Wave Dipole Research Articles

Vacuum Breakdown in Multibeam Configuration of a Magnetic Dipole Wave

Vacuum Breakdown in Multibeam Configuration of a Magnetic Dipole Wave

Spontaneous periodic polarization wave in helielectric fluids.

By analogy with spin waves in ferromagnetic systems, the polarization (or dipole) wave is the electric counterpart that remains elusive. Here, we discover that the helielectricity, i.e. a polarization field with helicoidal helices that corresponds to a quasi-layered chiral nematic environment, causes a spontaneous formation of large-scale polarization waves in the form of the sinusoidal function. Both experimental and theoretical analyses reveal that the polarization ordering over a threshold polarization strength violates the inherent periodicity of the polarization helices, thus penalizing the compression energy. It drives a second-order structural transition to a periodically modulated polarization wave state. The roles of chirality and confinement condition are discussed.

Joint inversion of formation radial shear-velocity profiles by dipole acoustic logging while drilling

Formation properties near a borehole are frequently altered by mechanical damage from drilling, leading to variations of formation elastic velocities in the radial direction. Inversions of radial shear profiles are necessary for a real-time evaluation of the drilling conditions. In this study, we investigate acoustic wave propagation in a logging-while-drilling (LWD) model excited by a dipole transducer in cylindrically layered media. It is revealed that the dispersion characteristics of the dipole waves of the LWD are sensitive to the radial formation velocity variation. Accordingly, we develop a joint inversion method that evaluates radial shear-velocity profiles using the dipole modes of the first and second orders. The propagation of these two modes is strongly influenced by formation alterations, but the inversion results obtained using a single dipole mode indicate ambiguity caused by the nonuniqueness problem. Through our joint inversion, the additional second-order dipole wave can effectively help address the nonuniqueness issue in dipole acoustic logging, although its dispersion features differ in fast and slow formations. It is validated that the joint inversion has considerably improved convergence and accuracy in evaluating the thickness and shear velocity of the altered zone, compared with the estimation by a single acoustic mode. Furthermore, we develop numerical results based on synthetic logging data to demonstrate the feasibility of this inversion in a continuously varying profile, regardless of whether the formation surrounding the borehole is fast or slow. Even when strong drilling noises of low frequencies are added to the receiver signal arrays, the means of joint inversion can remain stable, and the shear-velocity profiles can be evaluated with good precision.

Simulation of tsunami induced by a submarine landslide in a glaciomarine margin: the case of Storfjorden LS-1 (southwestern Svalbard Islands)

Abstract. A modelling approach to understand the tsunamigenic potentiality of submarine landslides will provide new perspectives on tsunami hazard threat, mostly in polar margins where global climatic change and its related ocean warming may induce future landslides. Here, we use the L-ML-HySEA (Landslide Multilayer Hyperbolic Systems and Efficient Algorithms) numerical model, including wave dispersion, to provide new insights into factors controlling the tsunami characteristics triggered by the Storfjorden LS-1 landslide (southwestern Svalbard). Tsunami waves, determined mainly by the sliding mechanism and the bathymetry, consist of two initial wave dipoles, with troughs to the northeast (Spitsbergen and towards the continent) and crests to the south (seawards) and southwest (Bear Island), reaching more than 3 m of amplitude above the landslide and finally merging into a single wave dipole. The tsunami wave propagation and its coastal impact are governed by the Storfjorden and Kveithola glacial troughs and by the bordering Spitsbergen Bank, which shape the continental shelf. This local bathymetry controls the direction of propagation with a crescent shape front, in plan view, and is responsible for shoaling effects of amplitude values (4.2 m in trough to 4.3 m in crest), amplification (3.7 m in trough to 4 m in crest) and diffraction of the tsunami waves, as well as influencing their coastal impact times.

Simulation of electric field response of horizontal circular electric half wave dipole antenna for seabed logging

Seabed logging (SBL) is a direct and remote application of controlled source electromagnetic (CSEM) method to detect hydrocarbon resources beneath the seafloor in offshore conditions. In this method, electromagnetic waves are used to detect the resistivity contrast between various sediment layers. The current source of electromagnetic waves is a horizontal electric dipole (HED) antenna. The antenna design represents a challenge in shallow waters (less than500 m seawater depth) due to the presence of airwaves that lead to a low signal-to-noise ratio, hence hindering the detection of a hydrocarbon reservoir. A horizontal circular electric half-wave dipole will be used in this work as the source of electromagnetic waves. The numerical solution for the electric field response will be developed based on solving the Maxwell equations in two modes: the poloidal and toroidal modes. Simulation results have shown that the new antenna is able to detect the presence of deep hydrocarbon reservoirs (up to 5000 m) in shallow-water environment. Comparison of the average percentage difference in delineation between the circular and the HED was carried out. The new antenna results in 61 % delineation compared to 15 % for the HED at 5000 m hydrocarbon depth and 200 m seawater depth, indicating the ability of the antenna to disperse the airwaves. The results also show that the airwaves are significantly reduced from nearly 15000 m (for the HED) to 10000 m offset for the proposed antenna, hence increasing the signal-to-noise ratio. These results seem to indicate the potential for the new antenna to be used as an EM source for SBL in shallow-water environment.

