Wave Coupling Research Articles

Abstract This research explores the propagation characteristics of piezo-photo-hygrothermoelastic waves in orthotropic semiconductor materials by incorporating the effect of nonlocal elasticity. The proposed model describes the complex interactions between piezoelectricity, photothermal excitation, plasma wave transport, and hygrothermal diffusion under continuous heat and moisture fluxes while accounting for the influence of spatial nonlocality on the elastic response. The nonlocal parameter is introduced into the elastic constitutive relation to capture the size-dependent and dispersive nature of elastic waves, which is essential for semiconductor devices operating at small scales. The study develops a generalized system of coupled equations involving the elastic, thermal, moisture, and plasma fields, all integrated within the framework of nonlocal piezo-photo-hygrothermoelasticity. The system is analytically solved using the normal mode technique to derive expressions for temperature distribution, moisture concentration, carrier density, electric potential, displacement fields, and stresses. Numerical simulations are carried out for the cadmium selenide (CdSe) semiconductor material. The results show that the nonlocal parameter significantly modifies the wave amplitudes, attenuation characteristics, and coupling between the involved physical fields. The proposed model offers valuable insights into the dynamic behavior of semiconductor devices subjected to coupled thermo-mechanical–electrical–moisture interactions, especially when nonlocal effects become significant due to micro- and nanoscale dimensions.

This study investigates the propagation of coupled waves in a nonlocal hygro-piezo-photo-thermoelastic semiconductor medium subjected to dual-moisture diffusion and fractional-order heat conduction. The mathematical model incorporates the effects of long-range nonlocal interactions, piezoelectric coupling, photothermal excitation, and dual-moisture transport mechanisms. A time-fractional Caputo derivative is introduced into the energy equation to account for memory-dependent heat conduction. The coupled system of partial differential equations governing displacement, temperature, carrier density, electric potential, and moisture concentration is analytically solved using the normal mode analysis. Numerical results are presented for cadmium selenide (CdSe) semiconductor material to evaluate the impact of fractional order, nonlocal parameter, pulsed laser excitation, and dual-diffusion effects on wave characteristics. The findings reveal that fractional and nonlocal effects significantly influence wave speed, attenuation, and coupling behavior, offering essential insights for the design of next-generation MEMS, sensors, and optoelectronic devices operating in humid or thermally transient environments.

Surface plasmon polaritons (SPPs) on metal surfaces excited by p-polarized light have long been a crucial method for achieving light–matter interactions due to their small mode-field volumes and strong optical localization properties. However, the significant losses generated in metals greatly limit the intensity of the SPPs and their potential application scenarios. In this paper, we leverage the high refractive index properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) to generate transverse-electric (TE) polarized waves excited by s-polarized light on the surface of gold nanofilms by accurately controlling the number of the TMDC layers and the spatial refractive index variations with the structure. Unlike the SPPs excited by p-polarized light, the TE surface waves on the surface of the gold film exhibit low loss and high quality factor (Q factor). Moreover, the difference in refractive index causes the TE surface waves to be electromagnetically separated in space, lifting the electric field component in the excited TE surface waves from the surface of the metal film into the TMDCs, thereby minimizing the ohmic loss in the metal and enabling strong coupling between the TE surface waves and the two-exciton states (A-exciton and B-exciton) in the TMDCs. Experimental results demonstrated the strong coupling of TE waves with double excitons (A-exciton and B-exciton) in multilayer MoS2 by exciting the Au/MoS2 heterostructure using a Kretschmann–Raether configuration, showing ultrahigh Rabi splitting up to about 310 meV. Furthermore, the number of MoS2 layers can be accurately determined by measuring the redshift of the Rabi splitting peak of the strong coupling spectra in the Au/MoS2 heterostructure. Our findings open a new avenue for manipulating strong exciton–photon coupling in 2D materials and offer a novel approach for accurately characterizing the thickness of TMDCs.

