Narrow Slot Research Articles

Simulation Design of G-Band FWG TWT Amplifier Enhanced by π-Mode Extended Interaction

This article studies and summarizes the operating characteristics of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> -band folded waveguide traveling wave tube (TWT) amplifier enhanced by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode extended interaction cavities. Compared with conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> -band TWTs, the proposed amplifier can at once obtain a higher gain in a shorter interaction circuit length and ensure a proper operating bandwidth. The key of the design is introducing the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode multigap resonant cavity with alternating wide and narrow slots, which will improve the working performance of the whole device by shortening the length of the interaction circuit, enhancing its interaction effect, and improving its gain of unit length. In this design, the operation bandwidth is expanded by stagger tuning technique. In addition, the influence of cavity loss is examined so that the optimal performance is achieved. The PIC simulation results show that when the operating voltage is 21 kV and the operating current 80 mA, the maximum average output power of the designed TWT amplifier is 65.78 W at 217.4 GHz, which is corresponding to the maximum gain and efficiency of 37.38 dB and 3.9%, respectively. The gain per unit length is 12.64 dB/cm and the 3-dB bandwidth is 3.5 GHz.

Bench tests of the friction drive of the vertical spindle made of poly-V belts for improving cotton harvesters

The article reports that in order to improve the functional characteristics of the friction drive of vertical spindles, it was proposed to replace its conventional V-belts with poly-V-belts. Therefore, rollers with changed parameters are installed on the spindles, while maintaining the magnitude of the rolling radius of serial rollers. To determine the functionality of the new drive, a stand with a single spindle drum was created, which allows you to determine all the performance indicators of the polyline drive. The main task of research on this stand was to determine the possibility of creating a traction (friction) force of the drive that always exceeds the resistance force of a cotton bush clamped in a narrow working slot of the harvesting apparatus. To assess the functionality of a new version of the friction drive, a comparison technique was used when at the beginning the friction (thrust) force of a serial roller with a V-belt drive was measured, and then, on the stand-pull force of the drive with a poly-V-belt. A special device was made to measure the pulling force of the belts.

Classification of Transmission Modes through a Narrow Slot in a Thick Conducting Screen

This paper examines electromagnetic energy transmission through a narrow slot in a thick conducting plate when a plane wave is incident to the slot. The slot in the thick plate creates a waveguide structure. From the perspective of cutoff frequency, the transmission characteristics are classified into three modes. The transmission cavity resonance (TCR) mode in the range above the cutoff depends on the plate thickness, and peak transmission cross-sections (TCSs) appear periodically along the plate thickness, known as Fabry-Perot resonance. The near-cutoff resonance transmission (NCRT) mode depends on the slot length and plate thickness, and the maximum TCS appears only once as a slot length resonance (or transverse resonance). The peak TCS for the NCRT mode occurs with a thin plate thickness, which produces slot length resonance. The non-transmission cavity (NTC) mode is a non-transmission and non-resonance mode and is not propagated. All the maximum TCSs for the TCR and NCRT modes occur in parallel resonance. The analysis results show that the classification of the three transmission modes through the thick plate slot is effectively explained by the TCS and aperture impedance.

Study on dynamically variable attitude EDM machining method of deep narrow slots

Study on dynamically variable attitude EDM machining method of deep narrow slots

Wideband Differentially-Fed Slot Antenna and Array With Circularly Polarized Radiation for Millimeter-Wave Applications

A wideband differentially-fed slot antenna is presented for millimeter-wave (mmWave) applications. A novel method of using stepped corner-shaped slot is first utilized to establish the wideband circularly polarized (CP) radiation. In the configuration of corner-shaped slot, two wide open slots at the ends are utilized for effective orthogonal radiation, while the narrow slot at the center is utilized for power transmission and quadrature phase delay. An equivalent circuit is given to illustrate the inner working principle for CP radiation. In addition, square cuts are etched on the four corners of the radiating patches to further increase the axial ratio (AR) and impedance bandwidth. Based on this design concept, the antenna element was first designed and fabricated for performance verification. Then, 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 $ </tex-math></inline-formula> 4 linear array with beam-scanning performance and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> 4 planar array with high gain and stable radiation were designed and fabricated. Both the simulated and measured results show that the <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 $ </tex-math></inline-formula> 4 linear array and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> 4 planar array can have the wide overlapped impedance and AR bandwidths of 30.6% and 33.6% with a thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.16\lambda _{0}$ </tex-math></inline-formula> , respectively. The advantages of compact size and wide bandwidth make the presented antenna a good candidate for mmWave applications.

