Metal Ridges Research Articles

A novel atmospheric microwave plasma source based on circular waveguide with double ridges for nitrogen fixation

Abstract The rectangular tapered waveguide is the most widely used atmospheric microwave plasma source because of its simple structure, reliable performance, and low cost. However, due to the small generated plasma volume and short residence time, this plasma source has low energy efficiency in gas conversion applications such as nitrogen fixation and methane reforming. This paper proposes a novel atmospheric-pressure microwave plasma source based on a circular waveguide to enlarge the plasma volume. Firstly, the microwave working mode in the circular waveguide is analyzed based on the electromagnetic theory. By optimizing the waveguide dimension and loading double metal ridges into the waveguide, the electric field will work in a superposition mode of TE111 and TM010 modes, focus on the discharge area, and reach its maximum intensity there. Secondly, this device is manufactured and used to generate plasma in different conditions. Compared with the rectangular tapered waveguide, this device can generate larger plasmas under the same conditions. Finally, an atmospheric microwave plasma experimental system is built for nitrogen fixation. Measured results show that the proposed device has higher nitrogen fixation production and lower energy cost compared to the rectangular tapered waveguide. Moreover, the proposed device is easy to cascade, thereby it has great potential for promotion in industrial applications.

Broadband ridge waveguide to rectangular waveguide transition design in D‐band

AbstractThis article presents a D‐band (110–170 GHz) double ridge waveguide (WG) to standard rectangular WG transition with an E‐bend near the WG end. The transition incorporates metal ridge steps as impedance transformers, resulting in a compact total size of 3.53 mm × 1.95 mm × 1 mm. Fabricated using micro metal additive manufacturing with copper in a monolithic back‐to‐back configuration, the transition demonstrates a bandwidth of 50% (105–175 GHz) with an average insertion loss of 0.72 dB and return loss better than 15 dB, respectively. Measurement results align closely with simulation expectations, with deviations attributed to fabrication and assembly errors.

Ultrawideband 3-D Printed Endfire TEM Horn Antenna Mounted on a Cylinder Conductor

An ultrawideband, three-dimensional (3-D) printed end-fire transverse electromagnetic (TEM) horn antenna mounted on a cylinder conductor is proposed. The system consists of four TEM horn antennas and a cylinder conductor. The proposed TEM horn antenna is composed of four parts: a metal exponential curve, a trapezoidal metal top cover, a cylindrical ground, and a metal ridge. To enhance impedance bandwidth and radiation characteristics, a metal ridge is introduced on the cylinder ground plane. To verify the proposed antenna, a prototype is 3-D printed with surface metallization. The proposed antenna has a broad bandwidth from 1 to 16 GHz (16:1) with a voltage standing wave rate (VSWR) < 2 and a profile of 0.134λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> being the free-space wavelength at the lowest frequency). A good radiation pattern is obtained over the impedance bandwidth, and the measured gain ranges from 3.5 dBi to 11.5 dBi.

Improved Cylindrical Cavity With Symmetric Double Ridges for High-Sensitivity Detection

In this letter, an improved cylindrical cavity for high-sensitivity detection is proposed. The cylindrical cavity is characterized by symmetric double ridges inside. The double-ridged cavity realizes the electric field compression of TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{01}{n}}$</tex-math> </inline-formula> modes by loading two symmetric metal ridges and further greatly improves the detection sensitivity. The parameters of the ridge are optimized and determined by considering the compromise between frequency detection sensitivity, quality factor, and the current fabrication technique. Several fiber monofilaments with diameters of only a dozen micros are separately inserted into the cavity and detected. To illustrate more clearly the advantage of the proposed cavity for the detection of slim materials, the sensitivity per unit of volume (0.32%) is compared and the value is higher than the related research works.

