FE SIMULATION OF THE GENERATION OF GUIDED WAVES BY AIR-COUPLED TRANSDUCERS

The measurements of the spatial and frequential ultrasonic fields generated by an air-coupled transducer furnish the value of its efficiency. Then the field in air can be simulated with absolute values of the pressure with commercial FE software. The field generated by the transducer is simulated by introducing a second member in the Helmholtz equation, used for computing the propagation from the transducer to a plate in the air, along a direction that makes an incident angle theta with the normal of the plate. Inside the plate the propagation is simulated with the dynamic equations of equilibrium and a complex stiffness tensor to take into account the viscoelastic anisotropy of the material. The two physics are coupled by introducing the boundary conditions at the interface fluid/solid. The theta angle is adjusted for generating the specified guided modes and for investigating the efficiency of the air-coupled technique. Experimental and numerical results will be given in terms of normal displacements in function of the incidence and the position for a Perspex plate in order to justify the model.