Absorbent structures that form superabsorbent polymers in situ. The surface acoustic wave device uses longitudinal surface acoustic waves having a phase speed greater than with the \u201cslow transverse wave\u201d, and has a great electromechanical coupling coefficient and small propagation loss, and is suitable for handling high-frequency signals. The frame includes a front with an air inlet and a back with an air outlet. The correction hypotheses for a subset may be evaluated to select one of the phase noise hypotheses as the trajectory for the subset.