Single Cavity Structure Research Articles

Numerical investigation of mixing performance in supersonic cold flow over dual-cavity in scramjet

Mixing performance in the combustion chamber is important in achieving the efficiency of scramjet for its compact structure and the short residence time caused by high velocity. This study focuses on predicting the mixing performance in a viscous supersonic flow past the cavity flame holder in the scramjet, using the discontinuous spectral element method with direct numerical simulation. The arrangement and distribution of a series of cavities are calculated at various inlet velocities. By comparing the contours of Mach number and static temperature, as well as analyzing the airflow residence time with a new calculating formula and the drag based on the numerical results, it is concluded that higher inlet velocities result in faster stabilization. It also leads to longer airflow residence time when the supersonic flow passes through the dual-cavity with a tandem connection rather than the parallel one or the single-cavity structures. As for the shortened rear wall of cavities, these structures can decrease the drag quickly, but they also decrease the airflow residence time seriously, which destroys the mixing performance. In addition, these conclusions are applied to a practical case of the cavity flame holder, verifying the effectiveness of tandem dual-cavity structures in enhancing the mixing performance by increasing the airflow residence time and maintaining or reducing the drag. This study can provide valuable suggestions in further design of cavity flame holders for different flow conditions.

Miniaturized Balanced Filtering Power Dividers With Arbitrary Power Division Ratio Using Multimode Dielectric Resonator in Single Cavity

In this brief, miniaturized balanced-to-unbalanced (BTU) and balanced-to-balanced (BTB) filtering power dividers (FPDs) are proposed. Using one multi-mode dielectric resonator with multiple feeding probes, a single-cavity structure for BTU FPD is constructed, showing a compact size. Then, the circuit topology is analyzed, where the impedance in each branch can be adjusted to distribute the input power to two outputs with different ratios by only controlling the coupling coefficients. In this way, a BTU FPD with a very simple structure can be designed with arbitrary power division ratio. Besides, by replacing the two unbalanced output feeding probes in the BTU FPD as balanced ones, a BTB FPD can also be realized with controllable power division ratios. The working mechanism of the proposed designs is detailed. The proposed circuits are verified with good simulated and measured results.

Lattice Boltzmann mesoscopic modeling of flow boiling heat transfer processes in a microchannel

Microchannel flow boiling has received increasing attention for its high heat dissipation intensity with a small temperature difference. In the present study, a multi-relaxation-time (MRT) phase change lattice Boltzmann model is employed to investigate the flow boiling heat transfer processes in a vertical microchannel under constant heat flux boundary conditions. The bubble dynamic behavior including nucleation, growth, slide, coalescence and departure is obtained and the periodic variations of wall superheat and heat transfer coefficient are evaluated using the Jacob (Ja) number and Nusselt (Nu) number. It is demonstrated that the cavity microstructure on the heating surface can enhance the flow boiling heat transfer, further the cavity height and cavity distance are optimized with single-cavity model and multi-cavity model, respectively. Phase change heat transfer and flow boiling curves from single-phase forced convection, nucleate boiling regime, transition boiling regime to stable film boiling regime are numerically predicted for both the single-cavity structure and multi-cavity structures. The simulation results show that increasing Reynolds (Re) number accelerates the bubble departure frequency and intensifies the external forced convection, thereby achieving enhanced flow boiling heat transfer performance. These findings advance our understanding of the bubble dynamics and heat transfer mechanisms in the microchannel flow boiling processes.

A Silicon-Based Photosensor With Photosensitive Cavity Structure

This study proposes a novel photodiode with photosensitive cavity structure, realized by simple KOH isotropic etching and ion implantation technology. The main design concept is using the photosensitive surface of the cavity to capture the light rays of the sensing area, so as to further increase sensing performance. A TracePro simulation shows that the light capture effect of a single cavity structure is enhanced as the etch depth increases due to increase in surface sensing area. However, since the etch depth is limited by the wafer thickness, this research proposes to increase the surface area of the photodiode by using an array of micro-cavity units to improve the sensing efficiency while reducing the needed etch depth. The experimental results show that under the same light-receiving conditions, the sensitivity of the photodiode with a single cavity and a multi-cavity is higher than that of the general planar design, by about 20% and 16%. In addition, at a luminance of 0 nt to 80 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> nt, the linear adaptation rate (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of the linear fitted curve is larger than 0.99.

