Wave Conversion Research Articles

Metasurface-Coated Liquid Microlens for Super Resolution Imaging.

Inspired by metasurfaces' control over light fields, this study created a liquid microlens coated with a layer of Au@TiO2, Core-Shell nanospheres. Utilizing the surface plasmon resonance (SPR) effect of Au@TiO2, Core-Shell nanospheres, and the formation of photonic nanojets (PNJs), this study aimed to extend the imaging system's cutoff frequency, improve microlens focusing, enhance the capture capability of evanescent waves, and utilize nanospheres to improve the conversion of evanescent waves into propagating waves, thus boosting the liquid microlens's super-resolution capabilities. The finite difference time domain (FDTD) method analyzed the impact of parameters including nanosphere size, microlens sample contact width, and droplet's initial contact angle on super-resolution imaging. The results indicate that the full width at half maximum (FWHM) of the field distribution produced by the uncoated microlens is 1.083 times that of the field distribution produced by the Au@TiO2, Core-Shell nanospheres coated microlens. As the nanosphere radius, droplet contact angle, and droplet base diameter increased, the microlens's light intensity correspondingly increased. These findings confirm that metasurface coating enhances the super-resolution capabilities of the microlens.

Resonant conversion of THz waves with orthogonal polarization upon transmission through a woven mesh

The possibility of resonant conversion of wave fields oriented along the orthogonal sinusoidal conductors forming a woven mesh structure has been experimentally investigated using THz time-domain spectroscopy. This coupling, which enables the conversion of wave energy between surface waves appearing at co- and cross-oriented wires, results in a 90° rotation of the polarization of the waves transmitted through the woven mesh. A strong dependence of the phenomenon on the orientation of the woven mesh relative to the propagation direction and polarization of the incident THz waves has been shown and discussed. We believe that such properties of the metallic woven meshes can open up new prospects for investigating the interaction of THz waves with structured-wire grids.

Particle conversions beyond the WKB approximation and solar-induced gravitational waves from dark photon dark matter

We investigate the conversion of kinetic mixing dark photon dark matter into gravitational waves within the magnetic field of the Sun. Our study reveals that the WKB approximation is invalid in this scenario. We derive an analytic solution for the conversion probability with unitary evolution feature. This solution aligns in form with previous studies on photon-gravitational wave conversion. Interestingly, it is applicable in situations where the WKB approximation fails. We extend the unitary evolution solution to other conversion processes, such as axion-photon and dark photon-photon conversions. When the WKB approximation conditions are met, this solution reduces to the WKB result. We compute the characteristic strain of gravitational waves resulting from dark photon conversion in the solar magnetic field, spanning frequencies from 10−5 Hz to 106 Hz. Our findings indicate that the characteristic strain derived from the unitary evolution solution differs significantly from that of the WKB solution. The resulting strain signal is far below the sensitivity of current gravitational wave interferometers. Nevertheless, we have proposed an exotic gravitational wave source, which could be useful in nonminimal dark sector models. Published by the American Physical Society 2024

Propagation of optical spatial solitons in nematic liquid crystals with quadruple power law of nonlinearity appears in fluid mechanics

Abstract The present research explores nematicons in liquid crystals (LCs) with quadruple power law nonlinearity utilizing the modified extended Fan sub-equation technique as an analytical tool to investigate the optical spatial soliton solutions. For the inaugural time, a novel version of nonlinearity is investigated in relation to LCs. There are distinct applications for the several wave solutions that have been created in optical handling data. The aforementioned modified extended Fan subequation approach offers novel, comprehensive solutions that are relatively easy to deploy in comparison to earlier, regular methodologies. This approach translates a coupled non-linear partial differential equation into a coupled ordinary differential equation through implementing a traveling wave conversion. This approach indicates that a large variety of traveling and solitary solutions that rely upon five parameters can be incorporated by the nematicons in LCs. In addition, the investigation yields solutions of the single and mixed non-degenerate Jacobi elliptic function form. Novel solutions, such as the periodic pattern, kink and anti-kink patterns, N-pattern, W-pattern, anti-Z-pattern, M-pattern, V-pattern, complexion pattern and anti-bell pattern, or dark soliton solutions of nematic LCs, have been constructed by means of modified extended Fan subequation technique through granting suitable values for the parameters. The computer software Mathematica 14 is used to illustrate several modulus, real and imaginary solutions visually in the form of contour, 2D, and 3D visualizations that help understand the concrete importance of the nematicons in LCs. This research additionally offers a physical comprehension of the obtained solutions and applications of model. The imposed approach is ultimately thought to be more potent and effective than alternative approaches, and the solutions found in this work could be beneficial in our understanding of soliton structures in LCs.

