Destructive Interference Patterns Research Articles

Mathematical analysis of spin transport in topological insulators to optimize memory devices performance using numerical simulations

Understanding spin transport in topological insulators (TIs) is crucial for the development of spin-based technologies, such as magnetic memory, sensors, and quantum bits. To optimize memory device performance, we developed a comprehensive mathematical model that describes the evolution of spin density, as a function of space and time, taking into account spin-momentum locking, spin-orbit coupling, spin dynamics, and diffusive transport processes (including phonon and impurity scattering). Using numerical simulations (finite element method and Backward Euler Method) implemented in Python, we analyzed the spin transport in TIs. Our study demonstrated a critical dependence of spin transport efficiency on device length, with a maximum efficiency of 75% at a length of 8 micrometers. Beyond a critical length of 10 micrometers, efficiency recovered, reaching 80% at 14 micrometers. We observed oscillatory behavior in spin polarization, with amplitude modulation indicating constructive and destructive interference patterns. The inclusion of spin-orbit coupling and Dirac terms in our model revealed a non-uniform spin polarization distribution, with a 30% increase in polarization near the center. Defects and boundaries significantly impacted spin transport, reducing polarization by 40% near the defect region. Through optimization, we achieved a 25% increase in spin transport efficiency and a 20% enhancement in memory device performance. Our results demonstrate the crucial role of optimizing device length, material quality, and interface engineering in achieving efficient spin transport and improved memory device performance, paving the way for the development of high-performance spin-based technologies.

Investigation of the effects of polarisation and alignment method of retarders in isoSTED microscopy

Stimulated emission depletion (STED) microscopy is a powerful tool for observing subcellular structures beyond the diffraction-limited resolution. To achieve improved isotropic three-dimensional (3D) resolution in STED microscopy, 4Pi-geometry, which is equipped with two opposing objectives, is adopted; this approach is known as isoSTED microscopy. In isoSTED microscopy, constructive and destructive interference occur at the shared focal plane for lateral and axial depletion, respectively. The performance of isoSTED microscopy depends critically on the polarisation status and optical power differences of the two beams of the 4Pi cavity, which are adjusted using retarders. Misalignment of the retarders creates a nonzero core of the depletion focus owing to partial destructive interference. We analytically investigated the effects of retarder misalignments and proposed a simple and accurate alignment method for retarders. We also demonstrate that the proposed method can generate a completely destructive interference pattern and consequently achieve a sub-40-nm 3D resolution.

Decoding flat bands from compact localized states

The flat band system is an ideal quantum platform to investigate the kaleidoscope created by the electron–electron correlation effects. The central ingredient of realizing a flat band is to find its compact localized states. In this work, we develop a systematic way to generate compact localized states by designing destructive interference patterns from 1-dimensional chains. A variety of 2-dimensional new flat band systems are constructed with this method. Furthermore, we show that the method can be extended to generate the compact localized states in multi-orbital systems by carefully designing the block hopping scheme, as well as in quasicrystal and disorder systems.

Numerical modelling of blast mitigation of pre-fractal obstacles

The mechanics of downstream blast wave attenuation caused by interaction with obstacles arranged into a pre-fractal shape based on the Sierpinski carpet was numerically investigated using a high-fidelity CFD solver. The blast mitigation was qualitatively and quantitatively assessed for four pre-fractal iterations at three different scaled distances ( Z = 1.87, 2.24, 2.99 m/kg1/3). Mitigation was seen to occur in zones associated with the location of destructive wave interference patterns in the downstream region. Crucially, these zones were found to widen spatially with increasing pre-fractal iteration, and strong shock-shock interactions that result in load amplification, commonly encountered in downstream regions of a solitary block-like obstacle, were not observed for the more fractal-like obstacles. The mechanisms of attenuation are explored in terms of wave impedance. It is found that pre-fractals reduce wave transmission in the downstream, increase reflection of the blast wave, and enhance trapping within the confines of the pre-fractal obstacle, dramatically changing the directionality and hence the strength of the transmitted wave. Reductions in peak pressure of up to 60% and peak specific impulse of up to 40% were recorded for the highest iteration pre-fractal, that is, obstacles that most closely represent a true fractal, thereby highlighting the effectiveness of such shapes for protective structure design for improved blast mitigation.

