Layout Of Unit Cells Research Articles

A Multipolarized Traveling-Wave Series-Fed Antenna Array Based on Patch

In this paper, a simple broadband multipolarized traveling-wave series-fed antenna array is proposed. The radiation unit cells are multiple squares. The square unit cell will change between circular polarized (CP) and linear polarized (LP) through a reasonable feeding mode. By adjusting the equivalent length of the unit cell, the Q value of the antenna can be reduced, resulting in the increase of the bandwidth of the array. The array consists of seven-unit cells and dual-port feeding. The unit cells which are connected by a microstrip line are arranged in a circular array. A reasonable layout of unit cells can achieve good port isolation of the array. The polarization performance of the array antenna is the same as that of the unit cell. The antenna is fabricated and measured. The measured results are consistent with the simulated results.

Optimal design of shape changing mechanical metamaterials at finite strains

Programmable metamaterials establish a new subset of metamaterials offering controllable and variable physical properties. As metamaterials, they are artificial materials and exhibit exotic and counter-intuitive material behavior, but are more specifically tailored for engineering purposes. Whereas for metamaterials a mostly homogeneous layout of unit cells is considered, programmable materials are constructed by an individual distribution in order to satisfy custom intentions regarding a specific shape change under given loading conditions. In order to tackle this customization of material response, a computational optimization framework similar to topology or material optimization is proposed. Our work is based on a multiscale and data approach, allowing a broad range of application with different classes of unit cells and target functions under finite strains. In this contribution, we present the complete process chain from a parametrized unit cell to the final model of the programmable material, ready to be manufactured. We show numerical results with different unit cells and compare them to fully resolved simulations. Further, with the development of new generative manufacturing processes, the production of such programmable materials consisting of spatially varying cells has also become possible on an industrial scale. One example of lab-scale production is shown in the paper and compared to simulation results.

Metasurface absorber with ultra-thin thickness designed for a terahertz focal plane array detector.

Terahertz (THz) refers to electromagnetic waves with frequency from 0.1 to 10 THz, which lies between millimeter waves and infrared light. This paper proposes an ultra-thin metasurface absorber which is perfectly suited to be the signal coupling part of terahertz focal plane array (FPA) detector. The absorptance of the proposed metasurface is higher than 80% from 4.46 to 5.76 THz (25.4%) while the thickness is merely 1.12 µm (0.018 λ). Since the metasurface absorber will be applied to terahertz FPA detector which requires planar array formation, it is divided into meta-atoms. Each meta-atom consists of the same unit cell layout, and air gaps are introduced between adjacent meta-atoms to enhance the thermal isolation, which is crucial for FPA detector to obtain desired imaging results. Due to the symmetrical layout of meta-atoms, absorptance keeps stable for different polarized waves, moreover, good absorptance could also be achieved for incidence angles range of ± 30 °. Spectral measurements show good agreement with the simulation. As a result, features of ultra-thin thickness, polarization insensitivity, and high absorptance make the proposed metasurface absorber well suited to highly efficient coupling of terahertz signals in FPA detector.

Three Scale Unfolding Homogenization Method Applied to Cardiac Bidomain Model

In this paper, we are dealing with a rigorous homogenization result at two different levels for the bidomain model of cardiac electro-physiology. The first level associated with the mesoscopic structure such that the cardiac tissue consists of extracellular and intracellular domains separated by an interface (the sarcolemma). The second one related to the microscopic structure in such a way that the intracellular medium can only be viewed as a periodical layout of unit cells (mitochondria). At the interface between intra-and extracellular media, the fluxes are given by nonlinear functions of ionic and applied currents. A rigorous homogenization process based on unfolding operators is applied to derive the macroscopic (homogenized) model from our meso-microscopic bidomain model. We apply a three-scale unfolding method in the intracellular problem to obtain its homogenized equation at two levels. The first level upscaling of the intracellular structure yields the mesoscopic equation. The second step of the homogenization leads to obtain the intracellular homogenized equation. To prove the convergence of the nonlinear terms, especially those defined on the microscopic interface, we use the boundary unfolding method and a Kolmogorov-Riesz compactness's result. Next, we use the standard unfolding method to homogenize the extracellular problem. Finally, we obtain, at the limit, a reaction-diffusion system on a single domain (the superposition of the intracellular and extracellular media) which contains the homogenized equations depending on three scales. Such a model is widely used for describing the macroscopic behavior of the cardiac tissue, which is recognized to be an important messengers between the cytoplasm (intracellular) and the other extracellular inside the biological cells. Contents 2020 Mathematics Subject Classification. 65N55 and 35A01 and 35B27 and 35K57 and 65M..

