Propagation Length Research Articles

Self-Progressive Near-Field Focusing 2-D Full Frequency Scanning Slot Array Antenna Based on Ridge-Gap Waveguide

A millimeter-wave self-progressive near-field focusing (NFF) 2-D full frequency scanning ridge-gap waveguide slot array antenna is proposed in this article. In the proposed array antenna, the adjacent linear NFF leaky-wave antennas (LWAs) are connected end to end in a double layer folded structure to construct a self-progressive phase shift feed network. Thus, the desired high phase progression in the design of the 2-D frequency scanning is provided by the linear NFF LWAs themselves with the superposed propagation length. As a result, the NFF 2-D frequency scanning performance can be achieved without increasing antenna area based on the proposed high-density self-progressive feed network, which is built by applying the ridge-gap waveguide. The proposed antenna prototype is fabricated through the computer numerical control (CNC) machining process and is verified by the experiment. The test information of the object under test in the near-field region can be directly obtained with a certain frequency band, showing good promise in the near-field detection application.

A corrugated epsilon-nearzero saturable absorber for a high-performance 1.3 μm solid-state bulk laser.

Epsilon-near-zero (ENZ) materials with vanishing permittivity exhibit unprecedented optical nonlinearity within subwavelength propagation lengths in the ENZ region, making them promising photoelectric materials that have achieved exciting results in ultrafast pulse laser modulations. In this study, we fabricated a novel saturable absorber (SA) based on a corrugated indium tin oxide (CITO) film with a symmetrical geometry using a low-cost self-assembly process. The strong saturable absorption of the CITO film triggered by the ENZ effect at normal incidence was comparable to that of the planar indium tin oxide (ITO) film at an optimal 60° incidence (TM polarization) at 1340 nm. In addition, the strong nonlinear optical properties of the CITO film were not limited by the incident angle and polarization state of the pump laser over a wide range of 0-20°. Benefiting from the excellent saturable absorption of CITO-based SA at normal incidence, a Q-switching operation with CITO-based SA at 1.34 μm was achieved in a Nd:YVO4 solid-state laser system, obtaining pulses of a duration of 85.6 ns, which was one order of magnitude narrower than that of the planar ITO-based SA. This study presents a new strategy for developing high-performance ENZ-based SAs and ultrafast lasers.

Effect of grain growth in bimodal microstructure on cutting performance of self-toughening Dy-α-SiAlON ceramic tool inserts

Although significant increase in mechanical properties has been achieved in ?-SiAlON ceramics by introducing self-toughening bimodal microstructure, the bimodal microstructure may not always result in better cutting performance of ?-SiAlON tool inserts. Herein Dy-?-SiAlON ceramics were prepared by hot-pressing at 1900?C under 30MPa. Diameter and aspect ratio of the large elongated ?-SiAlON grains pivotal to formation of bimodal microstructures were regulated by using 0-5wt.% Dy2O3 as a sintering additive. Mechanical properties and cutting performance of ?-SiAlON tool inserts were evaluated. The results showed good Vickers hardness (19.0-19.7GPa) and fracture toughness (3.61-4.18MPa?m1/2) increasing with crack propagation length. However, transverse section of the large elongated grains was revealed as critical crack to cause premature fracture of the ?-SiAlON ceramics. Fracture rather than attrition wear was recognized as dominant mechanism for tool failure, indicating that for better cutting performance of the ?-SiAlON tool inserts a selftoughening microstructure consisting of thinner grains with large aspect ratio is required.

