Selective wavelength tuning of multiple quantum well based infrared photodetector is achieved by nonuniform doping distribution as well as dimensional variation in the structure. Result is obtained from the computation of the intersubband transition energy through self-consistent solution of the Poisson's and Schrödinger equations with appropriate boundary conditions. Absorption coefficient is estimated in presence of external electric field applied along the direction of confinement. Suitable choice of structural parameters is required to tailor the peak position of absorption spectra for application in the infrared range as optical receiver.
The transmission and reflection coefficients of electromagnetic waves propagating through the finite periodically layered chiral structure are defined both theoretically (using the propagation matrix method) and experimentally. The coefficients of the propagation matrix of the periodically layered chiral medium are obtained. The boundaries of the forbidden bands for a periodic medium, whose unit cell consists of two different chiral layers were determined. It is shown that the boundaries of the forbidden bands do not depend on the chirality parameter of the layers. It is found that for certain values of the layers thicknesses, the forbidden band widths tend to zero and that the proposed method for calculation of the reflection and transmission coefficients can be used to determine the effective constitutive parameters of artificial chiral metamaterials. The transmission and reflection coefficients of plane electromagnetic waves propagated through the finite periodically layered chiral structure were determined experimentally for 20-40 GHz range. A good agreement between the experimental results and theoretical studies of the forbidden band spectrum for the structure under research has been shown.
As the boundary of the universe which is explored by human expanded, antenna used in deep space exploration (DSE) could become too large to carry and deploy, miniature deep space probe based antenna arrays (MDSPBAA) provide a novel solution for the problem. This kind of antenna array may lower the difficulty of sending antenna to the area where is tend to be detected and may also monitor cost effectively in the work of deep space detect. However, turbulence and positional errors provide a challenging operational environment when it comes to the implementation of these systems. Turbulence will deteriorate SLL badly. In some cases, the level could be changed by almost 10 dB. Therefore, a SLL control algorithm is presented, which could well compensate the SLL which is caused by positional error.
The Casimir force between an ellipsoid and a plate can be tuned by using the combination of anisotropic materials and nonlinear materials exhibiting the AC Kerr effect. The force was obtained numerically by using the FDTD method, based on the Maxwell's stress tensor. The results indicate that the force can be significantly varied by changing the intensity and location of the laser, as well as the properties of material. The sensitive changing between ellipsoid and plate structure with different materials' properties provides new possibilities of integrating optical devices into nano-electro-mechanical systems (NEMS).
In this paper, an efficient three-dimensional Laguerre-based finite-difference time-domain (FDTD) method is used to analyze planar circuits. An iterative procedure is introduced to improve the accuracy. Both the time-domain waveforms and the S-parameters are presented. The numerical results show that at the comparable accuracy, the efficiency of the Laguerre-based FDTD method with an iterative procedure is superior to the FDTD method and alternating-direction implicit (ADI) FDTD method.
Based on the conventional finite-difference time-domain (FDTD) method, a novel dual-meshed technique is presented to deal with the underwater detection problems applying in low frequency electromagnetic wave. A transformation surface connecting the coarse cell with the fine cell is implemented by applying a total-field scattered-field source (TSS) technique, which is carried out by two-step FDTD simulation. The ratio of a coarse cell size to a fine cell size can be set as an arbitrary integer, such as N=10. Moreover, it is illustrates that non-physical reflection fields from the TSS surface are avoided by introducing the TSS surface. We have derived, in detail, the update equations of fields on grids of the TSS surface. Three cases of dealing with different underwater electromagnetic problems are discussed. Numerical results show that by analyzing the magnitude and phase of scattered fields from obstacles underwater we can distinguish the category of the obstacles which belongs to either a high resistivity body or a low resistivity body. Therefore, the proposed method provides us an effective tool for analyzing the electromagnetic response of materials underwater.
Scattering from array antennas is a complicated problem, containing the structural and mode items in nature. The complexities in analyzing the latter one also come from the feeding network that follows antenna unit ports, where active or anisotropy devices may exist. Therefore, it is significant that an efficient method can be constructed to analyze array antenna scattering with arbitrary port reflections. In this work, we address this problem by adopting the S-matrix model for the antenna array, aiming to efficiently and accurately compose the mode scattering in case of arbitrary reflections at feeding ports. In the numerical process, the antenna reciprocity is utilized in obtainning the basis for the scattering composition analysis. In case of various loading conditions, numerical results are presented, showing that the composed scattering results by the S-matrix model agree well with that obtained by direct full scale simulations. Then the methods for obtaining radiation and scattering of a large antenna array based on results of a small array, are reviewed and extended in composing the large antenna array scattering in case of variable loading conditions. And, promising results are obtained.
The present paper describes an integrated approach for design, fabrication and encapsulation of RF MEMS switches in view of the optimal performance subsequent to packaging. `Top and bottom contact' fabrication approaches are explored using different RF MEMS switch topologies. In the `bottom contact package (BCP)' the packaging cap alignment is less critical as compared to the top contact packaging (TCP) approach where contact via is an integral part of the cap. In this case, the connection layout through silicon via holes is independent of the cavity geometry. For the devices under consideration, bulk etched silicon cavity height has been optimized to 50 μm for optimal RF performance e.g. isolation and insertion loss. Parasitic effects of top silicon cap are reduced by altering CPW impedance. Mechanical parameter damping is simulated for different cavity heights and found to be independent from cavity height after 20 μm onwards.