Transmission-type 2-bit coding polarization conversion metasurface with radiation characteristic.

A transmission-type 2-bit coding polarization conversion metasurface with radiation function is proposed in this paper. Polarization conversion is realized by two layers of grating structure and polarization conversion structure layer. Compared with conventional polarization conversion metasurface which is composed of two orthogonal grating layers and polarization conversion arrows, the two grating layers of the proposed design are parallel. With the help of such well-designed parallel grating, spoof surface plasmon polaritons (SSPPs) can propagate through the surface of the metasurface. The efficiency of polarization conversion is almost unchanged at the same time. That is, when modulating the surface impedance periodically by tuning the structure parameters of the grating, SSPPs can be radiated into free space but the transmitted polarization conversion beam is not affected. Radiation characteristic exhibits during the frequency range of 2.7-4.7 GHz, while polarization conversion of transmission wave is realized at 6.2 GHz. The total scanning angle of the radiated beam covers from -36° to 41°, with an average gain of 10.0 dBi. The transmission efficiency of polarization conversion reaches 90%. Such multifunctional transmission-type coding metasurface shows great potential in the believed to be new radar and satellite communication systems with compact requirement.

Surface wave manipulation by metasurfaces in unsaturated soil: theoretical study

Metasurfaces provide a promising solution for modulating low-frequency surface waves (SW) in sub-wavelength size. However, they were coupled with single-phase soil or saturated soil in previous investigations, rather than the more common unsaturated soil whose properties cannot be simply evaluated from single-phase and saturated soils. Otherwise, they would not be operational in the intended frequency range. In addition, the screening performance of metasurfaces in unsaturated soils is unknown to us due to the complex physical fields and constitutive relationships of unsaturated soils. In this work, an analytical formulation is proposed to investigate interactions between SW and an array of resonators located atop the free surface of unsaturated soil semi-space and to evaluate the vibration damping performance of the metasurface in single-phase, saturated and unsaturated soils. The incident and scattered wave fields are clearly captured by using the Green's functions of an unsaturated semi-space subjected to a harmonic excitation source. Based on the multiple scattering theory, the displacement of the total wave field as well as some complex phenomena (surface-to-bulk wave conversion) are obtained and also validated in a 2D finite element model. It is notable that incorporating a resonator with different natural frequency create a new bandgap, implying that we can broaden the bandgap by installing more resonators with different natural frequencies. We expect this analytical formulation could solve SW scattering problems in geotechnical engineering, and the system with a broad bandgap could provide a conceptual design for weakening SWs.

Metasurface‐Loaded Twin‐Port Circularly Polarized Microstrip Array Antenna With High Gain and Isolation Features for mm‐Wave‐Based 5G Communication System

ABSTRACTIn this article, a MIMO microstrip aerial in mm‐wave regime is structured and examined. A 1 × 2 array‐based structure is designed to get directional radiation beam, which in turn provides good gain value, that is, 10.2 dBi in mm‐wave regime. The use of defected ground structure (DGS) improves the impedance matching (more than 25 dB) of the proposed radiator. Metasurface is suspended over the twin port aerial for adding two important features: (i) reduction of mutual coupling between antenna ports, that is, less than −25 dB; and (ii) conversion of the linear waves into the circular one in between 30.45 and 30.95 GHz. Experimental measurement of designed radiator confirms that designed aerial works in between 30.4 and 31.5 GHz with separation level more than 25 dB. Stable field pattern and good diversity parameter confirms its employability for mm‐wave 5G communication system.

