The estimation of wavenumbers in two-dimensional structures

Wavenumber information is important, especially concerning the vibro-acoustic behaviour of structures at higher frequencies. This paper concerns wavenumber measurement in two-dimensional structures such as isotropic and anisotropic plates. A wavenumber estimation technique is described that uses spatial arrays of data measured by a scanning laser vibrometer. One consideration is that it is difficult to get good quality, noise free data at all points and all frequencies, which affects the subsequent data analysis method: for example, techniques such as two-dimensional Prony series become difficult to apply. Furthermore, the wavenumber composition of the resulting wavefield depends on the modal overlap due to the presence of distinct resonances, etc. A technique comprising continuous Fourier Transform decomposition and least-squares minimisation is described. Numerical and experimental results are presented for a flat isotropic panel and an anisotropic composite sandwich panel.