ABSTRACTThe current work explores the reflection behavior of coupled plane waves from the stress‐free boundary of a half‐space made of a fiber‐reinforced orthotropic nonlocal thermoelastic voided composite, employing Lord and Shulman's generalized thermoelastic theory. Four coupled time‐harmonic waves with distinct velocities are found to propagate through the medium, considering well‐suited boundary conditions. The explicit form of the expressions for the amplitude ratios and the energy ratios of the reflected coupled plane waves is derived. Numerically quantitative analysis for a magnesium‐like crystal is performed using MATLAB software, with the results visually interpreted through graphs. Nonlocal parameter, void parameter and material's anisotropy due to different levels of fiber reinforcement significantly affect the amplitude ratios of the reflected waves. It is verified that, during reflection phenomena, there is no dissipation of energy, that is, at every angle of incidence, the total of energy ratios remains conserved and sums to one.

This study presents a comprehensive analysis of reflectance properties by varying the number of distributed Bragg reflectors (DBRs) in amorphous silicon thin-film solar cells using the Rigorous Coupled Wave Analysis (RCWA) method. This amorphous silicon is emerging as a promising thin-film technology for harvesting solar energy due to its natural abundance and flexibility. The optimized reflectance was observed when varying the number of DBR layers from 1 to 10, enabling the improved and promising light-harvesting schemes in amorphous silicon thin-film solar cells. The optimized 5DBR configuration integrated as back reflector in amorphous silicon thin-film solar cells which is substantially enhances the light-trapping mechanism. The property of photonic crystals depends on various parameters, such as the refractive index, thickness, center wavelength (λc), and material selection. Here, focusing the optimized reflectivity of the 1D photonic crystal structure (Si/SiO2) determined by the center (incident) wavelength, such as 400 nm, with the highest reflectance (~100%) achieved using 5 DBR layers/stacks. In addition, the optimized 5DBR configuration was integrated as a backside reflector in amorphous silicon thin-film solar cells. The structure includes an anti-reflection coating (ARC) of Indium Tin Oxide (ITO), a top grating (ITO), and an absorber layer. The proposed thin-film solar cell achieved a maximum conversion efficiency of 18.0% (Jsc = 27.49 mA/cm2) and 17.65% (Jsc = 26.83 mA/cm2) under transverse electric and transverse magnetic field polarizations, respectively. The thickness of the amorphous silicon absorber region is only 40 nm.

Bulk acoustic wave (BAW) filters are essential in 5G wireless communication yet suffer from limited spectral selectivity near band edges. Here, we propose a topologically engineered acoustic reflector integrated into a solidly mounted resonator (SMR) to enhance wave confinement and coupling efficiency. By tuning the Zak phase through the SiO2 layer thickness in the topological reflector, we induce robust interface states that suppress reflections and improve acoustic energy transmission. Simulation results show that integrating this topological SMR into a hybrid integrated passive devices–BAW filter achieves a high-loss notch at 3851 MHz with −22.77 dB suppression, outperforming conventional LC filters. We also demonstrate that the electromechanical coupling coefficient is locally enhanced near topological resonance conditions, enabling frequency-selective control through geometric tuning. This work establishes a practical framework for topological acoustic reflectors in high-performance RF filter design, offering a scalable and CMOS-compatible approach for next-generation wireless systems.

Study of the influence of vertical magnetic field on the propagation and coupling of ICRF waves under CN-H1 non-axisymmetric magnetic field configuration

Abstract In tungsten—W—Environment in Steady-state Tokamak (WEST), the lower hybrid current drive (LHCD) system is key for achieving long pulse operation by providing most of the non-inductive plasma current, as well as a crucial source of electron heating. Therefore, determining the operational space for its application is fundamental. In the present study, the LHCD operational space is deeply analyzed for 0.5 MA pulses. This space is bounded by three limits: (i) the ratio of the LHCD power over density must be above a threshold to compensate tungsten radiation with enough core heating, (ii) the line-averaged density must be high enough to allow good coupling of the hybrid wave with the plasma, and (iii) fast electron ripple losses must be below a limit to avoid reaching a thermal threshold on plasma-facing components. If the tungsten radiation peak or burn-through phase is not safely overcome, a maximum electron temperature of 1.5 keV is obtained, confinement is degraded, and magnetohydrodynamic activity is frequently triggered, potentially causing a disruption. From experimental measurements and interpretative simulations, we highlight the main mechanisms that prevent the plasma from heating up during LHCD power ramp-up. Three parameters play a major role: plasma density, tungsten concentration and LHCD power deposition. A strategy to overcome this limitation is found: a precise density ramp-up performed simultaneously with the increase in LHCD power. Additionally, we show that boronization greatly facilitates the burn-through of tungsten by lowering its content during the heating phase. Finally, taking into account the three constraints given above, the LHCD operational space is determined at power ramp-up and during constant heating phases.

