Güllü Kızıltaş

Topology design optimization of dielectric substrates for bandwidth improvement of a patch antenna

Most literature studies dealing with design optimization for RF applications focused to a large extend on size and shape optimization. So far, material and topology optimization has not been pursued primarily due to the challenges associated with the fabrication of inhomogeneous materials and the limited access to analysis tools. In this paper, we focus on optimum topology/material design of dielectric substrates for bandwidth enhancement of a simple patch antenna. First, the possibility of designing arbitrary dielectric constant materials using off-the-shelf dielectrics is presented as is necessary for the practical fabrication of inhomogeneous substrates. Then, a formal design optimization procedure is conducted using the solid isotropic material with penalization (SIMP) method by relying on a fast full wave finite element-boundary integral (FE-BI) simulator. The SIMP method is a mathematically well-posed topology optimization algorithm because a continuous density function is used to relate the cell variable to the actual material properties. This also allows for a formulation in a versatile optimization framework. Sequential linear programming (SLP) is used to solve the nonlinear optimization procedure with the sensitivity analysis based on the adjoint variable method. An important advantage of the proposed design optimization approach is its generality to handle multiple objectives and multidisciplinary problems. Using the proposed automated design procedure, inhomogeneous substrates are designed which allow for 250% bandwidth enhancement of the square patch antenna. Typically, only a few iterations are needed to reach convergence. Finally, the designed substrate is post-processed with image processing and fabricated using thermoplastic green machining.

Polymer–Ceramic Composites for Microwave Applications: Fabrication and Performance Assessment

We present a novel technique to fabricate conformal and pliable substrates for microwave applications including systems-on-package. The produced materials are fabricated by combining ceramic powders with polymers to generate a high-contrast substrate that is concurrently pliable (bendable). Several such polymer-ceramic substrates are fabricated and used to examine the performance of a patch antenna and a coupled line filter. This paper presents the substrate mixing method while measurements are given to evaluate the loss performance of the substrates. Overall, the fabricated composites lead to flexible substrates with a permittivity of up to epsivr=20 and sufficiently low loss

Metamaterial design via the density method

We use the density/SIMP (solid isotropic material with penalization) method to design metamaterials for frequency selective surfaces/volumes. It is shown that significant improvement is attained by optimization of the material permittivity. The generality, low number of iterations and the simplicity of the demonstrated approach motivate application of the method for other microwave structures.

Antenna Miniaturization Using Magnetic-Photonic and Degenerate Band-Edge Crystals

Engineered materials, such as new composites and electromagnetic bandgap and periodic structures have been of strong interest in recent years, due to their extraordinary and unique electromagnetic behaviors. This paper discusses how modified materials, inductive/capacitive lumped loads, and magnetic materials/crystals are impacting antenna miniaturization and performance improvements (e.g., bandwidth and gain reduction, multi-functionality, etc.). Dielectric design and texturing for impedance matching has led to significant size reduction and higher-bandwidth low-frequency antennas, for example. The recently introduced magnetic-photonic crystals (MPCs) and double band-edge (DBE) materials, displaying spectral nonreciprocity, are also discussed. Studies of these crystals demonstrated that magnetic-photonic crystals exhibit the interesting phenomena of (a) drastic slowing down of the incoming wave, coupled with (b) significant amplitude growth, while (c) maintaining minimal reflection at the interface with free space. The phenomena are associated with diverging frozen modes that occur around the stationary inflection points within the band diagram. Taking advantage of the frozen-mode phenomena, we demonstrate that individual antenna elements and linear or volumetric arrays embedded within the magnetic-photonic crystal and double band-edge structures allow for antenna sensitivity and gain enhancements

SURALP: A new full-body humanoid robot platform

SURALP is a new walking humanoid robot platform designed at Sabanci University - Turkey. The kinematic arrangement of the robot consists of 29 independently driven axes, including legs, arms, waist and a neck. This paper presents the highlights of the design of this robot and experimental walking results. Mechanical design, actuation mechanisms, sensors, the control hardware and algorithms are introduced. The actuation is based on DC motors, belt and pulley systems and Harmonic Drive reduction gears. The sensory equipment consists of joint encoders, force/torque sensors, inertial measurement systems and cameras. The control hardware is based on a dSpace digital signal processor. A smooth walking trajectory is generated. A variety of controllers for landing impact reduction, body inclination and Zero Moment Point (ZMP) regulation, early landing trajectory modification, and foot-ground orientation compliance and independent joint position controllers are employed. A posture zeroing procedure is followed after manual zeroing of the robot joints. The experimental results indicate that the control algorithms presented are successful in improving the stability of the walk.

