Multiple scattering of seismic waves

Designing, constructing and testing of a new generation of sound barriers

PURPOSE

Nowadays, noise pollution is considered a major environmental problem which has affected the health and comfort of millions of people around the world. Solving the mentioned problems need to design a new generation of acoustic barriers. Acoustics experts believe that stopping and absorbing the low-frequency sound is difficult. The aims of this study were to remove the harmful frequency in industries and cities. This study concentrates on the reduction of the noise level and increasing the mass law and resonance at low frequencies.

METHODS

Sound measurement and frequency analysis did to fix the harmful frequency in the Shiraz city and in the Shiraz Gas Power Plant. COMSOL 5.3a software used for simulation. Suitable material chose for the manufacture of the sound barrier through the Cambridge engineering selection software 2013. The meta-material sound barrier made and tested in the acoustic room and in the free space. Results analyzed and optimized by Design of Experiment (DOE) and Response Surface Methodology (RSM) software. Mini Tab. 18.1 software used for Statistical Calculations. New sound barriers manufactured with adding new strategies to previous studies to improve the performance of meta-materials like beautification inspired from the flowers of nature and increasing of resonance in internal pipes.

RESULTS

Three mechanisms used in this scatterer model which included, resonance phenomenon, Band Gap (BG) without absorption mechanism and inner-fractal-like structure. Our technique showed an advantage to reduce at frequencies below 100 Hz without adsorbent usage. The results showed that reduced noise exposures about 17.8 dB at frequency 50 Hz, about 9.1 dB within the range of 250 Hz according to EN 1793-2 standard (Lab Test for Airborne Sound Insulation). The sound barrier reported in this work provides the best and updated solution in the field of noise control.

CONCLUSIONS

A novel generation of sound barriers introduced. We called this structure Interior Quasi-Fractal Sonic Crystal Acoustic Barrier (IQFSCAB). In this study, several different gaps used to remove various frequencies. It could be concluded that the outcomes of the meta-material models based on the Sonic Crystal (SC) could be used for the purpose of noise control system and could be helpful for decision-makers on the noise control legislations. Graphical abstractInteraction of waves with noise barriers and wave propagation inside periodic media is a hot topic in many branches of science and technology. The acoustic metamaterial can create green environments by reducing the low frequencies of industrial noise or traffic jam. New barrier have added a number of new strategies to previous studies in order to improve the performance of meta-materials. Our technique shows a clear advantage over to absorb at frequencies below 100 Hz without adsorbent usage. Innovative use of several different gaps and diameters for to remove various frequencies was done in this study. We called this structure IQFSACB due to fractal like interior pipes as those seen in some of the flowers in nature.

Wigner distribution of a transducer beam pattern within a multiple scattering formalism for heterogeneous solids

Diffuse ultrasonic backscatter measurements have been especially useful for extracting microstructural information and for detecting flaws in materials. Accurate interpretation of experimental data requires robust scattering models. Quantitative ultrasonic scattering models include components of transducer beam patterns as well as microstructural scattering information. Here, the Wigner distribution is used in conjunction with the stochastic wave equation to model this scattering problem. The Wigner distribution represents a distribution in space and time of spectral energy density as a function of wave vector and frequency. The scattered response is derived within the context of the Wigner distribution of the beam pattern of a Gaussian transducer. The source and receiver distributions are included in the analysis in a rigorous fashion. The resulting scattered response is then simplified in the single-scattering limit typical of many diffuse backscatter experiments. Such experiments, usually done using a modified pulse-echo technique, utilize the variance of the signals in space as the primary measure of microstructure. The derivation presented forms a rigorous foundation for the multiple scattering process associated with ultrasonic experiments in heterogeneous media. These results are anticipated to be relevant to ultrasonic nondestructive evaluation of polycrystalline and other heterogeneous solids.

Information transfer through disordered media by diffuse waves

We consider the information content h of a scalar multiple-scattered, diffuse wave field psi(r) and the information capacity C of a communication channel that employs diffuse waves to transfer the information through a disordered medium. Both h and C are shown to be directly related to the mesoscopic correlations between the values of psi(r) at different positions r in space, arising due to the coherent nature of the wave. For the particular case of a communication channel between two identical linear arrays of n>>1 equally spaced transmitters or receivers (receiver spacing a), we show that the average capacity <C> proportional, variant n and obtain explicit analytic expressions for <C>/n in the limit of n--> infinity and kl--> infinity, where k=2pi/lambda, lambda is the wavelength, and l is the mean free path. Modification of the above results in the case of finite but large n and kl is discussed as well. If the signal to noise ratio S/N exceeds some critical value (S/N)(c), <C>/n is a nonmonotonic function of a, exhibiting maxima at ka=mpi (m=1,2, em leader ). For smaller S/N, ka=mpi correspond to local minima, while the absolute maximum of <C>/n is reached at some ka approximately (S/N)(1/2)<pi. We define the maximum average information capacity <C>(max) as <C> maximized over the receiver spacing a and the optimal normalized receiver spacing (ka)(opt) as the spacing maximizing <C>. Both <C>(max)/n and (ka)(opt) scale as (S/N)(1/2) for S/N<(S/N)(c), while (ka)(opt)=mpi and <C>(max)/n approximately log(S/N) for S/N>(S/N)(c).

On the emergence of the Green's function in the correlations of a diffuse field: pulse-echo using thermal phonons

It is shown that a diffuse field is not devoid of phase information, but has a correlation function equal to the Green's function. More specifically, the cross-correlation between diffuse signals in two transducers is very nearly equal to the direct response of one transducer to an impulse applied to the other. This is true whether the diffuse field is one that was created by a distant source, or (if the detectors are sufficiently sensitive) created by thermal fluctuations in the specimen. Here we outline and review proofs, and laboratory demonstrations, from three recent archival publications.