Resonant conversion of gravitational waves in neutron star magnetospheres

High-frequency gravitational waves are the subject of rapidly growing interest in the theoretical and experimental community. In this work we calculate the resonant conversion of gravitational waves into photons in the magnetospheres of neutron stars via the inverse Gertsenshtein mechanism. The resonance occurs in regions where the vacuum birefringence effects cancel the classical plasma contribution to the photon dispersion relation, leading to a massless photon in the medium which becomes kinematically matched to the graviton. We set limits on the amplitude of a possible stochastic background of gravitational waves using X-ray and IR flux measurements of neutron stars. Using Chandra (2–8 keV) and NuSTAR (3–79 keV) observations of RX J1856.6-3754, we set strain limits hclim≃10−26–10−24 in the frequency range 5×1017 Hz≲f≲2×1019 Hz. Our limits are many orders of magnitude stronger than existing constraints from individual neutron stars at the same frequencies. We also use recent JWST observations of the Magnetar 4U 0142+61 in the range 2.7×1013 Hz≲f≲5.9×1013 Hz, setting a limit hclim≃5×10−19. These constraints are in complementary frequency ranges to laboratory searches with CAST, OSQAR and ALPS II. We expect these limits to be improved both in reach and breadth with a more exhaustive use of telescope data across the full spectrum of frequencies and targets. Published by the American Physical Society 2024

High-Efficiency Microwave Wireless Power Transmission via Reflective Phase Gradient Metasurfaces and Surface Wave Aggregation.

Microwave Wireless Power Transfer (MWPT) technology is crucial for emergency power supply during natural disasters and powering off-grid equipment. Traditional antenna arrays, however, suffer from low energy capture efficiency, difficult impedance matching, complex synthetic networks, and intricate manufacturing processes. This paper introduces a microwave energy receiver design utilizing Reflective Phase Gradient Metasurfaces (R-PGMs) and surface wave energy convergence technology. The design leverages the effective plane wave-to-surface wave conversion capability of R-PGMs to transform incident microwave energy into a surface wave mode, which is then efficiently harvested using a circular energy convergence array before being output to a coupling port. By optimizing R-PGM parameters, an ideal 60° phase gradient distribution is achieved, facilitating the focus of surface wave energy via dispersion characteristics. These components are integrated into a hybrid antenna array, complemented by a matched energy output port structure. Numerical simulations show that this array can efficiently convert microwave energy from plane waves to surface waves, achieving a conversion efficiency of 85.32% and a collection efficiency of 68.26%. Experimental results corroborate these findings, with peak energy collection efficiency reaching 64.68% at 5.8 GHz and an RF-DC conversion efficiency of 42%, confirming the design's efficacy. Compared to conventional methods, this design simplifies the system by avoiding complex combining networks and significantly enhances the efficiency of microwave MWPT.

Novel dynamics of the fractional KFG equation through the unified and unified solver schemes with stability and multistability analysis

Abstract The nonlinear fractional Klein–Fock–Gordon (KFG) equation represents an advanced theoretical physics and applied mathematical tool that provides a more extraordinary framework for studying fields with complex and non-standard behaviors. Here, we aim to delve into the new wave profiles of this fractional KGF equation. Initially, this system is successfully converted into an ordinary differential equation (ODE) with the help of wave conversion, and the ODE is solved through the unified and unified solver techniques for the first time. In addition, the 3D and 2D plots of these solutions are drawn using a mathematical software package for different parameters with different values. Therefore, some unique waveforms can be found in these solutions. Moreover, stability and multistability analyses are prepared and shown graphically to confirm the converging limitations of appropriate parameters. This work will be practiced more effectively in future research on nonlinear partial differential models.

Generation of bessel-like beam by a binary ultrasonic lens

Bessel beams have already been used in acoustic tweezers, ultrasonic medical imaging, and Doppler velocity estimation due to their non-diffractive and self-healing properties. We proposed a binary ultrasonic lens, with ultra-thin planar periodic structures for efficient conversion of the plane wave into a Bessel-like beam. The effectiveness of long-axis focusing has been demonstrated through simulations and experiments with FWHM of 8.5 mm and 9.5 mm around 10 mm. By varying the operating frequency of the incident wave from 1.9 MHz to 2.2 MHz, the position of the long-axis focusing point can be adjusted experimentally from 23.05 mm to 28.95 mm. Additionally, the beam generated by the binary ultrasonic lens can form a focused sound field when passing through multi-layered tissues and the self-healing capability of the Bessel-like beam has been numerically validated, showing strong robustness. This binary ultrasonic lens for a Bessel-like beam would conform better to ergonomic and miniaturization requirements, and expand versatile applications in clinical diagnosis and therapy.

