Asymmetric Corrugation Research Articles

Analysis of thermal-hydraulic comprehensive performance of composite corrugated tubes composed of simple droplet-shaped corrugations

Corrugation parameter design seeks to maximize the thermal-hydraulic comprehensive performance (THCP) of corrugated tubes as much as possible. Among them, composite corrugations composed of simple corrugations are proposed to strengthen the THCP of corrugated pipes. However, the rule and mechanism regarding the impact of composite corrugations on the THCP of corrugated tubes, particularly when those composite corrugations are composed of simple asymmetric corrugations, are not well understood. Therefore, in this work, the effect of composite corrugations consisting of two simple droplet-shaped corrugations on THCP is assessed numerically, where the first composite corrugation is concave-convex (CTCC1) and the second composite corrugation is concave-concave (CTCC2). In addition, the effect of traditional corrugation (CTSC) on THCP is also examined to further highlight the advantages of composite corrugation in enhancing the THCP of corrugated tubes. The results of the study indicated a 49 %, 55 %, and 61 % increase in THCP at a Reynolds number (Re) of 5000 for CTSC, CTCC1, and CTCC2, respectively, compared to a smooth tube, indicating that the combination of composite corrugations in CTCC2 is superior to that in CTCC1. In addition, a smaller corrugation width on the upstream side of CTCC2 is more conducive to enhancing THCP. Furthermore, it should be ensured that the corrugation depth on the upstream side of CTCC2 is not greater than the depth on the downstream side to achieve better THCP. The work confirms the advantages of composite corrugations over traditional corrugations in enhancing THCP and guides the selection of composite corrugation combination forms and the design of composite corrugation width and depth distribution.

Narrow-bandwidth Bragg grating filter based on Ge-Sb-Se chalcogenide glasses.

Bragg grating (BG) filters play important roles in integrated photonics such as signal processing and optical sensing. In silicon-based counterpart photonic platforms, the application of narrow-bandwidth (Δλ) filters is often restrained by fabrication limitations. In this study, narrow-bandwidth BG filters based on Ge-Sb-Se chalcogenide materials are investigated. The structure of the filter is designed by optimizing the grating period, corrugation height, and grating number. The large corrugation of chalcogenide BG is more friendly and convenient for manufacturing process. The symmetric and asymmetric corrugation filters are then fabricated and characterized. Experimental results show a half-maximum bandwidth of 0.97 nm and 0.32 nm for symmetric and asymmetric filters, respectively, which demonstrates excellent narrow-bandwidth filtering performance of chalcogenide BG.

Analysis of Asymmetrically Corrugated Goubau-Line Antenna for Endfire Radiation

We systematically analyze and describe a new type of traveling-wave endfire antenna based on an asymmetrically corrugated Goubau line that exhibits high efficiency and has a low profile. By proving that asymmetry is a necessary condition in addition to the Hanson–Woodyard condition for traveling-wave endfire radiation, we study the effect of asymmetric corrugation on the mode guide and coupling. We subsequently show that two different waves are independently guided along the two corrugated edges, whose phase difference leads to a transversally polarized dipole moment radiating in the endfire direction. A closed-form expression for the radiation pattern is derived based on the proposed analysis to approximately predict the antennas’ optimum length. To verify the proposed analysis and design principles, results from an experimental prototype operating at 13–15 GHz are also provided. The experimental results show that the antenna design has an average gain of 9.9 dBi and an average efficiency of 82%. The agreement between the predicted results and the final optimized results validates the proposed analysis.

Directed transport of liquid droplets on vibrating substrates with asymmetric corrugations and patterned wettability: a dissipative particle dynamics study

ABSTRACTThe development of digital (droplet-based) microfluidic (DMF) devices has received significant attention due to their importance for chemical and biomedical analyses. The precise control and manipulation of liquid droplets on a solid substrate is a major requirement for DMF devices. In this study, we propose a novel strategy to generate continuous droplet motion by combining asymmetric corrugations and patterned wettability on a vibrating substrate. The time periodic oscillations of the substrate with asymmetric triangle corrugations provide the input energy to transport a droplet along patterned stripes. Using dissipative particle dynamic (DPD) simulations, we demonstrate that hydrophobic stripes on a superhydrophobic substrate create a wettability step, which effectively constrains the droplet motion along the stripe. Due to the special design of asymmetric triangle corrugations and orientation of hydrophobic stripes, the proposed strategy enables the transport of multiple droplets with different initial locations towards a single spot and coalescence into a large droplet. We further identify a power-law dependence between the droplet velocity and the period of substrate vibration and show that this function is independent of the droplet size. The proposed droplet transportation strategy can be potentially useful for the efficient manipulation of liquid droplets in DMF devices.

