• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1493-1510
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• 2000

Theoretical models that can be used to predict the range of main lobe widths and the probability distribution of the peak sidelobe levels of two-dimensionally sparse arrays are presented here. The arrays are considered to comprise microphones that are randomly positioned on a segmented grid of a given size. First, approximate expressions for the expected squared magnitude of the aperture smoothing function and the variance of the squared magnitude of the aperture smoothing function about this mean are formulated for the random arrays considered in the present study. By using the variance function, the mean value and the lower end of the range i.e., the first I percent of the mainlobe distribution can be predicted with reasonable accuracy. To predict the probability distribution of the peak sidelobe levels, distributions of levels are modeled by a Weibull distribution at each peak in the sidelobe region of the expected squared magnitude of the aperture smoothing function. The two parameters of the Weibull distribution are estimated from the means and variances of the levels at the corresponding locations. Next, the probability distribution of the peak sidelobe levels are assumed to be determined by a procedure in which the peak sidelobe level is determined as the maximum among a finite number of independent random sidelobe levels. It is found that the model obtained from the above approach predicts the probability density function of the peak sidelobe level distribution reasonably well for the various combinations of two different numbers of microphones and grid sizes tested in the present study. The application of these models to the design of random, sparse arrays having specified performance levels is also discussed.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.10
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• pp.6-14
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• 2011

This paper presents the design of the battery sensor IC for instrumentation of current, voltage using delta-sigma ADC. The proposed circuit consists of programmable gain instrumentation amplifier (PGIA) and second-order discrete-time delta-sigma modulator with 1-bit quantization were fabricated by a 0.25 ${\mu}m$ CMOS technology. Design circuit show that the modulator achieves 82 dB signal-to-noise ratio (SNR) over a 2 kHz signal bandwidth with an oversampling ratio (OSR) of 256 and differential nonlinearity (DNL) of ${\pm}$ 0.3 LSB, integral nonlinearity (INL) of ${\pm}$ 0.5 LSB. Power consumption is 4.5 mW.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.9
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• pp.694-702
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• 2003

A cooling mechanism using acoustic streaming by ultrasonic vibrations and associated convective heat transfer enhancement is investigated experimentally and analytically. Acoustic streaming pattern and associated heat transfer characteristics are presented. Analytical transient temperature profile of the heated plate following Nyborgs theory is accomplished along with experimental measurement. A temperature drop of 30 C is obtained in 4 minutes with vibration amplitude of 10${\mu}{\textrm}{m}$. As the vibration amplitude is further increased to 25${\mu}{\textrm}{m}$ a temperature drop of 40 C is achieved that is the maximum temperature drop obtained with the current experimental apparatus. Analytical heat transfer solutions verified a temperature drop of 4$0^{\circ}C$ with a vibration amplitude of 25${\mu}{\textrm}{m}$ at 28.4 kHz which is experimentally obtained.

• Journal of the Korean Institute of Gas
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• v.14 no.4
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• pp.56-62
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• 2010

The purpose of this paper analyzes and investigates the failure case studies of electronic control sensors for a LP gas engine. The malfunction of crank angle sensor, which controls a fuel injection volume of LP gas, displays an irregular and non-uniform pulse wave form. The pulse form, which is related to the noise of the crank angle sensor, displays at the rectangular peak with a saw-toothed shape and is intermittently generated with a level of 2.46V noise signal. The malfunction of No. 1 TDC sensor in which is caused from the internal disorder affects to the reduction of engine power and engine stop suddenly. If the malfunction of oxygen sensor is occurred due to a wiring problem of a sensor connector, the LP gas vehicle may produce a shaking and disharmony of an engine because of no signal supply from the oxygen sensor. The air cleaner replica produces the clogging of continuous supply of fresh air. This may cause the retardation of vehicle acceleration and engine disharmony intermittently.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.974-984
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• 2012

This research introduces a new method to attenuate flip-over vibration generation in the flat blade windshield wiper by adjusting the contact pressure between the windshield glass and the blade. The knocking force in the flip-over action of the blade is decreased by inducing gradual tilting-over along the rubber strip of the blade. This gradual tilting-over is induced by introducing a non-uniform contact pressure distribution between the blade and windshield glass. The contact pressure distribution is adjusted by controlling the unloaded profile of the body spring in the blade using a procedure proposed in a previous study. Two blades, one blade designed to generate a uniform pressure distribution and the other designed to generate non-uniform pressure distribution, are developed using the procedure. Contact pressure distributions of the developed blades are measured using a special device and compared with the intended distributions confirming the similarities between the two groups. Vertical and lateral vibrations of the two blades are measured under realistic operating condition simulated by a wiper test rig. The vertical vibrations of the blade with non-uniform contact pressure are substantially smaller than corresponding vibrations of the blade with uniform contact pressure over the entire rubber strip.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.585-596
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• 2013

