Asymmetric Slot Research Articles

High-order-mode cavity fed 45° linear polarized antenna for 5G applications

Abstract In this paper, a high-order-mode (HOM) (TE330) cavity-fed 45° linear polarized 6×6 slot array antenna is proposed. The 45° linear polarization is achieved by introducing asymmetric cross slots on the HOM cavity, resulting in low profile and wide bandwidth. The antenna array was verified using standard printed circuit board technology. Measured results show that the impedance bandwidth ( $|S_{11}|\le$ −10 dB) is 13.9% (36.98–42.92 GHz), and the peak gain is 19.3 dBi with a 3-dB gain bandwidth of 13.6%. Attributed to its simple structure, low profile, and wide bandwidth, the presented antenna is a good candidate for 5G applications.

Efficient and Shape-Sensitive Manipulation of Nanoparticles by Quasi-Bound States in the Continuum Modes in All-Dielectric Metasurfaces.

Current optical tweezering techniques are actively employed in the manipulation of nanoparticles, e.g., biomedical cells. However, there is still huge room for improving the efficiency of manipulating multiple nanoparticles of the same composition but different shapes. In this study, we designed an array of high-index all-dielectric disk antennas, each with an asymmetric open slot for such applications. Compared with the plasmonic counterparts, this all-dielectric metasurface has no dissipation loss and, thus, circumvents the Joule heating problem of plasmonic antennas. Furthermore, the asymmetry-induced excitation of quasi-bound states in continuum (QBIC) mode with a low-power intensity (1 mW/µm2) incidence imposes an optical gradient force of -0.31 pN on 8 nm radius nanospheres, which is four orders of magnitude stronger than that provided by the Fano resonance in plasmonic antenna arrays, and three orders of magnitude stronger than that by the Mie resonance in the same metasurface without any slot, respectively. This asymmetry also leads to the generation of large optical moments. At the QBIC resonance wavelength, a value of 88.3 pN-nm will act on the nanorods to generate a rotational force along the direction within the disk surface but perpendicular to the slot. This will allow only nanospheres but prevent the nanorods from accurately entering into the slots, realizing effective sieving between the nanoparticles of the two shapes.

Asymmetrical Fabry-Perot cavity slot micro⁃ring resonator and its sensing characteristics

Asymmetrical Fabry-Perot cavity slot micro⁃ring resonator and its sensing characteristics

Flow deflection characteristics of two-dimensional synthetic jets generated from asymmetric stepped slots

Flow deflection characteristics of two-dimensional synthetic jets generated from asymmetric stepped slots

A Novel Single-layered Dual-wideband Circularly Polarized Asymmetric Slot Antenna for Wireless Applications

A Novel Single-layered Dual-wideband Circularly Polarized Asymmetric Slot Antenna for Wireless Applications

A Compact Slotted UWB Antenna Based on Characteristics Mode Theory for Wireless Applications

The development of electronic systems and wireless communication has led to a proportional increase in data traffic over time. One potential solution for alleviating data congestion is to augment the bandwidth capacity. This study presents a novel asymmetric circular slotted semi-circle-shaped monopole antenna design using a defective ground structure. The extended ultrawide bandwidth is achieved by implementing a design where the semi-circle radiator is etched in a specific asymmetric circular slot. This involves etching a circle with a radius of 1.25 mm at the center of the radiator, as well as a succession of circles with a radius of 0.75 mm along the edges of the radiator. In addition, the ground plane is situated at a lower elevation and features a U-shaped truncation that has been etched onto its surface. The expansion of the impedance bandwidth can be accomplished by making adjustments to the radiator and ground plane. The UWB antenna under consideration possesses a geometric configuration of 21.6 × 20.8 × 1.6 mm3 and the antenna is fabricated using an FR-4 glass epoxy substrate. The UWB antenna operates throughout the frequency range of 2.2–16.5 GHz, exhibiting a gain of at least 3.45 dBi across the entire impedance bandwidth and the maximum peak gain of 9.57 dBi achieved at the mid-resonance frequency of 10.5 GHz. The investigation of the antenna’s physical properties is conducted utilizing characteristic mode analysis. The investigation also includes an analysis of the time-domain characteristics, revealing that the group delay was found to be less than 1 ns across the operational frequency range. The predicted and measured findings demonstrate consistency and confirm that the suggested antenna is suitable for electronic systems and wireless applications.

Perfect Absorption and Reflection Modulation Based on Asymmetric Slot-Assisted Gratings without Mirrors.