A compact dual‐polarized omnidirectional slot antenna for WiFi dual‐band applications

A compact dual-polarized omnidirectional (DPO) antenna with dual-band characteristic is presented in this article. The main structure of the antenna is a metal box, which is composed of a horizontally folded narrower slot on the three sides for vertical polarization and a vertically folded wider slot lying on other three sides for horizontal polarization. Two different coupling feedings inside the box are designed for the two slots so as to obtain good omnidirectional radiation properties in two frequency bands of 2.4 and 5.5 GHz. The proposed structure is only 30 mm × 30 mm × 10 mm in size (0.24λ0 × 0.24λ0 × 0.08λ0, λ0 stands for the wavelength of corresponding lowest operating frequency). A prototype has been built and measured. The measured results present the proposed dual-band DPO antenna has two 10 dB return loss operating bandwidth of 3.7% (2.41–2.5 GHz) and 16% (5.05–5.93 GHz), with the isolation higher than 35 dB.

Effect of exit geometry of blowing air on friction drag of an underwater plate

Air layer drag reduction (ALDR) is one of the important techniques for reducing the frictional resistance of ships and underwater vehicles. The air injection configuration directly influences air layer coverage on the surface and hence drag reduction. Several shapes of air exit have been investigated in the past, including narrow slots, regular-shaped holes, porous media, and arrays/combinations of them. A new exit shape, i.e. modified Nekomimi, is proposed and investigated numerically for ALDR of an underwater flat plate. The work is inspired by air film cooling technology where it is desirable to have an air layer segregating wall from main gas flow. The Reynolds number examined is 6970–22890, based on local turbulent boundary layer thickness, for the incoming water flow or 700–5550, based on the equivalent exit diameter of blowing air. Results show that the Nekomimi exit produces a larger and more even air layer coverage, as indicated by the air volume fraction on the plate, accounting for a more pronounced drag reduction and net energy saving than a circular exit with the same area or spanwise dimension. Multi-Nekomimi-exit arrangement is also investigated to obtain a larger air-layer coverage on the plate, showing good promise in engineering applications.

Modelling of tungsten sputtering by argon particle bombardment on a fuzzy surface

• The physical sputtering of tungsten fuzz by the Ar ions have been investigated by SURO-FUZZ. • The detailed studies of the impacts of Ar incident energy and fuzzy layer thickness on tungsten physical sputtering have been conducted in this work. • The physical sputtering yield is in reasonable agreement with measurements. The physical sputtering yield of a tungsten (W) fuzzy surface by argon (Ar) plasma bombardment was measured in the linear plasma device PISCES-B, which showed an evident reduction in the physical sputtering yield on the fuzzy surfaces in comparison with a smooth surface (Nishijima D . et al 2011 J. Nucl. Mater. 415 S96). In order to reproduce and explain this phenomenon, dedicated modelling of W physical sputtering on smooth and fuzzy surfaces by Ar bombardment has been performed with the three-dimensional kinetic Monte Carlo code SURO-FUZZ. According to a measured porosity distribution, W fuzzy surface morphology is constructed in our simulation, on which physical sputtering, trapping and escaping of W atoms under Ar bombardment are simulated with SURO-FUZZ. Detailed comparison between simulation and experiment reveals that microscopic structures of W fuzzy nanofibers play a critical role in the trapping of W atoms and hence in the resulting physical sputtering yield. For the same porosity distribution, the simulated physical sputtering yields of W fuzzy surface morphology with shallow valleys are higher than the measured values, while W fuzzy surface structure with deep and narrow slots results in a lower physical sputtering yield compared to the experimental data. The good agreement between simulation and experiment can be attained for W fuzzy surface morphology with deep and relatively open recessions.

