The dynamics of low-frequency signal acoustic intensity vector vortex structure in shallow sea

Spatiotemporal vector and phase properties of interference field of low-frequency signalling tone between three local vortices in a real shallow sea wave-guide have been studied.It has been demonstrated that in the field of constructive interference,components of particle velocity field and acoustic pressure are coherent.As a consequence the transfer of signal energy alog the axis of a shallow sea wave-guide is accomplished with plane wave.Physical objects are detected in the field of destructive interference,which,according to known deterministic signs,can be defined as local vortices of the intensity vector.A large-scale vorticity with acoustic intensity vector curl,components different from zero originates in the vicinity of local vortices.Regular particle displacements of local vortices have been detected against combined receiving device phase centre along the axis of a wave-guide.It has been demonstrated that the structure of vortices depends on signal/noise ratio.Local vortices and vorticity form vortex structure of vector acoustic field.Signalling tone with frequency of 88 ± 1 Hz from near-surface moving sound source was taken into consideration.Introduced results of full-scale experiment expand our concepts of real fundamental properties of shallow sea acoustic field and are to be considered in theoretical models.     

The interference characteristics of platform and towed body noise in shallow water for active/passive towed array sonar

The interference characteristics of towed platform noise resulted from propeller and towed body for active/passive towed array is analyzed. It is shown that, in shallow water environment, the direct wave and bottom/sea surface reflected wave will seriously affect the performance of sonar system. The formula for calculating the direction of arrival (DOA) of interference in terms of various parameters, such as array depth, length of tow cable, is derived. The effect of interference noise for the detection performance of sonar system is described. The results of system simulation provide the method for reducing the effect of these kind of interferences.     

Radiation and reflection acoustical fields of an annular phased array

The characteristics of the radiation and reflection acoustical fields of an annular phased array are investigated. The effects of the element number, element radius, interelement spacing, centre frequency, focus position, and other parameters on the radiation acoustical field of the annular phased array is theoretically studied. In experiment, an annular transducer with 8 equal-area elements is designed and fabricated, and a series of experimental measurements are conducted. The radiation acoustical field and its reflection on a liquid-solid interface are theoretically and experimentally studied. The experimental result is in good agreement with the theoretical one.     

Acoustic characteristics analysis of slender cavity system with arbitrary impedance end conditions

A modeling method for the dynamic characteristics analysis of a slender acoustical cavity with impedance end conditions is established. In order to satisfy the continuity requirement at impedance ends for the first order differential of sound pressure, field function is constructed as the standard Fourier series supplemented by boundary smoothed auxiliary polynomials. System characteristic equation is derived by solving the governing differential equation and impedance acoustic boundary of slend...     

Numerical analysis of surface plasmon nanocavities formed inthickness-modulated metal－insulator－metal waveguides

The enhancement characteristics of the local field in the surface plasmon nanocavities are investigated numerically. The cavity is constructed by placing a defect structure in the thickness-modulated metal--insulator--metal waveguide Bragg gratings. The characteristic impedance based transfer matrix method is used to calculate the transmission spectra and the resonant wavelength of the cavities with various geometric parameters. The finite-difference time-domain method is used to obtain the field pattern of the resonant mode and validate the results of the transfer matrix method. The calculation and simulation results reveal the existence of resonant wavelength shift and intensity variation with structural parameters, such as the modulation period of the gratings, the length and the width of the defect structure. Both numerical analysis and theoretical interpretation on these phenomena are given in details.     

Time reversal focusing with variable depth and range based on mode extraction

A method for time reversal focusing with variable depth and range based on mode extraction was proposed.First,the normal modes of acoustic propagation in the shallow water are extracted by modal decomposition from the probe signals received by a source receiver array.Furthermore,a diagonal matrix and a vector determined separately by the depth and the range of the probe source are extracted from the received acoustic field data.And time reversal focusing at different depths and ranges can be achieved by modulating the depth-dependent diagonal matrix and the range-dependent vector properly.Then the diagonal matrix and the vector are modulated separately according to the depth and the range of the expected focal location to construct a new acoustic field vector.When this new acoustic field vector is retransmitted by the source receiver array in time reversal order(or phase conjugation in frequency domain),focusing of the resulting acoustic field at the expected location rather than the origin of the probe source can be obtained.Numerical simulations in typical shallow water environment demonstrate the effectiveness of the proposed method.     