In this paper, we present a detailed analysis on the invalidation of the polar format algorithm (PFA) for the dechirped echo signals in inverse synthetic aperture radar (ISAR) imaging. After the translational motion compensation, the polar section of the dechirped signals is often undermined, and then the PFA is invalid. A revised method by range shifting is proposed to compensate the echo signals, and the standard polar section is obtained. An improved performance was achieved on the simulated and real data experiments. The theoretical analysis and the proposed method are confirmed.
This study proposes an accurate estimation of whole-body averaged specific absorption rate (WBA-SAR) for far-field exposure of an isolated human body in the frequency range of 10-200 MHz based on a lossy homogenous cylindrical antenna model of the human body. Equations are derived for the total induced axial current and the whole-body averaged SAR based on a rigorous treatment of cylindrical antenna theory. An explicit formula for the resonance frequency in terms of the anatomical parameters and the dielectric properties of the body is proposed for the first time. Moreover, important phenomena in far-field radio frequency (RF) dosimetry, such as, the cause of resonance and the SAR frequency characteristics are discussed from an antenna theory perspective.
In this paper we present a detailed theoretical analysis of lateral and angular misalignment effects in RF coils. Radio-frequency (RF) coils are used extensively in the design of implantable devices for transdermal power and data transmission. A design procedure is established to maximize coil coupling for a given configuration to reduce the effects of misalignment on transmission efficiency. Formulas are derived for the mutual inductance between all possible coil configurations including the coils of cross section, thin solenoids, pancakes and filamentary circular coils whose axes are laterally and angularly displaced. Coils are in air. In this approach we used the filament method and the mutual inductance between filamentary circular coils placed in any desired position. We completely describe all mathematical procedures to define coil positions that lead to relatively easy method for calculating the mutual inductance between previously mentioned coils. The practical coils in implantable devices fall into two categories: disk coils (pancakes) and solenoid coils. From the general approach for calculating the mutual inductance between coils of rectangular cross section with lateral and angular misalignments the mutual inductance between misalignment solenoids and disks will be calculated easily and accurately.
The accuracy of scattering measurements in near-field millimeter-wave cylindrical scanning imaging system is often degraded by the contamination from additive noise and clutter. Thus, efficient noise removal technique is necessary to achieve accuracy improvement. This paper proposes an independent component analysis denoising algorithm, which relies on the assumption of statistical independence of the sources, where high order statistical properties are used. In the algorithm, the virtual noise components are incorporated into the independent component analysis model, which expands original one-dimensional observation to virtual multi-dimensional observations. The computationally efficient sources estimation technique is presented, based of joint diagonalization of fourth order cumulant matrix. The high speed millimeter-wave near-field cylinder scanning imaging system is set up to verify the denoising results of range profiles, three-dimensional scatter intensity and two-dimensional projection images. The results indicate both the feasibility and validity of the proposed denoising algorithm to be applied in the near-field millimeter-wave cylindrical scanning imaging system.
The analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) by confined electrons in rectangular quantum wires (RQWs) in the presence of laser radiation modulated by amplitude are calculated by using the quantum kinetic equation for electrons with the electron-optical phonon scattering mechanism. Then, the analytic results are numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results show that the ACF of a weak EMW in a RQW can have negative values, which means that in the presence of laser radiation (non-modulated or modulated by amplitude), under proper conditions, the weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case of the absence of laser radiation. The results also show that in some conditions, when laser radiation is modulated by amplitude, ability to increase a weak EMW can be enhanced in comparison with the use of non-modulated laser radiation.
In a real airborne synthetic aperture radar (SAR), its major phase errors are usually composed of two categories, such as slow-time varying phase errors (less than several cycles of change in phase during synthetic aperture time) and fast-time varying phase errors (otherwise, including wide band random) according to the motion of aircraft. If the fast errors are no more negligible compared to the slow errors, they should be estimated and then compensated accurately to obtain a well focused image. However, it is not proper to estimate all phase errors at the same time like conventional autofocus techniques because the estimation of the fast-time varying phase errors are seriously affected by blurring in image due to the slow-time varying phase errors. In this paper, we presents an accurate hybrid phase estimation technique using two independent estimation stages of sub-aperture and an iterative golden section search method, which has advantages over several existing methods, because of its better estimation accuracy and less sensitive to the quality of extracted range bins as well as requiring less computation time. The performance of our method is illustrated by simulations of point targets and an experiment with real SAR data.
