U-shaped Metal Research Articles

Terahertz perfect absorber of narrowband and broadband based on a U-shaped metal patch

Terahertz perfect absorber of narrowband and broadband based on a U-shaped metal patch

A compact wideband filtering rectangular dielectric resonator antenna with U-shaped metal strips

ABSTRACT In this paper, a compact wideband filtering rectangular dielectric resonator antenna (RDRA) loaded with a pair of U-shaped metal strips is proposed. By using a slot-coupled feeding structure, a rectangular DR with a length–width ratio of 3:1 is selected to combine the resonant frequencies of the TE 111 and TE 121 modes to achieve the passband. Two pairs of transverse branches with different lengths are added to the longitudinal microstrip feeding line, and the TE 111 , TE 11+δ1 , and TE 121 modes are successfully excited to enhance the bandwidth. The short pair of transverse branches can generate a null high-frequency radiation. A pair of U-shaped metal strips is loaded at both ends of the top of rectangular DR, introducing a low-frequency radiation null. Both radiation nulls can be independently adjusted. A pair of rectangular grooves is etched inside rectangular DR to boost the impedance matching level. The proposed filtering RDRA has been fabricated and measured for verification. The measured relative impedance bandwidth is 22.67% (4.34–5.45 GHz). The measured average gain and peak gain are 7.19 dBi and 8.06 dBi, respectively. RDRA filtering has broad application potential in modern communications, such as the N79 band.

Study on unseating prevention for multi-union long simply supported girder bridges under near-fault ground motions

Girder shifting is a common form of seismic damage for girder bridges. Unseating could occur when the displacement of the girder is too large, especially for bridges near faults, because the velocity impulse effect leads to greater displacement responses of structures. Setting metal dampers between girders and piers is a useful way to control the seismic behavior and reduce the risk of unseating. Since metal dampers are inevitably exposed to the erosive service environments, their mechanical properties may degrade due to corrosion. In this paper, a U-shaped metal damper made of stainless steel instead of mild steel (i.e., U-shaped stainless steel damper, which could be named simply as USSSD) is proposed and applied to the seismic reduction design of girder bridges. First, the finite element model (FEM) of the USSSD is built by the ABAQUS, and its force-displacement relationship is obtained based on the skeleton curve, which is fitted by the trilinear kinematic strengthening model. Then, a multi-union long simply supported girder bridge is taken as an example. The FEM of the adopted bridge is established via the Midas Civil to verify the seismic mitigation effect of the proposed USSSD excited by near-fault ground motions. The numerical analyses demonstrate that the unseating may occur without the use of the USSSDs. The relative displacement between the girder and pier is effectively controlled by the USSSDs, and the reduction is more than 50 %. When the bridge is equipped with the USSSDs, both the curvature ductility coefficient of the pier bottom and the maximum drift of the pier tip increase by a limited amplitude, which do not cause additional damage to the piers.

Triple-frequency terahertz modulator based on electronically controllable metamaterial from the coupling effect

This paper proposes a triple-frequency terahertz amplitude modulator that utilizes an I-shaped strip and four U-shaped metal patches within a common metal-substrate configuration. The top metal layer consists of an I-shaped strip and four U-shaped metal patches, while the bottom substrate layer is made of polyimide. Amplitude modulation is achieved through adjusting the plasma frequency of the high-electron-mobility transistors, resulting in a modulation depth of nearly 93% at resonance frequencies of 0.26 and 0.49 THz. At 0.6 THz, the modulation depth reaches 65%, demonstrating excellent performance. Resonance frequencies are determined by electric field and surface current distribution. The triple-frequency terahertz amplitude modulator is applicable in various fields, including terahertz communications and imaging.

Dual-frequency terahertz amplitude modulator based on the coupling effect of cross-shaped structure and U-shaped metal patches

This letter presents a dual-frequency terahertz amplitude modulator based on a cross-shaped structure and U-shaped metal patches. Its structural unit is a typical metal-substrate structure. The top metal consists of a cross-shaped structure and U-shaped metal patches, and the bottom substrate layer is made of quartz. Amplitude modulation is achieved by adjusting the temperature of the vanadium dioxide (VO2) patches. The modulation depth can be approximately 75 %. The mechanism of the resonance frequency is explained by the equivalent circuit model. The proposed structure shows good amplitude modulation capability at different incidence and azimuth angles by changing the location of the VO2 patches. The dual-frequency terahertz amplitude modulator can be used in terahertz communication, imaging, etc.

