• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3383-3388
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• 2007

To compare the sensor performance of AE leak diagnosis system which can measure valve leak conditions, AE activities such as RMS voltage level, AE signal trend, leak rate degree according to AE database, FFT spectrum were measured on valve of the simulated test system for power plant. AE activities were recorded and analyzed from various operating conditions including different temperature, pressure difference, valve size and fluid using both piezoelectric acoustic emission sensor and Pb-Free acoustic emission sensor. The results of this study are utilized to select the type of sensors, the frequency band for filtering and thereby to improve the signal-to-noise ratio for diagnosis or monitoring of valves in operation. As the final result of application study above, portable type leak diagnosis system by AE was developed. The outcome of the study can be definitely applied as a means of the diagnosis or monitoring system for energy saving and prevention of accident for power plant valve.

• Phonetics and Speech Sciences
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• v.3 no.4
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• pp.109-115
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• 2011

The purposes of this study were to identify acoustic parameters of connected speech and to contribute to acoustic analysis of dysphonic voice about patient's natural speech voice as well as sustained phonation of vowels. Acoustic parameters of sentences included LTAS (long-term average spectrum) mean and spectral slope over frequence ranges such as 0-4kHz, 0-6kHz, 0-8kHz, 0-12.5kHz as well as HNR. Acoustic parameters of the vowel 'a' included jitter, RAP, shimmer, NHR, and HNR. Based on 'G' of GRBAS for the severity of dysphonia, two experienced raters judged and classified as four groups including controls, mild, moderate and severe dysphonic group. Connected speech was two sentences extracted from 'stroll' passage. Parameters of the vowel and LTAS mean of the sentences were measured by CSL. The spectral slope of the sentences and HNR of the vowel and the sentences were measured by Praat. Data were statistically analyzed by Spearman correlation and Kruskal-Wallis test using SPSS 12.0. The results of this study are as follows: First, jitter, RAP, shimmer and NHR were significantly different between the groups. Second, for several frequencies, LTAS mean and spectral slope of the sentences were significantly different between the groups. Third, the HNR of the sentences were significantly different between the groups. Forth, there was a presence of correlation between HNR and NHR of the vowel and HNR of the sentences. Accordingly, this study concluded that LTAS, spectral slope, and HNR were predictive parameters of connected speech voice for dysphonic voice.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.413-421
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• 1990

Acoustic emission signals due to leak from circular holes of 0.4, 1, 2 and 4mm diameter and rectangular slits of different geometry having the same cross section as 4mm diameter hole was studied both analytically and experimentally. Acoustic emission signals from a wide-band type transducer were transformed to digital signals through a digital oscilloscope, and $V_{rms}$ and frequency spectrum were obtained by processing digital signals. Relationships between acoustic parameters and fluid mechanical parameters were derived analytically. A quadrapole aerodynamic model was applied in the analysis of leak from the circular holes and $V_{rms}$ was found to be proportional to the root square of leak rate through the circular hole. A modified model based on dipole source mechanism and laminar equivalent diameter was applied in the analysis of leak signals from the rectangular slits. In the case of constant pressure, $V_{rms}$ increased as the laminar equivalent diameter of slit decreased. In the case of constant laminar equivalent diameter, however the result was similar to that for leak from the circular hole. The frequency spectra of leak signals shows the same frequency characteristics irrespective of the pressure difference.rence.

• Journal of Biosystems Engineering
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• v.27 no.4
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• pp.293-300
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• 2002

Surface crack detection is an important aspect in the quality control process of egg markets. The acoustic vibration of an egg could be used as a critical factor in evaluating the eggshell quality. The mode shape indicates the egg vibration behavior at different locations with respect to the input impulse and provides important information for the optimum sensor location to obtain the desired acoustic measurements. Theoretical analysis and experimental measurements were conducted to determine the acoustic vibration modes in eggs. The resonant fiequencies of the first and second resonance mode of intact eggs were found to be distributed between 2kHz and 7kHz range. The measured mode shapes of an egg were similar to theoretical shapes of homogeneous, elastic spheres. An elliptical deformation at the equator ring of the egg was observed. The frequency peak of this mode was dominantly present in the frequency spectrum of an intact egg impacted at its sharp position. The mode shapes related to the first resonant frequency of an egg shelved that the optimum location for the measuring sensor was the 180 degrees position. A optimum location for the egg support was found to be the 90 degrees position having the smallest vibration magnitude.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.421-430
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• 2004

