Sealed Cavity Research Articles

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Effect of process parameters on residual gas in metal package

The effect of process parameters on the residual gases, H2O, O2, CO2 and H2 in the metal package were investigated in this study. It was found that the H2O mainly came from the surface adsorption of raw materials and the H2 was from the electroplated Ni/Au layers of Kovar alloy. The O2 primarily came from the water vapor and the environment, while the CO2 in the cavity was mainly generated by the reaction between the O2 and residual carbon. The temperature and holding time of the baking, parallel seam welding and screening aging process could effectively affect the content of H2O, O2, H2 and CO2 in the cavity. Prior to sealing, increasing the temperature of baking and parallel seam welding could reduce the contents of H2O, O2 and H2. However, after sealing, the H2O and H2 absorbed on the material surfaces continued to desorb into the sealed cavity during the screening aging process, leading to the increase of the H2O and H2 content. It was also found that the gas leakage has an important effect on the residual gas inside the cavity. In the long-term screening aging process, the O2 could leak into the cavity from the air because of the concentration gradient. In the meantime, the O2 reacted with the residual carbon to generate CO2, causing an increase in the CO2 content. As the CO2 concentration in the cavity was higher than that in the air, it would leak into the air until equilibrium was reached.

On the lightweight design of laminated insulating glass units in cruise ships

ABSTRACT Modern cruise ships employ many large windows to enable passengers to enjoy the marine environment. Most windows are insulating glass units (IGUs) consisting of laminated glass and a hermetically sealed cavity. These laminated IGUs exhibit three physical effects under bending: (1) geometric nonlinearity of the glass panes, (2) shear transfer in the laminated glass, and (3) load sharing due to the hermetically sealed cavity. The Authors have previously studied the (1) and (3) effects on the window mechanical behaviour and glass pane thickness determination. Hence, this paper investigates through optimisation how all these effects together lighten the IGUs, and how the shear transfer affects the IGU mechanical behaviour with the optimised thicknesses. All three combined effects have positive effects on the IGU weight. These results are more pronounced for large and thin IGUs subjected to high design loads. For example, the choice of interlayer material is less important (for optimum weight) for small windows subjected to a low design load. Since all the effects are important, using the finite element method is recommended to achieve a lightweight window design.

High-Yield Large-Scale Suspended Graphene Membranes over Closed Cavities for Sensor Applications.

Suspended membranes of monatomic graphene exhibit great potential for applications in electronic and nanoelectromechanical devices. In this work, a "hot and dry" transfer process is demonstrated to address the fabrication and patterning challenges of large-area graphene membranes on top of closed, sealed cavities. Here, "hot" refers to the use of high temperature during transfer, promoting the adhesion. Additionally, "dry" refers to the absence of liquids when graphene and target substrate are brought into contact. The method leads to higher yields of intact suspended monolayer chemical vapor deposition (CVD) graphene and artificially stacked double-layer CVD graphene membranes than previously reported. The yield evaluation is performed using neural-network-based object detection in scanning electron microscopy (SEM) images, ascertaining high yields of intact membranes with large statistical accuracy. The suspended membranes are examined by Raman tomography and atomic force microscopy (AFM). The method is verified by applying the suspended graphene devices as piezoresistive pressure sensors. Our technology advances the application of suspended graphene membranes and can be extended to other two-dimensional materials.

(Invited) High-Density, Flip-Chip Alkali Doping of Graphene and Observation of the Lifshitz Transition

