Ultrasonic characterization of porous silicon using a genetic algorithm to solve the inverse problem

Julien Bustillo (1) , Jérôme Fortineau (1) , Gaël Gautier (1) , Marc Lethiecq (1)

1 GREMAN - UMR 7347 - GREMAN (matériaux, microélectronique, acoustique et nanotechnologies)

This paper presents a method for ultrasonic characterization of porous silicon in which a genetic algorithm based optimization is used to solve the inverse problem. A one dimensional model describing wave propagation through a water immersed sample is used in order to compute transmission spectra. Then, a water immersion wide bandwidth measurement is performed using insertion/substitution method and the spectrum of signals transmitted through the sample is calculated using Fast Fourier Transform. In order to obtain parameters such as thickness, longitudinal wave velocity or density, a genetic algorithm based optimization is used. A validation of the method is performed using aluminum plates with two different thicknesses as references: a good agreement on acoustical parameters can be observed, even in the case where ultrasonic signals overlap. Finally, two samples, i.e. a bulk silicon wafer and a porous silicon layer etched on silicon wafer, are evaluated. A good agreement between retrieved values and theoretical ones is observed. Hypothesis to explain slight discrepancies are proposed.

Mots clés: genetic algorithm; inverse problem resolution; ultrasonic NDE; porous silicon

Domaines: Physique [physics]; Sciences de l'ingénieur [physics]

Julien Bustillo, Jérôme Fortineau, Gaël Gautier, Marc Lethiecq. Ultrasonic characterization of porous silicon using a genetic algorithm to solve the inverse problem. NDT International, 2013, 62, pp.93-98. ⟨10.1016/j.ndteint.2013.11.007⟩. ⟨hal-01080736⟩