Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"JUSTYNA GARUS"

The creation and shifts of band gaps in binary superlattices


  Superlattices are intensively tested materials [1÷24], the filtering capabilities are particularly attractive [21]. Multilayers are characterized by the presence of the photonic band gap, so that electromagnetic waves (EMW) at the specific frequencies does not propagate them. Using emulation properties of multilayer systems allows pretesting of the structure and the design to get the specific characteristics of the electromagnetic wave transmission bands. This reduces the number of samples performed and reduces the cost of examinations. Transmission superlattices are calculated using the matrix method [18÷21] and by the method of finite-difference in the time domain for one-dimensional structures (1D FDTD) [22, 25]. MATRIX METHOD The transmission of the multilayer structure is calculated from the following equation: 2 out out in in 11 T n cos 1 n cos [...]

Effect of point defects in a two-dimensional phononic crystal on the reemission of acoustic wave


  Phononic crystals (PC) in a rather broad sense are synthetic materials with periodically changing acoustic properties of the medium (eg. density and speed of propagation of the acoustic wave) and have been recently intensively investigated due to the wide application range as well as interesting physical properties of these systems [1]. In spite of considerable simplicity of the construction of such materials they enable the construction of frequency filters that will allow to suppress undesired frequencies. In some cases, with proper distribution of repetitive elements making up the crystal, PC allow to create sound barriers in any band of acustic spectrum. Certain frequency ranges which are subject to strong damping, i.e. when the phonons do not propagate through the crystal, are called phononic band gaps. Significant impact on the parameters of phononic crystals has location and the distance between the periodic components, which by the appropriate arrangement are allowing to modify the center frequency of the pass-filter, and thus adjust the position of band gap [2]. If the distance between these components are comparable to the acoustic wavelength of the incident wave, and the top layer of PC will be uniform across the width, the acoustic wave will leave the crystal plane with very good convergence even at considerable large distances from the sound source. This allows the construction of the so-called. directional speakers and opens wide possibilities of commercial use in many applications ranging from medicine up to military applications. Figure 1 shows the typical structure of two-dimensional PC. Fig. 1. Typical phononic crystal structure 1 - first material; 2 - second material: d - diameter of periodic element, a, b - distances between element centers Rys. 1. Typowa struktura kryształu fononicznego 1 - materiał pierwszy, 2 - materiał drugi: d - średnica części periodycznej, a, b - odległości między środkami elementów[...]

The impact of manufacturing inaccuracies on the filtration properties of Thue-Morse aperiodic superlattice systems


  Multilayers constructed with advanced composite materials are used in solid state physics, optoelectronics, optics and modern photonics [1÷8]. This refers mainly to the ongoing work on photonic crystals [9÷15], optical fiber photonics [16], quasicrystals [17÷24] and multilayer structures [5, 25÷30]. By superlattice we mean alternating layers constructed with differing properties of suitable topological configuration of the constituent components. Prediction by Veselago [31] in 1968 materials, which characterized by a negative refractive index, and the first experimental confirmation of their existence in the year 2000 [32] led to increased research on interesting properties of these structures [33÷39]. Thanks to high technology of multilayer systems production with specified configuration, the types of materials and layer thicknesses [40÷44] and the presence of the photonic band gap has become possible to design an applicationspecific materials. Consequently, it has become reasonable to carry out possible most detailed simulation of specific properties for multilayer structures, escpecialy the transmission properties which are the subject of research in this paper. In order to investigate the transmission properties of the superlattice, two most commonly used methods which are complementary to each other are used. The first one known as finite difference time domain method (FDTD) [39] is based on the study of the behaviour of electromagnetic waves described by differential Maxwell equations using an iterative algorithm. Fast Fourier Transform (FFT) [39] made simultaneously with the simulation, allows to determine the frequency characteristics of wave leaving test structure. The use of the matrix method allows to obtain of more information on the electromagnetic wave transmission by multilayer medium, which is made of layers of dielectric materials or modern composite materials with a negative refractive index otherwise known[...]

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