Development of a slotted waveguide antenna for lower hybrid fast wave coupling in KSTAR plasmas

Abstract Significant advancements have been achieved in facilitating high-power and long-pulse operation up to 310 seconds by developing novel techniques for Ion Cyclotron Range of Frequency (ICRF) wave heating systems on EAST. This paper presents an overview of the current status of the ICRF facility, spotlighting the principal modifications implemented on the original installation and the corresponding results. A new ICRF antenna has been devised, featuring an increased toroidal distance between the straps. This design reduces the parallel wave number, augments wave coupling efficiency, and boosts plasma heating performance. A novel active water-cooling mechanism for the Faraday Screen has been introduced to ensure the FS temperature remains within a safe range during long-pulse and high-power operations. An Impedance Transformer has also been developed to diminish the voltage in the transmission line. A load-tolerant matching network with a conjugate-T configuration guarantees stable operation by maintaining low reflection across a broad spectrum of antenna loads. Moreover, a rapid and real-time impedance matching methodology has been successfully incorporated, empowering the system to adapt the matching system to the fluctuating antenna load dynamically. Thanks to these optimizations and upgrades, during the EAST experiments, we attained 2.2 MW of ICRF power for 2 seconds and maintained 1.2 MW for 310 seconds.

We theoretically investigate the interplay between magnetohydrodynamic (MHD) waves and shear flows in a partially ionized solar plasma while focusing on the energy exchange mediated by the flow and the transformation between wave modes. We consider a simple model composed of a uniform partially ionized plasma with a straight magnetic field. A shear flow is present in the direction of the magnetic field with a velocity that varies linearly across the magnetic field. The linearized MHD equations in the single-fluid approximation are used, which include the ambipolar diffusion term due to ion-neutral collisions. A nonmodal approach was adopted in order to convert the flow spatial inhomogeneity into a temporal one, which added a temporal dependence into the component of the wave vector in the direction of the flow inhomogeneity. A system of three ordinary differential equations was derived, which generally governs the temporal evolution of the coupled MHD waves, their interaction with the shear flow, and their ambipolar damping. Numerical solutions were computed to study the coupling and mutual transformation between the fast magnetosonic wave and the Alfvén wave. A detailed parameter study was conducted demonstrating how the energy transfer and mode transformation are affected. The role of ambipolar diffusion was investigated by comparing the results of the ideal case with those obtained when ambipolar diffusion is included. We find that ambipolar diffusion can significantly affect the efficiency of the energy exchange between modes and that it introduces a new coupling mechanism. Additionally, a specific application to solar prominence threads is included, showing that wave coupling and energy exchange can occur within these and other similar structures in the solar atmosphere.

High freeform holographic optical elements (HOEs) offer significant advantages for augmented reality (AR) displays due to their high freeform design, thin structure, and high +1st-order diffraction efficiency. Traditional optical performance measurement methods fail to meet the demands of high freeform HOEs due to limited spatial resolution and prolonged measurement time. This paper introduces what we believe to be a novel K-vector microscope (KVM) based on the geometric theory of the Bragg Condition and Coupled Wave Theory (CWT). The method provides high spatial resolution (below 50 µm) and enables rapid spatial mapping of three-dimensional k-vectors and refractive index modulation (RIM) distributions. Results on the defective reflective grating and off-axis holographic lenses demonstrate its high-precision rapid measurement capability and powerful mapping functionality. The proposed KVM effectively integrates manufacturing and testing process of freeform HOEs, thereby enabling large-scale production and practical implementation in diverse optical systems.

