U-shaped Cavities Research Articles

Broadband low-frequency noise attenuation with parallel U-shaped membrane resonators

The attenuation of noise at low frequencies has been the subject of extensive research in the last two decades. Employing membrane-type acoustic metamaterials (MAMs) is one of the most promising solutions due to their lightweight structure and ease of fabrication. This study fabricated a metamaterial with four U-shaped cavities supporting a thin elastic nitrile rubber membrane. We print the U-shaped cavities using fused deposition modeling (3D printing). The sound absorption coefficient (SAC) is calculated using numerical simulations. For SAC computation, an electro-acoustic model is developed that constructs an equivalent electrical circuit based on an impedance analogy. Furthermore, the findings of the numerical and analytical analyses are supported by the actual data acquired from the experiments. We have determined that the average sound transmission loss (STL) is 29.84 dB, and the average SAC exceeds 82% within the frequency range of 500 Hz to 1000 Hz. Due to its lightweight, subwavelength thickness, ability to attenuate broadband noise, and very simple fabrication, this metamaterial is suitable for use in aircraft, automotive industries, and room/building acoustics.

A new turbulent viscosity modification method based on multiphase compressibility for cavitating flows

The alteration of physical properties in cavitating flows due to phase transition presents challenges for accurately expressing turbulent viscosity in Reynolds-Averaged Navier–Stokes models. Addressing this issue is crucial for capturing cavitating flow characteristics effectively. This study introduces a modification to turbulent viscosity by considering the compressibility of the vapor–liquid mixture, applied within the k-omega Shear-Stress Transport (SST k−ω) model framework. Simulations of cavitating flow around the Clark-Y hydrofoil, National Advisory Committee for Aeronautics 66 hydrofoil, and wedge are conducted to validate the proposed method. Results indicate that the modified model can reproduce the cavity inception, development, cutoff, and shedding processes observed in the experiment. Notably, the modification model accurately reproduces distinct cavitating flow features such as U-shaped cavities, secondary shedding, and high-pressure phenomena resulting from collapse. Moreover, the predicted time-averaged velocity, time-averaged Reynolds stress component, and dominant frequencies of pressure and phase volume fraction surpass those of the original SST k−ω model, demonstrating improved performance. These findings highlight the enhanced accuracy and reliability of the proposed SST-multiphase compressibility modification k−ω model for simulating cavitating flows, thus contributing to improved understanding and prediction capabilities in relevant engineering applications.

Assessment of cavitation erosion on an asymmetric hydrofoil based on energy conversion via a multiscale approach

Cavitation erosion is a long-standing issue, which plays a pivotal role in the material damage of much hydraulic machinery. However, despite abundant numerical research on cavitation erosion assessment, bubble dynamics has been commonly overlooked. Consequently, we develop an improved cavitation erosion model based on energy conversion and assess an ALE15 hydrofoil surface by its incorporation into a multiscale approach. Our erosion model stands out in considering the bubble behaviors throughout its entire lifespan to eliminate the influence of bubble oscillation on cavitation erosion. Using the bubble information in the well reproduced cavitating flow, we evaluate both the cumulative and instantaneous cavitation erosion, and the results show satisfactory agreement with the experimental pattern. Our findings demonstrate that frequent vapor-liquid alternations, induced by the collaborative effects of upstream pressure gradients and main flow, increase the potential for erosion risk at the hydrofoil leading edge. Downstream erosion primarily results from secondary shedding and the collapse of U-shaped cavities’ legs. By contrast, the acoustic energy emitted by the shedding cavities traveling farther and upwards away from the hydrofoil leads to negligible erosion on the surface.

