US Patent 9844251 Foldable display device

A foldable display device includes a shell. The shell has an expanding state and a folding state. A first direction and a second direction are defined to be orthogonal. When the shell is at the expanding state, the shell has a first length L1 along the first direction and a second length L2 along the second direction. The ratio of the first length L1 to the second length L2 is between 1.3 and 2. When the shell is at the folding state, the shell has a third length L3 along the second direction and a fourth length L4 along the first direction. The ratio of the third length L3 to the fourth length L4 is also between 1.3 and 2.