Investigations of sound waves generated by the Hall effect in electrolytes

Electrolyte ions moving in a magnetic field produce a velocity component transverse to the electric and magnetic fields. This phenomenon can be alternatively termed as the Hall effect, a magnetohydrodynamic transducer, or a liquid-state electromagnetic transducer. In electrolytes, the viscous drag of the electrolyte fluid is dominant, so the ion deflection soon reaches a terminal velocity dependent only on the electric field strength. The alternating velocity component transverse to the electric and magnetic fields produces a pressure wave due to the viscous drag of the fluid on the ions. Acoustic waves of very high frequencies can be produced since the mass of an ion is very small. Theory for this method of generating sound waves by ultrahigh frequency (UHF) electromagnetic wave impinging on a conducting medium in a magnetic field, causing a conduction current to flow near the surface (skin effect), is presented. Experiments were performed in an electrolyte at frequencies from 8 kHz to 1 MHz to study the effects of electrode size, ionic mobility, and ionic concentration. In the reciprocal effect, ions moving en masse with the particle velocity of a passing acoustic wave induce an alternating voltage between a pair of electrodes in a transverse magnetic field.