As a perfect graphene absorber without any external mirrors, we proposed asymmetric slot-assisted grating structures supporting two degenerate resonant modes of the guided-mode resonances (GMR) and the quasi-bound states in the continuum (quasi-BIC). The GMR mode functions as an internal mirror in conjunction with the background scattering, while the quasi-BIC, which is responsible for perfect graphene absorption, stems from the horizontal symmetry breaking by an asymmetric slot. By properly shifting the slot center from the grating center, the leakage rate of quasi-BIC can be controlled in such a way as to satisfy the critical coupling condition. We provide a comprehensive study on the coupling mechanism of two degenerate resonant modes for a one-port system mimicking the resonance. We also numerically demonstrated that our proposed grating structures show an excellent reflection-type modulation performance at optical wavelength ranges when doped double-layer graphene is applied. Due to the perfect absorption at the OFF state, a high modulation depth of ~50 dB can be achieved via a small Fermi level variation of ~0.05 eV. To obtain the lower insertion loss at the ON state, the higher Fermi level is required to decrease the graphene absorption coefficient.

Modeling and Simulation of a Novel Low-Speed High-Torque Permanent Magnet Synchronous Motor with Asymmetric Stator Slots

Focusing on the unstable electromagnetic performance of an air gap magnetic field caused by torque ripple and harmonic interference of a multi-slot and multi-pole low-speed high-torque permanent magnet synchronous motor (LHPMSM), an asymmetric stator slot is proposed to improve the comprehensive electromagnetic performance of the motor. Moreover, this paper develops an exact analytical model which predicts the magnetic field distribution based on Laplace’s and Poisson’s equations. The stator slot asymmetry is introduced into the model and solved by the method of separating variables. Taking a 40p168s LHPMSM as an example, numerical results of the no-load flux density field distributions are obtained by the finite element method (FEM) and employed to validate the analytical model. The influence of stator slot asymmetric structure on electromagnetic characteristics is subsequently analyzed. The results show that, compared with the semi-closed slot model, the asymmetric slot has better torque characteristics, and the electromagnetic characteristics of the motor can be significantly improved by optimizing the stator slot asymmetry. Finally, a prototype is manufactured and tested to validate the theoretical analysis.

Mid-infrared silicon photonic phase shifter based on microelectromechanical system.

Mid-infrared (MIR) photonic integrated circuits have generated considerable interest, owing to their potential applications, such as thermal imaging and biochemical sensing. A challenging area in the field is the development of reconfigurable approaches for the enhancement of on-chip functions, where a phase shifter plays an important role. Here, we demonstrate a MIR microelectromechanical system (MEMS) phase shifter by utilizing an asymmetric slot waveguide with subwavelength grating (SWG) claddings. The MEMS-enabled device can be easily integrated into a fully suspended waveguide with SWG cladding, built on a silicon-on-insulator (SOI) platform. Through engineering of the SWG design, the device achieves a maximum phase shift of 6π, with an insertion loss of 4 dB and a half-wave-voltage-length product (VπLπ) of 2.6 V·cm. Moreover, the time response of the device is measured as 13 µs (rise time) and 5 µs (fall time).

Slot hybrid-core waveguides for temperature-independent integrated optical sensors.

We propose a novel type of waveguides, called the slot hybrid-core waveguides (HCWs), for temperature-independent integrated optical sensors. The HCWs are composed of different core materials having the opposite thermo-optic coefficients (TOCs) and, therefore, are immune to temperature variations. On this basis, slot HCWs are proposed for the microring resonator-based optical sensors, enabling the sensors to simultaneously present high sensitivities and temperature independence. The temperature-dependent wavelength shifts of the proposed sensors are calculated to be less than 1 pm/K while the sensitivities to the cladding refractive indices attain 468 nm/RIU and 536 nm/RIU, respectively, for the asymmetric and symmetric slot structures.

Low-Profile Uni-Cavity High-Gain FPC Antenna Covering Entire Global 2.4 GHz and 5 GHz WiFi-Bands Using Uncorrelated Dual-Band PRS and Phase Compensation AMC

A design methodology of the dual-band Fabry–Perot-cavity (FPC) antenna is proposed, realizing dual-broadband high gain and keeping the simplicity of one low-profile resonant cavity. A ray optics model is applied to obtain the phase resonance condition for dual-band FPC antennas. The proposed antenna employs a tightly stratified partial-reflective-surface (PRS), an artificial-magnetic-conductor (AMC) ground, and a dual-band microstrip feed. The PRS modulates independently the dual-band reflection coefficient to maintain a large amplitude and a positive phase gradient. Meanwhile, an AMC ground is distinctively employed to compensate for the transmission phase difference of the lower band when the cavity height meets half the wavelength of the upper one, enabling eventually a low-profile uni-cavity. Furthermore, a dual-band microstrip feed with two asymmetric slots is customized as the primary radiator. Detailed electromagnetic studies are carried out to illustrate the operating mechanisms of these components. Finally, a proof-of-concept prototype is fabricated covering the entire global 2.4 and 5 GHz WiFi bands. The measurement results agree well with the simulation, and the 3 dB gain bandwidths of 7.2% and 16.2% with peak gains of 13.6 and 15.0 dBi over two wide bands of 2.42–2.60 and 5.1–6 GHz are achieved, respectively, with a single cavity height of 26.8 mm.

