Determining structural acoustic properties from noise-based holographic measurements

A facility has been constructed to determine the scattering properties of an arbitrary object in an external medium by measuring its response to a noise field in a laboratory. The measurements are made using a holographic array of a double layer of MEMS microphones placed in the near field of the object; the array is embedded in a 3-D printed scaffold structure which surrounds the object. Cross correlating the MEMS acoustic data together with holographic signal processing yields the structural impedance matrix which together with additional straightforward computation provides the scattering properties of the object when placed (loaded) in an external medium [J. Acoust. Soc. Am. 134, (6) (2013); J. Acoust. Soc. Am. 142(1) (2017)]. The theory underlying the experimental procedure is explained together with results from measurements of a capped cylindrical shell that are also compared to finite element calculations. [Work partially supported by the Office of Naval Research.]A facility has been constructed to determine the scattering properties of an arbitrary object in an external medium by measuring its response to a noise field in a laboratory. The measurements are made using a holographic array of a double layer of MEMS microphones placed in the near field of the object; the array is embedded in a 3-D printed scaffold structure which surrounds the object. Cross correlating the MEMS acoustic data together with holographic signal processing yields the structural impedance matrix which together with additional straightforward computation provides the scattering properties of the object when placed (loaded) in an external medium [J. Acoust. Soc. Am. 134, (6) (2013); J. Acoust. Soc. Am. 142(1) (2017)]. The theory underlying the experimental procedure is explained together with results from measurements of a capped cylindrical shell that are also compared to finite element calculations. [Work partially supported by the Office of Naval Research.]