Spherical Slot Research Articles

Gain manipulation of a slotted sphere using general bi-isotropic coating.

The gain characteristics of a general bi-isotropic (BI) coated slotted sphere have been studied using numerical calculations. An eigenfunction expansion method has been used to derive analytical expressions for the radiated electric and magnetic fields. The effects of various BI and Tellegen coatings upon the gain pattern are investigated. It is proven that the chirality and Tellegen parameters of the coating can significantly modify the gain. It is found that a lossless BI coating has the highest gain in the forward direction as compared to lossless dielectric, Tellegen, and chiral coatings. Such type of enhanced gains in the forward direction are desirable for point-to-point communication. It is further shown that the Tellegen coating guides most of the radiated field from the slot toward polar directions and reduces the gain in the forward direction provided that the Tellegen parameter is not close to unity. For a Tellegen coating whose Tellegen parameter is close to unity, the maximum gain in the forward direction is found. The proposed theory is also extended to realistic BI and low-loss dielectric coatings. It is investigated that by using a proper selection of coating thickness, the forward direction gain of a realistic BI coating can be enhanced or diminished as compared to a low-loss dielectric coating.

Gain characteristics of a metamaterial coated slotted sphere

An analysis about the effects of various metamaterial coatings and background media upon the gain characteristics of a slotted sphere is presented using numerical simulations. It is found that the gain characteristics of a coated slotted sphere can be controlled by varying the electromagnetic parameters of coatings and background media. It is studied that the thickness of different coating layers has a significant effect upon the gain in the forward direction. It is further investigated that a double negative metamaterial coating can be used to greatly enhance the forward direction gain for certain values of the permittivity and the permeability. It is also shown that single near zero and double near zero background media enhance the forward direction gain of a dielectric-coated slotted sphere and reduce the gains for angles closer to polar directions as compared to the free space background.

Gain properties of an uncoated and chiral coated slotted sphere embedded in a chiral background.

The gain properties of an uncoated and a chiral coated slotted sphere embedded in a chiral background have been investigated using numerical simulations. In this paper, it is found that a chiral background medium enhances the gain of an uncoated slotted sphere in the forward direction as compared to the free space background. It is shown that the forward direction gain of a chiral coated slotted sphere embedded in a chiral background increases with the increase in the background chirality. It is further determined that the maximum gain moves away from the polar direction toward the forward direction as the chirality of the coating increases for a fixed background chirality. Also, this maximum gain gradually decreases as the chirality of the coating increases. An interesting feature of an angular window is introduced for a chiral coated slotted sphere embedded in a chiral background where the gain is nearly constant for a specific range of angles.

A simple phase-field model for interface tracking in three dimensions

Based on a conservative phase-field lattice Boltzmann (LB) method, we present a 3D model for tracking an interface in multiphase flows. In addition to being mass-conserving, the main advantage of this LB method is that the collision process is made entirely local by invoking central moments in the calculation of vectors normal to the interface. We construct the model on different 3D lattices (D3Q7 and D3Q15) with inherently distinct isotropy properties. To test the model we conduct a variety of benchmark studies, such as the evolution of an interface in the form of a slotted sphere in a rotational flow field, and the evolution of a spherical interface in a vortex flow, a deformation flow, and a shear flow. The results of these benchmarks are compared against the finite-difference-based version of the LB model, in which a non-local finite-difference scheme is used to calculate the interface normal. In terms of error, the moment-based model, while competitive, is generally outperformed by the finite-difference model. Despite this, the moment-based interface tracking model is inherently more efficient, and deserves consideration, particularly for memory-distributed parallel computing. We also consider the interaction between a binary fluid and a solid wall, and introduce a method to implement the three-phase contact angle within this framework. The proposed model for dealing with the contact line is simple, clean, and straightforward to implement, and shown to recover desired contact angles very well.

Von Mises stress analysis on compliant-based Hooke's joint using the ANSYS software

Kinematically a Hooke's joint is equivalent to a slotted sphere type of a joint which has two degrees of rotational freedom. The original design consists of two identical parts assembled at right angles with respect to each other. To simplify the compliant joint into conventional rigid-body joint the pseudo-rigid-body model technique was used. Hooke's joint whose compliant parts are made of blue polished spring steel (AISI 1080) is considered for stress analysis. Stress analysis of the design performed by analytical method and then finite element analysis is used for comparison. First, both the geometries are sketched with CATIA V5, then finite element analysis was performed for different shaft angles. For finite element analysis, ANSYS 13.0 workbench software is used. Stress values are calculated for the design with 0.5-mm-thick material and for shaft angles 1° to 18°. It is verified that results of experiments are consistent with theoretical approaches. With the help of stress values, yield strength of the compliant-based Hooke's joint may be observed which will further help in defining the life of the compliant-based Hooke's joint. Design of compliant-based Hooke's joint has the advantages of having small number of different parts, ease of manufacturing and compactness.

Scattering analysis of curved FSS using Floquet harmonics and asymptotic waveform evaluation technique

In this paper, we present the scattering characteristics of infinite and finite array using method of moment (MoM) with Floquet harmonics and asymptotic waveform evaluation (AWE) technique. First, infinite cylindrical dipole array is analyzed using the MoM with entire domain basis function and cylindrical Floquet harmonics. To provide the validity of results, we fabricated the cylindrical dipole array and measured the transmission characteristics. The results show good agreements. Second, we analyzed the scattering characteristics of finite array. A large simulation time is needed to obtain the scattering characteristics of finite array over wide frequency range because Floquet harmonics can`t be applied. So, we used the MoM with AWE technique using Taylor series and Pade approximation to overcome the shortcomings of conventional MoM. We calculated the radar cross section (RCS) as scattering characteristics using the proposed method in this paper and the conventional MoM for finite planar slot array, finite spherical slot array, and finite cylindrical dipole array, respectively. The compared results agree well and show that the proposed method in this paper is good for electromagnetic analysis of finite FSS.

