Williams E.

An unusual and unique marriage of high level mathematics and metrology has led to the design and construction of a device that measures instantaneously the vector acoustic intensity throughout a cubic volume. In this volume the device provides either the instantaneous time domain or the frequency domain intensity field. Called the Volumetric Acoustic Intensity Probe (VIP) this device provides the ability to locate sources of sound in the interior spaces (or exterior) of ships, military vehicles, aircraft, etc, by mapping the magnitude and direction of the flow of acoustic intensity throughout the measurement volume in the frequency band from 0 to 1400 Hz. The probe consists of a nearly transparent spherical array of 50 microphones optimally positioned on an imaginary spherical surface and uses spherical NAH to convert the measured pressure field into a vector intensity field in the volume centered on the sphere origin. The array has a radius of 0.2m and the reconstruction volume is limited to a maximum radius of 0.4m. Being an ill-posed inverse problem regularization is used in the reconstruction algorithm. Front-end signal processing for the VIP is designed to deal with random, non-stationary acoustic fields by creating partial field holograms, constructed using either SVD or Cholesky decomposition methods from ensemble averages of the cross-PSD’s with fixed references. In a major application of this approach, experimental results taken during the flight of a Boeing 757 aircraft will be discussed. These results show excellent success at locating the dominant sound sources near the array along with the direction of their radiated power flow. This work was supported by the Office of Naval Research.