Circular Cavity Research Articles

Histological description of Saxifraga paniculata leaves with special focus on structures that release CaCO3

Saxifraga paniculata is a subalpine succulent perennial plant arranged in a rosette that is usually found in shallow soil among limestone rocks. Stereoscopic, light and scanning electron microscopy were used to describe the anatomical structure of S. paniculata leaves, paying special attention to structures related to CaCO3 (calcium carbonate) release. Anomocytic stomata are unevenly distributed on each leaf face, being absent in the lower third. The basal leaf margin presents translucent pluricellular trichomes of variable length and width. Towards the apical margin, trichomes become teeth. Both trichomes and teeth are completely covered with whitish CaCO3 crystals. Each tooth has a circular cavity connected to a single hydathode through pores. Clearing treatment revealed camptodromous leaf venation. Anatomical structure shows a bifacial cross-section with spongy mesophyll cells at basal part, becoming heterogeneous at the apex with palisade mesophyll on the adaxial face. Hydathodes are epithematic and connected to outer cavities via two kidney-shaped guard cells showing large substomatal cavity. The epithem is surrounded by a thickened sheath and is formed of highly packed elongated cells with interspersed tracheary elements. CaCO3 deposits consist of microscopic crystals with varying geometries, of which the rhombus is the basic unit.

Analytical solution to the SH wave scattering problem caused by a circular cavity in a half space with inhomogeneous modulus

In this work, the scattering problem of SH wave caused by circular cavity in half space with inhomogeneous shear modulus is solved. The shear modulus is assumed to vary in two dimensions. Based on the complex function theory and conformal mapping technique, the analytical expressions of the displacement field and stress field in half space are obtained. The unknown coefficient is determined according to the boundary condition. The numerical results show that the inhomogeneous parameters, the reference wave number, and the buried depth of the cavity have obvious effects on the displacement amplitude of the horizontal surface and the stress concentration around the circular cavity.

Fluorescence enhancement of a single germanium vacancy center in a nanodiamond by a plasmonic Bragg cavity.

Germanium vacancy (GeV) centers in diamonds constitute a promising platform for single-photon sources to be used in quantum information technologies. Emission from these color centers can be enhanced by utilizing a cavity that is resonant at the peak emission wavelength. We investigate circular plasmonic Bragg cavities for enhancing the emission from single GeV centers in nanodiamonds (NDs) at the zero phonon line. Following simulations of the enhancement for different configuration parameters, the appropriately designed Bragg cavities together with out-coupling gratings composed of hydrogen silsesquioxane ridges are fabricated around the NDs containing nitrogen vacancy centers deposited on a silica-coated silver surface. We characterize the fabricated configurations and finely tune the cavity parameters to match the GeV emission. Finally, we fabricate the cavity containing a single GeV-ND and compare the total decay-rate before and after cavity fabrication, finding a decay-rate enhancement of ∼5.5 and thereby experimentally confirming the feasibility of emission enhancement with circular plasmonic cavities.

Compact Dual-Band Dual-Mode SIW Balanced BPF With Intrinsic Common-Mode Suppression

In this letter, a compact dual-band dual-mode substrate integrated waveguide (SIW) balanced band-pass filter (BPF) with intrinsic common-mode (CM) suppression is designed by using a single perturbed SIW circular cavity. The vias and slot perturbations are introduced to tune the resonant modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">010</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> (a pair of degenerate modes), and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> of a circular cavity. Thus, they can be used to form two differential-mode (DM) passbands with independently adjustable center frequencies and bandwidths. The SIW can be seen as a natural balun with intrinsic CM suppression. Furthermore, the planar differential excitation structure is designed to excite the perturbed SIW cavity. The CM noise cannot excite SIW cavity due to the characteristics of hybrid electromagnetic boundary. Finally, a compact dual-band dual-mode SIW balanced BPF at 8 and 10 GHz is designed and fabricated, and the measured results show good agreement with the simulated ones.

