Parallel Strips Research Articles

Microstructure of NiTi superelastic alloy manufactured by selective laser melting

Nitinol is used in dental tools for its superelasticity, shape memory and biocompatibility. Selective laser melting (SLM) on a powder bed is a potential process for manufacturing such as dental tools. Microstructural studies are conducted on NiTi-SLM using a parallel strip strategy and 90° laser beam rotation. The multi-scale (nano-, micro- and mesoscopic) microstructure is revealed. Similar “cast” type microstructure features are found. The SLM melt is casted in a “micro-mold”. Fine micro-grains with random crystallographic orientation are formed near the mold walls and served as seats for the rapid growth of columnar dendritic grains along the 〈0 0 1〉 direction with epitaxial crystallographic relationships. The growth of the columnar grains curves towards the center of the “micro-mold”, coinciding with the center of the laser beam. It is proposed that SLM processing resembles “Metallic Self Micro-Mold Casting” (MSµMC) and/or “Self Micro-Molding” (S2M).

Wind-induced vibration of a square cylinder suspended by parallel elastic strips with nonlinear stiffness

A series of wind tunnel tests is conducted to investigate the wind-induced vibration of a square cylinder suspended by four parallel elastic strips. The elastic strip-suspended experimental setup, which provides the square cylinder with a cubic hardening nonlinear stiffness, is more convenient than existing nonlinear setups (e.g., the numerical computer-controlled feedback nonlinear setup or the physical magnet-induced nonlinear setup) and can be readily achieved in any wind tunnel. A theoretical formula is deduced for the nonlinear restoring force provided by parallel elastic strips, and the theoretical formula is validated against experimental measurements. The considered square cylinder exhibits vortex-induced vibrations (VIVs) at low wind velocities while galloping vibrations occur as the wind velocity becomes higher. The critical wind velocity for galloping instability can be remarkably reduced by adding two fins at the trailing-edge corners of the square cylinder. The influences of the pretension force of the elastic strips and the configuration of the trailing-edge fins on the vibration amplitude and kinetic energy of the square cylinder are also investigated.

Design of a Printed Dipole Antenna by Using the Substrate-Integrated Double Line Technology

In this article, a novel printed dipole antenna is proposed with gain enhancement by using the newly emerging substrate-integrated double line (SIDL) technology for potential 5G millimeter-wave (mm-wave) applications. As a three-wire transmission line, the SIDL incorporates two parallel inner strips and one grounded outer conductor. The inner strip pair protrudes and is bent bilaterally to form the dipole’s arms. The outer conductor is stretched out and splits into four strips in a fourfold symmetry along the longitudinal axis to boost the gain. A bilateral slotline technology is used to couple the energy from the feed to the SIDL structure, providing a broadband transition. The shaped SIDL and the transition contribute to the proposed dipole element and then are expanded to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> array, both of which are designed and fabricated by using the standard printed circuit board (PCB) process. The measurement discloses that the element has an actual −10 dB impedance bandwidth from 33.5 to 47.4 GHz (34.4%@40.4 GHz) with a practical peak gain of 7.00 dBi, which for the array are 32.0–45.1 GHz (34.0%@38.6 GHz) and 8.88 dBi, respectively. Good agreement between the simulated and experimental results demonstrates the feasibility of SIDL’s utilization in designing the printed dipole antenna for high-gain and wideband mm-wave applications.

Low-Profile High-Gain Endfire Antenna With Circular Polarization

A circularly-polarized (CP) traveling-wave endfire antenna featuring low profile, high gain, and simple feeding structure is presented in this communication. Offset parallel strips with proper dielectric loading are employed in a low-profile substrate to achieve two orthogonal electric field components with equal magnitude and 90° phase difference for CP endfire radiation. Meanwhile, periodic phase-loading technique is used to achieve a proper phase constant for high endfire gain. A prototype is designed and fabricated to verify the proposed method. Experimental results demonstrate CP endfire radiation within a frequency band of 9.78–10.09 GHz. The average endfire gain is 10.3 dBic with an average efficiency of 62.5%.

