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Electromagnetic Simulation Using The Fdtd Method

A review on developments of deployable membrane-based reflector antennas

The coastal zone offers among the world’s most productive and valuable ecosystems and is experiencing increasing pressure from anthropogenic impacts: human settlements, agriculture, aquaculture, trade, industrial activities, oil and gas exploitation and tourism. Earth observation has great capability to deliver valuable data at the local, regional and global scales and can support the assessment and monitoring of land- and water-related applications in coastal zones. Compared to optical satellites, cloud-cover does not limit the timeliness of data acquisition with spaceborne Synthetic Aperture Radar (SAR) sensors, which have all-weather, day and night capabilities. Hence, active radar systems demonstrate great potential for continuous mapping and monitoring of coastal regions, particularly in cloud-prone tropical and sub-tropical climates. The canopy penetration capability with long radar wavelength enables L-band SAR data to be used for coastal terrestrial environments and has been widely applied and investigated for the following geoscientific topics: mapping and monitoring of flooded vegetation and inundated areas; the retrieval of aboveground biomass; and the estimation of soil moisture. Human activities, global population growth, urban sprawl and climate change-induced impacts are leading to increased pressure on coastal ecosystems causing land degradation, deforestation and land use change. This review presents a comprehensive overview of existing research articles that apply spaceborne L-band SAR data for geoscientific analyses that are relevant for coastal land applications.

/pdf/spaceborne-l-band-synthetic-aperture-radar-data-for-hi3pz6vc2y.pdf

Spaceborne L-Band Synthetic Aperture Radar Data for Geoscientific Analyses in Coastal Land Applications: A Review

El problema de propagacion de ondas de radio sobre el suelo ha sido tema de interes por mas de un siglo. Dado que el problema es de naturaleza electromagnetica, su descripcion esta dada completamente por las ecuaciones de Maxwell. Sin embargo, dadas una condiciones de frontera especificas y segun el tiempo de fuente de los campos, la solucion de dichas ecuaciones puede ser extremadamente compleja y casi siempre se tienen que buscar soluciones numericas. Existe una gran cantidad de aplicaciones; el problema abordado en este trabajo trata sobre el modelado de la propagacion sobre suelo irregular de las ondas electromagneticas generadas por rayos, para su aplicacion a sistemas de localizacion de rayos. Se puede pensar inmediatamente en la siguiente pregunta: ?cual es el efecto que tienen las irregularidades del suelo sobre la propagacion de este tipo de ondas? Ademas, ?cual es la consecuencia de estos efectos de propagacion sobre los sistemas de localizacion de rayos que funcionan sobre regiones montanosas de altitudes que son comparables a la longitud de onda de la fuente de los campos? Estas son las preguntas de investigacion que fueron planteadas para ser respondidas mediante el presente trabajo.

El enfoque metodologico para responder a las preguntas planteadas consistio en el desarrollo de un modelo de simulacion numerica, especificamente el metodo de Diferencias Finitas en el Dominio del Tiempo (DFDT). Debido a los requerimientos de memoria computacional del metodo, fue necesario obtener una aproximacion en dos dimensiones a las ecuaciones de Maxwell, considerando la simetria azimutal del problema. Despues de que el modelo numerico fue validado y probado mediante resultados de modelos canonicos, se utilizo para predecir y observar la propagacion de ondas electromagneticas generadas por rayos bajo diferentes escenarios. Ademas, se modelaron seis perfiles de relieve reales sobre el territorio Colombiano y se usaron para determinar su efecto sobre la propagacion de ondas electromagneticas de rayo. Tambien se midieron los tiempos de arribo de las ondas a diferentes puntos de observacion y se compararon los casos de tiempos obtenidos para propagacion sobre terreno plano con los obtenidos para propagacion sobre terreno irregular. 

Los resultados mostraron que el efecto global de las irregularidades del suelo sobre la propagacion de las ondas puede ser de dos tipos: incremento o atenuacion del valor pico de la senal. Sin embargo, las derivadas temporales o tiempo de frente de las ondas no se vieron afectados de manera significativa. Esto es, las irregularidades del suelo unicamente, sin el efecto de la conductividad del suelo, pueden modificar unicamente la amplitud de las ondas electromagneticas. La atenuacion del valor pico de la senal se obtiene como resultado de la propagacion sobre obstaculos electricamente grandes y es debida a la reflexion de la onda. El incremento del valor pico de la senal de campo electromagnetico se explica a traves del fenomeno de interferencia constructiva de ondas cuando el punto de observacion se encuentra a cierta altitud por encima de la fuente. Se pueden dar algunos numeros; por ejemplo, para una fuente con una longitud de onda alrededor de 5000 m, y un obstaculo con altura de alrededor de 0.8 veces la longitud de onda, el valor pico del campo electrico vertical tuvo reduccion cercana al 22% del valor obtenido para propagacion sobre suelo plano. Para una fuente con longitud de onda alrededor de 790 m, el valor pico del campo electrico vertical sufrio una reduccion cercana al 43% de su valor cuando se propagaba sobre suelo plano. Los resultados descritos fueron obtenidos para el caso de propagacion sobre un obstaculo de igual altura, pero diferentes longitudes de onda de la fuente, lo cual demuestra que la discusion se debe dar en terminos de longitudes de onda y su relacion con el tamano de los obstaculos. El punto importante es que el cambio en el valor pico de la senal cuando se propaga sobre zonas montanosas de altura importante —como las que existen en Colombia debido a la Cordillera de los Andes— se deben considerar con el fin de obtener un modelado preciso de la propagacion. Los resultados tambien mostraron que los tiempos de arribo de las senales no se modificaron mas alla del 4% con respecto a los tiempos de arribo para propagacion sobre suelo plano. De hecho, cinco de los seis perfiles reales del relieve estudiados mostraron que el error en el calculo de los tiempos de arribo estaba por debajo del 1% cuando se incluyeron las irregularidades del terreno en el modelo de propagacion.

