• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.690-695
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• 2005

We have investigated on the development of 2-2 mode piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the electrical properties and acoustic impedance of 2-2 mode piezocomposite which were fabricated using the dice-and-fill technique for the different volume fractions of PZT The volume shrinkage of polymer is an important factor in 2-2 mode piezocomposites fabrication. The thickness mode electromechanical coupling factor($\kappa_t$) of PZT was compared with that of piezocomposites. It was shown that the 2-2 mode piezocomposites were much better than the PZT only. The acoustic impedance of 2-2 mode piezocomposites decreased linearly when PZT volume fraction was decreased.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.10
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• pp.766-772
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• 2002

In this investigation, experimental attempts were made to observe and determine the variations in elastic and damping properties of the PVC depending on the amounts of MBS added to the mixture, PVC/MBS, and also on the thicknesses of the specimens. An acoustic resonance technique was used for the tests In this investigation. It serves as a method to characterize properties of materials set in vibrational motions, which is initiated by low level stresses generated by externally supplied acoustic energy. Substantial variations were observed in the test results with the addition of the MBS to the PVC. It was found that the magnitudes of elastic constants decrease while the damping capacity improve when MBS rubber was added in the range up to 9 phr.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.12-19
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• 2001

In this study, the physical properties of the piezoelectric sounder with metal-piezoelectric ceramics were analyzed. The dielectric and piezoeletric properties of 0.5wt% MnO$_2$ and NiO doped 0.1Pb(Mg$\_$1/3/Nb$\_$2/3/)O$_3$-0.45PbTiO$_3$-0.45PbZrO$_3$ ceramics were investigated aiming at acoustic transducer applications. The acoustic characteristics of a thin circular disc-type with metal-piezoceramics have been investigated. Also, the acoustic characteristics for the geometrical form of case were investigated. The piezoelectric sounder with 200kHz resonant frequency and 20kHz bandwidth was designed by considering the sharp directivity and the sound pressure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.294-297
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• 2000

본 연구에서는 압전형 음향변환기를 제작하기 위한 금속과 세라믹스로 적층된 원형의 압전음향소자와 음향변환기 케이스를 설계하였다. 먼저 음향소자인 복합원형평판의 진동운동 방정식을 세우고 그 진동모드를 알아보았다. 음향소자의 세라믹스는 두께 1 mm, 지름 10 mm의 PZT(IV)를 사용하였고, 금속판의 지름과 두께를 다양하게 변화시키면서 음향소자의 공진주파수를 계산하고, 각각의 금속판에 따른 감도지수의 변화를 계산하였다. 설계하고자 하는 음향소자의 공진주파수를 200 KHz로 청하고, 위의 계산을 통하여 음향변환소자에 가장 적합한 금속진동판을 찾아보았다. 음향변환기의 복합원형평판으로 이루어진 음향소자의 물리적 변화에 따른 공진주파수와 감도지수를 구하고 음향변환기 케이스의 공진주파수를 계산하여 압전형 음향변환기에 알맞은 금속진동판과 음향변환기 케이스를 알아보았다.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2004.11a
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• pp.367-371
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• 2004

The purpose of this research is furnishing of basic material for acoustic planning hereafter, after understanding the acoustic merits and demerits through measuring and analyzing on room acoustic of small performance hall. As the result of the measurement, those physical evaluation indexes such as SPL, RT, EDT, $D_{50}$, $C_{80}$, RASTI have being kept the satisfiable acoustic condition for the service of performance hall. Therefore, as small performance hall is regarded as equipped with sufficient volume of sound, reverberatory feeling and diffusive feeling, it judges as an excellent performance place, also it is considered that it could be utilized as a useful material when design so similar performance hall, hereafter.

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.658-662
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• 2003

In this study, we have tried to find the optimized design variables of the matching layer which is important part of thickness mode ultrasonic transducer and finally reach the conclusion that the electrical property of piezo-element must be under consideration when the optimized acoustic impedance is estimated. Proper expression of the effective impedance of front load at free resonant frequency(: $Z_{f}$ $^{(0)}$ /) has been induced by introducing the principle of binomial multilayer transformer and gradient based numerical method is utilized to find the most acceptable value of $Z_{ f}$/$^{(0)}$ . Optimized point of acoustic impedance can be calculated directly from $Z_{f}$ $^{(0)}$ using some simple formula which we propose. We also verify our result by both numerical and experimental method and get a good enhancement especially it concern to the bandwidth of ultrasonic transducer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.183-188
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• 2003

This study is to make the fundamentals of sound quality evaluation in regard of acoustical characteristics of passenger compartment. The deviation of frequency response function level within audible frequency is evaluated at receiving point in the research of room acoustics. In this study, frequency response function is the one between speaker and driver's ear positions. The positions of driver and audio speakers are optimized by analysis of acoustic mode of acoustic cavity. The main reflection planes are determined by analysis sound ray path diffused at optimized speaker positions. Finally, designer selects acoustical material by analysis of absorption effect of acoustical materials on the main reflection planes in order to avoid to distortion and fluctuation of frequency response function..

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.744-750
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• 2001

Higher directivity acoustic transducer using the self-demodulation effect was fabricated. The structure of transducer was designed such as dimension and support type of the piezoelectric element, the vibrating metal plate, and the housing case. Based on the design, the transducer was fabricated and measured its acoustic characteristics. Also, AM modulated driving circuit was designed for using the self-demodulation effect. The piezoelectric sounder with 200kHz resonant frequency and 20kHz bandwidth was designed by considering the sharp directivity and the sound pressure. The design and fabrication method worked in this study can be utilized in development of various speakers with higher directivity and broader bandwidth.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.245-248
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• 1997

The distilled water is used for the ultrasonic wave propagating material in the measurements of broadband ultrasonic attenuation (BUA) that is applied in industrial and medical applications, The acoustic impedance of water is significantly changed with its temperature. Therefore, the quantitative evaluation of BUA with temperature and the ultrasonic wave propagating distance is highly needed. In this study, we evaluated the variation of attenuation with change in temperature. To measure the variation of BUA in the low frequency region at the temperatures, 27$^{\circ}C$, 29$^{\circ}C$, and 31$^{\circ}C$, we tested the Plyethylene, Teflon, MC-Nylon, Urethane specimens and analyzed the center frequency, frequency bandwidth, spectral peak amplitude. The results showed that BUA value appeared to be lower with increasing temperature. This may be due to the fact that the frequency feature of ultrasonic wave is affected by not only the specific gravity, acoustic impedence, but material crystalline, porosity, the distance of ultrasonic wave propagation in water.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.403-408
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• 2000

An acoustic field in a 3 dimensional enclosure is caused from interference between sound sources and the complex reflections from wall. Therefore, changing an acoustic property of wall such as admittance means generating another acoustic field. The purpose of this paper is utilizing the characteristic to make a quiet zone. First, this paper shows that the control material is essentially on the same road as active noise control(ANC). That is, we can consider the control material as the control source of ANC. However we cannot control the reflection strength of it. Second, through a numerical simulation, this paper shows that the position of the control material is an important variable of the control.