Elsayed Esam M. Khaled

Scattered and internal intensity of a sphere illuminated with a Gaussian beam

A method of calculating the internal and scattered electric fields of a spherical dielectric object illuminated with a Gaussian beam is presented. The vector nature of the beam is considered. The fields satisfy Maxwells equations, and the beam can be located arbitrarily with respect to the object. A polarized Gaussian beam is first represented as an angular spectrum of plane waves. These waves are then expanded in vector spherical harmonics. Although the details of the expansion are presented for a lowest-order Gaussian beam, the method can be applied to any wave which can be expressed as a sum of homogeneous plane waves. The interaction of an arbitrarily located Gaussian beam with a spherical object is analyzed using the T-matrix method. Calculated results for beams having waists much smaller than the radius of the sphere help in visualizing how a narrow beam reflects and refracts at the spherical dielectric interfaces. The combination of the plane-wave spectrum technique and the T-matrix method can be applied to the problem of an arbitrary beam interacting with an axisymmetric, nonspherical, homogeneous or layered object. >

Internal electric energy in a spherical particle illuminated with a plane wave or off-axis Gaussian beam

The electric energy in a lossless or lossy spherical particle that is illuminated with a plane wave or a Gaussian beam is investigated. The analysis uses a combination of the plane-wave spectrum technique and the T-matrix method. Expressions for the electric energy in any mode as well as the total electric energy inside the particle are given. The amount of energy coupling into the particle for different beam illuminations is also investigated. The high-Q (low-order) resonant modes can dominate the electric energy inside a spherical particle many linewidths away from the resonance location, particularly if the beam is focused at the droplet edge or outside the droplet. If the sphere is lossy, low-order modes can still dominate the electric energy if the beam is focused far enough outside the sphere. As the absorption coefficient of the particle increases, the energy in a high-Q mode decreases much faster at the resonance frequency than it does at near or off-resonance frequencies. The effects of the absorption on the dominance of the internal fields by a high-Q mode decreases as the beam is shifted farther away from the particle. As the beam is shifted farther away from the particle the fraction of the incident energy coupled into the sphere at resonance first increases and then decreases. Although the coupled energy decreases as the beam is shifted farther from the sphere, most of that energy is in the lowest-order mode.

Light scattering by a coated sphere illuminated with a Gaussian beam

The intensity of light scattered by a coated sphere illuminated with an off-axis Gaussian beam is calculated. Results are shown for different beam positions with respect to the sphere. As the beam is shifted further away from the surface of the sphere, the higher-Q morphology-dependent resonances become increasingly important in the backscatter spectra, and the angular scattering intensity becomes smoother. The scattered intensity depends on the beam position, the refractive indices of the core and coat, the radius of the core, and the thickness of the coat. As the beam is moved further away from the sphere, the effect of the core on the scattering intensity decreases. When the incident Gaussian beam is focused outside of a particle with a relatively small core, the scattering spectra and angular scattering patterns become similar to those of a homogeneous sphere having the refractive index of the coat. These calculated results suggest that measurements of spectral scattering and angular scattering patterns for several Gaussian beam positions could be useful for the characterization of coated spheres.

A Proximity-Fed Annular Slot Antenna with Different a Band-Notch Manipulations for Ultra-Wide Band Applications

A proximity-fed annular slot antenna for UWB applica- tions with a band rejection using difierent techniques is presented. The proposed antenna provides an UWB performance in the frequency range of … 2:84 to … 8:2GHz with relatively stable radiation parame- ters. Three difierent techniques to construct a resonant circuit for the proposed antenna are investigated to achieve the band-notch property in the band … 5:11 to … 5:69GHz band which include the WLAN and HIPERLAN/2 services without degrading the UWB performance of the antenna. Three resonators are considered; a single complementary split ring resonator (CSRR), a complementary spiral loop resonator (CSLR) and a spurline slot. Furthermore, the band-notched resonance frequency and the bandwidth can be easily controlled by adjusting the dimensions of the resonator. The proposed antenna is simulated, fab- ricated and measured. The measured data show very good agreements with the simulated results. The proposed antenna provides almost om- nidirectional patterns, relatively ∞at gain and high radiation e-ciency over the entire UWB frequency excluding the rejected band.

A Design of Miniaturized Ultra–Wideband Printed Slot Antenna with 3.5/5.5 GHz Dual Band–Notched Characteristics: Analysis and Implementation

A design and analysis of a novel proximity-fed printed slot antenna with 3.5/5.5GHz dual band-notched characteristics are presented. To obtain an ultra-wideband (UWB) response, a circular patch with a rectangular conjunction arm is etched concentrically inside a ground plane aperture. The antenna is proximity-fed by a microstrip line with an open shunt stub on the other side of the substrate. The designed antenna satisfles a i10dB return loss requirement in the frequency band from 2.7 to 17GHz. In order to obtain dual band-notched properties at 3.5 and 5.5GHz, an open ring slot is etched ofi the circular patch and a …-shaped slot is etched ofi the microstrip feeding line, respectively. A curve fltting formulation is obtained to describe the in∞uences of the notched resonators on the corresponding notched frequencies. The proposed antenna is designed, simulated and fabricated. The measured data show a good agreement with the simulated results and the equivalent circuit results through the use of a modifled Vector Fitting technique for a rational function approximation. The proposed antenna provides almost omnidirectional radiation patterns, relatively ∞at gain and high radiation e-ciency over the entire UWB frequency excluding the two rejected bands.