FSS superstrate loaded SIW circular cavity-backed cross-shaped slot antenna for wireless applications

In this paper, a low profile circular-shaped cavity-backed substrate integrated waveguide (SIW) antenna is designed and fabricated to operate at 5.38 GHz frequency in the U-NII-2B band in the dominant TM010 mode. A narrow cross-shaped slot is inserted in the ground plane of the parent antenna for radiation purposes. The antenna produces a gain of 4.7 dBi with an impedance bandwidth extending from 5.36–5.42 GHz. The gain of the antenna is augmented to 7.1 dBi through the use of a multi-layered cascaded frequency selective surface (FSS) as a superstrate. Arlon substrate materials are used to fabricate the antenna and frequency selective surface respectively. Parametric studies have been carried out in terms of return loss, antenna gain, and spacing between the antenna and FSS layer to obtain the best antenna results. All the simulation results have been carried out using HFSS v19.0. Both the simulated and the experimentally measured results show alike behavior.

A Compact Planar Multi-Resonant Multi-Broadband Fractal Monopole Antenna for Wi-Fi, WLAN, Wi-MAX, Bluetooth, LTE, S, C, and X Band Wireless Communication Systems

In this paper, a highly efficient tree-shaped fractal antenna with multi-broadband resonance characteristics is proposed. The proposed antenna exhibits broad operating bandwidth, high gain, and high efficiency characteristics due to the suggested modifications in the antenna geometry. The suggested circular patch is modified by introducing slots in the form of a tree-shaped fractal structure, and the partial ground plane is modified by incorporating a narrow rectangular slot. The proposed antenna is designed on an FR4 substrate of [Formula: see text][Formula: see text]mm3. The prototype of the proposed antenna has been fabricated and tested to justify the simulation results. The measurement results are in good agreement with the simulation that validates the multi-broadband design approach of the proposed fractal antenna. As per the measurement results, the proposed antenna operates at four distinct bands with [Formula: see text]10[Formula: see text]dB impedance bandwidths of 600[Formula: see text]MHz (2.2–2.8) GHz, 1070[Formula: see text]MHz (3.3–4.37) GHz, 2550[Formula: see text]MHz (4.75–7.3) GHz, and 2200[Formula: see text]MHz (9.7–11.9) GHz. Furthermore, a high peak gain of 10.23[Formula: see text]dB and a peak radiation efficiency of 96.65% are recorded for the suggested fractal antenna. The suggested compact bandwidth enhanced multi-band antenna can be useful for several wireless communication systems such as wireless fidelity (Wi-Fi), wireless local area network (WLAN), Bluetooth, long-term evolution (LTE), C, S and X bands.

Review of Shearography for Dual-Directional Measurement

Shearography is a coherent optical technique that allows the identification of the first derivative of deformation in the shearing direction. Due to direct measuring strain information, shearography is suited for non-destructive testing and evaluation (NDT/NDE). However, if there is a small defect parallel to the shearing direction, the first derivative of deformation in the direction has no noticeable change, and the defect is not visible. Therefore, the development of a shearography system with dual-directional simultaneous measurement of the first derivatives of deformation both in x- and y-directions is highly demanded in the field of NDT/NDE. It is suited to inspect complicated defects, such as long and narrow slots, microcracks, etc. This paper presents a review of shearography for different dual-directional systems developed in the last two decades. After a brief overview of shearography, the paper will display two dual-directional shearographic techniques—temporal phase-shift (TPS) and spatial phase-shift (SPS) methods. TPS dual-shearing systems are suited for static measurements, while the SPS dual-shearing systems are useful for dynamic measurements. The basic theories, optical layouts, and comparisons are presented. The advantages and disadvantages of practical applications are discussed.

A compact high isolation wideband MIMO antenna for multi-band applications

Ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antennas promise a wide range of interesting applications in various radio frequency (RF) systems. However, the prime challenges in realizing such systems include achieving a wider bandwidth, significant isolation between the antennas and compactness. This research demonstrates a compact MIMO antenna having a prominent isolation level for portable UWB applications. The proposed antenna comprises two modified rectangular radiating elements with narrow slots in the ground plane, achieving an enhanced bandwidth from 2.1 to 16.9 GHz covering the S, C, X and Ku bands. Meanwhile, two inverted L-shaped stubs are introduced into the ground structure to obtain a higher isolation greater than 16 dB in the entire spectrum. The proposed antenna is of compact size (36 × 38 mm2) and exhibits excellent performance in terms of return loss, mutual coupling, envelope correlation coefficient (ECC), diversity gain (DG) and total active reflection coefficient (TARC).

Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm–4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.

