The oscillation behavior of a spherical cavity in an infinite elastic medium is calculated for the case of an incident spherical dilatational wave entirely reflected at the cavity walls. It is shown that there exists for every Poisson's constant 0⩽σ⩽0.5 a frequency for which the amplitude of the oscillating cavity walls becomes a maximum. It is also shown that the amplitude resonance curves are symmetrical and that, assuming loss-free material, they have a finite half-width, which is caused by radiation losses and depends only on the ratio of shear wave and dilatational wave velocity. Pulsation oscillations of spherical, rotational-elliptical, cylindrical, and cubic cavities in rubber blocks were examined experimentally. The pulsation oscillations were excited by means of a sound source coupled to the surface of the rubber block. The sound pressure inside the cavities was measured with a probe microphone. The experimental results for spherical cavities are compared with the theory. Good agreement is found with respect to the resonance frequencies.

The ultrasonic absorption in aqueous solutions of a number of 2–2 electrolytes including the sulfates of the bivalent transition metal ions has been measured in the frequency range 105–109 Hz at temperatures between 5 and 50°C. Generally, three relaxations can be separated in this frequency range if the structural absorption of the electrolytic solution is properly taken into account. Relaxation times and corresponding maximum absorption per wavelength are allocated to the normal coordinates of a three-step association or dissociation mechanism. In order to be applicable to the new experimental results, the existing theory of the stepwise association had to be extended to a more general form. By means of suitable transformations the normal coordinates can then be expressed in terms of kinetic and thermodynamic parameters of the individual reaction steps. Values of the rate constants, equilibrium constants, reaction volumes, and activation energies calculated on the basis of the extended theory are presented for the individual reaction steps.

No abstract

No abstract

No abstract