6 Sample Abstracts of Papers from the Acoustical Society of America

TITLE: 2aPAb1. Determination of velocity and attenuation of shear waves using broadband pulse technique.
TIME: 8:30
AUTHOR: Junru Wu
LOCATION: Dept. of Phys. and Mater. Sci. Program, Univ. of Vermont, Burlington, VT 05405
ABSTRACT: The ultrasonic spectroscopy (broadband pulse) technique was applied to simultaneously measure phase velocity and attenuation coefficient of shear waves in a solid in the megahertz frequencies. This technique is an extension of the ultrasonic spectroscopy technique currently used in determining dispersion of longitudinal waves. Sources of error in measurements including diffraction loss and nonlinear distortion will be discussed. [Work supported by Hewlett--Packard Co.]

TITLE: 2aPAb14. Ultrasonic velocity and attenuation of nano-scaled copper measured by laser ultrasonic technique.
TIME: 12:00
AUTHOR: Xiaorong Zhang
AUTHOR: Changming Gan
AUTHOR: Shiyi Zhang
LOCATION: State Key Lab. of Modern Acoust. and Inst. of Acoust., Nanjing Univ., Nanjing 210093, China
AUTHOR: Yuying Hauny
AUTHOR: Dingchang Xian
LOCATION: Lab. of Synchrotron Radiation, Inst. of High Energy Phys., Chinese Acad. of Science, Beijing 100039, China
ABSTRACT: The velocity and attenuation of an ultrasonic longitudinal wave for nano-scaled copper are determined by a laser ultrasonic technique. The nano-scaled copper samples are composed of super fine particles 10-nm in size, and are prepared by a suppressing and sintering technique under a vacuum, and different pressures are used in the experiment. These samples are of thicknesses between 125--300 (mu)m. The experimental results show that the velocity dispersions and attenuation spectra of nano-scaled copper depend on their fabrication technology conditions, which are different from those of conventional Cu. The attenuation of nano-scaled copper is proportional to the frequency of ultrasound, and some absorption peaks appear at the curves of attenuation versus frequency, but the attenuation of conventional Cu is proportional to the square of the frequency. The velocity of nano-scaled copper is lower than that of conventional Cu. The experimental system, measurement method, results, analyses and discussions are also presented.

TITLE: 2pSPb9. Model reference signal processing for a laser ultrasonics experiment.
TIME: 4:15
AUTHOR: James V. Candy
AUTHOR: Graham H. Thomas
AUTHOR: Diane Chinn
LOCATION: Lawrence Livermore Natl. Lab., Univ. of California, P.O. Box 808, L-495, Livermore, CA 94550
AUTHOR: James B. Spicer
LOCATION: Johns Hopkins Univ., Baltimore, MD 21218
ABSTRACT: Laser ultrasonics is an exciting optical methodology of nondestructive evaluation offering a means of detecting flaws in materials especially in hostile areas where contact transducers cannot function such as high temperature environments or awkward areas where the laser is easily directed by mirrors for rapid scanning and measurement. Typical measurement techniques utilize laser interferometers to accurately measure surface displacements. In this paper the feasibility of applying model-reference signal processing techniques are investigated that would improve the performance of a moderate cost, Michelson interferometric measurement system. A model-reference approach is developed to solve the signal enhancement problem for a laser ultrasonics application in nondestructive evaluation. In this problem a sophisticated laser thermoelastic propagation model is used to predict the surface displacement of the specimen under test. Once synthesized, this model displacement response is used as the reference signal in an optimal (minimum error variance) signal enhancement scheme. Both fixed and adaptive processors are considered in this application where it is shown that a significant improvement in signal levels can be achieved over the usual methods to enhance noisy data acquired from a Michelson interferometric measurement system and increase its overall sensitivity.

TITLE: 4aEA1. Mode control of ultrasonic guided waves in thick cylinders for crack detection.
TIME: 8:00
AUTHOR: Zongbao Li
AUTHOR: Yves H. Berthelot
LOCATION: School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405
ABSTRACT: Experiments on ultrasonic propagation in thick annular structures show that one can simplify the modal structure of the received signals by carefully controlling the wedge angles of the generation and detection transducers. This is important if one is to detect cracks along the path between source and receiver. In particular, one should excite and detect only those modes whose energy is concentrated where the cracks are expected to form. To do so, the following methodology is used: First, experimental signals are obtained for various source--receiver configurations with a standard pulser/receiver; a wavelet transform is then applied to the signals to localize precisely in time the arrival of a given mode packet at a given frequency and to determine the corresponding group velocity. These modes are then identified by comparing the results with predictions from theoretical dispersion curves. One can then predict the energy distribution within the structure by using the method of normal mode expansion for transients. [Work supported by the ONR, Code 332.]

TITLE: 4aEA2. Practical implications of micromachined ultrasonic transducers.
TIME: 8:15
AUTHOR: Igal Ladabaum
AUTHOR: Butrus T. Khuri-Yakub
LOCATION: Stanford Univ., E. L. Ginzton Lab., Stanford, CA 94305
ABSTRACT: Micromachined ultrasonic transducers capable of airborne transmission of 1- to 12-MHz ultrasound have been reported. It has also been reported that these transducers should enable ultrasonic systems with 100 dB of dynamic range. A justification of the predicted dynamic range involves the careful consideration of the thermal noise limits of the system. Such analysis is developed and is based on the fluctuation dissipation theorem. In addition, the first scans produced with the new transducers are presented along with interpretations of their significant impact to nondestructive testing. Pictures of surface and bulk defects in composites and metals are included. Finally, the fabrication process is summarized and the issues involved in the development of immersion transducers are highlighted. [Work supported by the U.S. Office of Naval Research.]

TITLE: 5pPA7. Resonant ultrasound in circular pipes.
TIME: 3:45
AUTHOR: Fred M. Mueller
AUTHOR: Dipen N. Sinha
AUTHOR: Roger D. Hasse
AUTHOR: Kendall N. Springer
LOCATION: Los Alamos Natl. Lab., Los Alamos, NM 87545
ABSTRACT: Resonant ultrasound has found multiple applications, ranging from medical imaging to a variety of nondestructive testing techniques. Here focus is placed on nested cylinders. A series of ultrasonic measurements has been carried out in a geometry with an outer hollow steel cylinder, and a smaller, solid inner steel cylinder. In the interspace were placed several liquids. Ultrasound was introduced by a narrow contact transducer. A second set of narrow transducers was used as pickups and placed at angles ranging from 10 to 150 deg. The frequency of the ultrasound was varied from 1 to 5 MHz and showed a sequence of eight composite and sharp resonances spaced at about 0.5 MHz. The composite resonances showed a strongly skewed behavior as a function of frequency. The velocity potential has been modeled by using combinations of Hankel functions of complex argument. Convergence was achieved by using angular m's up to 150. These showed that the asymmetry of the composite resonance peaks is primarily a phase or geometrical optics effect.

Source:
Acoustical Society of America Homepage
Abstracts of Papers from the 131st Meeting
Indianapolis, IN
13 May - 17 May 1996
© Acoustical Society of America