Analysis of a micro pressure-sensor employing SiC-AlN-SiC structure

ABSTRACT In this research paper, we design a touch mode capacitive micro pressure-sensor with circular stepped-cavity and SiC-AlN-SiC material structure, which can be more precisely measured pressure in a high-temperature environment. Using the finite element analysis method (based on ANSYS software), we found that the sensitivity of the sensor reached 3.5 pF/MPa, up almost one-third from traditional single-cavity structure in the long linear working range as 0.9–1.4 MPa. Moreover, the research to thermal behaviours of the sensor is shown that high temperature has affected the diaphragm deformation and the von Mises stress of the sensor due to thermal buckling. But the thermal deformation did not change the intrinsic characteristics of this sensor. Consequently, the sensor packaging with high-temperature ceramic material is endured the higher temperature to be applied in a harsh environment.

A generalized approach for modeling and analysis of fiber Bragg grating based cavity structures

Z domain model of a single cavity structure as well as double cavity structure composed of fiber Bragg gratings (FBG) is developed and their performance analysis is presented in this article. A generalized approach for determination of transmittance in Z domain of FBG based cavities is introduced. Spectral characteristics in terms of peak transmittance, side lobes formation and bandwidth are determined for a single cavity structure of length 4.5 mm. The results are compared with previously published measured data of the same configuration and are found to be in very close agreement. An ultrashort single cavity structure is proposed and its transmission response is carried out in the article. The spectral characteristics of both symmetrical and asymmetrical double cavity structure of same length as that of single cavity FBG are determined. Performance parameters like FWHM, suppression of peaks, wavelength spacing are analyzed for the different configurations in Z domain.

Monolithic InAs/InP quantum dash dual-wavelength DFB laser with ultra-low noise common cavity modes for millimeter-wave applications.

We have developed and experimentally demonstrated a novel monolithic InAs/InP quantum-dash dual-wavelength distributed feedback (QD DW-DFB) C-band laser as a compact optical beat source to generate millimeter-wave (MMW) signals. The device uses a common gain medium in a single cavity structure for simultaneous correlated and stable dual-mode lasing in the 1550-nm wavelength range. A record narrow optical linewidth down to 15.83 kHz and average relative intensity noise (RIN) as low as -158.3 dB/Hz from 10 MHz to 20 GHz are experimentally demonstrated for the two optical modes generated by the laser. As a result, the beat note between these two lasing modes generates spectrally pure MMW signals between 46 GHz and 48 GHz. Such an efficient, coherent, and compact optical source is extremely attractive for applications in MMW systems, such as Radar and fiber-wireless integrated fronthaul for 5G and beyond.

Digital sensor based on multicavity fiber interferometers

Vernier effect systems with more than two reflectors or coupled-ring resonators are highly attractive for sensing applications, since one can have better control of tailoring their transmission response as compared to traditional single-cavity structures. Here, we propose and provide a prescription for designing a digital Vernier sensor that can be built from three off-the-shelf fiber Bragg gratings. The proposed sensor employs a tapered fiber in one of the cavities as a sensing head and senses changes in the form of discrete (digital) wavelength jumps of resonant modes. We show that the sensitivity, detection limit, and dynamic range of the sensor can be predictably controlled by careful selection of cavity lengths. As an example, we show by simulations that the detection limit of the proposed sensor reaches 10−6, which is eight times more than the previously proposed digital sensor based upon coupled-ring resonators.

Enhancement of magneto-optical responses in adjustable one-dimensional magnetophotonic crystals

We investigated the one-dimensional magnetophotonic crystals (1D − MPCs) created by magnetic defect layer sandwiched between dielectric photonic crystals (PCs) utilizing the 4×4 transfer matrix method (TMM). To simultaneously achieve high transmittance and large magneto-optical (MO) Faraday effect, we changed the repetition numbers of PCs and the thickness of defect layers. Using finite element method (FEM), we simulated the distribution of electric field in the length of structures. The efficient localization of light in the vicinity of defect layer led to MO responses enhancement and resonant transmittance inside the photonic band gap (PBG). For single cavity structure, the MO responses were enhanced for symmetric spatial configuration. By increasing the number of defect layer, the MO responses of MPCs were improved. The transmittance and Faraday rotation (FR) for MO multilayer structures having six cavities were obtained T = 0.92 and θF = 44.5° respectively. This is a proper case to design MO isolator applied in optical telecommunications.

In-Fiber Closed Cavity Interferometric High-Resolution Aqueous Solution and Alcohol Gas Refractometer.

