Uniform Wave Research Articles

Rotationally shearing interferometer for extra-solar planet detection: preliminary results with a solar system simulator.

We describe preliminary experimental results on the laboratory demonstration of a technique to detect an extrasolar planet using a rotationally shearing interferometer. We simulate a planet and a star in a laboratory solar system. It consists of two laser beams; each passed through a spatial filter, collimated and combined. We confirm the theoretical prediction that the on-axis star generates no fringes for any shear angle. The star generates a uniform wave front that is invariant to the shear angle. Additionally, we demonstrate that the off-axis planet produces straight fringes. Thus, the mere presence of fringes confirms the existence of a planet. Furthermore, we illustrate that the fringe density and their inclination increase with the shear angle in the rotational shearing interferometer. Therefore, the number of fringes and their direction may be changed from the Earth to confirm (or reject) the existence of a planet.

Refraction and Straining of Near-Inertial Waves by Barotropic Eddies

AbstractFast-moving synoptic-scale atmospheric disturbances produce large-scale near-inertial waves in the ocean mixed layer. In this paper, we analyze the distortion of such waves by smaller-scale barotropic eddies, with a focus on the evolution of the horizontal wavevector k under the effects of straining and refraction. The model is initialized with a horizontally uniform (k = 0) surface-confined near-inertial wave, which then evolves according to the phase-averaged model of Young and Ben Jelloul. A steady barotropic vortex dipole is first considered. Shear bands appear in the jet region as wave energy propagates downward and toward the anticyclone. When measured at a fixed location, both horizontal and vertical wavenumbers grow linearly with the time t elapsed since generation such that their ratio, the slope of wave bands, is time independent. Analogy with passive scalar dynamics suggests that straining should result in the exponential growth of |k|. Here instead, straining is ineffective, not only at the jet center, but also in its confluent and diffluent regions. Low modes rapidly escape below the anticyclonic core such that weakly dispersive high modes dominate in the surface layer. In the weakly dispersive limit, k = −t∇ζ(x, y, t)/2 provided that (i) the eddy vertical vorticity ζ evolves according to the barotropic quasigeostrophic equation and (ii) k = 0 initially. In steady flows, straining is ineffective because k is always perpendicular to the flow. In unsteady flows, straining modifies the vorticity gradient and hence k, and may account for significant wave–eddy energy transfers.

Modulational instability of two obliquely interacting waves in presence of a thin pycnocline

Nonlinear evolution equations, correct up to fourth order in wave steepness, are derived for a pair of obliquely interacting wave packets in the presence of a thin pycnocline. These evolution equations are then employed to perform stability analysis of a pair of obliquely interacting uniform wave trains. Figures plotted here reveal that the growth rate of instability decreases with the increase in pycnocline depth and also with the increase in density difference across the pycnocline. When the angle of interaction between the two wave packets is less than certain critical value the growth rate of instability decreases with the increase in angle and beyond this critical value the result is reversed.

Improved Design of Uniform SIW Leaky Wave Antenna by Considering the Unwanted Mode

An improved design for the uniform substrate integrated waveguide (SIW) long slot leaky wave antenna (LWA) is presented in this communication. To achieve the desired sidelobe level (SLL), beamwidth and beam direction, proper distributions for leakage constant and phase constant should be created along the slot. An accurate calculation of leakage and phase constants is performed by considering an unwanted mode, in addition to the leaky mode, along the uniform LWA structure. Considering this unwanted mode in the design procedure results in good consistency between the desired and designed radiation patterns. The presented LWA realizes a Taylor distribution with predefined SLL of -25 dB at 17 GHz. The radiation pattern, amplitude distribution, and phase distribution of the designed antenna are compared with the desired ones. This comparison shows the high accuracy of the proposed design procedure. Measurement results are also presented at 16.5, 17, and 17.5 GHz for validation of the design procedure.

