• 전자공학회논문지 IE
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• v.48 no.3
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• pp.10-15
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• 2011

In the case of designing an acoustic transducer for high power application, we usually aim to transfer the source electric energy to the output acoustic energy as large as possible. For this purpose, we should match the impedance of the power amplifier to the impedance combined with the acoustic transducer impedance and the radiation impedance. Especially if we have electrical source with almost zero impedance, we need improve the power factor of the acoustic transducer in the load. In this paper, we propose a broad band impedance matching method by the improvement of power factor, which applies ABCD matrix.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1372-1375
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• 2006

The simplified impedance model which can consider a combined flow condition was suggested. Although the strength and position of the shear layer cannot be obtained by a linear sum of two separate contributions when both flows occur together, it was simply assumed that the impedance under the combined flow follows from summing the separate flow impedance. To validate the simplified impedance model, acoustic properties of a concentric resonator was predicted and measured. The predicted transmission loss using the simplified model shows reasonable agreements with measurements. One can find that the simplified impedance model obtained by the superposition of the separate flow impedances can be adjusted to predict the acoustic properties of a concentric resonator.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.969-974
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• 2007

In this paper, a beamforming technique is introduced to measure the acoustic impedance at both normal and oblique incidence in a free field. The acoustic impedance is obtained by separating incident and reflected signals using the adaptive nulling method which is one of the various beamforming algorithms. To obtain better results, pressure vector commonly used in array signal processing is replaced with the transfer function vector between each microphone and the white Gaussian noise is suppressed by a wavelet shrinkage technique. The experiments conducted in a semi-anechoic room show that the proposed method is efficient and accurate in measuring the acoustic impedance of sound absorbing materials under a free field condition.

• The Journal of the Acoustical Society of Korea
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• v.25 no.1
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• pp.1-6
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• 2006

The Possibility of using acoustic impedance as an input Parameter for computation of underwater acoustic field in shallow waters was investigated. Analysis of the acoustic reflection from the ocean bottom with shear wave effect showed that acoustic impedances below the critical grazing angle have nearly angle-independent property and could be approximated with a single value of near-grazing impedance $Z_0$. Computations of the Propagation loss based on the concept of 'effective depth' indicate that near-grazing bottom acoustic impedances could be used as an input parameter for simulation of the acoustic fields in shallow waters.

• Journal of the Korean Wood Science and Technology
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• v.17 no.2
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• pp.26-33
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• 1989

The acoustic absorption coefficient and acoustic impedance of 5 species of softwood(sonamoo, sam namoo, gusang namoo, hwaback, sitka spruce) and 5 species of hardwood (Mulgusul namoo, Italian popular, white meranti, red meranti, kalantas) were measured by the standing wave method. which is simple in the setup and gives more accurate result than does any other measuring method. The dependence of the absorption coefficient and complex acoustic impedance on the wood sections. thickness of the sample itself and the back air gap was investigated experimentally in the frequency range from 200Hz to 1800Hz, and the result are as follows: 1. The acoustic absorption coefficient of wood sections was higher on the cross section than radial and tangential sections. 2) The acoustic absorption coefficient were higher in the frequency range from 400Hz to 600Hz, but decreased in the frequency above 600Hz. 3. The genenal tendency of the variation of the normal acoustic impedance was increased according to the frequency. 4. The acoustic absortion coefficient was increased in the to 7mm-thick sample and decreased in 9mm-thick sample. 5. The higher acoustic absorption coefficient was shown in the case with the backing an gap than in the case without the gap.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.352-353
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• 2005

In this paper, an ultrasonic level limit sensor with a new structure utilizing the acoustic impedance matching is proposed to be able to check it out a change of water-level. 2 PZT resonators with the same property are bonded directly on the polyethylene plate. One is for transmitter as an ultrasonic transducer, the other one is for receiver. In this case, a polyethylene plate will operate as an acoustic guider to transmit a transverse wave between 2 PZT resonators in air. While in the water, a polyethylene plate having a similar acoustic impedance with the water will be emitted an acoustic energy into the water as a longitudinal wave. According to this mechanism, there was a wide difference of acoustic signal output between underwater and in air. As a summary, it is believed that this proposed level limit sensor could be used as a new one with strong toughness from the external electrical and mechanical noise.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.16-23
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• 2012

3-D linear acoustic analysis has been performed to elucidate damping characteristics of large Helmholtz acoustic cavities in FASTRAC combustor. Acoustic impedance concept has been introduced to quantify combustion stabilization capacity. For a given acoustic cavity, sonic velocity in cavity to achieve an optimal tuning has been determined and satisfactory agreement with the previous results has been obtained. Feasible estimation of sonic velocity in acoustic cavity has been devised. Results show similar trends without significant deviations, which can be used in the procedure of design and verification of acoustic cavity. From the satisfactory results, investigation of other combustors with acoustic cavities which have shown combustion instabilities will be done as future works.

• The Journal of the Acoustical Society of Korea
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• v.28 no.2E
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• pp.51-59
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• 2009

Mutual radiation impedance becomes more important in the design and analysis of acoustic transducers for higher power, better beam pattern, and wider bandwidth at low frequency sonar systems. This review paper focused on literature survey about the researches of mutual radiation impedance in the acoustic transducer arrays over 60 years. The papers of mutual radiation impedance were summarized in terms of transducer array structures on various baffle geometries such as planar, cylindrical, spherical, conformal, spheroidal, and elliptic cylindrical arrays. Then the computation schemes of solving conventional quadruple integral in the definition of mutual radiation impedance were surveyed including spatial convolution method, which reduces the quadruple integral to a double integral for efficient computation.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3
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• pp.101-106
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• 2006

In this study, the impedance behavior of micro-speaker had been investigated as a function of hole area existing on the grille. In order to theoretically study the change of acoustical property due to the different total hole area, the holes were treated as a short open pipe system, such as an orifice. This theoretical result was in an excellent agreement with the experimental one. In detail, the acoustic impedance to be caused by the hole could be greatly increased with the decrease of hole area. Therefore, it can be concluded that the acoustic property of micro-speaker could be greatly changed by increasing the acoustic impedance of hole with reducing hole area.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1977.06a
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• pp.4.2-4
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• 1977

There are varying opinions about theories that the middle ear of Neonates is filled with mucous or other Material that interference with normal mobility of the middle ear system. DeDMon reported on the acoustic reflex as a tool for Neonatal screening, and Keith investigated the Middle ear function of Neonates during first few hours of life with an Electroacoustic impedance bridge. There are no reports on Neonstes in Impedance Audiometry in Korea. We tested 100 Neonates less than 24 hours old and this paper is dealt with its study related with tympanogram, static compliance and acoustic reflex.