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May 1981

Volume 69, Issue S1, pp. 31-S125

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back to top Session U. Physical Acoustics III: Relaxation Mechanisms: Techniques and Results
Contributed Papers
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Computer controlled measurements with a spherical resonator (A)

M. A. Barrett Gültepe, M. E. Gültepe, and E. B. Yeager

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S44-S44 (1981); (1 page)

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A microcomputer controlled spherical resonator apparatus has been developed for acoustic studies of liquids at 5–500 kHz. A programmable frequency synthesizer producing frequencies in steps down to 1 μHz is used as the source. The received signal is fed into a programmable tuned amplifier, and demodulated. A/D conversion is made with a high‐speed sample‐and‐hold digital voltmeter via a multiplexing scanner. The system allows for very detailed mode mapping of the sphere by accumulating amplitude data both while the sphere is being driven and after a specified decay time interval, along with recording of temperature. The experimental resonance frequencies have been compared with those predicted theoretically and decay rates of a large number of resonances measured. The amplitude decay can be followed through 70 dB with reproducibility within ±0.2 dB s−1 under favorable conditions. The system is also used for cylindrical resonators. [Research supported by ONR—Physics Program.]
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Observation of Q of 1 million in a water‐filled 100‐liter titanium spherical resonator at 25 kHz (A)

C. C. Hsu and F. H. Fisher

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S44-S45 (1981); (2 pages)

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Leonard (Tech Report No. 1, Department of Physics, UCLA, June 1950) reported a Q of 760 000 at 56 kHz for degassed distilled water in a 50‐liter glass spherical resonator suspended in a vacuum by piano wires. Using essentially the same technique we observed a very strong mode at 25.37 kHz with a decay rate of 0.67 dB/s. This mode corresponds to a Q of slightly greater than 106 and was exactly semilogarithmic over the entire potentiometer range of 50 dB. Two polar end caps for filling and pressurizing the sphere and an equatorial weld bead were the only departures from spherical symmetry. Otherwise the sphere, a ballast tank from the research submarine ALVIN, is concentric and true to within 0.00254 cm. Degassing time to achieve these results is about 100 h. The structure of the high Q mode is unknown. For cylindrical resonators azimuthal modes yielded the highest Q. The assumption for the spherical resonator is that radial modes yield the highest Q. [This research was supported by ONR, NSF and ARPA.]
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Sound absorption in seawater at pressures up to 307 atmospheres (A)

C. C. Hsu and F. H. Fisher

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S45-S45 (1981); (1 page)

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Using a 100‐liter titanium spherical resonator sound absorption from 45 to 350 kHz has been measured in Lyman and Fleming seawater at 25° and at pressures of 1, 71, 188, and 307 atm. Assuming a single MgSO4 relaxation process, the data were analyzed for the values of the maximum absorption per wavelength, (aλ)max, and of the relaxation frequency fr At 1 atm (aλ)max  =  (61.65 ± 0.34) × 10−6, in good agreement with that measured by Wilson and Leonard [J. Acoust. Soc. Am. 26, 223 (1954)] and by Simmons (Ph.D. thesis, University of California, San Diego, 1975). The relaxation frequency of 133 kHz is lower than those reported by Wilson and Leonard and by Simmons. At elevated pressures the relaxation frequency remained the same contrary to the increase observed by Bezdek [J. Acoust. Soc. Am. 53, 782 (1973)] in field measurements. Absorption decreased linearly with pressure according to the equation a(p)  =  a(l)(1− 9.1 × 10−4P), where P is in arm. This decrease is 25% smaller than Bezdek found but nearly the same as Fisher [J. Acoust. Soc. Am. 38, 805 (1965)] measured in 0.5 M MgSO4 solutions. [This research was supported by ONR, NSF and ARPA.]
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Low‐frequency sound absorption in sea water: A new chemical relaxation mechanism? (A)

R. H. Mellen, D. G. Browning, and V. P. Simmons

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S45-S45 (1981); (1 page)

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Excess sound absorption in sea water arises mainly from chemical relaxations involving MgSO4 and B(OH)3. The high‐frequency (100 kHz) MgSO4 relaxation has been identified as a multistep ion‐pair process. The low‐frequency (1kHz) and B(OH)3 relaxation apparently involves more complex interactions with other constituents. To investigate B(OH)3 interactions in a simpler system, we measured absorption in NH3 solution using the resonator method. We have found αmax to be proportional to the product of NH4+ and B(OH)4− concentrations; however, the magnitude is much too large to be caused by the ion pair. The mechanism, probably similar to that in sea water, resembles catalysis, the absorption being governed by the large volume change of the faster NH3/NH4+ equilibrium and the relaxation frequency by the slower B(OH)3/B(OH)4− equilibrium. [Work supported by NUSC and DARPA.]
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Sound absorption in sodium sulfate (1 atm) and sodium chloride (1–307 atm) solutions from 30 to 300 kHz (A)

C. C. Hsu and F. H. Fisher

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S45-S45 (1981); (1 page)

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Sound absorption from 30 to 300 kHz has been measured at 25° with a 100‐liter titanium spherical resonator technique for 0.03 M Na2SO4 and 0.16 M NaCl solutions at 1 atm and for 0.58 M NaCl solutions at pressures from 1 to 307 atm. The results show that these solutions exhibit the same absorption as that for deionized water; that is, within experimental error these solutions exhibit negligible absorption. These results are in agreement with J. Acoust. Soc. Am. 26, 223 (1954), Kurtze and Tatum [Acustica 3, 33 (1953)], and the recent work of Gilligan and Atkinson [J. Phys. Chem. 84, 208 (1980)]. These results are important for understanding the relation of sound absorption to ion pairing in MgSO4 and NaCl solutions including seawater, especially as a function of pressure. [This research was supported by ONR, NSF, and ARPA.]
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Vibrational‐rotational energy transfer in mixtures of nitrogen and water vapor (A)

Allan J. Zuckerwar and William A. Griffin

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S45-S45 (1981); (1 page)

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The following de‐excitation rates have been computed according to the theoretical treatments of Shin [J. Chem. Phys. 60, 1064–1070 (1974)], and Nagel and Rogovin [J. Chem. Phys. 72, 6593–6601 (1980)] for N2−H2O mixtures: k20. de‐excitation of N2 by H2O (VT); k30, near‐resonant transfer (VVR); and k50, de‐excitation of H2O by N2(VT). At 300°K the theoretical values are respectively 0.11, 1.76 × 105, and 3.1 × 104, as compared with the experimental values of <3 × 104, 1.25 × 1O5, and 4.6 × 104, all in (atm⋅s)−1, obtained acoustically in a resonant tube. These results demonstrate the dominance of VVR over VT transfer in the N2−H2O system, and support the conclusion of Nagel and Rogovin that the large rate k30 is “due to the vast number of VR modes H2O has available to absorb energy.”
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