Abstract
An electromagnetic acoustic source (EMAS) consists of a flat electrical coil, a thin insulating membrane, and a metal plate. The EMAS is excited by discharging a capacitor through the coil, and the resulting eddy currents produce a repulsive force on the metal plate launching acoustic waves. Here an EMAS was used to excite acoustic waves in a cylindrical chamber of mercury (75‐mm ID and 75‐mm long) with the metal plate bonded to the bottom of the tank. The lid of the chamber had a re‐entrant cylinder such that a steel plate was positioned 50 mm from the EMAS face. A laser Doppler vibrometer was used to monitor the deflection of the plate to ascertain the acoustic field. A 75‐mm‐diameter coil was wound with either 18, 27, or 36 turns. The EMAS plate was steel, aluminum, or just a Mylar insulating membrane with no metallic plate. Experiments were carried out for capacitances of 0.5, 2, and 4 μF, charging voltage of 0–10 kV, number of coils, and properties of the plate. For a 4‐μF capacitor charged to 10 kV,...
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