Optimum Aperture Research Articles

Synthesis of Orbital Angular Momentum Antennas for Target Localization

AbstractThe exploitation of Orbital Angular Momentum (OAM) is proposed to design circular‐support continuous aperture distributions and concentric‐ring arrays for target‐localization applications. The proposed approach allows generating a single isolated null of the field in the target direction, which is of interest with respect to common techniques leading to a line (or perpendicular lines) of power‐pattern zeroes in the spectral plane. In the presented design procedure, the optimal continuous aperture source is first identified by resorting to the most suitable OAM vortex and effective tools such as the Singular Value Decomposition of the involved operator and a smart Convex Programming optimization. Then, by exploiting fast deterministic algorithms, this continuous source is discretized into circular‐ring arrays emulating it at best. Relevant applications including equispaced arrays, sum‐difference reconfigurable arrays, and isophoric sparse arrays are presented. The proposed approach is also compared with the state‐of‐the‐art techniques and assessed through full‐wave electromagnetic simulations.

Study on Influencing Factors of Molecular Sieve Oxygen-Production System

Molecular sieve oxygen-production technology, as a kind of air separation–oxygen production, is receiving more and more attention from every oxygen industry. The two-bed molecular sieve oxygen-production system studied in this paper can generally produce enriched gas with an oxygen concentration of more than 90%, which has the characteristics of strong applicability, high reliability, low cost and high efficiency. However, the gas oxygen concentration of a production system is greatly affected by internal and external factors such as the molecular sieve materials, atmospheric pressure and temperature environment. Through the continuous research of the molecular sieve oxygen-production system, it has been found that the oxygen cycle of the molecular sieve bed and the diameter of the washing and sizing hole also have an effect on the gas oxygen concentration of the production system. Therefore, in this paper, the two-bed molecular sieve oxygen-production device is the research object, with different oxygen-production cycles (including pressure time) and different washing and sizing hole diameter simulation experiments used to explore the molecular sieve oxygen-production system’s optimal oxygen-production cycle (including pressure time) and the rinsing sizing hole’s optimal aperture, to find the structure of the oxygen-production system and the control parameters for the oxygen-production efficiency of the law. The results show that the optimal oxygen-production cycle of the molecular sieve system is 8.0 s (pressure equalization time is 1.3 s), and the optimal diameter of the washing and sizing hole is 0.8 mm.

Contrast-Enhanced Ultrasound with Optimized Aperture Patterns and Bubble Segmentation Based on Echo Phase.

Amplitude modulation (AM) suppresses tissue signals and detects microbubble signals in contrast-enhanced ultrasound (CEUS) and is often implemented with checkerboard apertures. However, possible crosstalk between transmitting and non-transmitting array elements may compromise tissue suppression in AM. Using AM aperture patterns other than the conventional checkerboard approach (one on, one off) may reduce the degree of crosstalk and increase the contrast-to-tissue-ratio (CTR) compared with conventional AM. Furthermore, previous studies have reported that the phase difference between the echoes in AM pulsing sequences may be used to segment tissue and microbubbles and improve tissue signal suppression and the CTR of CEUS images. However, the CTR of the image produced by alternative AM aperture patterns and the effect of segmentation approach on these alternative apertures have not been investigated. We evaluated a number of AM aperture patterns to find an optimal AM aperture pattern that provides the highest CTR. We found that the aperture that uses alternating groups of two elements, AM2, had the highest CTR for the probe evaluated. In addition, a segmentation technique based on echo phase differences (between the full and half-pulses, ΔΦAM, between the complementary half-pulses, ΔΦhalf, and the maximum of the two ΔΦmax) was also considered in the AM aperture optimization process. The segmentation approach increases the CTR by about 25 dB for all apertures. Finally, AM2 segmented with ΔΦmax had a 7-dB higher CTR in a flow phantom and a 6-dB higher contrast in a perfused pig liver than conventional AM segmented with ΔΦAM, and it is the optimal transmit aperture design.