This study introduces a hybrid approach combining numerical results with pre-developed analytical calculations for the sound radiation from the modal vibration of a thick, finite length cylinder with various boundary conditions. Structural vibrations of the cylinder are numerically investigated with the finite element method, and distributions of vibratory displacements on the cylinder surface are idealized as simple mathematical expressions based on the numerical results. Sound radiations from the normal vibration of the cylinder are calculated based on idealized modal displacements using a previously introduced theoretical solution. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the solutions suggested in this study have good accuracies in calculating the vibro-acoustic properties of a thick, finite cylinder with various boundary conditions. Also, the sound radiation characteristics of many practical components such as brake drums and motor housings are expected to be investigated using the procedure proposed in this study.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.135-141
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• 2021

Interest is growing in the design and development of square wave driven BLDC permanent magnet motors suitable for industrial automation, and the development of position detection circuits and drivers. However, this motor is somewhat limited in its application despite the price and functional advantages due to the decrease in efficiency due to switching loss and vibration and noise. In the process of designing and assembling a BLDC motor, the magnetic pole angle is not uniform or the magnetic flux distribution is distorted due to problems in magnetic circuit design or product non-uniformity in the assembly process. Therefore, these things cause position detection deviation and deteriorate the motor characteristics. In addition, the sine wave driven BLDC system can operate stably only when the signal generated from the position sensor is accurately fed back to the driver. However, since the generated signal cannot perform stable position detection due to the occurrence of DC offset component due to magnetic flux density deviation or magnetization technology, which is an external influence, this study intends to study the proposed circuit that can remove the DC offset component.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.1
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• pp.157-163
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• 2017

This system is a diagnosis system that checks whether it causes a partial discharge of a power cable or not. PD(Partial Discharge) is detected by FBDS(Frequency Band Detection Sensor). That is, it means a acoustic sensor capable of detecting each frequency band. The wave shape of PD sound is similar to noise and is systematically generated by partial discharge. Therefore, in this paper, we could discriminate between normal and abnormal case using relative level crossing rate(RLCR) and spectrogram of frequency energy rate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.458-466
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• 1998

In this work, a frequency domain method is tested numerically and experimentally to improve nonlinear model parameters using the frequency response function at the nonlinear element connected point of structure. This method extends the force-state mapping technique, which fits the nonlinear element forces with time domain response data, into frequency domain manipulations. The force-state mapping method in the time domain has limitations when applying to complex real structures because it needd a time domain lumped parameter model. On the other hand, the frequency domain method is relatively easily applicable to a complex real structure having nonlinear elements since it uses the frequency response function of each substurcture. Since this mehtod is performed in frequency domain, the number of equations required to identify the unknown parameters can be easily increased as many as it needed, just by not only varying excitation amplitude bot also selecting excitation frequency domain method has some advantages over the classical force-state mapping technique in the number of data points needed in curve fit and the sensitivity to response noise.

• Transactions of Materials Processing
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• v.18 no.7
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• pp.538-543
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• 2009

The cowl cross bar of an automobile is a frame component that is installed inside the cockpit module to provide a guide surface, to which functional components for electricity and air condition are attached. In the recent years, the geometries of cowl cross bars are getting more complex in order to meet the demands of a wide variety of embedded functional components and the reduced weight of frame parts with enhanced mechanical and noise/vibration characteristics. There for, welding processes between tubes with different diameters are widely conducted while the welded parts are experiencing various problems such as undermined appearance, low production efficiency and poor mechanical characteristics. Therefore, this paper seeks to develop an one-piece forming process which eliminate welding process for the cowl cross bar by applying the tube drawing process. However, it was predicted that a conventional tube drawing can not be applied directly to the current part since the area reduction ratio of the drawing process reaches 51.7% which exceeds the general limiting value. Therefore, in this study, a combined drawing process which adds a compressive force to a tensile force of the conventional drawing process was proposed and 2-stage drawing process was designed by using CAE analyses. In addition, drawing tryouts were carried out by using the manufactured combined drawing machine in order to verify the designed process.