Recovery of non-stationary free field with double-layer pressure measurements

Abstract

Abstract To remove the non-stationary incoming field from the back side of the measurement plane and the non-stationary scattered field caused by the incoming wave falling on the surface of the target source, a recovery method of the non-stationary free field with double-layer pressure measurements is proposed. In this method, the time-evolving mixed pressures on double-layer measurement planes are first measured and transformed into the time-wavenumber domain. Then, with the aid of these time-wavenumber pressure spectrums and the impulse response function, the non-stationary incoming and outgoing fields are separated by the conventional non-stationary sound field separation method. Subsequently, the time-wavenumber spectrum of the surface reflection coefficient of the target source is employed to establish the relationship between the non-stationary scattered and incoming fields, based on which the non-stationary scattered field is calculated. Finally, the non-stationary scattered field is removed from the outgoing field and the non-stationary sound field that would be radiated by the target source in free field is recovered. Numerical simulation with an exciting planar steel plate as the target source and a monopole source as the disturbing source is used to examine the feasibility of the proposed method. The recovered results demonstrate that the proposed method not only removes the influence of the incoming field in the time and space domains, but also clears the non-stationary scattered field, thus providing more accurate recovered results than the non-stationary sound field separation method. The experiment further proves the validity of the proposed method.