Many-body localization in the Bose-Hubbard model: Evidence for mobility edge

Motivated by recent experiments on interacting bosons in quasi-one-dimensional optical lattice [Nature {\bf 573}, 385 (2019)] we analyse theoretically properties of the system in the crossover between delocalized and localized regimes. Comparison of time dynamics for uniform and density wave like initial states enables demonstration of the existence of the mobility edge. To this end we define a new observable, the mean speed of transport at long times. It gives us an efficient estimate of the critical disorder for the crossover. We also show that the mean velocity growth of occupation fluctuations close to the edges of the system carries the similar information. Using the quantum quench procedure we show that it is possible to probe the mobility edge for different energies.

Investigation of capillary wave, cavitation and droplet diameter distribution during ultrasonic atomization

Droplet size distribution during ultrasonic atomization was investigated by laser diffraction based on two phenomena—capillary waves and cavitation. The former was visually illustrated using the photographic method, and the latter was examined by the potassium iodide decomposition rate test and Particle Image Velocimetry technique. This study also analyzed the effects of operating ultrasonic parameters such as input power, the flow rate of liquid and gas, liquid temperature, distance from the vibrational tip to laser, and physicochemical properties of liquids (surface tension and viscosity). The relationship among capillary waves, cavitation, and the droplet size distribution was developed for the first time. Results suggest that uniform capillary waves and low cavitation intensity contribute to narrow droplet size distribution. Bimodal droplet size distribution was observed with an increasing liquid flow rate and an assisted gas flow rate. The droplet size did not keep increasing or decreasing with increasing input power and liquid viscosity. A new correlation based on all data using dimensionless numbers was then proposed to predict droplet sizes. This work presents an effective ultrasonic atomization approach to obtaining desirable droplet size distribution by choosing optimum operating parameters, and establishes the controlling mechanism for ultrasonic atomization.

Entropy Generation in Magnetized Blood Flow Through a Finite Wavy Channel Under Slip Conditions

Abstract This study deals with the entropy generation in magnetized blood flow through a channel. The blood is modeled as a non-Newtonian fluid that circulates by a uniform peristaltic wave with slip at the boundaries. An inertia free flow is considered using an approximation of the long-wavelength peristaltic wave. The governing equations of the flow are formulated and numerically solved using computational software to identify the characteristics of this non-uniform and time-dependent flow system. In addition, several closed-form solutions of the problem are explicitly presented.

Effects of Voltage and Current Waveforms on Pulse Discharge Energy Transfer to Underwater Shock Waves for Medical Applications

The effects of voltage and current pulse durations of underwater discharge on shock wave generation are reported. In this article, underwater discharges were generated by using a magnetic pulse compression (MPC) circuit. The compression number of the MPC circuit was varied from two compressions to one and no compression; also the capacitance of an output peaking capacitor connected in parallel to discharge electrodes (load) was varied from 10 to 6 and 2 nF. As a result, electric pulses with different rise time/duration and variable peak voltages and currents were obtained and applied to generate shock waves. The shock waves were quantitatively measured with optical principles using a fiber optic probe hydrophone (FOPH) pressure transducer. By reflecting the generated shock waves from a reflector, uniform shock waves were produced, which made it possible to accurately measure the shock waves. The maximum pressure of the generated shock wave after the reflection was in the range of 40 MPa. The energies of the output shock waves were calculated from the pressure histories and the electrical to shock wave energy conversion efficiency was calculated from the electrical energy used to generate the shock waves. The results indicated that the rise time of voltage and current significantly affects the electrical energy that can be delivered to generate the shock waves. For the range of the electric pulse durations of 100 to 500 ns of this article, the shock waves pressures were independent of the pulse duration for the same input energy consumed during the rise and full width at half maximum times of the current. The method presented here gives possibility to select the shock wave profile, which would be crucial for successful medial applications.

