Topological Optimization Framework for the Automated Design of 3D Printable THz Lens Antennas

In the present paper, a model for growth of elastic bodies is proposed for purposes of shape and topology optimization. Growth of solid bodies is herewith considered in the framework of topology and shape optimization, with the goal of mimicking the natural generation of both stiff and light biological structures, consisting of a solid skeleton immersed into a softer phase. The growth process is modeled as the nucleation and subsequent growth of islands of a hard elastic phase within a softer elastic matrix, which plays the role of a reservoir of nutrients for the supply of the newly generated material. Islands of the generated solid skeleton are modeled as balls of small radius, and the position of their center is determined in such a way that the effective compliance, the product of the compliance by the relative density of the hard phase, is minimal for each new generation event. A growth model is set up from the mass balance with a source term involving the growth rate of mass, taken as a constant. The modeling of the growth process relies on the evaluation of the topological derivative of the effective compliance, which allows finding the optimal position of the center of new inclusions of the generated hard phase. This nucleation process is then followed by the shape optimization of the growing solid bodies. A proper mathematical formulation of the topology and shape optimization of growing elastic solid body is provided, relying on a domain decomposition technique allowing to replace the singularly perturbed geometrical domain by a regularly perturbation of Steklov-Poincaré operator. As an enrichment of this model, surface energy is lastly considered in the framework of a linear elastic constitutive model with surface stress.

In this chapter, we review several aspects of the analysis and the design of multi-shell spherical and circular cylindrical lens antennas. Such lens antennas are attractive for implementation in communication and radar systems, in particular in the millimeter-wave frequency band, due to their broadband behavior, excellent focusing properties, possibility of beam scanning, and the ability to form multiple beams. In order to develop an efficient analysis tool, needed for successful design of multi-shell lens antennas, we first demonstrate the principles of the analysis algorithm for calculating the EM field distribution in general multilayer structures (i.e., inside a structure with an arbitrary number of layers). This algorithm is designed for spherical and circular-cylindrical geometries with elementary excitation. To model realistic lens antennas, we introduce additional flexibility that allows the analysis of actual feed antennas that usually do not follow the symmetry properties of the lens. Finally, by connecting the algorithm with an optimization subroutine, a powerful analysis and design tool is created. All the aspects of the proposed analysis approach are explained and illustrated with examples. Furthermore, some practical problems which are encountered in the design of these types of lens antennas are highlighted and common solutions are presented and compared to the ideal situations.

We present a sequential topology and shape optimization framework to design compliant mechanisms with boundary stress constraints. In our approach, a density-based topology optimization method is used to generate the configuration of the mechanisms. Afterwards, a node-based shape optimization is invoked to obtain an exact boundary representation. A specialized, optimality criteria-based design update is formulated for the shape optimization. To avoid impractical hinges with point connections, stress constraints are imposed. The stress constraints are imposed using two strategies: Local stress constraints on the nodes of the boundary or global P-norm stress constraints in the domain. Further, an adaptive shape refinement strategy is adopted to increase the design space of shape optimization and to capture the fine-scale details of the geometry. Finally, numerical experiments are presented, showing that the proposed approach can be effectively applied to the design of compliant mechanisms with stress constraints.

Dispersion engineering is always the important topic in the field of artificial periodic structures. In particular, topology optimization of composite structures with expected bandgaps plays a key role. However, most reported studies focused on topology optimization for bulk waves, and the optimization for surface wave bandgaps (SWBGs) is still missing. In this paper, we develop a topology optimization framework based on the genetic algorithm and finite element method to design periodic barriers embedded in semi-infinite space for reducing surface waves on demand. The objective functions for SWBGs are proposed based on the energy distribution properties of surface waves. The numerical results show that the optimization framework has stable convergence for this problem and is effective to optimize SWBGs. Considering large SWBGs and low filling fraction of solids, we investigate single- and multi-objective optimizations, respectively, and obtain novel wave barriers with good performance. The beneficial configuration features and mechanism of broadband SWBGs from the optimized results are explored. The results indicate that for the first-order SWBG, most optimized structures consist of a main scatterer at the center and some subsidiary scatterers near the surface. The rigid body resonance of the main scatterer determines the lower edge of SWBG, and the subsidiary scatterers can regulate the upper edge. Higher-order SWBGs are generated from the interaction of multiple scatterers, whose relative distance has a great influence on the position of SWBGs. The optimized structures can make the surface waves propagate far away from the surface within the frequencies of bandgaps, leading to a strong attenuation of surface vibration. In practice, our topological optimization framework is promising in designing high-performance surface wave devices and novel isolating structures for earthquake or environmental vibration in civil engineering.