DESIGN AND CFD ANALYSIS OF CONICAL CAVITY RECEIVER FOR SCHEFFLER DISH

In the present paper, a conical cavity receiver is designed and analyzed for a 16 m<sup>2</sup> Scheffler dish concentrator. The optimum aperture diameter of conical cavity receiver is estimated using ray-tracing SolTrace software. The optimum aperture diameter of the conical cavity receiver for 16 m<sup>2</sup> Scheffler dish was found to be 0.4 m. Also, thermal and fluid flow analysis is performed using computational fluid dynamics (CFD) software, Ansys Fluent. The different parameters such as receiver temperature, heat losses, pressure drop, Nusselt number, and pumping power are analyzed. The maximum thermal efficiency was found to be 64% at receiver surface temperature 85°C and ambient temperature 25°C. Also, maximum pumping power required to circulate a flow through the receiver is found to be 1.03 W for 0.04 kg/s flow rate.

Three-dimensional density measurements of a heated jet using laser-speckle tomographic background-oriented schlieren

Tomographic background-oriented schlieren (TBOS) is a promising optical technique for 3D density field measurement in turbulent flows. Path-integrated information on refractive index gradients is captured by cameras looking through the flow at textured background patterns in the form of apparent displacements of the patterns. A tomographic reconstruction of the three-dimensional refractive index gradients is performed, from which the instantaneous three-dimensional density field is obtained. Most TBOS measurements to date have been limited by large temporal blurring and/or large defocus blurring. Our 15-camera experimental set-up uses a pulsed laser for both illumination and creation of a laser-speckle background pattern. The high-power laser ensures adequate exposures in nanoseconds, so temporal integration is minimised in each measurement. The beam is spread to illuminate a surface that is observed by fifteen cameras that are evenly spaced circumferentially around the flow. Laser speckle patterns are observed by the cameras due to the diffuse reflection and interference of coherent light from roughness on the surface. We develop a methodology for selecting the optimal focal length, focus distance, and lens aperture by considering the compromise between displacement sensitivity, defocus blurring and speckle size. Low temporal- and spatial-blurring 3D temperature field measurements with excellent resolution of turbulent flow features are obtained and good agreement with thermocouple. Classical behaviours of the potential core instability such as vortex rollup and radial ejections are identified. The behaviour of the potential core is examined further, which reveals that the potential core undergoes considerable deformation and fragmentation during the transition to turbulence.

A High-Gain Endfire Periodic Leaky-Wave Antenna Using DSPSL-Based Rhombic Element

An endfire periodic leaky-wave antenna (LWA) with high gain is presented in this communication, which consists of a series of rhombic elements based on double-sided parallel stripline (DSPSL). The endfire mechanism of the proposed antenna is illustrated by the phase difference of the far field of each arm in the rhombic element. Meanwhile, a tradeoff between the tilted angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{0}$ </tex-math></inline-formula> and the width <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$w$ </tex-math></inline-formula> is found, which assures an optimum transverse aperture for achieving high-gain endfire radiation. Moreover, the improved Hansen–Woodyard (IHW) condition is applied to predict the optimum endfire phase constant. Finally, a prototype is fabricated and tested. The maximum endfire gain of 19.8 dBi is measured at 11.4 GHz, which is close to the simulated and predicted results. The proposed periodic rhombic antenna provides more choice for the modern communication system.

Shape-stable Bi-Sn-In alloy/Ag/copper foam composite phase change material for thermal storage and management

