Woo-chul Kim

Microspeaker Diaphragm Optimization for Widening the Operating Frequency Band and Increasing Sound Pressure Level

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.

Polarization of a permanent magnet to yield specific magnetic field distribution

The objective of this research is to develop a method of finding the polarization distribution of a permanent magnet to produce a desired magnetic field on a target plane located at some distance away from the magnet. Even if the distance between a magnet and the plane is small, magnetic flux fringe effects make it difficult to configure the exact magnet polarization. To solve the problem of magnetic polarization distribution, an iterative numerical topology optimization is formulated. As specific applications, the permanent magnet polarization in the actuators of some optical disk drives is considered. The physics related to the magnetic field obtained by the identified polarization is also examined.

Stacked-Element Connectivity Parameterization for Topology Optimization of Nonlinear Magnetic Systems

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.

P‐64: A Simple Data Line Delay Compensation Scheme for AMOLED Panels

A simple and effective way to remove a double image, which appears on a 3D full high definition AMOLED panel, is presented. The double image results from timing mismatch between the data line delay and scan timing. Providing gradual delay of scan timing effectively eliminates the double image in the AMOLED panel.

Optimal arm configuration to reduce arm bending resonance-induced off-track in a hard disk drive

In order to reduce the off-track due to the arm bending mode, whose effect is considerable in a high capacity drive, an arm configuration with maximum arm bending stiffness should be considered. The objective of this work is to find the optimal arm configuration that maximizes the arm bending stiffness subject to the constraint imposed on the moment of inertia of the arm. Herein, the problem of finding the optimal arm configuration maximizing the arm bending stiffness is formulated as a topology optimization for eigenvalue maximization problem. By applying this method, an arm configuration having two balance holes instead of a single balance hole was obtained. Finally, the efficacy of the optimized arm is verified by measuring the position error signal (PES) of actual sample drives; when the optimized arm was used, the PES was reduced by 25%.

Optimal magnet shape design for wideband magnetic bias torque in a hard disk drive

In order to prevent the swing arm parked on the ramp from rotating due to a rotary shock, a wideband magnetic bias torque is generated on a retract pin. This paper presents the optimal magnet shape to generate a wideband magnetic bias torque. To find the optimal magnet shape, the standard shape optimization is employed. The physics behind why the optimized shape of the magnet yielded better performance is briefly explained using numerical simulation. To verify the effectiveness of the optimized magnet, the actual experiment was conducted. Experimental result shows that the optimized magnet shape generates a wideband magnetic bias torque while maintaining the maximum magnetic bias torque compared to a nominal magnet shape.