A least-square weighted residual method for level set formulation

In this paper, a least-square weighted residual method (LSWRM) for level set (LS) formulation is introduced to achieve interface capturing in two-dimensional (2D) and three-dimensional (3D) problems. An LSWRM was adopted for two semi-discretized advection and reinitialization equations of the LS formulation. The present LSWRM provided good mathematical properties such as natural numerical diffusion and the symmetry of the resulting algebraic systems for the advection and reinitialization equations. The proposed method was validated by solving some 2D and 3D benchmark problems such as those involving a rotating slotted disk, the rotation of a slotted sphere, and a time-reversed single-vortex flow and a deformation problem of a spherical fluid. The numerical results were compared with those obtained from essentially non-oscillatory type formulations and particle LS methods. Further, the proposed LSWRM for the LS formulation was coupled with a splitting finite element method code to solve the incompressible Navier–Stokes equations, and then, the collapse of a 3D broken dam flow was well simulated; in the simulation, the entrapping of air and the splashing of the surge front of water were reproduced. The mass conservation of the present method was found to be satisfactory during the entire simulation. Copyright © 2011 John Wiley & Sons, Ltd.

A circularly polarized conical beam spherical slot array antenna

This paper proposes a circularly polarized conical beam spherical slot array antenna which is suitable for a low elevation angle land mobile satellite communication subscriber. The structure of this antenna type is very simple to fabricate; i.e. a ring of perpendicular slot pairs is cut on an outer surface of a concentric conducting spherical cavity. From the assumption of weak coupling of the slots from the cavity, the conical beam pattern can be obtained. Experimental results that verify the conical beam radiation are in good agreement with the design.

Radiation characteristics of a slot antenna on a conducting prolate spheroid

In this paper, the radiation characteristics of an asymmetrical slot antenna on a conducting prolate spheroid are considered. The radiated fields are expanded in terms of prolate-spheroidal vector wave functions. The unknown expansion coefficients are determined by a system of equations derived from the boundary conditions. Numerical results for radiation patterns and conductance are obtained and compare well with published data for a slotted sphere. The effect of the slot length and the shape of the spheroid on the magnitude of the radiated field and radiation conductance is also presented.

A spherical slot array applicator for medical applications

A new type of microwave hyperthermia applicator is proposed and analyzed. A cavity, consists of concentric conducting partial spheres which are enclosed by a part of a conducting cone, is employed to excite an array of slots coherently. From numerical results that the authors obtained, it is possible to focus the electric field radiated from the slots to the center of the sphere where a tumor is assumed to be located. Furthermore, SAR distributions of some applicators are obtained by using computer, and these applicators have been designed. From the measured results of electric field distributions at 2450 MHz, it is found that the focusing characteristics are achievable. Thermographic studies show that the heating volume can be varied by using different number of slots and the maximum heating depth is 3 cm. >

Resonance Effects in Slotted Spherical Antennas Coated with Homogeneous Materials

Radiation from a perfectly conducting slotted sphere coated with a homogeneous material is investigated. It is found that for some values of the coating thickness certain modes become resonant, which greatly enhance the radiated power and affect the radiation field. The enhancement in the radiated power, however, depends on the loss tangent of the coating material and reduces rapidly as the loss tangent increases.

Electromagnetic fields in a spherical cavity with a concentric anisotropic shell system

The boundary-value problem consisting of a double-sheathed slotted sphere is solved. The inner sphere or core is perfectly conducting except for an infinitesimally thin annular ring which is excited by a voltage V0. Two thin plasma shells are located concentrically about the core. The inner one is effectively isotropic, whereas the outer one is anisotropic by virtue of a d-c. magnetic field whose radial component is assumed constant for present purposes. It is indicated that the cavity resonances of the system are significantly damped by the presence of the inner shell.

RADIATION FROM A SPHERICAL ANTENNA WITH AN ANISOTROPIC PLASMA SHEATH

The boundary-value problem for a concentric spherical system consisting of an infinitesimally thin shell of magnetoplasma surrounding a source-excited slotted sphere is solved. The solution is carried out in some detail under the assumption that the properties of the sheath do not vary with the angular coordinates. It is indicated that the anisotropy of the sheath introduces a cross-polarized component of the radiated field. The extension to a sheath, with a spatial variation of its properties, is outlined briefly.

A quasi-"Isotropic" antenna in the microwave spectrum

The general problem of radiation by apertures on spherical surfaces was first considered theoretically by Stratton and Chu in 1941. More recently, the problem was again considered by Bailin and Silver, and Mushiake and Webster. All numerical and experimental efforts to date have been restricted to the special case of a very small sphere as measured in wavelengths. This paper is in effect an extension of the previous results to the case of large spheres uniformly excited by an equatorial slot of varying size. The detailed numerical and experimental results are restricted to the first TM and TE modes. In general, it is possible to show that the large spherical slot antenna can be made unusually "isotropic" with a far-field coverage factor of over 98 per cent.