The energy harvester module of the capsule comprises: a primary oscillating structure subjected to an external low-frequency stress； a secondary oscillating structure comprising an elastic element and able to vibrate in high-frequency resonance； and an electrostatic structure with a first electrode coupled to the primary structure and a second electrode coupled to the secondary structure. The electrodes exert a mutual attraction between them driving the secondary structure away from its stable equilibrium position with tensioning of the elastic element, up to a limit beyond which the secondary structure is released by relaxation effect to vibrate at a resonance frequency. A transducer coupled to the secondary structure converts these high frequency vibration movements into electrical energy.
