Small Aperture Size Research Articles

Ultra-stable metal-organic framework-derived carbon nanocontainers with defect-induced pore enlargement for anti-corrosive epoxy coatings

Zeolitic imidazolate frameworks-8 (ZIF-8) have recently gained attention as nanocontainers for encapsulating corrosion inhibitors. However, two main challenges remain unsolved, casting doubt on their suitability as nanocontainers. The first challenge is their instability in acidic and basic environments, leading to structural decomposition and the second challenge is their mass diffusion limitation caused by micropore dominance and a small aperture size of 0.34–0.42 nm, limiting the efficient adsorption of corrosion inhibitors. To address both challenges, in this work, ZIF-8 nanostructures were transformed into nitrogen-doped ZIF-derived carbon-based nanocontainers (CZIF) via carbonization. This transformation not only stabilized the structure but also produced larger pore sizes (micro and mesopores), due to defects formed during carbonization. Benzotriazole (BTA) corrosion inhibitors were then encapsulated in CZIF structures to produce CZIF-BTA. Electrochemical impedance spectroscopy (EIS) demonstrated that the saline solution containing CZIF-BTA extract reduced the corrosion rate of steel by 50 % compared to a blank solution. The scratched epoxy (EP) coating containing 0.2 wt% of CZIF-BTA revealed an active inhibition performance with ∼100 % enhancement in the total resistance value compared to blank EP. Finally, the coating showed superior barrier properties with the impedance at the lowest frequency value of ∼2 × 1010 Ω cm2 after 71 days of immersion.

Optical Bench Evaluation of a Novel, Hydrophobic, Acrylic, One-Piece, Polyfocal Intraocular Lens with a "Zig-Zag" L-Loop Haptic Design.

The number of presbyopia-correcting (premium) intraocular lenses (IOLs) is growing steadily as the desire for spectacle independence after cataract surgery increases. The aim of this laboratory study was to evaluate a newly launched hydrophobic, acrylic, polyfocal, refractive intraocular lens with a new optical design and geometry. This polyfocal IOL has three different zones (within the optic) with radially asymmetric design. We performed optical bench tests to calculate the optical characteristics of the sample. The optical performance and quality of IOLs based on ISO 11979-2 and 11979-9 requirements were analyzed with the NIMO TR0815 (Lambda-X). In addition, optical quality metrics were evaluated with the IOLA MFD device (Rotlex). Sphere, Add, modulation transfer function (MTF), the energy distribution between the modes and the MTF along the whole range from far to near were analyzed. The power histogram showed that the tested IOL has the characteristics of a polyfocal IOL with a wide range of optical power between 20.5 and 24.5 diopters. Two distinct peaks were observed, indicating bifocal functionality. In the radial and axial power surface map, all three zones, stated by the company, could be detected. Larger apertures lead to a significant increase in MTF at the far peak, indicating better visual acuity for distant objects under low-light conditions. It was observed that in small aperture sizes, intermediate vision seems to be dominant. The energy distribution remained almost constant with increasing aperture size. This laboratory study was able to confirm the properties of the polyfocal lens stated by the company. Three optical zones could be identified. However, further optical bench tests should be performed to evaluate the new lens under tilted and decentered conditions. Clinical studies have to confirm that the presbyopia-correcting, polyfocal lens can achieve good clinical results with high patient satisfaction without disturbing side effects.

Achromatic metalenses for full visible spectrum with extended group delay control via dispersion-matched layers

Achieving achromaticity across the visible light spectrum is crucial for metalenses in imaging systems. Single-layer metalenses struggle with weak focusing power or small aperture sizes due to inadequate group delay control. Multilayer metalenses offer some improvement but come with increased design and fabrication complexity. Here, we demonstrate a strategy using meta-atoms with material layers engineered for matching dispersion, allowing large and fine adjustments of group delay. Our design substantially broadens the group delay range, allowing us to experimentally demonstrate several polarization-independent metalenses operating across the entire visible spectrum (400-700 nm). We design, fabricate, and characterize achromatic metalenses with aperture diameters of 16 μm, 66 μm, 200 μm, and 400 μm, and numerical apertures of 0.27, 0.11, 0.04, and 0.02, respectively. Among them, the 400-μm diameter, 0.02-numerical-aperture metalens is used to demonstrate full-color imaging capabilities. Our results exhibit diffraction-limited performance, high efficiency, and accurate full-color image reproduction.