Mass efficiency of strip-based coilable space structures

This paper presents a general semi-analytical study of the mass efficiency of coilable plate-like space structures. A bending architecture based on four diagonal booms that support parallel strips is compared to a cable-stayed architecture in which vertical booms and cable stays support the diagonal booms at the tip. Limiting conditions of global buckling, local buckling, material failure, and excessive deflection define the design space for each architecture. Considering pressure loads spanning several orders of magnitude, the optimal areal density of structures of size varying from a few meters to hundreds of meters is determined for both architectures. Design charts for optimal designs are provided for a range of sizes, loads, and deflection limits. It is shown that the cable-stayed architecture is always lighter than the bending architecture, from a few percent to over 30%.

High Spots for the Ice-Fishing Problem with Surface Tension

In the ice-fishing problem, a half-space of fluid lies below an infinite rigid plate (``the ice'') with a hole. We investigate the ice-fishing problem including the effects of surface tension on the free surface. The dimensionless number that describes the effect of surface tension is called the Bond number. For holes that are infinite parallel strips or circular holes, we transform the problem to an equivalent eigenvalue integro-differential equation on an interval and expand in the appropriate basis (Legendre and radial polynomials, respectively). We use computational methods to demonstrate that the high spot, i.e., the maximal elevation of the fundamental sloshing profile, for the ice-fishing problem is in the interior of the free surface for large Bond numbers, but for a sufficiently small Bond number the high spot is on the boundary of the free surface. While several papers have proven high spot results in the absence of surface tension as it depends on the shape of the container, to the best of our knowledge, this is the first study investigating the effects of surface tension on the location of the high spot.

Wideband Polarization Rotation Transmitarray Using Arrow-Shaped FSS at W-Band

Based on the passband characteristics of frequency selective surface (FSS), a wideband transmitarray (TA) with linear polarization rotation at W-band is proposed. The middle layer of the unit cell is a pattern of arrow-shaped structure, which can rotate the incoming wave by 90°. A pair of parallel strip polarizers is employed to enhance the polarization conversion efficiency. The prototype of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25\times 25$ </tex-math></inline-formula> -element TA is fabricated by the standard PCB technology. Within the 3 dB gain bandwidth of 20%, the measured peak gain of 28.7 dB with the corresponding aperture efficiency of 38.2% is achieved. The error analysis is also conducted by comparing the simulation and measurement. The performance of the proposed TA demonstrates that it is a suitable solution for wideband and low-cost applications in the millimeter-wave spectrum.

Spatially Modulus-Patterned dielectric elastomer actuators with oriented electroactuation

The oriented actuation of muscles is an important motion form in the locomotion of living beings. Dielectric elastomers (DE) as soft electroactive materials are considered as one of the leading candidates for artificial muscles. However, the electro-actuated deformations of most DE films are uniformly expanded, since synthetic elastomer films are generally mechanically isotropic. Here, we design an elastomer network with reserved double bonds, which allows post-crosslinking in as-prepared isotropic elastomer films with designed crosslinked patterns to spatially modulate the stiffness, and the elastic modulus in the post-crosslinked areas can be continuously increased by an order of magnitude. We reveal that introducing proper numbers of periodic parallel post-crosslinked strips enables the elastomer film to exhibit strong anisotropic mechanical behavior. Furthermore, we simulate and demonstrate the advantage of oriented electroactuation in DE actuators by using DE films with different numbers of parallel strips. Like the dexterous and elegant muscle-driven motions of creatures, our DE films capable of post-regulating mechanical properties can be potentially programmed for achieving complicated electroactuation via designing local crosslinked density and patterns.

Textural Characteristics of the Holocene Sandy Ridges in the Eastern Venetian Coastal Plain (North Adriatic Sea, Italy)

In the lower Piave river coastal plain (northeast of the Venice Lagoon, Italy), evidences of ancient sandy ridges testify to both the local coastline progradation and retrogradation that occurred during the Holocene. Their arrangement is recognizable in aerial photographs as they appear as groups of parallel sandy strips. The orientation of each group of ridges differs from the orientation of the others. Even if the ridges have not preserved their original relief and morphology, weak undulations are still locally present. Through the joint interpretation of textural parameters and geomorphological observations and measurements, an attempt has been made to define the depositional processes responsible for the formation of these sandy ridges. The results from grain-size analyses have given evidence of the foreshore and the backshore environments. They have confirmed the presence of both aeolian deposits in most of the sampled sandy ridges and fine-grained filling sediments containing organic matter in the old inter-ridge depressions. The investigations have also confirmed the existence of a well-preserved abandoned Piave river delta and four subsequent main stages of coastal progradation interrupted by episodes of coastal retreat. Therefore, this research has provided new insights into the evolution of the Holocene Venetian coastal plain by adding new information on the different coastal depositional environments and transporting agents.

