A brief history of magnetic fluid is described from a view point of the present magnetic fluid in practical use. The magnetic fluid is a suspension with nano-magnetic particles stably dispersed in a carrier liquid. The particle size is in a order of 10 nm. The appearance of practical magnetic fluid and the associated technology in 1960’s would be the first nano-technology in history of science. In order to consider a future trend, various applications of magnetic fluid are viewed together with the development of basic theory of continuum mechanics. From the progress of magnetic fluid, a future trend is thought in the present report.

　Smart fluids whose rheological properties are controlled by externally applied magnetic field are known as magneto-rheological fluids (MR fluids). MR fluids are actively and widely used for various fields such as automotive industry, civil environment, and welfare devices. This article is a review of development of MR fluids and its research history.

　This commentary article summarizes the results of MCF polishing liquid, circular tube and cylinder inner surface polishing, surface polishing, and polishing of complex shaped surfaces, which presents the finding of the series of their research of MCF polishing by the author. In each chapter, the characteristics and advantages of the MCF that have been clarified on the elucidation of their polishing characteristics are also explained. Finally, the future development of the MCF polishing is introduced.

　Present status and prospects of magnetic iron oxide nanoparticle (MION) synthesis and their properties for the development of the next generation magnetic fluid suitable for full-scale applications in engineering and medicine are reported. First, the progress in the development of monodispersed size and shape-controlled MION synthesis technology is reported. Then, the nanoscale magnetic properties and flow characteristics investigated using the fine tunned MIONs are reported. From the microscopic and macroscopic structural analysis of the needle-like condensed phase in a magnetic fluid under an external magnetic field, (a) internal spatial order free and (b) chain clustering condensation of small and large particles, respectively, were identified. On the other hand, the estimation of the magnetic anisotropy of individual MIONs was different from the inversely proportional relationship of surface magnetic anisotropy predicted from the size contribution. In the case of particles with isotropic shapes, magnetocrystalline anisotropy plays a significant role in the low-temperature magnetic properties for engineering and medical applications. Finally, based on the above findings, the guidelines for developing next-generation magnetic fluid are proposed.

　Multi-degree-of-freedom (DOF) oscillatory mechanisms are used in various applications such as active vibration isolation tables, vibration test systems, and haptic display devices. These conventional systems are required some actuators and links to drive in multi-axes. Therefore, the size and weight increase, and the oscillation center is shifted because some actuators are arranged in three-dimensional space. Then, we have been proposed the six-DOF oscillatory actuator with axial gap structure. However, it has interference between each axes. In order to solve this problem, we propose a novel six-DOF oscillatory actuator using Lorentz force. This paper describes the magnetic structure and operating principle of the six-DOF oscillatory actuator. The thrust and torque generating principle is shown. The basic characteristics are investigated by a magnetic field analysis using a three-dimensional finite element method. From the analysis results of the thrust and torque characteristics, it is clarified that the proposed six-DOF oscillatory actuator can drive 6-DOF without interference.

　Common multiple-degrees-of-freedom system consist of some uniaxial motors. In contrast, a spherical motor that has a spherical rotor realizes the motion of three degrees of freedom by the motor itself. So, a system by a spherical motor can reduce its size and has advantages such as shorter control time than the system combining uniaxial motors. Most of spherical motors driven by electromagnetic forces have a problem that it is difficult to generate high output torque. So, the development of a spherical speed reducer is required to increase the output. In the development of a spherical speed reducer, it is necessary to construct a rotation transfer model to generate required rotation of the output sphere. This study proposes a spherical speed reducer that the rotation axis of the small spheres, that are intermediate spheres, is constrained not to rotate around an axis in a fixed three-dimensional orthogonal coordinates system. A rotation transmission model from the rotor to the output sphere is constructed using the fact that the rotation of a small sphere is simplified by constraining the rotation around one axis. From the experimental results, the applicability of the rotation transmission model is confirmed.

　A 3-degree-of-freedom spherical actuator has a small size, light weight, and high positioning accuracy compared with conventional systems composed of several 1-degree-of-freedom motors. However, the torque of the spherical actuator is lower than that of the conventional systems, and there are some positions where the actuator cannot move due to a low torque. In order to increase the torque, iron core coils are used instead of air core coils. However, this increases the cogging torque and decrease the controllability. In this paper, for the purpose of reducing the cogging torque, a stator tooth structure with an auxiliary pole is proposed. In addition, the stator tooth arrangement is also optimized using a genetic algorithm.