Uniform propagation of cathode-directed surface ionization waves at atmospheric pressure

The uniform propagation of positive-polarity surface plasmas in air at atmospheric pressure has been achieved using a multi-layer structure, consisting of a silicon wafer covered by a 1 μm thick dielectric SiO2 layer as a propagation surface. Instead of the branched streamers observed in the same conditions when using conventional bulk dielectric surfaces, the plasma exhibits a homogenous ring-shaped structure with a high degree of reproducibility and stability. The plasma is generated by applying nanosecond positive voltage pulses to a tungsten wire touching the dielectric surface. The plasma has been imaged in single shot operation at high spatial resolution with an ultraviolet reflective microscope coupled with a fast intensified charge-coupled device camera. Time- and space-resolved optical emission spectroscopy shows that the homogenous ring corresponds to the propagation of an ionization front with a region of high N2+* emission. We discuss the origin of the ring-shaped ionization wave, considering the role of the Si–SiO2 interface and the effect of illumination by an external light source. The ring ionization wave may result from branching inhibition, due to a photoelectric effect at the interface created by the photons emitted by the plasma. The generation of stable uniform surface ionization waves, in ambient air at atmospheric pressure, could be of interest for further advanced plasma–surface interaction studies or flow control applications.

Morphodynamic Modelling of Flash Rip Current Driven Coastal Sediment Transport

Park, S.; Kim, D.-H., Yoo, H., 2020. Morphodynamic modelling of flash rip current driven coastal sediment transport. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1229–1234. Coconut Creek (Florida), ISSN 0749-0208.The characteristics of the sediment transport driven by flash rip currents at nearshore areas was investigated using a morphodynamic model coupled with a fully nonlinear Boussinesq-type model and a sediment transport model. Wave transform processes in surfzone such as shoaling, refraction, breaking, runup, and rundown processes were included in the numerical model. The vorticity and turbulent eddy viscosity were considered to account for rotational and turbulent flow characteristics. In addition, the horizontal density variation and bottom evolution caused by sediment transport were integrated into the fully nonlinear Boussinesq-type model. A fourth-order finite volume method, based on the MUSCL scheme with an approximate Riemann solver, was used to solve the governing equations. Uniform and parallel wave fields were simulated on a plain beach with a uniform sandbar with very small disturbance on the bathymetry. Because the wave generator was parallel to the beach, no significant longshore current and longshore sediment transport were generated. From the tested case, transient offshore-directed strong rip currents (the wave-averaged flow velocity 0.5 m/s) appeared in various locations. Turbid suspended sediment currents were also randomly generated by the waves and currents. The modelling results and analysis showed that the offshore direction sediment transport was strongly associated with the flash rip current generated within the surfzone.

Experimental and Numerical Analysis of a 10 MW Floating Offshore Wind Turbine in Regular Waves

Floating offshore wind turbines (FOWTs) experience fluctuations in their platforms, owing to the various wave and wind conditions. These fluctuations not only decrease the output of the wind power generation system, but also increase the fatigue load of the structure and various equipment mounted on it. Therefore, when designing FOWTs, efficient performance with respect to waves and other external conditions must be ensured. In this study, a model test was performed with a 10 MW floating offshore wind turbine. The model test was performed by scaling down a 10 MW FOWT model that was designed with reference to a 5 MW wind turbine and a semisubmersible platform by the National Renewable Energy Laboratory and the DeepCwind project. A scale ratio of 1:90 was used for the model test. The depth of the East Sea was considered as 144 m and, to match the water depth with the geometric similarity of mooring lines, mooring tables were installed. The load cases used in the model test are combined environmental conditions, which are combined uniform wind, regular waves and uniform current. Especially, Model tests with regular waves are especially necessary, because irregular waves are superpositions of regular waves with various periods. Therefore, this study aimed to understand the characteristics of the FOWTs caused by regular waves of various periods. Furthermore, in this model test, the effect of current was investigated using the current data of the East Sea. The results obtained through the model tests were the response amplitude operator (RAO) and the effective RAO for a six degrees-of-freedom motion. The results obtained from the model tests were compared with those obtained using the numerical simulation. The purpose of this paper is to predict the response of the entire system observed in model tests through simulation.