With the increasing challenge of heat dissipation in electronic device, the development of rapid thermal storage and management materials with high thermal conductivity becomes an important topic. This study developed a novel low melting point metal composite phase change material composed of Bi-Sn-In alloy, Ag particles (1–4 wt%) and copper foam (apertures 0.25–0.64 mm) using high thermal conductivity synergetic enhanced effect. The Ag particles were uniformly distributed in Bi-Sn-In alloy and they changed to Ag strips with high Ag content, and Bi-Sn-In alloy/Ag can be evenly filled in apertures of copper foam. Bi-Sn-In alloy/Ag/copper foam composite with optimal aperture of 0.42 mm exhibited highest shape stability, because it avoided molten alloy leakage for larger apertures and residual alloy which was not pressed into copper foam for small apertures. As Ag content increases, the melting points of Bi-Sn-In alloy/Ag and Bi-Sn-In alloy/Ag/copper foam with Ag content of 4 wt% respectively increased by 4.91 % and 2.46 %, while their enthalpy slightly decreases by 10.9 % and 2.49 %. More importantly, the synergistic effect of Ag strips and copper skeleton addition formed continuous channels for heat transfer. The thermal conductivities of alloy/Ag (4 wt%) and alloy/Ag (4 wt%)/copper foam were respectively 22.4 and 42.7 Wm−1 °C−1, and they were remarkably higher than that of Bi-Sn-In alloy (16.4 Wm−1 °C−1). Furthermore, thermal management test showed that Bi-Sn-In alloy/Ag/foam copper had the most prominent endothermic and exothermic properties. The outstanding performance of present Bi-Sn-In alloy/Ag/copper foam demonstrates a promising prospect for solving the thermal management problems of contemporary electronic devices.

Integration strategy optimization of solar-aided combined heat and power (CHP) system

Solar-aided combined heat and power (CHP) system is a practical way for green electricity generation and heating supply. This paper proposed a novel integration strategy (i.e., integration strategy IV), in which solar heat was designed to preheat the reheated steam via an oil/steam heat exchanger and then to replace the 1st-stage extraction steam via an oil/water heat exchanger. This integration strategy could integrate more solar heat with higher temperature without the temperature drop of reheated steam. To demonstrate its advantages in thermodynamic and economic, this integration strategy and three others were modeled and compared by analyzing solar energy conversion, annual performance and levelized cost of energy. Through case study, integration strategy IV achieved the highest solar heat-to-electricity efficiency (i.e., 37.1%) with the corresponding integrated solar heat being 54.45 MW. And this integration strategy also achieved the highest annual solar-to-electricity efficiency (i.e., 21.5%) and the lowest levelized cost of energy (i.e., 0.129 $/kWh) with the optimal aperture area being 103620 m2. Under this condition, the corresponding annual solar-generated electricity would be 33.28 GWh.

Electrically large aperture horn array antenna with low side lobe level for Ku‐band frequency

AbstractUsing electrically large antennas for array applications may cause grating lobes and this can change the array pattern. To achieve a low side lobe level for boresight pattern for linear or planar array antennas, in the literature it is seen that the common method is the use of feeding each antenna with some amplitude distribution and keeping the distance between the antennas less than a wavelength. However, in this study the distance between the antennas is chosen to be greater than a wavelength. Therefore, the common methods cannot be used. To achieve a low side lob level in the radiation pattern for an array of antennas composed of antennas with a distance greater than one wavelength. The aperture length of each antenna is chosen to be variable and an analytical solution method is used to calculate the amplitude of each aperture field of the horn antennas. Thus, the determination of unit horns' optimal aperture lengths Li can be considered a multivariable optimization problem. This challenging problem was achieved using a novel meta‐heuristic optimization algorithm called the differential evolutionary algorithm (DEA), where the aperture lengths of each array element are taken as inputs to find the optimal side lobe level (SLL). Based on the obtained solutions, a 4 × 1 horn array antenna design alongside its feed network was designed for Ku‐band applications. The design of the array is simulated in CST simulation software, and the obtained simulated results had been compared with experimental results and counterpart designs in the literature.

Effect of Shelf Aperture Ratio on the Temperature Distribution of an Open Refrigerated Display Cabinet

(1) Background: With the development of cold chain logistics in recent years, the demand for refrigerated display cases has greatly increased in the home and commercial markets. However, the difference of temperature and humidity between each layer of refrigerated display cabinet is great, which affects the health of consumers. In order to reduce the temperature difference for each layer in a cabinet and to improve the temperature uniformity inside the cabinet, an open-hole shelf is designed according to the principle of aerodynamics. (2) Methods: The influence of different shelf aperture ratios on the periodic temperature fluctuation, average temperature, temperature non-uniformity coefficient, and temperature maintenance coefficient inside the cabinet is studied by means of experiments with pork. (3) Results: The results show that when the aperture ratio increases from 0% to 90%, the average maximum temperature in a single cycle in the cabinet shows a trend of first decreasing and then increasing. The minimum temperature difference in the cabinet is 4.3 °C, and the corresponding aperture ratio is 25%. (4) Conclusions: The results show that 25% is the optimal aperture ratio for a shelf in the refrigerated display cabinet. The results provide a better reference for optimization of the structure and temperature in an open refrigerated display cabinet.

