Interior permanent magnet synchronous motors (IPMSMs) have high power densities and speed control performance, and they are widely used in the industry. The problem of reducing the torque ripple of an IPMSM is one of the hot issues in the field of electrical machine design. In order to determine the optimal combination of the geometric parameters to reduce the torque ripple of an IPMSM, a range analysis was conducted on the data from the orthogonal experiments in this study, dividing the rotor geometric parameters into two categories (important and ordinary) based on their degree of impact on the torque ripples of the IPMSM. Thereafter, an optimization of the ordinary parameters was carried out based on the results of the range analysis, whereas the optimization of the important parameters was carried out through a method that combined a multi-island genetic algorithm (MIGA) and Radial Basis Function (RBF) neural networks. The torque ripple of the IPMSM was effectively reduced without materially affecting the output power. Finally, the results of this optimization process were verified using a finite element simulation. The optimization method used in this study divided the motor geometric parameters into two categories and applied a different method of optimization to each parameter type, so it was able to efficiently optimize multiple geometric parameters for the IPMSM.INDEX TERMS Optimization, permanent magnet machines, genetic algorithms, torque.
Among the variety of stimuli-responsive materials, temperature-responsive materials (TRMs) can adapt to the surrounding environment in the presence of a thermal stimulus, and they have attracted considerable attention in sensors, actuators, and surface engineering. However, polymers, as the most representative TRMs, are far from ideal with respect to long-term reliability and durability. Here, for the first time, an inorganic material, ReS , is analyzed, which possesses an unexpected temperature-responsive behavior that is triggered by stable and reversible thermally induced bending (TIB). Due to thermal fluctuations in the ReS layers, intrinsic ripples tend to aggravate rapidly with rising temperature. Then, the weak interlayer interaction of ReS is further weakened, thus resulting in interlayer sliding. Due to a decrease in bending rigidity with increasing temperature, out-of-plane bending spontaneously occurs in the ReS layers. Interestingly, this TIB of ReS can recover to its initial configuration when the temperature drops, which is further confirmed by the reversible wetting measurement. Above all, the TIB behavior of ReS exhibits great potential in smart applications, such as smart windows and microfluidic devices, and fills the significant gaps of inorganic TRMs.
We report on the observation of multiple third-harmonic conical waves generated in an annular periodically poled nonlinear photonic crystal. We show that the conical beams are formed as a result of the cascading effect involving two parametric processes that satisfy either the transverse and/or longitudinal phase-patching conditions. This is the first experimental observation of third-harmonic generation based on nonlinear Raman-Nath diffraction. © 2011 Optical Society of America OCIS codes: 190.2620, 190.4410, 220.4000, 050.1940 Third-harmonic generation (THG, also called frequency tripling) is important in many applications as an effective way to achieve coherent light source at shorter wavelengths. To get efficient THG one often employs a two-step cascaded process that involves successive second-harmonic generation (SHG, ω þ ω ¼ 2ω) and sum-. In a nonlinear photonic crystal (NPC) [2][3][4], this process can be realized by using the quasi-phase-matching (QPM) technique [5][6][7][8] that involves a periodic variation to the sign of the second-order nonlinearity χ ð2Þ [9]. The resulting modulation enables one to phase-match the constituent processes via a set of reciprocal lattice vectors (RLV), i.e. k 2 − 2k 1 ¼ G 1 for SHG and k 3 − k 1 − k 2 ¼ G 2 for SFM, with k l ðl ¼ 1; 2; 3Þ being the wave vector of the interacting waves and G 1;2 being RLV [10][11][12]. While these two vectorial relations have been widely used in realization of efficient cascaded THG, it is interesting to see the emission of a third-harmonic (TH) via the socalled Čerenkov-type interaction [13]. The Čerenkov THG represents the type of noncollinear frequency tripling that satisfies only the longitudinal phase-matching conditions: k 2 cos θ 1 ¼ 2k 1 for SHG and k 3 cos θ 2 ¼ k 2 cos θ 1 þ k 1 for SFM, with θ 1;2 being the Čerenkov angles for the secondharmonic (SH) and TH waves, respectively.One question is raised whether it is possible to realize cascaded frequency tripling via transverse phasematching only. It was shown recently that the propagation of a light beam in periodic NPC leads to multiorder diffraction of the SH when the transverse phase-matching condition k 2 sin α ¼ mG (m is integer) is satisfied [14][15][16], in an analogy to linear Raman-Nath diffraction [17]. Thus, one may expect the nonlinear Raman-Nath diffraction of the TH wave via transverse phase-matched SHG and SFM. However, up until now, only the purely longitudinal (Čerenkov) phase-matched THG was observed [13]. In this Letter we report for the first time on experimental observation of THG which relies on cascaded transverse (Raman-Nath) phase-matching. Moreover, we observe for the first time the THG nonlinear diffraction based on cascading of transverse and longitudinal phase-matched processes. The different phase-matching possibilities provide a set of TH rings at different angles.The annular NPC was fabricated using electric poling of a Z-cut MgO:doped stoichiometric lithium tantalate (SLT) crystal (thickness 490 μm). The period is 7:5 μm and the duty factor var...
Fano resonances in plasmonic nanostructures exhibit sharp resonance and strong light confinement. These properties are very useful for sensing applications, which rely on plasmon line shape engineering. Fano resonances in plasmonic clusters depend on structure symmetry, and this study provides a general understanding of Fano resonances in clusters with D 2h symmetry. We show that, because of the excitation of B3u and B2u dark subradiant modes, four kinds of Fano resonances appear in the spectra for hexamers with D 2h symmetry. When a central particle is introduced to form a heptamer, it is shown that, aside from influence on the resonant behaviors or appearance of an additional Fano resonance for a specific polarization, several hybridized dark subradiant modes are excited for both polarizations, and up to eight kinds of Fano resonances appear in the spectra. Plasmonic clusters with D 2h symmetry are suitable for plasmon line shaping, and it is expected that these structures are useful for multiwavelength sensing applications. This study also reveals that cluster symmetry engineering is a favorable method for generating multiple Fano resonances and tuning spectral features. A similar result is obtained for clusters with other symmetries.
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