A novel permanent magnetic bearing and its anti-wear effect in impeller total artificial heart*

Abstract

A novel permanent magnetic bearing has been developed, which consists of two magnetic rings with differenl dimensions in the same direction of axial magnetization, located concentrically. Because of the effect of magnetic field, the magnetic rings keep a distance axially from each other. If the distance between the two rings changes, a rehabilitalion force is produced to return to the original po-sition. When this distance decreases, a repeiling force will be generated; its component in axial direction can be used as a magnetic spring and its radial component can function as a bearing. With this novel permanent magnetic bearing, an impeller totai artificial beart (TAH) is designed, manufactured and tested. The rotation is driven radially. On the left and right sides of the rotor magnets, two small magnetic rings are fixed onto the rotor, coupling with two big magnetic rings on both sides of the motor coil, to form the magnetic bearings. Hereby the bearings are used for wear reduction rather than rotor levitation. That means the magnetic bearings counteract the attractive force be-tween the motor coil iron and rotor magnets so as to reduce the friction between the motor stator and rotor. At the left and right ends of the rotor, two impellers with the same width but different diameters are mounted. Thus the device has only one moving part-rotor; both ihe left pump ancl the right pump eject the blood synchronically; the volume equilibrium of both pumps can be achieved automatically with-out need of control. The device weighing 250 g has a length of 60 mm and a diameter of 40 mm at its largest point, and can produce a blood flow up to 150 mm Hg and 6 L/min from left pump, 50 mrn Hg and 6 L/min from right pump, at rotating speed of 4000 r/min of the mo-lor. The consumed power is under 10 W.