Measurements of macrosonic standing waves in oscillating closed cavities

Measurements of macrosonic standing waves in gases in oscillating closed cavities are shown. The strong dependence of the pressure waveform upon cavity shape is demonstrated. This dependence is exploited to provide control of harmonic phase and amplitude, thus avoiding shocks and enabling resonant waveforms to reach macrosonic pressures. The exploitation of this dependence is referred to as resonant macrosonic synthesis (RMS). Power is delivered to the cavity by oscillating it with a linear actuator (entire resonator drive). Standing wave overpressures in excess of 340% of ambient pressure are demonstrated in RMS cavities, compared to maximum overpressures of 17% observed in cylindrical resonators. Ratios of maximum to minimum pressures of 27 were observed in RMS cavities compared to 1.3 for cylinders. Measurements are shown for four axisymmetric cavity shapes: cylinder, cone, horn-cone hybrid, and bulb. Cavities were filled with nitrogen, propane, or refrigerant R-134a (1,1,1,2-tetrafluoroethane). Physical effects which can be observed at macrosonic pressures are demonstrated. These effects include nonlinearly generated de pressures of 40% of ambient pressure as well as hardening and softening resonance behavior for the same gas but different cavity shape. RMS, together with the entire resonator drive, provides high-power transduction of energy through resonant sound waves and opens a wide range of new commercial applications for macrosonic waves. (C) 1998 Acoustical Society of America. [S0001-4966(98)04508-1]