We have synthesis ferrite-polymer nanocomposite structures, theoretically and experimentally investigated electromagnetic propagation, absorption properties of these nanocomposite materials at 8-20 GHz in microwave guides. The microwave properties of the samples were investigated by transmission line method, and reflection loss of -59.60 dB was found at 12 GHz for an absorber thickness of 2 mm. These nanocomposites may be attractive candidates for microwave absorption materials.
We propose an optofluidic based on two-dimensional (2D) rod-type silicon photonic crystal (PhC) waveguide that supports self-collimation effect over a large frequency and angle range without any defect or nano-scale variation in the PhC geometry. By analyzing the equi-frequency counter (EFC) of a triangular rod PhC-bands, we verify the optimum band of the structure which is suitable for self-collimation of light beams. By varying the refractive index of fluid being infiltrated into the background of PhC, we perform a systematic study of optofluidic self-collimation of light beams to achieve a wide range of angles and low loss of light. By means of selective microfluidic infiltration and remarkable dispersion properties, we show that it is possible to design auto-collimatator and negative refraction devices based on self-collimation effect with high transmission. We use the plane wave method (PWM) for analyzing the EFC and the finite difference time domain (FDTD) method for simulating the transmission properties.
In this paper, a chiral metamaterial (CMM) with complementary U-shaped structure assembly is proposed. The microwave experimental and simulated results of the proposed complementary structure exhibit giant optical activity. The experimental results are in good agreement with the numerical ones. The retrieval results reveal that negative refractive indices for right-handed and left-handed circularly polarized waves could be easily realized due to strong chirality. The mechanism of the chiral behaviors of resonance frequencies will be illustrated by simulated current distributions. Further, the complementary U-shaped structure assembly also exhibits stronger circular dichroism, giant optical activity, and negative index at near-infrared region by simulations.
The electromagnetic susceptibility model of discontinuous microstrip circuits with the presence of a uniform plane incident wave is established. First, the analytical expressions are modeled as equivalent voltage and current sources for discussing the global effect of the incident plane wave on the associated interconnects. Then, these field-induced equivalent source expressions are incorporated into ADS circuit solver, and a fast model is established for analyzing the output responses of discontinuous microstrip circuits, such as the cross bend, the band-rejection filter and the single-stage amplifier. The corresponding simulation results from the proposed model are validated by comparing the results from both simulation and measurement. The results also show that the incident plane wave may influence the output terminal responses significantly, and the proposed approach would be an efficient method to solve the electromagnetic susceptibility problems associated with the discontinuous microstrip circuits.
In the present communication, we have theoretically investigated and studied the reflection properties of one-dimensional birefringent-dielectric photonic crystal (1D BDPC) structure consisting alternate layers of BD material. From the analysis of the reflectance spectra it is found that 100% reflection region for both TE- and TM-mode can be enhanced significantly in comparison with 1D dielectric-dielectric photonic crystal (DDPC). In order to obtain the reflection spectra of the proposed structure we have used the transfer matrix method (TMM). The structure proposed by us, has a wider omnidirectional reflection (ODR) range in comparison to conventional all dielectric photonic crystals (PCs). The width of ODR can be enlarged by considering the suitable choice of lattice parameters.
A multilayered backscattering model for a lossy medium has been presented in this paper. This multilayered model has been used to calculate the total surface reflection coefficients of a snow pack for both horizontal and vertical co-polarizations. The total surface reflection coefficients include contributions from both surface and volumetric backscattering. The backscattering coefficients calculated by this model were compared with in situ measurements on dry and wet snow. Results show that good agreements are obtained between the model and measurements for the co-polarization modes, especially for the snow with less liquid water content.
In this paper, super-resolution imaging and negative refraction by a two-dimensional (2D) triangular lattices graded photonic crystal (GPC) were studied. The graded photonic crystal (GPC) was obtained by varying the radius in each row so that its effective refractive index changes along the transverse direction. By using Plane Wave Expansion (PWE) method and Finite-Difference Time-Domain (FDTD) method, we show that negative refraction and superlensing can be realized in the designed graded photonic crystal. Numerical simulations show that the photonic crystal structures and frequency have an impact on the resolution.
