Wave Angle Research Articles

Dual‐Function Microwave Devices Based on Metamaterials

AbstractMicrowave detectors play a crucial role in modern technological applications, but traditional detectors suffer from limited functionality, limited detection accuracy, and difficulties in large‐scale deployment. This study proposes a dual‐function microwave detector based on metamaterials, capable of simultaneously measuring microwave power and polarization angle. The detector consists of a metal disc with 12 concave grooves, a dielectric layer, a metal reflector, and a resistive network. The designed detector achieves efficient absorption of 93.54% of microwave energy, with 75.4% dissipated in the resistive component and converted into heat. By detecting the temperature using a thermocouple thermometer, the incoming wave power can be determined, and by discriminating between different resistive temperatures, the polarization angle of the incoming wave can be identified. Simulation and experimental results demonstrate the outstanding detection efficiency and stability of this detector. It exhibits a linear response to different incident power densities and polarization angles, showing potential application value in the field of microwave wireless power transmission.

Three-dimensional numerical simulations of oblique internal solitary wave-wave interactions in the South China Sea

Satellite images show that the oblique internal solitary wave-wave interactions frequently occur in the South China Sea, especially in the periphery of Dongsha Island. Depending on the amplitudes and angles of initial oblique waves, theoretical works illustrated that the evolution pattern falls into different regimes characterised by the respective four-fold augmentation of wave amplitudes (relative to the initial waves) and occurrence of Mach stem waves in the interaction region. Nevertheless, these results were based on the reduced theories rooted from the primitive Navier-Stokes equations and the disparities induced by these simplifications with the scenarios in realistic ocean are still unclear. To fill this research gap, three-dimensional numerical simulations in the South China Sea are used to evaluate the oblique internal solitary wave-wave interactions. It is found that transformations between mode-1 and mode-2 waves occur near the Dongsha Island when two waves obliquely collide, together with a small portion of energy is converted into higher modes, most of which is dissipated locally due to their unstable vertical structures. This conclusion has been seldom reported in previous studies (if any). These oblique interactions are essentially nonlinear and impacted by the dynamical factors, such as varying depth, background current, etc., exhibiting complicated variations of waveforms and energy, which, further, enhance the mixing at local sites in the mechanism of both shear and convective instabilities indicated by the Richardson number.

Polarization-independent full mode-converting elastic metasurfaces

This investigation proposes a novel elastic metasurface tailored to convert a longitudinal wave into a transverse wave and vice versa at an arbitrary refraction angle with full (100 %) conversion efficiency. The previous mode-converting elastic metasurface based on Snell's critical angle can convert a longitudinal wave into a transverse wave, but the refraction angle of the transverse wave cannot be smaller than the critical angle. In addition, the previous metasurface cannot convert a transverse wave into a longitudinal wave without generating a parasitic transverse wave. Here, we propose an elastic metasurface that enables full mode-converting transmission at an arbitrary refraction angle, regardless of whether the incident wave's polarization is longitudinal or transverse. To this end, we present a novel strategy to design unit cells that yield total mode-conversion efficiency as well as the desired phase shifts covering the entire 2π range. Shape optimization and geometry-flipping strategies were employed to design the unit cells constituting the metasurface. The concept of the unit cell's effective length was useful for the unit cell design. The designed metasurfaces were then used for various applications, such as longitudinal-to-transverse and transverse-to-longitudinal wave steering, splitting, and focusing. The performance of our metasurface was verified by ultrasonic experiments performed on an aluminum plate with the designed metasurface embedded. The realized full mode-converting transmission applicable for an arbitrary angle is expected to be critically valuable for nondestructive testing and medical ultrasounds requiring a specific elastic wave mode of the desired arbitrary beam pattern.

