• The Journal of the Acoustical Society of Korea
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• v.28 no.3E
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• pp.109-117
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• 2009

Identity recognition in real environment with a reliable mode is a key issue in human computer interaction (HCI). In this paper, we present a robust person identification system considering score-based optimal reliability measure of audio-visual modalities. We propose an extension of the modified reliability function by introducing optimizing parameters for both of audio and visual modalities. For degradation of visual signals, we have applied JPEG compression to test images. In addition, for creating mismatch in between enrollment and test session, acoustic Babble noises and artificial illumination have been added to test audio and visual signals, respectively. Local PCA has been used on both modalities to reduce the dimension of feature vector. We have applied a swarm intelligence algorithm, i.e., particle swarm optimization for optimizing the modified convection function's optimizing parameters. The overall person identification experiments are performed using VidTimit DB. Experimental results show that our proposed optimal reliability measures have effectively enhanced the identification accuracy of 7.73% and 8.18% at different illumination direction to visual signal and consequent Babble noises to audio signal, respectively, in comparison with the best classifier system in the fusion system and maintained the modality reliability statistics in terms of its performance; it thus verified the consistency of the proposed extension.

• The Journal of the Acoustical Society of Korea
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• v.36 no.2
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• pp.100-107
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• 2017

The focused MVDR (Minimum Variance Distortionless Response) can be applied for source localization in near field. However, if the number of sensors are increased, it requires a large amount of calculation to obtain the inverse of the covariance matrix. In this paper we propose a focused MVDR method using that beam space is formed from output of far field beamformer at the subarray. The performances of the proposed method was evaluated by simulation. As a result of simulation, the proposed method has the higher spatial resolution performance then the conventional delay-and-sum beamformer.

• Journal of Magnetics
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• v.21 no.3
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• pp.387-392
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• 2016

Lower flux leakage designs have become important in the development of microspeakers used in thin and miniaturized mobile phones. We propose four methods to reduce the flux leakage of the magnetic circuit in a microspeaker. Optimization was performed based on the proposed approach by using the response surface method. Electromagnetic analyses were conducted using the finite element method. Experimental results are in good agreement with the simulated results obtained in one degree-of-freedom analysis from 100 to 5 kHz. Both the simulated and experimental results confirm that one of the proposed methods is much more effective in reducing flux leakage than the other methods. In the optimized method, compared with a default approach, the average radial flux density in the air gap decreased only by 5.5%, the maximum flux leakage was reduced by 28.6%, and the acoustic performance at primary resonance decreased by 0.45 dB, which gap is indiscernible to the human ear.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.312-322
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• 1999

A ultrasonic transduce with a single acoustic matching layer has been designed as an attempt to increase the bandwidth of underwater transducer. The wideband resonance condition was accomplished by attaching a single matching layer on the front face of a ceramic resonator composed of a piezoelectric bar, a taper part and a head part. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedance and thickness of the matching layer in the water tank.The obtained results are summarized as follows:1. Measured resonant and antiresonant frequencies of the piezoelectric transducer with no matching layer in air were 24.7 kHz and 25.6 kHz, respectively. 2. Two resonant frequencies of the piezoelectric transducer with a single matching layer were 21.7 kHx and 26.9 kHz, respectively, in air and 21.4 kHz and 22.7 kHz, respectively, with a water load.3. Two distinct resonance peaks in the transmitting voltage response(TVR) of the developed transducer were observed at 22.0 kHz and 25.8 kHz, respectively, with center frequency of 24.0 kHz. The values of TVR at these frequencies were 130.1 dB re $1 \muPa$/V at 22.0 kHz and 128.5 dB re $1 \muPa$/V at 25.8 kHz, respectively.Reasonable agreement between the experimental results and the numerical values was achieved.

• Phonetics and Speech Sciences
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• v.8 no.4
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• pp.103-113
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• 2016

This paper aims to propose articulatory features as novel predictors for automatic pronunciation assessment of English produced by Korean learners. Based on the distinctive feature theory, where phonemes are represented as a set of articulatory/phonetic properties, we propose articulatory Goodness-Of-Pronunciation(aGOP) features in terms of the corresponding articulatory attributes, such as nasal, sonorant, anterior, etc. An English speech corpus spoken by Korean learners is used in the assessment modeling. In our system, learners' speech is forced aligned and recognized by using the acoustic and pronunciation models derived from the WSJ corpus (native North American speech) and the CMU pronouncing dictionary, respectively. In order to compute aGOP features, articulatory models are trained for the corresponding articulatory attributes. In addition to the proposed features, various features which are divided into four categories such as RATE, SEGMENT, SILENCE, and GOP are applied as a baseline. In order to enhance the assessment modeling performance and investigate the weights of the salient features, relevant features are extracted by using Best Subset Selection(BSS). The results show that the proposed model using aGOP features outperform the baseline. In addition, analysis of relevant features extracted by BSS reveals that the selected aGOP features represent the salient variations of Korean learners of English. The results are expected to be effective for automatic pronunciation error detection, as well.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.821-825
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• 2005

