Raed Malallah | University of Basrah (original) (raw)
Papers by Raed Malallah
The scattering problem for electromagnetic waves by perfect conducting bodies of revolution and u... more The scattering problem for electromagnetic waves by perfect conducting bodies of revolution and unrevolution is very important for many researchers because of its complexity in concerns of its boundary conditions.
This research focuses on the enhancement of computational ability to solve the scattering problem for perfect conducting Bodies of Revolution (BoR), so it is possible to solve the problems that concern with different bodies by using the general electric field equation where Fourior techniques, which are subjected to transformation process, provide additional information about the target scattering had been taken by the use method of moment (MoM).
We demonstrate theoretically and experimentally that the light can be self-focused and self-trapp... more We demonstrate theoretically and experimentally that the light can be self-focused and self-trapped in a self-written optical waveguide in a bulk acrylamide/polyvinyl alcohol (AA/PVA) solid photopolymer material volume. The manufacture method, i.e., how to prepare the AA/PVA photopolymer material is detailed. In our experimental observation the refractive index changes induced are permanent. The resulting optical waveguide channel has good physical stability and can be integrated with optoelectronic devices as part of integrated optical systems. The theoretical model developed predicts the formation/evolution of the observed self-written waveguides inside the bulk material. The model involves appropriately discretizing and then numerically solving the paraxial wave equation in Fourier space and the material equation in time space.
When the large thickness is used as the holographic storage materials, a non-ignorable problem is... more When the large thickness is used as the holographic storage materials, a non-ignorable problem is the light intensity attenuation in depth due to high absorptive of the dye. For this reason more completely modeling the evolutions inside the material is necessary to consider into the developed standard kinetic model. In this paper the photo-polymerization processes during the large thickness holographic grating formation are analyzed. A 3-dimensional algorithm is present by deriving the system partial differential rate equations governing each associated chemical species, and using the finite difference approximation, these equations can be solved numerically. This extended model describes the time varying behaviors of the non-uniform photo-physical and the photochemical evolutions in photopolymer materials. In this model both dye molecules consumption and light energy absorption are calculated time varyingly, and then the polymer and monomer concentrations distributions are obtained. Applying the Lorenz-Lorenz relationship, the non-uniform grating formatted in material depth, and its refractive index, which is distorted from ideal sinusoidal spatial distribution, can be more accurately predicted.
Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they ... more Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they can exhibit a large refractive index change and high photo-sensitivity. In free radical photo-polymerization systems, the dyes, functioning as the photosensitizer, strongly influence the material properties. During photo-illumination the spatial and temporal evolution of the dye concentration is an important factor leading to nonlinear absorption. In this paper, based on an investigation of the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated and used to iteratively estimate the evolving cross-sectional refractive index and loss coefficient values. The model enables a more accurate and physical description of the optically induced growth of SWWs in such systems. Then SWWs formed in dry acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer samples, containing different initial dye concentrations, are experimentally examined. The nonlinear absorptive behavior is quantified by comparing the model predictions and the experimental results.
The method of moment (MoM) technique with Galerkin approach is applied as a numerical technique t... more The method of moment (MoM) technique with Galerkin approach is applied as a numerical technique to predict the induced current on the surface and calculate the radiation fields of a spherically capped metallic biconical antenna excited by electromagnetic pulse.
This antenna is considered as a body of revolution having an equal or unequal cone angles. Good agreement has been obtained between the predicated results and those reported by other research workers.
The synthesis of uniformly excited equally and unequally spaced array employing physical optics t... more The synthesis of uniformly excited equally and unequally spaced array employing physical optics technique to achieve sidelobe reduction and narrow beamwidth by varying the elements number (N) and positions, with equal current magnitude of antenna. The elements of this array are considered to be short backfire antennas (SBFAs) fed by coaxial waveguide and excited by TE 11mode. It is observed that by employing the unequally spaced array synthesis technique, the first sidelobe level (FSLL) is reduced by 8.85 dB over that of an equally spaced array patterns for N=15.
Computational electromagnetics (CEM) may be broadly defined as that branch of electromagnetics th... more Computational electromagnetics (CEM) may be broadly defined as that branch of electromagnetics that intrinsically and routinely involves using a digital computer to obtain numerical results. This paper presents a technique for the measurement of the radiation fields of discone antenna by using moment method (MM). The measurements are carried out for the perfect conductors by using the dipole feed. The numerically calculated results are experimentally validated for a discone antenna from 300MHz -2.4GHz. The radiation patterns of discone antenna for multiple frequency and the effects of feed location on antenna's operations are discussed.
