A belt comprising an elastic band having a central portion and two end portions, wherein a cushion is fastened on the inner surface of the central portion of the band, centered relative to the transverse median axis. The heating medium is subjected to low doses of micro-radiation in order to become heated and thermally expand the encapsulated product. Moreover, frequencies of the registered alternating magnetic field, which are outside a predefined frequency band comprising the selected frequency and have an amplitude value above a predefined threshold value, are detected by means of a detection means.