The Effect of Ultrasonic Waves on the Conductivity of Salt Solutions

An adiabatic compression raises the conductivity of an aqueous salt solution because of direct pressure influence and of temperature increase. An ultrasonic wave therefore modifies periodically the conductivity of the solution. If a filament of current passes normal to the wave propagation, the wave train produces under proper conditions an alternating potential, which can be picked up. This gives per atmosphere pressure and volt applied about 220 microvolts in CuSO₄. (At wave-lengths shorter than the cross dimension of the current, the effect decreases.) This permits the construction of a convenient receiver indicating absolute intensity for the investigation of ultrasonic fields in water, provided the frequency is not above 1.5 megacycles.