# A Review of Innovative Electromagnetic Technologies for a Totally Artificial Heart
## 4 Linear Electromagnetic Actuators
### Dual-Mover MM-LOA  
In general, the literature suggests integrating LOA into VAD applications, replacing the function of a single ventricle. To emulate the complete functionality of the biological heart function, the TAH must drive two distinct components. The arrangement in Figure 9a shows a dual-mover LOA enclosed in a sealed cavity between two flexible pockets, provided with non-return valves, mimicking the ventricular operation. The LOA stator interaction with two distinct movers impresses on the latter ones, reciprocating opposite synchronous motion with alternative compression and dilation of the pockets to infuse the blood flow. Again, the tubular configuration is particularly profitable. The main features of the E-shaped stator with two PM movers (\(PM_{l}\) and \(PM_{r}\)) analyzed in [62] are:  
* Identical radially magnetized NdFeB-48 PMs in a repulsive configuration;
* Two distinct coils, enclosed in the outer high permeability stator core (CoFe alloy) and supplied by reverse currents to produce opposite thrusts in the nearby movers;
* The cross sections of the LV and RV coil cross sections are proportional to the related ampere-turn \(N_{l}I_{l}\) and \(N_{r}I_{r}\), respectively, in turn proportioned with the corresponding rated thrust peak values \(F_{2l}/F_{2r}=70\) N/25 N;
* A fixed hollow core in the inner part to provide a return path for both the PM and winding fluxes. High-performance magnetic materials are mandatory to satisfy the very binding limits on the overall volume (\(\cong\)153 cm\({}^{3}\)) and the active part mass (<1 kg). The moving mass is very low as well since movers have no back iron. Figure 11 reports the thrust as a function of the mover position for different values of \(N_{l}I_{l}\) and \(N_{r}I_{r}\), with a maintained constant over all the stroke length (\(\pm\)15 mm), a maximum current density of 6 A/mm\({}^{2}\), and total ohmic losses of 13 W. Eddy current losses can be assumed to be negligible because of the low-frequency operation (1.3 Hz). The force profiles evidence the following aspects:  
* The cogging force (\(N_{l}I_{l}=N_{r}I_{r}=0\)) benefits the forward stroke for both movers;
* Inverting the LV coil supply current near the end of the stroke (see point \(P_{1}\)) increases the thrust, which otherwise would even become negative, producing a braking effect;
* Due to the mutual linkage between the coils, the simultaneous current inversion in both coils slightly worsens the RV thrust;
* A residual cogging force opposes the backward motion in both movers (points \(P_{1}\) and \(Q_{1,2,3}\)), regardless of the current value. Figure 9: Double-mover LOA; (**a**) working principle showing the two movers pushing the ventricular chambers; (**b**) LOA electromagnetic configuration; \(PM_{l}\), \(PM_{r}\): PM movers acting on the LV and RV; \(F_{2l}\), \(F_{2r}\): thrust acting on \(PM_{l}\) and \(PM_{r}\); \(2_{0}\): mover position with respect to the backward bound; and sizes are in mm. Republished with permission of IEEE. Parametric analysis that involves the sizes of the main PM and the stator core, as well as the more convenient position \(z_{0}^{*}\) switching the current in both coils, leads to the optimized force profile shown in Figure 10.  
With constant power losses being predefined, various performance indices are considered, which mainly takes into account the TAH forward stroke operation. The profiles calculated by 2D finite element analyses are sufficiently smooth for most of the forward stroke, satisfying the peak force requirements (71.2 N for the LV, \(-36.8\) N for the RV) and with satisfactory mean values (58.2 N for the LV, \(-25.4\) N for the RV). The supply voltage to compensate both the resistance voltage drop and the induced counter e.m.f. is lower than 20 V, therefore being consistent with the portable battery pack. The cogging force, leading to a deadlock near the outward stroke end, represents a major concern for the backward stroke, especially for the RV mover, even if during such a phase a limited blood back-pressure aids the return motion.