cross section. The ratio Width/Length of the test plate must be cut according to the following formula: This ratio yields a so-called “Poisson plate”. The interesting property of a Freely suspended Poisson plate is that the modal shapes that are associated with the 3 first resonance frequencies are fixed: the first resonance frequency is associated with a torsional modal shape, the second resonance frequency is associated with a saddle modal shape and the third resonance frequency is associated with a breathing modal shape. 364x364px So, without the necessity to do an investigation to the nature of the modal shapes, the IET on a Poisson plate reveals the vibrational behaviour of a Poisson plate. The question is now how to extract the orthotropic Engineering constants from the frequencies measured with IET on the beams and Poisson plate. This problem can be solved by an inverse method (also called" Mixed numerical/experimental method") based on a finite element (FE) computer model of the Poisson plate. A FE model allows computing resonance frequencies for a given set of material properties In an inverse method, the material properties in the finite element model are updated in such a way that the computed resonance frequencies match the measured resonance frequencies.Problems with inverse methods are: · The need of good starting values for the material properties · Are the parameters converging to the correct physical solution? · Is the solution unique? The requirements to obtain good results are: · The FE-model must be sufficiently accurate · The IET measurements must be sufficiently accurate · The starting values must be close enough to the final solution to avoid a local minimum (instead of a global minimum) · The computed frequencies in the FE model of the Poisson plate must be sensitive for variations of all the material parameters In the case the Young’s moduli (obtained by IET) are fixed (as non variable parameters) in the inverse method procedure and if only the Poisson’s ratio v12 and the in-plane shear modulus G12 are taken as variable parameters in the FE-model, the Resonalyser procedure''' satisfies all above requirements. Indeed, IET yields very accurate resonance frequencies, even with non-expert equipment, a FE of a plate can be made very accurate by selecting a sufficiently fine element grid, the knowledge of the modal shapes of a Poisson plate can be used to generate very good starting values using a virtual field method