Hydrodynamic characteristics of bridge cofferdam under multidirectional focused waves

Abstract In the process of coastal bridge construction, cofferdams become necessary facilities to ensure the construction environment dry and safe. However, during the construction period of coastal bridges, extreme surges and waves caused by typhoons can impose huge hydrodynamic loads at the cofferdam and a potential threat to the safety and integrity of cofferdam. Therefore, it becomes valuable to assess the hydrodynamic loads of bridge cofferdam under extreme waves. Meanwhile, in the harsh marine environment, waves tend to propagate in multiple directions. However, previous studies mainly focused on the hydrodynamic characteristics of cofferdam by waves that propagate in one direction. Few studies were carried out on the hydrodynamic characteristics of cofferdam under the action of extreme waves in multiple directions. To fill in the gaps in previous research, this study numerically studied the complex wave hydrodynamics of cofferdam under multidirectional extreme waves. Effects of several major factors, i.e., significant wave height, peak wave period, water depth, spreading angle, incident wave angle and submergence depth were systematically analyzed. It is desired that present research could enhance our understandings on the complex wave hydrodynamics of bridge cofferdam under multidirectional focused waves.

Ultrathin acoustic metasurface carpet cloaking based on Helmholtz resonances

<sec>With the development of metamaterials, the acoustic cloaking has attracted extensive attention due to its novel physics and potential applications. In recent years, based on the phase compensation modulation from Generalized Snell’s law and coordinate transformation, the acoustic cloakings in underwater and air have been widely and deeply studied. However, there is still an urgent need to design acoustic cloaks that are thinner and less affected by the incident angle of acoustic waves. Further, the designed cloaks should have a wider operating band and be more suitable for irregular objects.</sec><sec>In this paper, an ultrathin curved acoustic metasurface carpet cloaking is studied by using of phase compensation modulation. The phase modulation is based on Helmholtz resonance (HR). The metasurface carpet is immersed in air, since the vibration mode of acoustic wave in the air is relatively single, thus the physical essence can be elucidated more clearly. The carpet cloak is composed of 52 Helmholtz resonant units, and the size of resonant unit is less than 0.2 of working wavelength.</sec><sec>The phase change of HR unit is solved analytically by using the Generalized Snell’s law, and confirmed by the Multiphysics COMSOL software. The parameter effects of HR unit on the phase change are studied, demonstrating that the phase change of HR unit is sensitive to the change of height and radius of HR unit, while the change of width of HR cavity neck can make the phase of HR unit change smoothly. Therefore, when building 52 HR units, the width of the HR cavity neck is designed, and the height and radius of HR unit stay fixed.</sec><sec>The simulating results demonstrate that the designed cloak works well in a frequency range from 5850 Hz to 7550 Hz. Also, we study the cloaking effect for oblique incidence, and the results show that the carpet cloak works well for incident angle less than 30°. To quantitatively analyze the bandwidth of the cloaking, we calculate the cosine similarity value. It elucidates that the value of the cloak is very close to that of the flat ground in a corresponding working frequency range. The cloak designed in this work is made of ultrathin Helmholtz Resonant structures. This cloak is simple and easy to realize and conducive to potential applications.</sec>

Photocontrolled ultra-broadband metamaterial absorber around the terahertz regime.

In this paper, we innovatively stack multiple resonant units of photoconductive silicon to design an ultra-broadband metamaterial absorber. By manipulating the conductivity of the silicon with a pump beam, adjustments are made to the amplitude of the wide absorption spectrum spanning 6.6 THz, enabling functional switching from total reflection to near-perfect ultra-broadband absorption. By integrating vanadium dioxide as an intermediary layer, a dual-mode switchable absorber is realized, offering dual control functionalities. Temperature changes enable the absorber to switch between dual-band absorption and ultra-broadband absorption, while variations in pump beam intensity allow for further amplitude adjustments within the absorption spectrum. Impedance matching theory and near-field analysis provide the necessary physical foundation for understanding broadband absorption. Structural parameters, incident angle, and polarization angle of the incident electromagnetic waves are also studied to demonstrate the device's robustness. Our proposed absorbers not only greatly broaden the absorption bandwidth of silicon-based absorbers, but also offer versatility, polarization insensitivity, and robustness over a wide range of incidence angles. Moreover, our design ideas are useful for broadening the bandwidth and enhancing absorption, which enables wider applications in ultra-broadband terahertz absorption and promises extensive prospects.

