Abstract:Magnetic linear gear provides a new and unique opportunity for coupling mechanical impedances and optimizing vibration damping. In the present paper a new magneto-mechanical vibration damper (the so-called Z-damper) is described. Its expected theoretical dynamic behavior shows a particularly high damping capability, a low frequency, as well as an optimal behavior for high frequencies.

Actual aerospace and defense technologies present multiple limitations that need to be overcome in order to evolve to less contaminating and more efficient aircraft solutions. Contactless technologies come with essential advantages such as the absence of wear and friction. This work describes the design, prototype, and performance test according to RTCA-DO-160 of an aeronautical magnetic torque limiter. The results show correct continuous transmission operation (2250 rpm and 24 Nm) from −50 • C to +90 • C. Moreover, overload protection has been demonstrated for more than 200 jamming events without damage or required maintenance to the device.

This paper theoretically analyses the miniaturization effects on torque, efficiency and thermal behaviour of high torque permanent magnet BLDC motors with ferromagnetic core coils for internal medical devices. Using a finite element model of a 2-phase BLDC motor, scalability laws are provided for diameters between 0.1 and 100 mm and current densities between 1 and 1000 A/mm2. Based in the impact of the cogging torque and overheating of the motor, scale dependent operational limits are calculated. Operational threshold can be determined at the point where cogging torque becomes dominating over total torque, limiting the use of traditional iron-core motors in the micro-scale. To overcome such limitation, a potential solution is to increase the current density in the windings. However, overheating of the motor limits such increase in the current density which is critical for internal medical applications. Current density limits are provided based on three representative in-body thermal scenarios: respiratory tract, body fluid and blood torrent. Maximum current densities and corresponding torque and efficiency have been obtained for different micro-motor sizes considering safe in-body operation as threshold. It is demonstrated the potential application of micro-motors in internal body environments with acceptable performance for sizes down to 0.1 mm diameter.

FeCo-based soft magnetic alloys are commonly used in macroscale devices to improve its electromagnetic performance, whereas they have been barely used in the microscale. Current FeCo alloy micromanufacturing processes present some difficulties like low structural strength, oxidation at high temperature processes, stoichiometry mismatches in deposition processes and tough workability. In this work, a microcutting of FeCo-2 V-based soft magnetic alloys process is presented and described as an alternative method to obtain microparts with high magnetic properties and good geometrical finish. The results of the machining process are analysed by varying the machining parameters such as depth of cut, tool diameter, rotation speed and feed speed on simple machining operations. The study has been done for 50-μm-diameter endmill and 250-μm-diameter endmill tools. It concludes that the roughness is minimized when machining parameter combination is 0.24 mm/min of feed rate and 8 μm of depth of cut size for a 250-μm-diameter tool, while for a 50-μm-diameter tool, the selected feed rate is 0.24 mm/min, for a depth of cut between 2 and 4 μm. An automated precision 3-axis CNC station is used. Shapes needed for actuators such as angular slots, disks, or slender square geometries are shown in this work with excellent magnetic and mechanical properties. Additionally, a complementary electropolishing process is described. This process helps to eliminate burr in edges and residuals of the milling operation. This study demonstrates that micromilling can be a good alternative for microfabrication of FeCo-2 V components, suitable for precision microassemblies on MEMS.

Satellites with cryogenic instrumentation have great potential for military, commercial, and scientific space missions due to the increased sensitivity of their sensors, even for Low Earth Orbit (LEO) missions. For these missions, magnetorquers are a common electromagnetic actuation solution for controlling the attitude and orientation of the satellite. As for any other component of a satellite, the optimization of power consumption and weight is always beneficial for the design. In this work, we propose a novel idea to reduce power consumption during magnetorquer operation: installing the magnetorquer in the cryogenic area of the satellite, instead of installing an actuator in the hot area. As the electric resistivity of the wire is greatly reduced, power consumption is also reduced. However, the heat generated in the magnetorquer, even if lower, must still be dissipated by the cryocooling system, which has an additional energetic cost. The cryogenic temperature range where this effect is beneficial, and the amount of power saved, was determined as a function of different cryocooler technologies’ efficiency and the purity of the copper wire material. It is analytically demonstrated that the operation of the magnetorquer in a temperature range from 10 to 40 K could save energy with respect to operation at 300 K if the copper wires have a residual resistance ratio larger than 200 RRR. A prototype magnetorquer suitable for cryogenic temperatures was manufactured and tested at liquid nitrogen temperature, 77 K, to experimentally demonstrate the variation in the energy consumption. The magnetorquer comprised an iron core with copper wire winding that achieved 1.42 Am2 by applying 0.565 W at 0.5 A. When operating submerged in liquid nitrogen at a temperature of 77 K, the power used by the magnetorquer was reduced by eight times due to the change in electrical resistivity.