Sound absorption characteristics of a thin plate with PZT and shunt circuit I. Theoretical analysis

The feasibility of sound absorbing by a vibrating plate with piezoelectric material and shunt circuits is theoretically investigated. Based on an equivalent compliance of a piezoelectric wafer shunted with RL circuits, the governing equations for the fiexural vibration of the plate with the piezoelectric wafer are derived using Lagrange＇s approach. The equations take into account not only the mass, stiffness and structural damping of the plate and the wafer, but also the electrical resistance and electrical inductance of the RL circuits. By using the governing equations derived, the surface impedance and sound absorption coefficient of the plate backed with a cavity are given. Numerical results show that the sound absorption coefficient of the plate near its first mode can be significantly improved by adjusting the RL parameters.     

Sound absorption characteristics of a thin plate with PZT and shunt circuitⅠ.Theoretical analysis

The feasibility of sound absorbing by a vibrating plate with piezoelectric material and shunt circuits is theoretically investigated.Based on an equivalent compliance of a piezoelectric wafer shunted with RL circuits,the governing equations for the flexural vibration of the plate with the piezoelectric wafer are derived using Lagrange's approach.The equations take into account not only the mass,stiffness and structural damping of the plate and the wafer,but also the electrical resistance and electrical i...     

Research on the sound absorption performance of metal rubber material

The sound absorption performance of Metal Rubber material was studied theoretically and experimentally. The acoustic impedance rate and the sound absorption coefficient were derived based on the acoustic parameters of metal rubber material. The relation of structure constant, compressibility modulus and structural parameters was investigated experimentally. The results showed that the specimen of metal rubber with the same mean porosity diameter had the same structure constant. For the same structural parameters, the compressibility modulus of metal rubber material was approximately constant in certain frequency range. The calculated acoustic parameters are in good agreement with the experimental results, demonstrating the effectiveness of theoretical models.     

Enhancement of low-frequency sound absorption of microperforated panels by adding a mechanical impedance

In order to solve the bad low frequency sound absorption of the Micro-Perforated panel(MPP)absorber,mechanical impedance was introduced in the back of the MPP absorber to form a composite structure.According to the same particle vibration velocity on both sides of a plate,the mechanical impedance plate transfer matrix could be obtained.The units of the mechanical impedance,cavity and MPP were connected in series with the use of the transfer matrix method,thus creating the composite structure’s theoretical calculation model.The quality factor affecting absorption bandwidth was analyzed.Bandwidth is inversely proportional to the mechanical impedance plate mass.During the experiments,when at close to 400 Hz,the composite structure reached an absorption peak with a coefficient of above 0.8.Experimental results concurred with theoretical calculations.Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism.Through this,the performance of low frequency sound absorption can be improved without increasing the thickness of the structure.The frequency band can be broadened by reducing the mechanical impedance plate mass and controlling its boundary-damping coefficient.     

Calculation of three-dimensional acoustic scattering from Gaussian rough under-ice surface using the Kirchhoff approximation method with modified reflection coefficient

The Kirchhoff approximation with a modified reflection coefficient is used to calculate the three-dimensional acoustic scattering of a Gaussian rough under-ice surface.The concept of a local statistical average reflection coefficient of an under-ice surface is proposed in the calculation model.The scattered sound field of a two-dimensional Gaussian rough under-ice surface is divided into coherent scattering and incoherent scattering.A formula is derived for the scattering coefficient of each scattering component,and the three-dimensional scattering intensity is obtained.The relationships between the scattering intensity and(ⅰ) the root-meansquare height of the Gaussian rough under-ice surface,(ⅱ) the angle of incidence,and(ⅲ) the sound frequency are analyzed.The scattering intensity of a Gaussian rough under-ice surface is measured in a laboratory water tank,and the calculation results of the theoretical model are verified.The experimental results are compared with those of the theoretical model using(ⅰ) the present local statistical average reflection coefficient of an under-ice surface and(ⅱ) the mirror reflection coefficient of an under-ice surface from the literature.The calculation results of the model using the local statistical average reflection coefficient agree well with the experimental results.     

MEASUREMENTS OF THE pH DEPENDENCE OF LOW FREOUENCY SOUND ABSORPTION IN SEA WATER

The dependence of sound absorption coefficient in natural sea water on pH at frequencies of 2.91,6.82and 10.76 kHz has been measured by the resonator method.Measure-ments were made at 12.6℃ in the pHrange 6.48—8.51.Comparison of the experimental results with predictions based on various equations isgiven.One of the principal objectives in this paper is to examine the contribution of the MgSO_4 absorption insea water by reducing pH to low enough values where the pH-dependent absorption losses become negligible.It seems clear that in order to predict sound absorption in sea water more accurately at both low and highfrequency ranges with an united equation,the equation should include the MgHCO_3~+ absorption term as wellas the MgCO_3 term.     

Optical and electrical characterizations of nanoparticle Cu2S thin films

Copper sulfide thin films are deposited onto different substrates at room temperature using the thermal evaporation technique. X-ray diffraction spectra show that the film has an orthorhombicchalcocite （7-Cu2S） phase. The atomic force microscopy images indicate that the film exhibits nanoparticles with an average size of nearly 44 nm. Specrtophotometric measurements for the transmittance and reflectance are carried out at normal incidence in a spectral wavelength range of 450 nm-2500 nm. The refractive index, n, as well as the absorption index, k is calculated. Some dispersion parameters are determined. The analyses of el and e2 reveal several absorption peaks. The analysis of the spectral behavior of the absorption coefficient, c~, in the absorption region reveals direct and indirect allowed transitions. The dark electrical resistivity is studied as a function of film thickness and temperature. Tellier＇s model is adopted for determining the mean free path and bulk resistance.     

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     

A Wide Band Strong Acoustic Absorption in a Locally Network Anechoic Coating

Composite materials with interpenetrating network structures usually exhibit unexpected merit due to the cooperative interaction. Locally resonant phononic crystals （LRPC） exhibit excellent sound attenuation performance based on a periodical arrangement of sound wave scatters. Inspired by the interpenetrating network structure and the LRPC concept, we develop a locally network anechoic coating （LNAC） that can achieve a wide band of underwater strong acoustic absorption. The experimental results show that the LNAC possesses an excellent underwater acoustic absorbing capacity in a wide frequency range. Moreover, in order to investigate the impact of the interpenetrating network structure, we fabricate a faultage structure sample and the network is disconnected by hard polyurethane （PU）. The experimental comparison between the LNAC and the fanltage structure sample shows that the interpenetrating network structure of the LNAC plays an important role in achieving a wide band strong acoustic absorption.     

Investigations on the acoustic transmission characteristics of underwater perforated panel structures

Perforated panel structures have a wide potential in underwater applications. However, up to now there has been little related research. The acoustic impedance of an underwater perforated panel is obtained based on the theories for air perforated panel sound absorption. In this paper sound transmission characteristics of underwater perforated panel structures are theoretically analyzed by the transfer matrix method. A formula for normal incidence sound transmission coefficients is given. The main factors that have effects on the acoustic transmission coefficient are analyzed by numerical simulations. The perforated panel structures made by ourselves are tested in a standing-wave tube by the four-sensor transfer-function method. The experimental results are well in accord with the results obtained by the numerical method, which proves that the theoretical analysis is correct. This paper has provided theoretical and experimental bases for the design of underwater perforated panel structures.