• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.5
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• pp.243-247
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• 2009

For obtaining high speed data rate, underwater acoustic communication has several problems by the different environmental problem compared to wireless communication. To overcome this problem, the research is going steadily. In this paper, the property of underwater acoustic channel is considered, and the explanation of recently various method of transmitting and receiving and the domestic and foreign trend of underwater acoustic communication are taken into account.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.368-371
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• 2008

Cellulose based Electroactive Paper (EAPap) has been developed as a new smart material due to its advantages of piezoelectricity, large displacement, low power consumption, low cost and flexibility. EAPap can be used fur a surface acoustic wave (SAW) device using the piezoelectric property of EAPap, resulting in the cost effective and flexible SAW device. In this paper, inter digit transducer (IDT) structure using lift-off technique with a finger gap of $10{\mu}m$ was used for micro fabrication of the cellulose EAPap SAW devices. The performance of IDT patterned SAW device was characterized by a Network Analyzer. The feasibility of cellulose EAPap as a potential acoustic device was presented and explained.

• 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.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.279-286
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• 2013

Brillouin spectroscopy has been widely used for the investigation of acoustic properties of condensed matters in the hypersonic region. A high-pressure Brillouin spectrometer was set up by combining a diamond anvil cell and a tandem multi-pass Fabry-Perot interferometer. It was successfully applied to liquid ethanol, and the pressure dependence of the sound velocity, the refractive index and other acoustic properties were derived based on the measurements. The detailed optical setup and experimental procedure are described.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1128-1133
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• 2008

Cellulose based electroactive paper(EAPap) has been developed as a new smart material due to its advantages of piezoelectricity, large displacement, low power consumption, low cost and flexibility. EAPap can be used for a surface acoustic wave (SAW) device using the piezoelectric property of EAPap, resulting in the cost effective and flexible SAW device. In this paper, inter digit transducer(IDT) structure using lift-off technique with a finger gap of 10mm was used for micro fabrication of the cellulose EAPap SAW devices. The performance of IDT patterned SAW device was characterized by a Network Analyzer. The feasibility of cellulose EAPap as a potential acoustic device was presented and explained.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.870-873
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• 2003

This research is about the sound attenuation in the duct with lining sound absorbing material in it. Many previous researches assumed the property of lining material as locally-reacting. As the thickness of lining material thickens or the upper limit of the interested frequency range goes higher, there is a growing tendency for the experiment results to deviate from the theoretical results based on the locally reacting assumption. In this paper, the acoustic performance of the two-dimensional dissipative silencer with the propagation of sound in the absorbent was derived theoretically and calculated. The effect of increase of sound absorbing material is also considered. These results are compared from the previous results with using the locally-reacting property of sound absorbing material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.242-243
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• 2005

SAW filters were fabricated on $LiNbO_3$ substrates to evaluate frequency response and properties of photolithography. In the both of etch and lift-off methods, lift off method was superior to etch method in fabrication process. Frequency response property was measured by network analyzer. From a measurement of acoustic property, SAW propagation velocity was 3574.9m/sec for $LiNbO_3$ SAW filter.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.92-99
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• 2000

In this paper, theoretical acoustic sensitivity was derived to describe acousto-optic transduction property of the mandrel type fiber optic acoustic sensor with respect to external acoustic field. The acoustic sensitivity was analyzed in relation to both material properties and geometrical influence factors of the constitutional parts of the sensor, analytically. Validity of the theoretical results were verified through comparison with the finite element analysis results. The variation trends of the sensitivity of the sensor in relation to the studied parameters showed good agreement for the two analysis methods. According to the results, it is considered more economical to design the basic structure of the sensor with the analytic equations developed in this paper, and then to carry out further detailed analysis with the finite element method for specific points of design interest.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.1870-1872
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• 2005

In this study, 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 resonator 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, this proposed level limit sensor could be used as a strong candidate with low cost and more stable one.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.7-10
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• 2000

This paper focuses on the development of speech enhancement techniques for hands-free audio terminals, including two major problems : noise cancellation and acoustic echo cancellation. The objective is to find a joint structure to get a near-end speech signal with minimum distortion and low levels of echo and noise. To solve the two problems, a new promising technique is studied and tested in computer simulation conditions.