Determination of size changes of optically trapped gas bubbles by elastic light backscattering.

A technique for the determination of size changes of gas bubbles by means of Fabry-Perot resonances in elastic light backscattering and optical trapping is presented. A theoretical description of the interaction of a strongly focused laser beam with gas bubbles is also given. The differences in elastic light scattering for particles with a relative refractive index larger than one and for gas bubbles with a relative refractive index smaller than one are discussed in detail. The results of elastic light scattering experiments verify the theoretical considerations.

Scattering of a focused Gaussian beam by an axisymmetric particle with a nonconcentric spherical core

Scattering of an on- or off-axis focused Gaussian beam by a dielectric spherical or a spheroidal particle with a nonconcentric spherical core is presented. The plane wave spectrum method is used to model the beam. The electric field intensities are calculated at any point using the T-matrix method, which is modified for the cases studied here. The calculated angular scattering intensities are shown for different cases of the cores offsets and for different cases of the beam-focusing positions with respect to the particle. The technique is applicable to a large-sized parameter particle with nonconcentric layers of different shapes illuminated with an arbitrarily shaped laser beam. Although the technique is applicable to a beam propagating in any direction and to an arbitrary shift of the core, all the calculations shown here are for an offset core and a beam propagating in the z-direction.

An integrated 3G/Bluetooth and UWB antenna with a band-notched feature

In this article, the design and analysis of a compact slot antenna that covers 3G, Bluetooth, and the UWB bands with the standard band-notched function at 3.6 GHz are presented and investigated. A rectangular wide-slot etched off the ground plane is used to control the low operating frequency band and the impedance matching of the proposed antenna. A manipulated rectangular tuning stub is used to enhance and control the operating bandwidth at the high frequency band. The proposed antenna is fabricated and is successfully simulated and measured. The results indicate that the proposed antenna yields an impedance bandwidth of about 7.75 GHz (from 1.9 to 9.65 GHz) defined by VSWR ≤ 2 for UMTS (1.920–2.170 GHz)/Bluetooth (2.4–2.484 GHz)/3GPP (2.57–2.62 GHz), and UWB (3.1–9.65 GHz) applications with good radiation characteristics. To reduce interference between the UWB system and the WiMAX system (3.3–3.9 GHz), a U-shaped slot is employed in the microstrip feeding line to create notched band of 3.2–4.0 GHz. Furthermore, a mathematical circuit model compatible with time-domain circuit simulators, which is based on a vector fitting technique, is also illustrated to investigate the proposed antenna characteristics.

Temporal behavior of short optical pulses scattered by small particles

Scattered time-dependent intensities for a dielectric microsphere illuminated with a very short pulsed plane wave are calculated. The incident pulse is considered to be a rectangular or Gaussian shaped pulse. The results are obtained for a sphere at a resonant mode. The frequency spectrum of the scattered field at a point is calculated using the incident field spectrum and the transfer function at that point. The transfer function at any frequency of the sphere at a space point is calculated using the T matrix method. The inverse Fourier transform of the frequency spectrum is used to calculate the time-dependence of the electric field. The scattered intensities are calculated for pulses of durations (~10 ps) smaller than the resonant lifetime. The computer codes are capable to calculate the scattered intensity of a shorter pulse but depend on the capacity and speed of the computer system. The main factors that affect the behavior of the scattered pulse are the incident pulse spectrum (or duration) and the lineshape of the resonant mode of the sphere.

A compact proximity-fed ultra-wide band patch antenna with four notched-band characteristics: Design and implementation

In this paper, a new printed cedar tree-shaped UWB antenna with four frequency band-rejection characteristics is presented. The equivalent electrical circuit of the antenna is also presented. The antenna is compact volume of size 20 × 20 × 1.5 mm3. Matching between the designed antenna and the 50 Ohm microstrip feed line is manipulated through a proximity-fed technique. Narrow rectangular slits and T-shaped slots are etched in the ground plane to provide four notched bands at frequencies 3.5, 3.9, 5.25 and 5.9 GHz to avoid the interference with the wireless networks which already occupy bands at these frequencies. The antenna is simulated, fabricated. Also an electrical equivalent lumped-circuit is obtained. The experimental data show good agreement with the simulation results along with the equivalent circuit results. The antenna provides almost omnidirectional radiation patterns, relatively stable gain and high radiation efficiency over the entire UWB frequency band excluding the four rejected bands.