| With fast developing society and accelerating pace of life,people are facing growing pressure from work and life.As a result,the population suffering from sleep problems has increased significantly.Because of its remarkable curative effect and no side effects,transcranial magnetic stimulation(TMS)has been widely used to regulate the brain activity and inhibit the neurons excitation which can induce sleep by alternating magnetic fields.Currently,there are problems,such as poor magnetic focusing,low magnetic stimulation intensity,high calorific value and large noise,in available coil TMS apparatus for sleep therapy,which lead to poor efficacy and cause clinical discomfort of the subject.The concept of sleep magnetic therapy apparatus based on permanent magnetic(PMTA)field has been proposed.Firstly,structures,working principles and operation methods of the apparatus are introduced in detail.Then,the structures are designed and optimized by means of magnetic circuit analysis method and finite element analysis method.According to magnetic circuit analysis,the magnetic circuit of PMTA belongs to the D-type magnetic circuit.The calculated length of permanent magnet does not match the actual size,indicating that there is a serious magnetic leakage problem in the magnetic circuit of PMTA.The two-dimensional finite element analysis shows that the path distribution of B has a parabolic shape with an upward opening and B in the center is the smallest.The maximum and minimum B in the center of the air gap are respectively 72 and 52 mT.Based on the first generation of PTMA,the distribution of B and magnetic force line has been studied.The oversize of soft magnets will provide a shortcut for the magnetic force lines,and as a result,it will reduce B in the air gap.After optimization,the maximum B reaches50.524 mT and the mass is 3785 g.Based on the second generation of PTMA,the relationship between the yoke size and its effect has been studied.When the distance between the yoke is 1,2,3 and 4 cm,the corresponding B is 1725,937,779 and 649 mT,respectively.Especially,when the distance is 1cm,the effect of the yoke is obvious,and B in the center is the biggest.As the distance increases,the effect is weakened.When the distance exceeds 4 cm,B decreases from the end of yoke to the center of the air gap.Based on the third generation of PTMA,the influence of the magnetization direction on the distribution of B in the air gap of PMTA has been studied.Under angles of 0~o,18~o and 90~o,the B in the air gap center is 29.521,28.662 and 11.409 mT and magnetization with angle of 0~o is the best.Through the analysis of magnetic force lines in permanent magnets under vertical magnetization,it is shown that vertical magnetization will lead to the shunt of the magnetic force line,thus reducing B in the air gap.The total weight and B decrease from first generation to third generation.And the weight decreases greater.The mass percentage of corresponding permanent magnets was 32.2,49.5and 50.4%.The ability to produce magnetic fields enhances with increasing mass ratio of the permanent magnets,corresponding to the unit mass permanent magnets being 0.0415,0.0509and 0.0574 mT/g,respectively.Optimization of the magnetic therapy instrument structure indirectly optimizes the magnetic circuit and the working point of permanent magnets. |
PDF Full Text Request