Wide-Temperature-Range (25–80 °C) 53-Gbaud PAM4 (106-Gb/s) Operation of 1.3-μm Directly Modulated DFB Lasers for 10-km Transmission

A 1.3- μ m directly modulated distributed feedback laser was newly developed by adopting an asymmetric corrugation pitch modulated grating structure and an InGaAlAs multiquantum well active layer with both a high optical confinement factor and a high differential gain. A low threshold current and a large saturation current in light-current characteristics at high temperature were obtained and a high 3-dB bandwidth and a high relaxation oscillation frequency in electro-optical characteristics were also achieved over a wide temperature range. As a result, clear back-to-back eye openings were achieved for 26-Gbaud PAM4 (53-Gb/s) operation from 25 to 95 °C with large outer extinction ratio and sufficiently small transmission dispersion eye closure quaternary. Furthermore, 53-Gbaud PAM4 (106-Gb/s) operation from 25 to 80 °C was successfully demonstrated for both back-to-back and after 10-km single mode fiber transmission. These excellent characteristics make our DFB laser a promising cost-effective and compact transceiver with low power consumption for next-generation 400GbE applications.

Low‐profile tilted‐beam waveguide slot antenna using corrugations for UAV applications

AbstractWe propose a low‐profile tilted‐beam waveguide slot antenna using corrugations for unmanned aerial vehicle (UAV) applications. The proposed antenna consists of a WR‐90 rectangular waveguide with a central slot on top and two asymmetric corrugations. The antenna satisfies a 10‐dB return loss from 9.82 to 10.18 GHz. To realize the low‐profile characteristic, the proposed antenna is fed from the flank instead of the bottom of the waveguide. In addition, the proposed antenna attains a tilted beam pointing 45 degrees from the broadside direction due to the asymmetric corrugations on the conducting plate. The antenna has a measured peak gain of 6.95 dBi at the center frequency of the operation band, which satisfies the gain requirement for UAV applications. The experimental and simulated results of the proposed antenna are in good agreement.

Numerical study on the cross-corrugated primary surface heat exchanger having asymmetric cross-sectional profiles for advanced intercooled-cycle aero engines

Due to its high volume goodness and light weight, the cross-corrugated primary surface heat exchanger is a promising candidate for application to an advanced intercooled-cycle gas turbine engine. The asymmetric corrugation profile considered in this paper has the possibility of achieving balanced pressure drops on both hot and cold sides of an intercooler matrix, which may enable significant weight reductions not only in counter-flow designs, but also in cross-flow designs. For the assessment of its performance, a numerical procedure incorporating a detailed three-dimensional computational fluid dynamics model and a lumped parameter flow-network model has been investigated. By developing a new parameterization method for the shape of the profile, the detailed aero-thermal performance of the asymmetric profile is summarized quantitatively. A cross-flow heat exchanger matrix sizing study for matrix weight minimization is carried out, and the results show the high dependency of the potential improvements on the given operating conditions and design requirements.

전자파 두뇌 영상장치용 비대칭형 Corrugated 테이퍼드 슬롯 안테나

최근 전자파를 이용하여 두뇌를 영상화하는 시스템이 제안되고 있다. 이러한 시스템은 초광대역 특성(0.5~2 GHz)과 주빔의 방향이 모든 동작 주파수 대역에서 일정하게 유지되는 소형 안테나를 요구한다. 위의 요구 조건을 만족하기 위해서 본 논문에서는 비대칭형 corrugation들을 일반 TSA에 적용하여 안테나의 크기는 14 % 감소시키고, 요구되는 동작 주파수 대역인 0.5 GHz에서 2 GHz까지 반사 손실이 10 dB 이하의 값을 가지도록 설계하였다. 특히 대칭형 corrugation들을 적용한 TSA가 가지는 주빔의 방향이 주파수에 따라 변하는 점을 개선하였고, 이러한 비대칭형 corrugated TSA는 전자파를 이용한 두뇌 영상장치의 구현을 위해서 요구되는 조건을 모두 만족한다. Recently, a brain imaging system with microwave devices has been proposed. The brain imaging system requires a small antenna which has ultra wide band(UWB) operating frequency bandwidth(0.5~2 GHz) and non-varying boresight of antenna over the frequency band. This paper proposes asymmetric corrugations on a tapered slot antenna (TSA) so that the size of the TSA is reduced by 14 % while 10 dB return loss bandwidth is satisfied over the operating frequency band from 0.5 GHz to 2 GHz. A miniaturized TSA with symmetric corrugations shows tilted boresight whilst frequency is getting lower; however, the proposed TSA with asymmetric corrugations maintains direction of boresight for different frequencies. This enhancements make an asymmetric corrugated TSA meet the requirement of the brain imaing system.