Clinically, it is almost impossible for a physician to distinguish subtle changes of frequency spectrum by using a stethoscope alone especially in the early stage of thrombus formation. Considering that reliability of mechanical valve is paramount because the failure might end up with patient death, early detection of valve thrombus using noninvasive technique is important. Thus the study was designed to provide a tool for early noninvasive detection of valve thrombus by observing shift of frequency spectrum of acoustic signals with computer aid diagnosis system. A thrombus model was constructed on commercialized mechanical valves using polyurethane or silicon. Polyurethane coating was made on the valve surface, and silicon coating on the sewing ring of the valve. To simulate pannus formation, which is fibrous tissue overgrowth obstructing the valve orifice, the degree of silicone coating on the sewing ring varied from 20％, 40％, 60％ of orifice obstruction. In experiment system, acoustic signals from the valve were measured using microphone and amplifier. The microphone was attached to a coupler to remove environmental noise. Acoustic signals were sampled by an AID converter, frequency spectrum was obtained by the algorithm of spectral analysis. To quantitatively distinguish the frequency peak of the normal valve from that of the thrombosed valves, analysis using a neural network was employed. A return map was applied to evaluate continuous monitoring of valve motion cycle. The in-vivo data also obtained from animals with mechanical valves in circulatory devices as well as patients with mechanical valve replacement for 1 year or longer before. Each spectrum wave showed a primary and secondary peak. The secondary peak showed changes according to the thrombus model. In the mock as well as the animal study, both spectral analysis and 3-layer neural network could differentiate the normal valves from thrombosed valves. In the human study, one of 10 patients showed shift of frequency spectrum, however the presence of valve thrombus was yet to be determined. Conclusively, acoustic signal measurement can be of suggestive as a noninvasive diagnostic tool in early detection of mechanical valve thrombosis.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.16-25
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• 1998

This paper attempts to examine the characteristics of underwater acoustic signals distorted in shallow water environments. Time signals are simulated using an acoustic model that employs the Fourier synthesis scheme. An acoustic experiment was conducted in the shallow sea near Pohang, Korea, where water depth is about 60m. The environment in the simulation is set up so that it approximates the experimental condition, which can be regarded as range-independent. The signal is LFM(linar frequency modulated) type centered on one of the four frequencies 200, 400, 600 and 800Hz, each being swept up or down with the bandwidth of 100Hz. To analyze the signal characteristics, the study introduces a spectrum estimation scheme, pseudo Wigner-Ville distribution (PWVD). The simulated and measured signals suffer great interference by the interaction of neighboring rays. Although there are constructive or destructive interference, the signals keep LFM characteristics well. This is thought that only a few dominant rays of small loss contribute to the receive signals in a shallow water environment.

• KSTLE International Journal
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• v.6 no.1
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• pp.17-20
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• 2005

The object of the present work is the natural lre%uency analysis of femto slider, HeaHdisk interaction during starustop and constant speed were detected by using the acoustic emission (AE) test system. The frequency spectrum analysis wasperformed using the AE signal obtained during the head/disk interaction. The FFT (Fast Fourier Transform) analysis of the AEsignals is used to understand the interaction between the AE signal and the state of contact. Natural frequency analysis wasperformed using the ANSYS program. The results indicate acceptable accordance of finite element calculation results with theexperimental results.

• Journal of Biosystems Engineering
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• v.24 no.3
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• pp.253-258
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• 1999

This study was conducted to develop an automatic egg inspection system for detecting creaked eggs based on acoustic impulse response. This system includes a sound generator, a sound sensor with signal conditioner, and a computer. The sound generator that hit the sharp of the dull edges of an egg was constructed with a ceramic ball pendulum attached to a rotary type solenoid. The signal conditioner included a pre-amplifier and a digital signal processing (DSP) board. The parameters for distinguishing cracked and normal eggs were the area, the geometric centroid and the resonance frequency of power spectrum of the acoustic signal generated. An algorithm for on-line detection of the continuous transferring eggs was developed. The performance tests resulted with 91% success rate to separate cracked and normal eggs at the rate of 1 second per an egg.

• Journal of Korea Multimedia Society
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• v.9 no.12
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• pp.1572-1579
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• 2006

An usual acoustic emission(AE) event has two widely characterized parameters in time domain, peak amplitude and event duration. But noise in AE measuring may disturb the signals with its parameters and aggrandize the signal incertitude. Experiment activity of detection of the nick inside of porcelain with AE was made and study on AE signal processing with statistic be presented in this paper in order to pick-up information expected from the signal with noise. Effort is concentrated on developing a novel arithmetic to improve extraction of the characteristic from stochastic signal and to enhance the voracity of detection. The main purpose discussed in this paper is to treat with signals on amplitudes with statistic mutuality and power density spectrum in frequency domain, and farther more to select samples for neural networks training by means of least-squares algorithm between real measuring signal and deterministic signals under laboratory condition. By seeking optimization with the algorithm, the parameters representing characteristic of the porcelain object are selected, while the stochastic interfere be weakened, then study for detection on neural networks is developed based on processing above.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.10
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• pp.530-535
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• 2001

Resonant-type electronic ballast for a metal halide discharge(MHD) lamp is proposed and implemented for 400W MHD lamp. HID lamps have good color rendition, long life and good focusing capability but they have flickers by acoustic resonance when driven at high frequency. A new control method is employed to remove acoustic resonance related instability in HID lamp. By using the amplitude modulation, a spread spectrum effect is employed on the ballast. The control loop of resonant inverter is analyzed and a current is designed. The ballast consists of a power factor controller, an half-bridge resonant inverter, a simple ignitor and an integrator with OP-amps. The experimental results show the good performance as PF 0.93, ballast loss 22W at output 400W and the conducted EMI level is below 60dBuV.