Comparative Analysis of Machine Learning Models for Predicting Crack Propagation under Coupled Load and Temperature

Crack propagation in materials is a complex phenomenon that is influenced by various factors, including dynamic load and temperature. In this study, we investigated the performance of different machine learning models for predicting crack propagation in three types of materials: composite, metal, and polymer. For composite materials, we used Random Forest Regressor, Support Vector Regression, and Gradient Boosting Regressor models, while for polymer and metal materials, we used Ridge, Lasso, and K-Nearest Neighbors models. We trained and tested these models using experimental data obtained from crack propagation tests performed under varying load and temperature conditions. We evaluated the performance of each model using the mean squared error (MSE) metric. Our results showed that the best-performing model for composite materials was Gradient Boosting Regressor, while for polymer and metal materials, Ridge and K-Nearest Neighbors models outperformed the other models. We also validated the models using additional experimental data and found that they could accurately predict crack propagation in all three materials with high accuracy. The study’s findings provide valuable insights into crack propagation behavior in different materials and offer practical applications in the design, construction, maintenance, and inspection of structures. By leveraging this knowledge, engineers and designers can make informed decisions to enhance the strength, reliability, and durability of structures, ensuring their long-term performance and safety.

All-Metal Phased Array With Full Polarization Reconfigurability

An all-metal phased array with full polarization reconfigurability is presented in this article. Septum polarizers as phased array elements are first used to achieve left-handed and right-handed circular polarizations (LHCP and RHCP), and arbitrary linear polarizations (LPs) can be further synthesized. Two pairs of metal ridges are loaded into the septum polarizer to reduce the profile and aperture size so that the spacing between the two adjacent array elements can be constrained to about half of the free-space wavelength at the center operating frequency. Phased arrays of <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> 8 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 elements covering 25.5–27 GHz are designed to demonstrate the 1-D and 2-D beam scanning performance with different polarizations. For demonstration, 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> 8 element phased array is implemented. Experimental results show that the array exhibits stable beam scanning performance for both circular polarizations (CPs) and LPs. The synthesized beam scanning range is up to ±55° with a gain-reduction of 4.7 dB for all polarizations. Under beam scanning, the axial ratio (AR) remains below 3.1 dB for the LHCP and RHCP, and the maximum gain variation during polarization reconfiguration is less than 0.8 dB.

A 3D printed bullet‐shaped filter based on zero‐gap circular waveguide cavities

This paper presents an improved zero-gap waveguide structure with convex-shaped gap waveguide pins and zero height air gap, which is used to enhance the structural strength and reduce the assembly errors due to the air gap variation. A fourth-order bullet-shaped circular waveguide filter is designed and fabricated to validate the proposed structure. To ease the 3D printing difficulty of the designed filter, the cosine-shaped top is utilized for self-supporting. Besides, a metallic ridge between adjacent cavities is introduced to enhance the electric coupling. The metallic ridge as well as the slots at the bottom plate help to increase the stopband suppression. Finally, the measured results of the fabricated filter excited with coaxial connectors match well with the simulation.

Full Metal Wideband Cosecant Squared Pattern Antenna With a Highly Compact Hybrid Feed Network

This article presents a full metal wideband high-performance cosecant squared (CSC2) pattern antenna. A highly compact structure is achieved by a convoluted feeding network routed in multiple layers. Double metal ridges are added to the flared radiation slot to reduce the aperture size of the antenna element. A line of 40 such elements are excited by a full-corporate feed network arranged longitudinally, so as to form a phased array in the future. A hybrid of single-ridge waveguide and coaxial line in a sandwich structure is used to construct the feed network. The absorbing wedge loaded coupler and magic-T are incorporated into the feed network to achieve high isolation and large power-division ratio, thereby improving the stability of the amplitude and phase distribution. This ensures the desired CSC2 patterns over a wide frequency band. A prototype operating at C-band is designed, fabricated, and measured. Experimental results show that the antenna has an impedance bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert &lt; -13.1$ </tex-math></inline-formula> dB) from 6 to 7.4 GHz. Stable CSC2 patterns in the E-plane with the peak gain of over 16.5 dB and sidelobe level (SLL) of less than −17.5 dB are observed across the same frequency band.

