Multiple scattering in random dispersions of spherical scatterers: Effects of shear-acoustic interactions

Experiment and simulation for ultrasonic wave propagation in multiple-particle reinforced composites

The study of ultrasonic wave propagation is a crucial foundation for the application of ultrasonic testing in particle-reinforced composites. However, in the presence of the complex interaction among multiple particles, the wave characteristics are difficult to be analyzed and used for parametric inversion. Here we combine the finite element analysis and experimental measurement to investigate the ultrasonic wave propagation in Cu-W/SiC particle-reinforced composites. The experimental and simulation results are in good agreement and quantitatively correlate longitudinal wave velocity and attenuation coefficient with SiC content and ultrasonic frequency. The results show that the attenuation coefficient of ternary composites (Cu-W/SiC) is significantly larger than that of binary composites (Cu-W, Cu-SiC). This is explained by numerical simulation analysis via extracting the individual attenuation components and visualizing the interaction among multiple particles in a model of energy propagation. The interaction among particles competes with the particle independent scattering in particle-reinforced composites. SiC particles serve as energy transfer channels partially compensating for the loss of scattering attenuation caused by interaction among W particles, which further blocks the transmission of incident energy. The present work provides insight into the theoretical basis for ultrasonic testing in multiple-particle reinforced composites.

Scaling relations for sound scattering by a lattice of hard inclusions in a soft mediuma)

Soft elastic materials embedded with resonant inclusions are widely used as acoustic coatings for maritime applications. A versatile analytical framework for resonance scattering of sound waves in a soft material by a lattice of hard inclusions of complex shape is presented. Analogies from hydrodynamics and electrostatics are employed to derive universal scaling relations for a small number of well-known lumped parameters that map resonant scattering of a complex-shaped hard inclusion to that of a sphere. Multiple scattering of waves between inclusions in proximity is also considered. The problem is then treated using an effective medium theory, viz, a layer of hard inclusions is modeled as a homogenized layer with some effective properties. The acoustic performance of hard inclusions for a range of shapes with spheres of the same volume are compared. Results obtained using this approach are in good agreement with finite element simulations.

Wave Dispersion Behavior in Quasi-Solid State Concrete Hydration

This paper aims to investigate wave dispersion behavior in the quasi-solid state of concrete to better understand microstructure hydration interactions. The quasi-solid state refers to the consistency of the mixture between the initial liquid-solid stage and the hardened stage, where the concrete has not yet fully solidified but still exhibits viscous behavior. The study seeks to enable a more accurate evaluation of the optimal time for the quasi-liquid product of concrete using both contact and noncontact sensors, as current set time measurement approaches based on group velocity may not provide a comprehensive understanding of the hydration phenomenon. To achieve this goal, the wave dispersion behavior of P-wave and surface wave with transducers and sensors is studied. The dispersion behavior with different concrete mixtures and the phase velocity comparison of dispersion behavior are investigated. The analytical solutions are used to validate the measured data. The laboratory test specimen with w/c = 0.5 was subjected to an impulse in a frequency range of 40 kHz to 150 kHz. The results demonstrate that the P-wave results exhibit well-fitted waveform trends with analytical solutions, showing a maximum phase velocity when the impulse frequency is at 50 kHz. The surface wave phase velocity shows distinct patterns at different scanning times, which is attributed to the effect of the microstructure on the wave dispersion behavior. This investigation delivers profound knowledge of hydration and quality control in the quasi-solid state of concrete with wave dispersion behavior, providing a new approach for determining the optimal time of the quasi-liquid product. The criteria and methods developed in this paper can be applied to optimal timing for additive manufacturing of concrete material for 3D printers by utilizing sensors.

