Marc Lessmann

New Linear Motor Concepts for Artificial Hearts

Total artificial hearts (TAHs), available in todays market, have the disadvantage of wear-prone components. Thus, their expectation of life is limited and the devices can only be used for temporary and not destination therapy. Durability- and wear-free operations are the critical requirements, as failure is an immediate threat to the patients life. These attributes are combined in linear motors. In this paper, the potential of a linear motor as TAHs drive is shown by a prototype. On the basis of this prototype, different motor concepts are employed. The dimensions of each concepts geometry are first roughly determined by analytical optimization, and in a second step, more finely tuned by means of finite-element (FE) calculations. After optimization, two concepts achieve the requirements, provided by the natural heart of the human body. The first motor consists of moving coils and static permanent magnets, which are embedded in a flux concentrating geometry. To avoid the disadvantage of wear-prone power connection of the coils, the other concept consists of static coils and moving permanent magnets, arranged in a Halbach array. After constructing and testing both concepts in laboratory, animal experiments will follow to identify the superior one.

Advanced iron-loss calculation as a basis for efficiency improvement of electrical machines in automotive application

The accurate prediction of iron losses of soft magnetic materials for various frequencies and magnetic flux densities is eminent for an enhanced design of electrical machines in automotive applications. For this purpose different phenomeno-logical iron-loss models have been proposed describing the loss generating effects. Most of these suffer from poor accuracy for high frequencies as well as high values of magnetic flux densities. This paper presents a comparison of the common iron-loss models to an advanced iron-loss formula. The proposed IEM-Formula resolves the limitation of the common iron-loss models by introducing a high order term of the magnetic flux density. Exemplarily, the iron-loss formula is utilized to calculate the iron losses of an induction machine for the drive train of a full electric vehicle.

Numerical computation can save life: FEM simulations for the development of artificial hearts

Cardiovascular diseases are the major cause of death worldwide. In conjunction with the restricted heart transplants due to the limited number of donor hearts, artificial hearts (AH) are the only therapy available for terminal heart diseases. Starting from the first design of an AH to its implantation into a human body, the AH has to pass several clinical trials, which result in redesigns and optimizations respectively. During this process, the dimensions, the weight and the required electromagnetic forces of the AH as well as blood damage, caused e.g. by shear forces or overheating, have to be considered. Thus, a coupling of analytical and numerical approaches permits an accurate design process to investigate force characteristics and losses of the drive. This contribution will give an example of an existing AH and provides exemplary the adoption of analytical and numerical approaches for the design of an AH developed by the authors. The presented heart prototype was already in operation during clinical animal tests.

Rotor design of a high-speed Permanent Magnet Synchronous Machine rating 100,000 rpm at 10kW

Rotors of electrical high speed machines are subject to high stress, limiting the rated power of the machines. This paper describes the design process of a high-speed rotor of a Permanent Magnet Synchronous Machine (PMSM) for a rated power of 10kW at 100,000 rpm. Therefore, at the initial design the impact of the rotor radius to critical parameters is analyzed analytically. In particular, critical parameters are mechanical stress due to high centrifugal forces and natural bending frequencies. Furthermore, air friction losses, heating the rotor and the stator additionally, are no longer negligible compared to conventional machines and must be considered in the design process. These mechanical attributes are controversial to the electromagnetic design, increasing the effective magnetic air gap, for example. Thus, investigations are performed to achieve sufficient mechanical strength without a significant reduction of air gap flux density or causing thermal problems. After initial design by means of analytical estimations, an optimization of rotor geometry and materials is performed by means of the finite element method (FEM).

Development and optimization of a tubular linear synchronous motor considering various skewing methods and eddy current losses

Electromagnetic force with minimum ripple is desirable in many applications. Therefore, the cogging force must be analyzed and solutions for its reduction must be worked out. This paper investigates two possible ways of skewing the magnets of a permanent magnet excited tubular linear synchronous motor to reduce the cogging force. In bioengineering applications, specially upper limb prostheses, minimizing losses is also an issue to prevent tissue overheating, which can lead to hemolysis and thrombogenicity. Hence, the eddy current and hysteresis losses are investigated and related to the ohmic losses.

The multi-slice method for the design of a tubular linear motor with a skewed reaction rail

A fundamental disadvantage of 3-dimensional finite-element simulations is high computational cost when compared to 2-dimensional models. However, for 3-dimensional specific features full models are essential, in principle. An approach to avoid this necessity is the multi-slice method. It is a well known procedure to determine the torque of electrical machines with a skewed rotor only deploying slices of the 3-dimensional full model. This paper presents the adoption of this method to a tubular linear motor and shows that it is applicable for this kind of machine as well. Furthermore, the number of slices and thereby computation time is minimised at the same accuracy of the simulation results.