Improvement of Torque Performance and Energy Density of PM-Type Vernier Motor Utilizing Saddle Coil and Salient Pole

In electric motors, the use of rare-earth magnets has been increasing rapidly. A stronger magnet force of the magnet enables the motor’s higher performance, resulting in the most high-performance motors generally using rare-earth magnets. However, these magnets have two crucial disadvantages: the potential restrictions on the supply of rare-earth magnetic materials and the sharp fluctuation in price. Thus, many recent researches focus on developing high-performance electric motors and reducing the use of critical rare-earth magnets. By increasing the torque density of the motor, we can reduce the use of permanent magnets. Focusing on this point, and we presented a double half permanent magnet (DHPM)-type vernier motor. This paper proposed a new saddle coil permanent magnet vernier motor with improved performance compared to its predecessor. The main feature of the proposed motor is that the permanent magnet and coil in the stator of a DHPM-type vernier motor is replaced by salient poles and saddle coils, respectively. We also investigate its characteristics through various simulations.

Homogenous nuclear magnetic resonance probe using the space harmonics suppression method

Nuclear magnetic resonance imaging (MRI) has became an unavoidable medical tool in spite of its poor sensitivity. This fact motivates the efforts to enhance the nuclear magnetic resonance (NMR) probe performance. Thus, the nuclear spin excitation and detection, classically performed using radio-frequency coils, are required to be highly sensitive and homogeneous. The space harmonics suppression (SHS) method, already demonstrated to construct coil producing homogenous static magnetic field, is used in this work to design radio-frequency coils. The SHS method is used to determine the distribution of the electrical conductive wires which are organized in a saddle-coil-like configuration. The theoretical study of these SHS coils allows one to expect an enhancement of the signal-to-noise ratio with respect to saddle coil. Coils prototypes were constructed and tested to measure 1H NMR signal at a low magnetic field (8 mT) and perform MRI acquired at a high magnetic field (3 T). The signal-to-noise ratios of these SHS coils are compared to the one of saddle coil and birdcage (in the 3 T case) of the same size under the same pulse sequence conditions demonstrating the performance enhancement allowed by the SHS coils.

Comparing Saddle, Slotted-tube and Parallel-plate Coils for Magnetic Resonance Imaging

The paper is concerned with a comparison of the properties of RF coils of three configurations for MRI measurements on small animals. In comparison with the classical saddle coil the proposed modification of slotted-tube coil exhibits identical homogeneity of B1 field in a larger space. The parallel-plate coil has a satisfactory homogeneity of B1 field over the whole internal space. The signal-to-noise ratio measured for all three coils is roughly the same and is given by the magnitude of RF pre-amplifier noise. As the slotted-tube and parallel-plate coils have a lower inductance compared with the saddle coil, they can be tuned to resonance on the 200 MHz frequency even at larger dimensions. The results show that the parallel-plate coil has very good properties for the measurement of small animals.