The technique of processing data in the wavenumber domain based on the Spatial Fourier Transform (SFT), is a powerful tool to compute higher-order partial derivatives occurred in the expressions of the structural intensity and its divergence. However, performing directly the SFT usually results in great distortions if a discontinuity occurs in spatial periodicity (leakage effect). The worst thing is that the divergence of a free plate cannot correctly be estimated by existing wavenumber processing such as the STF and zero padding method. In this paper, a new algorithm -- mirror processing, is developed. By the use of vibrating velocity measured from the technique of laser scanning vibrometry, the structural intensity, its divergence and the force distribution are evaluated by different techniques of wavenumber processing. It is shown that the distortions caused by leakage effects can be removed by using advanced algorithms.

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The use of a pseudo-random sequence and a single microphone is suggested for the experimental determination of the acoustical properties (surface impedance, reflection coefficient, etc.) of sound-absorbing materials. An experimental system is developed with which the surface impedance and reflection coefficient at oblique incidence are determined from measurements of the impulse-response function sequentially at two locations close to the surface of the material using a pseudo-random sequence and a single microphone. This technique is validated using the measurement of a residual pressure-intensity index. The advantage of this technique is that it is possible to perform measurements of the surface properties of materials without phase-mismatch errors that occur with two-microphone methods. Models for estimating the surface impedance from plane-wave and spherical-wave hypotheses are reviewed and compared. Measurements of impedance at oblique incidence are carried out on a sheet of glass fiber in an anechoic room, as well as in a semi-reverberant room, and the results are compared. Surface impedances and reflection coefficients are presented as a function of angle of incidence. The proposed experimental system can be used to measure the acoustical properties of materials at oblique angles of incidence and in semi-reverberant environments.

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The patch holography method allows one to make measurements on an extended structure using a small microphone array. Increased attention has been paid to the two techniques, which are quite different at first glance. One is to extrapolate the pressure field measured on the hologram plane while the other is to use statistically optimized processing. A singular value decomposition formulation of the latter is proposed in this paper. The similarity of the two techniques is shown here. Both use a convolution of the measured pressure patch to obtain a better estimate of the wavenumber spectrum backward propagated on the structure. By using the Morozov discrepancy principle to compute the regularization parameter, the two methods lead to very close results.