Academic literature on the topic 'Plane wave expansion method'

The work presented in this thesis is concerned with the propagation of acoustic waves through phononic crystal systems and their ability to attenuate sound in the low frequency regime. The plane wave expansion method and finite element method are utilised to investigate the properties of conventional phononic crystal systems. The acoustic band structure and transmission measurements of such systems are computed and verified experimentally. Good agreement between band gap locations for the investigative methods detailed is found. The well known link between the frequency range a phononic crystal can attenuate sound over and its lattice parameter is confirmed. This leads to a reduction in its usefulness as a viable noise barrier technology, due to the necessary increase in overall crystal size. To overcome this restriction the concept of an acoustically resonant phononic crystal system is proposed, which utilises acoustic resonances, similar to Helmholtz resonance, to form additional band gaps that are decoupled from the lattice periodicity of the phononic crystal system. An acoustically resonant phononic crystal system is constructed and experimental transmission measurements carried out to verify the existence of separate attenuation mechanisms. Experimental attenuation levels achieved by Bragg formation and resonance reach 25dB. The two separate attenuation mechanisms present in the acoustically resonant phononic crystal, increase the efficiency of its performance in the low frequency regime, whilst maintaining a reduced crystal size for viable noise barrier technology. Methods to optimise acoustically resonant phononic crystal systems and to increase their performance in the lower frequency regime are discussed, namely by introducing the Matryoshka acoustically resonant phononic crystal system, where each scattering unit is composed of multiple concentric C-shape inclusions.

In this thesis, design and simulation of optical logic gases based on different photonics crystals presented to used in the electronics and telecommunication industries. Optical devices perform faster with higher efficiencies compare to the electrical device.The photonic crystal applications to achieve higher transmission power and contrast ratio focus on the design criteria. Results proved promising insights toward the development of gas sensors. The proposed structures have small dimensions as well as a wide functional interval.In Chapter 1,before employing the wavelength-division multiplexing (WDM) method, the notion of the electromagnetic wave in free space and in conductors with a description of equations was defined.Chapter 2 is dedicated to studying literature and similar research,started by the review of photonic crystals and photonic band gap. The gates, characteristics and design layouts were discussed without using nonlinear materials and optical amplifiers.Chapter 3 describes schemes proposed structures.In chapter 4, simulation studies and analysis of six new structures are presented. The procedure is as follows to use the linear logic NOT, OR and AND gates first. These structures have an input waveguide for applying a Gaussian optical pulse at a wavelength of 1550 nm. By changing the radius of the defect, the best dimension with the highest transmission is obtained.Afterward, by coupling these gates, and getting NOR and NAND gates in to study a reasonable contrast ratio and transmission power in each case by changing the defect radius obtained and proved the design concept. A full adder based on metal-insulator-metal (MIM) waveguide-based plasmonic waves. We studied the 4-input OR gate to design and simulate a full adder circuit, which used plasmonic waves to transmit signals; the 4-input gate presented in this study has a simple structure and is manufactured at a low cost. By optimizing the structure's dimensions, the losses and achieve a transmission coefficient of about 0.62 and educe the losses to 25% less than the mentioned design in the references.The next propose structure is a 2DPC based eight channels demultiplexer. This structure is proposed and designed using an octagonal ring resonator for WDM applications.The functional parameters are resonant wavelength, Q factor, channel spacing, spectral width, output efficiency, and crosstalk, are investigated. In this attempt, the channel selection is carried out by altering the octagonal ring resonator's size. The average transmission efficiency, Q factor, spectral width, and channel spacing of the proposed demultiplexer are 98.65%, 2212, 0.76 nm, and 1.75 nm, respectively. The proposed demultiplexer's crosstalk is low (30 dB ) as the even number of channels and the odd number of channels are dropped separately. The demultiplexer's size is about 752.64 µm2, and the functional characteristics of the proposed demultiplexer meet the requirements of WDM systems. Hence this demultiplexer can be incorporated for integrated optics. We have shown that the device is perfectly suitable for communication applications.Chapter 5 is the conclusion of the thesis and recommendation of future studies which has been presented for industrial purposes. In this thesis, a new photonic crystal slab for its use in gas sensing applications is proposed. Theoretical studies have been done to determine the response of the proposed structure to carbon dioxide. A simple laser with around 1 nm spectral widths can be used to simulate this device. Measurements can be done in two steps, which can be done simultaneously by using a reference device: step one with synthetic air and then adding known concentrations of CO.The output is referenced to the measurement with synthetic air.Our theoretical results show that variations of 17% in the transmission intensity and a clear variation on the transmission peaks' central wavelength.These results are already promising for the development of gas sensors<br>En esta tesis, diseño y simulación de gases ópticos lógicos basados en diferentes cristales fotónicos presentados para ser utilizados en las industrias de la electrónica y las telecomunicaciones. Los dispositivos ópticos funcionan más rápido con mayor eficiencia en comparación con el dispositivo eléctrico. Las aplicaciones de cristal fotónico para lograr una mayor potencia de transmisión y una relación de contraste se centran en los criterios de diseño. Los resultados demostraron conocimientos prometedores hacia el desarrollo de sensores de gas. Las estructuras propuestas tienen pequeñas dimensiones así como un amplio intervalo funcional. En el Capítulo 1, antes de emplear el método de multiplexación por división de longitud de onda (WDM), se desarrolló la noción de onda electromagnética en el espacio libre y en conductores con una descripción de ecuaciones. El capítulo 2 está dedicado al estudio de la literatura e investigaciones similares, comenzando por la revisión de los cristales fotónicos y la banda prohibida fotónica. Se discutieron las puertas, las características y los diseños de diseño sin utilizar materiales no lineales ni amplificadores ópticos. En el capítulo 3 se describen los esquemas de estructuras propuestos, en el capítulo 4 se presentan estudios de simulación y análisis de seis nuevas estructuras. El procedimiento es el siguiente para utilizar primero las puertas lógicas NOT, OR y AND de lógica lineal. Estas estructuras tienen una guía de ondas de entrada para aplicar un pulso óptico Gaussi-an a una longitud de onda de 1550 nm. Al cambiar el radio del defecto, se obtiene la mejor dimensión con la mayor transmisión. Posteriormente, al acoplar estas puertas y hacer que las puertas NOR y NAND estudien una relación de contraste y potencia de transmisión razonables en cada caso, cambiando el radio de defecto obtenido y probado el concepto de diseño. Un sumador completo basado en ondas plasmónicas basadas en guías de ondas de metal-aislante-metal (MIM). Estudiamos la puerta OR de 4 entradas para diseñar y simular un circuito sumador completo, que usaba ondas plasmónicas para transmitir señales; la compuerta de 4 entradas presentada en este estudio tiene una estructura simple y está fabricada a bajo costo. Optimizando las dimensiones de la estructura, las pérdidas y logran un coeficiente de transmisión de alrededor de 0,62 y reducen las pérdidas a un 25% menos que el diseño mencionado en las referencias. La siguiente estructura propuesta es un demultiplexor de ocho canales basado en 2DPC. Esta estructura se propone y diseña utilizando un resonador de anillo octagonal para aplicaciones WDM. Los parámetros funcionales son la longitud de onda resonante, el factor Q, el espaciado de canales, el ancho espectral, la eficiencia de salida y la diafonía. En este intento, la selección de canal se lleva a cabo alterando el tamaño del resonador de anillo octagonal. La eficiencia de transmisión promedio, el factor Q, el ancho espectral y el espaciado de canales del demultiplexor propuesto son 98,65%, 2212, 0,76 nm y 1,75 nm, respectivamente. La diafonía del demultiplexor propuesto es baja (30 dB) ya que el número par de canales y el número impar de canales se eliminan por separado. El tamaño del demultiplexor es de aproximadamente 752,64 µm2 y las características funcionales del demultiplexor propuesto cumplen los requisitos de los sistemas WDM. Por tanto, este demultiplexor se puede incorporar para ópticas integradas. Hemos demostrado que el dispositivo es perfectamente apto para aplicaciones de comunicación. El capítulo 5 es la conclusión de la tesis y recomendación de futuros estudios que se ha presentado con fines industriales.En esta tesis, se propone una nueva placa de cristal fotónico para su uso en aplicaciones de detección de gases. Se han realizado estudios teóricos para determinar la respuesta de la estructura propuesta al dióxido de carbono. Se puede utilizar un láser simple con anchos espectrales de alrededor de 1 nm para simular este dispositivo. Las mediciones se pueden realizar en dos pasos, que se pueden hacer simultáneamente utilizando un dispositivo de referencia: el paso uno con aire sintético y luego agregando concentraciones conocidas de CO. La salida se refiere a la medición con aire sintético. Nuestros resultados teóricos muestran que las variaciones de 17% en la intensidad de transmisión y una clara variación en la longitud de onda central de los picos de transmisión, resultados que ya son prometedores para el desarrollo de sensores de gas.<br>Enginyeria electrònica