Shape effects of TEG mounted ventilated cavities with alumina-water nanofluids on the performance features by using artificial neural networks

Shape effects of TEG mounted vented cavities on the performance characteristic during alumina-water nanofluid convection are numerically assessed by using finite element method. Rectangular, triangular, l-shaped and Ushaped cavities are used. The interface temperatures of hot and cold side are varied by changing the cavity shape, opening ratio (OR) and Reynolds number (Re). The highest hot side temperature is obtained with l-shaped cavity followed by U, T and R-shaped cavities. When using T, L and U shaped cavities, the rise of the power are calculated as 38%, 78% and 76% atRe=1000 when compered to rectangular cavity. The power rises with higher OR while increment amounts are 83.9%, 63.5%, 42% and 87.8% for R, T, L and U cavities a Re=1000. When nanofluid is used at the highest loading, 11%, 10.3%, 9% and 8.5% rise of power are achieved for R, T, L and U shaped cavities while the amount is than 5% when different sizes of particles are considered. Neural network modeling with 10 neurons in the hidden layer provides accurate power outputs for all shaped cavities.

Optical refractive index sensor with Fano resonance based on original MIM waveguide structure

In recent years, optical refractive index sensors have received significant attention in the field of chemical and biological sensing owing to the advantages of small size. In order to achieve the requirements of small structure and high sensitivity of nano refractive index sensing, this paper proposes a Fano resonance–based waveguide structure in which a metal-insulator-metal (MIM) structure using surface plasmons and U-shaped cavities are coupled unilaterally. The transmittance spectrum of the waveguide-coupled resonator with different incident light wavelengths can be obtained. The U-shaped cavity and semi-annular straight waveguide are superimposed on and coupled to each other to form the Fano resonance transmittance spectrum. An extremely narrow impedance is formed in the transmittance spectrum. The proposed structure can obtain superior sensing performance at the nanoscale after the optimisation. The results confirm that the sensing sensitivity of the refractive index of the optimised waveguide structure can achieve up to 825 nm/RIU. The results of experiments show that this structure could accurately identify the five proposed pure edible vegetable oils at room temperature. But experiments have also shown that it could not effectively distinguish between the five proposed mixed edible vegetable oils. This structure provides an effective reference for the design and development of refractive index sensors for application to pure edible vegetable oils.

Tunable multimode plasmonic filter based on asymmetric dual side-coupled U-shape cavities resonators

In this paper, the plasmonic system composed of a Metal-Insulator-Metal (MIM) waveguide and dual asymmetric side-coupled U-shaped cavities is reported. It demonstrates that the strong coupling effect can lead to the opening of new transmission window. One of new peaks originates from the interference between the dual U-shaped cavities and bus waveguide, and the other is induced by the asymmetry of the structure, and each peak can be well tuned independently by changing the structural parameters of the U-shaped cavity. The effects of dielectric parameters on the transmission characteristics of the coupled system are also analysis, we find that the sensor sensitivity can reach 496 nm/RIU and a new sharp peak will exist in the short-wave region when dielectric parameter n = 1.2. By combining the magnetic field distributions, the internal physical mechanism is discussed. The proposed compact and simple plasmonic structure may have potential applications in nano-scale filter and other high density plasmonic integration circuits.

液晶填充光纤U型腔的偏振光谱及温度特性

液晶填充光纤U型腔的偏振光谱及温度特性

Self-Reference Refractive Index Sensor Based on Independently Controlled Double Resonances in Side-Coupled U-Shaped Resonators.

A plasmonic, refractive, index nanosensor is investigated theoretically and numerically in two U-shaped cavities side-coupled to a metal–dielectric–metal (MDM) waveguide. A transparency window between two transmission dips is observed. The physical origin of the transmission phenomenon is revealed by mapping the magnetic field distribution. Independent double resonances are realized through the proposed design. Double resonances showed diverse responses to the variations of the structural dimensions. In particular, they presented different dependences on a refraction index of the medium in an individual resonator. One resonance exhibited a remarkable shift with the increase of the refraction index; however, the other resonance remained unchanged. On the basis of this unique characteristic of differing sensitivities, self-reference sensing is discussed. The nanosensor yielded a high sensitivity of 917 nm/RIU and a figure of merit of 180 RIU−1. This work is helpful in terms of the design of on-chip optical sensors with high sensitivity and improved detection accuracy in complicated environments.

