Patent ID: 6976682

Claim:
A seal for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft, the seal comprising: (a) an annular magnet positioned between the shaft and the hub; (b) a top pole piece and a bottom pole piece coupled to opposite poles of the magnet, both the top and the bottom pole pieces comprising a magnetically permeable material, and having annular shapes with interior radii that are larger than a radius of the outer surface of the shaft, the top pole piece having a cross-sectional area that is substantially L-shaped, and includes a long horizontal portion orientated substantially parallel to a surface of one of the opposite poles of the magnet, and a shorter vertical portion orientated in a facing, non-contact relationship to the outer surface of the shaft, and wherein a first gap separating the top pole piece from the outer surface of the shaft is smaller than a second gap separating the bottom pole piece from the outer surface of the shaft; and (c) a ferrofluid magnetically held between the vertical portion of the top pole and the outer surface of the shaft to form a seal therebetween.