Left panel: Tubular phononic crystal (TPC) with a Fabry-Perot cavity filled with a set of propanol-water mixtures: representation of the acoustic field in the solid (up) and in the liquid (down). Right panel: Application of the sensor for the determination of the propanol-water mixtures with molar ratio x ranging from 0 to 59.6% as a function of the measured frequency (millimeter size).