STUDY OF ULTRASONIC PROPERTIES OF THE AQUEOUS SOLUTION OF GELATIN

The experimental investigation of aqueous solution of the gelatin has been made by usingultrasound at frequency 11.4 MHz.The relation between concentration and ultrasound absorptiondoes not reach its saturated value even at the weight concentration of the solution c=8.5%. When the concentration is more than l.5%,the solution transforms into jelly under room tem-porature,but the ultrasonic absorption does not change in the whole transformation proces.Whenthe temperature of the solution is decreased to the vicinity of gelling point,the viscosity η of the solutionincreases gradually with time,making the value of sound absorption calculated from η largerthan the experimental one by several orders.But when the temperature of the solution is appropriatelyhigher than the gelling point,the calculated value of sound absorption is smaller than the experimentalone but with the same order. The temperature at which the maximum sound velocity occurs in the concentrated(c=6.4%)solution is not much different from that     

ANALYSIS OF SURFACE EXCITATION OF ELASTIC WAVE FIELD IN A HALF SPACE OF PIEZOELECTRIC CRYSTAL——GENERAL FORMULAE OF SURFACE EXCITATION OF ELASTIC WAVE FIELD

This paper developes the general theory of the surface excitation of elastic wave field in a halfspace of piezoelectric crystal for both free and metallized surfaces.It is shown that the general elas-tic wave field U is equal to the convolution of the generalized Green's functions G and the general-ized forces T, U = G Twhere symbol,expresses dot-product-convolution. The generalized Green's functions are independent of excitation conditions and only dependenton material parameters and orientation. For the piezoelectric crystal,not only a mechanical source distribution at the surface,but anelectrical source distribution can also excite the elastic wave fields.Complete expressions of thegeneralized forces representing mechanical and electrical source distribution respectively are given.Especially for the free surface,the surface electrical sources can be composed of the discontinuityof normal electric displacement at the surface,and of the discontinuity of the tangential electric fieldas well.     

THEORY OF NONLINEAR INTERACTION OF FINITE AMPLITUDE RANDOM SOUND WAVES

In this paper a theory of nonlinear interaction for finite amplitude random sound waves is devel-oped.On the basis of the assumption that the velocity amplitude of source of sound should obeyRayleigh distribution,the authors successfully extend Fenlon's theory to the case of random soundwaves.A series of interesting formulas expressed in the form of the spectral dlstribution are derived(for example,the formulas for the nonlinear distortion of random sound waves,the suppression of theweak random sound wave by the intense regular sound wave,the parametric process of random soundwaves,etc.).In this paper it is also pointed out that some important results of statisitical phenomenaof nonlinear acoustics obtained by O.V.Rudenko can be easily derived from the present theory.     

ANALYSIS OF THE LOWER MODES OF FREE VIBRATION OF A PIEZOELECTRIC CERAMIC DISK POLARIZED IN THE THICKNESS DIRECTION

By means of the adjoints method of solving the differential equations of two-point boundaryvalue problems,the equations of motion of a boundary stress-free ceramic disk vibrator polarizedin the thickness direction are solved by numerical integration.The resonance frequencies of the lowermodes of radial vibration under the influence of motion in the thickness direction and the particledisplacement distribution patterns are obtained for disks whose thickness-diameter ratios are less than0.45.Correction curves for thickness effect on fundamental frequencies are given.Curves showing.the effect of Poisson ratio on the relation between the second harmonic-fundamental ratio and thethickness-diameter ratio are also given. In the numerical calculations,piezoelectric ptoperties of the ceramic disks are fully taken intoconsideration and no restrictions are set for the dimensions of the disks.Experimental results agreewell with those obtained by calculation.     

ON THE INVESTIGATION OF THE SOUND ABSORPTION OF LINEAR TRANSITION WEDGES

In this article the reflection coefficient of linear transition wedges is discussed,and an analyticalexpression and a simple real expression of the reflection coefficient under W.K.B.approximationare derived.The approximate expression of the reflection coefficient proves to be simple and con-venient for the design of absorbers. The sound absorbent structure of rib is also computed and analyzed,with emphasis on the rela-tionship between the size of the structure and the parameters of the material. In design of two types of wedges mentioned above,for the required frequency range,the materialperameters can be chosen properly and the dependence of the Wedge length on the lower limit fre-quency can be determined easily based on the derived expression.The theoretical computationsagree well with the experimental results.     