Quad-Port Circularly Polarized MIMO Antenna with Wide Axial Ratio.

This article studies a quad-port multi-input-multi-output (MIMO) circularly polarized antenna with good isolation properties. Using characteristic mode analysis (CMA), the first six distinct modes of the asymmetric square slot with an inverted L-strip are analyzed. In this study, modal parameter extraction is carried out for circular polarization (CP) radiation. A simple annular ring microstrip feed is excited to obtain broadband CP based on CMA. The single-unit feeding structure is replicated orthogonally four times to achieve a CP MIMO antenna. This antenna provides port isolation of more than 21 dB without the use of an additional decoupling element. The quad-port CP-MIMO antenna is simulated with a total dimension of 50 × 50 mm2. The antenna attains impedance matching (S11 < −10 dB) from 5.37 GHz to beyond 11 GHz with an axial ratio bandwidth (ARBW) of 4.65 GHz (5.61 GHz to 10.26 GHz). The peak realized gain of the MIMO antenna is measured at 5.69 dBi at 8.4 GHz. Additionally, the diversity performance parameters of the MIMO structure are computed. The advantages of the proposed structure have been evaluated by comparing it to previously reported MIMO structures. A prototype of the MIMO structure measurements was found to match the simulation results.

Efficient graphene-based circularly polarized MIMO antenna for THz applications.

In this paper, a graphene-based (MIMO) antenna is designed and examined. Two unique properties of the proposed terahertz (THz) MIMO antenna are (1) circular polarization is achieved through an asymmetrical cross slot, etched over the graphene patch; and (2) a bidirectional radiation pattern is achieved through oppositely oriented identical antenna ports. Mutual coupling between the antenna ports is less than -35dB. Due to the inclusion of the pattern diversity concept, a low value of envelope correlation coefficient is achieved. The proposed THz radiator operates over the frequency range of 4.67-4.87 THz, along with a 3 dB axial ratio between 4.76 and 4.81 THz. This type of antenna is widely employable for biomedical applications.

Dual circularly polarized aperture-coupled metasurface antennas with high-isolation for X-band synthetic aperture radars

ABSTRACT This paper describes a dual circularly polarized (CP) antenna with high isolation and its 2 × 2 element array for the X-band synthetic aperture radars. The antenna is an aperture-coupled metasurface of 4 × 4 periodic corner-truncated patches, which is fed by two orthogonal microstrip-lines to generate the dual-CP radiation. A novel asymmetric fence-shaped slot is utilized as the coupled aperture of the antenna to enhance the port-to-port isolation. To achieve a more robust dual-CP radiation, the 2 × 2 element array of the aperture-coupled metasurface antenna is designed, fabricated, and tested. Both simulation and measurement indicate that the array prototype achieves an excellent dual-CP radiation at 9.6 GHz, i.e., isolation of ≥ 30 dB, axial ratio ≤ 1-dB, radiation efficiency ≥ 80%, realized gain of 14.0 dBic, and cross-polarized level ≤ −20 dB at the broadside.

Four Element MIMO Antenna Systems with Decoupling Lines for High-Speed 5G Wireless Data Communication

A low-profile planar multiple-input multiple-output (MIMO) antenna consisting of four elements with isolation improvement is proposed for 5G mm Wave (24–40) GHz applications. Each radiating element of the MIMO antenna comprises of a microstrip-fed tilted spade-shaped radiator with four asymmetrical slots and a partial ground plane. The antenna is optimized to resonate at 35 GHz covering a wide impedance bandwidth from 23.9 to 40.1 GHz. Two cross lines are then loaded between the antenna elements to improve the isolation &gt; − 30 d B . The MIMO structure with the decoupling lines is fabricated and tested. The measured results are in good correlation with the simulated results. Other MIMO performance metrics such as the envelope correlation coefficient (ECC), channel capacity loss (CCL), diversity gain (DG), and total active reflection coefficient (TARC) are examined, and the results are found to be satisfactory for the device to be used for mm-wave 5G MIMO applications. Also, the antenna’s performance metrics such as radiation efficiency, gain, and radiation patterns over the operating band are presented.