Bending Forming Characteristics of CoCrFeMnNi High-Entropy Alloy Sheets Induced by Nanosecond Pulse Laser Irradiation.

Laser bending forming, as a flexible and die-less forming approach, facilitates the three-dimensional shaping of sheets through the generation of thermal stress via laser-material interaction. In this study, the bending forming characteristics of CoCrFeMnNi high-entropy alloy sheets induced by nanosecond pulse laser irradiation were systematically investigated. The effects of parameters including laser power, scanning speed, number of scans, scanning interval, and sheet size on the bending angle, cross-sectional morphology, and hardness were studied in detail under both the laser single-line and multi-line scanning modes. The experimental results confirmed the effectiveness of nanosecond pulse laser irradiation for achieving accurate formation of CoCrFeMnNi sheets, with the successful fabrication of J, L, and U-shaped metal components. Apart from the forming ability, the cross-sectional hardness was significantly increased due to the grain refinement effect of nanosecond pulse laser irradiation. Furthermore, employing the laser single-line scanning mode enabled the effective rectification of overbending parts, showcasing complete recovery for small-angle overbending, and a remarkable 91% recovery for larger-angle overbending. This study provides an important basis for the bendability of CoCrFeMnNi sheets by laser forming and elucidates the evolution of the microstructure and mechanical properties in the bending region.

Design, modeling and optimization of an adhesively bonded ring joint with U-section for ceramic cylindrical pressure hull of deep-sea underwater vehicles

The brittleness of ceramic increases the risk of damage or collapse when the ceramic cylindrical pressure hull is directly connected with a rigid part, especially under high hydrostatic pressure. To solve the above problem, this paper systematically explores the design, modeling and optimization of an adhesively bonded ring joint with U-section (ABRJ-U) to avoid the direct connection of the ceramic hull of a small hadal glider, Petrel, with the hemispherical metal end caps. The ABRJ-U is comprised of a U-shaped metal ring, a gasket, and epoxy adhesive layer. To optimize the design parameters, a mechanical model of ABRJ-U is established. The stress tests prove that the model has better efficiency in optimization, but lowered accuracy compared with regular finite element method. Considering the difficulty of obtaining a more accurate theoretical model, the optimization efficiency of regular finite element method is selected for further improvement by integrating the response surface methodology and multi-objective genetic algorithm. According to the optimization results, our optimization method considers the stress calibration of both the adhesive and gasket, simultaneously achieving a 20.8% reduction in the mass of ABRJ-U. The proposed methods also provide valuable reference for the design, modeling, and optimization of other bonded joints.

Tunable slow light device based on a graphene metasurface.

Slow light devices have significant applications in memory, switching, and quantum optics. However, the design and fabrication of slow light devices with large tunable group delay are still challenging. Here, a graphene-based slow light device that can electrically modulate the group delay of terahertz (THz) waves is proposed and experimentally demonstrated. The unit cell of the device consists of a U-shaped metal resonator and an Ω-shaped metal resonator, with three graphene ribbons embedded between the two resonators. Under electrical stimuli, a relatively high amplitude modulation depth of 74% is achieved and the maximum transmission amplitude is as high as 0.7 at the transmission peak of 0.6 THz. Most importantly, the maximum group delay variation reaches 5 ps at 0.76 THz and the maximum group delay amplitude is as high as 8.8 ps. The experiment shows good agreement with simulation. This study paves a new way for developing novel switchable nanophotonic devices and slow light devices.

A Slow Wave Folded Ridge HMSIW Using Spoof Surface Plasmon Polaritons Structure and Its Application in Coupler Design

In this article, a folded ridge half-mode substrate integrated waveguide (FRHMSIW) combined with the novel spoof surface plasmon polaritons (SSPP) is proposed to reduce both the lateral size and the longitudinal size. The SSPP structure consisting of sub-wavelength U-shaped grooves, metal patches and metal blind holes is loaded into the FRHMSIW. Firstly, the SSPP increases the effective permeability and permittivity in the waveguide, which can decrease the cutoff frequency and hence reduce the lateral size. Secondly, the SSPP has slow-wave effect, which can reduce the longitudinal size of the waveguide. Analytical formulas of the effective permeability and permittivity are derived based on anisotropic media theory, which are verified by comparing the calculation results with full wave simulation results. According to the derived analytical formulas, a prototype of the proposed FRHMSIW-SSPP waveguide is designed and fabricated using the PCB process. The measurement results show that the proposed waveguide reduces lateral width by 78.7% and the longitudinal dimension by more than 74% compared with the classical SIW with the same cutoff frequency. Subsequently, the FRHMSIW-SSPP structure is applied to design a 3-dB coupler. Results show that the coupler based on the FRHMSIW-SSPP can reduce the surface area by 92.5% compared with the classical SIW coupler.

