A projection lens includes a first lens group, a second lens group and a third lens group, all of which are arranged in sequence from an projection side to an image source side along an optical axis. Time delay and phase of the propagating SAW beam front are controlled by the varying of quantity of isolated fingers of the zebra-wave-guide. The service terminal receives information on a location of a transmitter device of the recipient. The lower peripheral edge of the headband is incised or grooved at regular intervals such that a stretching force thereon in the peripheral direction causes the headband to demonstrate teeth appearance. The display device further includes an optical compensation filter arranged between the front side and the lamp so as to implement any color impressions easily and inexpensively and in a preselectable manner. The body, magnet and shorting member are so configured and arranged such that when the shorting member is removed from the body, the magnet flux will follow a first flux path through the body and armature to cause the armature to move to a first position relative to the seat.