Transition from liquid droplet to solid particle investigated by ultrasonic spectroscopy

The size distribution and elastic modulus of micron-sized particles dispersed in liquid can be quantitatively evaluated by ultrasonic spectroscopy at a megahertz frequency range combined with a scattering theory. Conventional theories dealing with the wavelength comparable with the micron-sized particles consider viscosity for liquid droplets in emulsions and elasticity for solid particles in suspension, but very few studies have simultaneously considered viscosity and elasticity for the dispersed phase. In this study, a toluene (Tol) solution of polystyrene (PS) was dispersed in a continuous phase (water), and the ultrasonic properties of the PS-Tol/water emulsion were investigated. Furthermore, when Tol is dried from the PS-Tol droplet, spherical solid PS particles are obtained in water. Using such a drying-in-liquid method, the processes of solid PS particle formation from PS-Tol liquid droplets were analyzed ultrasonically. Since these solid PS particles are in a glassy state at room temperature, the process from emulsion to solid polymer must go through a rubbery state or transition region, where viscosity becomes important in addition to elasticity for solid particles. The objective of this study is to demonstrate a methodology to quantitatively reproduce the ultrasonic spectra of microparticles associated with the drying of organic solvents using a model that takes account of both elasticity and viscous loss.

Bioengineering of neem nano-formulation with adjuvant for better adhesion over applied surface to give long term insect control

Although safe and eco-friendly botanical pesticides have been intensively promoted to combat pest attacks in agriculture, but their stability and efficacies remain an issue for their wide acceptability as sustained and effective approaches. The purpose of this work was to develop stable neem oil based nano-emulsion (NE) formulation with enhanced activity employing suitable bio-inspired adjuvant. So, Neem NEs (with and without) natural adjuvants (Cymbopogon citratus and Prosopis juliflora) in different concentrations were prepared and quality parameters dictating kinetic stability, acidity/alkalinity, viscosity, droplet size, zeta potential, surface tension, stability and compatibility were monitored using Viscometer, Zetasizer, Surface Tensiometer, High Performance Liquid Chromatography (HPLC) and Fourier Transform Infrared Spectroscopy (FTIR). Nano-emulsion biosynthesis optimization studies suggested that slightly acidic (5.9-6.5) NE is kinetically stable with no phase separation; creaming or crystallization may be due to botanical adjuvant (lemongrass oil). Findings proved that Prosopis juliflora, acted as bio-polymeric adjuvant to stabilize NE by increasing Brownian motion and weakening the attractive forces with smaller droplets (25-50 nm), low zeta potential (-30 mV) and poly-dispersive index (<0.3). Botanical adjuvant (30%) based NE with optimum viscosity (98.8cPs) can give long term storage stability and improved adhesiveness and wetting with reduced surface tension and contact angle. FT-IR analysis assured azadirachtin's stability and compatibility with adjuvant. With negligible degradation (1.42%) and higher half-life (t_1/2) of 492.95 days, natural adjuvant based NE is substantially stable formulation, may be due to presence of glycosidic and phenolics compounds. Neem 20NE (with 30% adjuvant) exhibited remarkable insecticidal activity (91.24%) against whitefly (Bemisia tabaci G.) in brinjal (Solanum melongena) as evidenced by in-vivo assay. Results thus obtained suggest, bio-pesticide formulation may be used as safer alternative to chemical pesticides to minimize pesticide residues and presence of natural adjuvant may improves the stability and efficacy of biopesticides for safe crop protection in organic agriculture and Integrated Pest Management.

Fast and slow effective waves across dilute random distributions of elastic spheres in a poroelastic medium

A dilute random distribution of identical elastic spheres in a poroelastic isotropic matrix obeying Biot's theory is considered. Using Luppe, Conoir and Norris (LCN) multiple scattering formula up to the corrective second order term in concentration, approximations are sought in the low frequency domain (Rayleigh limit) for the fast and slow effective wavenumbers. The contribution of the corrective second order term - which contains the coupling (i.e. mode conversions) between the fast, slow and shear waves and accounts for multiple scattering - is discussed. Considering the fast and slow wavenumbers, some effective quantities (bulk modulus, mass density and diffusion coefficient) are estimated.

Sound absorption by a metasurface comprising hard spheres in a soft medium

We present a theoretical framework for acoustic wave propagation in a metasurface comprising a hexagonal lattice of hard spherical inclusions embedded in a soft elastic medium. Each layer of inclusions in the direction of sound propagation is approximated as a homogenized layer with effective geometric and material properties. To account for multiple scattering effects in the lattice of resonant inclusions, an analogy between the fluid dynamics of creeping flows and elastodynamics of soft materials is implemented. Results obtained analytically are in excellent agreement with numerical simulations that exactly model the geometric and material properties of the metasurface.