Analysis of the punch motion curve for the springback of U-shaped sheet metal

Servo presses achieve high formability by using different punch motion curves, thereby increasing their applicability in conventional processing fields. In this study, the punch motion curves of servo presses were optimized, and the effects of punch motion curves on the springback of U-shaped sheet metal were explored. Subsequently, the optimal punch motion curve was determined, and the springback effect after processing was investigated. Different punch motion curves were proposed and simulated for comparison with the results of conventional methods, and the equivalent stress values obtained using different motion curves and mold angles were analyzed. DEFORM software was used to conduct simulations to determine the differences between processing methods. In addition, the spring-go, springback, load–stroke characteristics, and stress and strain distributions of U-shaped sheet metal were investigated. The conventional motion curve resulted in springback, stress, strain, and required processing force higher than those achieved by the curves proposed in this study. The smaller the movement difference in the motion curve of the servo press was, the lower the springback, stress, and strain were. These results indicate that the punch motion curves obtained for different types of processing can serve as a reference for selecting appropriate parameter values for servo presses.

Spatial observation of highly directional radiation from a compact 3D photonic-crystal antenna in Ku band

A three-dimensional compact prototype of a photonic crystal directive antenna is constructed for beam steering and directional radiation in the microwave. Experiments demonstrate that the array of dielectric cylinders placed in a U-shape open metal cavity can be profitably exploited to act as a high-efficiency splitting directive antenna in particular modes. Highly directional radiation has been observed at the fundamental electromagnetic resonance of band edge crystal with a maximum gain of 20.73 dBi and an aperture efficiency of 49.77%. The side-lobes on the E-plane (yoz) are almost constrained in −20 dB benefitting from the band edge lattice-induced resonance on the H-plane (xoy), suppressing the effect of aperture diffraction, and retaining high directivity performance in space. The detected half-power beam widths on the E-plane and H-plane are 7.7° and 8.9°, respectively, agreeing well with the simulations. Different from traditional orientation approaches, the photonic crystal antenna delivers performance of high directivity gain with compact structure, facile preparation, low cost, and high efficiency, which make it suitable for spatial information transmission and modulation and offer potential applications in remote sensing and wireless communication.

A Frequency-Controlled Wide-Angle Scanning Antenna Based on Spoof Surface Plasmon Polariton

A frequency-controlled wide-angle scanning antenna based on spoof surface plasmon polariton (SSPP) is proposed. The SSPP is constructed by an array of U-shaped metal blocks, and a periodic array of open-loops shorted to the ground is placed above the SSPP as the radiating elements. Because of the SSPP and the open-loop radiators, the antenna has superior radiation properties including wide-angle scanning range and low fluctuations of gain. The proposed antenna uses an all-metal structure, including the SSPP and the radiators. Measurement results show that the proposed antenna can achieve wide-angle scanning from −55° to 51° over a frequency range from 12.2 to 16.2 GHz with a gain fluctuation less than 2 dB. The average gain of the proposed antenna is 12.96 dBi and the total efficiency is more than 74.1% within the entire operating frequency band.

Enhanced performance on piezoelectric MEMS vibration energy harvester by dynamic magnifier under impulsive force

Vibration energy harvesters that use resonance phenomena exhibit a high output power density for constant frequency vibrations, but they suffer from a significant drop in performance for non-steady-state vibrations, which are important for practical applications. In this work, we demonstrate that the output power under an impulsive force can be increased significantly by placing a U-shaped metal component, called a dynamic magnifier (DM), under an MEMS piezoelectric vibration energy harvester (MEMS-pVEH) with a 6 mm long cantilever using a 3 μm thick Pb(Zr,Ti)O3 film. Based on the results of numerical calculations using a model of pVEH with a two-degree-of-freedom (2DOF) system, the DM was designed to have the same resonant frequency as the MEMS-pVEH and a high mechanical quality factor (Qm). The waveforms of the output voltage of the fabricated 2DOF-pVEHs were measured for impulsive forces with various duration times, and the output power was calculated by integrating the waveforms over time. The output power of the MEMS-pVEH placed on the DM with a Qm of 56 showed a gradual change according to the duration of applying an impulsive force and a maximum of 19 nJ/G2 (G: gravitational acceleration) when the duration of the impulsive force was 3.8 ms. This result was about 90 times greater than the output power of the MEMS-pVEH without a DM. While it is not easy to fabricate pVEHs with a complex 2DOF structure using only the MEMS process, we have demonstrated that the output power can be significantly improved by adding a spring structure to a simple MEMS-pVEH.