High-Capacity Splitting of Mono- and Dibranched Hexane Isomers by a Robust Zinc-Based Metal-Organic Framework.

High-efficiency separation of C6 alkanes, particularly the mono- and dibranched isomers by using porous solids, is of paramount significance in the petrochemical industry and, remains a daunting challenge. In this work, we report the complete separation of linear/monobranched hexanes from their dibranched isomers through selective size-exclusion by a microporous MOF, Zn-tcpt (H3 tcpt=2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine), with a two-fold interpenetrated structure of hms nets. Importantly, its adsorption capacity and selectivity are notably higher than those of the previously reported adsorbents that can split mono- and dibranched alkane isomers. Dynamic breakthrough measurements verify the excellent separation of C6 alkane isomers by Zn-tcpt, and the size-exclusion based separation mechanism has been confirmed by ab initio materials modeling. The high-efficiency separation of alkane isomers by Zn-tcpt can be attributed to its optimal pore dimensions as well as high porosity.

Sensitivity Analysis of Factors Affecting Fracture Height and Aperture

• The in-situ stress ratio, not the individual stress values, is more influential on fracture geometry; thus, stresses in both directions (not just σ h m i n ) are considered influential. Because making small changes in viscosity has caused extreme changes in fracture height and aperture, the injected fluid viscosity is considered influential as well. This is an expected result. • For fracture height, the stresses (and their ratio), viscosity, Poisson's ratio, elastic modulus, and fluid injection rate are more influential than other variables. • For a fracture's maximum aperture, the stresses (and their ratio), viscosity, the elastic modulus, and fluid injection rate are more influential than other variables. • We have shown that the interaction of Geometry and Geology is fundamental to understanding induced fracture geometry. Apart from the fluid viscosity and injection rate, influential parameters are related to the geology (and geomechanics) of the rock. • This research can be useful for researchers and decision makers. Hydraulic Fracture Stimulations (HFS) are designed to improve well production while minimalizing environmental and geomechanical stability issues such as unintended “frack hits”, excessive height growth, and unintended break-through to thief zones or water production zones. Planning a fracture geometry with the optimal height, aperture, and length is the goal, and factors affecting the geometry include geological and geomechanical properties (natural fractures, bedding fabric, stresses, geomechanical properties, permeability, etc.) play significant roles. These properties are usually predetermined and are considered as design inputs; other parameters such as the pumping rate, fluid viscosity and density, and proppant concentration and schedule are determined (designed) when proposing a stimulation. The proper HFS design should take into account all technical and environmental aspects, meaning that the design (operational) parameters are chosen based on geological factors and the designer's experience to target a desired fracture geometry. HFS design is therefore the interaction of G eometry and G eology, the G&G interaction . A commercial two-dimensional coupled discrete element software, UDEC TM , is used to study geometry outcomes from ranges of geology inputs and designed operational parameters. The sensitivity analysis methodology employs the Morris technique to assess which geological and operational parameters have greater impacts the geometry of a single vertical fracture. Emphasizing parameter ranges more applicable to shallow formations ensures that the results can help assess fracture height outcomes near the surface and groundwater, where variability in fracture height is of environmental concern. Geomechanics; Hydraulic Fracture Stimulation; Sensitivity Analysis; Fracture geometry; Fracture Height

Effect of bubble cutting on spray characteristics and dust control performance in the effervescent atomization