An optical fiber interferometric refractometer for alcohol gas concentration and low refractive index (RI) solution (with 1.33–1.38 RI range) measurement is theoretically and experimentally demonstrated. The refractometer is based on a single-mode thin-core single-mode (STS) interferometric structure. By embedding a suitably sized air cavity at the splicing point, high-order cladding modes are successfully excited, which makes the sensor more suitable for low RI solution measurement. The effect of the air cavity’s diameter on the sensitivity of alcohol gas concentration was analyzed experimentally, which proved that RI sensitivity will increase with an enlarged diameter of the air cavity. On this basis, the air cavity is filled with graphene in order to improve the sensitivity of the sensor; and the measured sensitivity of the alcohol gas concentration is −1206.1 pm/%. Finally, the characteristics of the single-cavity structure, graphene-filled structure and double-cavity structure sensors are demonstrated, and the linear RI sensitivities are −54.593 nm/RIU (refractive index unit), −85.561 nm/RIU and 359.77 nm/RIU, respectively. Moreover, these sensor structures have the advantages of being compact and easily prepared.

Introducing a ψ-shaped cavity for cooling a heat generating medium

Reducing the excess temperature in the heat generating pieces such as electronic devices is becoming a formidable challenge. The competition for introducing more efficient tools to cool down the hot pieces still continues. In this paper, a new configuration of an inverted fin (‘cavity’), penetrated into a heat generating medium, is proposed, evolved and optimized. On account of its particular shape, the new configuration is called the ‘ψ-shaped’ cavity. A big picture of how this flow configuration evolves to become better, is provided. To accomplish this, a numerical optimization based on a finite element code and exhaustive search algorithm is performed to seek for the best geometric structure of the ψ-shaped cavity. The optimization objective is to minimize the excess (hot spot) temperature of the heat generating piece subjected to a fixed volume of the cavity constraint. It is convincingly indicated that the ψ-shaped cavity with optimum geometrical structure performs dramatically superior among the single-cavity structures investigated in the literature. For example, the lowest hot spot temperature obtained in the ψ-shaped cavity is found about 25% lower than that obtained in the best cavity investigated in the literature when the cavity occupies 10% of the heat generating body.

Realization of mode independent multichannel transmission filter by controlling the photon localization in symmetric cavities

Modern optical communication system requires multiple channel transmission in different spectral band for different applications. Here we are proposing a microresonator structure for closely spaced, mode independent multiple channel transmission in 3rd transmission window by controlling the localization of photons in its cavity. To design the proposed structure, the spectral filtering properties of a single cavity planar microresonator are studied initially. In conventional multilayer dielectric filter, the localization of light in the microcavity is generally controlled by controlling the number of layers. Here we have shown that application of electric field across the structure, designed with suitable materials can also affect the localization of light in the cavity as well as the Q values of the transmission spectra. The mode independent characteristic of the structure is found from the study of its transmittance characteristics at different angle of incidence of light. It is found that the results of single cavity structure hold well for multicavity resonator structure also, in the regime of optical communication wavelength range. A method to increase the number of transmission channels is also proposed here keeping the fabrication perspective in mind.

Sound absorption of microperforated panel with L shape division cavity structure

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP with limited cavity space is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP with limited cavity space, MPP with L shape division cavity structure is introduced. Based on the MPP and electro-acoustical equivalent circuit principle, sound absorption properties of MPP with L shape division cavity are studied. Simulation and experimental results show that MPP with L shape division structure have better sound absorption performance than MPP with single cavity structure. Building on L shape division cavity, the extended plate can further improve the sound absorption of MPP. Wide band sound absorption of MPP can be realized with limited cavity space.

Dual-mode substrate integrated hexagonal cavity (SIHC) filter with uncoaxial feeding structure

Novel uncoaxial dual-mode substrate integrated hexagonal cavity (SIHC) filters are presented for high selectivity application. The SIHC filters with uncoaxial feeding structure can add two extra coupling paths to their topologies: one is a source–load coupling path, and the other is a non-physical higher order modes cross-coupling path. Under the circumstances, the proposed filter can generate up to three transmission zeros (TZs) for improving stopband performance. Meanwhile, the numbers and the locations of TZs can be controlled conveniently by tuning the uncoaxial feeding structure. Accordingly, the filter not only has good selectivity due to flexible TZs, but also has a small size by virtue of its single-cavity structure. Two experimental filters at the same central frequency of 10 GHz but with different fractional bandwidths of 2 and 5% and numbers of TZs from 2 to 3 are designed, fabricated, and measured to validate the proposed structure. The measured results agree well with the simulated ones, with their good performance just as pedicted.