A Modular Design of Continuously Tunable Full Color Plasmonic Pixels with Broken Rotational Symmetry

AbstractColor tuning is a fascinating and indispensable property in various applications. Thus far, a variety of reconfigurable approaches have been implemented to achieve color change. However, it is still a challenge to enable continuous color tuning over the entire hue range in a simple, stable, and rapid manner without changes in configuration and material properties. Here, an all‐optical continuously tunable plasmonic pixel scheme is demonstrated via a modular design approach to realize polarization‐controlled full color tuning by breaking the intrinsic symmetry of the unit cell layout. The polarization‐controlled full color tunable plasmonic pixels consist of three different types of color modules corresponding to three subtractive primary colors. Without changing the structural properties or surrounding environment, the structural colors can be continuously and precisely tuned across all hues by illuminating linearly polarized light with different polarization directions. Meanwhile, the plasmonic pixels can be flexibly customized for various color tuning processes through the appropriate choice of component modules and the elaborate design of module layouts. Furthermore, the color tuning is extended to achromatic colors with the utilization of a single module or the introduction of a black module. The proposed plasmonic pixels hold considerable potential to function as next‐generation color pixels integrated with liquid‐crystal polarizers.

Derivation of a new macroscopic bidomain model including three scales for the electrical activity of cardiac tissue

In the present paper, a new three-scale asymptotic homogenization method is proposed to study the electrical behavior of the cardiac tissue structure with multiple heterogeneities at two different levels. The first level is associated with the mesoscopic structure such that the cardiac tissue is composed of extracellular and intracellular domains. The second level is associated with the microscopic structure in such a way the intracellular medium can only be viewed as a periodical layout of unit cells (mitochondria). Then, we define two kinds of local cells that are obtained by upscaling methods. The homogenization method is based on a power series expansion which allows determining the macroscopic (homogenized) bidomain model from the microscopic bidomain problem at each structural level. First, we use the two-scale asymptotic expansion to homogenize the extracellular problem. Then, we apply a three-scale asymptotic expansion in the intracellular problem to obtain its homogenized equation at two levels. The first upscaling level of the intracellular structure yields the mesoscopic equation and the second step of the homogenization leads to obtain the intracellular homogenized equation. Both the mesoscopic and microscopic information are obtained by homogenization to capture local characteristics inside the cardiac tissue structure. Finally, we obtain the macroscopic bidomain model and the heart domain coincides with the intracellular medium and extracellular one, which are two inter-penetrating and superimposed continua connected at each point by the cardiac cellular membrane. The interest of the proposed method comes from the fact that it combines microscopic and mesoscopic characteristics to obtain a macroscopic description of the electrical behavior of the heart.

Topology optimization of magnetic composite microstructures for electropermanent magnet

This paper presents topology optimization for the design of magnetic composite applicable to electropermanent magnet. Here, the magnetic composite is built from a periodic microstructure consisting of air, iron and permanent magnet (PM) materials. The combination of non-magnetic, soft and hard magnetic materials in a microscopic scale enables to produce its own persistent magnetic field like PM material, and also enables the control of the magnetic field by an external current like iron material. This work aims to find the optimal microstructure unit cell layout of the electropermanent magnet, and estimate its cross-property bounds. Here, the cross-property bounds connect the effective magnetic permeability and residual flux density, which are calculated using the asymptotic homogenization method. The design objectives (i.e. desired effective properties) are theoretically studied with consideration of application to electromechanical devices. Then, an multi-objective optimization problem to achieve desired effective properties is formulated and solved with a multi-material gradient-based topology optimization formulation. As a result, the optimal composite unit cell layouts that constitute the Pareto fronts are successfully obtained. From the Pareto fronts, cross-property bounds of the electropermanent magnet are numerically constructed and discussed.