Holocene sediments of an inundated sinkhole: facies analysis of the “Great Blue Hole”, Lighthouse Reef, Belize

Anoxic sinkholes are unique geomorphological features of modern reef systems and in terms of “lake-like” sediment successions very special marine depositional environments. This study presents results of a sedimentological survey, which focuses on the “Great Blue Hole”, a circular Pleistocene karst cavity, situated in the shallow eastern lagoon of Lighthouse Reef Atoll (Belize, Central America). The investigated Blue Hole is located within the tropical cyclone belt and acts as consequence of its unique geomorphology as a giant sediment trap for both fair weather and storm sedimentation. As an important innovation step, we applied a multi-proxy approach based on textural, compositional and geochemical data to ensure a more reliable differentiation between sediments with fair weather and storm condition affiliation. Sediments having formed under both conditions were texturally categorized by determination of classical sedimentary parameters such as mean grain size and sorting. Sediment composition has been quantified in thin sections based on 40 samples discretely taken along a core from the bottom of the 125 m deep and 320 m wide cavern. Classification of sedimentary facies follows a modified scheme for unconsolidated carbonate sediments based on the Dunham nomenclature. Fair-weather sediments are generally finer than 20 μm and consist on average of 81% carbonate fine material, 12% Halimeda platelets, 3% coral fragments, 2% organic material, 1% mollusc shells, 1% foraminifer tests, and minor portions of coralline red algae and echinoderm plates (0–1%). Intercalated event bed sediments are coarse-silt to sand-sized (> 20 μm) and differ in terms of generally lower fine carbonate material amounts (50%) and increased abundances of over-washed Halimeda platelets (28%) and coral fragments (6%). Combined analyses of this study have revealed four primary sedimentary facies with affiliation either to the background (mudstone) or cyclonic event sedimentation (Halimeda wackestone, algae-rich packstone, coralgal rudstone) as well as a transitional sub-facies indicating storm-induced background overprinting (background wackestone). The striking compositional and textural differences of the Halimeda wackestone, algae-rich packstone and coralgal rudstone facies are considered to be another helpful (semi)-quantitative proxy to identify event beds of tropical cyclones in unconsolidated sinkhole sediment successions.

Dynamic analysis for a vertical interface crack and the nearby circular cavity located at the piezoelectric bi-material half-space under SH-waves

The present problem aims to study the scattering behavior of SH-waves by a circular cavity near two symmetrically permeable interface cracks in the piezoelectric bi-material half-space. The steady-state response of the problem is obtained, with the aid of the Green’s function method and the complex function method. Above all, the essential expression of Green’s function is constructed by the mirror method. This expression satisfies the conditions of being stress-free and electric insulation on the horizontal boundary of the orthogonal space where the circular cavity is located, and the condition of bearing a harmonic out-plane line source force on the vertical boundary. Next, on the basis of dividing the bi-material medium into two parts along the vertical boundary, the first kind of Fredholm integral equation with uncertain anti-plane forces is established by using the conjunction method and the crack-division technology. Then, the solution is obtained by solving an algebraic equation with finite terms, which is an effective truncation of the integral equation. Finally, the dynamic stress concentration factor around the edge of the circular cavity and the dynamic stress intensity factor at the crack tip are calculated numerically. On this basis, the effects of incident wave frequency, crack length, crack location and circular cavity position on the dynamic stress concentration factor and dynamic stress intensity factor are discussed.

Boundary rounding effect in the hexagonal and oval two-dimensional optical microcavity

In this paper, the boundary rounding effects of two types of non-circular GaN microcavity system are numerically simulated by the finite element method. When the rounding parameter [Formula: see text] of the hexagonal microcavity decreases, the six corners of the regular hexagon are gradually rounded, the results show that the optical mode gradually changes from the hexagonal whispering-gallery mode (WGM) to the perfect circular WGM, and the quality factor of the modes increases correspondingly. For the oval microcavity, the structure parameter [Formula: see text] increases from 0 to 1 when the oval microcavity gradually changes from a stadium cavity to a circular cavity. The simulation results show that the quality factor increases with [Formula: see text], and the optical mode changes from high-leak mode to WGM. Our results demonstrate the effect of the boundary rounding on the mode pattern and quality factor in hexagonal and oval microcavities.

