摘要:

A combined finite element and analytical method is presented here for analyzing scattering of time harmonic horizontally polarized shear (SH) waves by material and geometric irregularities in an isotropic linearly elastic infinite plate. All the irregularities are assumed to be contained in a bounded region. The problem of scattering is solved by replacing this region with a finite element mesh. A nodal force‐displacement relation is developed to satisfy the continuity conditions along the boundaries separating the inner finite‐element region from the exterior regular region. The method is illustrated by solving the problem of scattering of SH waves by a surface breaking crack. The crack is taken to be normal to the surface of the plate. The reflection and transmission coefficients are computed for zeroeth, first, and second incident wave modes. The validity and accuracy of the results are checked by satisfaction of the energy conservation principle and the reciprocity relations.

ISSN:0021-8979    

DOI:10.1063/1.332096

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The intensity fluctuations of incoherent radiation are used to determine the position of sources with respect to a detector system. For electromagnetic radiation the system uses square‐law detectors and for acoustic waves the detector output is squared before being processed. The theory is developed forndetectors and the results are applied to two‐, three‐, and four‐detector arrangements. The two‐detector intensity inteferometer measures the square of the first‐order correlation function and can determine the angular size of a source. The three‐detector intensity interferometer yields two coordinates of the location of a source, and a modified version involving only one detector functions as a Fourier transform spectrometer. It measures the first‐order correlation function and thus can be used to obtain the spectrum of the source. The four‐detector intensity interferometer can simultaneously determine the three‐dimensional coordinates of several sources. The operation of several acoustic multidetector intensity interferometers are described and a number of applications are discussed.

ISSN:0021-8979    

DOI:10.1063/1.332097

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We analyze the statistical properties of Gaussian and non‐Gaussian signals detected by a nonideal photon detector. Such a detector is assigned a realistic response function, and parameters like average intensity and bunching property are evaluated. We show that there is a significant difference between the signal detected by an ideal and a nonideal detector.

ISSN:0021-8979    

DOI:10.1063/1.332098

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An alternative method to that of Caldwell [J. Phys. D12, 1653 (1979)] is used to calculate the effects of iron on the magnetic field produced by a current‐carrying axisymmetric conductor. In this way a neater solution is obtained by constructing the Green’s function from an eigenfunction expansion. Good agreement with the previous results is achieved and an indication is given of the advantages of this Green’s function approach.

ISSN:0021-8979    

DOI:10.1063/1.332099

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The magnetostatic self‐energy is expressed in terms of integrals which are easier to manipulate than the conventional Green function of the potential. Specific expressions are derived for a finite ferromagnetic particle, in the form of a right‐circular cylinder, which has no volume charge.

ISSN:0021-8979    

DOI:10.1063/1.332100

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The current distribution on a two‐coupled circular microstrip disk antenna fed by two probes is rigorously derived using the Vector Hankel Transform. It is shown that the current on the two disks is governed by a set of vector integral equations. These equations are solved approximately for the amplitudes of the currents on the two disks, in the limit of thin substrate. Expressions for the self, mutual, and input impedances are then rigorously derived. It is shown that excitation of the odd symmetric TM11mode can cause the two‐disk antennas to act as a better radiator than the single‐disk antenna, while the odd antisymmetric modes can cause the two‐coupled disk structures to act as a better resonator than the single‐disk structure. Expressions for the radiation pattern are then derived, and the impedance parameters and the radiation patterns plotted.

ISSN:0021-8979    

DOI:10.1063/1.332101

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

New simple formulas are obtained as an approximation of the exact general integrals for the components of the magnetic field generated by a horizontal electric dipole in a half‐space of water or earth near its boundary with air. These formulas supplement the earlier derivation of the three components of the electric field which are repeated here for completeness. The formulas for the transverse and vertical components are needed in treating the reflection of lateral waves from plane or cylindrical boundaries.

ISSN:0021-8979    

DOI:10.1063/1.332102

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Time‐resolved photography of Cherenkov emission has been used to study large‐area electron‐beam uniformity and electron‐beam propagation in air. For the 50‐ns pulse widths used, we show that the time‐dependent electron emission from large‐area cathodes is typically very nonuniform. Pinching of the electron beam by its self‐magnetic field can be prevented by the use of an applied axial magnetic field approximately equal to the self‐magnetic field generated by the electron beam. When an applied field is used, beam nonuniformities introduced by the anode support structure persist through tens of centimeters of air outside the diode. These nonuniformities can reduce efficiency and beam quality of the laser. Beam rotation in the diode caused by the applied magnetic fields can result in significant loss of electron‐beam energy to the anode chamber and foil‐support structure. However, we have shown that emission can be reduced on areas of the cathode which map onto obstructions on the anode so the electron energy loss can be reduced.

ISSN:0021-8979    

DOI:10.1063/1.332103

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The electrical field distribution over the focal region of a Gaussian beam, incident at 45° and focused onto a perfectly conducting infinite plane, is calculated numerically by summing the plane waves in an angular spectrum representation. The beam is plane‐polarized with the transverse electric field perpendicular to the plane of incidence. The configuration and parameters were chosen to agree with our experiments on plasma initiation near a metallic conductor by 35‐GHz/8.6‐mm microwave radiation. The results of the calculation show that the field distribution determines the ignition threshold, spatial location, and initial development of the microwave plasma at a metal surface.

ISSN:0021-8979    

DOI:10.1063/1.332104

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The reflection of electromagnetic waves at a plane boundary between isotropic and biaxial media has been investigated using thekDBapproach. The general case has been considered in which the principal dielectric axes of the biaxial medium are oriented at an arbitary angle to the normal of the plane boundary. In general, two characteristic waves propagate in the biaxial medium, leading to coupling of vertical and horizontal polarizations in the reflected waves. Some special cases are illustrated. The results have applications to problems in remote sensing and integrated optics.

ISSN:0021-8979    

DOI:10.1063/1.332105

出版商:AIP    

年代:1983

数据来源: AIP