LONG-RANGE REVERBERATION AND BOTTOM SCATTERING STRENGTH IN SHALLOW WATER

According to the method of angular power spectrum for averaged sound field in shallow water,the transformation relation between arbitrary angle dependence of hottom scattering and the rangedependence of long-range reverberation in shallow water homogeneous layer is established.Ascompared with the conventional model of boundary reverberation at short range in deep sea,a multipath correction factor is added.By using the transformation relation,the bottombackscattering strength for the frequency band of 0.8—4.0kHz and grazing angle range of 2—10°has been derived from shallow-water reverberation data at five locations in the Yellow Sea,theBobai Sea and the East China Sea.It is shown that the bottom scattering constant(μ)and theangle index(2n)for high speed sediment of the continental shelf depend not only on sea area andfrqucncy,but also on angle range.     

Resonating properties of passive spherical optical microcavities

As an optically pumped device, the lasing characteristics of a spherical microcavity laser depend on the optical pumping processes. These characteristics can be described in term of the Q factor and the optical field distribution in a microsphere. We derived analytical expressions and carried out numerical calculation for Q factor and optical field. The Q factor is found to be oscillatory functions of the radius of a microsphere and the pumping wavelength, and the pumping efficiency for a resonating microsphere is much higher than that for an anti-resonating microsphere. Using tunable lasers as pumping sources is suggested in order to achieve a higher pumping efficiency. Numerical calculation on optical field distribution in spherical microcavities shows that a well focused Gaussian beam is a suitable incident wave for cavity quantum electrodynamics experiments in which strong confinement of optical field in the center of a microsphere is requested, but higher order spherical wave should be used instead     

The scale-transformation of electromagnetic theory and its applications

The scale-transformation of electromagnetic theory is investigated in detail based on the form of Maxwell equations in scale-transformation being unchanged in different coordinate systems. The relations of electromagnetic parameters in a rectangular coordinate system and in a spherical coordinate system are presented respectively. The scale-transformation invariants for electromagnetic field are derived and their physical meaning is also presented. It is indicated by simulation that the electromagnetic waves located in medium can be considered to be isotropic due to the fact that the size of propagating vector affected by the scale factors and observing azimuth is on a size of 10^-9, which provides a new approach for investigating the electromagnetic characteristics of ellipsoidal targets.     

Sound Field Calculations of Elliptical Pistons by the Superposition of Two—Dimensional Gaussian Beams

We present an alternative approach to calculate the sound field of ultrasonic transducers.The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions.The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions.This treatment does not require the condition that the shape of the source is of circular axial symmetry.A numerical example is presented for the uniform elliptical piston transducer and this is in good agreement with the results given by complicated computation.     

Effect of Source＇s Height on Air-to-Water Sound Transmission with a Small-Scale Rough Sea Surface

A self-consistent perturbation approach is presented/or analyzing the effect of theairborne source＇s height on the air-to-water sound transmission in shallow water with a randomly rough sea surface. It is shown in early researches that, in shallow water with a smooth sea surface, the airborne source＇s height mostly affects the phase of the sound field and barely influences the amplitude. However, in shallow water with a rough sea surface, few researches about such a problem have been published. In this work, the sound fields in shallow water with a randomly rough sea surface induced by an airborne source at different heights are calculated by a seff-consistent perturbation approach. The numerical simulation results show that the fluctuation of the scattered field decreases as the source＇s height increases, in contrast, the averaged energy of the total field is hardly influenced by the source＇s height in the statistical sense.     

Researches on the distribution law of vector sound field in elastic wedge bottom

The method based on elastic parabolic equation method for calculating the sound vector field has been studied.The vector field in water and corresponding seismic wave field had been calculated for infra-sound in oceanic environment with elastic wedge bottom.The effects on sound field distribution for different frequency and depth of sound source had been researched,result shows that there is sound energy leakage into the bottom,the position where leakage occurred can be determined by the ratio of the ocean depth to the wavelength,as compared with normal mode theory.     

Arbitrary direction incident Gaussian beam scattering by multispheres

Based on spherical vector wave functions and their coordinate rotation theory,the field of a Gaussian beam in terms of the spherical vector wave functions in an arbitrary unparallel Cartesian coordinate system is expanded.The beam shape coefficient and its convergence property are discussed in detail.Scattering of an arbitrary direction Gaussian beam by multiple homogeneous isotropic spheres is investigated.The effects of beam waist width,sphere separation distance,sphere number,beam centre positioning,and incident angle for a Gaussian beam with two polarization modes incident on various shaped sphere clusters are numerically studied.Moreover,the scattering characteristics of two kinds of shaped red blood cells illuminated by an arbitrary direction incident Gaussian beam with two polarization modes are investigated.Our results are expected to provide useful insights into particle sizing and the measurement of the scattering characteristics of blood corpuscle particles with laser diagnostic techniques.     