　A 2-degree-of-freedom (2-DOF) linear-rotary (Z-θ) actuator can realize a linear motion (Z-axis) and rotary motion (θ-axis). It is expected that the positioning accuracy of a 2-DOF mechanism can be increased and the size and weight can be reduced. However, previous Z-θ actuators have many current phases or complicated structures. In this paper, a transverse type Z-θ actuator which is driven by 6 phase currents and has a simple structure is proposed. The operational principle is investigated by a magnetic field analysis using the 3-D finite element method.

　This paper presents magnetic energy propagation mode excited on nonlinear LC circuit. First, we propose an inductor whose flux is a cubic function of current. The excitation and propagation of the magnetic energy was successfully confirmed through 3-D axisymmetric finite element analysis. Next, we propose the inductor whose flux is exponential function of current. The magnetic energy propagation called soliton is successfully observed under the nonlinear LC circuit.

　In recent years, it has become a world problem that periodic inspection of aging transport infrastructures need huge costs and manpower. As a solution for it, we propose a magnetostrictive vibration power generator from vehicle-induce highway vibrations for battery-free LPWA(Low Power Wide Area) module. We investigate the magnetostrictive vibration power generator, which is suitable for power supply because it has features of simple, robust, and high output. In this paper, we applied this generator to vehicle-induced highway vibration. First, we scale up our generators for increasing output power to generate practical electric power under highway vibrations. The size of the large type generator is 150mm×60mm×50mm and 0.6kg in weight utilizing 16mm×2mm×50mm plate of iron-gallium (Fe-Ga) alloy. Then, we reproduced the highway vibrations in laboratory with simulative vibration experiment system to measure character of generator. We confirmed that it generates a peak voltage of 7V, instantaneous maximum power of 36mW, and total power 52mJ from reproduced highway vibrations for 5minutes. Finally, we tested this system in field, and succeeded in activating battery-free LPWA modules from vehicle-induced highway vibration.

　Heating analysis of CFRP and carbon fiber dry cloth for aircraft structures, which is expected for a medium-sized aircraft, is performed. Comparing the temperature of test pieces between numerical and experimental results, validity of both experimental and analytical methods is confirmed for both aluminum and carbon dry cloth sheet. Analysis is made for the layers of carbon dry cloth sheet and CFRTP plate.

　In this study, a magnetostrictive vibrational power generator was proposed for high-frequency vibration occurring in a machine tool and high-efficiency power conversion circuit for a battery-free wireless sensor. A conventional device was miniaturized according to the scale effect, and a device composed of a Fe-Ga alloy plate, of 2×0.25×8 mm³ with a frame of 0.5 mm thickness, was fabricated and evaluated. As a result, a generated voltage of 2 V and effective power of 234 μW were confirmed at a vibration of 522 Hz and 10 m/s². In addition, the operating principle was verified in the power conversion circuit composed of an LC circuit (resonant circuit), a diode and a storage capacitor. As a result, it was confirmed that by using a large inductance, the Q value could be increased, and a considerable amount of energy could be stored in a 330 μF capacitor.

　The IoT used in recent years often uses a button battery or the like, but it has disadvantages in terms of labor and cost of replacement. In addition, IoT applications include the detection and monitoring of abnormalities in rotating machinery. These systems are composed of sensors, wireless modules, and power supplies. There is a demerit in the wiring of the comparator point. Therefore, we are conducting research on vibration power generation to replace these batteries. In this research, speed is detected from the voltage generated by the vibration power generation device, and at the same time, wireless communication is performed using the generated power. This time, we constructed a self-sensing system that generates such self-power and detects and transmits the speed change of the target. Then, this operation was verified.

　The purpose of this study is the application of bistable magnetic device (BMD) to magnetic energy harvesting (MEH). This paper presents the new large-diameter BMD for the application to energy harvesting. To improve the BMD output characteristics, multiple twists were applied to the FeCoV wire with a diameter of 1 mm. As a result, it was confirmed that the applying twists reduced the pulse-induced magnetic field and increased the output peak voltage. In addition, the prototype MEH-device using this BMD was able to generate approximately 5 mW of DC power in the magnetic field of 10 mT.

　This paper presents measured results of the two-dimensional vector magnetic properties in the electrical steel sheets under rotational flux conditions. In the vector magnetic characteristics under rotating magnetic flux conditions, the ratio of alternating hysteresis and rotating hysteresis differs depending on the change in the axial ratio under rotating magnetic flux conditions. This axis rate change from vector magnetic hysteresis loop characteristics are analyzed and clarified details.