Vacuum breakdown in magnetic dipole wave by 10-PW class lasers.

The vacuum breakdown by 10-PW-class lasers is studied in the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. Using 3D PIC simulations we calculated the threshold of vacuum breakdown, which is about 10PW. We examined in detail the dynamics of particles and identified particle trajectories which contribute the most to vacuum breakdown in such highly inhomogeneous fields. We analyzed the dynamics of the electron-positron plasma distribution on the avalanche stage. It is shown that the forming plasma structures represent concentric toroidal layers and the interplay between particle ensembles from different spatial regions favors vacuum breakdown. Based on the angular distribution of charged particles and gamma photons a way to experimentally identify the process of vacuum breakdown is proposed.

Particle trajectories, gamma-ray emission, and anomalous radiative trapping effects in magnetic dipole wave.

In studies of interaction of matter with laser fields of extreme intensity there are two limiting cases of a multibeam setup maximizing either the electric field or the magnetic field. In this work attention is paid to the optimal configuration of laser beams in the form of an m-dipole wave, which maximizes the magnetic field. We consider in such highly inhomogeneous fields the advantages and specific features of laser-matter interaction, which stem from individual particle trajectories that are strongly affected by gamma photon emission. It is shown that in this field mode qualitatively different scenarios of particle dynamics take place in comparison with the mode that maximizes the electric field. A detailed map of possible regimes of particle motion (ponderomotive trapping, normal radiative trapping, radial, and axial anomalous radiative trapping), as well as angular and energy distributions of particles and gamma photons, is obtained in a wide range of laser powers up to 300 PW, and it reveals signatures of radiation losses experimentally detectable even with subpetawatt lasers.

Polarization singularities and Möbius strips in sound and water-surface waves

We show that polarization singularities, generic for any complex vector field but so far mostly studied for electromagnetic fields, appear naturally in inhomogeneous yet monochromatic sound and water-surface (e.g., gravity or capillary) wave fields in fluids or gases. The vector properties of these waves are described by the velocity or displacement fields characterizing the local oscillatory motion of the medium particles. We consider a number of examples revealing C-points of purely circular polarization and polarization Möbius strips (formed by major axes of polarization ellipses) around the C-points in sound and gravity wave fields. Our results (i) offer a new readily accessible platform for studies of polarization singularities and topological features of complex vector wave fields and (ii) can play an important role in characterizing vector (e.g., dipole) wave–matter interactions in acoustics and fluid mechanics.

Design and Implementation of Wide Band for Biconical Antenna for X Band Applications

This paper reflects architecture and pattern synthesis for biconical antenna. The Biconical Antenna Radiation Pattern is identical to the half wave dipole antenna. The ramp shaped Radiation pattern is obtained by varying different antenna parameters such as amplitude distribution, phase distribution, spacing between the element and number of elements. Biconical antennas (2-14) GHz operating range gives reflection co-efficient- 0.46; return loss- 10dB, VSWR- 2.5:1, Gain (2-4) dB with 50Q input impedance.Biconical antenna was designed using CST Microwave Studio.

Critical phenomena in the gravitational collapse of electromagnetic dipole and quadrupole waves

We report on critical phenomena in the gravitational collapse of electromagnetic waves. Generalizing earlier results that focused on dipole electromagnetic waves, we here compare with quadrupole waves in axisymmetry. We perform numerical simulations of dipole and quadrupole wave initial data, fine-tuning both sets of data to the onset of black hole formation in order to study the critical solution and related critical phenomena. We observe that different multipole moments have different symmetries, indicating that the critical solution for electromagnetic waves cannot be unique, at least not globally. This is confirmed in our numerical simulations: while dipole data lead to a single center of collapse, at the center of symmetry, quadrupole data feature two separate centers of collapse on the symmetry axis, above and below the center of symmetry -- reminiscent of similar findings reported for critical collapse of vacuum gravitational waves. While the critical solution for neither the dipole nor the quadrupole data is exactly self-similar, we find that their approximate echoing periods appear to differ, as do the critical exponents. We discuss whether the centers of collapse found for dipole and quadrupole data might all have the same properties, which would suggest a "local uniqueness" of the critical solution. Instead, we provide some evidence -- including the differing echoing periods and critical exponents -- suggesting that the critical solutions are distinct even locally. We speculate on the implications of our findings for critical phenomena in the collapse of vacuum gravitational waves, which share with electromagnetic waves the absence of a spherically symmetric critical solution.