Effervescent atomization performance depends on the bubble size inside the mixing chamber, consequently influencing the spray dust control performance. This paper proposes an optimization of atomization quality and dust control performance by incorporating a bubble cutter in the atomizer mixing chamber. The effects of the bubble cutter aperture on spray characteristics and flow characteristics were experimentally investigated under different operating conditions. Experimental results showed that Sauter means diameter (SMD) decreases with increasing injection pressure and gas-liquid mass flow ratio (GLR). Furthermore, SMD initially increased and then decreased by reducing the aperture of the bubble cutter from 500 µm to 80 µm. In particular, high injection pressure (Pi =0.6 MPa) and low gas-liquid mass flow ratio (GLR=0.09) strengthened the effects of the bubble cutter aperture on SMD. Moreover, bubble cutter causes a contiguous concentrated droplet size distribution, but it has little effect on droplet velocity. Ultimately, the optimal bubble cutter aperture on the efficiency of respirable dust control efficiencies was theoretically calculated. The dust control efficiency is a maximum at the bubble cutter with an aperture of 230 µm for the effervescent atomizer in this paper. Spray dust control efficiency reaches 93.15 %, which effectively solves the problem of high dust concentration pollution in the mechanized working environment.

A compact, low-profile, and high-performance monopulse antenna array for missile seeker

In this paper, the authors presented a compact, low-profile, and high-performance ku-band monopulse antenna array (MAA) for missile seekers with reduced complexity involved in fabrication, assembly, and installation. They investigated a multilayered microstrip patch Antenna technology by systematically developing an efficient synthesis process, high-performance design of radiating elements as well a feed network integrated with monopulse circuitry, and innovative multiple layered joining processes, which overcome limitations of the existing MAA system. Optimum aperture distribution corresponding to desired radiation characteristics is synthesized using a hybrid synthesis technique in which collapse distribution (CD) is employed to initialize the Genetic Algorithm (CD-AvGA). The authors designed the proposed MAA with computed coefficient and carried out fabrication, assembly, and functional validation. The obtained experimental results are in close agreement with simulated ones and satisfy the missile seeker’s stringent functional and platform requirements.

Influence of the aperture area on the performance of a solar funnel cooker operating at high sun elevations using glycerine as load

Five funnel solar cookers have been tested to investigate the influence of the aperture area on their performance. The largest cooker had an aperture area of 0.5 m2 and it was tested side by side with two other two smaller cookers. Each cooker was tested with the same amount of glycerine.The linear performance curves relating the efficiency with the specific temperature difference was determined. Then, the determined regressions of the cooker opto-thermal ratio and the reference time on the aperture area were used to predict: i) the influence of the solar irradiance and the aperture area on the maximum temperature achieved by the load, ii) the time duration required for achieving load temperature from 65 to 140 °C, and iii) the power of the cooker. It was found that for a solar irradiance range of 600–1100 W m−2, the pasteurization temperature can be achieved even by the smallest cooker, and the efficiency of the largest cooker is close to the efficiency of a cooker with optimum aperture area. Moreover, when using the largest cooker, under an irradiance of 1100 W m−2 and ambient temperature 20 °C, the load can achieve 180 °C, implying that frying is possible.

Design and optimization of hybrid superhydrophobic–hydrophilic pattern surfaces for improving fog harvesting efficiency

Inspired by the fog harvesting capacity of a wettability gradient pattern on the back of Stenocara beetles, we provide a facile and low-cost method for the fabrication of hybrid superhydrophobic–hydrophilic pattern surfaces, with smooth aluminum alloy substrate as the hydrophilic component and superhydrophobic sticky paper of varying hole sizes as the superhydrophobic component. The fog harvesting efficiency is evaluated by adjusting and combining the hole size of the hybrid superhydrophobic–hydrophilic pattern surfaces. The prepared single aperture hybrid superhydrophobic–hydrophilic pattern surface exhibits an enhanced fog harvesting efficiency compared with the uniform superhydrophobic and hydrophilic surfaces. Furthermore, the fog harvesting efficiency of the prepared combined aperture hybrid superhydrophobic–hydrophilic pattern surface is 88.3 % higher than that of the single set-up. The dynamic fog harvesting mechanism demonstrates that the optimal combined aperture hybrid surface maximizes the number of coalesced droplets within a certain period to collect additional water droplets, thus optimizing the fog harvesting efficiency. The fog harvesting efficiency reaches a maximum of 362.5 mg/cm2/h. The hybrid superhydrophobic–hydrophilic pattern surface prepared in this study has potential applications in atmospheric water collecting.