Mechanical Performance Study of Beam-Column Connection with U-Shaped Steel Damper.

The article proposes the use of a semi-rigid energy-dissipation connection combined with a U-shaped metal damper to avoid brittle failure of rigid steel beam–column connections under seismic loading. The U-shaped metal damper connects the H-section column and the H-section beam to form a new energy-dissipation connection as an energy-dissipation member. Compared with the existing research, this connection has a stable energy-dissipation performance and great ductility. To clarify the mechanism of energy dissipation, mechanical models under two U-shaped damping deformation modes are established. The calculation formulas for the yield load and stiffness are derived for the corresponding deformation mode using the unit load method. Taking the T-shaped beam–column connection and the application of U-shaped steel damper in the beam–column connection as an example, the mechanical model of the connection is established and the calculation formulas for the yield load and stiffness are derived. At the same time, the connection is subjected to a quasi-static test under cyclic loading. The results show that the hysteretic curve of the test is complete and that the skeleton curve is accurate compared to the theory. The error range of the initial stiffness and yield load obtained by the test and the theoretical formula is kept within 20%, indicating that the theoretical formula is reasonable and feasible. In addition, the correctness of the finite element model is verified by establishing a finite element model and comparing it with the test. The mechanical responses of purely rigid connections and rigid semi-rigid composite connections are compared and analyzed using a multi-story and multi-span plane frame as an example. The results show that the model with semi-rigid connections, compared to the model with rigid connections, avoids the gradual loss of bearing capacity caused by the failure of the connection area of the second floor of the main structure and improves the seismic performance of the main structure.

Mechanism of Mechanical Analysis on Torsional Buckling of U-Shaped Bellows in FLNG Cryogenic Hoses

Floating liquefied natural gas (FLNG) cryogenic hoses can be employed for the transmission of liquefied natural gas (LNG). Usually, U-shaped metal bellows can be applied as the inner lining of FLNG cryogenic hoses. In installation, positioning and other working conditions, torsion is one of the main loads, and torsional buckling instability is a major failure mode of U-shaped metal bellows of FLNG cryogenic hoses. In the current research, the buckling instability of bellows under torsional loads has been investigated in detail, the mechanical mechanism of deformation in torsional buckling mode of bellows has been analyzed and the influence of the structural design parameters on the stability performance has been summarized. It was seen that the axis of the bellows was presented as a spiral line shape during the torsional buckling stage. At the same time, the torsional buckling properties of toroid and spiral bellows were analyzed. The obtained results showed that the torsional buckling stability of the spiral bellows was weaker than that of the toroid bellows and increase of the spiral angle of the spiral bellows intensified this trend. In addition, the post-buckling analysis of U-shaped bellows under torsional loads was carried out by means of experiments and finite element simulation. It was shown that the results obtained from finite element (FE) analysis in this research presented a relatively accurate critical torque value and a consistent buckling instability mode, compared with the experimental results. On this basis, the effects of common defects such as thickness thinning on the torsional stability of bellows were investigated. Considering the geometric defect of thickness thinning, the error of FE analysis was reduced further, and it was found that the defect could significantly decrease the stability of the bellows. The above analysis results could provide a reference for structural design and post-buckling analysis of bellows.

Numerical Analysis of Natural Frequency for U-Shaped Expansion Bellows in Fixed-Fixed and Fixed-Free Conditions

In this study, MATLAB code was used to analyze the natural frequency in two types of U-shape metal expansion bellows with various supporting conditions (fixed-fixed and fixed- free). The first bellow has a 10 mm inner diameter., and a length of (100, 200, 300) mm, has (36, 75, and 111) convolutions. While the second bellow, with an inner diameter of 20mm and (100,200,300) mm, has a number of convolutions (25,54 and 82). The result shows that by lowering the bellow length and increasing the bellow diameter, the natural frequency was raised. Were. Where, the maximum frequency was recorded at a maximum value of 20 mm in diameter and a length of 100 mm, about (13549.167 Hz) in the case of fixed-fixed and (13097.528 Hz) in the case of fixed-free. In general, the natural frequency depends directly on the stiffness and total mass of the pipe conveying fluid. The stiffness of the material is determined by the moment of inertia. As a result, increasing the diameter will increase the moment of inertia, which will result in an increase in stiffness, which will result in an increase in natural frequency.

