The present teachings relate to an air feed device with at least one impeller, with at least one housing that at least partially surrounds the impeller, with at least one intake opening for inward suction of air into an operating space of the impeller, with at least one opening to blow out air from the operating space of impeller. The braking device includes brake shoes and a handle that is readily accessible for engaging and disengaging the brake shoes. The field effect transistor includes a gate electrode coupled to a source of gate voltage, a source electrode, a drain electrode and a graphene channel disposed between the source electrode and the drain electrode and electrically connected thereto. When ion implantation is performed on the low concentration drain region beneath the opening region to form a high concentration drain region, the insulating film around the opening region prevents impurities from passing through. Subsequently, the DVD player generates a source side session key and encrypts the session key by using the generated license key.