Synthesis of Latex Particles with a Complex Structure As an Emulsifier of Pickering High Internal Phase Emulsions

A one-pot surfactant-free emulsion polymerization was described to produce uniform copolymer particles with core–shell structure, single-cavity structure, single-cavity with multiprotrusions in edge structure, or multiprotrusions structure. The structure of the copolymer particles was tailored by simply varying the cross-linker divinylbenzene (DVB) concentration in the emulsion. The formation of the nonspherical shape of the polymer particles was attributed to the presence of local cross-linking domains in the latex particles at low conversion and the phase separation between the hydrophilic polymer rich region and hydrophobic polymer rich region in further polymerization. With the copolymer particles as an emulsifier, Pickering high internal phase emulsions (HIPEs) having an internal phase fraction of 85 vol% were obtained. The use of nonspherical particles not only stabilizes the Pickering emulsions against coalescence but also enhances the roughness of the void wall in the emulsion-templated porous pol...

Design Method for Circularly Polarized Fabry–Perot Cavity Antennas

A new class of circularly polarized (CP) Fabry-Perot cavity antennas is introduced that maintain the simplicity of a linearly polarized primary feed and a single cavity structure. The proposed antennas employ a double-sided partially reflective surface (PRS), which allows independent control of the magnitude and phase responses for the reflection and transmission coefficients. In conjunction with an anisotropic high-impedance surface (HIS) ground plane, this arrangement allows for the first time a single cavity antenna to produce a specified gain in CP from a linearly polarized primary source. A design procedure for this class of antennas is introduced. The method exploits a simple ray optics model to calculate the magnitude and phase of the electric field in the cavity upon plane wave excitation. Based on this model, analytical expressions are derived, which enforce the resonance condition for both polarizations at a predetermined PRS reflectivity (and hence predetermined antenna gain) together with a 90 ° differential phase between them. The validity of the concept is confirmed by means of an example entailing an antenna with gain of approximately 21 dB at 15 GHz. Full-wave simulation results and experimental testing on a fabricated prototype are presented and agree well with the theoretical predictions.

Synthesis of anisotropic TiO2 hollow microspheres using cave particles as templates and application in water treatment

Anisotropic polystyrene (PS) particles with single cavity structures were synthesized using a modified dispersion polymerization method with divinylbenzene (DVB) as a crosslinker. Using the PS cave particles as templates, anisotropic titanium dioxide (TiO2) hollow microspheres were fabricated facilely. Due to possessing excellent photocatalytic activities, the obtained anisotropic TiO2 hollow spheres have potential applications in detoxification extraction and waste removal with very simple and efficient procedures.

Novel hexagonal dual-mode substrate integrated waveguide filter with source-load coupling.

Hexagonal dual-mode cavity and its application to substrate integrated waveguide (SIW) filter are presented. The hexagonal SIW resonator which can combine flexibility of rectangular cavity and performance of circular cavity is convenient for dual-mode bandpass filters design. By introducing coupling between source and load, the filter not only has good selectivity due to two controllable transmission zeros, but also has a small size by the virtue of its single-cavity structure. A demonstration filter with a center frequency of 10 GHz and a 3 dB fractional bandwidth of 4% is designed and fabricated to validate the proposed structure. Measured results are in good agreement with simulated ones.

Ultranarrow dual-transmission-band filter based on an all-fiber two-cavity structure composed of three fiber Bragg gratings

An all-fiber flexible two-cavity structure composed of three fiber Bragg gratings (FBGs) is proposed to realize a kind of ultranarrow dual transmission band filter. General condition for transmission spectra with symmetric two resonant peaks is presented and analyzed. The influences of various structure parameters on transmission responses are simulated and discussed, including index modulation depths and lengths of three FBGs and cavity lengths. By properly designing the structure parameters, two identical and symmetric transmission peaks can be produced in the stop band. The 3-dB bandwidth of each peak can be as narrow as 1pm or even less than 1pm. The spacing between the two transmission peaks can be flexibly designed. The fabrication error tolerances of the structures, including inaccurate cavity lengths and index modulation depths of FBGs, are investigated. Comparing with the conventional single-cavity structure, the proposed two-cavity structures provide better control on the suppression of sidebands. In applications of fiber lasers, the proposed two-cavity structure with the ultranarrow dual transmission-band can help in building the dual-wavelength single-longitudinal-mode operation at room temperature.

Fabrication of monodisperse anisotropic silica hollow microspheres using polymeric cave particles as templates

Monodisperse anisotropic poly(styrene-co-divinylbenzene) (PS-DVB) particles with single cavity structures were synthesized using a modified dispersion polymerization method. The effects of DVB adding modes and speeds on the particle morphologies were studied. Using the PS-DVB cave particles as templates, monodisperse anisotropic silica (SiO2) hollow microspheres were fabricated facilely. The obtained anisotropic silica hollow spheres had a potential application in rapid waste removal and detoxification extraction with a very simple procedure.