A Multi-criteria Design Optimization Framework for Haptic Interfaces

This paper presents a general framework for optimization of haptic interfaces, in particular for haptic interfaces with closed kinematic chains, with respect to multiple design objectives, namely kinematic and dynamic criteria. Both performance measures are discussed and optimization problems for a haptic interface with best worst-case kinematic and dynamic performance are formulated. Non-convex single objective optimization problems are solved with a branch-and-bound type (culling) algorithm. Pareto methods characterizing the trade-off between multiple design criteria are advocated for multi-criteria optimization over widely used scalarization approaches and Normal Boundary Intersection method is applied to efficiently obtain the Pareto-front hyper-surface. The framework is applied to a sample parallel mechanism (five-bar mechanism) and the results are compared with the results of previously published methods in the literature. Finally, dimensional synthesis of a high performance haptic interface utilizing its Pareto-front curve is demonstrated.

Topology optimization of dielectric substrates for filters and antennas using SIMP

SummaryIn this paper a novel design procedure based on the integration of full wave Finite Element Analysis (FEA) and a topology design method employing Sequential Linear Programming (SLP) is introduced. The employed design method is the Solid Isotropic Material with Penalization (SIMP) technique formulated as a general non-linear optimization problem. SLP is used to solve the optimization problem with the sensitivity analysis based on the adjoint variable method for complex variables. A key aspect of the proposed design method is the integration of optimization tools with a fast simulator based on the finite element-boundary integral (FE-BI) method. The capability of the design method is demonstrated by two design examples. First, we developed a metamaterial substrate with arbitrary material composition and subject to a pre-specified antenna bandwidth enhancement. The design is verified and its performance is evaluated via measurements and simulation. As a second example, the material distribution for a Thermo-Photovoltaic (TPV) filter subject to pre-specified bandwidth and compactness criteria is designed. Results show that the proposed design method is capable of designing full three-dimensional volumetric material textures and printed conductor topologies for filters and patch antennas with enhanced performance.

Multi-criteria Design Optimization of Parallel Robots

This paper presents a framework for multi-criteria design optimization of parallel mechanisms. Pareto methods characterizing the trade-off between multiple design criteria are advocated for multi-criteria optimization over widely used scalarization approaches and Normal Boundary Intersection method is applied to efficiently obtain the Pareto-front hyper-surface. The proposed framework is compared against sequential optimization and weighted sum approaches. Dimensional synthesis of a sample parallel mechanism (five-bar mechanism) is demonstrated through estimation of the relative weights of performance indices that are implicit in the Pareto plot. The framework is computational efficient, applicable to any set of performance indices, and extendable to include any number of design criteria that is required by the application.

Design of a frequency selective structure with inhomogeneous substrates as a thermophotovoltaic filter

In this paper, the design of a thermophotovoltaic (TPV) filter with high-pass characteristics is presented. The filter is in the form of a frequency selective structure (FSS) with cascaded inhomogeneous dielectric substrates. The goal is to allow for more design flexibility using dielectric periodic structures to deliver a sharper filter response. Therefore, the primary focus is to design a periodic material substrate composition (supporting FSS elements) using a topology optimization technique known as the density method. The design problem is formulated as a general nonlinear optimization problem and sequential linear programming is used to solve the optimization problem with the sensitivity analysis based on the adjoint variable method for complex variables. A key aspect of the proposed design method is the integration of optimization tools with a fast simulator based on the finite element-boundary integral method. The capability of the design method is demonstrated by designing the material distribution for a TPV filter subject to pre-specified bandwidth and compactness criteria.

Textured LTCC substrates for printed antenna miniaturization and bandwidth improvement

The use of textured low temperature cofiring ceramics (LTCC) substrates for printed antennas is presented. An aperture fed patch antenna resonating at 1.56 GHz is developed and analyzed. This antenna has a volume reduction by a factor of 10 as compared to patches on traditional dielectrics. Moreover, measurements of the gain and return loss show that miniaturization has remarkably little effect on the gain value and bandwidth.