Design of Differential Loudspeaker Line Array for Steerable Frequency-Invariant Beamforming

Differential beamforming has attracted much research since it can utilize an array with a small aperture size to form frequency-invariant beampatterns and achieve high directional gains. It has recently been applied to the loudspeaker line array to produce a broadside frequency-invariant radiation pattern. However, designing steerable frequency-invariant beampatterns for the loudspeaker line array has yet to be explored. This paper proposes a method to design a steerable differential beamformer with a loudspeaker line array. We first determine the target differential beampatterns according to the desired direction, the main lobe width, and the beampattern order. Then, we transform the target beampattern into the modal domain for representation. The Jacobi-Anger expansion is subsequently used to design the beamformer so that the resulting beampattern matches the target differential beampattern. Furthermore, based on the criterion of minimizing the mean square error between the synthesized beampattern and the ideal one, a multi-constraint optimization problem, which compromises between the robustness and the mean square error, is formulated to calculate the optimal desired weighting vector. Simulations and experimental results show that the proposed method can achieve steerable frequency-invariant beamforming from 300 Hz–4 kHz.

Crushing responses and energy absorption characteristics of the dynamic stiffening porous material subjected to different strain rates

Crushing responses and energy absorption characteristics of the dynamic stiffening porous material subjected to different strain rates

Theoretical analysis and validation of high-sensitivity and broadband ultrasonic sensors for under-display fingerprint imaging

Theoretical analysis and validation of high-sensitivity and broadband ultrasonic sensors for under-display fingerprint imaging

Wide-angle non-uniform optical phased array using compact and efficient antenna design

In the need for a more compact and efficient optical phased array with a wide steering beam for LIDAR applications, a wide steering array with high resolution is desirable. However, in the published work, a trade-off is often made for one over another. Apodized grating antennas have shown good efficiency with a compact size and wide beam profile, which improve optical phased array beam steering capability and are also compatible with the CMOS silicon photonics process. A promising studies shows enhancement in steering range with good resolution utilizing a non-uniform optical phased array. In this work, we present two highly efficient optical antennas with 94% and 93.5% upward power at the center frequency for the first and second antenna respectively, exceeding state-of-the-artwork to the best of our knowledge, and wide full-width half maximum of 8.88° x 78.05° and 7.53° x 69.85° in elevation and azimuthal planes, respectively. Both antennas provide a broad bandwidth across the 1400–1700 nm wavelength range with more than 80% efficiency in the S, C, and L bands. To overcome the limited scan ranges and small aperture size, a two-dimensional non-uniform array of 10 × 10 elements is utilized to increase the beam steering capability. A genetic algorithm is used to optimize the position of array elements, resulting in an aliasing-free array with a wide steering range of 160° with beam width 0.5° and consistent −11 dB maximum side lobe level across the steering range.

Investigation of Rutting Performance in Geogrid-Reinforced Asphalt by Penetration Test.

Permanent deformation, or rutting, is one of several critical distresses in flexible pavements. This paper introduced a novel experimental method, a penetration test, for asphalt mixtures to quantify the effects of glass fibre geogrids embedded in asphalt under repeated loading. It was found that the evolution of permanent deformation (εp) and its strain rate have three clearly identifiable stages. It was also observed that the presence of the geogrid increased the flow number and the number of cycles to failure significantly compared to control samples. Some of the current εp fitting models were found to be valid for deformation prediction under penetration. In addition, a new simple FN calculation method was also proposed based on strain rate and it showed consistent results. In particular, geogrid type "Grid10", which has smaller aperture size (12.7 mm) had slightly better reinforcement performance regarding the rutting resistance due to its larger contact area. Overall, the test and data analysis method presented in this study could be an important reference for future investigations on geosynthetic-reinforced pavement materials.