Statistical and simulation study on the separation in junction frequencies between ordinary (O) and extraordinary (X) wave in oblique ionograms

The most important aim in interpreting an oblique ionogram is to obtain the accurate Junction Frequencies (JFs) of the ordinary (O) and extraordinary (X) mode. This requires the correct identification of O- and X-mode traces, so it is very helpful and worthy to grasp the relative position between the two modes. This paper presents a statistical and simulation study of the separation in JFs between O- and X-waves based on observed oblique ionograms over three mid-latitude paths within China and a 3D ray-tracing program. The dependence on local time, season, geomagnetic activity, O-wave JF and group path, solar activity, direction, and length of propagation is investigated. The main conclusions are as follows: (a) the separation on east–west path is susceptible to ionospheric variability, while the separation on north–south path does not show a significant correlation with local time and season; (b) a general diurnal tendency and a summer anomaly on east–west propagation are first proposed and discussed, which may be related to the diurnal variation of hmF2 above the reflection point and the strong lower layers below the reflection point; (c) the separation varies approximately as a cosine function with the propagation direction owning two maxima in the north–south direction and two minima in the east–west direction; (d) the variation patterns of the separation with the propagation length are obviously not the same in different directions. In the case of east–west propagation, the separation decreases to a minimum near ground range of 2000 km and then increases very slowly with increasing ground range, while it monotonically increases for the north–south propagation path.Graphical

Relaxing Graphene Plasmon Excitation Constraints Through the Use of an Epsilon-Near-Zero Substrate

Graphene plasmons have attracted significant attention due to their tunability, potentially long propagation lengths and ultracompact wavelengths. However, the latter characteristic imposes challenges to light-plasmon coupling in practical applications, generally requiring sophisticated coupling setups, extremely high doping levels and/or graphene nanostructuring close to the resolution limit of current lithography techniques. Here, we propose and theoretically demonstrate a method for alleviating such a technological strain through the use of a practical substrate whose low and negative dielectric function naturally enlarges the graphene polariton wavelength to more manageable levels. We consider silicon carbide (SiC), as it exhibits a dielectric function whose real part is between \(-1\) and 0, while its imaginary part remains lower than 0.05, in the 951 to 970 cm\(^{-1}\) mid-infrared spectral range. Our calculations show hybridization with the substrate’s phonon polariton, resulting in a polariton wavelength that is an order of magnitude longer than obtained with a silicon dioxide substrate, while the propagation length increases by the same amount.

Performance of bit error rate of laser beams for LIDAR used in marine atmospheric weak turbulence

The performance of laser beams is investigated for light detection and ranging (LIDAR) systems in marine weak atmospheric turbulence by using the Rytov method. Formulation, on-axis, of the scintillation indices of LIDAR systems, which is obtained for plane, collimated Gaussian, and spherical beams, is appraised for average bit error rate (BER) by utilizing the log-normal distributed intensity. Values, obtained for these beams, are checked against source sizes, target sizes, normalized target size parameters, propagation lengths, and the average signal-to-noise ratio (SNR) for specified parameters. It is observed that the target size that minimizes the scintillation index is independent of the source size. The target size minimizing scintillation index is approximately 10 − 3 c m . Variations in source size and target size values, independently of each other, affect the scintillation index and the performance of marine LIDAR system links. The contribution of the outer scale turbulence to the deterioration is more evident than the inner scale turbulence.

Microscopic model on indoor propagation of respiratory droplets

Indoor propagation of airborne diseases is yet poorly understood. Here, we theoretically study a microscopic model based on the motions of virus particles in a respiratory microdroplet, responsible for airborne transmission of diseases, to understand their indoor propagation. The virus particles are driven by a driving force that mimics force due to gushing of air by devices like indoor air conditioning along with the gravity. A viral particle within the droplet experiences viscous drag due to the droplet medium, force due to interfacial tension at the droplet boundary, the thermal forces and mutual interaction forces with the other viral particles. We use Brownian Dynamics (BD) simulations and scaling arguments to study the motion of the droplet, given by that of the center of mass of the viral assembly. The BD simulations show that in presence of the gravity force alone, the time the droplet takes to reach the ground level, defined by the gravitational potential energy being zero, from a vertical height H,tf∼γ−0.1 dependence, where γ is the interfacial tension. In presence of the driving force of magnitude F0 and duration τ0, the horizontal propagation length, Ymax from the source increase linearly with τ0, where the slope is steeper for larger F0. Our scaling analysis explains qualitatively well the simulation observations and show long-distance transmission of airborne respiratory droplets in the indoor conditions due to F0 ∼ nano-dyne.