Plasmonic Hybrid Cavity-Channel Structure for Tunable Narrow-Band Optical Absorption

A hybrid plasmonic structure consisting of adjacent U-shaped cavities separated by a nanochannel is proposed for tunable and narrow-band selection of light. The hybrid cavity-channel structure achieves absorption resonance with a bandwidth, defined as the full-width at half-maximum, of 1.5 nm and tunable property in the near-infrared and infrared regions. The hybrid structure resonance originates in the coupling of horizontal surface plasmon mode of the U-cavity with channel mode, which sustains stationary-surface-plasmons in the channel with antinodes at the channel entrances enabling light concentration and nodes at the channel exits enabling light confinement. As a result of the coupling, a sharp and strong absorption resonance is readily adjustable by varying the geometrical parameters of the U-cavity while keeping the channel parameters unchanged.

Light Trapping in Finite Arrays of Metallic U-Shaped Cavities for Sensing With High Figures of Merit

We report conditions for light trapping in subwavelength metallic U-shaped cavities. Full and partial light trapping exhibiting optical power flow vortices originate in coupling of surface plasmons into cavity modes. Localized surface plasmons coupled into cavity modes realize full light trapping, whereas propagating surface plasmons coupled into cavity modes result in partial light trapping. For full light trapping, an intense power flow is entirely confined in the cavities, reaching its maximum values on the cavities' surfaces. The full light trapping resonance realizes high sensitivity and figure of merit in structures as short as five adjacent cavities.

Plasmonics: Hollow Plasmonic U‐Cavities with High‐Aspect‐Ratio Nanofins Sustaining Strong Optical Vortices for Light Trapping and Sensing 6/2014)

Perfect light confinement in hollow, high-aspect-ratio, plasmonic U-shaped cavities is demonstrated by J.-J. Delaunay and co-workers on page 522 through the coupling of the cavity ridge hot spots with scalable mirrored surface plasmon U-cavity resonances. Light is fully trapped in intense optical vortices and confined on the extended cavity surfaces, thus accumulating energy in tunable, strong, and sharp resonances that generate sensitive reflectance dips.

Electromagnetically-induced transparency in a multi-cavity coupled waveguide system

The plasmonic analogue of electromagnetically-induced transparency (EIT) was investigated in a plasmonic waveguide system composed of a straight waveguide, with rectangular and U-shaped (split-ring resonator) cavities. An EIT-like transparency window occurs in the transmitting spectrum of the waveguide system and the magnetic field is dramatically changed due to the destructive interference between two resonance pathways. It is demonstrated that the EIT-like spectra can be modified by varying the coupling strength and tailoring the degree of asymmetry of the structure, and we study the coupling mechanisms between the elements of the structure, including magnetic coupling, electric coupling, and inductive coupling. In addition, a cascaded structure which consists of an SRR pair with 180° rotation asymmetry has been studied. It is found that the strong couplings between two asymmetric plasmonic nanostructures can lead to EIT-like transmission in both visible and near-infrared regions, simultaneously.

Coupling of localized surface plasmons to U-shaped cavities for high-sensitivity and miniaturized detectors

We report numerical analysis of the coupling of localized surface plasmons to the modes of U-shaped cavities. The coupling results in intense resonance for which the electric field is strongly enhanced on the cavity surfaces. As a result, an optical vortex in the power flow is formed in the cavities and a sharp and strong resonance dip is observed in the reflectance spectrum. High sensitivity of the dip wavelength to change in the refractive index of the surrounding medium is reported. The high sensitivity is realized with a small number of cavities, thus enabling miniaturization of detectors based on U-shaped cavities.

