Characteristics and FEA verification of the attraction between like magnetic poles.

The attraction between unequally sized like magnetic poles is characterized herein. Finite element analysis (FEA) simulation has verified that attraction can occur between like poles. Between two unequally sized like poles with various dimensions and alignments, a turning point (TP) appears on the curves of force vs. distance between them, which is caused by the localized demagnetization (LD). The LD plays a role far before the distance between the poles reduces to the TP. The LD area may have a changed polarity, making the attraction possible and not in violation of basic laws of magnetism. Here, the LD levels have been determined using FEA simulation, and the factors affecting the LD have been explored, including the geometry, the linearity of the BH curve, and the alignment of the magnet pairs. Novel devices can be designed with attraction between the centers of such like poles and repulsion when off-center.

Model and parameter identification of soft tissue response to a movement of remotely navigated magnetic sphere.

Accurate and controlled movement of small, untethered objects within soft tissues has many potential applications in medical robotics. While medium reaction forces due to slow movement of solid objects in viscoelastic fluids are well-known, such forces have received much less attention in soft media and tissues where the movement is accompanied by highly non-linear and history dependent phenomena. This paper develops a model of such forces for spherical solids. The reaction forces are investigated experimentally in the limit when the spherical solid moves at only a small fraction of its diameter per second. A mathematical model consistent with observations is proposed. The key element of the model is the history-dependent nature of the medium reaction force. A method of the model parameter identification is described, and its experimental implementation is demonstrated in gels that simulate soft tissues. In the experiments, known magnetic forces are employed as the external forces to drag a permanent magnet sphere inside Agarose gel phantom, and video tracking assisted by template matching calculations is used to accurately track the sphere translation. Numerical simulations of the model illustrate results that are consistent with observations.