The physical properties of 2D materials can be tuned by doping to extreme charge carrier density, enabling the investigation of phenomena such as superconductivity, charge density waves, band inversion and Lifshitz transitions. For example, it is variably estimated that an electron density of 3.7 − 5.1 × 1014 cm−2 is required in order to induce a Lifshitz transition in monolayer graphene [1,2]. At this charge density, the Fermi surface passes through the hyperbolic saddle point of graphene at the M-pointin the Brillouin zone, where the Fermi surface geometry changes and the density of states diverges at a van Hove singularity. Achieving charge density sufficient to reach the Lifshitz transition has been limited to chemical doping in ultra-high vacuum (UHV) conditions and observation by angle resolved photoemission spectroscopy (ARPES). Integrating experimental methods for charge transport measurements with UHV chemical doping conditions is typically difficult. Field-effect methods including dielectric gating and ionic liquid gating are readily integrated with charge transport measurements, but achieve lower charge carrier density than UHV chemical doping methods.We report here an integrated flip-chip method to dope graphene by alkali vapour in the diffusive regime, suitable for charge transport measurements at ultra-high charge carrier density. We introduce a liquid cesium droplet source into a sealed cavity filled with inert gas (argon) to dope a monolayer graphene Hall bar on a quartz substrate by the process of cesium atom diffusion, adsorption and ionization at the graphene surface (Fig. a). Doping can be monitored by operando ac Hall measurement of longitudinal Rxx and transverse Rxy resistance of graphene (Fig. b). An optical image of a representative graphene Hall bar is shown in Fig. c (scale bar = 100 μm). The measured time dependent Rxx and Rxy during Cs exposure can be used to determine the time dependent electron density n and electron mobility μ.Upon sealing, the flip-chip assembly containing doped graphene is stable in ambient conditions, enabling sample characterization by various means, including non-resonant Raman scattering measurement through the transparent quartz window. Charge transport versus temperature and magnetic field in a variable temperature insert was performed, including Hall measurements to B = 7 T (Fig. d). By these methods, we confirm that flip-chip doping with Cs can be used to achieve charge density exceeding 4 × 1014 cm−2 . The Lifshitz transition is observed via the inversion of cyclotron effective mass, corresponding to sign inversion of the Hall coefficient RH (Fig. d). Employing a third-nearest-neighbour tight binding (3NNTB) calculation, we estimate the Fermi energies and Fermi surfaces corresponding to the charge densities observed by high field magnetotransport (Fig. e). At the Lifshitz transition, the Fermi surface transforms abruptly from that of electron pockets around the K and K' points, to a hole pocket around Γ. Further experimental observations will be discussed.In summary, our findings show that chemical doping, hitherto restricted to ultra-high vacuum conditions, can be applied in a diffusive regime at ambient pressure in an inert gas environment. We anticipate that our flip-chip doping method can be applied to a variety of 2D materials and dopant speciies beyond monolayer graphene and Cs.[1] P. Rosenzweig et al., "Overdoping graphene beyond the van Hove singularity", Physical Review Letters 125, 176403 (2020).[2] A. Zaarour et al., "Flat band and Lifshitz transition in long-range-ordered supergraphene obtained by Erbium intercalation. Physical Review Research 5, 013099 (2023). Figure 1

Experiment research on the characteristics and mechanism of noise caused by a car door sealing cavity at wind excitation

Due to the various geometric shapes of cavities within car door sealing systems, the resulting cavity noise induced by wind excitation exhibits complex characteristics, leading to unclear noise mechanisms. To address this, a study was conducted to examine the acoustic properties of door sealing cavities located in the B-pillar, C-pillar, and backdoor of an SUV within a full-scale aeroacoustic wind tunnel. The main objective was to explore the relationship between cavity noise and interior noise. The results showed that peak components in the sound pressure level spectrum of the cavities significantly contribute to interior noise, particularly for cavities located close to the car’s interior. To gain further insight, the geometric characteristics of the cavities were extracted and transformed into equivalent regular cavities. These equivalent cavities were subsequently tested for their noise performance in a small-scale aeroacoustic wind tunnel, and the occurrence mechanisms were thoroughly investigated. The results demonstrated that the noise spectra of different cavities, whether they had sealing strips or leakage gaps, exhibited typical multipeak characteristics, with some cases even leading to whistling (e.g. backdoor cavity). The reason for the whistling was a resonance when the self-sustained oscillation frequencies of the cavities coincided with or approached the Helmholtz resonance frequencies or modal frequencies of the cavities. Interestingly, the self-sustained oscillation frequency and cavity modal resonance still persisted even when the two frequencies were somewhat separated, albeit with peaks of lower magnitude in the sound pressure spectrum (e.g. in the sealed cavities of the B-pillar and C-pillar).