Quantization of the radiation field in an anisotropic dielectric medium

There are both loss and dispersion characteristics for most dielectric media. In quantum theory the loss in medium is generally described by Langevin force in the Langevin noise (LN) scheme by which the quantization of the radiation field in various homogeneous absorbing dielectrics can be successfully actualized. However, it is invalid for the anisotropic dispersion medium. This paper extends the LN theory to an anisotropic dispersion medium and presented the quantization of the radiation field as well as the transformation relation between the homogeneous and anisotropic dispersion media.     

Theoretical study of acoustic field patterns of 2-D ultrasound phased arrays for hyperthermia therapy

Acoustic field patterns of 2-D ultrasound phased arrays for the high intensity focused ultrasound (HIFU) hyperthermia therapy are studied, and controlling algorithms of field patterns are provided. The 2-D phased array using the conventional single-focus scanning pattern can exactly control the focal distance and the steering direction of the beam, but in general produce a single focus. Extremely high intensity levels will be needed when this pattern is used to treat large tumors. However, a direct synthesis method of the acoustic field based on the pseudo-inverse matrix can produce the multiple-focus field pattern. The rectangular radiator method of the acoustic field was used to simulate the single-focus scanning pattern and the multiple-focus pattern which are produced by a 2-D phased array consisting of 20×20 elements, and simulation results show that the 2-D array using the multiple-focus pattern can produce several foci with lower intensity levels simultaneously. Furthermore, the improved eigenvec     

Comparative study of electrical characteristics for n-type 4H–SiC planar and trench MOS capacitors annealed in ambient NO

The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal–oxide–semiconductor(MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states.These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the(1120) and(1100) faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the(0001) face under the same NO annealing condition. In addition, it is found that Fowler–Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device.However, Poole–Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO_2/Si C interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO_2/Si C interfaces.     

Monte Carlo Simulation of Magnetization Behaviour of Co Nanowires

Based on the Monte Carlo method, we simulate the magnetization curves with various magnetic field orientations for various single Co nanowires at room temperature. The simulated switching field as a function of angle between the field and the wire axis is consistent well with the experimental data. Correspondingly, the coercivity as a function of angle θ is presented, which together with the switching field plays an important role on explaining the magnetic reversal mechanism. It is found that the angular dependence of coercivity depends on the diameter of nanowires, and the coercivity and switching field versus θ deviate markedly from the prediction from the classical uniform rotation mode in the chain-of-sphere model. Furthermore, the magnetic reversal configurations display that magnetization reversal in the wires with small diameters is a nucleation-propagation process, and it is similar to the curling spread process in the larger wires.     

Field Emission Characteristics of BN Films with Cubic－BN Phase

Boron nitride (BN) thin films with cubic boron nitride (c-BN) phase were prepared on the (100)-oriented surface of n-Si (0.008-0.02 Ωm) by rf magnetron sputtering physical vapor deposition. The c-BN content is determined to be around 50% by using Fourier transform infrared spectroscopy for the BN thin films. The field emission characteristics of BN films were measured in an ultrahigh vacuum system. It is found that the field emission of the BN film with c-BN phase is evidently more excellent than that without c-BN phase. A turnon field of 5 V/μm and a current of 460μA/cm^2 were obtained for the BN film with c-BN phase. The Fowler-Nordheim plots of emission characteristics of BN films indicate a straight line, which suggests the presence of the FN tunneling.     

Effects of rough surface on sound propagation in shallow water

Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how randomly fluctuating surface influences transmission loss(TL) in shallow water. The one-dimension wind-wave spectrum, Monterey–Miami parabolic equation(MMPE) model, Monte Carlo method, and parallel computing technology are combined to investigate the effects of different sea states on sound propagation. It is shown that TL distribution properties are related to the wind speed,frequency, range, and sound speed profile. In a homogenous waveguide, with wind speed increasing, the TLs are greater and more dispersive. For a negative thermocline waveguide, when the source is above the thermocline and the receiver is below that, the effects of the rough surface are the same and more significant. When the source and receiver are both below the thermocline, the TL distributions are nearly the same for different wind speeds. The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory. In conclusion, the statistical characteristics of TL are affected by the relative roughness of the surface, the interaction strength of the sound field with the surface, and the changes of propagating angle due to refraction.     

Sound transmission from air into shallow water through rough sea surfaces by small slope approximation

The first-order small slope approximation is applied to the problem of the sound transmission from an airborne source into shallow water through a rough sea surface.By assuming a three-layer homogeneous fluid model and decomposing the sound field in water layer into up-going and down-going waves,the expressions for the down-going wave and thus the total field are derived.The expressions can be calculated by the FFT,but the alias problem will arise.To mitigate the alias effect,additional medium a...