In order to see the various properties of surface acoustic waves on
liquids, we performed experiments analyzing the laser beam
diffracted by interfering liquid surface waves. The surface acoustic
waves were generated by vertical oscillations of long m...
In order to see the various properties of surface acoustic waves on
liquids, we performed experiments analyzing the laser beam
diffracted by interfering liquid surface waves. The surface acoustic
waves were generated by vertical oscillations of long metallic bars
glued to a small speaker, that was driven by a frequency generator.
The relation between the intensity of the diffraction pattern and
the amplitude of the surface acoustic wave was observed by
increasing the applied voltage. We found zeros of the the Bessel
function experimentally by measuring the voltages at which the
various diffraction orders vanished. In addition, we could measure
the wavelength of the surface acoustic wave and the surface tension
of the liquid. The obtained surface tension of pure water was 7.0
$\times$ 10$^{-2}$ (N/m), and the surface tension of a 30 \%
ethylene glycol aqueous solution was 5.5 $\times$ 10$^{-2}$ (N/m).
The wavelength of thet surface acoustic waves in pure water was 1.7
$\times$ 10$^{-3}$ (m), and the wavelength of the surface acoustic
waves in the 30 \% ethylene glycol aqueous solution was 1.9 $\times$
10$^{-3}$ (m). Although invisible to the naked eye, the
characteristics of fine surface acoustic waves and liquid surface
waves can be optically observed by using the characteristic features
of laser-beam diffraction patterns.