A numerical model approach of wave dynamic

The numerical model of wave field distribution using time dependent of wave combination from refraction-diffraction equation on a gentle slope was carried out in Modeling Laboratory of Marine and Fisheries Faculty of Syiah Kuala University. The research of numerical modeling was conducted to understand how the impact of the presence of coastal structures on the coast toward the wave dynamic approach. In the theory, the greater of wave angle, the greater of wave height distribution will be behind the breakwater, thus allowing large sediment transport to make changes to the coast. Therefore, this research is important because the knowledge of the relationship between waves and coastal structure is still limited while the dynamics of the coast have a distinctive significance in the regions. The study aims to determine the wave phenomena that interact with the structure of the coastal building so that the results of this study can be used and utilized as substantial study for future coastal planning. The method used in this study is the application of wave equations that may be solved by numerical model. The model results show that the greater the angle of incidence of waves on the southwest coast, the greater the wave height produced when it hits coastal structures. However, this characteristic does not occur in the west coast region. This is caused by the topographic nature of coastal areas and different coastal characteristics.

Comparison of a Circular Patch Unit Cell Performance for Reflector Applications between Using FR4 and F4BMX220 Substrates at 3.5 GHz Frequency

This paper presents a performance comparison of the circular patch unit cell as a unit cell for reflector application at 3.5 GHz frequency using a dielectric substrate between FR4 and F4BMX220 substrates. A circular patch is chosen as the unit cell of a reflector because it is commonly used, fabricated, and has a wider bandwidth compared to other structures. A performance comparison of the circular patch on both dielectric substrates is presented in a graph of S-parameters, reflection phase, and operating bandwidth, as well as in the table of dimensions, where the result is performed by simulation using CST software. Based on the simulated results, the F4BMX220 has a better performance compared to the FR4 in terms of the reflection value, operating bandwidth, and dielectric substrate thickness. However, a circular patch diameter when using the F4BMX220 is bigger than when using the FR4 substrate because the FR4 substrate has a higher dielectric constant than the F4BMX220, which is twice the F4BMX220 dielectric constant. Also, the F4BMX220 substrate has a narrower bandwidth compared to the FR4 substrate, which is a difference of around 0.1 GHz. The circular patch when using the F4BMX220 substrate has 0.96 of a reflection value, 0.007 of an absorption value, -6.77° of the reflection phase, and 0.24 GHz of the operating bandwidth at the normal incident wave angle (0°). Also, it can be properly worked if the incident wave angle is moving until 60°. The F4BMX220 substrate has the best performance compared to the FR4 substrate because the reflection value is much better value, even at the incident wave angle of 60°.

ON THE STRUCTURAL VALUATION IN OBLIQUE WAVES OF A LARGE LIQUEFIED NATURAL GAS CARRIER BY 3D-FEM MODEL APPROACH

This structural valuation in oblique equivalent waves has as a study case a large LNG liquefied natural gas carrier, with an overall length of 289.3 m, structural gas membrane tanks, and a double hull. From the operation load cases, for the numerical study, a selection of the main cases is made, full cargo and ballast. The selected oblique design wave conditions are specific to unrestricted navigation areas, sagging and hogging wave-free surface, with the heading angle covering the oblique relevant cases. The computation of the LNG carrier equilibrium in oblique design waves is done by a three-parameter nonlinear approach, with the own P_QSW software. The 3D-FEM large LNG carrier model is developed by Femap/NX Nastran software. The structural valuation in oblique design waves, by strength and freeboard criteria, of the large LNG carrier involves 3D and 1D models. For practical purposes, the strength valuation results are synthesized as polar diagrams, for the relevant heading angles of the oblique design waves, representing the wave height safety limits for preserving the large LNG carrier structural integrity.

Experimental and numerical study on eccentric compression performance of partially encased composite columns with corrugated web

SummaryPartially encased composite (PEC) members are becoming increasingly popular because of their high strength and suitability for prefabrication and assembly. Corrugated steel plate has higher out‐of‐plane stiffness than flat steel plate. When it is combined with concrete, the bonding between corrugated steel plate and concrete is more obvious than that between flat steel plate and concrete. For this reason, a new type of corrugated web PEC column (CPEC column) was proposed in this paper, and its eccentric compression performance was studied by experiment and numerical method. Nine specimens were tested, of which two were subjected to axial compression and seven were subjected to eccentric compression. The key factors considered in the experiment were the loading direction, load eccentricity, link spacing, and width‐to‐thickness ratio of flange. A three‐dimensional finite element model of the CPEC columns was established and verified, and the influence of the wave angle of corrugated web on the behavior of CPEC columns under eccentric compression was investigated using a parametric study. Finally, the current design codes for estimating the interaction curve and bearing capacity of CPEC columns were assessed.

