• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.841-847
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• 2009

This paper describes the propagation characteristics of acoustic signals as a function of distance from the location of partial discharge(PD) occurrence to analyze correlation between discharge magnitude and acoustic signal in insulation oil. To measure small acoustic signals produced by PD, we fabricated an amplifier and simulated PD at a needle-plane electrode system set in insulation oil. The amplifier has the gain of 40 dB and the frequency bandwidth of 1.6 kHz$\sim$1.6 MHz. These are enough characteristics for the measurement of acoustic signals. After a comparative calibration experiment by a standard pulse generator and a coupling capacitor, we analyzed the propagation characteristics of acoustic signals in insulation oil.

• 센서학회지
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• 제28권5호
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• pp.318-322
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• 2019

In shooting training, an impact point identification system that uses the impact wave of the bullet to check the impact point in the target plate has been recently used. Acoustic sensors used in these systems must be able to detect shock waves of high sound pressure levels and be both waterproof and dustproof for rainy weather and dusty environments, respectively. In this study, membranes with excellent waterproof, dustproof, and sound transmitting characteristics were selected through a characteristics test; a protection cap was installed to install the selected materials. After coupling the produced protection cap to the acoustic sensor housing, the sensitivity and phase characteristics of the acoustic sensor were checked. Through the waterproof and dustproof test, the performances of its sensitivity and phase characteristics were confirmed. Finally, the normal shockwave of a 5.56 mm diameter bullet was measured using a shockwave detection signal collecting plate equipped with a prototype of the acoustic sensor at a 100 m firing range.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.145-152
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• 2004

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.413-416
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• 2000

In this study, the physical properties of the acoustic element and case with metal-piezoelectric ceramics were analyzed. The dielectric and piezoelectric properties of 0.5 wt% 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 vibration characteristics for the laminated circular plate was analyzed for the various thickness and diameter of the piezoceramic layer and metal layer. Also, the acoustic characteristics for the geometrical form of case have been investigated. The design and fabrication method worked in this paper can be utilized in development of actuator and acoustic device.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.703-706
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• 2000

The acoustic characteristics radiated from the acoustic transducer with metal-piezoceramic laminated circular plate were simulated. The Vibrational modes of metal-piezoceramic laminated circular plates were calculated by using the finite element method. After meshing the inside closed boundary of the acoustic transducer, the pressure gradients and the isotaric lines were calculated for the various frequencies. It has been observed that the characteristics of the sound pressure calculated for the various frequencies. Also, the directivity patterns and the sound pressure radiated from the acoustic transducer were calculated by 2-dimensional analysis.

• 대한기계학회논문집B
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• 제28권8호
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• pp.945-952
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• 2004

Acoustic characteristics of combustion chamber having various baffle configurations are numerically investigated by linear acoustic analysis to suggest reliable baffle specifications in first stage of KSLV-I. To determine the configuration of baffles, an acoustic modal analysis as well as the macroscopic analysis has been done. Hub has another effect of suppressing transverse acoustic mode by confining flow in baffled compartment over general effect of increase in acoustic damping of radial acoustic modes. So, a sufficient number of hub needs to be installed to obtain acoustic damping capacity. 3-blade configuration designed to suppress the first tangential mode has relatively low damping capacity, compared to 5 or 6-blade one. Optimum value of axial baffle length has been determined by comparing acoustic characteristics of combustion chamber having various baffle lengths.

• 말소리와 음성과학
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• 제5권4호
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• pp.25-32
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• 2013

This research is aimed at finding the acoustic characteristics of different voice rehabilitation techniques, the electrolaryx (EL), standard esophageal (SE), and tracheoesophageal (TE), used on 17 patients with laryngectomees. The analysis of the voice qualities was achieved using MDVP. In order to compare the acoustic characteristics, patients were asked to produce the vowel /a/ sound. The acoustic analysis included fundamental frequency (f0), jitter, shimmer, and noise-to-harmonic ratio (NHR). The main acoustic results showed no significant statistical differences between the average measurements of SE and TE speakers. It was found that the current study showed the same tendency found in previous studies. There was also a significant difference between SE and EL speakers. On the other hand, there were no significant statistical differences between the average measurements of TE and EL speakers on all acoustic measurements. This research will contribute to establishing a baseline related to speech characteristics in voice rehabilitation for patients with laryngectomees. In future, the present findings and issues should be considered in the context of gender. Specifically, the number of women who are diagnosed with laryngeal cancer continues to rise and their acoustic characteristics may indeed differ from those of men.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1742-1756
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• 1997

The acoustic characteristics of a direct radiator type loudspeaker has been studied in this paper. The natural modes of the speaker cone vibration analyzed numerically by the finite element method have been verified by comparing them with experimental results. The so-ap-proved finite-element model has been used to calculate the vibration response of the cone excited by the voice coil. The vibration displacement of the speaker cone paper has been converted into the vibration velocity and used as a boundary condition for the acoustic analysis. The frequency characteristics, directivity, and sound pressure distribution of the loudspeaker have been calculated by the boundary element method. The numerical results have been verified by the experiments carried out in an anechoic chamber. The variations of the acoustic characteristics due to the changes of some design parameter values can be examined using the numerical model.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.457-462
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• 2007

This paper reports on the research which investigates acoustic signals acquired in turning with rough and finish simultaneously. The material is aluminum thin pipe. Two acoustic sensors were set on CNC machine. One was set on the finish bite and the other the rough. Two signals were first analyzed in order to consider how much the acoustic signal from the finish bite was coupled by that from the rough. A simple data collecting system to acquire signals from the finish was then determined because two acoustic signals were little coupled. Second the fundamental experiments were accomplished to study the effects of machine vibration and material state. The signal characteristics due to surface defects were studied from the collected acoustic signal data. The signal analysis was based on real time data, root mean squared average and frequency spectrum by fast fourier transform. As a result, the acoustic signals were made effects by machine condition, material structure. The acoustic signal from the finish bite was closely correlated with surface quality. Two types surface micro defects were then evaluated by the signal characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.763-766
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• 2004

Recently, various acoustic artifacts that contains speaker have been produced such as cellular phone. Speaker consists of diaphragm generating sound and coil vibrating diaphragm. Generally, good speaker means that it has a wide frequency range, high output power rate to input power and flat sound pressure level in specified frequency range. Acoustic characteristic was estimated through the experiment and computer simulation, or sound power was controlled with acoustic sensitivity in a natural frequency range fer last decade. However, the flatness of sound pressure level has not been considered to enhance the sound quality of a speaker. Tn this study, a method for speaker design is proposed for a good acoustic characteristic, which is flatness of SPL(sound pressure level) and wideness between the first and second natural frequency. SYSNOISE is used fer acoustic analysis and ANSYS is used for harmonic response analysis and modal analysis. Optimization for acoustic characteristics of a speaker diaphragm is performed using ModelCenter. All analyses are done within a frequency domain. And we confirm that the experimental and computational simulations have similar trend.