Full-duplex two-way no-relay cross-media communication method based on acoustic wave conversion

Abstract Due to the difference in acoustic impedance between water and air, the water interface becomes a natural barrier. Underwater sound waves will bounce when they propagate to the water surface. Electromagnetic waves and light waves in the air will rapidly attenuate after passing through the water surface and going underwater, making it difficult to complete air-water cross-media information transmission. In this article, we first analyze the theoretical characteristics and vibration model of the water surface after medium collision, and develop a new full-duplex communication method across the air-ocean medium, which does not rely on relay equipment and only uses three transmission media in the air. Propagate signals in the sea channel physical field to achieve two-way communication, using the mutual conversion between laser, acoustic, and radio frequency signals to fill the gap in cross-media communication technology that can simultaneously achieve two-way, full-duplex and non-relay. It has been verified through experimental installations carried out in laboratory water tanks and large comprehensive anechoic pools that it is able to achieve full-duplex communication links across the air-sea surface, indicating that the combination of laser acousticization and radio frequency-acoustic wave conversion can be used across medium full-duplex wireless communication provides a feasible method for communication that breaks through the water interface.

Photoacoustic Signal Propagation Modes in Bone Tissue: a Simulation Study

Abstract Photoacoustic (PA) imaging has great potential in brain imaging. However, the strong acoustic attenuation and reverberation caused by the skull bone layers present challenges for PA brain imaging. In this work, we developed a three-dimensional (3D) photoacoustic numerical simulation platform using the finite difference time domain (FDTD) method to study PA signal generation and propagation in the human brain. This platform can simulate not only the propagation of longitudinal waves in soft tissues but also shear and longitudinal waves in hard tissues. Using this numerical simulation platform, we extensively simulated the propagation of PA waves in skull models with varying porosities, The results demonstrate that our 3D PA simulation platform accurately captures the propagation details of PA signals in the skull, including the refraction, reflection, and mode conversion of photoacoustic waves at tissue boundaries. Furthermore, an increase in skull porosity prolongs the duration of the photoacoustic signals and leads to high attenuation of PA signals for high frequency components. We expect that this study will contribute to the understanding of the impact on acoustic propagation of photoacoustic signals in cranial bone photoacoustic imaging.

Subsurface defect detection of high-temperatured components with laser induced surface wave

Abstract Subsurface defects are detrimental to the safety and integrity of critical components in various fields, particularly for those used in high-temperature environments. For this reason, a reliable non-destructive evaluation (NDE) method for in-situ inspection of subsurface defects of high-temperatured components is highly desired. Laser ultrasonic technique offers a promising potential to accommodate the demands in virtue of non-contact generation and detection of ultrasonic waves. In this work, laser ultrasosnic inspection of subsurface defects in high-temperatured components is proposed, which exploits the modal conversion of surface longitudinal wave to Rayleigh wave. The modal conversion was firstly investigated with finite element simulation, from which the phenomenon of modal conversion can be readily identified. Thereafter, an experimental setup is built to verify the feasibility and effectiveness of proposed method. Notably, a delay-and-sum method based on a scanning procedure is conducted to coherently increase the detection sensitivity of subsurface defects, since the surface longitudinal wave rapidly vanishes with propagation distance., and the temperature-dependant velocity variation can be adaptively compensated. This work provides a viable route for in-situ inspection of subsurface defects in high-temperatured components where conventional ultrasonic method fails, and it would find potential applications in broad fields, such as coating quality evaluation in fabrication, bearing assessment under load, and in-situ monitoring for additive manufacturing.

