A method and system for co-molding a thermoplastic material with a thermoplastic sandwich material to form a thermoplastic sandwich article having a thermoplastic inner portion are provided. The gear head forms a gear housing, in which a free wheel or ratchet gear having an output rotational axis is arranged. At least one of the pinching elements of each pair comprises a delaying element for delaying or postponing a pivotal motion of the pinching elements towards the pinching position. The electrodes are formed on the base material and detect the terahertz electromagnetic wave incident on the incident surface of the base material.