Comparative Analysis of Supersonic Flow in Atmospheric and Low Pressure in the Region of Shock Waves Creation for Electron Microscopy.

This paper presents mathematical-physics analyses in the field of the influence of inserted sensors on the supersonic flow behind the nozzle. It evaluates differences in the flow in the area of atmospheric pressure and low pressure on the boundary of continuum mechanics. To analyze the formation of detached and conical shock waves and their distinct characteristics in atmospheric pressure and low pressure on the boundary of continuum mechanics, we conduct comparative analyses using two types of inserted sensors: flat end and tip. These analyses were performed in two variants, considering pressure ratios of 10:1 both in front of and behind the nozzle. The first variant involved using atmospheric pressure in the chamber in front of the nozzle. The second type of analysis was conducted with a pressure of 10,000 Pa in front of the nozzle. While this represents a low pressure at the boundary of continuum mechanics, it remains above the critical limit of 113 Pa. This deliberate choice was made as it falls within the team's research focus on low-pressure regions. Although it is situated at the boundary of continuum mechanics, it is intentionally within a pressure range where the viscosity values are not yet dependent on pressure. In these variants, the nature of the flow was investigated concerning the ratio of inertial and viscous flow forces under atmospheric pressure conditions, and it was compared with flow conditions at low pressure. In the low-pressure scenario, the ratio of inertial and viscous flow forces led to a significant reduction in the value of inertial forces. The results showed an altered flow character, characterized by a reduced tendency for the formation of cross-oblique shockwaves within the nozzle itself and the emergence of shockwaves with increased thickness. This increased thickness is attributed to viscous forces inhibiting the thickening of the shockwave itself. This altered flow character may have implications, such as influencing temperature sensing with a tipped sensor. The shockwave area may form in a very confined space in front of the tip, potentially impacting the results. Additionally, due to reduced inertial forces, the cone shock wave's angle is a few degrees larger than theoretical predictions, and there is no tilting due to lower inertial forces. These analyses serve as the basis for upcoming experiments in the experimental chamber designed specifically for investigations in the given region of low pressures at the boundary of continuum mechanics. The objective, in combination with mathematical-physics analyses, is to determine changes within this region of the continuum mechanics boundary where inertial forces are markedly lower than in the atmosphere but remain under the influence of unreduced viscosity.

A Communication Anti-Jamming Scheme Assisted by RIS with Angular Response.

By optimizing the reconfigurable intelligent surface (RIS) reflection coefficients, the channel capacity of legitimate users can be increased, thereby enhancing the anti-jamming performance of communication systems. However, existing studies on RIS-assisted anti-jamming assume that there is no coupling between the RIS reflection coefficients and the incident angle of electromagnetic (EM) waves, which is quite unreasonable. Therefore, we consider the effect of the incident angle of EM waves on the reflection coefficients of the RIS and propose a communication anti-jamming scheme assisted by an RIS with angular response. Specifically, a problem is formulated to optimize the RIS reflection coefficients so that the legitimate signal is amplified, but the jamming signal is attenuated, thus enhancing the legitimate channel capacity. However, the coupling of the EM incident angle and the RIS reflection coefficients causes the problem to be non-convex. To tackle this problem, we equivalently transform the RIS reflection coefficients optimization problem into a quadratically constrained quadratic programming (QCQP) problem using the complex Taylor expansion and the multidimensional complex quadratic transform (MCQT) and solve it utilizing the alternating direction method of the multipliers (ADMM) algorithm. The simulation results reveal that, compared to other schemes supported by RIS without angular response, the proposed scheme is able to achieve a significant improvement in the anti-jamming performance.