Relic Gravitational Wave Conversion into Photons in the Cosmological Magnetic Field

Relic Gravitational Wave Conversion into Photons in the Cosmological Magnetic Field

A high-efficiency hybrid microwave power receiving metasurface array with dual matching of surface impedance and phase gradient

This paper proposes a hybrid microwave power receiving (MPR) metasurface array with efficient dual matching of surface impedance and phase gradient. The hybrid array comprises three components: a reflective phase gradient metasurface (R-PGM) array, a surface wave focusing array, and an energy harvesting port. The R-PGMs efficiently convert incident electromagnetic waves into surface waves. The surface wave focusing array then concentrates the energy onto the integrated harvesting port through dual matching of surface impedance and phase gradient. Connecting a rectifier circuit enables efficient microwave energy reception and RF-DC conversion, avoiding the need for multiple rectifiers or complex feeding networks in traditional MPR designs. Numerical analysis and experimental tests verify the superior performance of this hybrid array design in efficient microwave energy harvesting and RF-DC conversion, achieving 90.84% plane wave-to-surface wave conversion efficiency, 76.67% surface wave energy harvesting efficiency, and 49.28% overall RF-DC conversion efficiency. Across the wideband range of 5.6–6.0 GHz, the energy harvesting efficiency remains consistently high, demonstrating the superior characteristics and promising potential of this design in MPR device development.

Controlling surface acoustic waves (SAWs) via temporally graded metasurfaces

In this manuscript, the temporal rainbow effect for surface acoustic waves (SAWs) is illustrated through a temporal analog of space metagradings. We show that a time-modulated array of mechanical resonators induces a wavenumber-preserving frequency transformation which, in turn, dictates Rayleigh-to-Shear wave conversion. The process is unfolded through the adiabatic theorem, which allows us to delineate the transition between a solely frequency-converted wave packet and a temporally-driven mode conversion. In other words, our paper explores the role of time modulation in the context of elastic metasurfaces, and we envision our implementation to be suitable for designing a new family of SAW devices with frequency conversion, mode conversion, and unusual transport capabilities.

Nonlinear dynamics driving the conversion of gravitational and electromagnetic waves in cylindrically symmetric spacetime

Nonlinear dynamics driving the conversion of gravitational and electromagnetic waves in cylindrically symmetric spacetime

Converting evanescent waves into propagating waves by hyper-hemi-microsphere.

Hyper-hemi-microspheres (HHMS) have shown promise in enhancing super-resolution imaging when combined with conventional optical microscopy. To offer actionable guidance for optimizing HHMS and hold broad applicability in the field of super-resolution imaging, the mechanism underpinning the enhanced imaging facilitated by HHMS is revealed by deriving the conversion and transmission conditions for evanescent waves. This is achieved by elucidating the intricate interplay between evanescent wave conversion and factors including refractive index, thickness, and surroundings of HHMS. Using the finite-difference time-domain (FDTD) method, influences of various HHMS properties on the conversion and transmission process are analyzed in detail. To fully harness the potential of HHMS in super-resolution imaging, the immersion conditions are elucidated.

Distortions in sound: Bridging acoustics and psychoacoustics in auditory perception

The field of acoustics encompasses the examination of sound, encompassing both its physical characteristics and the way in which humans perceive auditory input. Acoustics is the study of how sound waves are created and spread physically, while psychoacoustics connects these physical characteristics to our auditory perceptions. Comprehending these two features is essential for progress in audio technology and understanding auditory perception aberrations such as paracusia and diplacusis. This research consolidates information from multiple investigations to examine the interaction between acoustics and psychoacoustics. The technique entails examining the current body of literature on the fundamental principles governing sound waves, their interaction with various materials, and their movement across space. The examination of psychoacoustic elements involved the conversion of sound waves into brain impulses. The study also examines certain psychoacoustic phenomena, such as the sense of pitch and auditory distortions. By combining acoustic and psychoacoustic concepts, we can gain a thorough comprehension of how we perceive sound. Sound waves, generated by mechanical vibrations, pass through substances such as air, causing compression and rarefaction cycles that move at a speed of about 344 m/s at a temperature of 20°C. Psychoacoustics studies the perception of sound waves, specifically how they are processed by the ear and converted into neural signals that the brain can understand. The key findings reveal the subjective nature of pitch perception, where alterations in intensity or length impact the perceived frequency and the precise sensitivity of pitch discrimination. Furthermore, abnormalities such as paracusia and diplacusis emphasize the intricacies of auditory perception. The study highlights the significance of psychoacoustics in audio technology, where principles are utilized in audio compression and noise reduction to improve sound quality and clarity. The comprehensive comprehension of acoustics and psychoacoustics lays the groundwork for advancements in audio technology and the creation of auditory experiences.