Scale Effects on Performance of BLDC Micromotors for Internal Biomedical Applications: A Finite Element Analysis

Abstract

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.

Model‐based systems engineering approach to the study of electromagnetic interference and compatibility in wireless powered microelectromechanical systems

“…Exploring high torque density micromotors for micro-robotic joints is one of the main objectives of H2020 UWIPOM2 project. See the papers of Villalba-Alumbreros et al 70 and Diez-Jimenez et al 71 This project seeks to develop a micrometric-size wireless powered micromotor. The micromotor will be wireless powered through gigahertz electromagnetic waves, thus providing infinite autonomy to any tool.…”

“…Exploring high torque density micromotors for micro‐robotic joints is one of the main objectives of H2020 UWIPOM2 project. See the papers of Villalba‐Alumbreros et al 70 . and Diez‐Jimenez et al 71 .…”

Microfabrication of Sm2Co17 micromagnets for MEMS and micromotors using ultrashort pulsed hydro laser micromilling process

“…In MEMS (Micro-ElectroMechanical Systems) [6][7][8] and micromachines [9][10][11][12], high quality magnets of NdFeB and SmCo in micrometric size are required. Small micro magnets have been used in several small applications such as sensors [13], actuators [14,15] [16] robotic manipulators [17] [18], and medical devices [19], in particular, actuators [20] [21] and wireless intrabody power transmission systems [22]. Not only small magnets are used, structures of magnets with micrometric features, specific geometries, or magnetic multipole pattern distributions [23] are also required in MEMS applications [24].…”

Microfabrication of Sm2Co17 micromagnets for MEMS and micromotors using ultrashort pulsed hydro laser micromilling process

“…In MEMS (Micro-ElectroMechanical Systems) [6][7][8] and micromachines [9][10][11][12], high quality magnets of NdFeB and SmCo in micrometric size are required. Small micro magnets have been used in several small applications such as sensors [13], actuators [14,15] [16] robotic manipulators [17] [18], and medical devices [19], in particular, actuators [20] [21] and wireless intrabody power transmission systems [22]. Not only small magnets are used, structures of magnets with micrometric features, specific geometries, or magnetic multipole pattern distributions [23] are also required in MEMS applications [24].…”