Noise recognition of moving parts in a sealed cavity based on the fusion of recognition results and high-dimensional mapping

The detection and identification of noise from moving parts inside a sealed cavity is crucial for ensuring the reliability of sealed equipment. However, traditional noise recognition methods struggle to meet the stringent demands for high detection accuracy. Inspired by the idea of ensemble learning, this paper proposes a noise recognition method that combines recognition results with high-dimensional mapping to enhance the recognition of noise. Firstly, a built noise identification experimental system is used to collect signals. Then, features are filtered and extracted based on acoustic emission principles and signal properties. Ultimately, a new fusion method is devised incorporating recognition results as new features into the original dataset and designing multiple layers of single algorithms based on their individual strengths to enhance the feature extraction capabilities of the algorithm. In the first layer of the fusion algorithm, CatBoost learns from the original dataset and incorporates its recognition results into the dataset. XGBoost then trains on the new dataset as the training set. Finally, the sparse output matrix generated by XGBoost is input into a logistic regression (LR) algorithm for training and prediction. The proposed method is verified by experiments on datasets and the results show that the accuracy of this method is higher than that of a single recogniser. It also performs better than current mature stacking fusion methods and mapping-based fusion methods. This fusion approach is of great significance for improving noise recognition accuracy and for innovating fusion methods.

Energy optimization of parabolic dish solar concentrator coupled to organic Rankine cycle: Experimental and analytical investigation of cavity receiver design and covering effects

Concentrated solar power (CSP) systems offer a promising solution for sustainable energy, but achieving high and stable efficiency requires careful design optimization. This study evaluated the overall performance of a parabolic dish solar concentrator coupled to an Organic Rankine Cycle (ORC) system through experimental and analytical assessments. The research examined the impact of cavity receiver shape (cylindrical vs. spherical) and the use of a glass cover on thermal efficiency. Additionally, the effectiveness of a cone structure to reduce spillage losses and improve optical efficiency was explored. Testing showed a significant improvement in system performance, with an increase from 75 % for the open cavity to 90 % for the sealed cavity equipped with the cone structure (15 % increase). This highlights the importance of receiver design in reducing heat loss. To further optimize the system, a numerical model was developed and validated against experimental measurements. The simulation demonstrated that the overall system performance is significantly influenced by the water outlet temperature from the cavity receiver and the pressure drop within it. The model suggests that overall performance could be enhanced from 4.6 % to higher than 6 % by optimizing factors like water mass flow rate, cavity tube diameter, and the selection of a more suitable ORC working fluid (e.g., R245fa instead of R134a).

Attractant spray enhances nesting preference and reduces macroparasite infestation of Osmia cornuta

AbstractMason bees (Osmia. spp) can provide an alternative for crop pollination management in addition to the Western honeybees (Apis mellifera). Targeted evidence‐based guidelines can improve cost‐effective management of mason bees. Here, I test the effect of an attractant spray developed in the United States for improving the nesting preference for artificial trap nests of mason bees in Belgium. More specifically, this study investigates the effect of the attractant spray on the nesting preference and nesting performance of the European orchard bee (Osmia cornuta), as well as its effect on the infestation of nest‐associated macroparasites. The number of sealed nesting cavities was twice as high in the trap nests that were treated with the attractant spray. Nesting performance expressed as number of brood cells per cavity, successful cocoon formation, adult emergence, proportion of female bees in the offspring and the number of dead larvae was not different between the treated and the untreated nests. Overall infestation of macroparasites, and infestation of drosophilid flies in particular, were both twice as high in untreated nests. This study provides evidence that the attractant spray improves nesting preference and reduces macroparasite infestation in O. cornuta. The use of this attractant can provide growers and stakeholders with an effective management strategy to prevent infestation by macroparasites and promote efficient bee breeding.

High-Precision Peg-in-Hole Assembly with Flexible Components Based on Deep Reinforcement Learning

The lateral thrust device is a typical high-pressure sealed cavity structure with dual O-rings. Because the O-ring is easily damaged during the assembly process, the product quality is unqualified. To achieve high-precision assembly for this structure, this paper proposes a reinforcement learning assembly research method based on O-ring simulation. First, a simulation study of the damage mechanism during O-ring assembly is conducted using finite element software to obtain damage data under different deformation conditions. Secondly, deep reinforcement learning is used to plan the assembly path, resulting in high-precision assembly paths for the inner and outer cylinder under different initial poses. Experimental results demonstrate that the above method not only effectively solves the problem that the O-ring is easily damaged but also provides a novel, efficient, and practical assembly technique for similar high-precision assemblies.

