Multilayered Sphere Research Articles

Formation of hot spots in multilayer spheres.

A theoretical study of the distribution of the normalized heating potential resulting from a plane wave incident in a multilayered sphere simulating a human head with skin, fat, bone and brain tissue layers has been undertaken. It was found that for spheres of radii 10 cm and 5 cm a relative peak of the normalized heating potential occurs in the vicinity of the center of the sphere. For the case of the 5 cm sphere in the range of frequencies 400 MHZ to 2.76 GHZ the maximum value of the heating potential occurs at the center suggesting the possibility of a hot spot. A comparison between the multilayer and a single layer model shows that the maximum values of the heating potential are the same.

X-Ray Measurement of Residual Stresses in a Multi-Layered Sphere

X-Ray Measurement of Residual Stresses in a Multi-Layered Sphere

Absorption characteristics of multilayered sphere models exposed to UHF/microwave radiation.

The interaction of electromagnetic plane waves with multilayered spherical models composed of lossy dielectric media that represent different biological tissues found in human and animal heads is examined in the frequency range 0.1 to 10 GHz. The model ranges in size from 2 to 12.5 cms outer radius and consists of a core of brain-like material surrounded by five outer layers of CSF, bone, fat and skin-dura tissues. The absorption properties of the model have been analyzed throughout this range of size and frequency. The distribution of internally deposited energy has also been investigated in detail for three basic spheres of 3.3, 6 and 10 cms radii, with emphasis on the creation of localized regions of strong heating (hot-spots). Based on these results, some generalized conclusions are presented on the interaction of microwaves with different sized biological objects.

X-Ray Measurement of Residual Stresses in Multi-Layered Sphere

X-Ray Measurement of Residual Stresses in Multi-Layered Sphere

Love waves and the torsional free modes of a multilayered anelastic sphere

abstract A simple algorithm for the rapid, exact computation of the attenuation factors of the torsional free modes has been developed. The calculations for torsional modes of radial order numbers from 1 to 10 and angular order numbers up to 300 show that, for periods shorter than 120 sec, the attenuation factor (but not Q ) is approximately independent of radial order number j for angular order number v less than about 20. For low angular order numbers, and j > 1, both the period and attenuation factor are roughly independent of angular order number for a given j .

Static Deformation of a Multilayered Sphere by Internal Sources

Summary The Thomson-Haskell matrix device is used to solve the problem of the static deformation of a multilayered spherical Earth model by buried sources. The model consists of p-1 concentric spherical shells plus an inner core; each shell as well as the core being homogeneous, isotropic and perfectly elastic. The point source is represented as a discontinuity in the motion-stress vector across the spherical surface passing through the source. Explicit series expressions in terms of layer matrices are obtained for the displacements and stresses at any point in the medium for three sources: a vertical strike-slip fault, a vertical dip-slip fault and a centre of explosion. The singular case corresponding to the Legendre polynomial of the first degree (n= 1) has been discussed in detail.

Diffraction by a multilayered dielectric-coated sphere with an azimuthal slot

The wall air-gap concept for low-loss lines and reactive-wall waveguides is employed in the exterior problem of a dielectric-coated sphere with an aximuthal slot. The results for the gain and radiation pattern for a specific case are based on a boundary-value solution, and are optimised numerically to establish the concept. It is shown that, for a spherical antenna of electrical radius k0a = 5, coated with a dielectric layer (of thickness and relative permittivity equal to 0.254λ and 16, respectively), which encloses a wall airgap (of 0.00303λ thickness), the increase in gain over the uncoated antenna is 5.17 dB, while the shift in the main lobe is 12.5°.

Spectral response of an elastic sphere to dipolar point-sources

Abstract A stratified elastic sphere is excited by an harmonic dipolar source of arbitrary orientation and depth. The total field is expanded in series of vector spherical harmonics and then condensed into a convenient form of a displacement dyadic. The Haskell-Gilbert matrix method is employed to obtain the radial factor of the displacements for a multilayered sphere. The dependence of the field on the azimuth angle and the fault elements is obtained for the case of a double-couple at depth. Expressions are also developed for the radiation pattern of surface waves over a spherical stratified earth.