Conformal Multifunction FSS With Enhanced Capacitance Loading for High Angle Stable Stopband Filtering and Microwave Absorption

This article presents a new method of enhancing the capacitance of a single-layer conformal frequency selective surface (FSS) for multifunctional operation. The unit cell of the FSS consists of gridded square loop-loaded modified Jerusalem cross (JC) element. End capacitance of the conventional JC FSS is enhanced by placing parallel diagonal strips, resulting in a pair of reflection zeros near the sidebands. The modified geometry provides high selective stopband filtering that reflects the signal at 20.16 GHz with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> < −10 dB stopband bandwidth of 20.52%. The FSS shows stable stopband reflection up to a high incidence angle of 85°. The stability in the filter response is also achieved at various conformal angles. The proposed FSS is optimized for dual-band near-perfect absorption. At two resonances 12.76 and 22.54 GHz, the absorption are 99.88% and 99.1%, respectively. Prototypes of the stopband FSS and the dual-band absorber are fabricated to verify the feasibility of the proposed concept. The measured filter and absorber responses are found consistent with the simulated results. As a conformal multifunctional structure, the proposed FSS has the merits of electromagnetic interference shielding and radar cross section reduction in stealth application.

Site-specific seeding for maize production using management zone maps delineated with multi-sensors data fusion scheme

Uniform rate seeding (URS) density may result in under- or over-optimal plant population that negatively affects crop growth and yield. Site-specific seeding (SSS) is one of the solutions to manage in-field soil variation by optimizing the input seed rate to match soil fertility. This study has evaluated the agronomic and economic response of maize to SSS compared to the URS using a data fusion scheme. Two fields of 5.5 ha and 10 ha in Belgium and France, respectively, were scanned using an on-line visible and near-infrared spectroscopy sensor to measure soil pH, organic carbon (OC), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sodium (Na), moisture content (MC), and cation exchange capacity (CEC). Crop normalized difference vegetation indices (NDVI) were retrieved from several Sentinel-2 images. Measured crop yield, retrieved NDVI and on-line measured soil attributes were then fussed using k-means clustering algorithm to delineate management zone (MZ) maps, whose classes were ranked based on their fertility level and crop yield. A parallel strips experiment was overlaid upon the MZ map, to allow comparing the performance of SSS against URS. Two SSS treatments were implemented in the strip experiment, e.g., the “Kings” approach that recommended the highest seeding density for the highest fertile MZ class and vice versa, and the “Robin Hood” approach followed the opposite principle. Results revealed that SSS treatments increased maize grain yield by 0.25–0.70 Mg ha−1 and thus improved gross margin by 26.7–92.67 € ha−1, compared to the URS. Besides, the SSS-Kings treatment outperformed the URS and SSS-Robin Hood in both fields, whereas the SSS-Robin Hood outperformed the URS treatment only in one field. Soil OC, MC, Mg, and pH revealed a positive correlation each with grain yield in the SSS-Kings treatment. The SSS-Kings treatment is therefore recommended to manage in-field soil variation, which can result in optimizing input seed rates for increasing maize productivity and profitability.

A modified rectangular resonant cavity utilizing frequency selective coupled end‐plate for dielectric constant measurement by perturbation technique

In this article, a modified rectangular resonant cavity consisting of a rectangular waveguide (RWG) and two frequency selective coupled (FSC) end-plates with embedded parallel metallic strips (PMS) is proposed. The proposed FSC end-plate converts the semi-constant coupling mechanism of the conventional iris-coupled end-plate to the tunable FSC characteristics. This is due to adding capacitive coupling properties to inductive coupling characteristics of the conventional iris-coupled end-plate by embedding PMS inside the iris-hole. So, the proposed FSC end-plate enhances output power of the resonant frequency of the cavity. Consequently, the proposed modified cavity can determine the permittivity properties of the high-loss specimens. Also, the parametric study of the effect of variation of the physical dimensions and position of these strips to tune and trim the performance of the proposed FSC end-plate is presented. Also, the present study proposes an approach for determining the maximum complex permittivity with the rectangular resonant cavity perturbation method. Based on WR-229 RWG specifications, conventional and investigated cavities are fabricated and measured. The evaluated results of the proposed configuration and conventional model indicate about 184% determination enhancement in the imaginary part of the dielectric constant. Also, this design is validated by distilled water specimen and TiO2 films at a various partial pressure of oxygen that are deposited by utilizing radio frequency magnetron sputtering technologies and their complex permittivity are determined by manufactured cavities.