Optimal audio beam pattern synthesis for an enhanced parametric array loudspeaker

A parametric array loudspeaker (PAL) generates highly directional audible sound in air with a small aperture size compared to a conventional loudspeaker. But in indoor applications, the long propagation distance of a PAL causes reflections, which disturbs the reproduction of narrow audio beams. Moreover, sound distortion appears along the off-axis direction due to the frequency dependence of the beam width. This study proposed an optimal audio beam pattern synthesis for a PAL-based convex optimization, which can design the audio beam of a PAL with an optimal solution. The proposed method overcame the mentioned limitations by applying it to a length-limited PAL for audio spot control and a multichannel PAL array for a constant beam width audio beam. In a length-limited PAL, the proposed method restricts the audio spot to a smaller region and weakens the sound leakage along the off-axis direction. Whereas in a multichannel PAL array, the proposed method also achieves a constant beam width near the radiator axis. Simulations and experiments verify the effectiveness of the proposed method, which will enhance the performance of a PAL in scenarios where control of the audio beam is required.

Energy consumption of a laboratory jaw crusher during normal and high strength concrete recycling

This paper presents the measurement and analysis of energy consumption of a laboratory jaw crusher during concrete recycling. A method was developed to estimate the power requirements of a lab-scale jaw crusher. The impact of material properties on the crusher performance is studied. Eight concrete strength classes (C20/25–C80/95) were considered in the approach. Concrete specimens were cured for 28 days; at which time, concrete properties were obtained through tests such as bulk density, compressive strength, tensile strength, rebound number and ultrasonic pulse velocity. The impact of different aperture size (5 mm and 25 mm) on the energy consumption was also studied. From the experimental results, it is demonstrated that there is a strong dependance of energy consumption on the compressive strength of concrete. Energy of crushing for specimens with a 90 MPa compressive strength was four times higher than the energy needed to crush specimens with a 28 MPa compressive strength. Furthermore, the crushing requires three times more energy when the smaller aperture size is used to process concrete specimens. The results of this study can form a basis for a future large-scale field analysis and a detailed determination of the energy and economic efficiency of concrete recycling.

A grating lobes suppression method for a steerable parametric array loudspeaker

A parametric array loudspeaker (PAL) is a highly directional sound source with small aperture size. To achieve accurate sound projection, the steerable PAL is implemented by the use of the phased array technology. In this paper, the sound field model based on the Westervelt equation of a practical steerable PAL is presented, and a quasi-linear approximation is adopted to obtain the spatial sound pressure distribution. By applying the phased array technology, the audio beam can steer to the target direction. However, the grating lobe arises when the transducers are spaced more than half a wavelength, which disturbs the effect of beam steering. We further propose the grating lobes suppression method and apply it to the steerable PAL. Simulation results validate the performance of the proposed method.

Fine-Tuning of the Pore Aperture and Framework Flexibility of Mixed-Metal (Zn/Co) Zeolitic Imidazolate Framework-8: An In Situ Positron Annihilation Lifetime Spectroscopy Study under CO2 Gas Pressure.

The mixed-metal (Zn/Co) strategy has been used to enhance the gas separation selectivity of zeolitic imidazolate framework-8 (ZIF-8)-based membranes. The enhancement in selectivity has been attributed to possible modifications in the grain boundary structure, pore architecture, and flexibility of the frameworks. In the present study, we used in situ positron annihilation lifetime spectroscopy (PALS) under varying CO2 pressure to investigate the tuning of the pore architecture and framework flexibility of mixed-metal (Zn/Co) ZIF-8 frameworks with varying Co contents. The random distribution of Zn and Co metal nodes within the highly crystalline frameworks having an SOD topology was established using electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The inherent aperture as well as cavity size of the frameworks, and the pore interconnectivity to the outer surface, were observed to vary with the Co content in ZIF-8 due to the random distribution of Zn and Co metal nodes in the frameworks. The aperture size is reduced with the incorporation of an additional metal (Zn or Co) in ZIF-67 or ZIF-8, respectively. The aperture size remains the smallest for a lower Co content (∼0.20) in ZIF-8. The framework flexibility determined by in situ PALS measurements under CO2 pressure continuously reduces with increasing Co content in ZIF-8. A smaller aperture size as well as low flexibility of ZIF-8 with a low Co content is seen to be directly correlated to a higher separation selectivity of membranes prepared with this mixed-metal composition.