A high-order three-scale reduced asymptotic approach for thermo-mechanical problems of nonlinear heterogeneous materials with multiple spatial scales

An effective high-order three-scale reduced asymptotic (HTRA) approach is developed to simulate the coupled thermo-mechanical problems of nonlinear heterogeneous materials with multiple spatial scales. In this paper, the heterogeneous structures are constructed by periodical layout of unit cells on microscopic and mesoscopic scale. At first, the linear and nonlinear higher-order local cell functions defined at microscale and mesoscale are derived by multiscale asymptotic expansion approach. Further, two types of homogenized parameters are introduced, and related nonlinear homogenized solutions are obtained on the macroscopic domain. Then, the high-order three-scale temperature and displacement solutions are established by assembling the various multiscale local solutions and homogenization solutions. The key characteristic of the presented methods is an efficient reduced form for evaluating higher-order local cell problems, and hence greatly reducing the calculating amount in comparison to direct numerical simulations. Also, the new high-order nonlinear homogenization solutions that do not require higher-order continuity of the macroscale solutions. Finally, the effectiveness and accuracy of the multiscale algorithms are verified by some typical numerical examples.

A three-scale asymptotic expansion for predicting viscoelastic properties of composites with multiple configuration

A novel three-scale asymptotic expansion used to evaluate viscoelastic analysis of composites with multiple configuration is systematically studied. The heterogeneities of composite structures are described by periodic layout of unit cells on the microscale and mesoscale. Firstly, the three-scale asymptotic formulations based on homogenization approach and Laplace transform are established, and the local cell solutions in microscale and mesoscale are also defined. Further, two kinds of homogenized coefficients are derived by upscaling methods, and the homogenized equations are obtained on whole macroscopic domain. Also, the strain and stress fields are constructed as three-scale asymptotic solutions by assembling the unit cell solutions and homogenized solutions. Then, the finite element algorithms based on inverse Laplace transform and the three-scale asymptotic homogenization are proposed. Finally, some typical numerical results are employed to validate the presented approaches. They illustrate that the three-scale asymptotic approaches proposed in this paper are efficient and accurate for analyzing the viscoelastic problems of the composites with multiple configuration.

Thermo-mechanical coupling analysis of statistically inhomogeneous porous materials with surface radiation by second-order two-scale method

A novel second-order two-scale method is developed to predict thermo-mechanical coupling performance of statistically inhomogeneous porous materials. For these materials, the sophisticated microstructure information of pores, including their shapes, orientations, sizes, spatial distributions, volume fractions and so on, leads to changes of the macroscopic thermo-mechanical properties. Also, radiation effect at microscale is considered in this study which has an important influence on the macroscopic temperature fields. Firstly, the microscopic configuration for the structure with random distribution is briefly characterized by a periodic layout of unit cells. Secondly, the second-order two-scale formulations for computing the thermo-mechanical coupling problems which consider the interaction between temperature and displacement fields are given in detail. Then, the statistical prediction algorithm based on the two-scale model is brought forward. Finally, some numerical examples for porous materials with varying probability distribution models are calculated by the algorithm proposed, and compared with the data by the theoretical method and experimental results. The comparison shows that the statistical two-scale model is validated for determination of the thermo-mechanical coupling properties of porous materials and demonstrates its potential applications in actual engineering computation.

The properties of optimal two-dimensional phononic crystals with different material contrasts

By modifying the spatial distribution of constituent material phases, phononic crystals (PnCs) can be designed to exhibit band gaps within which sound and vibration cannot propagate. In this paper, the developed topology optimization method (TOM), based on genetic algorithms (GAs) and the finite element method (FEM), is proposed to design two-dimensional (2D) solid PnC structures composed of two contrasting elastic materials. The PnCs have the lowest order band gap that is the third band gap for the coupled mode, the first band gap for the shear mode or the XY34Z band gap for the mixed mode. Moreover, the effects of the ratios of contrasting material properties on the optimal layout of unit cells and the corresponding phononic band gaps (PBGs) are investigated. The results indicate that the topology of the optimal PnCs and corresponding band gaps varies with the change of material contrasts. The law can be used for the rapid design of desired PnC structures.

