Browsing by Subject "Materials science"

Now showing 1 - 9 of 9

Open Access
A perspective on plant robotics: from bioinspiration to hybrid systems
(IOP Publishing Ltd., 2022-11-25) Meder, F.; Baytekin, Bilge; Dottore, E. D.; Meroz, Y.; Tauber, F.; Walker, I.; Mazzolai, B.
As miscellaneous as the Plant Kingdom is, correspondingly diverse are the opportunities for taking inspiration from plants for innovations in science and engineering. Especially in robotics, properties like growth, adaptation to environments, ingenious materials, sustainability, and energy-effectiveness of plants provide an extremely rich source of inspiration to develop new technologies—and many of them are still in the beginning of being discovered. In the last decade, researchers have begun to reproduce complex plant functions leading to functionality that goes far beyond conventional robotics and this includes sustainability, resource saving, and eco-friendliness. This perspective drawn by specialists in different related disciplines provides a snapshot from the last decade of research in the field and draws conclusions on the current challenges, unanswered questions on plant functions, plant-inspired robots, bioinspired materials, and plant-hybrid systems looking ahead to the future of these research fields.
Open Access
Characterization and tilted response of a fishnet metamaterial operating at 100 GHz
(Institute of Physics Publishing Ltd., 2008) Alici, K. B.; Özbay, Ekmel
We numerically and experimentally investigate a fishnet metamaterial operating at around 100 GHz. Qualitative effective medium theory and standard retrieval characterization methods are performed to demonstrate the double negative nature of the fishnet structure. This study is extended to include the effects of a finite number of unit cells at each layer and the number of layers in the propagation direction. Finally, we study the response of the metamaterial layer when the metamaterial plane normal and the propagation vector are not parallel.
Open Access
Development of micro-structured metamaterials for innovative antenna layouts
(IEEE, 2007) Bilotti F.; Capolino F.; Gonzalo, R.; Özbay, Ekmel; Romeu J.; Schuchinsky, A.; Tretyakov, S.; Vardaxoglou, Y.
In this paper, we present the joint activities developed in the frame of the FP6 European Network of Excellence METAMORPHOSE in the field of new micro-structured materials for antenna applications. One of the key scientific goals of the research efforts developed within this network is to design innovative micro-structured materials to improve the performances of conventional radiators. Miniaturization, multi-functionality, reduced interference with electronic circuitry, are some of the main challenges in the design of antennas for the next generation of electronic transceivers in the microwave frequency range. The employment of different classes of metamaterials in innovative antenna layouts has been demonstrated to be effective to reach most of the desired goals. The theoretical, numerical and experimental efforts carried out by the leading European institutions working in this field, in fact, show how metamaterial antennas with unusual features are ready to push the innovation in the antenna research. The collaborative dimension of this research is described in this paper, as well as the related scientific achievements. © 2007 EuMA.
Open Access
Experimental observation of cavity formation in composite metamaterials
(Optical Society of American (OSA), 2008) Caglayan H.; Bulu I.; Loncar, M.; Özbay, Ekmel
In this paper, we investigated one of the promising applications of left-handed metamaterials: composite metamaterial based cavities. Four different cavity structures operating in the microwave regime were constructed, and we observed cavity modes on the transmission spectrum with different quality factors. The effective permittivity and permeability of the CMM structure and cavity structure were calculated by use of a retrieval procedure. Subsequently, in taking full advantage of the effective medium theory, we modeled CMM based cavities as one dimensional Fabry-Perot resonators with a subwavelength cavity at the center. We calculated the transmission from the Fabry-Perot resonator model using the one-dimensional transfer matrix method, which is in good agreement with the measured result. Finally, we investigated the Fabry-Perot resonance phase condition for a CMM based cavity, in which the condition was satisfied at the cavity frequency. Therefore, our results show that it is possible to treat metamaterial based cavities as one-dimensional Fabry-Perot resonators with a subwavelength cavity. © 2008 Optical Society of America.
Open Access
Location and visualization of working p-n and/or n-p junctions by XPS
(Nature Publishing Group, 2016) Copuroglu, M.; Caliskan, D.; Sezen, H.; Özbay, Ekmel; Süzer, Şefik
X-ray photoelectron spectroscopy (XPS) is used to follow some of the electrical properties of a segmented silicon photodetector, fabricated in a p-n-p configuration, during operation under various biasing configurations. Mapping of the binding energy position of Si2p reveals the shift in the position of the junctions with respect to the polarity of the DC bias applied. Use of squared and triangular shaped wave excitations, while recording XPS data, allows tapping different electrical properties of the device under normal operational conditions, as well as after exposing parts of it to harsh physical and chemical treatments. Unique and chemically specific electrical information can be gained with this noninvasive approach which can be useful especially for localized device characterization and failure analyses.
Open Access
MLFMA solutions of transmission problems Involving realistic metamaterial walls
(IEEE, 2007-08) Ergül, Özgür; Ünal, Alper; Gürel, Levent
We present the solution of multilayer metamaterial (MM) structures containing large numbers of unit cells, such as split-ring resonators. Integral-equation formulations of scattering problems are solved iteratively by employing a parallel implementation of the multilevel fast multipole algorithm. Due to ill-conditioned nature of the problems, advanced preconditioning techniques are used to obtain rapid convergence in the iterative solutions. By constructing a sophisticated simulation environment, we accurately and efficiently investigate large and complicated MM structures. © 2007 IEEE.
Open Access
Negative phase advance in polarization independent, multi-layer negative-index metamaterials
(Optical Society of American (OSA), 2008) Aydın, Koray; Zhaofeng, Li; Şahin, Levent; Özbay, Ekmel
We demonstrate a polarization independent negative-index metamaterial (NIM) at microwave frequencies. Transmission measurements and simulations predict a left-handed transmission band with negative permittivity and negative permeability. A negative-index is verified by using the retrieval procedure. Effective parameters of single-layer and twolayer NIMs are shown to be different. Negative phase advance is verified within the negative-index regime by measuring the phase shift between different sized negative-index metamaterials. Backward wave propagation is observed in the numerical simulations at frequencies where the phase advance is negative. ©2008 Optical Society of America.
Open Access
Negative refraction and subwavelength focusing using left-handed composite metamaterials
(SPIE, 2008-01) Özbay, Ekmel; Aydın, Koray
We review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ, through a flat LHM superlens.
Open Access
Solutions of large integral-equation problems with preconditioned MLFMA
(IEEE, 2007) Ergül, Özgür; Malas, Tahir; Ünal, Alper; Gürel, Levent
We report the solution of the largest integral-equation problems in computational electromagnetics. We consider matrix equations obtained from the discretization of the integral-equation formulations that are solved iteratively by employing parallel multilevel fast multipole algorithm (MLFMA). With the efficient parallelization of MLFMA, scattering and radiation problems with millions of unknowns are easily solved on relatively inexpensive computational platforms. For the iterative solutions of the matrix equations, we are able to obtain accelerated convergence even for ill-conditioned matrix equations using advanced preconditioning schemes, such as nested preconditioned based on an approximate MLFMA. By orchestrating these diverse activities, we have been able to solve a closed geometry formulated with the CFIE containing 33 millions of unknowns and an open geometry formulated with the EFIE containing 12 millions of unknowns, which are the largest problems of their classes, to the best of our knowledge.