Al inicio de esta investigacion, la hipotesis indicaba que el efecto mas significativo de las irregularidades del terreno sobre la propagacion de ondas electromagneticas generadas por rayo era sobre la precision de localizacion de los sistemas de localizacion de rayos. Sin embargo, los resultados obtenidos sugieren un cambio de direccion al pensar en estos efectos, puesto que los tiempos de arribo de la senal de campo dependen fuertemente del tiempo de frente de la senal, pero este parametro no puede ser modificado significativamente por las irregularidades del terreno unicamente. Con respecto a esto, los efectos de la conductividad del terreno son de hecho mas importantes porque estos causan atenuacion selectiva de ciertas componentes de frecuencia, como ha sido demostrado por varios autores en la literatura cientifica. Por lo tanto, esta tesis demostro que los efectos de propagacion debidos a las irregularidades del terreno tienen su efecto mas importante en otros aspectos de la aplicacion a sistemas de localizacion de rayos, como por ejemplo la eficiencia de la deteccion y principalmente, la estimacion de parametros de rayo a partir de la informacion contenida en sistemas de localizacion de rayos.

Propagation of LF AND VLF lightning electromagnetic waves: the ground effects. Applications to Lightning Locating Systems in Mountainous Regions.

Design of agile satellite constellation based on hybrid-resampling particle swarm optimization method

The design and experimentation of conformal printed traveling wave antenna composed of interdigital capacitor structures is presented. The antenna which is designed to work around center frequency of 2.35MHz for experimental-rocket communication with the ground station is deployed on a 0.127mm thick of RT/Duroid R® 6010LM dielectric substrate. The use of very thin dielectric substrate for antenna realization intends to be conformable with the cylindrical body of experimental-rocket. Prior hardware realization, the parameters of antenna including reflection coefficient, gain, and radiation pattern are investigated to obtain the optimum performance design. From experimental characterization, it shows that the realized proposed antenna which consists of 7 blocks of interdigital capacitor structure with total dimension of 238.64mm (length) × 22mm (width) and fits 76mm diameter of experimental-rocket body resonates at frequency of 2.375GHz with gain and −10dB working bandwidth of −18.763dB and 13MHz, respectively.

Conformal printed traveling wave antenna composed of interdigital capacitor structure

An anechoic chamber is a notable facility in developing radar technology, electromagnetic wave research, communications, satellite systems, and for the usage of both civil and military fields. In this work, the pyramidal particle board is designed and fabricated as radar absorber material (RAM) based on activated carbon of coconut shell that has extensive porosity and high absorption. Geometrically tapered microwave absorber such pyramidal are preferred due to their better performance. The pyramidal shape produces an impedance gradient which results in high reflectivity levels in anechoic chambers at both normal and off-normal angles of incidence. Pyramidal absorber material to be designed with a thin thickness, this be important where allows it to be used in limited buildings. The coconut shell activated carbon is mixed with resin which has high adhesive power, low water absorption, and high surface hardness. This pyramidal radar absorber was created with has many advantages such us high broadband performance, non-flammable, self-extinguishing, and resistant to high humidity conditions. The microwave simulation software is operated in obtaining the optimum geometry of the pyramidal. The fabricated pyramidal absorber is characterized using a Vector Network Analyzer (VNA) in the frequency range 2 to 8 GHz (C-band). Various parameters that influence the absorption performance of the pyramidal were investigated such as the percentage of resin added, the distance of the source port and angles between the signal source as well as the surface of the pyramidal radar absorber. The experimental results show that the absorption of the pyramidal board is very high and meets it for use as an absorbent material in anechoic chamber.

Pyramidal Radar Absorber Based on Coconut Shell Activated Carbon for Anechoic Chamber Application

Suhu dan kelembaban merupakan aspek penting dalam menentukan kondisi cuaca suatu daerah. Aplikasi penelitian ini berfungsi untuk mendeteksi suhu tanah dan kelembaban udara pada suatu tempat. Komponen utama yang digunakan adalah IC LM35 sebagai sensor suhu tanah dan HIH 3610 sebagai sensor untuk mendeteksi kelembaban udara. Rancang bangun sensor suhu tanah dan kelembaban udara ini dikembangkan untuk Automatic Weather Station (AWS). Kata kunci:Suhu Tanah, LM35, Sensor kelembaban, HIH3610.

http://103.16.223.27/index.php/jurnal_sains/article/download/359/311

Rancang bangun sensor suhu tanah dan kelembaban udara

This paper presents a circular polarization plane antenna using linearly truncated triplate stripline resonator. Glass epoxy substrate is used in place of Teflon substrate for low cost fabrication. In spite the electrical dimension differs only √3 (root three), the dimensions of circular disk, its truncation, and feeding lines have to be chosen precisely and accurately to get better characteristics comparable to Teflon substrate.

Circular Polarization Antenna with Truncated Feed-and Reactance-Elements using GlassEpoxy Substrates

Electromagnetic wave backscattering by corner reflectors in an anechoic chamber is studied using our developed computational tool. The tool applies the Finite-Difference Time-Domain (FDTD) method to simulate the propagation of the wave’s electric and magnetic fields. Experimental measurement in an anechoic chamber is also carried out as a comparison. The two results show agreement, including the finding that the backscatter intensity variation amongst the four circularly polarized modes is significantly smaller than the variation amongst the four linearly polarization modes.

https://www.mdpi.com/2079-3197/7/4/55/pdf

Computation and Experiment on Linearly and Circularly Polarized Electromagnetic Wave Backscattering by Corner Reflectors in an Anechoic Chamber

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