Sparse 2-D optical phased array with large grating-lobe-free steering range based on an aperiodic grid.

Two-dimensional (2-D) optical phased arrays (OPAs) usually suffer from limited scan ranges and small aperture sizes. To overcome these bottlenecks, we utilize an aperiodic 32 × 32 grid to increase the beam scanning range and furthermore distribute 128 grating antennas sparsely among 1024 grid points so as to reduce the array element number. The genetic algorithm is used to optimize the uneven grid spacings and the sparse distribution of grating antennas. With these measures, a 128-channel 2-D OPA operating at 1550 nm realizes a grating-lobe-free steering range of 53° × 16°, a field of view of 24° × 16°, a beam divergence of 0.31° × 0.49°, and a sidelobe suppression ratio of 9 dB.

Costas Sparse 2-D Arrays for High-Resolution Ultrasound Imaging.

Two-dimensional arrays enable volumetric ultrasound imaging but have been limited to small aperture size and hence low resolution due to the high cost and complexity of fabrication, addressing, and processing associated with large fully addressed arrays. Here, we propose Costas arrays as a gridded sparse 2-D array architecture for volumetric ultrasound imaging. Costas arrays have exactly one element for every row and column, such that the vector displacement between any pair of elements is unique. These properties ensure aperiodicity, which helps eliminate grating lobes. Compared with previously reported works, we studied the distribution of active elements based on an order-256 Costas layout on a wider aperture ( 96 λ×96 λ at 7.5 MHz center frequency) for high-resolution imaging. Our investigations with focused scanline imaging of point targets and cyst phantoms showed that Costas arrays exhibit lower peak sidelobe levels compared with random sparse arrays of the same size and offer comparable performance in terms of contrast compared with Fermat spiral arrays. In addition, Costas arrays are gridded, which could ease the manufacturing and has one element for each row/column, which enables simple interconnection strategies. Compared with state-of-the-art matrix probes, which are commonly 32×32 , the proposed sparse arrays achieve higher lateral resolution and a wider field of view.

Numerical Study of a Miniaturized, 1–3 Piezoelectric Composite Focused Ultrasound Transducer

This study aimed to develop an optimal methodology for the design of a miniaturized, 1–3 piezoelectric composite focused ultrasound transducer. Miniaturized focused ultrasound (FUS) devices, generally guided through catheters, have received considerable attention in the biomedical and ultrasound fields as they can overcome the technical restrictions of typical FUS transducers. However, miniaturized transducers cannot readily generate a high acoustic intensity because of their small aperture sizes and the vibration mode coupling. As such, 1–3 composite transducers, having a high electromechanical coupling and efficient vibration directivity, break through the current technical restrictions. However, the systematic methodology for designing miniaturized FUS transducers has not been thoroughly discussed so far. Therefore, in this study, we designed 1–3 piezoelectric composite transducers using analytical and numerical methods. Specifically, extensive parametric studies were performed through finite element analysis under the coupled field with piezoelectricity, structural vibration, and acoustic pressure. The simulation results confirmed that the optimal design of the 1–3 composite type transducer produces much higher (>160%) acoustic pressure output at the focal point than the single-phase device. Furthermore, the array type of the interstitial transducer was predicted to produce an unprecedented acoustic intensity of approximately 188 W/cm2 under a short duty cycle (1%). This study will provide valuable technical methodology for the development of interstitial, 1–3 composite FUS transducers and the selection of optimal design parameters.

Reflective Metasurface With Steered OAM Beams for THz Communications

The abundant spectrum resources and low beam divergence of the terahertz (THz) band, can be combined with the orthogonal propagation property of orbital angular momentum (OAM) beams to multi-fold the capacity of wireless communication systems. Here, a reflective metasurface (RMTS) is utilized to enhance the coverage of the high gain THz OAM beams by enabling the non-line-of-sight (NLoS) component by reshaping the planar wavefront of the incident wave into the helical wavefront, so that it is re-directed towards the direction of interest. This can contribute to alleviating the concern of the small aperture size, since improving the channel capacity can be achieved at the low spectrum blocks of the THz band (larger aperture size). For validation, three <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90 \times 90$ </tex-math></inline-formula> mm RMTSs are simulated, fabricated, and tested in the frequency range 90–110 GHz, to re-direct single and dual OAM beams towards the desired location.

