Also, with respect to a cross-sectional structure of the second coupling line L2, the second coupling line L2 (see, e.g., FIG. 7) formed along the edge of the second plate P2 and the second coupling line L2 (see, e.g., FIG. 8) formed around the slit S of the second plate P2 may have different cross-sectional structures from each other. This may be because, while the second coupling line L2 (see, e.g., FIG. 7) formed along the edge of the second plate P2 may form the coupling with one second boundary portion P2a formed at the edge of the second plate P2, the second coupling line L2 (see, e.g., FIG. 8) formed around the slit S of the second plate P2 may form the coupling with two second boundary portions P2a formed at both sides of the slit S, based on the slit S of the second plate P2. For example, the second coupling line L2 (see, e.g., FIG. 7) formed along the edge of the second plate P2 may have an asymmetrical cross-sectional structure, and the second coupling line L2 (see, e.g., FIG. 8) formed around the slit S of the second plate P2 may have a symmetrical cross-sectional structure. Here, the cross-sectional structure may correspond to a cross-sectional structure across the second coupling line L2 in the second direction Z2 corresponding to the width direction of the accommodation space G.
