舰船声场的近程分布式声源模型

根据舰船声场的近程分布式声源特性,采用三轴声强测量法建立了模型,提出了提高其精度的方法.     

Reply: On the evanescent field of dipole

Abstract

Recent controversy over the otherwise tuitional topic of separate contributions of evanescent and propagating waves in dipole radiation in free space has triggered a series of publications. I insisted on the use of changing plane-wave expansion for the decomposition, while other authors persisted on obtaining the field components with fixed plane-wave expansion.     

Terahertz pulse propagation in the near field and the far field

We present a detailed investigation of the propagation properties of beams of ultrashort terahertz (THz) pulses emitted from large-aperture (LA) antennas. The large area of the emitter is demonstrated to have substantial influence on the temporal pulse profile in both the near field and the far field. We perform a numerical analysis based on scalar and vectorial broadband diffraction theory and are able to distinguish between near-field and far-field contributions to the total THz signal. We find that the THz beam from a LA antenna propagates like a Gaussian beam and that the temporal profile of the THz pulse, measured in the near field, contains information about the temporal and spatial field distribution on the emitter surface, which is intrinsically connected to the carrier dynamics of the antenna substrate. As a result of pulse reshaping, focusing of the THz beam leads to a reduced relative pulse momentum, with implications in THz field-ionization experiments.     

Evanescent waves in the magnetic field of an electric dipole

The magnetic field of radiation emitted by an electric dipole contains travelling and evanescent waves when represented as an angular spectrum. The evanescent waves decay exponentially away from the xy-plane, and will therefore not contribute to the detectable radiation in the far field, in general. It is well known, however, that in a small region around the z-axis the evanescent waves of the electric field do end up in the far zone. We have studied the corresponding magnetic evanescent waves, and we have found that the evanescent waves of the magnetic field do not contribute to the far zone in the neighbourhood of the z-axis. When considering the neighbourhood of the xy-plane, it appears that both the electric and magnetic evanescent waves end up in the far field, and the travelling and evanescent waves contribute equally to the radiation in the far zone. Close to the dipole the radiation field diverges, and we have shown that this is entirely due to the evanescent waves.     

H-type dipole model for future plan at KEK

For the bending magnet of the electron ring of the so-called TRISTAN project at KEK, the H-type dipole, full scale model with 4 m in length, has been investigated at first to examine the feasibility to the electron storage ring from some points such as magnet performance, accessibility for the field measurement and vacuum chamber installation, manufacturing problem and magnet cost. Here, the magnet performance is treated. To measure the magnetic field inside the air gap, the specially designed flip coils were used. Fields of 11 points at the same longitudinal positions could be measured at once by rotating probe containing 11 flip coils on its axis.     

Design of an electrodynamic model of a variable electric field meter with dipole antenna

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 45–48, June, 1992.     

Electric field meter with dipole antenna in an alternating nonuniform electric field

Translated from Izmeritel'naya Tekhnika, No. 11, pp. 55–59, November, 1992.     

Magnetic field intensity in near field zone of loop antenna for RFID systems

The structure of a loop antenna of electrically large diameter with the loop perimeter split by capacitors in the form of planar two-wire (PTW) lines is considered. The antenna characteristics are calculated for one- and two-sided arrangement of the PTW lines and the obtained data are compared to the results of measurements. It is shown that the arrangement of PTW lines significantly influences the distribution of current over the loop perimeter.     

Electric field meter with a dipole antenna in a nonuniform alternating electric field

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 44–47, December, 1992.     

Electric field meter with a dipole antenna in an elliptically polarized electric field

A model of an electric field meter with a dipole antenna is analyzed. The model takes into account the fact that the meter incorporates other elements with a conducting surface in addition to the dipole antenna, viz.: a matching device, a signal cable, and a voltmeter. Alternative forms of the measurement equation are obtained, which differ in the error associated with the currents induced by the measured electric field on the braid of the signal cable and on the casing of the voltmeter. It is shown that this error can be eliminated partially or completely by performing additional measurements with the dipole antenna in different positions.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 45–48, February, 1994.     