Simulation of the lubricant flow in thin slot channels with a moving wall under slip boundary conditions

The article presents the results of studying the flow of a Newtonian fluid in a narrow wedge-shaped slot with a moving wall. A solution to the problem with slip boundary conditions on the channel walls is obtained. The influence of the slip conditions on the walls on the flow parameters is shown. In diverging and converging sections of the channel, different types of flow take place. In the region of the diverging flow near the stationary wall, a reverse flow zone is formed, the width of which increases with an increase in the Knudsen number, which is due to an increase in the flow velocity on the stationary wall due to the slip condition. Calculations elucidated the effect of slippage on the variation of the hydrostatic lifting force and hydraulic resistance in the slot channel. The dependence of the relative hydrostatic lifting force on the Knudsen number and the opening angle of the channel were revealed. It has been determined that with an increase in the Knudsen number, the magnitude of the hydrostatic lifting force decreases, since in this case the influence of the flow on the wall weakens. With an increase in the opening angle of the channel, slip effect weakens.

Electromagnetic and Thermal Analysis of Interior Permanent Magnet Motors Using Filled Slots and Hairpin Windings

This paper analyzes the electromagnetic and thermal design of interior permanent magnet motors using filled slots and hairpin windings for electric vehicle applications. Two models of ∇ shape of the interior permanent magnet motors have been proposed to evaluate the temperature distribution and cogging torque performance. A narrow opening slot of the interior permanent magnet of 48 slots/8 poles with the filled winding has been designed to investigate the electromagnetic torque because the cogging torque depends on opening stator slots. A parallel–rectangle slot of the interior permanent magnet with the hairpin winding has been also implemented with finite element analysis to evaluate their performances. Normally, the slot opening of the interior permanent magnet stator equals the slot width, it is greater than the size of hairpin windings, and the cogging torque is increased significantly with a bigger slot opening. The main advantage of the hairpin winding design is the high slot fill factors. Hence, the lower the current density, the higher torque, and efficiency are, than the normal design with the same geometry parameters. To improve the cogging torque due to the wide slot opening, the step–skew rotor slices have been arranged to minimize the torque ripple with different skewing angles.

A Multi-Slot Two-Antenna MIMO with High Isolation for Sub-6 GHz 5G/IEEE802.11ac/ax/C-Band/X-Band Wireless and Satellite Applications

A tapered symmetrical coplanar waveguide (S-CPW) fed monopole antenna is initially studied. To achieve multiband characteristics, the radiating element of this monopole antenna is loaded with multiple narrow slots and multiple slotted stubs (MSS). The designed slot-loading monopole is further transformed into a two-antenna MIMO type with a gap distance of only 0.12λ (at 5 GHz), and thus it has a small overall size of 32 × 20 × 0.8 mm3. By deploying five concentric ring elements between the two adjacent antenna elements, the desirable isolation of better than 20 dB is yielded. As the low band and high band operation of the proposed two-antenna MIMO is 81.08% (3.3–7.8 GHz) and 40% (8.0–12.0 GHz), respectively, it can therefore satisfy the Sub-6 GHz 5G New Radio (NR) n77/78/79, IEEE 802.11ac/ax, X-band/C-band wireless and satellite applications. Furthermore, it has shown a desirable gain of above 3 dBi and a radiation efficiency greater than 69% throughout the two bands of interest.

Numerical investigation on thermal-hydraulic characteristics of the micro heat sink with gradient distribution pin fin arrays and narrow slots

Targeting at decreasing the pressure drop in the micro heat sink, a gradient distribution pin fin arrays and narrow slots (GPN) is proposed. In addition, in order to further reduce the pressure drop of the micro heat sink, three improved are proposed, including GPN48, GPN2244, GPN264 by changed the number and position distribution of the pin fin arrays in the narrow slots. The results show that the pressure drop of the three improved gradient distribution pin fin arrays and narrow slots decreases by 28.7%–33.4% at a certain volumetric flow rate (Qv = 120 ml/min, Re = 563) when comparing with the conventional gradient distribution. Furthermore, when Re ranged from 188 to 1125, the maximum wall temperature of the three improved gradient distribution pin fin arrays and narrow slots decreases by 4.4 K–26.6 K when comparing with the gradient distribution (GPN). When the Re = 563, the heat flux limit of GPN is only 82 W/cm2, while GPN48, GPN2244 and GPN264 reached 109 W/cm2, 114 W/cm2 and 120 W/cm2 respectively. Especially, comparing with GPN, the average heat transfer coefficient of GPN48, GPN2244 and GPN264 increases by 11.9%–23.0% (Re = 118), which greatly improves the application reliability in the micro heat sink.

