The sensitivity of magnetic Barkhausen noise (MBN) profile to changes in the excitation field strength and the number of turns of the detection coil was investigated in inhomogeneous material. Generally, the 0.5 mm ca...The sensitivity of magnetic Barkhausen noise (MBN) profile to changes in the excitation field strength and the number of turns of the detection coil was investigated in inhomogeneous material. Generally, the 0.5 mm case depth EN 36 steel specimen shows a double peak profile indicative of inhomogeneity through the detected depth the magnetized landscape. Various excitation field amplitudes were applied to the specimen and the induced MBN emission was analyzed for each magnetizing current. Excitation field at the lowest level induced an MBN emission of two peaks of equivalent heights. The first peak occurs at lower field than the second peak in the magnetization period. As the excitation field increased, the height of both peaks increased but the second peak increased in a higher rate than that of the first peak. Beyond certain excitation level, both peaks began to saturate and no increase in the MBN intensity was observed with increased excitation field strength. However, peak position and the number of Barkhausen events, indicated linearly as a function of the applied field strength. The experiment also establishes that the number of turns in the detection coil is important parameter which controls the height of the first peak. Low field peak height increases as the number of turn of the detection coil increases. The results indicate that the potential difference applied to the electromagnet and the sensitivity of the detection coil, determine the MBN profile characteristics.展开更多
For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. T...For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. This study introduces Braunbeck coil that can be used in magnetic field excitation system. Braunbeck coil can produce homogeneous magnetic field within a limit space, and occupy a small volume. In addition, this study presents mathematical expressions that can be used to calculate the area of uniform magnetic field. Experimental test verifies the effectiveness of the proposed design, and the results accord closely with the actual simulation.展开更多
传统永磁无刷直流电机(brushless direct current motor,BLDCM)无法控制永磁磁通量及永磁体固有缺陷,限制了其在许多高科技领域中的应用。该文提出新型双凸极无永磁BLDCM。突破传统结构原理,用轴向线圈磁场辅助径向定子励磁,取消永磁材...传统永磁无刷直流电机(brushless direct current motor,BLDCM)无法控制永磁磁通量及永磁体固有缺陷,限制了其在许多高科技领域中的应用。该文提出新型双凸极无永磁BLDCM。突破传统结构原理,用轴向线圈磁场辅助径向定子励磁,取消永磁材料特性制约。线圈辅助定子励磁电机更高输出转矩特性可通过提高气隙磁通及电枢绕组的电流实现。用有限元软件进行数值分析并验证其准确性和有效性;基于该电机的特殊结构和电感模型,搭建联合仿真模型,用三相六状态角度导通方式,增加输出转矩,减小转矩脉动;根据辅助励磁线圈调磁特性,进行励磁线圈和电枢绕组混合之励磁电流-转矩控制。实验验证新型结构电机样机及控制方法的可行性和有效性。展开更多
文摘The sensitivity of magnetic Barkhausen noise (MBN) profile to changes in the excitation field strength and the number of turns of the detection coil was investigated in inhomogeneous material. Generally, the 0.5 mm case depth EN 36 steel specimen shows a double peak profile indicative of inhomogeneity through the detected depth the magnetized landscape. Various excitation field amplitudes were applied to the specimen and the induced MBN emission was analyzed for each magnetizing current. Excitation field at the lowest level induced an MBN emission of two peaks of equivalent heights. The first peak occurs at lower field than the second peak in the magnetization period. As the excitation field increased, the height of both peaks increased but the second peak increased in a higher rate than that of the first peak. Beyond certain excitation level, both peaks began to saturate and no increase in the MBN intensity was observed with increased excitation field strength. However, peak position and the number of Barkhausen events, indicated linearly as a function of the applied field strength. The experiment also establishes that the number of turns in the detection coil is important parameter which controls the height of the first peak. Low field peak height increases as the number of turn of the detection coil increases. The results indicate that the potential difference applied to the electromagnet and the sensitivity of the detection coil, determine the MBN profile characteristics.
基金the National Natural Science Foundation of China(Nos.30800235 and 31271069)the Shanghai Aerospace Science and Technology Innovation Fund(No.SAST2016084)+1 种基金the Medical Engineering and Science Interdisciplinary Fund of Shanghai Jiao Tong University(No.YG2013MS24)the Shanghai Sailing Program(No.17YF1408200)
文摘For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. This study introduces Braunbeck coil that can be used in magnetic field excitation system. Braunbeck coil can produce homogeneous magnetic field within a limit space, and occupy a small volume. In addition, this study presents mathematical expressions that can be used to calculate the area of uniform magnetic field. Experimental test verifies the effectiveness of the proposed design, and the results accord closely with the actual simulation.
文摘传统永磁无刷直流电机(brushless direct current motor,BLDCM)无法控制永磁磁通量及永磁体固有缺陷,限制了其在许多高科技领域中的应用。该文提出新型双凸极无永磁BLDCM。突破传统结构原理,用轴向线圈磁场辅助径向定子励磁,取消永磁材料特性制约。线圈辅助定子励磁电机更高输出转矩特性可通过提高气隙磁通及电枢绕组的电流实现。用有限元软件进行数值分析并验证其准确性和有效性;基于该电机的特殊结构和电感模型,搭建联合仿真模型,用三相六状态角度导通方式,增加输出转矩,减小转矩脉动;根据辅助励磁线圈调磁特性,进行励磁线圈和电枢绕组混合之励磁电流-转矩控制。实验验证新型结构电机样机及控制方法的可行性和有效性。
