Note that although FIGS. 5A1 and 5A2 illustrate the structure in FIGS. 4B1 and 4B2 in which the ferromagnets in the housings 111 and 113 are replaced with the soft magnetic substances 122, one embodiment of the present invention is not limited thereto. For example, as illustrated in FIGS. 5B1 and 5B2, the ferromagnets in the housing 112 may be replaced with the soft magnetic substances 122. Alternatively, the ferromagnet in one housing of the adjacent housings in the structure illustrated in FIGS. 3A1 to 3C or another structure in FIGS. 4A1 to 4C2 may be replaced with the soft magnetic substance 122 as illustrated in FIGS. 18A1 to 18C. Further alternatively, when a mixture of the ferromagnet 121 and the soft magnetic substance 122 is provided for one housing and the two adjacent housings are overlapped with each other, the ferromagnet 121 and the soft magnetic substance 122 may be disposed so as to face each other.
Instead of the soft magnetic substance 122, a soft magnetic substance material may be used for part of a region of the surface or the vicinity of the surface of the housing.
[Modification Example 2]
Although the ferromagnets and the soft magnetic substances are disposed along the upper surface or the lower surface of the housing in the above example, they may be provided at the side of the housing.