Some proposed satellite-based mobile communication systems require multibeam systems at millimeter-wave frequencies. This is a primary factor in the renewed interest in Luneberg lenses. Luneberg (1944) lenses prove useful in a variety of antenna and scattering applications. In antenna applications, their chief advantages are an ability to form multiple beams that may point in arbitrary directions, and their broadband behavior. Lens weight, and complexities involved in manufacturing such lenses, remain their primary drawbacks. Unfortunately, no significant advances in the fabrication techniques have come to pass in forty years. However, operation at millimeter-wave frequencies makes the lens weight inconsequential. The vast majority of the research on spherical lenses took place before computers were commonplace in antenna design. The author reviews some of the applications of Luneberg lenses, and adds some more recent data, generated using a numerical model. >

This paper presents the novel design of an ultrawideband (UWB) antipodal Vivaldi antenna using periodic elliptical slots (PES-AVA) for microwave and radar imaging applications. Further, the high permittivity (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> =10.2) dielectric lens which triangular in shaped is introduced in-front (PESAVA-D) to improve the linear polarization performance, gain as well as directivity of the antenna. The antenna design and its optimization process offer good outcomes by using low-cost substrate material, fiberglass reinforced grade 4 (FR4) with a thickness of 1.57mm and permittivity of (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> =4.3) respectively. The (PES-AVA) antenna design produces the average effects of gain (5-9dB) and directivity of (5-10dBi). However, the addition of the triangular-shaped dielectric lens placed in front of an antenna is able to improve the peak gain up to 10.6dB with 11.9dBi in directivity. The radiation patterns of the proposed antenna have been also improved by using the dielectric lens where the magnitude of the main lobe is larger than (PES-AVA). Around 2dB improvements in gain at different UWB frequency level with better directivity using the dielectric lens with antenna (PES-AVA-D) as compared to regular (PES-AVA). The dimension of the proposed antenna is 60.75mm x 66mm approximately. The designed antenna operates with in frequency range of (3GHz-to-10GHz). The structural layout and comparative validation of (PES-AVA) with or with-out dielectric lens have been certified using CST simulation software.

Transient sensitivity analysis and topology optimization of particle suspended in transient laminar fluid

In this paper we present the design of a dielectric flat lens antenna to operate in the 60 GHz band for WPAN applications. In order to overcome the specific atmospheric attenuation, which characterizes the propagation in the 60 GHz band, high directive antennas are required. Moreover, due to high user random mobility in indoor environments, beam-steerable antennas are also needed. For these reasons, we propose a design based on a dielectric flat lens antenna with scanning capabilities from -30° to +30° with around 20 dB of gain in the whole entire band of interest (57 to 66 GHz), and up to ±60° of beam-steering capabilities with around 15 dB of gain. The dielectric flat lens also leads to low-profile antenna configuration, easy to manufacture and low-cost, in order to integrate the design together with a commercial RF CMOS chip.

Cube satellites (CubeSats) have become increasingly popular in recent years due to their cost-effectiveness and the rapid production capabilities enabled by commercial off-the-shelf components. This research comprehensively reviews 45 antenna designs for CubeSats operating in high-frequency bands, specifically the Ku, K, and Ka bands. Among the antennas reviewed are fourteen patch and patch array antennas, one slot antenna, two leaky wave antennas, three array antennas, seven reflector antennas, eight reflectarray antennas, three metasurface antennas, four cavity-backed antennas, one helical antenna, one lens antenna, and one horn antenna. These antennas are evaluated based on performance parameters such as gain, bandwidth, reflection coefficient, CubeSat size, and deployability to determine which designs suit the limited space available on CubeSats. Particular attention is given to the challenges in designing CubeSat antennas, including achieving high gain, broad bandwidth, multi-band capability, low profile, and circular polarization. This research aims to enhance our understanding by identifying high-frequency antenna designs that may benefit future CubeSat missions.

Lens antenna is a good substitute for the Cassegrain antenna at millimeter-wave frequencies, especially at W-band. On one hand, the antenna design, which is bulky and heavy at low frequencies, becomes compact and light-weighted at W-band. On the other hand, without the blockage caused by the sub-reflector and the feed horns which are unavoidable in a Cassegrain antenna, the lens antennas show better radiation characteristics. In this paper, several lens antennas fed by metal horns are analyzed using a full-wave method-finite element method based on the weak form of the Helmholtz equation (WF-FEM). Numerical results show that the lens antennas presented have low side lobe level (SLL), and good sum and difference performances.