Analysis of Optical Modulator Based on Silicon Waveguide using FDTD

We propose a novel and compact optical modulator based on a silicon microring resonator with a side-coupled circular cavity. The proposed modulator has been numerically and theoretically inspected using the finite-difference time-domain (FDTD) method. To benchmark of the proposed structure, with Firely optimization algorithm, the effect of geometrical parameters to the performance parameters including modulation depth, full with at half the maximum (FWHM), loss, and bandwidth are explored. Then the suitable parameters of an efficient structure are determined in the light of the former studies. The obtained results show that the resonance dips of the modulator have a high transmission quality ratio and that the resonance wavelengths have a reverse relationship with the radius of the in cavity. Also, the numerical results achieved from the transmission spectra are used to analyze the modulation characteristic of the structure. The bandwidth can be tuned to a value as high as 70 GHz with a modulation depth of 58% around the resonance wavelength of 1550 nm and an extinction rate of 18 dB utilizing the novel configuration and by optimizing the structural parameters. Besides, the coupling modulation phase characteristic of the modulator for different input FWHM is also discussed in this paper. The obtained results are compared with other theoretical results and present good agreement. This model can constitute a handy tool for both theoreticians and experimentalists in future research on related topics.

Equivalent inclusion method for arbitrary cavities or cracks in an elastic infinite/semi-infinite space

Shallow tunnels free of or subjected to the surface effects excavated in an elastic rock mass are usually simplified as an elastic infinite or semi-infinite plane problem with cavities in mechanics, respectively. In this paper, the equivalent inclusion method (EIM), a classic solution due to Eshelby usually used for predicting the elastic field caused by inhomogeneities embedded in a heterogeneous material, is extended to predict the elastic field induced by an arbitrarily shaped cavity. Similar to that of the inhomogeneity problems, the implementation of the EIM for the cavity problem is conducted by treating a cavity whose elastic modulus is zero as an inclusion having identical material properties to the matrix but containing eigenstrains. Based on an elementary solution for the eigenstress arising from the eigenstrains representing the cavity of an arbitrary shape can be calculated with the help of numerical discretization and superposition of contributions from each discretized element. A circular or rectangular cavity can be reduced to a crack when the distance between their upper and lower surfaces approaches an infinitesimal but not a zero value, hence the elastic field caused by cracks can be also resolved with the proposed solution method. The results obtained with the proposed method and the finite element method (FEM) for both the cavity and the crack are in good agreements. Parametric analyses on the effects of depth, length of the crack and the interactions among multiple cavities and cracks on the elastic field demonstrates the EIM as a good potential application in some significant applications in fracture behaviors for the excavated material.

Sound field enhancement based on multiple-cavity metamaterial

Owing to the low energy density of sound energy in nature, it is difficult to realize the local enhancement effect of sound field in air. Therefore, it is of great significance to explore new physical mechanisms and methods to achieve sound field enhancement. In recent years, artificial Mie resonance structure as a kind of acoustic metamaterial has attracted considerable attention, which has a variety of resonant modes, such as monopolar, dipolar, quadrupolar and higher multipolar modes. Compared with local resonance, acoustic Mie resonance mode has strong acoustic interaction, which can effectively enhance the acoustic field by the coupling of the Mie resonance. In this paper, we design an acoustic metamaterial composed of multiple-cavity unit cells, which is capable of realizing sound field enhancement. The multiple-cavity unit is circular in external shape and it is composed of a circular central cavity and twelve resonators. The twelve resonators are evenly distributed around the circular central cavity, with three resonators combined into a group. This exotic function arises from the compound monopole Mie resonance introduced by mutual coupling between the system structure and the monopole Mie resonance of each unit cell. Symmetric and asymmetric metamaterials are constructed by arranging several multiple-cavity unit cells in different forms. These two kinds of metamaterials can be used to achieve sound field enhancement with different effects. The results show that due to the symmetry of metamaterial structure, the symmetric metamaterials with square, circle, rectangle and regular hexagon shapes can realize the sound field enhancement, which is independent of the direction of incident wave. However, for the asymmetric metamaterial with equilateral triangle shape, the sound intensity in the center of the system varies with incident direction, which indicates that the designed asymmetric metamaterial has a strong dependence on the direction of incident wave. These two kinds of metamaterials constructed in this research can possess a number of potential applications such as in sound insulation, acoustic sensor, noise location, acoustic communication and asymmetric acoustic device. These two kinds of metamaterials constructed in this research can possess a number of potential applications such as in sound insulation.