In this paper, an analytical solution is investigated for the twodimensional problem of electromagnetic scattering of a line source from a perfect electromagnetic conductor (PEMC) circular cylinder coated with an anisotropic media. In the anisotropic region, the relative permittivity and permeability tensors, when referred to principal axes (ρ, φ, z), are biaxial and diagonal. It is demonstrated that the relations of electromagnetic field vectors in anisotropic medium is equal to a PEMC boundary conditions when the parameters of the anisotropic region are chosen in an appropriate manner. Therefore, this region can act as a PEMC cylinder.
We consider the relativistic polarization of a rotating magnetized medium in the framework of the approach suggested earlier (A L Kholmetskii and T Yarman 2010 Eur. J. Phys. 31 1233), which is based on the charge conservation law and relativistic generalization of the first Kirchhoff law to a closed moving circuit carrying steady current. We show that the polarization of a magnet brought to a rotation differs, in general, from the relativistic polarization of a translationary moving magnet, and on this way we give one more explanation to the familiar Wilson & Wilson experiment, with the explicit demonstration of the implementation of the charge conservation law.
A time-dependent nonlinear theory for complex cavity gyrotron is presented in this paper. The theory includes generalized telegrapher's equations and electron motion equations, which are deduced in detail. A calculation code for the self-consistent nonlinear beam-wave interaction is developed based on the presented theory. Using the code, a 94 GHz complex cavity gyrotron operating in TE021-TE031 modes is thoroughly studied. Numerical results show that an output power of 180 kW, about 36% efficiency is achieved with a 50 kV, 10 A electron beam at a focused magnetic field of 1.78 T and a beam velocity ratio of 1.65. The results from MAGIC simulation are also given and an output power of 192 kW, 38.4% efficiency is obtained. This tells the agreement with these two simulation codes.
The calculation of electromagnetic (EM) fields and waves inside finite-sized structures comprised of different media can benefit from a diakoptics method such as linear embedding via Green's operators (LEGO). Unlike scattering problems, the excitation of EM waves within the bulk dielectric requires introducing sources inside the structure itself. To handle such occurrence, we have expanded the set of LEGO sub-domains - employed to formulate an EM problem - to deal with the inclusion of elementary sources. The corresponding subdomains (bricks) play the role of ``generators'' in the equivalent model. Moreover, if a source is ``turned off'', as it were, the enclosing brick can be utilized as a numerical ``probe'' to sample the EM field. In this paper, we present the integral equations of LEGO modified so as to accommodate generator/probe bricks. Numerical results are provided which demonstrate the validity and the efficiency of the approach.
Generation of a wide-band response using partial information from the time domain (TD) data and frequency domain (FD) data has been accomplished in this paper through the use of three different orthogonal functions, such as the continuous Laguerre functions, the Bessel-Chebyshev functions, and the associate Hermite functions. In this hybrid approach, one can generate the early-time response using the method of marching-on-in-time (MOT) and use the method of moment (MOM) to generate the middle-frequency response, as the low-frequency data may be unstable. Since the early-time and the middle-frequency data are mutually complimentary, they can provide the missing low- and high-frequency response and the late-time response, respectively. Even though obtaining middle-frequency response from an object needs more computation time than the low-frequency response, this approach has better performance for the interpolation and extrapolation of a wide-band response.
We present a polarisation rotator based on a dielectrically embedded metal Mesh Half Wave Plate (MHWP) working in the W-band frequency range (75-110 GHz). The device was realised using metallic grids with sub-wavelength anisotropic geometries able to mimic the behaviour of natural birefringent materials. The device was designed using a combination of transmission line codes and finite-element analysis able to achieve phase accuracy down to a fraction of degree. Very accurate intensity and phase measurements were carried out using coherent radiation from a Vector Network Analyser (VNA). The presented device performs better and it is much thinner than previous devices having reduced the number of grids by a factor two and minimised their inductive losses. The new mesh HWP has excellent performances in terms of differential phase-shift flatness and cross-polarisation, respectively 180.4±2.9° and -28 dB across a 25% bandwidth.