Assessment of adaptive capacity to sea level rise using open-loop system, case study: Cirebon and Pangandaran

This research aims to assess the adaptive capacity of three adaptive strategies applied in Cirebon and Pangandaran by estimating community assets under threat of Sea-Level Rise (SLR) through open-loop system. Firstly, SLR in Cirebon and Pangandaran each month from 2006 to 2100 is simulated using ocean heat flux and ice melting model data by Representative Concentration Pathways (RCP) 8.5, Intergovernmental Panel of Climate Change Assessment Report (IPCC AR) 5. This simulation result is then added with ocean phenomena such as tide, Indian Ocean Dipole (IOD), Madden-Julian Oscillation (MJO), storm surge, and Kelvin wave along with their frequencies. By the year 2100, the sea level in Cirebon will reach 115.65 cm and 148.09 cm in Pangandaran. Secondly, the SLR and applied strategies are converted to be inundation maps of community assets. Overall, the result shows the best policy for both regencies is protect which has an adaptive capacity value of 96.30% and 76.65% respectively. But deeper, the adaptive strategy for each district in both regencies differs one to another.

Wideband Triple Sleeve Dipole Antenna with Loading for UHF Applications

ABSTRACT A novel miniaturized dipole antenna design incorporating triple sleeves and shorting load leading to enhanced bandwidth is proposed in the present work. The Triple Sleeve Dipole Antenna with Shorting Loads is designed from 500 to 3000 MHz with no tuning mechanism. The concept of triple sleeve and distributed shorting loads reduced the length of the antenna by 51.5% compared to a half wave dipole antenna at the lowest frequency. The equivalent circuit of the antenna in terms of lumped elements is determined by using a Genetic algorithm. The proposed antenna is simulated in CST Microwave Studio, fabricated, evaluated and the results are presented. The antenna can be used for trans-receive applications of wireless communications in military systems.

Design of reduced dipole yagi – Uda antenna

This work provides design and analysis of a dipole antenna whose height is reduced. Any Dipole antenna can be designed with λ/2 height. A half wave dipole is formed with ‘λ/2’ height to get desirable characteristics of dipole antenna. Minimizing antenna height is always a desirable in antenna design. Hence, an attempt is made in this work to reduce the height of a dipole and as an application, Yagi-Uda antenna is constructed using this reduced dipole and optimized for better gain. The results are discussed in detail.

Design and Simulation of Half Wave-dipole Antenna for LTE Applications Using CST microwave Studio

One of the most important and widely used Radio frequency (RF) antennas is the dipole antenna. This is commonly used on its own and is also integrated into many other prototypes of the RF antenna, where it is the guiding factor for the antenna. An effort has been made in this project to study the latest half wave dipole antenna for LTE Applications. The dipole antenna, which is nearly one-half wavelength long, is known as the half-wave dipole antenna. The antenna was designed for resonating at the frequency of 2.6 GHz. For the simulation and design calculations CST is used. In this project various factors of antenna such as the return loss, standing wave ratio from Smith charts, Real power Vs Frequency, VSWR, E-field and H-field distribution, gain and radiation pattern are also evaluated.

Borehole elastic wave anisotropic scattering and application to hydraulic fracturing

Anisotropy is an important property of inhomogeneous underground rocks and a central topic for geophysical exploration. Detecting the inhomogeneous anisotropy of rocks is key for rational oil and gas reservoir utilization and well placement optimization. Conventional cross dipole measurements can only evaluate the anisotropy of formation rocks near the borehole wall, and are therefore unable to evaluate the rock anisotropy at a distance from the borehole. This study investigates the anisotropic distribution of rock heterogeneity and the resulting azimuthal variation of the acoustic scattering intensity. The results show that this azimuthal scattering intensity variation of the dipole shear-wave acoustic logging data can be used to evaluate the anisotropic distribution of the rock heterogeneity. A borehole model with a three-dimensional heterogeneous and anisotropic elastic formation was established first, and the dipole acoustic logging along the borehole model was simulated using a finite difference technique. The wave-scattering effect in the borehole dipole wave data, measured in terms of a coda wave attenuation, was analyzed. The scattering attenuations of coda waves measured in different azimuthal directions exhibit significant variations, which are related to the azimuthal variation of the formation inhomogeneity. Based on the results of theoretical modeling, a method for the evaluation of the anisotropic variation of formation inhomogeneity (via azimuthal pattern of the scattering attenuations) was proposed. The method was applied to dipole acoustic logging data, acquired before and after hydraulically fracturing a tight reservoir. The field data results show that the scattered dipole-shear coda wave attenuation of the after-fracturing data exhibits an elongated, anisotropic variation pattern, where the direction of elongation coincides with the fracture extension direction. This indicates good potential for using the proposed method for hydraulic fracture evaluation. Because wave scattering occurs in a large volume around the borehole, application of this method and analysis can significantly enhance the measurement volume of the cross-dipole logging technology. This extends its effectiveness toward the evaluation of hydraulic fracturing results for unconventional reservoirs (e.g., shale gas).