Electromagnetic mode matching in a Wilson basis: optical fiber connections with a gap

On the basis of two optical fibers with an optional lateral and longitudinal displacement in a homogeneous background medium, we describe a general full-vectorial Wilson-basis discretized mode-matching method that evaluates the converged electromagnetic fields after all resonances in the possible gap cavity have settled. Wilson basis functions feature strong localization in both the spatial and the spectral domain, which allows for efficient modal electromagnetic field expansions, adequate truncation of field propagation operators, and sparse translation operators, which in turn allow to make ad hoc electromagnetic field-matching operators. For physical contact connections between single-mode fibers with a mode-field diameter mismatch, we obtain attenuation curves that are right between those obtained from approximation methods that either effectively match the electric field or the magnetic field under the assumption of a vanishing reflection. For fibers separated by a growing gap, constructive and destructive interference patterns in the cavity are computed by the successive application of Love’s equivalence principle and the propagation operator. By leveraging the physical width of the Wilson basis functions and the stepsize of the propagation operator, the initial operators may be reused in solving the interface problem for other wavelengths. For multi-mode fiber connections, we provide attenuation curves on a modal electromagnetic field level, as well as for overfilled and core-confined target encircled-flux compliant launches. A comparison to geometrical-optics based approaches shows attenuation differences in the order of several hundredth of a dB, and although that is small, it is significant for modern connection attenuation specifications. In the final example of connections between regular and trench-assisted multi-mode fibers, we notice that the relative change in the cumulative near-field power distribution can be significant, despite a marginally small attenuation. The influence of a core diameter and/or numerical aperture mismatch can be examined with a deliberate lateral misalignment.

Capturing the amplitude and phase profile of the vortex beam based on coherent detection

In this study, we propose a scheme to capture the amplitude and phase profile of the orbital angular momentum (OAM) beam based on coherent detection. In the scheme, the OAM beam to be measured is interfered with a local plain wave which is prepared at the receiver, and two charge-coupled devices (CCDs) are used to record the constructive and destructive interference patterns. By setting the phase of the plain wave to π/2 and π, one can extract the amplitude and phase profile of the OAM beam from the two interference patterns. We verify the feasibility of the scheme by simulation and experiments. The results show that both amplitude and phase profiles of single OAM and OAM superposition modes can be captured by using the proposed scheme, and the proposed scheme shows strong robustness even under the presence of atmospheric turbulence.

Relationship between Boreal Summer Circulation Trend and Destructive Stationary–Transient Wave Interference in the Western Hemisphere

AbstractThis study examines the role of the latent heating in exciting the upper-level circulation anomaly, which destructively interferes with the climatological stationary wave in the Western Hemisphere during boreal summer. This destructive interference pattern closely resembles the circulation trend that is known to be responsible for surface heat extreme trends. To investigate the mechanism behind this circulation anomaly, daily stationary–transient wave interference and related meteorological variables are analyzed using reanalysis data for the period of 1979–2017. Numerical model simulations forced by reanalysis heating anomalies indicate that the destructive interference pattern is most effectively excited by latent heating anomalies over the North Pacific Ocean and eastern Canada. The North Pacific heating anomaly drives circulation anomalies that not only resemble the destructive interference pattern, but also transport moisture into eastern Canada. The resulting latent heating over eastern Canada drives circulation that further reinforces the destructive interference pattern, which includes a prominent high pressure system over Greenland. Tropical heating also plays a role in driving the destructive interference pattern. On intraseasonal time scales, the destructive interference pattern is preceded by suppressed Indo–western Pacific heating and enhanced North American monsoon heating. On decadal time scales, both heating centers have strengthened, but the trend of the North American monsoon heating was greater than that of the Indo–western Pacific heating. These uneven heating trends help to explain the resemblance between the destructive interference pattern and the circulation trend over the Western Hemisphere.

Entanglement beating in a cavity optomechanical system under two-field driving

An optomechanical cavity driven by a periodically amplitude-modulated laser can generate steady light-mechanical entanglement with time periodicity. Similar results can be alternatively obtained by pumping an especially tuned optical degenerate parametric amplifier (DPA) inside the cavity. While the two laser beams are simultaneously applied, the optomechanical entanglement can exhibit constructive and destructive interference patterns, depending on their cooperative phase, which further gives rise to beating in entanglement dynamics if the two modulation frequencies are slightly different, followed by a beating frequency-dependent dynamical behavior in the energy exchange between light and a mechanical oscillator. The optimal dynamical entanglement goes beyond what is attainable by the scenario with two superimposed cavity drivings, as a result of the specially DPA-modulated quantum dynamics. Moreover, we calculate correlation spectra between the cavity and mechanical modes, and we find correspondence between the light-oscillator entanglement and the correlation spectra under the cooperative effect. The cooperation-enhanced optomechanical entanglement is robust against the thermal temperature, and is potentially useful for continuous variable quantum information processing.

Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep.

A terahertz continuous wave system is demonstrated for thickness measurement using Gouy phase shift interferometry without frequency sweep. One arm of the interferometer utilizes a collimated wave as a reference, and the other arm applies a focused beam for sample investigation. When the optical path difference (OPD) of the arms is zero, a destructive interference pattern is produced. Interference signal intensity changes induced by the OPD changes can be easily predicted by calculations. By minimizing the difference between the measured and the calculated signal against the OPD, the thicknesses of sub-100-μm-thick samples are determined at 625 GHz.

Strain sensing based on a core diameter mismatch structure

AbstractIn this paper, it is proposed and experimentally investigated a sensor structure based on a core diameter mismatch technique for strain sensing. An uncoated short section of multimode fiber is spliced between two standard single mode fibers forming the sensor structure, called the SMS (single‐mode‐multimode‐single‐mode) sensor. The proposed SMS sensor, in the strain analysis, generates destructive or constructive interference patterns as load or strain are applied, changing the power of the optical signal only, without varying the wavelength. The sensor configuration offers several motivating attributes, such as easy fabrication, low‐cost, high‐efficiency and high sensitivity, moreover allows interrogation of the optical signal using the transmitted or reflected total optical power. The results and these advantages indicate that the proposed SMS sensor device is suitable for strain measurement, which is helpful in a broad range of applications, for instance, structural health monitoring.

Aerial Channel Prediction and User Scheduling in Mobile Drone Hotspots

In this paper, we investigate the aerial wireless channel, where a moving drone is deployed to stream content to a set of mobile clients on the ground over a small cell size. Experimental traces collected over more than twenty flights with multiple clients suggest that drone mobility in lateral or vertical path leads to time-selective and frequency-selective wireless channel for a low-altitude drone. The resulting aerial wireless channel can be predicted reasonably well when we model the channel based on the constructive and destructive interference patterns between the line-of-sight path and other propagation paths via nearby reflectors. We propose a novel channel prediction approach to predict the subcarrier SNRs for all clients as drone moves and a novel scheduling approach to select the subset of clients that maximize the network utility using the predicted SNRs. We have implemented the proposed approach on a commodity 802.11n chipset and evaluated in the field over twenty flights, each serving up to 17 live clients. Experiments demonstrate, for the first time, the feasibility of tracking and predicting the aerial Wi-Fi channel, resulting in up to a 56% increase in overall throughput as compared to the conventional 802.11n hotspot, while maintaining fairness across clients.

Ridge number in bat ears is related to both guild membership and ear length.

The ears of many mammals have a set of uniformly spaced horizontal ridges that form groove arrays. Contact of coherent waves (e.g. acoustic waves) with a series of slits or grooves causes diffraction, which produces constructive and destructive interference patterns. Increases in signal strength will occur but will depend on the frequencies involved, the groove number and their separations. Diffraction effects can happen for a wide range of frequencies and wavelengths, but no array can diffract wavelengths greater than twice the groove separation, and it is for those wavelengths comparable in size with the groove separation that the effects are greatest. For example, when ridges in bat ears are 1 mm apart, the strongest influence will occur for a 1 mm wavelength which corresponds to a frequency of 343 kHz. If bats could use these wavelengths, it would help them to resolve objects or surface textures of about 0.5 mm. Given how critical acoustics are for bat function, we asked whether bats may be taking advantage of diffraction effects generated by the grooves. We hypothesize that groove number varies with bat foraging strategy. Examining 120 species, we found that groove number is related to both guild and ear length. Bats in guilds that glean prey items from foliage or ground have on average more grooves than bats in other guilds. Harmonics generated by echolocation calls are the most likely source for the wavelengths that would correspond to the groove separations. We apply the physical principles of wave reflection, diffraction, and superposition to support the hypothesis that acoustic responses generated from grooves may be useful to bats. We offer an explanation why some bat species do not have grooves. We also discuss the presence of groove arrays in non-echolocating Chiropterans, and five additional mammalian orders.