Precision design of slot arrays in reduced-height, dielectric-filled or substrate-integrated waveguide using the full T-network equivalent circuit for array elements

ABSTRACT Precision design of narrow-beam or shaped-beam slot arrays in reduced-height, dielectric-filled or substrate-integrated waveguide demands accurate control over the excitation of individual elements. Conventional design methods are restricted by assumptions pertaining to the symmetry of slot fields and the simplified shunt-element equivalent circuit for slots. In this paper, we present a detailed formulation of a design technique that accommodates asymmetric slots fields and uses the full T-network equivalent circuit for each slot. The method is efficient and capable of rapid design of arrays of arbitrary dimension.

Studying the Richtmyer–Meshkov instability in convergent geometry under high energy density conditions using the Decel platform

The “Decel” platform at Sandia National Laboratories investigates the Richtmyer–Meshkov instability (RMI) in converging geometry under high energy density conditions [Knapp et al., Phys. Plasmas 27, 092707 (2020)]. In Decel, the Z machine magnetically implodes a cylindrical beryllium liner filled with liquid deuterium, launching a converging shock toward an on-axis beryllium rod machined with sinusoidal perturbations. The passage of the shock deposits vorticity along the Be/D2 interface, causing the perturbations to grow. In this paper, we present platform improvements along with recent experimental results. To improve the stability of the imploding liner to the magneto Rayleigh–Taylor instability, we modified its acceleration history by shortening the Z electrical current pulse. Next, we introduce a “split rod” configuration that allows two axial modes to be fielded simultaneously in different axial locations along the rod, doubling our data per experiment. We then demonstrate that asymmetric slots in the return current structure modify the magnetic drive pressure on the surface of the liner, advancing the evolution on one side of the rod by multiple ns compared to its 180° counterpart. This effectively enables two snapshots of the instability at different stages of evolution per radiograph with small deviations of the cross-sectional profile of the rod from the circular. Using this platform, we acquired RMI data at 272 and 157 μm wavelengths during the single shock stage. Finally, we demonstrate the utility of these data for benchmarking simulations by comparing calculations using ALEGRA MHD and RageRunner.

Analysis and Design of Plasmonic-Organic Hybrid Electro-Optic Modulators Based on Directional Couplers

We present a detailed simulation study on plasmonic-organic hybrid electro-optic modulators based on coupled symmetric or asymmetric plasmonic slots. An electro-optic polymer is exploited as an active material, and the device is compatible with a silicon photonics platform. The proposed device operates at 1550 nm wavelength, typical of data center or long-haul telecommunication systems. The device performance in terms of area, plasmonic losses, optical bandwidth, intrinsic modulation bandwidth and energy dissipation are comparable to already proposed Mach-Zehnder solutions, but with potentially better extinction ratio, coupling losses due to photonic-plasmonic transitions, and flexibility in exploiting, without any performance penalty, asymmetric slots to shift the ON and OFF states bias. Finally, the bias dependence of the modulation chirp is investigated, comparing through and cross-coupling configurations.

Effect of Coolant Crossflow on Film Cooling Effectiveness of Diffusion Slot Hole With and Without Ribs

Abstract The coolant flow condition at the film hole entrance has a notable effect on film cooling effectiveness. The previous studies about internal ribbed crossflow effects are the hole with a circular inlet cross section. In this study, a diffusion slot hole with a race-track inlet cross section is examined in a low-speed wind tunnel by the pressure-sensitive paint (PSP) technique. The film cooling effectiveness of three different hole configurations are investigated: a normal diffusion slot hole, a compound angle diffusion slot hole, and a lateral inclination angle diffusion slot hole. Two internal perpendicular crossflow conditions with and without ribs for the 45 deg inline crossflow and the 135 deg counter crossflow are discussed. The blowing ratios are varied from 0.5 to 2.5 at a constant crossflow-to-mainstream velocity ratio of 0.36. A detailed method for the uncertainty analysis of the PSP is also presented. It is found that the normal diffusion slot hole always shows the best cooling performance than other holes. The ribs under the crossflow condition have a positive effect on the film cooling effectiveness for the normal diffusion slot hole even though the compound angle changes the hole’s orientation. However, the ribs have a negative effect on the film cooling effectiveness for the geometrically asymmetric diffusion slot hole.

High-Efficiency Plasmonic Lens Based on Archimedes-Spiral with Cross Section of an Asymmetric Slot

A high-efficiency plasmonic lens composed of a single Archimedes-spiral slot with a cross section of an asymmetric slot is proposed. By adding an auxiliary nanocavity under the primary spiral slot, unidirectional plasmonic waves can be efficiently transmitted in the inward direction and focused on a hot spot in the center. Due to the asymmetric slot, the finite-difference time-domain (FDTD) method is used to numerically optimize the geometric parameters of the single spiral slot, which can achieve high-intensity unidirectional inward focusing. The proposed structure can decrease background noises and prevent cross-talk of nearby components in optical networks, which significantly improves the integration level of nanophotonic circuits and devices.