摘要 :
The purpose of the Resonance Meeting was to cover a broad range of uses of acoustic resonances to determine physical properties of matter. The meeting grew out of prior meetings in 1994 and 1995 that were devoted entirely to Reson...
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The purpose of the Resonance Meeting was to cover a broad range of uses of acoustic resonances to determine physical properties of matter. The meeting grew out of prior meetings in 1994 and 1995 that were devoted entirely to Resonant Ultrasound Spectroscopy (RUS). The international list of participants included cutting edge users of RUS and other resonance techniques, as well as researchers and graduate students who wanted to learn about and use these techniques. Universities from the United States and Japan, national laboratories and private research organizations were represented. The Resonance Meeting proved to stimulate extended discussions outside the scheduled sessions. The proceedings of the Resonance Meeting consist of two volumes. Volume 1 contains a verbatim transcript of each presentation. Volume 2 contains accompanying transparencies for each transcript. Anyone interested in obtaining more information on a particular presentation may contact the author(s). Volume 1 contains a complete list of participants and addresses.
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摘要 :
Long-Term Goals: To understand and exploit the resonance scattering by swimbladder-bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acou...
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Long-Term Goals: To understand and exploit the resonance scattering by swimbladder-bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acoustic scattering in terms of meaningful biological parameters compared with traditional higher frequency approaches and other lower frequency narrowband approaches. Objectives: To conduct a new class of quantitative acoustic studies of scattering by swimbladder-bearing fish utilizing new broadband-acoustic technology that is optimized for use in the resonance scattering region of fish.
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摘要 :
A system is described which incorporated a Hewlett-Packard 85 desk-top computer to control a frequency synthesizer and read the output of a lock-in analyzer to measure, display and record the resonant frequencies, amplitudes, and ...
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A system is described which incorporated a Hewlett-Packard 85 desk-top computer to control a frequency synthesizer and read the output of a lock-in analyzer to measure, display and record the resonant frequencies, amplitudes, and quality factors of several modes of an acoustical resonator. The system is capable of locating, measuring, and tracking the resonant modes as parameters which affect sound speed and attenuation are varied. An algorithm for rapidly fitting good quality measured data to a resonance lineshape is described which determines quality factors to precisions of better than 0.1 percent, amplitudes to better than 0.01 percent and center frequencies to better than 0.1 ppm. Sample output is provided for the lowest three plane-wave modes of an air filled cylindrical resonator in the temperature range of -15 to 25 degrees Celsius. (Author)
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摘要 :
To understand and exploit the resonance scattering by swimbladder- bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acoustic scattering ...
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To understand and exploit the resonance scattering by swimbladder- bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acoustic scattering in terms of meaningful biological parameters compared with traditional higher frequency approaches.
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摘要 :
To understand and exploit the resonance scattering by swimbladder- bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acoustic scattering ...
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To understand and exploit the resonance scattering by swimbladder- bearing fish (typically in the 1-10 kHz frequency region). Exploitation of the resonances can significantly reduce ambiguities in interpreting acoustic scattering in terms of meaningful biological parameters compared with traditional higher frequency approaches.
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摘要 :
We are exploring the use of acoustic resonant techniques to identify defective components by monitoring the fundamental modes of vibration that arise following an impulse load. We employ the spectrum of the filtered data as a feat...
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We are exploring the use of acoustic resonant techniques to identify defective components by monitoring the fundamental modes of vibration that arise following an impulse load. We employ the spectrum of the filtered data as a feature for use in automated statistical pattern recognition. The feature provides a measure of the severity of the defect using the acoustic signature of a defect free component as a baseline. Defects change the signature by shifting or splitting the frequencies and introducing beats. Identifying these changes in the spectrum relative to baseline data is difficult because of the large number of natural frequencies associated with complex geometries and the presence of noise in the data. In the case of real-time health monitoring, obtaining a representative spectrum is challenging since averaging cannot be employed without the use of multiple transducers. We have developed a new approach to obtain a smoother spectrum by analyzing sequential data using an approach similar to Rayleigh's quotient method for eigenvalue problems and super-resolution techniques. The resulting spectrum enhances the natural modes of vibration and provides a better feature for automated classification techniques. The numerical implementation of the algorithm requires modest computational resources. The algorithm for generating the Rayleigh quotient has been successfully tested on numerically generated waveforms and experimentally acquired data. In all cases, there was a significant reduction in the inherent noise and the numerically generated noise from digital filtering.