Surveillance of Immunological Status after Vaccination by two Serological Assays based on SARS-CoV-2 Spike Protein

PurposeTwo serological assays, an Enzyme-Linked Immunosorbent Assay (ELISA) and a Lateral Flow Assay (LFA), have been developed based on the SARS-CoV-2 recombinant Receptor Binding Domain (RBD-ELISA) and the combination of Trimeric Spike (S) and Nucleoprotein (N), S-LFA and N-LFA, respectively, as candidate tools for both indirect measurement of virus circulation and assessment of infection and vaccine-induced immunity.Methods & MaterialsA total of 1272 human serum samples collected from volunteers (SARS-CoV-2 infected, non-infected or vaccinated) were evaluated by the two assays. For the RBD-ELISA, plates were coated with RBD, sera were added at 1/5 dilution and bound antibodies were detected with RBD labelled with Horseradish Peroxidase. For the LFA, two parallel strips were used: one for detection of N-specific antibodies (Hoste A. el al, 2020); and another one for detection of S-specific antibodies, using S both as capture and detector reagent. Twenty microliters of blood or ten microliters of serum were applied to each cassette and results were interpreted after ten minutes.A seroneutralization assay was used as reference for the detection of neutralizing antibodies with RBD-ELISA and Reference sera (World Health Organization), for determination of the Limit of detection (LoD). MedCalc® 10 software was used for statistical analysis.ResultsThe potential diagnostic application with sera from naturally infected and non-infected volunteers showed sensitivity, specificity and agreement (kappa) values of 95.1%, 99.0% and 0.94 respectively for RBD-ELISA; while 97.2%, 99.3% and 0.967 respectively for N-LFA; or 93.2% 98.3 %, 0.923, respectively for S-LFA. Serum samples from vaccinated individuals were analyzed for the specific detection of antibodies to the S protein: for vaccinated but non-infected individuals, sensitivity reached 97.3% after 15 days post-second vaccination dose whereas for previously infected people reached 100% after only 15 days post-first dose. The performance of RBD-ELISA showed good agreement with seroneutralization and excellent agreement with S-LFA (kappa 0.979).ConclusionThe dual N/S LFA represents a valuable tool to detect SARS-CoV-2 infection due to its complementary information on N and S-specific antibody response. Furthermore, the S-LFA and RBD-ELISA are both proven to be able to determine the extent of antibody response after vaccination.

Quad-band terahertz metamaterial absorber using three parallel gold strips surrounded by two identical gold ring arcs

Quad-band terahertz metamaterial absorber with near-perfect absorption is given in this paper. It is designed by a patterned Au layer and a continuous Au film separated by an insulating dielectric layer, of which the patterned Au layer is consisted of three parallel Au strips (a longer and two shorter) surrounded by two Au ring arcs of the same size. Four separated terahertz absorption peaks with narrow bandwidths and large absorptance are realized. The first three absorption peaks are due to the fundamental modes of the Au strips and the Au ring arcs, while the fourth absorption peak is ascribed to the excitation of three-order resonance in the Au ring arcs. The field distributions of the four absorption peaks are presented to verify their physical mechanisms. The influence of geometrical dimensions of the proposed configuration on the performance of the quad-band light absorption is discussed. Moreover, considering the potential sensing applications, the sensing performance of the proposed absorption device is also explored. The suggested scheme could provide considerable application prospects in selective thermal radiation, spectral imaging, sensing, detecting, electromagnetic stealth, etc.

Simulation of daylight in buildings with curved facades for rational use of solar energy

Simulation of daylight conditions in buildings with curved facades was carried out to show the possibility of more efficient use of solar energy with a constant change in the azimuth of the windows orientation. To optimize daylighting, a smart window with optical filter is proposed having an angular selectivity of light transmission due to two surface gratings with alternating transmissive and chromogenic parallel strips. Unlike conventional smart windows, the entire area of which is covered with chromogenic layers, a grating filter weakens or completely blocks direct solar radiation by allowing diffused sky light and reflected light to pass through. Methods for calculating the geometric parameters of the gratings are presented and the optimal slope angles of the filter gratings for windows with different azimuths of a building with round facade and the temporal characteristics of the light transmission of these windows are calculated. The results substantiate the advisability of using smart windows with grating filters in buildings with curved facades to improve the comfort of daylighting and insolation, to protect against direct rays when passing diffuse sky light and albedo by adapting the light transmission of windows to a change in the position of the sun relative to them.

