scholarly journals Characteristic Mode Analysis of Unit Cells of Metal-Only Infinite Arrays

2019 ◽  
Vol 8 (2) ◽  
pp. 134-142 ◽  
Author(s):  
Y. Haykir ◽  
O. A. Civi
Keyword(s):  
Periodic Structures ◽  
Unit Cell ◽  
Mode Analysis ◽  
Radiation Characteristics ◽  
Characteristic Mode ◽  
Unit Cell Size ◽  
Characteristic Modes ◽  
Unit Cells ◽  
Physical Insight ◽  
Cost Efficient

Characteristic mode analysis of metal only unit cells of periodic structures is performed using Method of Moments based formulation. Ewald’s transformation is incorporated for a fast and cost efficient solution and the advantages over spatial Green’s function are discussed. The influence of the unit cell size on the characteristic modes is demonstrated. Various metal-only reflectarray elements are compared and their radiation characteristics are interpreted using the theory of characteristic modes. It is shown that characteristic modes of the unit cell can help us to understand the radiation and scattering behavior of the unit cell and this physical insight can be used in periodic array unit cell design.

Determination of Optimal Unit-Cell Size of Homogeneous Conformal Unit-Cell Lattice Structure Using Solid Shape Matching

2016 ◽  
Author(s):  
Mahmoud A. Alzahrani ◽  
Seung-Kyum Choi
Keyword(s):  
Cell Size ◽  
Solid Body ◽  
Strain Energy ◽  
Lattice Structure ◽  
Weight Ratio ◽  
Unit Cell ◽  
Optimal Size ◽  
Lattice Structures ◽  
Unit Cell Size ◽  
Unit Cells

With rapid developments and advances in additive manufacturing technology, lattice structures have gained considerable attention. Lattice structures are capable of providing parts with a high strength to weight ratio. Most work done to reduce computational complexity is concerned with determining the optimal size of each strut within the lattice unit-cells but not with the size of the unit-cell itself. The objective of this paper is to develop a method to determine the optimal unit-cell size for homogenous periodic and conformal lattice structures based on the strain energy of a given structure. The method utilizes solid body finite element analysis (FEA) of a solid counter-part with a similar shape as the desired lattice structure. The displacement vector of the lattice structure is then matched to the solid body FEA displacement results to predict the structure’s strain energy. This process significantly reduces the computational costs of determining the optimal size of the unit cell since it eliminates FEA on the actual lattice structure. Furthermore, the method can provide the measurement of relative performances from different types of unit-cells. The developed examples clearly demonstrate how we can determine the optimal size of the unit-cell based on the strain energy. Moreover, the computational cost efficacy is also clearly demonstrated through comparison with the FEA and the proposed method.

scholarly journals Characteristic Mode Analysis of surface current distributions on metallic structures exposed to HIRF- and DCI-excitations

2020 ◽  
Vol 18 ◽  
pp. 33-41
Author(s):  
Jan Ückerseifer ◽  
Frank Gronwald
Keyword(s):  
Three Dimensional ◽  
Surface Current ◽  
Resonance Region ◽  
Mode Analysis ◽  
Surface Currents ◽  
Characteristic Mode ◽  
Metallic Structures ◽  
Current Distributions ◽  
Characteristic Modes ◽  
Physical Quantities

Abstract. This paper treats Characteristic Mode Analyses of three-dimensional test objects in the context of EMC. Based on computed Characteristic Modes and mode-specific physical quantities, series expansions for HIRF- and DCI-induced surface currents are deduced. The contribution of single Characteristic Modes to surface currents at different test frequencies is analyzed. HIRF- and DCI-excitations are compared with regard to their surface current distributions in their resonance region determined by Characteristic Mode Analysis.