Punch Motion Curve in the Extrusion–Drawing Process to Obtain Circular Cups

Servo press technology is gaining attention because its punch motion curve offers greater formability than that of a conventional stamping press. This study investigated the effect of punch motion curves on the circular cup extrusion–drawing process. Various punch motion curves were analyzed, and the optimal curve for application was determined. Both the extrusion–drawing process and spring back of U-shaped sheet metal were investigated. In the circular cup extrusion–drawing process, the punch motion curve of a conventional stamping press (Case A) and three punch motion curves of a servo press (Cases B–D, the strokes of which differed from that of Case A by 0.5, 1.5, and 2.5 mm, respectively) were compared, particularly regarding the effect of the coefficient of friction on the circular cup extrusion–drawing process. The simulation analysis was performed using the software program DEFORM. A set of simulated parameters were compared with experimental results. The formability, cup shape, cup height, cup thickness, extrusion force–displacement curve, stress distribution, and strain distribution were analyzed for the design of the die required. Additionally, experimental and simulation results were compared to determine the reliability and precision of the DEFORM simulations. The results indicated that the conventional punch motion curve resulted in a shorter cup, greater stress, greater strain, and the need for a greater extrusion force. By contrast, the servo punch motion curves resulted in taller cups, less stress, and less strain. The findings can serve as a reference for the development of servo presses.

Impact resistance of unequal diameter double U-shaped metal energy dissipation bearing

To effectively improve energy dissipation buffer performance in shed tunnel and building roof rockfall disasters, we designed and developed a metal energy dissipation buffer bearing for an overhead roof rockfall protection system and studied its impact resistance through an experiment using the finite element method. The results showed that the energy dissipation capacity of the unequal diameter double U-shaped bearing increased linearly with displacement, and it could be reused by mechanical stretching. Hence, it was an ideal energy dissipation bearing device. The optimal inner diameter ratio of the upper and lower U-shaped structure was 5/9, and the structural load-bearing and energy dissipation capacity could be adjusted by changing the thickness of the structure. The strain mode of the structure was large deformation in geometry and small deformation in material; hence, the structure gave full play to the deformation performance of the material. The structure could be used repeatedly, and the cushioning performance remained unchanged. These conclusions provide a scientific basis for the design of roof sheathing and tunnel sheds in practical engineering.

Ultimate bending performance and fatigue life of U-shaped metal bellows

Metal bellows used in the flexible connection of metallurgical converter oxygen lance compensates for pipeline displacement through its bending deformation, and adjacent waveforms in the concentrated deformation area are squeezed, resulting in premature fracture. The bending geometric model of U-shaped metal bellows is established in this paper, and the geometric relationship between waveform structure parameters and ultimate bending radius is derived. Moreover, a mathematical model of bending moment (M) with bending angular displacement (θ) about wave height H and wave crest fillet radius Rc is established. Then, combined with Fe-safe fatigue life analysis software, the fatigue life and failure location of metal bellows are obtained. The optimal waveform parameter design range of DN80 metal bellows with high repeated bending fatigue life under large bending is determined. Finally, the bending performance and fatigue life of bellows are tested on a bending fatigue testing machine. The distribution law of fatigue life and the propagation law of cracks at the wave trough of metal bellows under different bending angular displacement amplitudes are obtained. The crack propagation mechanism and fracture mechanism under different displacement amplitudes are revealed by a scanning electron microscope. In the engineering application of large bending, the pipeline failure caused by the ultimate bending deformation of metal bellows can be avoided according to the prediction results of fatigue life.

Miniaturized high selectivity bandpass filter based on hairpin two-conductor stripline resonators

A resonator based bandpass filter miniature design formed by two U-shaped metal strip conductors located at different sides of a suspended dielectric substrate is developed. In each conductor one end is grounded to the screen and the other is free. A resonators are connected in pairs with overlapping sections of strip conductors, it leads not only to the reduction in the dimensions of the device, but also to the increase in its selectivity due to transmission zeros near the passband. The prospects of the proposed design are proved by the measured characteristics of the 6th-order filter made on a substrate with the relative permittivity er = 80 (TBNS-ceramic) and the thickness of 0.5 mm. The filter passband central frequency f0 = 150 MHz, and the fractional bandwidth Δf/f0 = 25 %, while the size of the device is only 42 × 20 × 8.25 мм3 (0.02λ0 × 0.01λ0 × 0.005λ0, where λ0 is the wavelength at the center frequency f0). The filter has high slope steepness and a wide stopband, which extends up to the frequency of 3f0 at the level of –50 dB.