Mass Inversion at the Lifshitz Transition in Monolayer Graphene by Diffusive, High-Density, On-Chip Doping.

Experimental setups for charge transport measurements are typically not compatible with the ultrahigh vacuum conditions for chemical doping, limiting the charge carrier density that can be investigated by transport methods. Field-effect methods, including dielectric gating and ionic liquid gating, achieve too low a carrier density to induce electronic phase transitions. To bridge this gap, we developed an integrated flip-chip method to dope graphene by alkali vapor in the diffusive regime, suitable for charge transport measurements at ultrahigh charge carrier density. We introduce a cesium droplet into a sealed cavity filled with inert gas to dope a monolayer graphene sample by the process of cesium atom diffusion, adsorption, and ionization at the graphene surface, with doping beyond an electron density of 4.7 × 1014 cm-2 monitored by operando Hall measurement. The sealed assembly is stable against oxidation, enabling measurement of charge transport versus temperature and magnetic field. Cyclotron mass inversion is observed via the Hall effect, indicative of the change in Fermi surface geometry associated with the Liftshitz transition at the hyperbolic M point of monolayer graphene. The transparent quartz substrate also functions as an optical window, enabling nonresonant Raman scattering. Our findings show that chemical doping, hitherto restricted to ultrahigh vacuum, can be applied in a diffusive regime at ambient pressure in an inert gas environment and thus enable charge transport studies in standard cryogenic environments.

Optimization and experimental study of stationary endwall of stator labyrinth cavity in a low-speed research compressor

Controlling the leakage flow of the labyrinth seal cavity is very important for the efficiency and aerodynamic matching design of aero-engine high-pressure compressor. However, due to the complexity of the geometry and internal flow of the labyrinth seal cavity, the design optimization of the labyrinth seal cavity is rarely studied. In this paper, a multi-objective design optimization method was used to optimize the stationary endwall of the shrouded stator labyrinth cavity, and the optimal endwall shape was obtained. Based on the optimal geometry, the 3D printing and aerodynamic testing of experimental parts were carried out, and the aerodynamic performance and flow field details of the optimal geometry were analyzed by unsteady numerical simulation. The experimental results show that for the optimal geometry, it has a little effect on the total pressure ratio, but the efficiency at the design point is increased by 1.4 %. The numerical results show that the optimal cavity shape reduces low-energy fluid, thus reduces the total pressure loss of S3. At the near stall point, the optimal S3 still has a better performance, which means that the optimal shape is not limited to the design point. From the result, an engineering design criterion can be concluded. It is suggested that the labyrinth seal cavity should be designed to match the velocity components of the leakage flow with the mainstream of the stator properly to make the leakage flow go evenly in the blade passage instead of gathering to the suction side.

Fully Enclosed Composite Micro/Nano‐Package for High‐Quality Micro‐LED Display Pixels and In Situ Nanoimprint Technology

AbstractMicro/mini‐light emitting diode (LED) arrays are regarded as the most promising next generation of display devices. However, the inherent Lambertian radiation of LED chips results in a significant pixel crosstalk. To improve the display quality, high‐quality micro/mini‐LED display pixels with fully enclosed composite micro/nano‐packages and in situ nanoimprint technology are proposed and demonstrated in this work. The nanoimprint template is designed as a composite structure comprising an intermediate sandwich cavity array and thin‐bottom nanostructure layer. Contact is maintained between the template and LED chips array substrate. By vacuuming the sealed sandwich cavities, the thin‐bottom nanostructure layer is deformed to drive the upward protrusion of the liquid optical polymer. Moreover, the nanocavities on the thin nanostructure layer are fully filled by the polymer, forming a composite micro/nano‐package. The characteristics of the composite micro/nano‐package, such as the aperture and protrusion height, can be flexibly adjusted by changing the template structure or process parameters. A 6 × 8 array LED chips display device enclosed by a composite micro/nanopackage is developed. The divergence angle of the single LED chip decreases to 72° from the original 138°, the light‐extraction efficiency increases18.4%, and the luminescence spectrum and current‐voltage characteristics changes only minimally.

