Amr M. Mahros

Magnetic and magnetotransport properties of (AlGaN∕GaN):Mg∕(GaMnN) heterostructures at room temperature

Dilute magnetic semiconductor films (GaMnN) are highly resistive, making transport measurements difficult to achieve. However, when GaMnN films are sandwiched between p-type doped (AlGaN∕GaN) strained-layer superlattices, holes from the superlattice interact with the Mn3+∕2+ ions and transport measurements were realized. The authors have found also that the ferromagnetic properties of GaMnN critically depend on the level of p-type doping in the superlattice. They report anomalous Hall effect measurements in this (AlGaN∕GaN):Mg∕(GaMnN) multilayered structure. The current results also demonstrate the role of carriers, especially holes, in mediating the ferromagnetic properties of GaMnN dilute magnetic semiconductor films.

Correlation between photoluminescence and magnetic properties of GaMnN films

GaMnN films grown by metal-organic chemical vapor deposition were studied by photoluminescence (PL) spectroscopy and hysteresis measurements. Depending on the growth conditions of these GaMnN films, hysteresis measurements along the easy axis of magnetization show a transformation from magnetic to nonmagnetic behavior. The PL spectra of both magnetic and nonmagnetic GaMnN films exhibited GaN band edge and deep-level impurity transitions at 3.4 and 1.3eV, respectively. The PL emission intensity of the 1.3eV emission peak is stronger considerably for magnetic GaMnN films and is believed to be due to the Mn3+ intraband transition.

Investigating the Optical Transmission Spectra of Plasmonic Spherical Nano-Hole Arrays

Plasmonic nano-structures are important for many photonic devices and applications. The optical transmission spectra of such structures are extraordinary. In this paper, we investigate the optical transmission spectra of thin gold films perforated with imperfect circular nano-hole arrays using the finite difference time domain (FDTD). It is observed that both of the intensity and resonance positions of the transmission spectra of perfect plasmonic circular nano-hole arrays are strongly modified due to nano-holes imperfection. Furthermore, we comprehensively study the transmission spectrum of plasmonic spherical nano-hole arrays as a simple example for hole imperfection.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures

Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.

On the investigation of voltage standing wave ratio to design a low noise wideband microwave amplifier

In this paper, a new trend in the design of a microwave amplifier is proposed. The pivot element in the design is to numerically investigate the the relation between VSWR with different frequencies, reflection coefficients, and noise figures. Multiple curves relating the VSWR with both the reflection coefficient and the transducer gain facilitates the location of a starting point for the optimization process involved in the design of microwave amplifiers. The designs obtained by the proposed procedure proved to be accurate and simple.

Investigating the fabrication imperfections of plasmonic nanohole arrays and its effect on the optical transmission spectra

We investigate the extraordinary optical transmission spectra of thin gold films perforated with imperfect nanohole arrays using the finite difference time domain (FDTD) method. Exponential shapes for the nanohole sidewalls are used. To the best of our knowledge, such investigation of transmission spectra of imperfect nanohole arrays has not previously been demonstrated. It was found that the asymmetry between the two openings of the circular nanoholes or bending to their sidewalls strongly modifies both the intensity and resonance positions of the transmission spectra. Furthermore, the results of this study assist in explaining the technicality of extraordinary optical transmission phenomenon and why some experimental results on transmission differ from those expected.

A new visualization technique to design a wideband LNA

For a minimum noise figure (NFmin) operation, this paper presents a new graphical model that characterizes the boundaries of the transducer gain (GT) for an unconditionally stable transistor. First, a full visual view of the transistor operating at minimum noise figure (NFmin) is given. Second, the transistor operating capacity is determined through monitoring both the GT and the voltage standing wave ratio (VSWR). This will aid designers identify suitable transistors according to the required design goals. The model is based on constructing a database to be used for visual representation and fetching appropriate matching impedances for design purposes. A validation is done by using the proposed matching procedure to update circuit component values of a low noise amplifier (LNA) given in literature. The simulation results after update compares favourably with those of the original circuit. Moreover, noticeable improvement in gain flatness, NF and VSWR were achieved.

A Novel Performance Analysis of the Microstrip Antenna Printed on a Cylindrical Body

Performance of a circular patch microstrip antenna is highly affected by the effective dielectric constant of a used substrate material. When the circular patch is conformed on a cylindrical body, the effective dielectric constant is changing with curvature due to the changing in the fringing field. Consequently, some of antenna parameters such as resonance frequency, input impedance, voltage standing wave ratio, return loss, quality factor, and antenna bandwidth are functions of curvature. In this work, we study the effect of curvature on the performance of circular patch microstrip antenna. A mathematical model for the antenna parameters as functions of curvature is also introduced. The model is applied in case of using two substrates of different refractive index values. By extension, the antenna performance was studied through simulation by using method of moments (MoM) which is reliable in solving Maxwell’s integral equations in the frequency domain. The results from simulation compare very favorably with the described analytical results.