Experimental study of multichromatic terahertz wave propagation through planar micro-channels

Previous theoretical and numerical studies [Y. M. Shin and L. R. Barnett, Appl. Phys. Lett. 92, 091501 (2008) and Y. M. Shin et al., Appl. Phys. Lett. 93, 221504 (2008)] have reported that a planar micro-channel with an asymmetric corrugation array supports strongly confined propagation of broadband THz plasmonic waves. The highly broad spectral response is experimentally demonstrated in the near-THz regime of 0.19–0.265 THz. Signal reflection and transmission tests on the three designed micro-channels including directional couplers resulted in a full-width-half-maximum bandwidth of ∼50-60 GHz with an insertion loss of approximately −5 dB, which is in good agreement with simulation data. These micro-structures can be utilized for free electron beam and electronic/optic integrated devices.

Unidirectional transmission in photonic-crystal gratings at beam-type illumination

Unidirectional transmission is studied theoretically and experimentally for the gratings with one-side corrugations (non-symmetric gratings), which are based on two-dimensional photonic crystals composed of alumina rods. The unidirectional transmission appears at a fixed angle of incidence as a combined effect of the peculiar dispersion features of the photonic crystal and the properly designed corrugations. It is shown that the basic unidirectional transmission characteristics, which are observed at a plane-wave illumination, are preserved at Gaussian-beam and horn antenna illuminations. The main attention is paid to the single-beam unidirectional regime, which is associated with the strong directional selectivity arising due to the first negative diffraction order. An additional degree of freedom for controlling the transmission of the electromagnetic waves is obtained by making use of the asymmetric corrugations at the photonic crystal interface.

Complete transformation of a normally incident wave to the −1st diffraction order by a smooth echelette

We study the regime of complete transformation of a wave, which is incident normally on a corrugated metal surface, to the −1st diffraction order (to one side) for rather simple smooth corrugation profiles without losses. The study is based on the numerical solution of the integral equation by using an interactive computer code developed by the author. It is shown that the regimes under consideration can take place only in the case of asymmetric corrugation profiles. Realization of such regimes requires a comparatively great number of parameters in the profile description. One can develop the profiles which ensure the specified regimes for both H- and E-polarized waves. Several examples of such profiles are presented and illustrated with detailed graphical descriptions of their diffraction properties.

Effects of asymmetric surface corrugations on fully metal-coated scanning near field optical microscopy tips

We propose a new configuration for a fully metal coated scanning near field (SNOM) probe based on asymmetric corrugations in the metal coating. The variation in the metal surface induces coupling mechanisms leading to the creation of a localized hot spot under linearly polarized excitation. Field localization is an effect of paramount importance for resolution but cannot be achieved with standard axisymmetric fully metal-coated probes, unless a more cumbersome radially polarized excitation is used. Our simulations show that this promising structure allows one to simplify the mode injection procedures circumventing the need for a radially polarized beam.

Enhancement of fiber–matrix adhesion by laser ablation-induced surface microcorrugation

Micrometer-sized surface corrugations produced on Kevlar fiber surfaces by laser ablation were found to dramatically enhance the mechanical adhesion between the fibers and the epoxy matrix in a fiber-reinforced composite. Symmetric and asymmetric corrugation structures were produced by irradiating the fibers with high-fluence UV laser pulses at various incidence angles. The interfacial shear strength (IFSS) between the fibers and the matrix was measured using the microbond fiber-pullout method. Upon laser ablation treatment, the IFSS increased by 120% with symmetric corrugation profiles obtained with laser irradiation normal to the fiber axis, and 5-fold with asymmetric corrugation profiles obtained with the laser incidence angle at 45° to the fiber axis. A similar enhancement was observed in pullout tests under wet conditions. A simple model based on an elementary analysis of the expected strain field in the presence of interface corrugation is found to provide a quantitative explanation of the observed strength enhancement factors.

Control of the lateral Casimir force between corrugated surfaces

The general perturbative expression for the lateral Casimir force between two plates covered by longitudinal corrugations of arbitrary shape is obtained. This expression is applicable for corrugation periods larger than the separation distance. The cases of asymmetric corrugations are considered, which allow to increase the maximum to minimum force ratio and affect the character of equilibrium points. This opens new opportunities to control the lateral Casimir forces for use in microelectromechanical devices based entirely on the vacuum fluctuation properties.

The complex coordinate scattering theroy and its application to the study of the surface asymmetry effect in helium diffraction from copper

AbstractThe Complex Coordinate Scattering Theory is reformulated for the general case of a time‐independent Hamiltonian. It is applied to scattering of He atoms from a Cu(115) crystal surface by constracting the Green operator for the T‐matrix from the eigenvectors of both the complex scaled Hamiltonian and its transposed (“right” and “left” eigenvectors), which are different in this case. The weakly asymmetric corrugation function describing the (115) face of Cu is shown to cause a strong dependence of the calculated diffraction intensities upon the direction of the incident atomic beam. The calculated transition probabilities are in excellent agreement with the experimentally measured ones, previously obtained by Perreau and Lapujoulade. We show that additional information about the gas atom/surface physisorption interaction potential can be obtained if the incident angle of the atomic beam (the angles between the beam and the surface normal) is changed from γ to −γ. © 1993 John Wiley & Sons, Inc.