Analysis for vortex superposition state evolution of microcavity exciton polariton excited by ring-shaped pump

Owing to its light effective mass, polariton can easily realize Bose-Einstein condensates (BEC) and can also produce gyro effect under external drive. Therefore, it has a promising application prospect. Based on the Gross-Pitaevskii equation, the evolution of the exciton polaron BEC system in the annular microcavity is studied. Two key parameters affecting the characteristics of the exciton polaron system, namely the size of the microcavity and the configuration of the ring-shaped pumped beam, are investigated. The size of microcavity often directly affects the volume and power consumption of integrated devices. In addition, the number of coherent petals of exciton polariton superposition state matter wave propagated in microcavity is closely related to the precision and sensitivity of gyro, and the size of microcavity has a direct effect on the number of coherent petals. At the same time, whether the pumping region is continuous or not also has a key effect on the evolution of the system, and different pump configurations will affect the evolutions of the system. We find that in the microcavity radius on a micron scale, the annular microcavity can excite the petal of vortex superposition state when pumped by pumping light, and the petals can be stable, but circular cavity with a certain radius can “accommodate” a limited vortex quantum number, when vortex quantum number is too large, the system will be unstable and unable to support the formation of stable petals. However, with the increase of the radius of the annular microcavity, the superposition petal number of the exciton polariton system contained in the annular region will also increase, and the maximum petal number contained in the exciton polariton system has a positive linear correlation with the inner radius of the annular microcavity. At the same time, we find that when the pump laser configuration is changed, the system will evolve into a special form of steady state. The calculation results show that when microcavity parameters are the same but for only changing the radial width of single pump, the number of petals obtained is three times that before changing the radial width. In such a case, the number of superposition petals not only exceeds the previously calculated maximum number of petals accommodated by the annular cavity under the radius but also there appear the multiple petals combined radially. Under the double-ring pump system, changing the width of the hollow ring may produce not only the new exciton polariton condensation in the hollow ring, but also vortex states in the original petal. Under each of the three-ring and four-ring pumping condition, the evolution of the system finally presents a multi-petal state in the radial direction. Because these vortex superposition states contain the information about the density and the phase, it has important guiding significance for designing the new system of gyroscope. Therefore, these special evolutionary results open a new direction for studying the new system gyroscope.

Theoretical investigation on communication bandwidth of an orthogonal symmetry-based photonic crystal waveguide for wavelength division multiplexing

To realize wavelength division multiplexing for high-capacity optical communications, we theoretically investigate the properties of a photonic crystal waveguide structure in which a row of air holes is displaced by a/2 (a is the lattice constant). We calculate transmission loss and coupling efficiency to circular defect cavities of this waveguide structure, which we call an orthogonal lattice waveguide (OLW). The communication bandwidth of the OLW is estimated to be about 20 nm, which is twice that of the conventional line-defect (W1) waveguide. This result indicates that improvements in characteristics of the wavelength division multiplexing are expected by using the OLW instead of W1.