The impact of incident wave angle and air hole radius parameter on the optical responses of a GaAs-based 2D photonic crystal, using the FDFD method

The impact of incident wave angle and air hole radius parameter on the optical responses of a GaAs-based 2D photonic crystal, using the FDFD method

Forward and backward propagation guided-mode waves of electric dipole resonances in an h-BN metasurface

The generation of a backward propagation (BP) and forward propagation (FP) guided mode in a double ridge h-BN metasurface (DRM) is investigated. h-BN is a hyperbolic metamaterial with two Reststrahlen frequency bands (RBs). The incident wave can excite guided modes in DRM, where the Poynting vector parallel component of the FP mode is identical and the BP mode is opposite to that of the incident wave. Based on the optimized structure, the frequency range of the BP mode for TE waves was found near the type II hyperbolic band (HB II), while for TM waves, it was found in the gap between the range of HB I and HB II in h-BN. To comprehensively understand the physics underlying BP and FP modes, we present the electric and magnetic field intensities in DRM, the electric field profile of beam steering, and the radiated powers of multipole resonances. The electric dipole (ED) moment contributes most significantly to the FP and BP modes, with its power being much greater than that of other multipolar moment modes. A proportion of BP mode power and incident power decreases with increasing incident angle of TE waves. There are two peaks of the proportion with TM waves. The maximum proportion is near 75% ofTE waves and 16% ofTM waves. The DRM has shown promising potential in the field of sensors based on BP mode, with a sensitivity of 3.9675 µm/RIU of TE waves and 5.1479 µm/RIU of TM waves. These findings suggest that DRMs hold significant promise for the development of optical metasurfaces, optical switches, and high-performance sensors.

Terahertz metamaterial-induced multiple transparency windows through bright-bright mode couplings

Metamaterials that offer optical control over multiple transparency windows have paved the way for advancements in terahertz (THz) modulation technology. In this paper, we have conducted a systematic investigation into the interaction between THz waves and “bright” split-ring resonators (SRRs). Through manipulation of the quantity and spatial arrangement of SRRs within metamaterial structures, we have successfully induced multiple transparency windows within the THz spectrum. Furthermore, we have explored the transmitted switching ratio of both the designed single transparency window and double resonance frequency bands as a function of the azimuthal angle of the THz wave. This work offers a general strategy for designing the number of electromagnetically induced transparency windows and holds the potential for realizing multichannel memories.

Stochastic dynamic analysis of floating bridges exposed to inhomogeneous and irregular waves

As future floating bridges gets longer, the likelihood of significant inhomogeneous wave conditions across them increase. Consequently, a proper assessment of the effects of inhomogeneous wave conditions is needed. In this paper, we present an approach to model inhomogeneous sea states by representing the stochastic process using generalized harmonic decomposition, retaining the coherency inherent in Airy wave theory. The methodology is applied to a concept model of a floating bridge to cross the Bjørnafjord in Norway, which is more than five kilometres wide. The paper emphasizes on frequency-domain simulation, but the required steps to generate time-domain representations are given. To suggest what might be critical considerations in design, the response effects due to some selected conceptual inhomogeneities are highlighted. For varying wave heights alone, it is found that it is likely conservative to approximate the inhomogeneous sea state as homogeneous by assuming the harshest conditions across the full width of the strait. By modulating the mean wave angle of a 100-year swell sea state, a spherical wave front matching the curvature of the bridge girder is found to produce significantly more severe response than the homogeneous reference swell; an increase of 14% of the maximum axial force response is found. Furthermore, a proper treatment of the coherency for swell sea states is found to be crucial, in contrast to typical wind sea conditions.

Experimental and numerical investigation on hydrodynamic performance of a 3D land-fixed OWC wave energy converter

The hydrodynamic performance of a land-fixed oscillating water column (OWC) wave energy device was thoroughly investigated under various wave conditions and geometric parameters through both experimental and numerical studies in a three-dimensional (3D) wave tank. The study involved the measurement and comparison of water surface elevation, air pressure in the OWC chamber, and hydrodynamic efficiency with the results obtained from the 3D Higher-Order Boundary Element Method (HOBEM). The influences of 3D effects, incident wave amplitude, front wall draught, and incident wave angle on the hydrodynamic performance of the OWC device were analyzed. The results demonstrate that, under actual sea conditions, the 3D effects significantly affect the hydrodynamic efficiency of the OWC, making it exceed unity near the resonance frequency. On the other hand, the incident wave angle was found to have minimal effect on the resonant frequency and varied trend of efficiency. However, the hydrodynamic efficiency decreases with increasing incident wave angle. These results highlight the importance of the consideration of the 3D effects and incident wave angles in optimizing the design and performance of fixed OWC wave energy devices.

