• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.525-528
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• 2002

The speed of sound, transmission coefficient, and attenuation are measured around the center frequency 1 and 2 MHz in solid materials such as bone, sediment, rubber, and Lucite materials. Common and different characteristics of such materials in the sound speed, transmission coefficient, and attenuation are discussed. Ambiguities in estimating such acoustic characteristics we also addressed. Ultrasonic properties of the first and second kind waves are clarified for different materials. Discussions are concentrated on classes of sound speed, broadband ultrasonic attenuation (BUA), and correlations of sound speed and BUA with apparent density. New correlations of inverse sound speed square and BUA with apparent density are suggested.

• The Journal of the Acoustical Society of Korea
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• v.24 no.4E
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• pp.132-138
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• 2005

The purpose of this study is to measure the acoustic properties of Tofu and Acorn Curd (Dotori Muk), which are possibly used as tissue mimicking materials (TMMs). Due to its availability and low cost, Tofu was suggested as a TMM by several researchers who measured only sound speed and attenuation. The acoustic properties of Tofu and Muk including the backscattering coefficient were measured in this paper. Sound speed was measured by the time shift in a pulse echo setup. Attenuation coefficients and backscattering coefficients were measured by a broadband method using both 5 MHz and 10 MHz transducers in the frequency domain. The measured acoustic properties of both Tofu and Muk are observed to be similar to those of biological tissues such as beef liver or beef heart.

• The Journal of the Acoustical Society of Korea
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• v.34 no.4
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• pp.257-263
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• 2015

Acoustic identification of inner materials in a single-layer cylindrical shell is investigated with acoustic resonance theory. The theoretical resonance peak frequencies for a cylindrical shell are little affected by the density variation, but remarkably changed by the sound speed variation of inner materials. Such acoustic dependency can be utilized to identify inner materials in a cylindrical shell. Acoustic resonance spectrogram for a single-layer cylindrical shell is theoretically plotted as functions of normalized frequency and sound speed of inner materials. The inner materials can be acoustically identified by overlapping acoustic resonance peaks from measured backscattering sound field on the spectrogram. To experimentally confirm this method, backscattering sound field of cylindrical shell filled with water, oil or ethylene glycol was measured in water tank. The inner materials could be identified by acoustic resonance peaks of the backscattering sound field monostatically measured with a transduce of 1.05 MHz center frequency.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.214-221
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• 2019

In this paper, a temperature dependent acoustic receiving characteristics of underwater acoustic sensor is studied by theoretical and experimental investigations. Two different types (low mid frequency sensor and high frequency sensor) of underwater acoustic sensors are designed with different configuration of baffle and conditioning plate. The temperature dependent characteristics of the acoustic sensors are investigated within the temperature range from $-2^{\circ}C$ to $35^{\circ}C$. The material properties of the piezoelectric ceramics, molding and baffle, which are the primary materials of the acoustic sensors, are measured with temperature change. The temperature dependent RVS (Receiving Voltage Sensitivity) characteristics of the acoustic sensors are simulated by using the measured material properties. The RVS changes of the acoustic sensors are measured by changing temperature in the watertank where the acoustic sensors are installed. The measured and the simulated data show that the temperature dependent characteristics of the acoustic sensors are mainly dependent for the sound speed changes of the molding material.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.1
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• pp.1-6
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• 2009

Propagation of electromagnetic wave in the water or underground is very difficult because of the conductivity of the propagation materials. In this case, we usually use acoustic signal as ultrasonic but, it is not easy to transfer long distance with coherent method because of time varying multipath, doppler effect, and attenuations. So, we use noncoherent method as FSK to communicate between long distances. But, as the propagation speed of acoustic sound is very slow, the BW of the channel is narrow. It is very hard to guaranty the enough speed of communication like digital image data. In this paper, we proposed a new data communication protocol which can transmit multi-bit digital data with every single ping, and improve the data communication speed in the water.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.31-37
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• 2021

In this paper, we design an acoustic meta-material silencer that operates at low frequency to reduce noise in duct. A high refractive index meta-material silencer is demonstrated with a combination of zigzag structured thin waveguide and helmholtz resonator, which reduces the speed of sound. Finite Element Method (FEM) analysis via thermo-viscous acoustic mesh is performed in order to calculate thermo-viscous dissipation in sub-wavelength waveguide. Sound power reflection, transmission and absorption coefficients are obtained utilizing 4-Microphone Method. The results show that cut-off frequency and transmission loss can be controlled through adjusting intervals of the zigzag structures. A wide-band acoustic silencer is also suggested by connecting meta-materials in series or parallel.

• Journal of radiological science and technology
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• v.33 no.3
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• pp.245-252
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• 2010

This study analyzed speed of sound, impedance, attenuation coefficient in accordance with acoustic characteristic standard of body soft tissue corresponding with Annex DD of IEC standard 60601-2-37(2007) which is about tissue mimicking materials (TMM) synthesized by polyurethane as a main material and new type of n-type scatter materials. This study reached the following conclusion after analyzing and evaluating image characteristic with SONOACE 9900 c PRIME (MEDESON Co.) and brightness, maximum penetration with convex probe (2.5~5.0 MHz). When n-type scatter materials are increasingly synthesised 0~8% with prepolymer as a main material and polyol mixture as a catalyst, 1. The more scatter materials are increased, the more sound speed of TMM becomes closely similar to soft tissue. 2. The more scatter materials are decreased, the more acoustic impedance becomes closely similar to soft tissue. 3. The more scatter materials are increased, the more attenuation coefficient is increased. 4. The more scatter materials are increased, the more average brightness of images is increased, but there is threshold. 5. The maximum penetration becomes closely similar to soft tissue at the 6% TMM as a scatter material.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.23 no.1
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• pp.33-42
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• 2012

Background and Objectives : Dysarthria refers to speech disorder that causes difficulties in speech communication due to paralysis, muscle weakening, and incoordination of speech muscle mechanism caused by damaged central or peripheral nerve system. Pitch, strength and speed are influenced by dysarthria during detonation due to difficulties in muscle control. As evaluation items, alternate motion rate and diadochokinesis have been commonly used, and articulation is also an important evaluation items. The purpose of this study is to find acoustic characteristics on sound production of dysarthria patients. Materials and Methods : Research subjects have been selected as 20 dysarthria patients and 20 subjects for control group, and voice sample was composed of bilabial, alveolar sound, and velar sound in diadochokinetic rate, while consonant articulation test was composed of bilabial plosive, alveolar plosive, velar plosive. Analysis items were composed of 1) speaking rate, energy, articulation time of diadochokinesis, 2) voice onset time (VOT), total duration (TD), vowel duration (VD), hold of plosives. Results and Conclusions : The number of diadochokinetic rate of dysarthria was smaller than control group. Both control group and dysarthria group was highly presented in the order of /t/>/p/>/k/. Minimum energy range per cycle during diadochokinetic rate of dysarthria group was smaller than control group, and presented statistical significance in /p/, /k/, /ptk/. Maximum energy range was larger than control group, and presented statistical significance in /t/, /ptk/. Articulation time, gap, total articulation time during diadochokinetic rate of dysarthria group was longer than control group and presented statistical significance. The articulation time was presented in both control group and dysarthria group in the order of /k/>/t/>/p/, while Gap was presented in the order of /p/>/t/>/k/ for control group and /p/>/k/>/t/ for dysarthria group. VOT, TD, VD regarding plosives of dysarthria group were longer than control group. Hold showed large deviation compared to control group that had appeared due to declined larynx and articulation organ motility.