The heating effect of electromagnetic waves in ion cyclotron range of frequencies (ICRFs) in magnetic confinement fusion device is different in different plasma conditions. In order to evaluate the ICRF heating effect in different plasma conditions, we conducted a series of experiments and corresponding TRANSP simulations on the EAST tokamak. Both simulation and experimental results show that the effect of ICRF heating is poor at low core electron density. The decrease in electron density changes the left-handed electric field near the resonant layer, resulting in a significant decrease in the power absorbed by the hydrogen fundamental resonance. However, quite a few experiments must be performed in plasma conditions with low electron density. It is necessary to study how to make ICRF heating best in low electron density plasma. Through a series of simulation scans of the parallel refractive index (n//) of the ICRF antenna, it is concluded that the change of the ICRF antenna n// will lead to the change of the left-handed electric field, which will change the fundamental absorption of ICRF power by the hydrogen minority ions. Fully considering the coupling of ion cyclotron wave at the tokamak boundary and the absorption in the plasma core, optimizing the ICRF antenna structure and selecting appropriate parameters such as parallel refractive index, minority ion concentration, resonance layer position, plasma current and core electron temperature can ensure better heating effect in the ICRF heating experiments in the future EAST upgrade. These results have important implications for the enhancement of the auxiliary heating effect of EAST and other tokamaks.

Abstract Anomalies in the stratospheric polar vortex (SPV), such as sudden stratospheric warming (SSW) events, significantly impact surface weather patterns. While the influence of SSWs on the troposphere is robust on average, individual events exhibit large variability, partly due to the substantial difference in dynamics and SPV evolution across events. Understanding the physical processes driving SSWs is therefore important. In this study, we investigate SPV dynamics, focusing on nonlinear coupling between planetary wave modes. We use potential enstrophy and eddy total energy budget analyses to quantify the contributions of different physical processes to SPV evolution. These budget analysis frameworks are unique in being able to study the contribution of nonlinear wave–wave interactions to the dynamical evolution of the SPV. When applying this framework to both an idealized simulation and reanalysis data of the 2003 SSW, we find that nonlinear wave–wave interactions can play a crucial role during SSWs. In the idealized simulation, wave-2 structures emerge in the stratosphere without a prescribed wave-2 source, attributed to the nonlinear transfer of enstrophy and energy from wave 1 to wave 2. In the 2003 case study, interactions between wave 1 and wave 2 contribute to a displacement-to-split transition. We also find indications of quasilinear coupling and upscale enstrophy transfer from wave 2 to wave 1 during this period. The use of the enstrophy budget analyses highlights the significant impact of nonlinear wave–wave interactions in SPV transitions. These complex interactions contribute to the uniqueness of each SSW event and may help explain the variability observed across different SSWs.

Abstract The present investigation is concerned with the reflection of plane waves from the thermally insulated rigid boundary of a linear, homogeneous fiber‐reinforced thermoelastic medium under the Green and Lindsay (GL) model of generalized thermoelasticity. It has been found that three sets of coupled thermoelastic plane waves may travel in the medium with distinct speeds. Using the thermally insulated rigid boundary conditions, the reflection coefficients and the corresponding energy ratios for the reflected waves are derived, and the numerical computations have been carried out with the help of MATLAB programming. The numerical values of the modulus of reflection coefficients are presented graphically. The expressions of energy ratios have also been obtained in explicit form and are shown graphically as functions of angle of incidence. It has been verified that during reflection phenomena, the sum of energy ratios is equal to unity at each angle of incidence.

