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We report on the optimization of a microspeaker diaphragm for widening the working frequency band between its first and second eigenfrequencies and increasing its sound pressure level (SPL). A metallic diaphragm produces a larger magnetic force and thus a higher sound pressure level; therefore a Ni-coating on a common poly ethylene naphthalene (PEN) diaphragm is appropriate. For the best diaphragm design, it is important to simultaneously optimize the diaphragm shape and the Ni-coating distribution on the top of the diaphragm. Since complete Ni-coating increases SPL but also reduces the frequency band, special attention must be paid to the Ni-coating. We solved the optimization problem by a two-step approach: standard shape optimization of a PEN diaphragm for widening the frequency band, followed by distribution optimization of the Ni material on the diaphragm. To facilitate the Ni distribution optimization, we formulated the problem as a special topology design optimization. Since the optimization requires a coupled analysis involving the electromagnetic field, mechanical vibration and sound radiation, the multiphysical system behavior should be properly modeled. After presenting the fundamental multiphysical equations, we provide shape and topology optimization procedures to find an optimal microspeaker diaphragm. We verified the validity of an optimized diaphragm configuration optimized by our method from a physical viewpoint. [ABSTRACT FROM AUTHOR]

MnTe layers of high crystalline quality were successfully grown on Si(111) and Al2 O3(0001) substrates by molecular beam epitaxy. We have investigated the structure, magnetic and electric transport properties of MnTe layers by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, physical properties measurement system (PPMS), and X-ray photoelectron spectroscopy (XPS). Characterization of MnTe layers on Si(111) and Al2 O3 (0001) substrates by X-ray diffraction (XRD) revealed a hexagonal structure of polycrystalline growth for MnTe/Si(111) and epitaxial growth for MnTe/Al2 O3(0001), respectively. Investigation of magnetic properties for MnTe layers showed ferromagnetic properties above room temperature unlike antiferromagnetic bulk MnTe materials. The great irreversibility between zero-field-cooling and field-cooling magnetization were observed. Apparent ferromagnetic hysteresis loops are measured at room temperature. In electro-transport measurements, the temperature dependence of resistivity revealed a noticeable semiconducting behaviors and showed a conduction via variable range hopping (VRH) at low temperature. From XPS results, we assume that the origin of ferromagnetism in samples may be due to the breaking of superexchange antiferromagnetic correlations between Mn spin moments arising from Tellurium vacancies. [ABSTRACT FROM AUTHOR]

To design a magnetic system under a high-strength magnetic field, a nonlinear B-H relation must be considered. However, topology optimization using the nonlinear relation is rare. If the standard topology optimization formulation-varying the densities of design domain-discretizing magnetic finite elements-is used for nonlinear magnetic systems, the nonlinear material behavior will have to be interpolated. Because no consistent interpolating scheme is available, it is difficult to obtain converged distinct air-nonlinear material distributions without several trial-and-error attempts. Furthermore, the sensitivity analysis is very complicated because of the interpolated material nonlinearity. We have devised an alternative topology optimization formulation, called stacked-element connectivity parameterization (S-ECP), for the topology optimization of magnetic systems involving nonlinear B-H relations. The key idea is to discretize the design domain in terms of linear air elements, stack modified nonlinear magnetic material elements on the air elements, and control the element connectivity by varying the permeability of linearly behaving zero-length one-dimensional magnetic links. The links are introduced mainly to connect the air and nonlinear elements. Because a link is modeled by a linear material, the sensitivity analysis does not require complicated analysis involving the differentiation of nonlinear B-H relations, unlike the standard density method. Furthermore, it is much easier to find interpolation functions yielding converged distinct air-magnetic material states. We present numerical examples of C-shaped core design to demonstrate the effectiveness of the formulation. [ABSTRACT FROM AUTHOR]

We report on an investigation of the voltage output from a magnetostrictive sensor for the measurement of elastic flexural waves in a cylindrical steel waveguide. Since the sensor performance is strongly influenced by the bias magnetic field, the bias field optimization is one of the most critical issues in the design of magnetostrictive sensors. For a magnetic system consisting of a yoke and an electromagnet, we formulate a method for optimizing yoke topology in order to maximize the sensor output. Both linear and nonlinear magnetization relations are considered in our analysis. For the verification of the performance of the proposed sensors, we conducted several experiments involving flexural waves to assess the performance of the optimized sensors, and we analyze their results here. [ABSTRACT FROM AUTHOR]

A GaN epilayer was grown on Al2O3 substrate by metal-organic chemical vapor deposition, and Co- ions with a dose of 3×1016 cm-2 were implanted into GaN at 350°C. The implanted samples were postannealed at 700°C-900°C to recrystallize the samples and to remove implantation damage. We have investigated the magnetic and structural properties of Co ion-implanted GaN by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and X-ray photoelectron spectroscopy (XPS). XRD results did not show any peaks associated with the second phase formation, and only the diffraction from the GaN layer and substrate structure were observed. The temperature dependence of magnetization taken in zero-field-cooling and field-cooling conditions showed the features of superparamagnetic system in films annealed at 700°C-900°C. The magnetization curves at 5 K for samples annealed at 700°C-900°C exhibits ferromagnetic hysteresis loops, and the highest residual magnetization (MR) and coercivity (Hc) of MR=1.5×10-4 emu/g and Hc=107 Oe were found in the 800°C annealed sample. XPS measurement showed the metallic Co 2p core levels and the metallic valence band spectra for as-implanted and 700°C-900°C annealed samples. From these, it could be explained that the magnetic property of our films originated from Co and CoGa magnetic clusters. [ABSTRACT FROM PUBLISHER]

A novel two-phase design method based on the topology optimization formulation is proposed in order to configure not only the optimal coil shape, but also the optimal number of coils without using any initial layout The specific design objective is to find an optimal coil configuration maximizing the Lorentz force in the desired direction and minimizing the force in other directions under a given magnetic field. The problem complexity comes from the fact that the location and the number of coils should be determined during the optimization process. To overcome this difficulty, a two-phase topology optimization method is developed where the location and number of coils are determined in the first phase, and the detailed coil shape in the second phase. [ABSTRACT FROM AUTHOR]