One-step formation of a plasmonic grating with an ultranarrow resonance linewidth for sensing.

Nanograting-based plasmonic sensors are capable of real-time and label-free detection for biomedical applications. Simple and low-cost manufacturing methods of high-quality sensors are always demanding. In this study, we report on a one-step etch-free method achieved by directly patterning a photoresist on a copper substrate using laser interference lithography. Large area uniform gratings with a period of 600 nm were fabricated on the copper film, and its refractive index sensing performance was tested using glucose as analyte. By replacing the metallic grating ridges with photoresist ridges, the Ohmic absorption and radiative scattering losses of surface plasmons were greatly reduced. As a result, a much sharper resonance linewidth (∼ 10 nm) was experimentally obtained. Compared with pure metallic gratings, the reported structure is characterized by sharper resonance and a much easier fabrication process, making it a cost-effective plasmonic sensor with high quality.

Cross-talk reduction in a graphene-based ultra-compact plasmonic encoder using an Au nano-ridge on a silicon substrate

Plasmonic waveguides have been widely studied in the rapid development of optically integrated circuits. The cross talk between plasmonic waveguides is a critical issue that should be considered. Nano-plasmonic waveguides with tunable graphene-free patterns on silicon ridge have very attractive features. Despite these attractive features, the low confinement in plasmonic waveguides reduces the coupling length. This issue results in high cross talk in optical integrated circuits. We present a solution to the mentioned problem. A metal ridge under the plasmonic channel helps to reduce the cross-talk value. A new graphene-based plasmonic waveguide has been proposed for achieving the switching operation at terahertz frequencies. Based on the designed waveguide, a 4-to-2 plasmonic encoder with the cross talk of -17.33dB has been presented. Using six waveguides, the encoder is designed with a contrast ratio of 14.44 dB and an area of 0.36µm2. Concerning the obtained results, the presented structure can be used in optical integrated circuits.

Design of a Broadband Antenna Array With Compact Surface-Wave Antenna Elements

This letter presents a 1x16 surface-wave phased array that exhibits compact size, high gain, and broadband characteristics. The antenna element consists of a surface wave launcher, a tapered radiating structure, and a large metallic ground. The width of the single element is only 0.56_0 at the center frequency. Despite its compact design, the antenna achieves a wide bandwidth by employing a tapered metallic ridge and a cone-shaped coaxial probe. The metallic ridge is critical to enhance the bandwidth and smoothen the transition from the parallel-plate waveguide to the radiating structure. When arranging 16 antenna elements to form a linear array, some metallic stacks are introduced between adjacent antenna elements to adjust the mutual coupling so that an excellent return loss can be achieved over the operating frequency range (6.2 to 12 GHz). Two prototypes of the proposed array with radiation beams pointing at 0 and 30 degrees, respectively, have been fabricated. The measured results agree well with the simulated ones.

Numerical simulation of the interaction between double cathode spot craters in vacuum arc

In this paper, a numerical simulation on the interaction between the double cathode spot craters in the vacuum arc is carried out. By establishing a double-cathode spot ablation model, the crater development process when two spots coexist is simulated, and the formation mechanism of cathode spot groups is analyzed. The simulation results show that the two cathode spots appearing on the flat electrode would squeeze each other to form a liquid metal ridge, which changed the ablation morphology of the cathode spots. When the double-spot arc craters appear simultaneously, the metal ridge will be squeezed into a straight line, otherwise, when the spots appear one after another, the liquid metal ridge will shift toward the side of the spot that appears first. The relative experimental results are adopted to compare with the simulation results. By comparison, it is found that the morphology of the multi-spot crater in the experiment is in agreement with the simulation results.