This research investigates resonator width optimization for simultaneously enhancing electrical performance and mechanical reliability in wideband RF MEMS filters through systematic evaluation of three configurations: 0% (L1), 60% (L2), and 100% (L3) matching ratios between cap and bottom wafers using Au-Au thermocompression bonding. The study demonstrates that resonator width alignment significantly influences both electromagnetic field coupling and bonding interface integrity. The L3 configuration with complete width matching achieved optimal RF performance, demonstrating 3.34 dB insertion loss across 4.5 GHz bandwidth (25% fractional bandwidth), outperforming L2 (3.56 dB) and L1 (3.10 dB), while providing enhanced electromagnetic wave coupling and minimized contact resistance. Mechanical reliability testing revealed superior bonding strength for the L3 configuration, withstanding up to 7.14 Kgf in shear pull tests, significantly exceeding L1 (4.22 Kgf) and L2 (2.24 Kgf). SEM analysis confirmed uniform bonding interfaces with minimal void formation (~180 nm), while Q-factor measurements showed L3 achieved optimal loaded Q-factor (QL = 3.31) suitable for wideband operation. Comprehensive environmental testing, including thermal cycling (-50 °C to +145 °C) and humidity exposure per MIL-STD-810E standards, validated long-term stability across all configurations. This investigation establishes that complete resonator width matching between cap and bottom wafers optimizes both electromagnetic performance and mechanical bonding reliability, providing a validated framework for developing high-performance, reliable RF MEMS devices for next-generation communication, radar, and sensing applications.

A set of experiments were conducted on the LArge Plasma Device (LAPD) at UCLA to test the operational principles of a traveling wave antenna of the comb-line type. This antenna was designed to launch helicon waves (fast waves in the lower hybrid range of frequencies) on DIII-D. With the order-of-magnitude lower static magnetic field on LAPD, the antenna excites waves in a different regime. Whenever fast waves can propagate in LAPD, slow waves are also supported by the plasma so it is necessary to distinguish between the two cold-plasma branches in evaluating the effectiveness of the launcher. The results show that the launcher couples well to fast waves when the plasma supports fast-wave propagation; control of the principal imposed parallel wavenumber can be achieved through varying the launch frequency on the antenna within its bandwidth of operation; and that the launched waves exhibit strong directionality. We also investigate the role of the plasma profile and wave mode on the loading characteristics. Additionally, a comparison with full-wave modeling of the propagating waves is shown using both a cold-plasma model in COMSOL and a hot-plasma model in RFPisa, which obtain similar results in the present regime.

In this paper, we show the classical global stability of the flat Kaluza–Klein spacetime, which corresponds to Minkowski spacetime in \mathbb{R}^{1+4} with one direction compactified on a circle. We consider small perturbations which are allowed to vary in all directions including the compact direction. These perturbations lead to the creation of massless modes and Klein–Gordon modes. On the analytic side, this leads to a PDE system coupling wave equations to an infinite sequence of Klein–Gordon equations with different masses. The techniques we use are based purely in physical space using the vector field method. In addition to Kaluza–Klein stability, our techniques can be easily adapted to provide a new proof of the stability of the Minkowski solution to the Einstein–Klein–Gordon equations.

Stabilization of Two Coupled Wave Equations with a Localized Singular Kelvin–Voigt Damping

Abstract A plume model applied to radiosonde observations and ERA5 reanalysis is used to assess the relative importance of lower tropospheric moisture and temperature variability in the convective coupling of equatorial waves. Regression and wavenumber-frequency coherence analyses of satellite precipitation, outgoing longwave radiation (OLR), and plume model estimates of lower tropospheric vertically integrated buoyancy (〈B〉) are used to identify the spatial and temporal scales where these variables are highly correlated. Precipitation and OLR show little coherence with 〈B〉 when zero-entrainment is prescribed in the plume model. In contrast, precipitation and OLR vary coherently with 〈B〉 when “deep-inflow” entrainment is prescribed, highlighting that entrainment occurring over a deep layer of the lower troposphere plays an important role in modifying the thermodynamic properties of convective plumes in the Tropics. Consistent with previous studies, moisture variability is found to play a more dominant role than temperature variability in the convective coupling of the Madden-Julian Oscillation (MJO) and equatorial Rossby (ER) waves, while temperature variability is found to play an important role in the convective coupling of Kelvin (KW) and inertio-gravity (IG) waves. Convective coupling is most strongly impacted by moisture variations in the 925-850 hPa and 825-600 hPa layers for the MJO and ERs, and by 825-600 hPa temperature variations in KWs and IGs, with 1000-950 hPa moist static energy variations playing a relatively small role in convective coupling. Simulations of the E3SM V2 and a pre-operational prototype of NOAA GFS V17 are examined, the former showing unrealistically high coherence between precipitation and 1000 hPa moist static energy, the latter a more realistic relationship.