The acoustic sound field above a porous layer and the estimation of the acoustic surface impedance from free-field measurements

An exact evaluation of the acoustic field created by a point source in a semi-infinite fluid above a layer of another fluid of finite thickness is worked out. A method of measuring the characteristic impedance and the propagation constant in a layer by a two-microphone technique is presented. An example is given where the semi-infinite fluid is air and the layer is a fluid equivalent to a porous material.