Paul D. Panetta

Ultrasonic Attenuation as Influenced by Elongated Grains

Reliable nondestructive evaluation of structural/machine components fabricated from polycrystalline materials require the knowledge of attenuation and dispersion of an ultrasonic wave propagating through such microscopically inhomogeneous medium. Expected propagation characteristics of ultrasonic waves in randomly oriented equiaxed grains are relatively well understood. But when the grains are elongated and/or preferentially oriented, the wave propagation constants exhibit anisotropic behavior. The authors have published a number of research articles on propagation of ultrasonic waves in materials with macroscopic texture and elongated grains. The present paper sheds more light on the effect of grain shape on the attenuation and dispersion of ultrasonic waves in polycrystals. Specifically, theoretical results are presented showing the effects of different grain aspect ratios. It is observed that for the same effective grain volume, grain elongation has smaller effect on attenuation.

An estimate of biofilm properties using an acoustic microscope

Noninvasive measurements over a biofilm, a three-dimensional (3-D) community of microorganisms immobilized at a substratum, were made using an acoustic microscope operating at frequencies up to 70 MHz. The microscope scanned a 2.5-mm by 2.5-mm region of a living biofilm having a nominal thickness of 100 mum. Spatial variation of surface heterogeneity, thickness, interior structure, and biomass were estimated. Thickness was estimated as the product of the speed of sound of the medium and the interim between the highest signal peak and that of the substratum plane without biofilm. The thickest portions of biofilm were 145 mum; however, slender structures attributed as streamers extended above, with one obtaining a 274-mum height above the substratum. Three-dimensional iso-contours of amplitude were used to estimate the internal structure of the biofilm. Backscatter amplitude was examined at five zones of increasing height from the substratum to examine biomass distribution. Ultrasound-based estimates of thickness were corroborated with optical microscopy. The experimental acoustic and optical systems, methods used to estimate biofilm properties, and potential applications for the resulting data are discussed

Characterization of solid liquid suspensions utilizing ultrasonic measurements

Rapid, online, noninvasive measurements of the particle size and concentration of moderate to highly concentrated slurries is required for the efficient process measurement and control for many processes. High concentrations are often found in government applications such as waste remediation for the Department of Energy sites and in industrial applications such as chemical and pharmaceutical manufacturing. However, existing methods based on ultrasonic attenuation can become inaccurate for nondilute suspensions due to the complex interactions of ultrasonic waves with the constituents of the slurries. Further complications arise because of the necessity for careful transducer alignment. We are developing two measurements that help to overcome these difficulties, the ultrasonic backscattering and measurements of the diffuse field properties. The backscattering measurement is attractive because viscous, thermal, and inertial effects have small contributions to backscattering. Furthermore, the backscattering theories are simpler than attenuation theories and lend themselves to more stable inversion process. In addition, the measurements of backscattering and diffuse fields do not require long travel distances and can be performed with a single transducer thus eliminating alignment problems. We will present ultrasonic measurements on solid liquid suspensions designed to elucidate the particle size and concentration at high concentrations.

A Formal Approach to Include Multiple Scattering in the Estimation of Ultrasonic Backscattered Signals

An ultrasonic wave propagating through a microscopically inhomogeneous medium, such as polycrystalline materials, is subject to scattering at the grain boundaries. The fraction of energy removed from the incident wave is responsible for important phenomenon like attenuation, dispersion, and background “noise” associated with a given ultrasonic inspection system. Since the backscattered signals tend to mask the signals from small and subtle defects, the estimation of probability of detection of such defects requires the quantitative description of these signals. Although considerable attention has been given to the understanding of mean propagation characteristics of an ultrasonic beam, until recently there have been relatively little efforts devoted towards rigorous treatments of backscattered signals. In this research, we attempt to include some degree of multiple scattering in the calculation of the backscattered signals by developing a formalism that relates mean wave propagation characteristics to the...

