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 dc 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.

A condenser microphone has been fabricated for measuring low-frequency sound pressure. The goal of this design is to keep the background noise as low as possible. The microphone features a high membrane compliance with a large backchamber volume, a prepolarized backplane, and a high impedance preamplifier located inside the backchamber. Methods for characterizing the performance of the microphone will be presented including background noise levels, which will be compared to commercially available microphones.

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Measurements of macrosonic standing waves in oscillating closed cavities are shown. These cavities (resonators) were designed by MacroSonix using resonant macrosonic synthesis (RMS) to shape the resultant waveform. By controlling the nonlinear processes by which energy is transferred to harmonic frequencies, RMS allows design of resonators that give high-amplitude shock-free waveforms. Measurements in cavities designed with RMS show standing-wave overpressures in excess of 340% of ambient pressure, compared to maximum overpressures in cylindrical cavities of about 17%. Power is delivered by oscillating the entire resonator along its axis with a linear actuator (entire resonator drive). Measurements are shown for four axisymmetric resonator shapes: cylinder, cone, horn-cone hybrid, and bulb. Resonators were filled with nitrogen, propane, or refrigerant R-134a (1,1,1,2-tetrafluoroethane). Ratios of peak-to-minimum pressures of 27 were observed. Since practical compressors for air, refrigerants, or other gases require pressure ratios (discharge to suction) of 3 or more, RMS technology can be used in a wide range of applications. Frequency sweeps show softening or hardening behavior, depending on resonator shape. High-amplitude resonance sweeps show significant hysteresis.

Previous work has demonstrated resonant macrosonic synthesis (RMS) for shaping pressure waves in oscillating closed cavities. Additional measurements of pressure waves are presented, with peak overpressures in excess of 400% of ambient pressure. Characteristic power consumption of various resonator shapes is presented. Resonator shape as well as pressure amplitude is shown to be important in determining power consumption. For a change in resonator geometry, one example shows a 765% increase in pressure amplitude for a fixed power delivery. The dependence on resonator geometry of hardening and softening resonance behavior is demonstrated by showing results for both different resonator shapes and different gases in the resonators. Physical effects of macrosonic pressures and particle velocities are demonstrated with pulverization of objects placed in the resonator cavity.