RECOGNITION OF SHIP OBJECTS ACCORDING TO THE SHAPE OF AVERAGE POWER SPECTRUM OF RADIATED NOISE

The methods of recognizing different types of ship objects according to the shape of average powerspectrum of the radiated noise are discussed in this paper.The pre-processing of the data is con-sidered first.After applying general correlation method,the distance method and weighted distancemethod,a new method i.e.M-m_2 plane partition method,is proposed.The basis of this methodis the shape of averaged power spectrum of ship radiated noise may be approximately described bythe Ece noise model.Such a noise model,which may be characterized by a set of three parametersf_0,f_m and K or w_0,a and K is described in detail.The approaches of extraction these parameters arealso discussed.By using of the recognition features M.which is the location of the maximum value ofaverage power spectrum curve,and m_2,which is the second central moment of normalized averagepower spectrum level and applying a piece-linear classifier,a 92% of correct recognition rateis obtained for two different types of ship objects.Compared w     

MULTIDIMENSIONAL ANALYSIS OF PERCEPTIONAL CONFUSION OF CHINESE CONSONANTS

The perceptional features of Chinese consonants has been analysed in multidimensional scalingby means of optimizing the fitting to the confusion probabilities of consonants as observed in articula-tion tests.The dependence of minimum Stress as criterion for fitting on dimensions has beenobtained. In this paper,a method of multidimensional scaling is described briefly.A program for perform-ing calculations on a programmable calculator and the questions of handling the blank data as wellas setting the starting configurations are discussed.Some typical results of calculation are given.     

GROWTH TECHNIQUE OF MOLECULAR CRYSTAL OF NAPHTHALENE

A furnace for growing single crystal naphthalene of diameter 1-1.3cm and length up to15cm has been constructed by the Bridgman method in combination with zone-melting technique.The furnace is simple in its construction,convenient in its operation and convenient for the observa-tion of the crystal growth process.The effect of the shape of crystal growth container on crystalgrowth is discussed and the experiment in vapor growth of small naphthalene flakes is described.The preparation procedure of naphthalene samples for ultrasonic measurement,which may be alsouseful for preparation of other soft crystals,is given.     

ACOUSTICAL PROPERTIES OF QING

The qing was an important percussion musical instrument in ancient China.Qing is a stone plate withspecial form.The vibration of qing is studied both theoretically and experimentally in this paper.Thevibrational modes of a qing have been calculated by using finite element method in accordance with the ex-perimental results.As compared with a rectangular plate,the frequency relations between the overtones arevaried with the changes of shape of the qing.From the analysis,it is possible to speculate upon the idea ofdesign of the qing in ancient time.In order to confirm the idea,the sound of qing has been simulated bycomputer and judged subjectively.An empirical formula for the calculation of the pitch frequency of qingsound is given.     

STATUS OF COMMUNITY NOISE IN THE PEOPLE'S REPUBLIC OF CHINA

Noise surveys have been carried out in Beijing,Tianjin and in 22 smaller towns in the generalmetropolitan area.This region has a population of about 18 million.The results of these surveys give apicture of the situation of the community noise in a typical section of China and the change in the last tenyears,showing the effectiveness of various noise control measures,both technical and legal.     

DESCRIPTION OF A CALCULATION METHOD OF ELASTIC CONSTANTS OF CRYSTALS

With the help of the decline method,a computer-aided analysis program of Christoffel equation is des-cribed which makes it possible to calculate elastic and viscous constants of crystals precisely and easily.Theelastic constants of LiNbO_3 and Bi_(12)GeO_(20)crystals are calculated with an Apple-Ⅱcomputer and theFortran program suggested,and the calculated data are compared with the values achieved by others.     

CHARACTERISTICS OF THE FLOW RATE AND NOISE RADIATION OF MICROPORE MUFFLER

In the present work,the flow rates and noise radiations of micropore and micropore muffler atdifferent chamber pressures are investigated.When the number of micropores of a micropore muffleris small(the total geometrical area of micropores is,say,less than 1.5 times the cross section area of theexhaust pipe)and the flow is choked at the micropores,the flow rate and noise radiation are proportionalto the number of pores and the back pressure is very low,around 0.1 atmosphere pressure or so.Theflow rate through each micropore is proportional to the chamber pressure(or the stagnation pressureof microjet),but the effective area of micropore is only about 60 percent of its geometrical area.Whenthe total geometrical area of pores is near or greater than 1.5 times the cross section area of the mufflerinlet pipe,the increase of flow rate with the increase of the number of micropores will slow down andfinally the total flow reaches a limit va1ue equal to that of the bare exhaust pipe.The noise radiationof each mi     

RECONSTRUCTIONS OF PHASE SPECTRUM AND TRANSIENT RESPONSES OF SPHERICAL PIEZOELECTRIC TRANSDUCER

In this paper,a simple method deriving the transfer function of a spherical piezoelectric transducerhas been given.Transient responses have been obtained from the analytical expression of transferfunction by using FFT.Calculated results show that the impulse response of the spherical piezoelectrictransducer also exhibits the minimum phase behaviour and so the phase spectrum of its transfer func-tion can be reconstructed from the amplitude spectrum by using the Hilbert transform,the reconstruct-ed phase spectrum is in good agreement with that calculated from the analytical expression of transferfunction directly. Based on above-mentioned results,the phase spectrum of transfer function of a F42-c spherical pic-zoelectric transducer has been reconstructed from the measured values of its amplitude spectrum for thefirst time.The reconstructed phase spectrum is basically consistent with the measured values of phasespectrum. In addition,the impulse response and step response of F42-c spherical piezoelectric tra     

ACOUSTICAL PROPERTIES OF CMME BELLS

The acoustic characteristics of chime bells have been studied by the measurements of vibrationalmodes and the power spectra of bell sound.Each of the chime bell has two tones depending on thestriking positions on the bell.At the tone frequencies,the modes of vibration are similar,but thepositions of nodal lines are different.The short-time sound spectra of chime bells were measured bythe use of FFT.The sound of chime bell can also be analyzed by the method of linear predictionused in signal processing.     

