Gun-Yong Hwang

Development of brushless and sensorless vibration motor used for mobile phone

With the wide use of mobile phones, a paging signal by a sound transducer acts as an environmental noise on many occasions, thus necessitating an alternative paging signal by a vibration motor. Conventional vibration motors employ three-phase windings with mechanical brushes for commutation, which is disadvantageous to manufacturing cost and productivity. In this paper, a new one-phase brushless and sensorless vibration motor is introduced utilizing digital signal processor chips in mobile phones. For electromagnetic field analysis, two-dimensional modeling can be implemented to determine the back electromotive force using axisymmetric boundary conditions. Geometric design parameters, such as coil pitch and magnet pitch. are considered for performance optimization. Through the experiments, it is shown that the proposed design has the equivalent performance with reduced number of parts, thus enhancing manufacturing productivity and reducing manufacturing cost.

New development of combined permanent-magnet type microspeakers used for cellular phones

In mobile phones of multimedia era, microspeakers of high-quality sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical, acoustical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.

New Development of Hexahedral Type Vibration Motor Used for Mobile Phones

Mobile communication industry powered by electronics and information technology is building a transforming way for human communication. The latest electronics is so saturated to forget the difficulty in size reduction of electronic parts. However, mechanical parts, such as dynamic speakers and vibration motors, are intrinsically not easy to realize size reduction due to their construction. In this paper, a hexahedral type with simpler configuration is introduced to substitute for the conventional vibration motors. For uneven magnetic field analysis of the hexahedral type, FEM was used to determine magnetic flux density. After an analysis of magnetic and mechanical characteristics, it is shown that the coil configuration is the most important parameter to increase the output torque, and thus vibration. For optimization, genetic algorithm is used to find the optimal configuration of coil to maximize the output torque. Experimental results are also followed to confirm the validity of the proposed design.

Performance comparison between inner and outer permanent magnet type microspeakers used for mobile phones

In mobile phones of the multimedia era, microspeakers of high quality sound are essential parts to generate the human voice in speaker phones and MP3 song players. In this article two types of microspeakers, inner permanent magnet (PM) and outer PM type, are analyzed using electromagnetic, mechanical, acoustical, and their coupling analysis. For performance comparison, a voice coil diameter is chosen as a design parameter to change magnet volume and excitation position for both types. With the decreased voice coil diameter of the outer type, magnet volume is increased to produce higher sound pressure level (SPL) and the first resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range.

An Experimental Study of Scale-up, Oxidant, and Response Characteristics in PEM Fuel Cells

It is important for fuel cell to become flexible in order to accommodate the situations of application areas for reducing costs and expanding coverage. Scale ups in series and parallel to 1-kW class proton exchange membrane (PEM) fuel cell stack are characterized experimentally with oxidant as air and oxygen. Through a serial scaled-up 4-cell stack with an active area of 25 cm² and a parallel scaled-up single cell with an active area of 100 cm², respectively, the 1-kW class 20-cell stack with an active area of 150 cm² per cell is scaled up from the basic unit cell with maintaining their performances. The polarization and power curves of the 1-kW class PEM fuel cell stack with the reactants H₂/air and H₂/O₂ are evaluated. Sufficient power of the PEM fuel cell can operate at flexible nominal current of 40-80 A and nominal voltage of 12-15 V for providing durability and balance between cells. The 1-kW class PEM fuel cell stack is characterized through the comparison of cell voltage differences utilizing H₂/air and H₂/O₂. Both cell voltages with H₂/air and H₂/O₂ follow well the one-twentieth of the responding stack voltages with the small difference.

Application of Response Surface Methodology (RSM) in Microspeaker Design Used in Mobile Phones

This paper proposes a technique for designing magnetic circuits for use in microspeakers, using the finite element method (FEM) and response surface methodology (RSM). RSM is a collection of statistical and mathematical techniques, used to find the best-fit representation of the response of the physical system under investigation. RSM was used to optimize the dimensions of the magnetic circuit. The optimization resulted in the following dimensions: an inner magnet radius (variable A) of 3.595 mm, a yoke thickness (variable B) of 0.4 mm, and a top plate thickness (variable C) of 0.25 mm.

Development of solenoid-type vibrators used for mobile phones

In this paper, we introduce a simpler solenoid type vibrator and enhanced manufacturing productivity and reduced manufacturing cost. For the electromagnetic field analysis, 3D FEM is utilized with Maxwell stress tensor, structural analysis is also followed to determine the resonant frequency of the system.

Application of Taguchi method to robust design of acoustic performance in IMT-2000 mobile phones

This paper describes an approach to design of acoustic devices, such as microspeaker and dynamic receiver, considering the acoustic characteristics improvement in IMT-2000 mobile phones. The analysis of a newly designed microspeaker considering mechanical, electrical, and magnetic coupling effects is performed using the finite-element method (FEM) and its validity is confirmed as well by experiments. Also, a statistical approach is suggested to identify a certain relationship between a mobile phone and a newly designed microspeaker. The approach is based on the Taguchi method and utilizes the orthogonal array for design of experiments (DOE). The concept of signal-to-noise (S/N) ratio is applied to evaluate the acoustic performance in mobile phones.

Performance design of a dynamic receiver for personal communication devices using finite element method

A dynamic receiver, a mechanical component in personal communication devices, needs to be smaller, lighter and flatter in its frequency responses. In this paper, a design tool considering mechanical and electromagnetic coupling effects is proposed using finite element method confirmed by experiments. After a sensitivity analysis of mechanical and electromagnetic design parameters, a new design is also proposed with less volume and weight but with better performances.

Development of Hi-Fi microspeakers with a woofer and a tweeter used for mobile phones

For mobile phones, high performance microspeakers with broader frequency range are essential parts to realize various multimedia functions such as MP3 playback, speaker phones, and 64 poly-harmonic melody. Noting that the operating frequency range of conventional microspeakers ranges from 900Hzto10kHz, that of 400Hzto10kHz for hi-fi microspeakers is required to meet customer demand in a multimedia era. One possible way of achieving this is to integrate two-way microspeakers (woofer and tweeter) within one device sharing not only magnetic circuit but also vibration space. Noting that the characteristics of the microspeakers are a coupled phenomenon of electromagnetic, mechanical and acoustic system, a systematic analysis must be implemented to fully consider the coupling effects. In this article, a hi-fi microspeaker with a woofer and a tweeter is introduced and the sound pressure level is also calculated and compared with the experimental results. Results show the development can be a successful alternati...