Design of Three-Dimensional, Triply Periodic Unit Cell Scaffold Structures for Additive Manufacturing

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Mazher Iqbal Mohammed ◽  
Ian Gibson
Keyword(s):  
Additive Manufacturing ◽  
Periodic Structures ◽  
Three Dimensional ◽  
Unit Cell ◽  
Final Size ◽  
Fused Filament Fabrication ◽  
Cell Structures ◽  
Triply Periodic ◽  
Unit Cells ◽  
Scaffold Structure

Highly organized, porous architectures leverage the true potential of additive manufacturing (AM) as they can simply not be manufactured by any other means. However, their mainstream usage is being hindered by the traditional methodologies of design which are heavily mathematically orientated and do not allow ease of controlling geometrical attributes. In this study, we aim to address these limitations through a more design-driven approach and demonstrate how complex mathematical surfaces, such as triply periodic structures, can be used to generate unit cells and be applied to design scaffold structures in both regular and irregular volumes in addition to hybrid formats. We examine the conversion of several triply periodic mathematical surfaces into unit cell structures and use these to design scaffolds, which are subsequently manufactured using fused filament fabrication (FFF) additive manufacturing. We present techniques to convert these functions from a two-dimensional surface to three-dimensional (3D) unit cell, fine tune the porosity and surface area, and examine the nuances behind conversion into a scaffold structure suitable for 3D printing. It was found that there are constraints in the final size of unit cell that can be suitably translated through a wider structure while still allowing for repeatable printing, which ultimately restricts the attainable porosities and smallest printed feature size. We found this limit to be approximately three times the stated precision of the 3D printer used this study. Ultimately, this work provides guidance to designers/engineers creating porous structures, and findings could be useful in applications such as tissue engineering and product light-weighting.

scholarly journals Influence of Unit Cell Size and Fiber Packing on the Transverse Tensile Response of Fiber Reinforced Composites

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2565 ◽  
Author(s):  
Royan J. D’Mello ◽  
Anthony M. Waas
Keyword(s):  
Cell Size ◽  
Unit Cell ◽  
Fiber Reinforced Composites ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
Unit Cell Size ◽  
Tensile Response ◽  
Transverse Tensile ◽  
Macro Scale ◽  
Unit Cells

Representative volume elements (RVEs) are commonly used to compute the effective elastic properties of solid media having repeating microstructure, such as fiber reinforced composites. However, for softening materials, an RVE could be problematic due to localization of deformation. Here, we address the effects of unit cell size and fiber packing on the transverse tensile response of fiber reinforced composites in the context of integrated computational materials engineering (ICME). Finite element computations for unit cells at the microscale are performed for different sizes of unit cells with random fiber packing that preserve a fixed fiber volume fraction—these unit cells are loaded in the transverse direction under tension. Salient features of the response are analyzed to understand the effects of fiber packing and unit cell size on the details of crack path, overall strength and also the shape of the stress-strain response before failure. Provision for damage accumulation/cracking in the matrix is made possible via the Bazant-Oh crack band model. The results suggest that the choice of unit cell size is more sensitive to strength and less sensitive to stiffness, when these properties are used as homogenized inputs to macro-scale models. Unit cells of smaller size exhibit higher strength and this strength converges to a plateau as the size of the unit cell increases. In this sense, since stiffness has also converged to a plateau with an increase in unit cell size, the converged unit cell size may be thought of as an RVE. Results in support of these insights are presented in this paper.

Kinematics of the Morph Origami Pattern and its Hybrid States

2020 ◽  
Author(s):  
Phanisri P. Pratapa ◽  
Ke Liu ◽  
Glaucio H. Paulino
Keyword(s):  
Configuration Space ◽  
Poisson’S Ratio ◽  
Plane Deformation ◽  
Mode Locking ◽  
Unit Cell ◽  
Poisson's Ratio ◽  
Form Complex ◽  
Mountain Valley ◽  
Characteristic Modes ◽  
Unit Cells