Dynamic Response of Shallow Buried Tunnel Subjected to SH Wave

The dynamic stress concentration on quadratic and U-shaped cavities in half space, which are similar to the cross-section of the tunnels, is solved in this paper impacted by SH-wave. The analytical solution for the cavity in elastic half space is gained by the complex function method. In the complex plane, the scattering wave which satisfies the zero-stress condition at the horizontal surface can be constructed, the problem can be inverted into a set of algebraic equations to solve coefficients of the constructed scattering wave by least square method. For the earthquake-resistance researches, the numerical examples of the dynamic stress concentration around the quadratic and U-shaped cavities impacted by SH-wave are given. The influences of the dynamic stress concentration by the incident wave number and angle, the depth and shape of the cavity are discussed. It is showed that the interaction among the wave, the surface and the shallow buried tunnels should be cared in half space. In this situation, the dynamic stress concentration around the tunnel is greater obvious than the whole space.

Iptycene Quinones: Synthesis and Structure

A practical and efficient method to synthesize iptycene quinones has been developed. As a result, a series of pentiptycene quinones 8-16 were conveniently synthesized by one-pot reaction of triptycene quinone 4 or 5 with anthracene 1 or its derivatives 2-3 in refluxing acetic acid in the presence of p-chloranil, followed by CAN oxidative demethylation. Similarly, a series of heptiptycene quinones 17-23 with U-shaped cavities were achieved with pentiptycene quinone 10 and triptycene diquinone 6 as precursors. Non-iptycene triquinones 24 with one tweezer-shaped cavity and 25 with two U-shaped cavities were synthesized by one-pot reactions of anthracene with pentiptycene triquinones 16a and 16b, respectively. Non-iptycene triquinone 26 with a dendritic structure was conveniently obtained by the reaction of anthracene with either pentiptycene diquinone 12 or triptycene triquinone 7. The structures of regioisomers 16a and 16b were determined by the single-crystal structure analysis of 16b. The structures of other regioisomers, including heptiptycene tetraquinones 19a/19b/19c and heptiptycene triquinones 23a/23b, were identified by comparative reactions.

Plastic- and liquid-crystalline architectures from dendritic receptor molecules.

Host molecules with U-shaped receptor cavities have been derivatized at their convex side with two n-hydrocarbon tails (1), two first-generation (2), and two second-generation (3) monodendritic hydrocarbon tails. Although hosts 1 and 2 display plastic-crystalline behavior, evidence suggests that host 3 forms a cubic liquid-crystalline phase. In this phase, molecules of 3 are arranged in spherical supramacromolecular assemblies, in which the receptor cavities are situated in the core and the hydrocarbon tails at the periphery. The 1:1 host-guest complex of 3 with methyl 3,5dihydroxybenzoate forms a similar liquid-crystalline phase, with the guest included in the core of the assemblies.

Lamellar organic thin films through self-assembly and molecular recognition.

Molecular clips possessing U-shaped cavities have been functionalized on their convex side with long aliphatic tails. These molecules form dimers which self-assemble into malleable lamellar thin films. Upon addition of a guest (methyl 3,5-dihydroxybenzoate), a 1:1 host-guest complex is formed, which prohibits clip dimerization. As a result, the lamellar structure of the material is lost. Complexation of 3,5-dihydroxybenzoic acid in the clip results in host-guest complexes which dimerize by hydrogen bonding interactions between the carboxylic acid functions of the bound guests. This dimerization restores the lamellar type architecture of the material.

Tritriptycene: a D3h C62 hydrocarbon with three U-shaped cavities [Erratum to document cited in CA105(25):225994P

Tritriptycene: a D3h C62 hydrocarbon with three U-shaped cavities [Erratum to document cited in CA105(25):225994P

Tritriptycene: a D3h C62 hydrocarbon with three U-shaped cavities

Tritriptycene: a D3h C62 hydrocarbon with three U-shaped cavities