Simulation of Patterned Cathode Catalyst Layer-Electrolyte Interface, with Gaussian Roughness, for Improved PEMFC Power Performance

Proton Exchange Membrane fuel cells (PEMFCs) are becoming an increasingly promising piece of power generation technology that can fit into the changing economy as we strive towards a sustainable energy based future. However, PEMFCs struggle to meet the energy demands of the world, falling short of the capability of other energy sources such as fossil fuels, mainly due to price and energy output compared to the already establish combustion engines. Looking internally into the PEMFC itself, one of the main issues is the limitations of the electrode-membrane interface leading to low ion transfer performance from the catalyst layer to the polymer electrolyte membrane. If we can improve the cathode-membrane interface facilitating the oxygen reduction reaction (ORR) rate at the cathode, the rate limiting step, we can increase the overall performance of the fuel cell.It is believed that by increasing the interfacial area of the cathode catalyst layer-membrane interface, by applying a prismatic pattern to the morphology, we can thus increase the active surface area for the membrane electrode assembly (MEA). By varying the frequency of prisms, and the relative height of these prisms compared to the fixed total height of the catalyst layer and membrane, the interfacial area can be increased, improving the current density, which would result in an improved overall power performance of the PEMFC.In this work, with a LiveLink connection between Matlab and multiphysics software COMSOL, we model the electrode-membrane interface to investigate the influence of the operating conditions and the morphology of the membrane surface on the ion-transfer performance of PEMFCs. By varying the number and size of prism peaks applied to the interface, it is shown that we can influence the fuel cell performance whilst maintaining a constant membrane and cathode volume as well as the amount of platinum used in the catalyst layer whilst, due to economies of scale, maintaining a similar cost per membrane compared to a flat membrane interface.Previous research has shown that there is a negative impact on power performance when the cathode catalyst layer-electrolyte interface is patterned with a low number of peaks with small relative heights compared to the total height of the electrolyte and catalyst layer. However, at higher frequencies of peaks and relative peak heights, an improvement of up to 25% was achieved in the power performance, and a 21% improvement was seen in the polarization curve.However, this model suggests perfectly smooth interfaces between the electrolyte and the catalyst layer. In reality, there would be a level of roughness to this interface, which would have an impact on the results of the simulated fuel cell performance.This research looks into how the application of the roughness to the interface, created using a combination of Gaussian and Uniform wave functions, will impact any previous results observed, and allow us to simulate a model that fits better with the real world findings.The results obtained here could help determine the appropriate parameters required to validify our experimental work, and provide reference for the future work carried out in this research field. Figure 1

Precision analysis of turbulence phase screens and their influence on the simulation of Gaussian beam propagation in turbulent atmosphere.

The slip-step method is widely used in simulating optical wave propagation in turbulent atmosphere, which treats propagation and phase perturbations caused by turbulence separately and in discrete steps along the propagation axis. The phase perturbations are represented by a series of phase screens, and hence, the precision of the phase screen concerns the accuracy of the simulation. In this paper, we first discuss the precision and computational performance of phase screens generated by the subharmonic complemented discrete Fourier transformation (DFT) (DFT-SH) method, three kinds of randomized spectral sampling techniques (sparse spectrum (SS) technique, sparse spectrum technique with uniform wave vectors (SU), randomized DFT technique), and optimization-based (OB) method; then, the simulations are implemented with the phase screens generated by these methods. Some statistical quantities of the received optical field are calculated, such as beam wander variance, long-term beam radius, short-term beam radius, and on-axis scintillation index. The statistical results show that the undersampling of phase screen in the low-frequency region causes underestimation of the values of beam wander variance, long-term beam radius, and focused beam on-axis scintillation index because these quantities are sensitive to the large-scale inhomogeneities. However, the undersampling does not affect the predicted values of the short-term beam radius and collimated beam on-axis scintillation index because these quantities are insensitive to the large-scale inhomogeneities.