A localized SPR D-shaped fiber optic sensor utilizing silver grating coated with graphene: Field analysis

A D-Shaped fiber optic plasmonic sensor with silver grating coated with graphene is proposed in this paper. The proposed structure is compared to planar silver, grating silver, and planar silver with graphene grating. Performance defining parameters based on transmittance curves [resonance wavelength (λr), shift in λr (δλr), minimum transmittance (Tmin), and bandwidth (BW)] as well as based on field intensity [penetration depth (PD) and propagation length (PL)] are determined and compared. The proposed structure has the highest λr, δλr, and lowest Tmin, indicating that it has a high sensitivity. However, its BW is slightly larger than that of other structures, which deteriorates its detection accuracy. Furthermore, the proposed structure's PD and PL are the lowest of all the other structures. At different refractive indices of sample, the PD of the proposed structure (33 nm–55 nm) is one significant digit lower than others (232 nm–299 nm). As a result, the proposed structure acts as a localized surface plasmon resonance (LSPR) sensor, which may be utilized to detect molecules with a dimension of less than 50 nm, such as viruses and cancer cells provided that these molecules should adhere on the graphene surface.

Narrow-area average method for measurement of the propagation length of surface plasmon polaritons using nanoslit-grating structures

The propagation attenuation of surface plasmon polaritons (SPPs) has an important impact on the performance of plasmonic devices, so measuring their propagation length is important for designing plasmonic devices. Here we propose a method using a single nanoslit surrounded on both sides by surface gratings to measure the propagation length of SPPs. In this method, the propagation length of SPPs is obtained by using a narrow-area statistical averaging method to process the data of the intensity ratio of two diffracted light waves, which are converted from two SPPs that have the same initial intensity but travel different distances in opposite directions in a narrow area of a surface of a metal film. We demonstrate experimentally that at the illumination wavelength of 632.8 nm, the mean value of the propagation length of SPPs propagating at the interface between the air and a gold film with a thickness of about 360 nm measured using the proposed method is 9.88 μm, with a standard deviation of 0.23 μm (i.e., 2.33 % of the mean value). In addition, we demonstrate experimentally that the measurement error of the proposed method in measuring the intensity ratio of the two diffracted light waves, which is the dominant error of the proposed method in measuring the propagation length of SPPs, can be smaller than 2 % of its theoretical value.

Microwave radiation associated with positive narrow bipolar events

In this paper, we examined seven isolated positive Narrow Bipolar Events (NBEs), one positive NBE that initiated an IC flash progressed to a single-stroke Cloud-to-Ground (CG) flash, and one positive NBE that initiated an IC flash. Seven NBEs have been accompanied by significant Very-High Frequency (VHF) and microwave radiation pulses. We recorded all NBEs from two measurement stations (ST1 and ST2) separated at 13.3 km apart which consisted of fast antenna (FA) and slow antenna (SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (0.97 GHz). The waveforms were sampled at 2.5 GHz (400 ps). The key finding is that all microwave radiation pulses have been found to precede both the VHF radiation pulses and NBEs with average lead time of 63 ± 39 ns and 122 ± 143 ns, respectively. In comparison to stepped leader pulses or SLPs (conventional breakdown), the average lead time of microwave to VHF for NBEs (fast breakdown) was 88% faster compared to the average lead time of microwave to VHF for SLPs. Moreover, the average lead time of VHF to NBEs was 56% faster when compared to the average lead time of VHF to SLPs. The VHF interferometer map for an isolated NBE (NBE6) showed upward propagation of VHF radiation sources (fast negative breakdown) with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 10.2 ± 0.3 km, 2.9 ± 0.6 km, and 1.8 × 108 and 2.8 × 108 ms−1, respectively. On the other hand, interferometer map for an NBE that initiated a single-stroke CG (NBE3) showed bidirectional fast streamers propagation with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 14.0 ± 0.4 km, 2.9 ± 0.82 km, and 1.6 × 108 and 2.8 × 108 ms−1, respectively. Clearly, the microwave and VHF radiation pulses associated with positive NBEs have been emitted by different processes of fast breakdown mechanism. Therefore, it can be suggested that the microwave radiation is emitted by electron avalanches/corona while the VHF radiation is emitted by fast propagating streamers.

