US Patent 9995304 Centrifugal fan and impeller thereof

A centrifugal fan includes an impeller. The impeller includes a hub, a plurality of connecting structures, an annular structure and a plurality of blades. The hub includes a circumferential surface. The connecting structures are disposed on the circumferential surface of the hub at intervals. Any adjacent two of the connecting structures define a first minimum distance on the circumferential surface. At least two first minimum distances are not equal. The annular structure is connected to the connecting structures. The blades are disposed on the annular structure at intervals.