METHOD OF DYNAMIC TENSILE TESTING OF HIGH STRENGTH FIBERS

The work proposes and tests an experimental method for determining the high-speed tensile strength of high-strength fibers, based on a combination of the modified Kolsky compression method and the method of a thin ring made of the test material expanding under internal pressure. To create a pulsed internal pressure that causes expansion of the ring, accompanied by stretching and rupture of its constituent material, hydrodynamic loading is used in a split Hopkinson bar system under compression. To do this, between the ends of the measuring bars there is a sealed cavity with a liquid that transmits compressive pressure to the inner surface of the ring. Machine oil was used as a medium transmitting the compression impulse from the measuring rods to the inner surface of the thin-walled annular sample. The transmitting pressure bar performs the function of a dynamometer, which allows, based on the deformation pulse registered in it, to measure the amplitude of the pressure developed in the oil. Since the liquid inside the ring is practically incompressible, the measured stress transmitted into the liquid based on the transmitted pulse is equal to the pressure developed in it, which causes an axisymmetric expansion of the annular sample with the development of tangential stress in the body of the ring, leading to the rupture of high-strength reinforcing fibers. The maximum tangential stress, which corresponds to the maximum of the transmitted pulse recorded in the transmitting pressure bar, can be considered the required tensile strength of the composite ring material. To evaluate the performance of the proposed technique, samples in the form of thin rings made of four layers of carbon fibers impregnated with polymer glue were used. Trial tests of a composite material with unidirectional reinforcement were carried out. The stretching was carried out in the direction of the fiber. As a result of the tests of the ring sample, based on the transmitted pulse in the transmitting pressure bar, the time dependence of the development of circumferential stresses in the ring was obtained. The maximum value of tangential stresses in the ring, corresponding to the tensile strength of the carbon fibers, was approximately 2120 MPa. The rate of stress growth in this case is 35000 GPa/s. The combined use of the Kolsky method and the expanding ring method made it possible to obtain a characteristic of the tensile strength of the composite material.

The effect of lypolitics on atherosclerotic plaques of the artery

Endovascular removal of atherosclerotic plaques from the artery is of critical strategic importance, is a new direction and represents a primary task. The innovative capabilities of our invention make it possible to create a sealed cavity in the lumen of the artery with continuous blood flow, and to directly influence atheromas with the drug online. This served as the basis for studying the effect of 8 lipolytics on atheromas of 124 arterial vessels directly on anatomical preparations: 35 coronary, 31 carotid, 51 abdominal aorta and 7 iliac arteries. Visual observation, histology, endoscopy, video endoscopy and scanning electron microscopy during an observation period of 5 minutes to 5 days did not reveal significant changes in the structure, consistency, shape and number of arterial atheromas when exposed to 6 lipolytics, with the exception of Bile acid factors and phosphatidylcholine lipolytics. These lipolytics have demonstrated their effect - reducing the size, loosening and softening the consistency of plaques, as well as facilitating their detachment from the muscle layer and intima of the artery. However, the studied lipolytics did not dissolve or destroy atherosclerotic plaques completely.

Structure-function relationships in the nasal cavity of Arctic and subtropical seals

The heating and moistening of inhaled air, and the cooling and moisture removal from exhaled air, are crucial for the survival of animals under severe environmental conditions. Arctic mammals have evolved specific adaptive mechanisms to retain warmth and water and restrict heat loss during breathing. Here, the role of the porous turbinates of the nasal cavities of Arctic and subtropical seals is studied with this in mind. Mass and energy balance equations are used to compute the time-dependent temperature and water vapor profiles along the nasal passage. A quasi-1D model based on computed tomography images of seal nasal cavities is used in numerical simulations. Measured cross-sectional areas of the air channel and the perimeters of the computed tomography slices along the nasal cavities of the two seal species are used. The model includes coupled heat and vapor transfer at the air-mucus interface and heat transfer at the interfaces between the tissues and blood vessels. The model, which assumes constant blood flow to the nose, can be used to predict the temperature of the exhaled air as a function of ambient temperature. The energy dissipation (entropy production) in the nasal passages was used to measure the relative importance of structural parameters for heat and water recovery. We found that an increase in perimeter led to significant decreases in the total energy dissipation. This is explained by improved conditions for heat and water transfer with a larger complexity of turbinates. Owing to differences in their nasal cavity morphology, the Arctic seal is expected to be advantaged in these respects relative to the subtropical seal.

