Ux Densities Research Articles

EFFECTS ON THE ENERGY FLUX DENSITY DUE TO PITCH IN TWISTED CLAD OPTICAL FIBERS

The paper deals with the propagation of electromagnetic waves through twisted clad dielectric optical flbers. The structure of these flbers is analogous to travelling wave tubes used in microwave devices, and the usefulness would be in the areas of optical sensing. This is because the twists in flber would be afiected due to the imposed stress and/or strain, leaving thereby the possibility to alter the propagation characteristics. A rigorous analytical investigation has been carried out with the emphasis on the energy ∞ux density patterns due to the difierent propagating modes in the flber. The dispersion relations of the system are deduced and the energy ∞ux densities are evaluated under difierent pitch angles of twist. The efiect due to conducting helix pitch on the electromagnetic wave propagation is emphasized.

MULTILEVEL GREEN'S FUNCTION INTERPOLATION METHOD SOLUTION OF VOLUME/SURFACE INTEGRAL EQUATION FOR MIXED CONDUCTING/BI-ISOTROPIC OBJECTS

This paper proposes a multilevel Green's function interpolation method (MLGFIM) to solve electromagnetic scattering from objects comprising both conductor and bi-isotropic objects using volume/surface integral equation (VSIE). Based on equivalence principle, the volume integral equation (VIE) in terms of volume electric and magnetic ∞ux densities and surface integral equation (SIE) in terms of surface electric current density are flrst formulated for inhomogeneous bi-isotropic and conducting objects, respectively, and then are discretized using the method of moments (MoM). The MLGFIM is adopted to speed up the iterative solution of the resultant equation and reduces the memory requirement. Numerical examples are presented to show good accuracy and versatility of the proposed algorithm in dealing with a wide array of scattering problems.

Flares of Sagittarius A* at Short Millimeter Wavelengths

We have performed intensity monitoring observations toward the Galactic center compact nonthermal radio source, Sagittarius A*, at λ = 3 and 2 mm (100 and 140 GHz) from 1996 to 2002 using the Nobeyama Millimeter Array (NMA). In 1996, 1997, 1998, and 2000, the observations were performed during a period of one to two months for each year in a single (intermediate resolution) array con.guration in order to exclude a systematic error caused by sampling different source structures with the different beam sizes. From November 2000 to May 2001, and from November 2001 to May 2002, the observations were carried out over several months in order to investigate the longer term variability. We have detected two .ares in March 2000 and April 2002 as well as a .are observed in March 1998 (Tsuboi et al. 1999). The peak .ux densities of the .ares were 2-3 Jy at 3 mm, while the mean quiescent .ux densities was ∼1 Jy. In particular for the March 2000 .are, the .ux densities of Sgr A* at 2 mm had also reached a peak, ∼4 Jy, on 8 March and increased ΔS/S ∼ 300%. The .ux density decreased by half in a day. We have detected the intra-day variability of Sgr A*. The upper limit for size of the variable component estimated from timescale of the .are is a few tens of AU. For spectra made from our observations at mm-wavelengths, the variability of .ux density increases with frequency. It appears that the variability in the .are propagates from higher to lower frequency. The folded lightcurve with 106 days cycle, which determined from the analysis of the VLA cm-wavelength data, shows distinct high and low activity states. These results provide evidence for quasiperiodic variability of the .ux density of Sgr A* at mm-wavelengths.

Three-Dimensional Piezoelectric Boundary Element Method

The boundary element method is applied to problems of three-dimensional linear piezoelectricity. The continuum equations for conservation of linear momentum and charge are combined into one governing equation for piezoelectricity. A single boundary integral equation is developed from this combined e eld equation and Green’ s solution for a piezoelectric medium. Green’ s function and its derivatives are derived using the radon transform, and the resulting solution is represented by a line integral that is evaluated numerically using standard Gaussian quadrature. The boundary integral equation is discretized using eight-node isoparametric quadratic elements, resulting in a matrixsystem ofequations. Thesolution of theboundary problem forpiezoelectricmaterialsconsistsof elastic displacements, tractions, electric potentials, and normal charge e ux densities. The complete e eld solutions can be obtained once all boundary values have been determined. The accuracy of this linear piezoelectric boundary element method is illustrated with two numerical examples. The e rst involves a unit cube of material with an applied mechanical load. Thesecond exampleconsistsof a spherical holein an ine nitepiezoelectricbody loaded by a unit traction on itsboundary. Comparisonsare made to the analytical solution for the cube and an axisymmetric e nite element solution for the spherical hole. The boundary element method is shown to be an accurate solution procedure for general three-dimensional linear piezoelectric material problems. I. Introduction T HEbrothersPierreandJacquesCuriediscoveredpiezoelectricity in 1880 during their investigation of crystals. A coupling occurs between the electrical and mechanical e elds in these materials, such that application of an external mechanical loading induces achangeinpolarizationproportionaltoit.Conversely,applicationof an electric e eld produces a proportional material deformation. This phenomenon was discovered in ceramics in the 1940s, and the subsequent manufactured piezoceramic materialshave higher coupling properties than their naturally occurring predecessors. This strong piezoelectric effect has made these materials an important part of the emerging technologies of smart materials and structures. Smart structures are those that incorporate actuators and sensors that are integrated into the structure and have structural functionality. The sensors and actuators are used to ine uence the structure’ s states