Confinement of electrons in the focus of the dipole wave

Based on the numerical modelling of the electron dynamics in the focal region of a dipole wave, we have found the confinement time of electrons in the region of the strongest electric field in a wide (up to 200 PW) power range. By comparing confinement times of particles and the spatial structures of their escape, we have determined the regimes of ponderomotive escape and radiation-dominated escape corresponding to normal and anomalous radiative trapping, as well as the threshold powers of these regimes. It is shown that in the regimes of ponderomotive escape, the confinement time decreases with increasing power and stabilises at the level of one third of the wave period with the particles leaving the focal region predominantly across the electric field. In the radiation-dominated regime, the confinement time, on the contrary, increases with increasing power, the rate of transverse particles’ escape decreases, and the particles leave the focal region in the form of compact beams.

Laser-cooled cesium atoms confined with a magic-wavelength dipole trap inside a hollow-core photonic-bandgap fiber

We report loading of laser-cooled caesium atoms into a hollow-core photonic-bandgap fiber and confining the atoms in the fiber's 7 $\mu m$ diameter core with a magic-wavelength dipole trap at $\sim$935 nm. The use of the magic wavelength removes the AC-Stark shift of the 852nm optical transition in caesium caused by the dipole trap in the fiber core and suppresses the inhomogeneous broadening of the atomic ensemble that arises from the radial distribution of the atoms. This opens the possibility to continuously probe the atoms over time scales of a millisecond -- approximately 1000 times longer than what was reported in previous works, as dipole trap does not have to be modulated. We describe our atom loading setup and its unique features and present spectroscopy measurements of the caesium's D$_{2}$ line in the continuous wave dipole trap with up to $1.7 \times 10^{4}$ loaded inside the hollow-core fiber.

Constraining the Braking Index and Energy Partition of Magnetar Spindown with Swift/XRT Data

Abstract The long-lasting X-ray plateau emission in long gamma-ray bursts (GRBs) shows observational evidence for ongoing energy injection, which may be from magnetar spindown due to energy released via either magnetic dipole (MD) or gravitational wave (GW) radiation. In this paper, by systematically analyzing the Swift/XRT light curves detected before 2018 July, we find 45 light curves with a measured redshift that monotonically decay as a smooth broken power law. By assuming that the central engines of these GRBs are newly born magnetars, we measure the braking index n of putative millisecond magnetars, due to MD and GW radiations. The inferred braking indices are not close to 3 or 5, but range between them with a normal distribution ( ). We define a dimensionless parameter , which is the ratio between the MD and GW components, and find that the energy released via magnetar spindown in most GRBs of our sample is dominated by GW radiation for ms and ϵ = 0.005 and 0.01. On the other hand, we find that and the braking index n seem to be anticorrelated within a large systematic error at t = 0, but depend on the values of the parameters P 0 and ϵ. These results suggest that the contribution of GW radiation cannot be ignored, and that a larger braking index leads to GWs dominating the energy released during magnetar spindown if indeed magnetars are operating in some long GRBs.

Towards attosecond-scale highly directed GeV gamma-ray sources with multipetawatt-class lasers

We consider a possibility of constructing a gamma-ray source based on the multibeam configuration of a multipetawatt laser system which we simulate using a converging dipole wave. It is shown that such a configuration of fields allows the generation of gamma radiation with narrow directivity of about 1 mrad in the form of pulse trains or isolated pulses on the attosecond timescale. The influence of quantum electrodynamic cascade development on the parameters of generated gamma bursts is studied.

Enhancing antenna performance and SAR reduction by a conductive composite loaded with carbon-silica hybrid filler

In this paper, we describe a technique for reducing the specific absorption rate (SAR) and human effects on antenna performance, based on combined use of rubber conductive composite loaded with carbon-silica hybrid filler used like a single director and a resonant half wave dipole. The finite-difference time-domain method was used to evaluate SAR and antenna performance for different antenna-composite configurations and distances. Bandwidth, gain, and radiation efficiency for different antenna-composite configurations were compared. It was found that the presence of a conductive composite loaded with carbon-silica hybrid filler can effectively reduce maximum SAR value (up to 70%) in a human head model, increasing the radiation efficiency (up to 67%) and the bandwidth (up to 110%) of the antenna.