Ultrasonic Waves In Water Research Articles

Effects of Progressive Ultrasonic Waves on a Narrow Light Beam Experimental

An experimental study of slit diffraction of a light beam which is also diffracted by an ultrasonic wave in water is described. The time-average intensity distribution in the broadened source slit image is presented as a function of several parameters. The experimental results are compared with the theoretical results of Zankel. (This research was supported by the Office of Ordnance Research, U. S. Army.)

Attenuation of Ultrasonic Waves of Finite Amplitude in Liquids

Measurements are reported for the effect of finite amplitude on the attenuation of the fundamental component of an ultrasonic wave in water and in aqueous solutions of acetic acid and manganous sulfate. A two crystal continuous wave method was employed. The results in water indicate that the rate of increase of α/ν2 with pressure becomes less with increasing frequency. This result is in contrast to earlier results of Towle and Lindsay. The rate of increase of α/ν2 with pressure was lowered in the aqueous solutions as the concentration was increased.

Scattering of Ultrasonic Waves in Water by Cylindrical Liquid Filled Obstacles

The scattering of an underwater ultrasonic beam from effectively infinitely long cylindrical liquid filled obstacles is studied. The wave-length of the radiation used is 1.3 mm and the obstacle diameter is 13 mm, thus placing this type of scattering between the extremes of scattering from obstacles large compared with the wave-length, and scattering from very small obstacles. In a previous paper the obstacles studied were air and steel, affording the two extremes of ρc mismatch, and the scattering was found to be a diffraction phenomenon. The present communication describes the scattering patterns produced by a cylinder of methyl alcohol, the first of a series of liquids used to determine the type of scattering (i.e., diffraction, refraction, or combinations) produced, as the ρc of the obstacle is varied slowly from values smaller, to values greater than that of water.

The Absorption of Ultrasonic Waves in Liquids and its Relation to Molecular Constitution

Measurements of the absorption of ultrasonic waves in water and ethyl alcohol were made by the pulse method, and are more accurate than those made by other methods. The absorption coefficient α in water was found to vary as the square of the frequency ν over a wide range of temperatures. The measurements in water were made at frequencies between 7.5 and 67.5 Mc/s. and temperatures between 0 and 95° c. The absorption decreased with increasing temperature by a factor of 8 between freezing and boiling points. The observed absorption was about three times that calculated from Stokes formula and this ratio was nearly independent of temperature. In ethyl alcohol measurements were made at 52.4 Mc/s., and at temperatures between - 50° and + 60° c. The absorption decreased by a factor of 3 in this range and observed values were about twice those given by Stokes' formula. Values of (α/ν2) at 25° c. are 22.0 x 10-17 sec2/cm. for water and 50.5 x 10-17 sec2/cm. for ethyl alcohol. Published values of the absorption coefficients of a wide range of pure liquids and of some mixtures are reviewed, and a classification proposed. The experimental results suggest that the absorption in associated liquids is due to a different mechanism from that in non-associated liquids. In the latter the absorption is probably due to the same phenomenon as in gases: a slow exchange of energy between different degrees of freedom. The relaxation frequencies must be above 200 Mc/s. for most liquids. A simple theory is given to explain the observed variation of the absorption with concentration in mixtures of non-associated liquids. The semi-quantitative agreement of theory with experiment lends support to the relaxation hypothesis.

The Scattering of Ultrasonic Waves in Water by Cylindrical Obstacles

An ultrasonic beam produced in water by an oscillating quartz crystal (frequency, 1145 kc; wave-length, 1.3 mm) is scattered by cylindrical obstacles. Three different obstacles are used: (i) a 14″ steel rod, (ii) a 12″ steel rod, and (iii) 58″ hollow polystyrene tube. Lateral pressure amplitude distribution curves are obtained at different points along the axis of the beam for various positions of the obstacles on the axis. The effect of lateral displacements of the obstacles is studied. Wave-front determinations are made with and without obstacles. The conclusion is reached that transmission through and reflection by the obstacles play an insignificant role compared with diffraction around them.

Ultrasonic Absorption in Water in the Temperature Range 0°–80°C

Absorption of ultrasonic waves in water has been measured at temperatures from 0°C to 80°C at six frequencies between 12.25 megacycles and 40.50 megacycles. The experimental values are shown to agree within experimental error with the theoretical values calculated by L. H. Hall on the basis of a structural absorption.

Scattering of Ultrasonic Waves in Water by Solid Cylinders

An x-cut quartz crystal with natural frequency about 1075 kc, placed at the center of one end of a water-filled steel tank (3′×3′×20′), was driven off resonance at 1145 kc. One side of the crystal vibrated in air. The driving circuit consisted of a Colpitts oscillator, buffer amplifier, and power amplifier. The crystal was matched to the output of the power amplifier by link coupling. The radiation in the water was received by a pick-up system consisting of an ammonium dihydrogen phosphate microphone connected to a tuned radiofrequency amplifier. The detected output was measured by means of an electronic voltmeter; readings were proportional to the maximum excess pressure. The obstacle used was a 14″ steel rod, placed in the beam where the latter's half-width was slightly greater than the diameter of the obstacle. Three types of measurements were made: (1) intensity distributions across the beam at different distances along the axis of the beam, (2) wave-front determinations at different distances along the axis, and (3) observations of the effect of moving the obstacle across the beam. The following results have been obtained: (1) The obstacle scatters the original beam into three major peaks flanked by a considerable number of subsidiary peaks. Any asymmetries in the original beam are magnified in the scattered beam. The peaks diverge along rays which appear to originate from a point somewhere between the crystal and obstacle. (2) The undiffracted wave front consists of two sides and a central portion, the three having roughly the same curvature. The obstacle flattens the central portion and steepens the sides. This steepening is to be expected since the velocity of sound is greater in steel than in water. (3) Moving the obstacle causes a continuous change in the scattering pattern. Actual splitting of the beam into three parts occurs only as the center of the beam is approached. Similar experiments are planned for rods of different sizes and for hollow rods of varying thicknesses and acoustic impedance