Aberration Estimation for Synthetic Aperture Digital Holographic Microscope Using Deep Neural Network.

Digital holographic microscopy (DHM) is a valuable technique for investigating the optical properties of samples through the measurement of intensity and phase of diffracted beams. However, DHMs are constrained by Lagrange invariance, compromising the spatial bandwidth product (SBP) which relates resolution and field of view. Synthetic aperture DHM (SA-DHM) was introduced to overcome this limitation, but it faces significant challenges such as aberrations in synthesizing the optical information corresponding to the steering angle of incident wave. This paper proposes a novel approach utilizing deep neural networks (DNNs) for compensating aberrations in SA-DHM, extending the compensation scope beyond the numerical aperture (NA) of the objective lens. The method involves training a DNN from diffraction patterns and Zernike coefficients through a circular aperture, enabling effective aberration compensation in the illumination beam. This method makes it possible to estimate aberration coefficients from the only part of the diffracted beam cutoff by the circular aperture mask. With the proposed technique, the simulation results present improved resolution and quality of sample images. The integration of deep neural networks with SA-DHM holds promise for advancing microscopy capabilities and overcoming existing limitations.

Direction independent broad-band wide angle metamaterial absorber for “K” band applications

Abstract In this work, the design of broadband, wide-angle, direction-independent metamaterial (MM) electromagnetic wave (EM) absorber for K-band frequency application is investigated and validated experimentally. The unit cell of the metamaterial absorber consists of four 90° rotated L-shaped metallic patches imprinted on a dielectric substrate backed by a metallic sheet. The structure yield absorption in the broad frequency ranges from 22.5 to 29.3 GHz for both TE and TM polarized waves with more than 90 % absorptivity having a wide fractional bandwidth of (6.8 GHz) 25.8 %. The structure is four-fold symmetric and hence yields polarization insensitivity for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80 % absorptivity holds up to 45° incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonance in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. Measured results are showing good agreement with the simulated responses. The novelty of the proposed absorber lies in its unique metallic pattern on a λ 0/8 (concerning the canter frequency of absorption bandwidth) thin FR-4 substrate while showing the wide absorption bandwidth and direction independence to normal and oblique incidence. The compact nature of the absorber and broadband response with good polarization insensitivity at normal and oblique incidence makes it commercially suitable for the reduction of radar cross section (RCS) in stealth applications at the K-band.

Multiband terahertz metamaterial perfect absorber for microorganisms detection

We report a multi-resonant terahertz (THz) metamaterial perfect absorber (MPA)-based biosensor in the working frequency range of 0 - 3.8 THz for sensing of microorganisms (such as fungi, yeast) and wheat pesticides. Nearly 100% absorption is realized at f_1= 1.7THz, f_2= 2.8THz, f_3=3.2THz, and f_4=3.5THz. We designed our THz MPA sensor making resonators’ gap area compatible with the microorganisms’ size. To obtain optimum performance of the MPA, a mapping of amplitudes and shifts in the absorption resonance peaks with different structural parameters of the resonators is carried out. A very high-frequency shift is obtained for microorganisms such as Penicillium chrysogenum (fungi), yeast, and pesticides (Imidacloprid, N, N-Diethyldithiocarbamate sodium salt trihydrate, Daminozide, N, N-Diethyldithiocarbamate sodium salt hydrate, and Dicofol). An equivalent circuit model using Advance Design System (ADS) software is developed. The calculated results through the model show similar trends as obtained in the simulations using CST. Investigations of the effect of incidence angle of THz wave on the absorption spectra of the MPA are also carried out. It is found that incidence angle does not impact the stability of the lower resonance absorption peak (1.79THz). Due to the wide working frequency range, the proposed sensor is extremely suitable for the detection of all range of pesticides because their specific absorption fingerprint lies in the frequency range of 0–3.8THz. We believe that our sensor could be a potential detection tool for detecting pesticide residues in agriculture and food products. The THz MPA-based biosensor is capable of detecting a very small change in the effective dielectric constant of the MPA environment. Therefore, it can also offer huge opportunities in label-free biosensing for future biomedical applications.