Mechanism and Control of Grout Propagation in Horizontal Holes in Fractured Rock

It is important to control grout propagation and ensure the engineering effectiveness of the advanced regional grouting process in the Middle Ordovician limestone (MOL) aquifer. In our study, we found that the physical and mechanical properties of cement grout are affected mainly by the water–cement ratio, followed by water glass content and finally by hydro-chemical type. In a horizontal grouting hole inclined single fracture, the grout spread over time depended on the water–cement ratio, grouting pressure, width of fracture and angle between fracture and grouting hole and the rate of spread increased over time. However, when the grout propagation length was hundreds of meters or more, the length in the fracture above the grouting hole was greater than that in the fracture below. The sensitivity sequence of influencing factors of grout propagation length in an inclined fracture of a horizontal grouting hole was as follows, from large to small: width of fracture, fracture angle, water–cement ratio, grouting pressure.

Numerical Analysis of a GaAs-Based Hybrid Plasmonic Waveguide with Nanoscale Optical Confinement and Low Losses

A numerical analysis of a hybrid plasmonic waveguide (HPW) for deep subwavelength optical confinement and long-range propagation with low loss is presented here. Two types of material platforms, namely, Si/SiO2/Au and GaAs/SiO2/Ag, were analyzed to optimize the HP waveguide. The mode character, an important and crucial design parameter for HP waveguides, was calculated based on the coupled mode theory, providing the coupling strength between the SPP and optical mode. As for the Si/SiO2/Au HP waveguide, the coupling strength varied from 0.47 to 0.60 with a mode area ranging from 0.0002/μm2 to 0.001/μm2 and mode character near to the SPP mode character (i.e., |a+(tsi, w, td)|= 0.47). While for the GaAs/SiO2/Ag HP waveguide, the coupling strength varied from 0.57 to 0.69 with a mode area ranging from 0.0002/μm2 to 0.0004/μm2 and mode character to SPP approached as |a+(tGaAs, w, td)|= 0.49. Finally, a finite element method (FEM) model was used to investigate the modal properties. The simulation analysis shows that at td = 10 nm the GaAs/SiO2/Ag waveguide gives 50% larger propagation length (205 μm), ten times smaller mode area (0.0002) with 60% lower modal propagation loss (0.021 db/μm), and 20% stronger coupling strength (0.62) with HPP mode character as 0.48 as compared to Si/SiO2/Au.

Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer

Abstract Nanometric metallic stripes allow the transmission of optical signals via the excitation and propagation of surface-localized evanescent electromagnetic waves, with important applications in the field of nano-photonics. Whereas this kind of plasmonic phenomena typically exploits noble metals, like Ag or Au, other materials can exhibit viable light-transport efficiency. In this work, we demonstrate the transport of visible light in nanometric niobium stripes coupled with a dielectric polymeric layer, exploiting the remotely-excited/detected Raman signal of black phosphorus (bP) as the probe. The light-transport mechanism is ascribed to the generation of surface plasmon polaritons at the Nb/polymer interface. The propagation length is limited due to the lossy nature of niobium in the optical range, but this material may allow the exploitation of specific functionalities that are absent in noble-metal counterparts.