The scattering problem for electromagnetic waves by perfect conducting bodies of revolution and u... more The scattering problem for electromagnetic waves by perfect conducting bodies of revolution and unrevolution is very important for many researchers because of its complexity in concerns of its boundary conditions.
This research focuses on the enhancement of computational ability to solve the scattering problem for perfect conducting Bodies of Revolution (BoR), so it is possible to solve the problems that concern with different bodies by using the general electric field equation where Fourior techniques, which are subjected to transformation process, provide additional information about the target scattering had been taken by the use method of moment (MoM).
We demonstrate theoretically and experimentally that the light can be self-focused and self-trapp... more We demonstrate theoretically and experimentally that the light can be self-focused and self-trapped in a self-written optical waveguide in a bulk acrylamide/polyvinyl alcohol (AA/PVA) solid photopolymer material volume. The manufacture method, i.e., how to prepare the AA/PVA photopolymer material is detailed. In our experimental observation the refractive index changes induced are permanent. The resulting optical waveguide channel has good physical stability and can be integrated with optoelectronic devices as part of integrated optical systems. The theoretical model developed predicts the formation/evolution of the observed self-written waveguides inside the bulk material. The model involves appropriately discretizing and then numerically solving the paraxial wave equation in Fourier space and the material equation in time space.
When the large thickness is used as the holographic storage materials, a non-ignorable problem is... more When the large thickness is used as the holographic storage materials, a non-ignorable problem is the light intensity attenuation in depth due to high absorptive of the dye. For this reason more completely modeling the evolutions inside the material is necessary to consider into the developed standard kinetic model. In this paper the photo-polymerization processes during the large thickness holographic grating formation are analyzed. A 3-dimensional algorithm is present by deriving the system partial differential rate equations governing each associated chemical species, and using the finite difference approximation, these equations can be solved numerically. This extended model describes the time varying behaviors of the non-uniform photo-physical and the photochemical evolutions in photopolymer materials. In this model both dye molecules consumption and light energy absorption are calculated time varyingly, and then the polymer and monomer concentrations distributions are obtained. Applying the Lorenz-Lorenz relationship, the non-uniform grating formatted in material depth, and its refractive index, which is distorted from ideal sinusoidal spatial distribution, can be more accurately predicted.
Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they ... more Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they can exhibit a large refractive index change and high photo-sensitivity. In free radical photo-polymerization systems, the dyes, functioning as the photosensitizer, strongly influence the material properties. During photo-illumination the spatial and temporal evolution of the dye concentration is an important factor leading to nonlinear absorption. In this paper, based on an investigation of the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated and used to iteratively estimate the evolving cross-sectional refractive index and loss coefficient values. The model enables a more accurate and physical description of the optically induced growth of SWWs in such systems. Then SWWs formed in dry acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer samples, containing different initial dye concentrations, are experimentally examined. The nonlinear absorptive behavior is quantified by comparing the model predictions and the experimental results.
The method of moment (MoM) technique with Galerkin approach is applied as a numerical technique t... more The method of moment (MoM) technique with Galerkin approach is applied as a numerical technique to predict the induced current on the surface and calculate the radiation fields of a spherically capped metallic biconical antenna excited by electromagnetic pulse.
This antenna is considered as a body of revolution having an equal or unequal cone angles. Good agreement has been obtained between the predicated results and those reported by other research workers.
The synthesis of uniformly excited equally and unequally spaced array employing physical optics t... more The synthesis of uniformly excited equally and unequally spaced array employing physical optics technique to achieve sidelobe reduction and narrow beamwidth by varying the elements number (N) and positions, with equal current magnitude of antenna. The elements of this array are considered to be short backfire antennas (SBFAs) fed by coaxial waveguide and excited by TE 11mode. It is observed that by employing the unequally spaced array synthesis technique, the first sidelobe level (FSLL) is reduced by 8.85 dB over that of an equally spaced array patterns for N=15.
Computational electromagnetics (CEM) may be broadly defined as that branch of electromagnetics th... more Computational electromagnetics (CEM) may be broadly defined as that branch of electromagnetics that intrinsically and routinely involves using a digital computer to obtain numerical results. This paper presents a technique for the measurement of the radiation fields of discone antenna by using moment method (MM). The measurements are carried out for the perfect conductors by using the dipole feed. The numerically calculated results are experimentally validated for a discone antenna from 300MHz -2.4GHz. The radiation patterns of discone antenna for multiple frequency and the effects of feed location on antenna's operations are discussed.