Demonstration of a high extinction ratio TiN-based TM-pass waveguide polarizer

A high extinction ratio transverse magnetic (TM)-pass plasmonic waveguide polarizer has been designed and optimized. This device exploits two parallel TiN strips embedded in a silicon dioxide cladding to cut off the transverse electric (TE) polarization state, which is either reflected or absorbed, while the TM mode can pass through the main silicon waveguide with significant low losses. Given a device of 5 µm length, an extinction ratio as high as 60.7 dB and an insertion loss of 2.23 dB were achieved at the target wavelength of 1.55 µm. To our knowledge, this extinction ratio is one of the highest values ever reported. In the wavelength of 1.45–1.59 µm, the proposed device provides an optical bandwidth of 140 nm for an extinction ratio more than 30 dB and an insertion loss less than 3 dB. This device is relatively simple and is easier to be fabricated than other architectures that are found in the literature.

Anisotropic frontal polymerization in a model resin-copper composite.

This work investigates experimentally and numerically frontal polymerization in a thermally anisotropic system with parallel copper strips embedded in 1,6-hexanediol diacrylate resin. Both experiments and multiphysics finite element analyses reveal that the front propagation in the thermally anisotropic system is orientation-dependent, leading to variations in the front shape and the front velocity due to the different front-metal strip interaction mechanisms along and across the metal strips. The parameters entering the cure kinetics model used in this work are chosen to capture the key characteristics of the polymerization front, i.e., the front temperature and velocity. Numerical parametric analyses demonstrate that the front velocity in the directions parallel and perpendicular to the metal strips increases as the system size decreases and approaches the analytical prediction for homogenized systems. A two-dimensional homogenized model for anisotropic frontal polymerization in the metal-resin system is proposed.

Wideband RCS Reduction of Slot Array Antenna Utilizing 3-D Absorptive Frequency-Selective Structure

A low radar cross-section (RCS) slot array antenna based on absorptive frequency-selective structure (AFSS) is presented in this letter. The AFSS unit cell is constructed by two lossy layers and four double-sided parallel strip lines (DSPSLs). The radiation performance of the antenna can be preserved due to the transmission window of the lossy layers. Wide absorption bands of the AFSS are achieved due to periodic impedance of the DSPSL and the combination of the lossy layers. The operating principle of the design is demonstrated, and a prototype is fabricated and measured to validate the design. The proposed design features both wide RCS reduction band of the antenna and wide transmission band of the AFSS.

Design of an Ultrawideband Planar Guanella Balun

This article presents the design and implementation of an ultrawideband multioctave planar Guanella balun (balanced-to-unbalanced) using double-sided parallel strip lines (DSPSLs). The operating frequency of the balun is found to be 0.5–2.6 GHz. The DSPSL is a type of balanced transmission line where two metal strips are present on the opposite sides of a flat dielectric substrate. Wideband transition between these balanced lines to a microstrip line has also been implemented. The measured amplitude and phase imbalance between the output signals at the balanced ports are less than 0.75 dB and 7°, respectively. The impact of these amplitude and phase imbalances on the combining loss of the balun has been presented. In order to understand the behavior of the balun with respect to differential and common mode signals, the mixed-mode <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters have been calculated. The physical size of the fabricated balun is 27.25 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times\,\,49$ </tex-math></inline-formula> mm. The design has been validated with the help of its measurement results.

A filtering antenna with wide out‐of‐band suppression based on open‐stubs resonator

In this paper, a wide out-of-band suppression antenna with simple structure, low profile and filtering characteristics is presented. In order to improve the selectivity of the passband edge, two simple structures, namely U-shaped slot and two slits, are introduced into the antenna to generate radiation nulls. To obtain a wide out-of-band suppression, the feeder with π-shape stub is applied. The transmission nulls generated by the feeder are used to suppress stopband harmonics. In addition, a pair of parallel strips is introduced to enhance the gain suppression effect at the upper stopband. The measured results show that the average gain is 7 dBi, and the stopband suppression reaches 2.84 f0 (f0 is the center frequency of the proposed antenna). The overall height of the presented antenna is 0.03 λ0 (λ0 is the wavelength at the center frequency).