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This thesis examines the feasibility of parametrically exciting a mode of an acoustic resonator. Such excitation may result in substantially larger amplitudes than by direct excitation, and would thus be useful in acoustic devices...
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This thesis examines the feasibility of parametrically exciting a mode of an acoustic resonator. Such excitation may result in substantially larger amplitudes than by direct excitation, and would thus be useful in acoustic devices that require high-amplitude standing waves. Parametric excitation of a mode occurs if the natural frequency is modulated at twice its value, and if the drive amplitude is above a threshold value due to dissipation. It is theoretically shown to be possible to excite the fundamental longitudinal mode of a pipe of any length filled with sulfur hexafluoride if the length is modulated with an Electrovoice EVX-150A driver. For carbon dioxide, excitation is predicted to occur if the pipe is longer than 1.2 meters. Also investigated is parametric excitation of the fundamental radial mode of a cylindrical cavity by modulating the height and thus the temperature. In this case, no driver was found to be capable of exceeding the threshold, regardless of the gas. Use of an electromagnetic wave source to modulate the temperature was also considered as a means of parametrically exciting the fundamental radial mode. Preliminary investigations show that sufficient heat conduction cannot occur over an acoustic cycle, indicating that this method is infeasible.
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摘要 :
A system is described which incorporated a Hewlett-Packard 85 desk-top computer to control a frequency synthesizer and read the output of a lock-in analyzer to measure, display and record the resonant frequencies, amplitudes, and ...
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A system is described which incorporated a Hewlett-Packard 85 desk-top computer to control a frequency synthesizer and read the output of a lock-in analyzer to measure, display and record the resonant frequencies, amplitudes, and quality factors of several modes of an acoustical resonator. The system is capable of locating, measuring, and tracking the resonant modes as parameters which affect sound speed and attenuation are varied. An algorithm for rapidly fitting good quality measured data to a resonance lineshape is described which determines quality factors to precisions of better than 0.1 percent, amplitudes to better than 0.01 percent and center frequencies to better than 0.1 ppm. Sample output is provided for the lowest three plane-wave modes of an air filled cylindrical resonator in the temperature range of -15 to 25 degrees Celsius. (Author)
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Research on thermoacoustic devices has been carried out during the 36 monthperiod ending 14 July, 1992. In the area of general thermoacoustics: (1) Several different setups were constructed to apply arbitrary sound fields to therm...
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Research on thermoacoustic devices has been carried out during the 36 monthperiod ending 14 July, 1992. In the area of general thermoacoustics: (1) Several different setups were constructed to apply arbitrary sound fields to thermoacoustic structures. (2) Detailed computer modeling of the effect of varying the phase of the acoustic impedance of the sound field has been carried out. (3) A simple equivalent thermodynamic circuit model has been developed and computer tested. (4) These setups were used to measure thermoacoustic properties of various grades of steel wool, filter sand, layered stainless steel, and layered mylar. In the area of acoustic resonators: several rotating wave acoustic resonators were built and tested as means to efficiently apply an arbitrary phased sound field to a thermoacoustic device. Single point excitation of these was achieved. Experiments on an arbitrary phased cryocooler were made.
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Research is reported in the following areas: (1) High frequency enhancements ofthe scattering of sound by tilted elastic cylinders in water are analyzed and observed. (2) The interaction of sound with sound mediated by dilute aque...
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Research is reported in the following areas: (1) High frequency enhancements ofthe scattering of sound by tilted elastic cylinders in water are analyzed and observed. (2) The interaction of sound with sound mediated by dilute aqueous suspensions was studied using the frequency shift of a resonator. (3) The coupling of oscillating magnetic fields to the quadrupole quasi-flexural and torsional modes of a stainless steel spherical shell in water is investigated. (4) As an extension of the experimental methods developed for item (1), a PVDF sheet source was used to excite elastic responses of a target but now the target is a large spherical shell in a lake. (5) Transmitted ray contributions and a caustic merging transition for penetrable tilted cylinders are studied using an optical analogy.
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