Optical properties of metal-dielectric multilayers in the near UV region

Metal-dielectric multilayers have versatile optical properties that can be used in many applications. The special properties of metal films in the near UV region are analyzed in terms of the d-band contribution to the plasma oscillation. The important parameters that determine the multilayer optical properties such as skin depth dependence on the wavelength and the thickness of silver films have been calculated. The morphology of silver films on titanium dioxide has been observed by TEM. The results indicate that an optimal thickness exists for near UV transparency, and that may be related to the resonance of voids and interface enhanced resonance-tunneling transmission of semi-continuous silver films. A special heat mirror with high transparency in the near UV region was designed and fabricated according to the optimal thickness of silver; it has been found to exhibit sound optical properties.     

Optimizing the near field around silver tips

Owing to their promise of obtaining optical as well as topographic information in nanometer scale, apertureless near-field scanning optical microscopy (NSOM) and apertureless near-field scanning optical spectroscopy have drawn much attention recently. However, NSOM is still not a mature technique. A proper understanding of and the ability to tune the near field around the tip end is critically important in NSOM instrumentation and in NSOM image interpretation. On the basis of reflection geometry, we systematically studied the effects of a number of parameters pertinent in the application of apertureless NSOM, e.g., polarization, incident angle, wavelength of the incident laser, tip material, and tip length, by using the generalized field propagator technique. Our results show that all the above parameters have a significant influence on near-field enhancement and that care must be taken in the design of the experiment in order to maximize the near field. In addition to apertureless NSOM and spectroscopy, apertureless near-field lithography can benefit from these simulation results.     

A bound for the range of a narrow light beam in the near field

We investigate the possibility of light beams that are both narrow and long range with respect to the wavelength. On the basis of spectral electromagnetic field representations, we have studied the decay of the evanescent waves, and we have obtained some bounds for the width and range of a light beam in the near-field region. The range determines the spatial bound of the near field in the direction of propagation. For a number of representative examples we found that narrow beams have a short range. Our analysis is based on the uncertainty relations between spatial position and spatial frequency.     

Optical absorption near the fundamental absorption edge in some vanadate glasses

The fundamental absorption edges of some samples of V₂O₅-P₂O₅ and V₂O₅-P₂O₅-TeO₂ glasses were measured in the short wavelength part of the visible region, and it was found that the fundamental absorption of these glasses is dependent on composition and arises from direct forbidden transitions and occurs at a photon energy in the range 1.9 to 2.6 eV, depending on composition.     

Computer model for vedavati ground water basin. Part 1. Well field model

It is shown that a leaky aquifer model can be used for well field analysis in hard rock areas, treating the upper weathered and clayey layers as a composite unconfined aquitard overlying a deeper fractured aquifer. Two long-duration pump test studies are reported in granitic and schist regions in the Vedavati river basin. The validity of simplifications in the analytical solution is verified by finite difference computations.     

Transition elements matching the near crack-tip strain field

New transition elements used with the collapsed triangular singular elements are constructed by using the improved isoparametric transformations. Without 1/r singular terms, the new transition elements' strain fields contain only % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaac+% cadaGcaaqcaawaaiaadkhaaKqaGfqaaaaa!3B47!\[1/\sqrt r \] singularities and match the Williams solution quite well near the crack tip. It is convenient for the new transition elements to be constructed and introduced in the general purpose finite element programs by adding some modifications. Numerical results show that the transition elements possess good properties and are worth being applied to linear fracture computations.     

Optical model for use in oceanic ecosystem models

Modeling the plankton ecosystem requires a code for simulating the profile of irradiance from the chlorophyll profile at each time step of the integration. We have compared two existing codes with data from the Biogeochemical Ocean Flux Study: the Hydrolight radiative transfer model is accurate but too slow to use interactively in ecological models; Morel's [J. Geophys. Res. 93, 10, 749 (1988)] empirical model is much faster but produces substantial error. We have developed a streamlined version of the Hydrolight radiative transfer model that is 20 times faster than the full Hydrolight code, while limiting errors to less than 12% within the euphotic zone. This new code is both fast and accurate and is, therefore, suitable for use interactively in oceanic ecosystem models.