Vertical Cylinders in the Presence of Currents

The interaction of waves and currents with marine structures finds interesting applications, including the study of offshore and shoreline protection systems, as in the case of permeable breakwaters. The latter systems exhibit various benefits, including a decrease in wave run-up, reflected wave energy and load excitation, allowing for the propagation of part of the incident flow to the lee side, facilitating the improvement of water quality in the protected areas. The present work focuses on the modelling and numerical simulation of wave fields, interacting with arrays of vertical cylinders in the presence of currents. The problem is treated in the framework of potential theory in the frequency domain, assuming waves of small steepness, in conjunction with boundary integral formulation. Numerical results are presented and discussed, concerning the structure of the reflected and transmitted 3D flow fields, making the model suitable for optimization purposes; however, it presents increased computational cost. On the other hand, for small current velocities the problem can be approximately considered on the horizontal plane, modelled by the 2D Helmholtz equation with variable coefficients, which is numerically treated by a coupled BEM–FEM scheme. Numerical examples are presented, demonstrating that the latter model is cost-efficient, providing reasonable predictions, and can be used for the preliminary study of the hydrodynamic characteristics of the considered configurations and the support of the design.

Non-Hermitian planar elastic metasurface for unidirectional focusing of flexural waves

Metasurfaces exhibiting spatially asymmetric inner structures have been shown to host unidirectional scattering effects, benefiting areas where directional control of waves is desired. In this work, we propose a non-Hermitian planar elastic metasurface to achieve unidirectional focusing of flexural waves. The unit cells are constructed by piezoelectric disks and metallic blocks that are asymmetrically loaded. A tunable material loss is then introduced by negative capacitance shunting. By suitably engineering the induced loss profile, a series of unit cells are designed, which can individually access the exceptional points manifested by unidirectional zero reflection. We then construct a planar metasurface by tuning the reflected phase to ensure constructive interference at one side of the metasurface. Unidirectional focusing of the incident waves is demonstrated, where the reflected wave energy is focused from one direction, and zero reflection is observed in the other direction. The proposed metasurface enriches the flexibility in asymmetric elastic wave manipulation as the loss and the reflected phase can be tailored independently in each unit cell.

Wave energy reflection by the Bragg breakwater composed of rectangular bars on the horizontal permeable seabed

Wave energy is a kind of renewable and clean energy. When waves meet the breakwaters, wave energy reflection will happen. In this paper, the modified mild slope equation for waves propagating over the permeable seabed is introduced, and the finite difference model to solve the equation is set up. The accuracy and applicability of the model is verified with Zeng et al’s analytical solution for wave reflection by the rectangular Bragg breakwaters on the impermeable seabed. Furthermore, in case of a permeable seabed, the effects of the seabed permeability, the bar width, the bar number and the submergence of the bars on wave reflection coefficient, as well as the difference with the case of an impermeable seabed, is studies in details. The results show the reflection coefficient of the Bragg resonant reflection increases with the increase in the bar number, but decreases with the increase in the seabed permeability and the submergence of the bars. When the bar number increases from 1 to 8, the Bragg resonance reflection coefficient increases from 0.146 to 0.772. When the permeability parameter of the seabed increases from 0.005 s to 0.03 s, the coefficient decreases from 0.403 to 0.347. When the bar submergence increases from 0.5 to 0.875, the coefficient decreases from 0.842 to 0.195. Moreover, there exists a particular value of the bar width, that is half of the distance between two adjacent rectangular bars that maximizes the wave energy reflection.