Soil density is one of the important parameters to be investigated in civil, geological and agricultural works. Unfortunately, the challenging issue is found on the suitable model in determining accurately the soil density. In this article, a new soil density model based on radio-wave surface reflection method is presented. The development of the model is based on result analysis collected from the experiment. Then, comparisons with related theoretical models, Hallikainen and Topp, are performed. The experiment is performed by using a vector network analyzer (VNA) that generates radar signal and recording return loss (S11) from a horn antenna. In the analysis, two new proposed soil density models have shown good agreement for soil density from 1.1 g/cm3 to 1.7 g/cm3 for sand and silty sand samples. This is verified when the model able to predict real samples as the one used in the experiment and result shows a very small relative error within 0.05% and 6.87%. Additionally, spectrograms in real time were produced in this study in order to observe more on the soil density. By using the proposed developed models, soil density estimation can be easily determined with minimal data input such as soil type, return loss and reflection coefficient by using regular radio-wave devices.
Three-dimensional Finite-Difference in Time-Domain method is applied to simulate Low Frequency antennas in the presence of natural environments. All antennas are made up of wires set down on a square shaped ground plane and their dimensions depend on the wavelength of the source. Both monopole and inverted L antennas are considered in this paper. The antenna systems are computed in the presence of two examples of natural elements: a large forest and then on the top of a hill. The main aim of this paper is to show the effects of these environments on the properties of the antennas and on the efficiency of the ground wave excitation. The outcome of these investigations shows a power ratio enhancement of several decibels when the two kinds of antenna described in this paper are located on the top of a hill. On the other hand, the effects of a large forest depend on the geometry of the antenna. It doesn't affect the radiation of a quarter-wave monopole antenna, on the contrary losses disrupt radiation when an inverted L antenna is built in the middle of a large forest.
Enhancement of the reflection bands in ultraviolet region by using one-dimensional multi quantum well (MQW) photonic crystal (PC) structure has been investigated theoretically. The proposed structure is composed of three MgF2/SrTiO3 MQWs. The range of reflection band is investigated from the reflectance spectra of the one-dimensional MQW photonic crystal structure obtained by Transfer Matrix Method (TMM). From the numerical analysis it is observed that a range of reflection band for a single MQW PC is very narrow though it increases as the thickness of layers increases. But when three MQWs of MgF2/SrTiO3 are used we get much enlarged reflection band covering the range 119.8 nm-311.3 nm (reflectivity > 99%) with bandwidth 191.5 nm, for normal incidence. Further, we see that when the angle of incidence is increased, the width of reflection band increases in case of TE wave with a decrease for TM wave, because this omnidirectional reflection (ODR) band is very much narrow in UV region. We have computed ODR band upto incidence angle 50˚ for single as well as combined MQW PC. Analyzing the reflectance curve for incidence angle up to 50˚ for both TE and TM polarizations we find that by applying the combine MQW PC, omnidirectional reflection band increases significantly in comparison to single MQW structure. The proposed MQW photonic crystal structure is very useful in designing ultraviolet shielding for drugs, ultraviolet reflector for protecting damage of DNA and in skin diseases especially for skin cancer.
In this paper, we theoretically study the phase treatment of reflected waves in one-dimensional Fibonacci photonic quasicrystals composed of nano-scale fullerene and semiconductor layers. The dependence of the phase shift of reflected waves for TE mode and TM mode on the wavelength and incident angle is calculated by using the theoretical model based on the transfer matrix method in the infrared wavelength region. In the band gaps of supposed structures, it is found that the phase shift of reflected wave changes more slowly than within the transmission band gaps. Furthermore, the phase shift decreases with the incident angle increasing for TE mode, and increases with the incident angle increasing for TM mode. Also, for the supposed structures it is found that there is a band gap which is insensitive to the order of the Fibonacci sequence. These structures open a promising way to fabricate subwavelength tunable phase compensators, very compact wave plates and phase-sensitive interferometry for TE and TM waves.
Here the hollow vortex Gaussian beam is described by the exact solution of the Maxwell equations. By means of the method of the vectorial angular spectrum, analytical expressions of the electromagnetic fields of a hollow vortex Gaussian beam propagating in free space are derived. By using the electromagnetic fields of a hollow vortex Gaussian beam beyond the paraxial approximation, one can calculate the orbital angular momentum density distribution of a hollow vortex Gaussian beam in free space. The overall transverse components of the orbital angular momentum of a hollow vortex Gaussian beam are equal to zero. Therefore, the influences of the topological charge, beam order, Gaussian waist size, and linearly polarized angle on the distribution of longitudinal component of the orbital angular momentum density of a hollow vortex Gaussian beam are numerically demonstrated in the reference plane. The outcome is useful to optical trapping, optical guiding, and optical manipulation using the hollow vortex Gaussian beams.
The prediction of Radar Cross Section (RCS) of complex targets which present shadowing effects is an interesting challenge. This paper deals with the problem of shadowing effects in the computation of electromagnetic scattering by a complex target using Iterative Physical Optics (IPO). The original IPO is limited to cavities applications, but a generalized IPO can be applied to arbitrary geometries. This paper proposes a comparison between the classical PO approach and a physical approach based on shadow radiation (around forward direction) with PO approximation for the consideration of shadowing effects in generalized IPO. Based on the integral equations, a rigorous demonstration of this physical shadowing is provided. Then simulation results illustrate the interest of using physical shadowing both from the transmitter and towards the receiver, compared to the classical approach.