Solar Influences on the Return Direction of High‐Frequency Radar Backscatter

AbstractCoherent‐scatter, high‐frequency, phased‐array radars create narrow beams through the use of constructive and destructive interference patterns. This formation method leads to the creation of a secondary beam, or lobe, that is sent out behind the radar. This study investigates the relative importance of the beams in front of and behind the high‐frequency radar located in Hankasalmi, Finland, using observations taken over a solar cycle, as well as coincident observations from Hankasalmi and the Enhanced Polar Outflow Probe Radio Receiver Instrument. These observations show that the relative strength of the front and rear beams is frequency dependent, with the relative amount of power sent to the front lobe increasing with increasing frequency. At the range of frequencies used by Hankasalmi, both front and rear beams are always present, though the main beam is always stronger than the rear lobe. Because signals are always transmitted to the front and rear of the radar, it is always possible to receive backscatter from both return directions. Examining the return direction as a function of local time, season, and solar cycle shows that the dominant return direction depends primarily on the local ionospheric structure. Diurnal changes in plasma density typically cause an increase in the amount of groundscatter returning from the rear lobe at night, though the strength of this variation has a seasonal dependence. Solar cycle variations are also seen in the groundscatter return direction, modifying the existing local time and seasonal variations.

Intracochlear Measurements of Interaural Time and Level Differences Conveyed by Bilateral Bone Conduction Systems.

Intracochlear pressures (PIC) and stapes velocity (Vstap) elicited by bilaterally placed bone-anchored hearing devices (BAHD) will be systematically modulated by imposed interaural time (ITD) and level differences (ILD), demonstrating the potential for users of bilateral BAHD to access these binaural cues. BAHD are traditionally implanted unilaterally under the assumption that transcranial cross-talk limits interaural differences. Recent studies have demonstrated improvements in binaural and spatial performance with bilateral BAHD; however, objective measures of binaural cues from bilateral BAHDs are lacking. Bone-conduction transducers were coupled to both mastoids of cadaveric specimens via implanted titanium abutments. PIC and Vstap were measured using intracochlear pressure probes and laser Doppler vibrometry, respectively, during stimulation with pure-tone stimuli of varied frequency (250-4000 Hz) under ipsilateral, contralateral, and bilateral ITD (-1 to 1 ms) and ILD (-20 to 20 dB) conditions. Bilateral stimulation produced constructive and destructive interference patterns that varied dramatically with ITD and stimulus frequency. Variation of ITD led to large variation of PIC and Vstap, with opposing effects in ipsilateral and contralateral ears expected to lead to "ITD to ILD conversion." Variation of ILD produced more straightforward (monotonic) variations of PIC and Vstap, with ipsilateral-favoring ILD producing higher PIC and Vstap than contralateral-favoring. Variation of ITDs and ILDs conveyed by BAHDs systematically modulated cochlear inputs. While transcranial cross-talk leads to complex interactions that depend on cue type and stimulus frequency, binaural disparities potentiate binaural benefit, providing a basis for improved sound localization and speech-in-noise perception.

Plasmonic-Photonic Interference Coupling in Submicrometer Amorphous TiO2-Ag Nanoarchitectures.

In this study, we report the crystallinity effects of submicrometer titanium dioxide (TiO2) nanotube (TNT) incorporated with silver (Ag) nanoparticles (NPs) on surface-enhanced Raman scattering (SERS) sensitivity. Furthermore, we demonstrate the SERS behaviors dependent on the plasmonic-photonic interference coupling (P-PIC) in the TNT-AgNP nanoarchitectures. Amorphous TNTs (A-TNTs) are synthesized through a two-step anodization on titanium (Ti) substrate, and crystalline TNTs (C-TNTs) are then prepared by using thermal annealing process at 500 °C in air. After thermally evaporating 20 nm thick Ag on TNTs, we investigate SERS signals according to the crystallinity and P-PIC on our TNT-AgNP nanostructures. (A-TNTs)-AgNP substrates show dramatically enhanced SERS performance as compared to (C-TNTs)-AgNP substrates. We attribute the high enhancement on (A-TNTs)-AgNP substrates with electron confinement at the interface between A-TNTs and AgNPs as due to the high interfacial barrier resistance caused by band edge positions. Moreover, the TNT length variation in (A-TNTs)-AgNP nanostructures results in different constructive or destructive interference patterns, which in turn affects the P-PIC. Finally, we could understand the significant dependency of SERS intensity on P-PIC in (A-TNTs)-AgNP nanostructures. Our results thus might provide a suitable design for a myriad of applications of enhanced EM on plasmonic-integrated devices.