Although it is possible to directly solve an entire flow-acoustics problem in one computation, this approach remains prohibitively large in terms of the computational resource required for most practical applications. Aeroacoustic problems are therefore usually split into two parts; one consisting of the source computation and one of the source propagation. Although both these parts entail great challenges on the computational method, in terms of accuracy and efficiency, it is still better than the direct solution alternative. The source usually consists of highly turbulent flows, which for most cases will need to be, at least partly, resolved. Then, acoustic waves generated by these sources often have to be propagated for long distances compared to the wavelength and might be subjected to scattering by solid objects or convective effects by the flow. Numerical methods used solve these problems therefore have to possess low dispersion and dissipation error qualities for the solution to be accurate and resource efficient. The wave expansion method (WEM) is an efficient discretization technique, which is used for wave propagation problems. The method uses fundamental solutions to the wave operator in the discretization procedure and will thus produce accurate results at two to three points per wavelength. This thesis presents a method that uses the WEM in an aeroacoustic context. Addressing the propagation of acoustic waves and transfer of sources from flow to acoustic simulations. The proposed computational procedure is applied to a co-rotating vortex pair and a cylinder in cross-flow. Overall, the computed results agree well with analytical solutions. Although the WEM is efficient in terms of the spatial discretization, the procedure requires that a Moore-Penrose pseudo-inverse is evaluated at each unique node-neighbour stencil in the grid. This evaluation significantly slows the procedure. In this thesis, a method with a regular grid is explored to speed-up this process.<br><p>QC 20161121</p>