Optimized design of the restrictor for a MEMS thermal gas flowmeter

To improve the linear range of measurement, a restrictor is usually added to the main flow channel of a capillary-tube-type thermal mass flowmeter. However, as the linear range of the flowmeter increases, the singularity will occur in the low mass flow velocity section of the flowmeter calibration data, which will lead to a significant decrease in the measurement accuracy in this section. To address this issue, first, this paper developed a microelectromechanical system (MEMS) thermal gas flowmeter based on the principle of capillary-tube-type thermal mass flow. Then, the effect of the bypass ratio on its performance was further investigated using quantitative analysis and was verified using Fluent numerical analysis. In addition, to explain the singularity, the bypass ratio-sensitivity relationship model was built. Based on this model, the bypass ratio can be changed by adjusting the restrictor parameters to optimize the performance of the MEMS thermal gas flowmeter. Moreover, six numerical simulation models of restrictors with different aperture diameters and aperture numbers were designed. The numerical analysis results show that within a certain range of aperture diameters and aperture numbers, the singularity is more easily weakened when the aperture diameter decreases or the aperture number increases. Finally, the restrictor with the optimum aperture number and suitable aperture diameter was selected as the test model for calibration, and the goodness of fit R2 of the calibration results is improved from 0.9937 to 0.9972, the singularity in the low mass flow velocity section is significantly weakened, and the sensitivity is improved.

Fast least-squares prestack time migration via accelerating the explicit calculation of Hessian matrix with dip-angle Fresnel zone

Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers (CIGs). The blurring can be optimally corrected using the blockwise least-squares prestack time migration (BLS-PSTM), where common-offset migrated sections are divided into a series of blocks related to the explicit offset-dependent Hessian matrix and the following inverse filtering is iteratively applied to invert the corresponding reflectivity. However, calculating the Hessian matrix is slow. We present a fast BLS-PSTM via accelerating Hessian calculation with dip-angle Fresnel zone (DFZ). DFZ is closely related to optimal migration aperture, which significantly attenuates migration swings and reduces the computational cost of PSTM. Specifically, our fast BLS-PSTM is implemented as a two-stage process. First, we limit the aperture for any imaging point with an approximated the projected Fresnel zone before calculating the Hessian matrix. Then, we determine whether a seismic trace contributes to the imaging point via DFZ during calculating the Hessian matrix. Numerical tests on synthetic and field data validate the distinct speedup with higher-quality CIGs compared to BLS-PSTM.

Transmission conditions for clear depiction of thoracic spine based on difference between reflection and scattering characteristics of medical ultrasound

In epidural anesthesia, it is difficult to specify the puncture position of the anesthesia needle. We have proposed an ultrasonic method to depict the thoracic spine using the different characteristics of reflection from bone and scattering from muscle tissue. In the present paper, we investigated the transmission aperture’s width of the ultrasound probe to emphasize the differences in the reflection and scattering characteristics. First, we determined the optimum transmission aperture’s width using a simulation experiment. Next, we measured reflection and scattering signals by changing the transmission aperture’s width in a water tank experiment and confirmed that the results corresponded to the simulations. However, as the transmission aperture’s width increased, the lateral resolution at the focal point improved. Therefore, better imaging of the human thoracic vertebrae can be achieved by selecting the transmission aperture’s width, which considers the effect on lateral resolution.

An ultrawideband TEM horn with dielectric filling characteristics investigation with the dependence on an aperture angle

AbstractThis article presents a study on the optimal aperture angle for the ultrawideband TEM horn with the dielectric filling. The electromagnetic simulation is performed at a wide range of frequencies and angles. Comparison of the considered parameters, such as radiation pattern and voltage standing wave ratio of the horn with and without dielectric filling allows defining optimal angles of the antenna.