Water entry of spheres with impact-axis channels

Spheres are the most studied water entry projectile due to their symmetry and simplicity, but in practical applications, it is rare that an impacting body is perfectly spherical. Perturbations to the classical impactor are thus critical for aligning fundamental investigation with more advanced engineering applications. This study investigates the water entry of hydrophilic and hydrophobic spheres with through-channels along the water entry axis and producing deep seal cavities. The channels allow water to pass through the sphere to create a jet tailing the sphere and hastening cavity pinch-off. Channeled spheres produce smaller cavities than their intact counterparts and suppress the onset of cavity formation. Spheres with channels show similar drag coefficients as solid, intact spheres.

Resonant Gas Sensing in the Terahertz Spectral Range Using Two-Wire Phase-Shifted Waveguide Bragg Gratings.

The development of low-cost sensing devices with high compactness, flexibility, and robustness is of significance for practical applications of optical gas sensing. In this work, we propose a waveguide-based resonant gas sensor operating in the terahertz frequency band. It features micro-encapsulated two-wire plasmonic waveguides and a phase-shifted waveguide Bragg grating (WBG). The modular semi-sealed structure ensures the controllable and efficient interaction between terahertz radiation and gaseous analytes of small quantities. WBG built by superimposing periodical features on one wire shows high reflection and a low transmission coefficient within the grating stopband. Phase-shifted grating is developed by inserting a Fabry-Perot cavity in the form of a straight waveguide section inside the uniform gratings. Its spectral response is optimized for sensing by tailoring the cavity length and the number of grating periods. Gas sensor operating around 140 GHz, featuring a sensitivity of 144 GHz/RIU to the variation in the gas refractive index, with resolution of 7 × 10-5 RIU, is developed. In proof-of-concept experiments, gas sensing was demonstrated by monitoring the real-time spectral response of the phase-shifted grating to glycerol vapor flowing through its sealed cavity. We believe that the phase-shifted grating-based terahertz resonant gas sensor can open new opportunities in the monitoring of gaseous analytes.

Design of a wideband and tunable radar absorber

To effectively address the challenges posed by intricate and dynamic electromagnetic environments, we propose a wideband and tunable radar absorber in this paper. The proposed absorber, composed of graphene capacitor, plasma enclosed within a sealed glass cavity, radar absorbing material (RAM), FR-4 and copper plate, allows for tunable radar absorbing performance through the manipulation of the electromagnetic properties of the graphene capacitor and plasma. Based on the equivalent circuit model, the reflectivity of the radar absorber is analyzed using transmission line theory (TLT). Good agreement is observed between the full-wave simulations and the TLT. The study thoroughly investigates the influence of graphene, plasma, and RAM components, as well as their sequential arrangement within the radar absorber, on its reflectivity, expounding the fundamental mechanism of these materials’ synergistic integration. Additionally, the effects of key factors, including the surface resistance R g of graphene, plasma frequency collision frequency and plasma thickness on the radar absorbing performance are examined. Our findings reveal that adjusting surface resistance R g controls the absorbing amplitude, and manipulation of the plasma frequency and collision frequency tunes the absorbing frequency and effective absorbing band. By appropriately adjusting the surface resistance R g of graphene, plasma frequency and collision frequency the proposed radar absorber exhibits superior performance in the frequency range of 1 GHz to 10 GHz. The radar absorber we propose serves as a significant reference for the application of tunable radar absorbers and adaptive radar stealth techniques.

Study on sound absorption properties of micro perforated plates with acoustic black hole back cavities

In this paper, the finite element method is used to investigate the sound absorption performance of the micro perforated plates (MPPs) with acoustic black hole (ABH) back cavities. First, the finite element models of MPPs with sealed back cavities and ABH back cavities are developed. The simulation results show that the absorption bandwidth of ABH back cavities increases by 63.8% compared to the sealed back cavity of the same size, but the frequency of the highest absorption coefficient is increased. Second, the mechanism for expanding the band width is illustrated by the pressure distribution inside two cavities. Finally, the effect of different cavity numbers of stages and lengths on the sound absorption performance is analyzed. This study broadens the application scenario of MPPs by incorporating ABH back cavities and can provide a reference value for acoustic modulation.