Resonant oscillation of a liquid metal column driven by electromagnetic Lorentz force sources

In this paper, a theoretical study is conducted in order to establish the feasibility of a liquid metal acoustic resonator (liquid gallium or liquid aluminum) for high-amplitude acoustic oscillations. The fundamental resonant frequency typically lies between 5 and 40 kHz. The oscillations are induced by an alternating Lorentz force density applied directly to the liquid metal volume. Depending on the boundary conditions, two different resonator types (open-closed and open-open) are theoretically investigated. The analysis incorporates the effects of impedance termination, volume absorption, wall friction, acoustic radiation from the open end, and nonlinear inflow-outflow losses. The actual elasticity of the container, either a ceramic or quartz tube, and the coupled solid-liquid interactions are taken into consideration. Based on this investigation, theoretical predictions are conducted for the quality factor and the pressure level for the liquid metal resonator under various geometric and boundary conditions. They indicate that resonant amplitudes of 10-20 arm can be achieved using commercially available high-current audio amplifiers. (C) 1999 Acoustical Society of America. [S0001-4966(99)03104-5].