Bandwidth-Enhanced High-Gain Full-Metal Filtering Slot Antenna Array Using TE101 and TE301 Cavity Modes

In this letter, a bandwidth-enhanced high-gain full-metal cavity-backed filtering slot antenna array is proposed. By replacing one radiating slot with 2 × 2 radiating slots, the enhanced gain is obtained without enlarging the antenna size. Besides, two cavity modes, i.e., TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">301</sub> , are combined to obtain an enhanced bandwidth. Metal ridges and metal posts are employed to make the two modes close to each other. Due to a similar radiating field of the two specific cavity modes under the proper perturbation and placement of the 2 × 2 radiating slots, a high gain over the enhanced bandwidth is obtained. In addition, the high-quality factor of the two cavity modes can inherently produce a filtering performance in terms of the realized gain and efficiency. The final measurement shows that the proposed slot antenna array can achieve 6.2% bandwidth, 97% total efficiency, and 10.4–11 dBi stable realized gain with a small aperture size of 0.84 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Good agreement between the simulation and measurement has well validated the proposed design concept.

A Slow Wave Ridged Half-Mode Substrate Integrated Waveguide With Spoof Surface Plasmon Polaritons

In this article, a slow wave (SW) ridged half-mode substrate integrated waveguide (RHMSIW) combined with spoof surface plasmon polaritons (SSPPs) structure is proposed. The SW feature is achieved by integrating the SSPP structure into the metal ridge of RHMSIW. Besides, the proposed structure has a compact lateral size because the ridge of the RHMSIW introduces a step capacitance in the waveguide. Due to the loading of the SSPP structure, the proposed RHMSIW-SSPP structure has the ability of strong electric field confinement. Compared with the RHMSIW structure, the proposed RHMSIW-SSPP structure has a low crosstalk feature. A prototype of the proposed RHMSIW-SSPP structure with band-pass 4.5-14 GHz is designed and fabricated under PCB process. The proposed RHMSIW-SSPP structure reduces the longitudinal size over 50% and the lateral width by 40% compared with the HMSIW, and reduces the longitudinal size over 50% and the transverse width by 70% compared with the SIW. Therefore, the proposed structure has potential applications in miniaturized microwave and RF systems.

Generation of High-Order Waveguide Modes with Reduced Symmetric Protection

Single-mode operation in a rectangular waveguide is very important, since the existence of multimodes may arouse distortions of carried signals due to the modal dispersion. High-order mode means multiple periods of field in the transverse cross section, with distinct electromagnetic properties from the dominant mode. Although numerous methods are proposed to achieve mode selection within the waveguide, they only permit specific high-order modes to survive in a frequency range. However, it still remains a great challenge to control the bandwidth freely for single-mode operation. Here, we propose an approach for high-order mode generation, in which the desired mode operates in the band gap of other modes, and the working bandwidth can be engineered independently by reducing the symmetry of the loaded periodic metallic ridges in the waveguide. Two examples are demonstrated, where only ${\mathrm{TE}}_{20}$ and ${\mathrm{TE}}_{30}$ modes are supported. The proposed method can also be applied to generate other high-order TE modes in the future.

Measurement of the Complex Dielectric Constant of Materials Based on a Ridge Waveguide

Abstract—The problem of determining the complex dielectric constant of materials in the centimeter and millimeter wavelength ranges is solved using the waveguide method with an double-ridged waveguide. The use of a segment of an double-ridged waveguide as the measuring cell made it possible to expand the operating frequency range and increase the measurement accuracy due to localization of the electromagnetic field energy in the space between metal ridges. The electromagnetic fields of hybrid types of waves in the double-ridged waveguide were calculated by the partial region method taking into account the peculiarities of the electromagnetic field on the metal and dielectric ridges. The results of measuring the complex dielectric constant for samples made of ebonite, Teflon, and fiberglass are presented.

