• Journal of Magnetics
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• v.21 no.3
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• pp.387-392
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• 2016

Lower flux leakage designs have become important in the development of microspeakers used in thin and miniaturized mobile phones. We propose four methods to reduce the flux leakage of the magnetic circuit in a microspeaker. Optimization was performed based on the proposed approach by using the response surface method. Electromagnetic analyses were conducted using the finite element method. Experimental results are in good agreement with the simulated results obtained in one degree-of-freedom analysis from 100 to 5 kHz. Both the simulated and experimental results confirm that one of the proposed methods is much more effective in reducing flux leakage than the other methods. In the optimized method, compared with a default approach, the average radial flux density in the air gap decreased only by 5.5%, the maximum flux leakage was reduced by 28.6%, and the acoustic performance at primary resonance decreased by 0.45 dB, which gap is indiscernible to the human ear.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.556-561
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• 2008

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small and constant at low frequency region and shows about 70 dB at 10 kHz. However, in case of a compressively stressed composite diaphragm, the SPL of the fabricated microspeakers shows higher output pressure than those of a tensile-stressed diaphragm. It produces more than 66 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with $20V_{peak-to-peak}$, sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone. From the experimental results, it is superior to have a compressively composite diaphragm in order to produce a high SPL in piezoelectric microspeaker.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.183-189
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• 2006

In mobile phones of multimedia era, microspeakers of high qualify 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 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.497-502
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• 2005

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.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.495-498
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• 2004

핸드폰등에 사용되고 있는 마이크로스피커를 개발하는 과정에서 마이크로스피커의 진동특성과 음향특성 을 전산해석하였다. 해석과정에서 기초 데이터를 얻기 위하여 하이브리드 방법을 이용하여 각 부품들의 제원 및 마이크로스피커 모델링을 위한 매개변수들을 규명하였다. 전산 해석 결과와 측정한 전기 임피던스 및 음향 응답특성은 잘 일치함을 보였다. 또한, 진동특성을 분석하여 각 주파수에서의 다이아프램의 변위등 진동특성을 분석하여 다이아프램등의 형상에 따른 이상 진동현상 등을 파악할 수 있었다. 전산해석 방법을 이용하면 최적 음향특성을 위한 마이크로스피커의 다이아프램 형상 및 전자기 회로 개선에 사용할 가능성을 알 수 있었다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.5 no.1
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• pp.52-57
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• 2005

This paper describes a fabrication method of a circular diaphragm using boron etching stop method. It will be applied to acoustic transducers such as microphones or microspeakers and so on. The sensitivity is expected to be increased with the circular diaphragm through the simulation results to compare with a general rectangular diaphragm. The borondoped layer which is doped with solid source is sufficient for achieving an etching stop in 20 wt% TMAH, and the thickness is about $7.4{\mu}m$. The diameter of the circular silicon nitride diaphragm was measured to be 2 mm with $1{\mu}m$ thickness. The fabrication of piezoelectric acoustic devices was completed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.983-992
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• 2007

It was proposed to identify Thiele Small Parameters for loudspeaker attached to closed-box using known dynamic mass of moving parts. Also, enhanced PSPICE circuit model for closed-box loudspeaker system was proposed to more accurately simulate real closed-box loudspeaker system. Frequency dependent parameters were used to model voice coil inductor. Acoustic pressure response curves and electrical impedance curves were simulated and investigated by PSPICE circuit model according to compensation filter's parameters. Finally, proposed method is expected to be utilized for identification of pseudo Thiele Small parameters of microspeaker.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.8
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• pp.1455-1460
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• 2007

This paper reports the piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film deposited onto Mo/Ti electrode. This successful achievement, compared to the previous results, is followed by manipulating two material properties: the one is to use a compressively stressed silicon nitride film as a supporting diaphragm (even tensile stressed, around +20 MPa) and the another is to use high quality AlN thin film with compressive residual stress (less than -100 MPa). With these materials, the Sound Pressure Level (SPL) of the fabricated micro speakers shows more than 60 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with 20 Vpeak-to-peak sinusoidal input and with 10 mm distances from the fabricated micro speakers to the reference microphone (B&K Type 2669 & 4192L).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.37-38
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• 2007

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small. However, the SPL of the fabricated microspeakers that have compressive-stressed composite diaphragm show higher output pressure than those of tensile-stressed diaphragm. It produces more than 60dB from 100Hz to 15kHz and the highest SPL is about 100dB at 9.3kHz with 20 Vpeak-to-peak sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.403-409
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• 2011

Micro speakers are used to reproduce sound in small electric and information and communications devices, such as cellular phones, PMPs, and MP3 players. The acoustical properties and sound quality, which are changed due to the decreased size of the speaker, are often adjusted varying the type and thickness of the diaphragm. The most widely used diaphragm material is thin polymer. It was previously reported by the author of this paper that the resonance frequency of a micro speaker is changed by the type and thickness of a polymer diaphragm. In this paper, the frequency response near the resonance frequency of a micro speaker was studied as functions of the type and thickness of the polymer diaphragm. While $R_{max}$ and $R_{DC}$ were affected by the type and thickness, an analysis of the electrical impedance curve revealed that $R_o(= R_{max}/R_{DC})$ and ${\Delta}f$ were not changed. Thus, $Q_{TS}$ which was function of $R_o$, ${\Delta}f$, and the resonance frequency, is only related to the resonance frequency. The increase of the resonance frequency led to a proportional rise of $Q_{TS}$. The change of the frequency response near the resonance frequency was not dependent on the type or thickness of the polymer diaphragm, but was affected by the resonance frequency.