Comparison of four techniques for turbulent phase screens simulation.

In the study, we introduce a new technique, sparse spectrum with uniform wave vectors (SU), for generation of phase screen samples. In a manner similar to the known sparse spectrum (SS) technique, it uses a trigonometric series with random discrete spectral support. However, in contrast to the SS technique, random wave vectors are uniformly distributed on individual segments of the wave vector plane partition in the SU technique. We compare the accuracy and computational effectiveness of the SU technique with the subharmonics complemented discrete Fourier transform (DFT) technique, SS technique, and randomized DFT technique [ J. Opt. Soc. Am. B36, 3249 (2019)JOBPDE0740-322410.1364/JOSAB.36.003249]. The SU and SS techniques generate unbiased samples and indicate superior computational effectiveness for 1 MP and larger screens.

Shaking table test verification of traveling wave resonance in seismic response of pile-soil-cable-stayed bridge under non-uniform sine wave excitation

The traveling wave resonance phenomenon exhibits in the seismic response of the symmetric bridge structure. However, there is a scarcity of shaking table tests validating the traveling wave resonance. A 1/70-scale pile-soil-cable-stayed bridge model was fabricated following the preliminary design of a cable-stayed bridge with a main span of 1400 m. Shaking table tests were performed to verify the traveling wave and mode shape resonances in the seismic response of the bridge model when separately subjected to two specific sine waves longitudinally. The vertical acceleration frequency spectra and seismic response of the bridge model were compared between uniform and non-uniform sine wave excitation. The results showed that the traveling wave and mode shape resonances were examined in the seismic response of the pile-soil-cable-stayed bridge model under non-uniform excitation of the specific sine waves. The traveling wave excitation increased the symmetric response at the symmetric girder location but decreased the antisymmetric responses of the towers and girder, compared to the uniform excitation regarded as antisymmetric input. Finally, a finite element model was developed in OpenSees that could capture the seismic response changes caused by the traveling wave effects of the specific sine waves and proximately reproduce the experimental results. Therefore, the traveling wave and mode shape resonances were verified by the numerical simulations.

Hybrid U-Shaped-Microbend SMF Evanescent Wave Sensor for River Water Quality Assessment: A Preliminary Study

A hybrid U-shaped-microbend fiber optic evanescent wave sensor was developed by combining two types of bending structures on the optical communication single mode optical fiber (SMF28). To study the effect optical microbending on the output power, corrugated plates consisted of cylindrical structured surface with various distance between the glass rods of 6 cm, 12 cm and 18 cm were constructed. The macrobending effect was introduced by bending the SMF into two shapes, namely U-shaped and Sshaped. The bare SMF with various bending designs were immersed into numerous water sources from Sg. Simin, Sg. Batang Benar and Sg. Klang. The output demonstrated that Sg. Simin was the most polluted river, followed by Sg. Klang and Sg. Batang Benar using U-shaped microbend SMF with distance between glass rod of 6cm and 1310 nm laser source. This result showed an excellent agreement with water quality index (WQI) data released by the Department of Environment (DOE), Malaysia. Maximum optical output power was obtained by using Sg. Simin’s water sample due to better light absorption from the evanescent waves by the pollutant particles, that avoided light leakage in comparison with less polluted water sources. The optimum sensing performance was successfully resulted by using U-shaped SMF due to its durability and uniform evanescent waves radiated from the cladding. In conclusion, the hybrid U-shaped-microbend SMF sensor based on evanescent waves propagation portrays an excellent potential to detect water pollution by monitoring the presence of pollutants around the fiber.

