Magnetic Suspension of the Rotor of an Artificial Heart - Improvements to the Radial Stiffness

– This report presents some improvements to the radial stiffness of a magnetic suspension in a new ventricular assist device (VAD) that has been jointly developed by Dante Pazzanese Cardiology Institute (IDPC) and Escola Politecnica of São Paulo University. This VAD has a novel architecture that distinguishes it from other known VADs. In this, the rotor that impels and pressurizes the blood has a conical geometry with spiral impellers. Whereas, in the first VAD models, the rotor was held by ball bearings. One of the objectives of this project is to develop a VAD that uses a magnetic bearing to bear the rotor. The magnetic suspension minimizes hemolysis and improves VAD lifetime, thanks to the absence of any contact between pump rotor and body. A hybrid type magnetic bearing that combines permanent magnets with electromagnets and executes active control in only axial direction of the rotor is used. This magnetic bearing suspension architecture is simpler and less expensive than those that use active control in two or more degrees of freedom in a rotor and also has low energy consumption and heat dissipation, because the control of each degree of freedom requires a sensor, an electromagnetic actuator, an amplifier and a controller. However, the absence of active control along radial directions can be a source of problems, unless a higher radial magnetic passive stiffness is assured. So, after presenting in a past work, the design procedure of the magnetic bearing, the first prototype has been constructed. In addition to presenting the prototype, this report also describes the problems of poor radial stiffness in it and a way of achieving a higher level of radial stiffness. In this sense, different types of electromagnetic actuators are proposed and the action of each actuator studied by numerical methods and by experiments.