Hybrid Image Graphene Polaritons with Extremely Confined Mode and Field Enhancement in the Terahertz Regime

AbstractGuiding terahertz waves below the diffraction limit of light typically excite graphene plasmons (GPs). However, the mode confinements of conventional GPs using graphene–dielectric interfaces are limited. To further squeeze the optical mode sizes, a graphene–dielectric–metal (GDM) configuration supporting an image graphene plasmon (IGP) has been reported recently through the plasmon interactions in a graphene sheet and its mirror image inside a metal with out‐of‐phase charge oscillations. This study proposes a waveguide structure consisting of a cylindrical dielectric wire over a GDM to achieve an ultraconfined mode area by coupling a dielectric waveguide and an IGP mode. Furthermore, this work examines the dependence of waveguide dimensions and material properties on the mode characteristics of the proposed hybrid IGP (HIGP). This HIGP achieves plasmon wavelengths 20 times shorter and normalized propagation lengths twice longer than GPs, accompanying a mode size of 3 × 10−8A0, where A0 is the diffraction‐limited mode area. Moreover, the simple structure makes the HIGP easy to be verified experimentally. This work demonstrates that the HIGP delivering strong light–matter interactions at extremely compact dimensions can be exploited for building highly integrated, enhanced nonlinear, high‐resolution sensing and imaging THz devices.

Phonon Polaritons Assisted Extraordinary Transmission in α-MoO-Silver Grating and Its Application in Switching

Sub-wavelength metal grating structures exhibit extraordinary transmission (EOT) due to constructive interference of surface plasmon polaritons (SPPs) tunneling. Phonon polaritons (PhPs) having several advantages over metal-supported plasmons, such as zero ohmic loss and larger propagation lengths, can further enhance the transmission. We propose the design of silver gratings filled with anisotropic Molybdenum Trioxide (α - MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) to exhibit EOT by utilizing PhPs. We also numerically demonstrate the tunability (amplitude) of EOT by introducing a layer of graphene nanoribbon in the proposed device and show its application as a mid-infrared switch with bandwidth of 650 nm. α-MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /silver grating produces normalized transmission as high as ∼5.5 for [100] and ∼6 for [001] crystalline directions. This extraordinary effect is attributed to the formation of (i) hybrid modes, specifically cavity modes coupled with SPPs outside the reststrahlen band (RB) and (ii) cavity modes coupled with PhPs inside the RB. The reported work can be employed in diverse applications including molecular sensing, space communications, remote controlling and, imaging.

Insight into the mechanical coupling behavior of loose sediment and embedded fiber-optic cable using discrete element method

Distributed fiber optic sensing (DFOS) has recently emerged as a novel sensing technology for obtaining spatially continuous deformation of loose sediment. During the measurement, the mechanical coupling between the sediment and embedded fiber-optic cable determines the accuracy of the results. However, it remains a major challenge to properly assess such coupling behavior in both laboratory and in-situ tests. To investigate the pullout characteristics of a fiber-optic cable embedded in loose sediment, we established a two-dimensional model consisting of 205,909 active elements using high-performance discrete element numerical simulation software (MatDEM). We found that the simulations using the discrete element method well reproduced the pullout behaviors of fiber-optic cable embedded in soil, and this was verified by the experiment. In particular, the simulations obtained the interfacial shear stress distributions along the cable-sediment interface and the energy conversion processes, which were both determined by the confining pressures. The results revealed that the slip depth (Ls) can better indicate the cable-soil coupling capability than the strain propagation length (Lε). Accordingly, we suggested two evaluation methods for the mechanical coupling of cable and sediment, one employing Ls obtained by the simulations and the other employing the effective critical strain (εcr) obtained from the actual measurements. The discrete element method filled the gaps in understanding the mechanical coupling of the sediment and the embedded fiber-optic cable and it can be a useful tool for evaluating the cable-sediment coupling behaviors.

Initiation and Propagation of Multiple Fractures in the Horizontal Well of Shale Reservoirs Under Pulse Injection Hydraulic Fracturing

Pulse injection hydraulic fracturing (HF) can release high-energy peak pressure in a split-second, forming a complex hydraulic fracture network in shale reservoirs. However, the initiation and propagation of multiple fractures in the horizontal well of shale reservoirs under pulse injection HF have been inadequately studied. Hence, in this study, a HF model coupling the fracturing fluid flow along the fracture and the rock deformation was adopted, and the effect of the pulsed injection method on multistage HF of horizontal wells was determined. The results show that the pulsed injection HF can improve the fracturing effect of horizontal wells. However, no matter how the injection displacement and pulse frequency change, the propagation length of cracks at both ends seriously disturbed by stress almost remains unchanged. When the dominant fracture is temporarily shielded, the fluid pressure of the non-dominant fractures at both ends disturbed by stress compression increases, and the non-dominant fractures can be further expanded. Thus, a new composite multistaged HF scheme suitable for horizontal wells with pulse-temporary shielding in shale reservoirs was proposed. The method presented here can be adopted to optimize the fracture growth regime and provide a scientific basis for the fracturing operation of the horizontal well in shale reservoirs.