Tilt rotor aircraft was developed for satisfying VSTOL (vertical short take off and landing) capability and cruise performance. However the noise generated by tilt rotor system causes one of the most serious problems. In this paper, noise characteristics of tilt rotor system in hovering flight are predicted by using free wake method and Lowson's formula. The flow field of the tilt rotor is simulated by using time marching free wake method, and the free field acoustic pressure is calculated through Lowson's formula. The predicted results are compared with experimental data at various observing positions. In the near field, they show good agreement with experimental data regardless of rotating speed and collective pitch angles of 6, 8 and 10 degree, although there are some discrepancies between prediction and experiment in the far field and at the rotating axis in the near field. It seems that the reason of these discrepancies is difference of unsteady force fluctuation between experiment and calculation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.488-492
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• 2007

Since Equipment-Noises occurring in machine room penetrate wall-body and travel to the adjacent room in the form of air-borne sound and structure-borne sound, it is appearing as the main factor that injures a peaceful residential environment, and due to this, such noise-damage is currently increasing rapidly. Consequently, despite the measures for sound-insulation and soundproof against the equipment-noise penetrated wall-body is urgently required, but as the subjective evaluation considered for psychological response about the equipment-noise was not practiced, many dissatisfactions are still raising even after some measure was taken. On such point of view, this Research, at the spot, has actually measured the equipment-noise that had permeated various wall-bodies, and examined its physical characteristics, thence based upon this, has conducted Psycho-Acoustics Experiment and investigated the interrelation between the physical evaluation value and psychological reaction value. It is considered that such study result could be utilized as the useful material at the time of establishment of the Grading Standard for the insulation performance against the Architectural Plumbing Noise, in the future.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1366-1370
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• 2007

Predicting the noise radiated from vibrating structures is important in the automotive, aerospace, construction equipment, and defense industries. In this paper, a numerical implementation of the boundary element method in solving the Helmholtz integral equation for radiated noise prediction is presented. To predict the noise emitted by vibrating structure, the developed code can use the results from a structure analysis performed by a multi-purpose structural finite element code like ANSYS and directly measured data by non-contact vibration sensor like Laser Doppler Vibrometer. To verify the accuracy of developed code, two kinds of verification are perfomed. Firstly, the computer code used the harmonic analysis results of ANSYS in simple model and try to match with SYSNOISE. After matching with simulation results, the code compared with the result from SYSNOISE which used the velocity data from the LDV measurement with different number of points. The performance of the developed code for vibro-acoustic noise prediction is presented using the experimental results of the non-contact sensor

• Journal of Welding and Joining
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• v.33 no.4
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• pp.7-16
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• 2015

New lasers such as high power, high brightness and short wavelength laser are using diverse industry. Also new technologies are developing actively to solve various issues such as spattering, process monitoring, deep penetration and key-hole stability. ICALEO is the international congress where recent technology for laser material processing and laser system are present. At 2014, it was held at San Diego in USA and more than 260 papers were presented from 28 country. The effect of the laser beam shape such as Gaussian like and top-hat was investigated on acoustic emission signal and pore formation in welding. Inline penetration depth was measured with ICI(Inline Coherent Imaging) technique and the data was verified with real time X-ray image on laser welding. The laser welding performance at low pressure environment was evaluated for the thick plate alloy steel. UV laser was used to weld various metals such as Cu, Aluminum, steel and stainless steel. The effect of the wavelength of the laser on the formation of the wave at the wall of the key-hole front and the absorptivity was investigated.

• The Journal of the Acoustical Society of Korea
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• v.6 no.3
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• pp.17-22
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• 1987

This study is to propose more reliable test method in evaluating the sound insulation performance of building element in fields. This method involves the measurements of the incident acoustic intensity and transmitted surface intensity. The incident intensity is determined from measurements of the space averaged sound pressure level in source room. The transmitted surface intensity is measured directly using one microphone and one accelerometer. The results of experiments indicate that this new method makes it possible to give more reliable data than the conventional field test method. The values of trans-mission loss measured by this new method are compared favorably with those obtained using the sound intensity method and theoretical calculation(mass law).