Abstract
  The work introduced in this doctoral thesis deepens in the superficial rough phenomenon and its contribution to the acoustic response of the quartz crystal resonator in liquid medium. The main contribution is focused on the study of the geometric parameters that can represent in an optimum manner the effect of the roughness over the acoustic impedance of the sensor. A semi-empiric model of the rough effect based on the results of this study is proposed. Another contribution of this thesis is a detailed study of one of the models most recently proposed: the Arnau’s Model. This model raises the possibility of modeling the roughness by means of a semi-spherical shells distribution. A correction for this model which includes the effect of the interference between shells is proposed in this doctoral thesis. This correction is employed in the behavioral study of the rough effect in random surfaces. It has been proved that the roughness effect of a random surface over the acoustic impedance can be modeled by the response of an equivalent surface made of a regular distribution of semi- spherical shells over a flat surface. Furthermore, it has been demonstrated that the geometric parameters of the equivalent surface are linearly correlated with the projection of the real random surface in the direction of the movement. This statement has been checked by means of experimental measurements with atomic force microscopy (AFM).

Keywords: Piezoelectricity, quartz sensors, roughness, thickness-shear mode