• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.217-222
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• 2004

In this paper, the efficient channel estimation schemes for DRM system(AM band digital radio broadcasting standard) are investigated. In frequency domain, by means of the linear interpolation, the second order interpolation, cubic spline interpolation, and time domain interpolation, the channel impulse response is estimated respectively to compensate the attenuation due to the fading. And in time domain, the frequency channel impulse response is averaged to reduce the attenuation due to the AWGN. By the simulation, the performance of MSE, BER and the complexity of calculation is compared and analyzed for each interpolation scheme.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.69
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• pp.65-73
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• 2001

The objective of this study is to evaluate the vibration attenuation effects of the different type of gloves and drilling mode while operating a light-weighted powered hand drill. For the experimental design, five different kinds of glove(barehanded cotton partly coated anti-vibration, and open-finger vibration glove) two types of push force level(100N and 200N) and two types of drilling mode(impact and non-impulsive) were considered. Six healthy male subjects were employed to drive screws into a vertically mounted marble plate with a powered hand drill in a randomly ordered experimental conditions. The findings of this study are summarized as follows; (1) It was found that the best combination of overall BMS transmissibility was using impact drilling mode with anti-vibration glove among evaluated experimental conditions (2) The wearing open finger vibration glove in mid-frequency level and anti-vibration glove with impact drill in high-frequency were the best in the result from mean corrected transmissibility equation of ISO 10819.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.135-138
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• 1998

This paper presents the results of measured permittivity of PCB sheet material in the frequency range of 0.1[GHz] - 2[GHz] and temperature range of $25[^{\circ}C]$ - $85[^{\circ}C]$. Microstrip lines with different physical length are implemented to measure the attenuation and phase shift of the signals though these lines. The loss factor of these materials could be obtained with the dielectric constant and the attenuation of the microstrip lines.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.4
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• pp.672-678
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• 1994

A design of 5th-order Elliptic OTA-C filter for operation at 4.2MHz is presented. the filter structure is composed entirely of five OTAs(Operational transoonductance Amplifiers), one buffer and seven capacitors. To prevent decreasing of frequency charaoteristios due to the parasitic effeots of OTA and buffer, the design considering of parasitic capacitance and finite resistane of OTA and fuffer is pertormed. As the result of the simulation using SPICE with $2{\mu}m$ CMOS parameters, The performances were found to be essentially within the specifications` less than 0.25dB passband attenuation, 30dB stopband attenuation and 4.2MHz cut-off frequency were satisfactorily obtained. The number of elements is also considerably reduced than other design methods.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.35-40
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2E
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• pp.45-52
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• 1999

This paper presents the integrated speech enhancement system for hands-free mobile communication. The proposed integrated system incorporates both acoustic echo cancellation and engine noise reduction device to provide signal enhancement of desired speech signal from the echoed plus noisy environments. To implement the system, a delayless subband adaptive structure is used for acoustic echo cancellation operation. The NLMS based adaptive noise canceller then applied to the residual echo removed noisy signal to achieve the selective engine noise attenuation in dominant frequency component. Two sets of computer simulations are conducted to demonstrate the effectiveness of the system; one for the fixed acoustical environment condition, the other for the robustness of the system in which, more realistic situation, the acoustic transmission environment change. Simulation results confirm the system performance of 20-25dB ERLE in acoustic echo cancellation and 9-19 dB engine noise attenuation in dominant frequency component for both cases.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.1
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• pp.75-82
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• 2002

In this paper, the robust PID(Proportional-Integral-Derivative) controller was designed for speed control of BLDC motors using the frequency region model matching method. It was designed the robust PID controller satisfying disturbance attenuation and robust tracking performance using an H$\infty$ control method. The robust PID controller gains with the performances of the designed H$\infty$ controller are determined using the model matching method at frequency domain. Consequently, simulation results show that the proposed PID speed controller satisfies load torque disturbance attenuation and robust tracking performance, and this study has usefulness and applicability for the speed control system design of BLDC motors.

• Coupled systems mechanics
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• v.12 no.2
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• pp.103-125
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• 2023

The present research is focused on the study of plane harmonic waves in a two-dimensional orthotropic magneto-thermoelastic media with fractional order theory of generalized thermoelasticity in the light of two-temperature and rotation due to time harmonic sources. Here, we studied three types of waves namely quasi-longitudinal (QL), quasi-transverse (QTS) and quasi thermal (QT) waves. The variations in the wave properties such as phase velocity, attenuation coefficient and specific loss have been noticed with respect to frequency for the reflected waves. Further the value of amplitude ratios, energy ratios and penetration depth are computed numerically with respect to angle of incidence. The numerical simulated results are presented graphically to show the effect of fractional parameter based on its conductivity (0<α<1 for weak, α=1 for normal, 1<α≤2 for strong conductivity) on all the components.

• ETRI Journal
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• v.46 no.4
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• pp.716-726
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• 2024

An ultrawide stopband lowpass filter is reported using three stepped impedance resonators with high selectivity. The filter extends the stopband frequency range and attenuation, and two quarter-wave open stubs and three circular ground slots are introduced. The lumped and distributed equivalent models are derived and analyzed. The corresponding results are validated experimentally in a fabricated prototype. The prototype lowpass filter has a 3 dB cutoff frequency (f_c) of 2.9 GHz, and the stopband is extended up to 35 GHz (12.07f_c), with an attenuation level better than 20 dB throughout. The passband-to-stopband transition (3 dB-20 dB) bandwidth is 0.18 GHz, and the roll-off factor is 135 dB/GHz at 30 dB. The insertion loss is 0.3 dB at 1.6 GHz. The normalized circuit size of the proposed filter with respect to the guided wavelength is 0.04.

• 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.