Influence of RVGA's height on suppressing the aero-optical effects induced by a supersonic mixing layer.

The supersonic mixing layer formed on the surface of hypersonic/supersonic flight vehicles' optical windows is the main structure that induces aero-optical effects (AOEs), which may cause severe imaging degradation. Previous research has found that the ramp vortex generator array (RVGA) with a height of 1mm can suppress the AOE of a M c=0.17 supersonic mixing layer. In this paper, three RVGAs with different heights are considered. The nano-tracer-based planar laser scattering technique and ray tracing method are applied to do the aero-optical analysis. The root mean square of the optical path difference (O P D r m s ), Strehl ratio (SR), imaging displacement (ID), and angle deviation (AD) are taken as evaluation parameters. It is found that a smaller aperture size (A D ) corresponds to a better SR in the aperture size range of 5m m∼100m m. Then a beam with an incident angle α=15∘ and a 15mm A D is used to study the influence of RVGA's height on suppressing the AOE. When the RVGA is applied, the I D¯ and A D¯ (overline means time-averaged results) in different sections of the supersonic mixing layer are significantly normalized, which can simplify the AOE's correction procedure. The higher the RVGA is, the more the O P D r m s ¯ is reduced and the weaker the AOE is. RVGA1 (h=1.2m m) has the best performance in suppression of the AOE because it introduces much more disturbance than RVGA2 (h=1.0m m) and RVGA3 (h=0.5m m) and achieves better inhibition of the formation and development of the K-H vortices and more reduction of the whole thickness of the supersonic mixing layer.

Large-aperture, widely and linearly tunable, electromagnetically actuated MEMS Fabry-Perot filtering chips for longwave infrared spectral imaging.

Longwave infrared spectral imaging (LWIR-SI) has potential in many important civilian and military fields. However, conventional LWIR-SI systems based on traditional dispersion elements always suffer the problems of high cost, large volume and complicated system structure. Micro-electro-mechanical systems Fabry-Perot filtering chips (MEMS-FPFC) give a feasible way for realizing miniaturized, low cost and customizable LWIR-SI systems. The LWIR MEMS-FPFC ever reported can't meet the demands of the next-generation LWIR-SI systems, due to the limitation of small aperture size and nonlinear actuation. In this work, we propose a large-aperture, widely and linearly tunable electromagnetically actuated MEMS-FPFC for LWIR-SI. A multi-field coupling simulation model is built and the wafer-scale bulk-micromachining process is applied to realize the design and fabrication of the proposed MEMS-FPFC. Finally, with the rational structural design and fabrication process, the filtering chip after packaging has an aperture size of 10 mm, which is the largest aperture size of LWIR MEMS-FPFC ever reported. The fabricated electromagnetically actuated MEMS-FPFC can be tuned continuously across the entire LWIR range of 8.39-12.95 µm under ±100 mA driving current with a pretty good linear response of better than 98%. The developed electromagnetically actuated MEMS-FPFC can be directly used for constructing miniaturized LWIR-SI systems, aiming for such applications as military surveillance, gas sensing, and industry monitoring.

The effects of grid design on the performance of 3D-printed dry powder inhalers

The effects of grid design on the performance of 3D-printed dry powder inhalers

Array‐based Fabry–Pérot cavity antenna for flat‐topped radiation pattern

AbstractIn this letter, an array‐based ray tracing model and Fabry–Pérot cavity antenna covered by frequency selective surfaces (FSS) are proposed to realize the flat‐topped radiation pattern (FTRP). Based on the array‐based model, a good FTRP can be obtained by combining the initial directivity of the feed array with the additional directivity of FSS‐type partially reflective surface. By using the proposed method, a low‐cost, lightweight, simple structure and dual‐polarization Fabry‐Pérot cavity antenna with small aperture size for FTRP is designed. From the measured results, the FTRP with more than 58° beamwidth and less than 2 dB ripple level in the frequency band of 2.4 to 2.7 GHz for indoor communication are obtained.