Abstract A new degree-four vertex origami, called the Morph pattern, has been recently proposed by the authors (Pratapa, Liu, Paulino, Phy. Rev. Lett. 2019), which exhibits interesting properties such as extreme tunability of Poisson’s ratio from negative infinity to positive infinity, and an ability to transform into hybrid states through rigid origami kinematics. We look at the geometry of the Morph unit cell that can exist in two characteristic modes differing in the mountain/valley assignment of the degree-four vertex and then assemble the unit cells to form complex tessellations that are inter-transformable and exhibit contrasting properties. We present alternative and detailed descriptions to (i) understand how the Morph pattern can smoothly transform across all its configuration states, (ii) characterize the configuration space of the Morph pattern with distinguishing paths for different sets of hybrid states, and (iii) derive the condition for Poisson’s ratio switching and explain the mode-locking phenomenon in the Morph pattern when subjected to in-plane deformation as a result of the inter-play between local and global kinematics.

Importance of Unit Cells in Accurate Evaluation of the Characteristics of Graphene

2016 ◽  
Vol 71 (4) ◽  
pp. 315-320 ◽  
Author(s):  
Hassan Sabzyan ◽  
Narges Sadeghpour
Keyword(s):  
Electric Field ◽  
Density Functional ◽  
Unit Cell ◽  
Atomic Charges ◽  
Dft Methods ◽  
Functional Theory ◽  
Accurate Evaluation ◽  
Unit Cell Size ◽  
Unit Cells ◽  
Cell Energy

AbstractEffects of the size of the unit cell on energy, atomic charges, and phonon frequencies of graphene at the Γ point of the Brillouin zone are studied in the absence and presence of an electric field using density functional theory (DFT) methods (LDA and DFT-PBE functionals with Goedecker–Teter–Hutter (GTH) and Troullier–Martins (TM) norm-conserving pseudopotentials). Two types of unit cells containing nC=4–28 carbon atoms are considered. Results show that stability of graphene increases with increasing size of the unit cell. Energy, atomic charges, and phonon frequencies all converge above nC=24 for all functional-pseudopotentials used. Except for the LDA-GTH calculations, application of an electric field of 0.4 and 0.9 V/nm strengths does not change the trends with the size of the unit cell but instead slightly decreases the binding energy of graphene. Results of this study show that the choice of unit cell size and type is critical for calculation of reliable characteristics of graphene.

scholarly journals Modal Analysis of a Circular Slot Monopole Antenna for UWB application

2019 ◽  
Vol 18 (3) ◽  
pp. 34-43
Author(s):  
Adamu Halilu Jabire ◽  
Anas Abdu ◽  
Salisu Sani ◽  
Sani Saminu ◽  
Aliu Uba Taura ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Time Domain ◽  
Monopole Antenna ◽  
Slot Antenna ◽  
Design Stage ◽  
Radiation Characteristics ◽  
Characteristic Mode ◽  
Physical Insight ◽  
The Time Domain ◽  
Antenna Model

 In this study, a wideband double slot antenna is introduced. The proposed monopole antenna is designed using the theory of characteristic mode for slot monopoles. A circular shape is used as the initial design stage, to enhance the bandwidth, two circular slots are employed. Four modes have been excited to gain a physical insight and to find out which mode is dominant. The design and analysis were completed utilizing both the time domain and multilayer solver in CST 2017, without considering the feeding port. An antenna model in UWB frequency is constructed. Experimented and simulated results shows that the proposed planar structure has a wide impedance width with good radiation characteristics.

scholarly journals Metamaterial superstrate microstrip patch antenna for 5G wireless communication based on the theory of characteristic modes

2019 ◽  
Vol 70 (3) ◽  
pp. 187-197
Author(s):  
Ehab K. I. Hamad ◽  
Ahmed Abdelaziz
Keyword(s):  
Wireless Communication ◽  
Patch Antenna ◽  
Split Ring Resonator ◽  
Microstrip Antennas ◽  
Unit Cell ◽  
Dual Band ◽  
Mode Analysis ◽  
Electromagnetic Properties ◽  
Characteristic Mode ◽  
Antenna Structure