Ultrasonic methods for characterization of liquids and slurries

In the field of process monitoring and control technology, Pacific Northwest National Laboratory is utilizing unique technical capabilities and drawing upon knowledge gained through many years of government- and industry-sponsored research activities to develop and deploy advanced sensor and measurement systems for the monitoring and control of process operations. This includes non-invasive, on-line and realtime technologies that use ultrasound characterization to measure the physical and chemical properties of flowing materials, such as liquids and slurries. Ultrasonic velocity, attenuation, reflection coefficients, and scattering amplitudes are measurable parameters related to fundamental physical properties of fluids and slurries of interest to food processors and manufacturers of consumer products. Accordingly, ultrasonic methodologies have been developed that offer on-line, real-time analysis of many physical properties, including particle size distribution, concentration, settling and plug formation, fluid viscosity, density and shear rate, fouling and pipeline wall buildup detection, liquid-liquid interface detection, and chemical identity confirmation.

Nuclear Energy Research Initiative Project No. 02 103 Innovative Low Cost Approaches to Automating QA/QC of Fuel Particle Production Using On Line Nondestructive Methods for Higher Reliability Final Project Report

This Nuclear Energy Research Initiative (NERI) project was tasked with exploring, adapting, developing and demonstrating innovative nondestructive test methods to automate nuclear coated particle fuel inspection so as to provide the United States (US) with necessary improved and economical Quality Assurance and Control (QA/QC) that is needed for the fuels for several reactor concepts being proposed for both near term deployment [DOE NE & NERAC, 2001] and Generation IV nuclear systems. Replacing present day QA/QC methods, done manually and in many cases destructively, with higher speed automated nondestructive methods will make fuel production for advanced reactors economically feasible. For successful deployment of next generation reactors that employ particle fuels, or fuels in the form of pebbles based on particles, extremely large numbers of fuel particles will require inspection at throughput rates that do not significantly impact the proposed manufacturing processes. The focus of the project is nondestructive examination (NDE) technologies that can be automated for production speeds and make either: (I) On Process Measurements or (II) In Line Measurements. The inspection technologies selected will enable particle “quality” qualification as a particle or group of particles passes a sensor. A multiple attribute dependent signature will be measured and used for qualification or process control decisions. A primary task for achieving this objective is to establish standard signatures for both good/acceptable particles and the most problematic types of defects using several nondestructive methods.

Internal Friction in a Diffuse Field Used as a Measure to Characterize Material Properties

Ultrasonic attenuation values of metals deduced using conventional pulse/echo methods contain contributions from both grain scattering and energy absorption (arising from internal friction). In contrast, the energy loss mechanisms, which contribute to diffuse field measurements, are believed to be insensitive to scattering, and hence provide information on internal friction only. In this work several metal specimens are studied, some of which have attenuation values in good agreement with the predictions of grain‐scattering models, and others which do not. The diffuse field decay rate of each specimen is measured, and used to deduce Q inverse, which is a measure of the internal friction in a material. The comparison of the attenuation and diffuse field measurements indicate that specimens in which the measured and predicted values of attenuation were not in good agreement have a significant internal friction contribution towards attenuation, indicating that absorption and not grain scattering is the domin...

Effects of Layer Properties on the Ultrasonic Resonance of Composite Spheres

The efficient calculation of the resonance frequencies is required for the effective application of resonant ultrasound spectroscopy (RUS) to determine the relevant properties of an elastic object. If a suitable number of the resonance frequencies of an elastic object are known, in principle, one can deduce a number of its physical properties like elastic constants, density, dimensions, shape, etc. However, general analytic expressions are not available for the normal mode free vibrations of a body with arbitrary shape and elastic properties. It was noticed by Holland and Demarest (1971) that a simple variational principle can be applied to compute the normal mode frequencies of an elastic body with free boundaries. Based on this variational method, Visscher et al. (1991) developed the XYZ algorithm which can be applied to compute the resonance frequencies of a body with arbitrary shape and elastic properties. Since layered systems are finding increasing use in engineering applications, computational stud...