Formation of Rectangular Pulses in an Active Microwave Compressor With an Oversized Compact Storage Cavity

The microwave compressor of a new design forms high-power rectangular pulses of a spatial length exceeding several folds the longitudinal dimension of a storage cavity. Similar to the known compressor with the single-mode circular cavity, the new one has small overall dimensions due to making the cavity as a meander formed by parallel waveguide sections. The input coupler is the input port of the first section, and the output unit is the output port of the last section. Unlike the known compressor, the waveguide elements of the proposed one are oversized. Requirements for the design are determined and characteristics are estimated. Comparing with the analog compressor, the gain of the proposed one is greater by 7 dB. The processes of energy storing and extraction and the characteristics of the X-band compressor were analyzed by computer simulation. The compressor was tested experimentally, and the results were compared with the simulation data. It was shown that the microwave compressor with the oversized compact cavity worked similar to the analog compressor.

Compact SIW-Based Self-Quadruplexing Antenna for Wearable Transceivers

This letter proposes a low-profile substrate integrated waveguide (SIW) cavity backed self-quadruplexing antenna for wearable transceivers. The full-mode circular SIW cavity is split into four unequal quarter-mode SIW (QMSIW) cavities using the two slots on the upper layer of the cavity. The proposed antenna uses C-shaped and arc-shaped slots of different dimensions in each QMSIW resonator to operate at wireless local area network bands (3.5, 4.9, 5.4, and 5.8 GHz). The measured gains are 4.4, 5.07, 5.40, and 5.7 dBi at 3.5, 4.9, 5.4, and 5.8 GHz, respectively. The antenna is simulated and optimized inside a 48 $\times \text{76}\times$ 21 mm3 rectangular device by keeping the device on the chest of a realistic human model. The proposed antenna has unidirectional radiation patterns in all four operating bands with low backward radiations. Thus, it has low specific absorption rate at all four operating bands.

Compact Diplexers With Folded Circular SIW Cavity Filters

This work presents diplexers realized with folded circular substrate integrated waveguide (FCSIW) cavity filters. The properties of such cavities are analyzed, and empirical equations for calculating the resonant frequencies are given. The analysis relies on an even-/odd-mode decomposition. A 10-GHz filter is designed based on this approach. In the second step, its size is reduced, still maintaining the passband behavior. An asymmetric taper is used to connect two such filters to realize a diplexer. Two diplexers with center frequencies of 10/15 and 12/13.5 GHz are presented. The diplexers are several times more compact than comparable devices reported in the literature. The components are manufactured, and the functionality is demonstrated by simulation and measurements.

Dual band bandpass filter based on semi‐circular mushroom loaded substrate integrated waveguide

AbstractThis paper presents a dual band bandpass filter by loading two semi‐circular mushroom resonators (ScMRs) inside the cavity of a circular substrate integrated waveguide (SIW). TM101 and TM201 modes of the mushroom resonator loaded circular SIW cavity are excited to generate the first and second passbands respectively. As the proposed bandpass filter is based on circular SIW cavity, the passbands of the filter undergo relatively low insertion loss (IL) compared to other referred works. The selectivity is improved by generating four transmission zeros (TZs); two TZs are generated in between the two passbands by cross coupling the excited modes of the resonators and other two TZs are generated in lower and upper stopband by the source to load coupling. The passbands of the proposed filter are centred at 2.24 GHz and 4.35 GHz with 13% and 6.2% fractional bandwidth (FBW) respectively. A prototype of the proposed dual bandpass filter occupying a compact area of 0.3λ0 × 0.3λ0 is fabricated in Rogers RT/Duroid 5880. The measured minimum insertion losses for the first and second passbands are 0.9 dB and 1.1 dB respectively with a good agreement observed between simulated and measured results.