A stochastic second‐order and two‐scale thermo‐mechanical model for strength prediction of concrete materials

SummaryA stochastic thermo‐mechanical model for strength prediction of concrete is developed, based on the two‐scale asymptotic expressions, which involves both the macroscale and the mesoscale of concrete materials. The mesoscale of concrete is characterized by a periodic layout of unit cells of matrix‐aggregate composite materials, consisting of randomly distributed aggregate grains and cement matrix. The stochastic second‐order and two‐scale computational formulae are proposed in detail, and the maximum normal stress is assumed as the strength criterion for the aggregates, and the cement paste, in view of their brittle characteristics. Numerical results for the strength of concrete obtained from the proposed model are compared with those from known experiments. The comparison shows that the proposed method is validated for strength prediction of concrete. The proposed thermo‐mechanical model is also employed to investigate the influence of different volume fraction of the aggregates on the strength of concrete. Copyright © 2016 John Wiley & Sons, Ltd.

A stochastic multiscale model for predicting mechanical properties of fiber reinforced concrete

A stochastic multiscale computational model for predicting the mechanical properties of fiber reinforced concrete (FRC), subjected to tensile loading, is proposed. It involves the microscale, the mesoscale and the macroscale. On the mesoscale, the heterogeneity of the material is taken into account by a periodic layout of unit cells of matrix–fiber materials, consisting of short fibers and mortar. Material modeling on the microscale is characterized by a periodic layout of unit cells of matrix-aggregate composite materials, consisting of randomly distributed fine aggregate grains and cement matrix. A new unified micro–meso–macro homogenization procedure, based on two-scale asymptotic expressions, has been established. It is used for deriving formulae for multiscale analysis of FRC. The numerical results for the elastic modulus of FRC are compared with experimental results. The comparison shows that the proposed stochastic multiscale computational method is useful for determination of this mechanical property. The developed model is also applied to investigating the influence of different fiber materials on the elastic modulus, and Poisson’s ratio of FRC.

Liquid crystal-based tunable CRLH-transmission line for leaky wave antenna applications at Ka-Band

In this work, a liquid crystal based tunable composite right/left-handed transmission line for future leaky wave antennas working at the Ka-band is presented. The tuning of the liquid crystal is achieved by means of magnetic and electric biasing. For this purpose, different prototypes are fabricated for each biasing technique and their dispersive characteristics compared. Electric tunability is achieved by implementing highly resistive bias lines in the unit cell layout. Both techniques yield similar tuning capabilities at the operation frequency of 27GHz whereas the electric one has the advantage of being easily integratable in the layout.

Highly integrated CMOS RF SPDT switch with ESD and unit cell optimisation in MCM

Presented is the performance of a highly integrated RF single-pole double-throw (SPDT) switch fabricated in a 0.18 µm bulk CMOS process and housed in a low-cost laminated multi-chip module (MCM-L) package. A switch controller is also implemented and consumes ∼40 µA from a 3.4 V supply. The switch, based upon the 1.8 V thin-oxide devices with resistive body-floating and unit cell layout optimisation techniques, achieves an insertion loss of 0.52/0.78 dB at 0.9/2.45 GHz, respectively. TX-to-RX isolation of > 29 dB and return loss of > 15 dB are achieved at these frequencies. The measured IP1dB of 21.7/21.2 dBm and IIP3 of 38.3/37.4 dBm are accomplished at 0.9/2.45 GHz, respectively. Finally, the switch achieves a RF electrostatic discharge (ESD) rating of 4 kV for the ± 2 kV human body model and 500 V for the ± 200 V machine model.

Modeling of coplanar waveguide meander-line inductors

A unique and simple method of modeling a coplanar waveguide meander-line inductor is presented. Using only the lower frequency response of electrically smaller inductors, their higher frequency response is predicted. In addition, the responses of physically larger inductors can also be made using circuit models synthesized directly from the unit cell layout of the inductors. The modeling and prediction results for an ideal metal and lossless substrate is presented, together with comparisons made for various lossy parameters. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12, 520–529, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce.10052