DETECTION OF THIN LAYER OF FOREIGN MATERIAL IN PLATES BY ULTRASONIC FREQUENCY SPECTRUM

The detection of thin layer of foreign material in solid is an extremely difficult problem by theconventional ultrasonic pulse-echo method.The ultrasonic spectrum technique is used to studythe problem both theoretically and experimentally.It shows that: 1. The amplitude-frequency plot of an ultrasonic echo from the thin layer would contain spectraldepressions when the thickness of the thin layer is a multiple of the half wavelength. 2. The depression depth is related to the reflectivity of ultrasonic waves on the surface of the thinlayer.Therefore,it is possible to measure the thickness of the layer and its characteristics by the measurement of the depression and its frequency.     

A NEW METHOD OF ADAPTIVE ARRAY PROCESSING FOR SIGNALS OF UNKNOWN CHARACTERISTICS

This paper describes a new method of adaptive array processing for signals of unknown frequencycharacteristics.Under practical circumstances,it is easier to obtain the estimation of the power spec-trum in the observed direction than to obtain that of the frequency characteristics.Thus the maximumentropy spectral analysis can be used to incorporate with the adaptive array processing. In this paper the autocorrelation function is calculated from the power spectrum and the predictedcoefficients of MEM(maximum entropy method)can be obtained by solving the normal equation of thecorrelation matrix,and the predicted coefficients are used as the constrained conditions of the algorithmfor adaptive array processing. The above method is further extended and an adaptive array processor is presented for the moregeneral cases,in which the signal characteristics in the observed direction are completely unknown.Firstly the space filtering of the adaptive array is performed by the all-pass constrained conditions inthe fr     

ACOUSTICS IN INVESTIGATION OF CERAMIC MATERIALS

Ⅰ.INTRODUCTION This work presents the use of acoustic methods for investigation of ceramic materialthat is a typical example of inhomogeneous matter.Inhomogeneity is due to various crys-talline phases,the presence of glass in the structure,the appearance of grains separated byboundaries,containing large amount of inclusions and impurities,typical defects of the crystallattice and,first of all,the content of the gaseous phase.The BASIC feature of this groupof materials is the use of high-temperature firing and the tendency to prepare the techno-     

THE STUDY OF HORIZONTAL DIRECTIVITY OF CYLINDRICAL(ARC)ARRAYS WITH BAFFLE

The influence of baffle on horizontal directivity and the frequency response of elements is analysedin detail in this paper.Some formulas of calculating the received response and the horizontal directi-vity of the cylindrical(arc)array are given.The influence of parameters of arrays on the performanceof the array is discussed.A comparison between the theoretical values and a part of the experimentalresults is shown.     

PRINCIPLE OF PIEZOELECTRIC-TUNABLE TRANSDUCER

The effect of electric load on the characteristics of piezoelectric vibration systems was presentedin our recent papers.The resonance frequency of such systems can be changed continuously withthe electric load.In accordance with this effect,the piezoelectric-tunable transducers have been built. In this paper,the principle of the piezoelectric-tunable transducers is demonstrated while thepiezoelectric-tuning of the sandwich piezoelectric transducers are analysed theoretically and a sandwichtransducer of a longitudinal vibrating bar with field parallel to the length is investigated experimen-tally.The theoretical and experimental results show that such piezoelectric-tuning is effective inthree-halves octaves.This piezoelectric-tuning is convenient for the piezoelectric-tunable transducers,and can be carried out continuously and instantaneously.     

THE ACOUSTIC FUNCTIONS OF THE MELON OF THE CHINESE RIVER DOLPHIN(Lipotes vexillifer)

In this paper,the acoustic functions of the melon of the Chinese river dolphin(Lipotes vexillifer)are studied.Based on the comparison between the directivity patterns of the whole head and the skull,it is suggested that the melon plays an important role in beamforming.At the frequencuy of 40 kHz,the—3 dB beamwidth of the emitted vertical beam of the whole head is approximately 21.6°,withthe major axis elevated 10°above the ristrum plane;the—3 dB beamwidth of the horizontal beam ofthe whole head is approximately 20°,with the major axis deviated 12°rightward from the body axis.The vertical and horizontal—3dB beamwidths of the whole head are 9.4°and 13°,narrower than thoseof the skull respectively,and the directions of the major axes are different for both cases.It canbe seen that the melon narrows the width of the main beam and greatly reduces the side lobes of thebeam formed by the skull.The distribution of the sound velocity in the melon tissue is measured andthe distribution pattern is drawn.Fr