Particle size distribution analysis of oil-in-water emulsions using static and dynamic ultrasound scattering techniques

Dynamic ultrasound scattering allows us to investigate the particle motion and its average size via the time-evolution analysis of the scattering amplitude in optically turbid media. Recently, we proposed a novel particle sizing method that simultaneously analyzes the depth dependences on the sedimentation velocity and the scattered intensity without prior knowledge about the shape of the size distribution (Ultrasonics, 65 (2016) 59-68). In this study, the applicability of the technique to Fluorinert/water dilute and concentrated emulsions (up to 40 vol%) was examined. For the bimodal distribution of the emulsion, the size distribution of the particles was successfully obtained by directly probing the particle motion with different sizes as a function of the sample depth. The validity of the analysis was also investigated by comparing with conventional ultrasonic spectroscopy.

Low frequency propagation through random polydisperse assemblies of cylindrical or spherical poroelastic obstacles

The effective wavenumbers, moduli, and mass densities are found for polydisperse assemblies of poroelastic obstacles (considering fluid flow and solid deformation in the porous medium). The obstacles are infinite length cylinders and spheres. To achieve this, recent formulas for the effective wavenumbers, given by Linton and Martin [SIAM J. Appl. Math. 66(5), 1649-1668 (2006)] and Norris and Conoir [J. Acoust. Soc. Am. 129(1), 104-113 (2011)] in the dilute monodisperse case (obstacles of identical sizes in a fluid matrix), have been modified. Given the uncertainty in predicting the distribution in size of the obstacles, three quite different probability density functions are studied and compared: uniform, Schulz, and lognormal. Specifically, the Rayleigh approximation (low frequency regime) is considered, in which the wavelengths can be assumed very large compared to the size of the obstacles. Within this limit, simplified formulas are provided for the concentrations depending on the parameter characterizing the size dispersion.

Effective dynamic properties of random complex media with spherical particles

The effective dynamic bulk modulus and density are presented for random media consisting of particles in a viscous host fluid, using a core-shell, self-consistent effective medium model, under the large compressional wavelength assumption. These properties are relevant to acoustic or dynamic processes in nano- and micro-particle fluids including particle density determination, resonant acoustic mixing, and acoustic characterisation. Analytical expressions are obtained for the effective bulk modulus and mass density, incorporating the viscous nature of the fluid host into the core-shell model through wave mode conversion phenomena. The effective density is derived in terms of particle concentration, particle and host densities, particle size, and the acoustic and shear wavenumbers of the liquid host. The analytical expressions obtained agree with prior known results in the limit of both static and inviscid cases; the ratio of the effective bulk modulus to that of the fluid is found to be quasi-static. Numerical calculations demonstrate the dependence of the effective mass density on frequency, particle size (from nano- to micro-regime), and concentration. Herein it is demonstrated both theoretically and numerically that the viscosity, often neglected in the literature, indeed plays a significant role in the effective properties of nanofluids.

Modelling viscous boundary layer dissipation effects in liquid surrounding individual solid nano and micro-particles in an ultrasonic field

Upon application of ultrasonic waves to a suspension of solid particles in liquid, multiple scattering occurs at the particle/liquid interfaces leading to attenuation. It was recently shown through experimental verification that multiple scattering theory must include shear wave influences at the boundary between the liquid and solid particles in a nanofluid when the concentration of the scatterers is even as low as a few percent by volume. Herein, we consider silica spheres of 50–450 nm diameter in the long-wavelength regime to elucidate the form of the shear decay fields at the liquid/solid interface for individual particles. This is important because the overlap of these fields ultimately leads to the conversion of a compressional wave to shear waves and back into the compressional wave, the effect originating due to the density contrast between the particle and the liquid. Therefore, we examine in detail the velocity, vorticity and viscous dissipation in the shear wave field and around the silica spheres using finite element modelling, giving clarity to the viscous boundary effects. We also compare the numerical modelling to semi-analytical results.