Optimized Scheme of Antenna Diversity for Radio Wave Coverage in Tunnel Environment

To suppress the deep fading of radio waves caused by the tunnel waveguide effect, this paper presents an optimized scheme for the spatial and polarization diversities of tunnel antennas. Through the correlation coefficient analysis of path loss curves obtained by antennas placed at different positions, the two antenna positions that generate path loss curves with the lowest correlation coefficient are found, and these two antennas are defined as a diversity antenna pair. Using this scheme, the spatial diversity properties of the transmitting antenna and receiving antenna, as well as the spatial-polarization combined diversity property of the transmitting antenna, are obtained. Furthermore, the impact of antenna polarization on the spatial diversity property is investigated. The performance of the proposed scheme for spatial and polarization diversities is evaluated in terms of the intensity and uniformity of the path loss. The simulation results illustrate that the proposed diversity optimization scheme can suppress the influence of the waveguide effect and achieve more uniform and flatter radio wave coverage in a tunnel environment.

Writing arbitrary distributions of radiant exposure by scanning a single illuminated spatially random screen

Arbitrary distributions of radiant exposure may be written by transversely scanning a single known spatially-random screen that is normally illuminated by spatially but not necessarily temporally uniform radiation or matter wave fields. The arbitrariness, of the written pattern of radiant exposure, holds up to both (i) a spatial resolution that is dictated by the characteristic transverse length scale of the illuminated spatially random screen, and (ii) a background term that grows linearly with the number of random-illumination patterns. Two classes of the method are developed. The former assumes the distance between the illuminated random mask and the target plane to be sufficiently small that the effects of diffraction may be neglected. The latter accounts for the effects of Fresnel diffraction in the regime of large Fresnel number. Numerical simulations are provided for both variants of the method. Contrast and signal-to-noise ratio are also considered. The method may be parallelized, and is suited to both magnifying and de-magnifying geometries. Possible applications include spatial light modulators and intensity projectors for those matter and radiation wave fields for which such devices do not exist, printing or micro-fabrication in both two and three spatial dimensions, and lithography.

Scaling relationships between acoustic and electromagnetic scattering by an infinite cylinder

The conversion relationships, including the scaling of frequencies and sizes, between the scattering of a uniform plane electromagnetic wave by a dielectric cylinder and the scattering of a uniform plane acoustic wave by a non-shear-stress cylinder are studied. Owing to the dependence of electromagnetic scattering on polarization, especially for dielectric materials, a simulation method using two acoustic materials is proposed for cases with complex polarization, such as circular polarization. The scaling relationships are verified by simulation. This approach proves to be an effective supplement to the indirect method of measuring electromagnetic scattering by acoustic scattering. A preliminary study of scattering by three-dimensional objects is also performed for the simplest case of spheres. Although the results are not as good as those for two-dimensional objects, the errors after processing are sufficiently small for these results to be accepted as estimates.

Early detection of cancerous tissues in human breast utilizing near field microwave holography

AbstractThis work demonstrates an application of near field indirect microwave holography for the detection of malignant tissues in human breast in an effective way. The holograms are recorded by two directive antennas aligned along each other's boresight while performing a raster scan over a 2D plane utilizing XY‐linear motorized translation stage and a uniform reference wave. The whole information that is, amplitude and phase of an object has been provided by indirect holography at microwave frequencies. The extracted phase values are used to determine the dielectric permittivity values which are further utilized for the identification and validating the positions of malignant tissues in the breast phantom. The experimental evaluations performed on the in‐house designed and developed tissue mimicking 3D printed breast phantoms. The experimental results demonstrate the ability of microwave holography using directive antennas in detecting and identifying the tumors upto the minimum size of 4 mm and maximum depth of 25 mm in fabricated phantom. The quantitative results present the potential of the Near Field Indirect Holographic Imaging (NFIHI) in order to develop an efficient and economical tool for breast cancer detection.