Robust speed measurements with standard wireless devices

Speed measurements are crucial for controlling traffic and in supporting automation of industrial processes. The speed of moving objects is typically measured from a stationary position using time-of-flight or the Doppler effect. Existing approaches require either relatively bulky physical devices or complex signal processing. The authors propose a new method for measuring the speed of (metal) objects moving on a fixed track. The authors' method is applicable, e.g. to cars on a road, trains on rails, or goods sliding on a conveyor belt. The method relies on the constructive and destructive interference patterns created by the reflections from the moving target. Speed is determined by measuring the signal strength of received messages as perceived by standard wireless devices. The method requires only minimal signal processing and only two commodity wireless transceivers, which are independent of the moving target. The advantages of their system compared to other technologies are reduced size, reduced cost, and in some scenarios robustness.

On the changes in optical interferometry induced by the relativistic motion of an optical medium

We investigate the effects of the relativistic movement of an optical medium on the conditions of constructive and destructive interference, reflection and transmission pattern, and performance of spectroscopes. First, we consider the case of two beams reflected from a relativistically moving thin film and derive the conditions of constructive and destructive interference. Then we broaden the idea to multiple beam interference and formulate a new modified equation of reflection and transmission pattern of light from a relativistically moving plane parallel dielectric film. Finally, we determine the new effective resolving power of a Fabry–Perot spectroscope, which has a moving dielectric medium in its etalon. Here, we consider the case where the optical media move parallel to the plane of incidence of light. Throughout this paper, we use the basic Lorentz transformation of space and time co-ordinates and electromagnetic fields to conduct these investigations. This paper can strongly motivate undergraduate physics students to associate the concepts of special relativity and optical interference.

Curvature and Vibration Sensing Based on Core Diameter Mismatch Structures

Core diameter mismatch structures are proposed and experimentally investigated for curvature and vibration sensing. Two configurations are suggested, one approach uses a structure formed by splicing an uncoated short section of multimode fiber between two standard single-mode fibers (SMFs) single-mode–multimode–single-mode (SMS), combined to a fiber optical mirror at its end, and the other approach uses a structure made by splicing a section of SMF between two multimode fibers (SMSMS). In the curvature analysis, the proposed SMS sensor generates the destructive interference patterns when it is bent, varying only the attenuation of the optical signal without wavelength shifts. The SMSMS vibration sensor proved to be suitable to monitor very low frequencies such as 0.1 Hz. The configuration of the proposed sensors presents several interesting features, such as easy fabrication, low cost, high efficiency, and high sensitivity. These advantages make such sensors very useful in a wide range of applications, for instance, structural health monitoring.

Acoustic scattering cancellation of irregular objects surrounded by spherical layers in the resonant regime

In this work, acoustic scattering cancellation is expanded to cases of acoustic waves interacting with non-spherical elastic objects and collections of closely packed objects. The proposed method for achieving this is by using spherical fluid layers to represent the objects as effective spherical targets, with multiple fluid layers and an elastic core, for which scattering cancellation is used to determine the necessary layer properties. Three representative objects are considered here to illustrate this approach: a sphere with dimples, a sphere with bumps, and a bicone. Theoretical results are presented for each of the non-spherical objects in water, which indicate a reduction of 30–40 dB in scattering strength when coated with a two-layer fluid cancellation shell. This cancellation is achieved for objects in the resonant scattering regime, which is characterized by constructive and destructive interference patterns that arise from higher scattering modes. The analytical results are verified using three-dimensional finite element simulations.

Plasmon resonances of Ag capped Si nanopillars fabricated using mask-less lithography.

Localized surface plasmon resonances (LSPR) and plasmon couplings in Ag capped Si Nanopillar (Ag NP) structures are studied using 3D FEM simulations and dark-field scattering microscopy. Simulations show that a standalone Ag NP supports two LSPR modes, i.e. the particle mode and the cavity mode. The LSPR peak position of the particle mode can be tuned by changing the size of the Ag cap, and can be hybridized by leaning of pillars. The resonance position of the cavity resonance mode can be tuned primarily via the diameter of the Si pillar, and cannot be tuned via leaning of Ag NPs. The presence of a substrate dramatically changes the intensity of these two LSPR modes by introducing constructive and destructive interference patterns with incident and reflected fields. Experimental scattering spectra can be interpreted using theoretical simulations. The Ag NP substrate displays a broad plasmonic resonance band due to the contribution from both the hybridized particle LSPR and the cavity LSPR modes.