Magnetic Miniature Actuators with Six‐Degrees‐of‐Freedom Multimodal Soft‐Bodied Locomotion

Magnetic miniature robots (MMRs) are mobile actuators that can exploit their size to noninvasively access highly confined, enclosed spaces. By leveraging on such unique abilities, MMRs have great prospects to transform robotics, biomedicine, and materials science. As having high dexterity is critical for MMRs to enable their targeted applications, existing MMRs have developed numerous soft‐bodied gaits to locomote in various environments. However, there exist two critical limitations that have severely restricted their dexterity: 1) MMRs capable of multimodal soft‐bodied locomotion have only demonstrated five‐degrees‐of‐freedom (five‐DOF) motions because the sixth‐DOF rotation about their net magnetic moment axis is uncontrollable; 2) six‐DOF MMRs have only realized one mode of soft‐bodied, swimming locomotion. Herein, a six‐DOF MMR is proposed that can execute seven modes of soft‐bodied locomotion and perform 3D pick‐and‐place operations. By optimizing its harmonic magnetization profile, the MMR can produce 1.41–63.9‐fold larger sixth‐DOF torque than existing MMRs with similar profiles, without compromising their traditional five‐DOF actuation capabilities. The proposed MMR demonstrates unprecedented dexterity: it can jump through narrow slots to reach higher grounds; use precise orientation control to roll, two‐anchor crawl, and swim across tight openings with strict shape constraints; and perform undulating crawling across three different planes in convoluted channels. An interactive preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164087652.25227465.

Influence of Laser Beam Wobbling Parameters on Microstructure and Properties of 316L Stainless Steel Multi Passed Repaired Parts.

The results of experimental studies of repair of the supporting structure components made of 316L steel multi-pass laser cladding with filler wire are presented. The influence of the wobbling mode parameters, welding speed, and laser power on the formation of the deposited metal during multi-pass laser cladding with filler wire of 316L steel samples into a narrow slot groove, 6 mm deep and 3 mm wide, are shown. Non-destructive testing, metallographic studies, and mechanical tests of the deposited metal before and after heat treatment (2 h at 450 °C) were carried out. Based on the results of experimental studies, the optimal modes of laser beam wobbling were selected (amplitude—1.3 mm, frequency—100 Hz) at which the formation of a bead of optimal dimensions (height—1672 μm, width—3939 μm, depth of penetration into the substrate—776 μm) was ensured. A laser cladding technology with ESAB OK Autrode 316L filler wire has been developed, which has successfully passed the certification for conformity with the ISO 15614-11 standard. Studies of the chemical elements’ distribution before and after heat treatment showed that, after heat treatment along the grain boundaries, particles with a significantly higher Mo content (5.50%) were found in the sample, presumably precipitated phases. Microstructure studies and microhardness measurements showed that the upper part metal of the third pass, which has a lower microhardness (75% of base metal), higher ferrite content, and differently oriented dendritic austenite, significantly differs from the rest of the cladded metal.

A Study on the Electromagnetic-Thermal Coupling Effect of Cross-Slot Frequency Selective Surface.

In high-power microwave applications, the electromagnetic-thermal effect of frequency selective surface (FSS) cannot be ignored. In this paper, the electromagnetic-thermal coupling effects of cross-slot FSS were studied. We used an equivalent circuit method and CST software to analyze the electromagnetic characteristics of cross-slot FSS. Then, we used multi-field simulation software COMSOL Multiphysics to study the thermal effect of the FSSs. To verify the simulation results, we used a horn antenna with a power of 20 W to radiate the FSSs and obtain the stable temperature distribution of the FSSs. By using simulations and experiments, it is found that the maximum temperature of the cross-slot FSS appears in the middle of the cross slot. It is also found that the FSS with a narrow slot has severer thermal effect than that with a wide slot. In addition, the effects of different incident angles on the temperature variation of FSS under TE and TM polarization were also studied. It is found that in TE polarization, with the increase in incident angle, the maximum stable temperature of FSS increases gradually. In TM polarization, with the increase in incident angle, the maximum stable temperature of FSS decreases gradually.