Perfectly-matched-layer method for optical modes in dielectric cavities

The optical resonance problem is similar to but different from time-steady Schr\"{o}dinger equation. One big challenge is that the eigenfunctions in resonance problem is exponentially growing. We give physical explanation to this boundary condition and introduce perfectly matched layer (PML) method to transform eigenfunctions from exponential-growth to exponential-decay. Based on the complex stretching technique, we construct a non-Hermitian Hamiltonian for the optical resonance problem. We successfully validate the effectiveness of the Hamiltonian by calculate its eigenvalues in the circular cavity and compare with the analytical results. We also use the proposed Hamiltonian to investigate the mode evolution around exceptional points in the quad-cosine cavity.

A level set based immersed boundary method for simulation of non-isothermal viscoelastic melt filling process

In this work, the polymer melt filling process is simulated by using a coupled finite volume and level-set based immersed boundary (LS-IB) method. Firstly, based on a shape level set (LS) function to represent the mold boundary, a LS-IB method is developed to model the complex mold walls. Then the non-isothermal melt filling process is simulated based on non-Newtonian viscoelastic equations with different Reynolds numbers in a circular cavity with a solid core, and the effects of Reynolds number on the flow patterns of polymer melt are presented and compared with each other. And then for a true polymer melt with a small Reynolds number that varies with melt viscosity, the moving interface, the temperature distributions and the molecular deformation are shown and analyzed in detail. At last, as a commonly used application case, a socket cavity with seven inserts is investigated. The corresponding physical quantities, such as the melt velocity, molecular deformation, normal stresses, first normal stress difference, temperature distributions and frozen layer are analyzed and discussed. The results could provide some predictions and guidance for the polymer processing industry.

Some Approximate Solutions of the Dynamic Problem of Axisymmetric Shock Deformation of a Previously Unstressed Incompressible Elastic Medium

Approximate theoretical solutions are presented for the boundary value problem of the shock load on the boundary of a circular cylindrical cavity in the space occupied by an incompressible elastic medium undeformed previously. We assume that the shock load causes the movement of the medium particles along helical trajectories. Data on the types and velocities of shock waves are based on the analysis of the dynamic conditions for the compatibility of discontinuities; and these conditions are supplemented by the relations along the characteristic directions. We show that the leading front of the dynamic process in an undeformed previously medium is a plane-polarized shock wave which is simultaneously included in one of the families of characteristics. This property results in the constancy of shear direction on the plane-polarized shock wave. This condition makes it possible to significantly simplify the obtaining of approximate theoretical solutions for the near-front neighborhood of the shock wave. The two approximate solutions of the problem are presented. One of them bases on solving a system of evolutionary equations that was obtained using the matched asymptotic expansions method; and the second solution, on a version of the ray method.

Experimental investigation on swirling spray forced ignition of embedded multi-channel plasma igniter

An embedded multi-channel plasma igniter with C-shape and circular cavities is designed to solve the problem of secondary ignition and starting under extreme conditions, and compared with the surface multi-channel plasma igniter without cavity, the ignition process of three igniters at ground state and 12 km altitude state is recorded by high-speed camera. The results show that the ignition probability of C-shape embedded multi-channel plasma igniter is highest with the same fuel-air ratio, the ignition probability of reaching 100% is lower, and the advantage is more obvious at 12 km altitude state than at ground state. In the process of flame development, C-shape embedded multi-channel plasma igniter has the largest flame projection area, the fastest flame development speed and the shortest flame evolution time. At an altitude of 12 km, the flame stagnation stage occurs in the flame development process of the three igniters, and the ignition process of the embedded plasma igniter is less affected by the interference of air flow, which is more advantageous than the surface multi-channel plasma igniter. Flame instability occurs when the global fuel-air ratio approaches the lean ignition limit, and the flame stationary position is related to the flow field and the distribution of fuel-air ratio. The lean ignition fuel-air ratio increases exponentially as the height increases, and the advantages of C-shape embedded multi-channel plasma igniter become more and more obvious. Compared with the surface multi-channel plasma igniter, the widening percentage of lean ignition boundary of the C-shape embedded multi-channel plasma igniter can reach 21.4% at 12 km state, which is better than that of the circular embedded multi-channel plasma igniter.