# A Review of Innovative Electromagnetic Technologies for a Totally Artificial Heart
## 3 TAH Electromechanical Components
### Motor Pumps and Bearings
Figure 4c shows how coupling the pump to a bearingless motor in a CF-TAH leads to a more compact design: there are eight PMs on each rotor side, facing two distinct concentrated stator windings, one of which is for motoring and axial control and the other for tilt control, thus providing full active control for all DOFs [51]. This configuration ensures a relatively large clearance between the rotating and static parts and the accurate rotor-impeller position control. The latter feature enables the flow modulation through the two ventricles to meet the different requirements of the LV and RV [36]. Unlike CFPs, the flow in AFPs cannot be accurately evaluated without a flow sensor; moreover, at a lower flow rate, the risk of tissue damage of the tissues around the inlet channel increases as a result of a higher inlet suction. Due to the high axial force component, the AFP impeller requires an adequate support bearing, whose reliability and efficiency are critical issues. Furthermore, it is difficult to reproduce natural pulsation unless a suitable rotation speed control operates the thrust modulation. Alternatively, an oscillating pushing plate driven by a suitable-shaped bearing mounted on the motor shaft can replace the impeller [52]. Another mechanical arrangement involves the adoption of an undulation pump composed of a pump housing with a partition be  
Figure 4: Magnetic bearings for blood pumps; (**a**) PM assisted by hydrodynamic thrust bearing; (**b**) electromagnetic bearings; (**c**) bearingless axial flux motor for CFPs; and (**d**) bearingless BLDC motor for CFPs. Republished with permission of IEEE. tween the inlet and outlet ports, a disk with a slit located in the partition of the housing, an undulation shaft at the center of the pump, and a pair of seal membranes between the disk and the housing to seal the shaft from the pump room [53]. The mechanism of the undulation shaft prevents the rotation of the disk and converts the rotation of the shaft to the wave motion of the disk. A close line between the disk and the housing enables blood squeezing from the inlet to the outlet of the pump. A TAH requires two of such units that need the implementation of a rather sophisticated hierarchical control protocol [54]. More conveniently, electromagnetic bearings can compensate for axial and radial force components, as in the implementation described in Figure 4d [55]. The impeller is mounted on the inner surface of the hollow rotor, and the suspension of the rotor is based on two passive radial magnetic bearings at the ends of the impeller and an electromagnetic actuator to control the axial position. The main issue is the presence of uncompensated oscillations in the radial directions related to the actuator axial control. Based on the implementation of magnetic bearings, a novel design concept has been proposed for the Dragon Heart at Drexel University [56]. The hybrid design integrates two blood pumps for pediatric patients, in which an axial pump impeller supports the right side of the heart and the pulmonary circulation, and a centrifugal pump impeller supports the left side of the heart and the systemic circulation (Figure 5). By such an arrangement, they share a common rotational axis with distinct fluid domains. Magnetic bearings lift the rotating impeller inside the pump housing and facilitate much wider clearances between the rotating and stationary domains, thus reducing fluid shear stress levels. The design is shaftless and guided by two magnetically coupled PM rings with radial magnetization: one is placed on the extended hub physically coupled to the impeller (hub PM ring), the other one is driven by an external BLDC motor (outer PM ring). The passive radial suspension denoted some limitations in combination with the hydrodynamic bearing, as high shear stresses occurred in areas with narrow fluid gaps, resulting in wear problems on the interior of the inner magnet ring. The implementation of a fully active magnetic suspension was therefore advised for future development.