This research focuses on the improvement of porosity distribution within the electrode of an all‐vanadium redox flow battery (VRFB) and on optimizing novel cell designs. A half‐cell model, coupled with topology and shape optimization framework, is introduced. The multiobjective functional in both cases aims to minimize pressure drop while maximizing reaction rate within the cell. Topology optimization results reveal dependencies on initial value, porosity constraint, and flow rate. The distribution with lower porosity is preferred downstream of the inlet manifold. This design enhances active surface area, thus facilitating more effective conversion of incoming educts and improving mass transport of products. Compared to homogeneous electrodes, two‐part design demonstrates superior performance at specific porosity values. For combined porosities of 0.7 and 0.95, optimized distribution results in 81 % reduction in pressure drop, while conversion rate decreases by 7%. As regards various cell designs, optimization suggests a need to reconsider the vertical format of a rectangular cell. Horizontal cells are favored for nearly all porosities and flow rates. Trapezoidal and radial designs characterized by reduced downstream cross sections lead to higher pressure drops and are not preferred. This work provides further valuable insight into optimizing VRFB electrodes and challenges conventional cell design assumptions.

Luneburg lens antenna radiation field is calculated with Green's functions of a layered cylindrical structure. Electric field components of Luneburg lens excited by electric and magnetic dipoles, Huygens source and a circularly polarized antenna formed by two crossed electric dipoles with 90-degree phase shift are considered. Electric field calculation for the Luneburg lens antenna in the far zone is simplified by saddle-point method. Radiation patterns are shown. The influence of an outer cylinder radius and number of layers on radiation efficiency is investigated. Polarization properties of a cylindrical Luneburg lens excited by a source with circular wave polarization are analyzed. The proposed method significantly reduces computing time for multilayered lens in comparison with the most commonly used in antenna design.

A new class of irregularly shaped dielectric lens antennas with a supershaped microstrip antenna feeder is presented and detailed in this work. The surface of the lens antenna and the feeder shape have been modelled by using the three and two-dimensional Gielis formula, respectively. The antenna design has been carried out by integrating an home-made software tool with the CST Microwave Studio®. The radiation properties of the whole antenna system have been evaluated using a dedicated high-frequency technique based on the tube tracing approximation. Moreover, the effects due to the multiple internal reflections have been properly modeled. The proposed model was applied to study unusual and complex lens antenna systems with the aim to design special radiation characteristics.

Thermal interface resistance remains a bottleneck for thermal transport in electronic systems, comprising a significant portion of overall system thermal resistance. Performance of thermal interface materials (TIMs) is largely dependent on the bulk thermal conductivity of the TIM but also on the bond-line thickness (BLT) of the applied material as well as interfacial contact resistances. Recently, Hierarchically Nested Channels (HNCs), created by modifying the surface topology with hierarchical arrangements of microchannels in order to improve flow, were proposed to reduce both required squeezing force and final BLTs in interfaces. In this paper, a topological optimization framework that enables the design of channel arrangements is developed. The framework is based on a resistance network approximation to Newtonian squeeze flow. The approximation, validated against finite element method (FEM)-based solutions, allows efficient, design-oriented solutions for squeeze flow in complex geometries. A comprehensive design sensitivity analysis exploiting the resistance network approximation is also developed and implemented. The resistance approximation and the sensitivity analysis is used to build an automated optimal channel design framework. A Pareto optimal problem formulation for the design of channels is posed and the optimal solution is demonstrated using the framework.

Efficiency improvement is of great significance for simulation-driven antenna design optimization methods based on evolutionary algorithms (EAs). The two main efficiency enhancement methods exploit data-driven surrogate models and/or multi-fidelity simulation models to assist EAs. However, optimization methods based on the latter either need ad hoc low-fidelity model setup or have difficulties in handling problems with more than a few design variables, which is a main barrier for industrial applications. To address this issue, a generalized three stage multi-fidelity-simulation-model assisted antenna design optimization framework is proposed in this paper. The main ideas include introduction of a novel data mining stage handling the discrepancy between simulation models of different fidelities, and a surrogate-model-assisted combined global and local search stage for efficient high-fidelity simulation model-based optimization. This framework is then applied to SADEA, which is a state-of-the-art surrogate-model-assisted antenna design optimization method, constructing SADEA-II. Experimental results indicate that SADEA-II successfully handles various discrepancy between simulation models and considerably outperforms SADEA in terms of computational efficiency while ensuring improved design quality. Highlights An EFFICIENT antenna design global optimization method for problems requiring very expensive EM simulations. A new multi-fidelity surrogate-model-based optimization framework to perform RELIABLE efficient global optimization A data mining method to address distortions of EM models of different fidelities (bottleneck of multi-fidelity design).