Abstract Metamaterials (MTMs) have received considerable attention due to their novel electromagnetic properties. Their applications include enhancing gain and bandwidth in microstrip antennas. In this article, a dual band microstrip antenna design based on characteristic mode analysis (CMA) using MTM superstrate is proposed for 5G wireless communication. The CMA is used for the modelling, analysis and optimization of the proposed antenna to examine the underlying modal behaviour of the MTM unit cell and to guide mode excitation. The antenna structure consists of a microstrip feed line connected to a rectangular patch. Then triangular split ring resonator unit cell is inserted on the ground of a traditional patch antenna that resonates at 15 GHz to produce additional resonance at 10 GHz. A planar array of 2 × 3 triangle MTM unit cells is used as superstrate to improve the gain and bandwidth at both resonances simultaneously. The optimal distance between MTM superstrate and the antenna patch is determined using the Fabry-Perot cavity theory to maximize power directivity and efficiency of the proposed antenna. The CST microwave studio software is used to model and optimize the proposed antenna. A prototype of the designed antenna that was fabricated showed good agreement between measurement and simulation results.

Design of Disordered Periodic Structures for Mode Localization

2017 ◽  
Author(s):  
Gabriele Cazzulani ◽  
Emanuele Riva ◽  
Edoardo Belloni ◽  
Francesco Braghin
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Unit Cell ◽  
Band Gaps ◽  
Mode Shapes ◽  
Mode Localization ◽  
Geometrical Properties ◽  
Unit Cells ◽  
The Mean ◽  
Propagation Properties

Periodic structures are the repetition of unit cells in space, that provide a filtering behavior for wave propagation. In particular, it is possible to tailor the geometrical, physical and elastic properties of the unit cells, in order to attenuate certain frequency bands, called band-gaps or stop-bands. Having each element characterized with the same parameters, the filtering behavior of the system can be described through the wave propagation properties of the unit cell. This is technologically impossible to obtain, therefore the Lyapunov factor is used, in order to define the mean attenuation of a quasi-periodic structure. Tailoring Gaussian unit cell properties potentially allows to extend the stop-bands width in the frequency domain. A drawback is that some unexpected resonance peaks may lie in the neighborhood of the extended regions. However, the correspondent mode-shapes are localized in a particular region of the structure, and they partially decrease the global attenuating behavior. In this paper, the aperiodicity introduced in the otherwise perfect repetition is investigated, providing an explanation for the mode-localization problem and for the stop-bands extension. Then, the proposed approach is applied to a passive quasi-periodic beam, characterized from a localized peak within a designed band-gap. The geometrical properties of its aperiodic parts are changed in order to deterministically move the localization peak in the frequency response. Numerical and experimental results are compared.

scholarly journals Design of a Dual-Band Frequency Reconfigurable Patch Antenna Based on Characteristic Modes

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Zakaria Mahlaoui ◽  
Eva Antonino-Daviu ◽  
Adnane Latif ◽  
Miguel Ferrando-Bataller
Keyword(s):  
Patch Antenna ◽  
Ground Plane ◽  
Design Procedure ◽  
Dual Band ◽  
Mode Analysis ◽  
Characteristic Mode ◽  
Band Frequency ◽  
Lower Band ◽  
Varactor Diodes ◽  
Characteristic Modes

A frequency reconfigurable patch antenna design based on the characteristic mode analysis is presented. The antenna presents a reconfigurable lower band and a steady band at higher frequencies. A slot is etched on the ground plane of the antenna, where two varactor diodes are placed on each side of the slot in order to tune the lower band. The first resonant frequency shifts down by varying the reverse voltage of the varactor, whereas the second operating frequency keeps stable. The proposed antenna is designed to cover WLAN bands, offering a first band operating at 2 GHz and a second band ranging from 5.3 GHz to 5.8 GHz. A prototype has been fabricated and measurements are provided, which validate the proposed analysis, method, and design procedure.

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