Microstrip to Ridge Empty Substrate-Integrated Waveguide Transition for Broadband Microwave Applications

The empty substrate-integrated waveguide (SIW) (ESIW) is an evolution of the SIW. Just as the SIW, the ESIW is of low cost and low profile, and can be integrated into a printed circuit board, but the losses in the ESIW are lower than in those in the SIW thanks to the removal of the dielectric material, which results in ESIW devices with performances close to those implemented with standard rectangular waveguides. In order to increase the operational (monomode) bandwidth of the rectangular waveguides, a metal ridge can be inserted (leading to the ridge waveguide). Extrapolating this idea to the ESIW, in this letter, a study of possible ridge ESIW (RESIW) geometries has been performed, and a novel transition from microstrip line to RESIW is proposed. In order to validate the performance of transition, a back-to-back prototype has been manufactured and measured.

Spatially asymmetric transients of propagating exciton-polariton modes in a planar CdZnTe/CdMgTe guiding structure

We report on ultrafast time-resolved pump-probe studies in a CdZnTe/CdMgTe planar guiding structure covered with a metallic grating. The one-dimensional periodic gold structure allows for efficient coupling into the guiding layer for $p$-polarized 30 fs optical pulses with a large spectral bandwidth of about 60 nm. The resulting spectral width of optical pulses propagating inside the guiding layer corresponds to 20--30 nm. We demonstrate that the excitation of exciton-polariton modes in the guiding layer leads to a modulation of the optical response in the vicinity of the excitonic resonance. Spatially resolved pump-probe measurements show an asymmetric behavior in the optical response when the relative position of the pump and probe spots is varied on the scale of ten micrometers perpendicular to the metal ridges. This is attributed to the excitation of resonant and off-resonant exciton-polariton modes which propagate in opposite directions inside the guiding layer in accordance with their dispersion relations. Two main mechanisms are considered and evaluated, namely, Pauli blocking and excitation-induced dephasing, which are shown to be responsible for the pump-induced changes in the exciton absorption spectrum. While both of these processes lead to the generation of photoexcited carriers in the guiding layer, their impact on the optical properties (transmission and reflection) are different which leads to the asymmetric behavior of the spatially resolved transients.

Design of Ku-band Size-reduced Waveguide Slot Filter Antenna Loaded with Metal Ridges

A filter antenna based on waveguide structure is proposed in this paper, which reduces the size of the resonator by loading a metal ridge in the rectangular waveguide resonator to produce a capacitive effect. The filter antenna integrates the waveguide filter and the waveguide slot antenna radiation array, and achieves a better matching of filtering characteristics and impedance. The simulation results show that the centre frequency of waveguide filter antenna is 15GHz and the relative bandwidth 2%; the return loss is more than 16.78dB; the peak gain of waveguide filter antenna reaches 12dBi.To summarize, the performance is excellent under the case of simple structure. The proposed filter antenna lays the foundation for the realization of integrated communication system and can be used in satellite and radar communication system.

Narrow plasmonic surface lattice resonances with preference to asymmetric dielectric environment.

Plasmonic surface lattice resonances (SLRs) supported by metal nanoparticle arrays exhibit narrow linewidths and enhanced localized fields and thus are attractive in diverse applications including nanolasers, biochemical sensors and nonlinear optics. However, it has been shown that these SLRs have much worse performance in a less symmetric environment, hindering their practical applications. Here, we propose a novel type of narrow SLRs that is supported by metal-insulator-metal nanopillar arrays and that has better performance in a less symmetric dielectric environment. When the dielectric environment is as asymmetric as the air/polymer environment with a refractive index contrast of 1.0/1.52, the proposed SLRs have high quality factors of 62 under normalincidence and of 147 under oblique incidence in the visible regime. We attribute these new SLRs to Fano resonance between an in-plane dipole and an out-of-plane quadrupole (or dipole) that are respectively supported by the two metal ridges under normal (or oblique) incidence. We also show that the resonance wavelength can be tuned by varying the geometric sizes or by changing the angle of incidence. By doing this, we clarify the conditions for the formation of the proposed SLRs and illustrate their attractive merits in sensing applications. We expect that this new SLR can open up applications in asymmetric dielectric environments.