Ultrasonic Transducer Beams Model, Using Transient Angular Spectrum

For ultrasonic non destructive evaluation of defects or of materials, the knowledge of transducer field in the material to be tested is essential in order to locate the detected flaws and even more to evaluate them in a precise way. Researchers have been attempting for many years to perfect methods in order to foresee these fields, first from analytical models and then from numerical models. Generally speaking, analytical models are easier to handle, but are less suited to real transducers particularities. First approaches were often limited to a monochromatic representation. In this way, we have developed models based upon a monochromatic plane waves decomposition (angular spectrum) of the ultrasonic field. From the knowledge of the field into a reference plane, this decomposition is simply obtained through a Fourier Transform. This Fourier Transform was done numerically (FFT algorithm): it permits the field to be defined in the plane in the general case, either from experimental or analytical results. Once the propagation of plane waves was studied, even in complex geometric configurations (anisotropic media [1], anisotropic multilayer media [2]), the searched field is given by the recomposition of these waves at any point of the space. In this way, we have successively developed field models in a fluid, in an isotropic solid after crossing interfaces [3,4], in an anisotropic solid [5]. The last model gives the reflected and transmitted fields by an anisotropic multilayered medium [6]