A systematic investigation for mode-I fracture properties of stitched composites

Three-dimensional stitched composite (3DSC) is one kind of 3D textile structural composite with higher performance on the interlaminated properties. This work demonstrates a systematic analysis of the Mode I fracture behavior of the 3DSC by designing the stitch pitch and fineness of the stitch yarn in the experiments. In the finite element model, a mixed model combining the homogeneous and microstructural parts was developed to reveal the mechanism of stitch pitch and fineness of the stitch yarn on the mode I fracture behavior of the 3DSC. The results show that the effect of the stitch pitch on the mode I fracture behavior of the 3DSC is related to the crack propagation length of the first stitch yarn, which is also dependent on the tension properties of the stitch yarn. The thickness of stitch yarn can significantly improve the fracture toughness of the 3DSC. However, the relative improvement efficiency of the stitch yarn gradually decreases with the rise of the yarn fineness. According to this phenomenon, this work proposed an optimized design to improve the mode I fracture properties of the 3DSC.

Static and dynamic analyses of the effects of shim material stiffness on insert crack initiation and propagation

Microcracks can form on the surface or inside an insert during forming or cutting processes. These microcracks tend to expand rapidly under impact loading, eventually leading to tool fracture and failure. Fracture and breakage of inserts cause significant limitations to the improvement of processing efficiency and safe production. This study investigated the effects of shim stiffness (using Young's modulus) on the stress distribution in the insert and at the crack tip under static and dynamic (impact) loading conditions, thereby providing a theoretical basis for correctly designing and selecting inserts for indexable tools. The extended finite element method (XFEM) was used to develop a 3D simulation model for an insert–shim system. The model was used to study crack initiation and expansion in the insert for different rigid shims under static and dynamic loading. Analyses of the crack tip stress intensity factor, the maximum principal stress, the strain, and the angle and direction of crack deflection were performed. Additionally, interrupted cutting experiments were conducted with cemented-carbide tools for four rigid shim materials. It was concluded that under static loading conditions, a weakly rigid shim reduced the crack tip stress intensity factor and the maximum principal stress, thus reducing the probability of insert fracture and that the stiffness of the shim has no effect on the angle of crack deflection on the insert surface. The shim stiffness has a more obvious effect on the crack propagation length and internal propagation direction during dynamic loading, and a weakly rigid shim increases the deflection angle as the crack expands inside the insert, thereby reducing the downward fracture length.

Investigation of 3D Dirac semimetal supported terahertz dielectric-loaded plasmonic waveguides

The tunable propagation properties of 3D Dirac semimetal (DSM)-supported dielectric-loaded surface plasmons structures have been investigated in the THz regime, including the influences of the Fermi level of 3D DSM layer, the fiber shape and operation frequencies. The results indicate that the shape of dielectric fiber affects the hybrid mode significantly, on the condition that if a x (the semi-minor axis length of the dielectric semi-ellipse) is relatively small, the fiber shows good mode confinement and low loss simultaneously, and the figure of merit reaches more than 200. The propagation property can be manipulated in a wide range by changing the Fermi level of 3D DSM, e.g. if the Fermi level varies in the range of 0.05 eV–0.15 eV, the propagation length changes in the range of 9.073 × 103–2.715 × 104 μm, and the corresponding modulation depth is 66.5%. These results are very helpful to understand the tunable mechanisms of the 3D DSM plasmonic devices, such as switchers, modulators, and sensors.