Features of the spatial power spectrum (SPS) of multiple scattered ordinary and extraordinary waves in randomly inhomogeneous magnetized plasma are investigated using the smooth perturbation method taking into account diffraction effects. Second order statistical moments are derived for arbitrary correlation function of electron density fluctuations at oblique illumination of magnetized plasma by mono-directed incident radiation. Numerical calculations have been carried out for anisotropic Gaussian correlation function taking into account anisotropy factor and angle of inclination of prolate irregularities with respect to the external magnetic field. It was shown that SPS has a double-peaked shape. External magnetic field narrows SPS for ordinary wave and the gap arises in the direction of prolate irregularities. For extraordinary wave the gap increases with a distance passing by the wave in anisotropic magnetized plasma, the width broadens and maximum slightly displaced.
This paper presents a novel contribution to the analysis of skin-effect like phenomena in radially inhomogeneous tubular geometries that fit in the category of Euler-Cauchy structures (ECS). The advantage of ECSs is that solutions for the electromagnetic field can be described by very simple closed form formulae. This work addresses the evaluation of the per unit length complex magnetic reluctance of tubular ferrites, taking into account that their complex permeability strongly depends on the frequency. The motivation for this research is linked up with the nascent theory of magnetic transmission lines (MGTL), where the wave guiding structure is made of a pair of parallel ferrimagnetic pieces, and whose performance is critically dependent on the complex magnetic reluctance of its component pieces. The analysis presented is mainly focused on high frequency regimes up into the GHz range.
In this paper, transient electromagnetic scattering by general Chiral objects is investigated using time-domain integral equations with the Poggio, Miller, Chang, Harrington, Wu, and Tsai (PMCHWT) formulations. By introducing a pair of equivalent electric and magnetic currents, electromagnetic fields inside a homogeneous Chiral region can be represented by these sources over its boundary. The uncoupled equations are solved numerically by the Galerkin's method that involves separate spatial and temporal testing procedures. The scaled Laguerre functions are used as the temporal basis and testing functions. The use of the Laguerre functions completely removes the time variable from computation, and the results are stable even at late times. Numerical results are presented and compared with analytical results, and good agreements are observed.
Time reversal focusing of electromagnetic waves is investigated in case of source motion. We extract analytical formulation of uniformly moving source in presence of ideal time reversal cavity (TRC) and a more realistic model, time reversal mirror (TRM). Similar to the acoustic case, it has been observed that in case of moving point source spatial focusing is still achievable. Furthermore, we also investigate super resolution effects on time reversal (TR) focusing of moving source in continuous random media. Results shows that an increase in (multipath) leads to better focusing resolution of the time-reversed signals.
Tapered resistive strip realized by patterning the constant resistive strip is used to suppress edge scattering of a finite wedge. The suppression effect is simulated and evaluated by the reduction in mono-static RCS (Radar Cross Section). This reduction is compared with the one which loaded by the ideal tapered resistive strip. The result indicating that patterning a constant resistive strip to create a gradient in sheet resistance is feasible. To verify this method of fabricating tapered resistive strip, patterned resistive strip with a proper gradient in sheet resistance is conducted and loaded on the wedge target for test. The gradient in sheet resistance used for test is obtained from the optimization. Resistive strip with this sheet resistance gradient renders a promising effect of edge scattering suppression. The test result shows a reduction of 20dB for the geometric mean of mono-static RCS in the angular range of 45º. This value is close to the one of 23dB in simulation.
The internal electric-field distribution from single layers of dielectric spheres with high refractive index (n=2.65) has been analyzed for a number of different compactness cases by FDTD (Finite-Difference Time-Domain) method. The field distributions from the transmission spectra were compared with the internal electric-field distribution of the Mie modes of an isolated sphere. In general, the agreement is very good in almost all cases studied. The results show that TE and TM Mie modes are the origin of the resonances in the transmission spectra of the single layers. The resonances of the monolayer attributed to TE11 and TM11 Mie modes are only excited for compactness values lower than 0.38, suggesting a dependence of periodical arrangement effects for these modes. Moreover, the field distribution corresponding to some of the dips in the spectrum cannot be directly attributed to Mie modes (TE21). The result indicates these are formed by degenerated or weakly coupled Mie modes induced by the periodic structure.
ΛOptical bistability (OB) behavior of a Kobrak-Rice 5-level quantum system is investigated. It is demonstrated that the OB of the system can be controlled by either the intensity or relative phase of driving fields. We have also shown that by applying an incoherent pumping field, the OB behavior of the system changes and the considerable output is obtained for zero input in the gain region induced by incoherent pumping field.