Sound power of vibrating cylinders using the radiation resistance matrix and a laser vibrometer.

Research has shown that using acoustic radiation modes combined with surface velocity measurements provide an accurate method of measuring the radiated sound power from vibrating plates. This paper investigates the extension of this method to acoustically radiating cylindrical structures. The mathematical formulations of the radiation resistance matrix and the accompanying acoustic radiation modes of a baffled cylinder are developed. Computational sound power calculations using the vibration-based radiation mode (VBRM) method and the boundary element method are then compared and shown to have good agreement. Experimental surface velocity measurements of a cylinder are taken using a scanning laser Doppler vibrometer and the VBRM method is used to calculate sound power. The results are compared to sound power measurements taken using ISO 3741.

Extending the bandwidth of an acoustic beamforming array using phase unwrapping and array interpolation.

A method is presented to suppress grating lobes in beamforming using phase unwrapping and array interpolation. When the phase of each cross spectrum is successfully unwrapped, the magnitude and phase of the cross spectral matrix may be interpolated; for cases where these quantities vary smoothly, interpolation is straightforward, even above the spatial Nyquist frequency. Two applications are presented: localization of a broadband source and characterization of a source with frequency-dependent location. In both cases, grating lobes are suppressed and the source is localized at frequencies up to at least 8 times the spatial Nyquist frequency.