• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.4
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• pp.429-434
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• 2012

This paper presents a technology for manipulating external devices by Brain Computer Interface (BCI) system. Recently, BCI based rehabilitation and assistance system for disabled people, such as patient of Spinal Cord Injury (SCI), general paralysis, and so on, is attracting tremendous interest. Especially, electroencephalogram (EEG) signal is used to organize the BCI system by analyzing the signals, such as evoked potential. The general findings of neurophysiology support an availability of the EEG-based BCI system. We concentrate on the event-related synchronization of motor imagery EEG signal, which have an affinity with an intention for moving control of external device. To analyze the brain activity, short-time Fourier transform and particle swarm optimization are used to optimal feature selection from the preprocessed EEG signals. In our experiment, we can verify that the power spectral density correspond to range mu-rhythm(${\mu}8$~12Hz) have maximum amplitude among the raw signals and most of particles are concentrated in the corresponding region. Result shows accuracy of subject left hand 40% and right hand 38%.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.8 s.111
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• pp.760-766
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• 2006

In this paper, we present a wideband patch antenna with folded and shorted structure for 5 GHz WLAN(Wireless Local Area Network). The proposed antenna used folded and shorted structure in the rectangular patch for miniaturization and wide frequency bandwidth. The antenna was designed by using 3D simulation program, HFSS(High Frequency Structure Simulator) software of the Ansoft company and the implemented antenna was measured by using HP 8720c network analyzer and far field measurement chamber. Simulation result on the return loss shows fairly good characteristic of at least 13.41dB in whole frequency range of interests, and the 10dB bandwidth is 1,523MHz which shows wide bandwidth characteristic. And the simulated maximum gain of the proposed antenna is 6.57 dBi at 5.825GHz. Measured result for the 10dB bandwidth of the implemented folded and shorted structure antenna is 1,377 MHz. Measured maximum gain of the implemented antenna is 6.87dBi at 5.775GHz. Measured results for the implemented antenna showed applicable performances for the 5 GHz WLAN.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.202-206
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• 2005

The present investigation provides an electromagnetic radiation absorptive composition which comprises silver-coated ferrite microspheres dispersed in silicon rubber matrix for the aim of thin microwave absorber in GHz frequencies. Ni-Zn ferrite spheres with $50{\mu}m$ size in average were prepared by spray-drying and sintering at $1130^{\circ}C$. Conductive silver layer was plated on ferrite spheres by electroless plating. Conductive Ni-Zn ferrite sphere with uniform silver layer were obtained in the concentration of 10 g/L $AgNO_3$ per 20 g ferrite spheres. For this powder, electrical resistance is reduced as low as $10^{-2}\~10^{-3}\;\Omega$. The most sensitive material parameters with silver plating is real and imaginary parts of complex permittivity. The conductive Ni-Zn ferrite spheres have large values of dielectric constant. Due to this high dielectric constant of microspheres, matching thickness is reduced to as low as 2 mm at the frequency of 7 GHz, which is much thinner than conventional ferrite absorbers.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.6
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• pp.39-47
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• 1998

A fourth-order $\Sigma$-$\Delta$ modulator is designed and implemented in 0.6 $\mu\textrm{m}$ CMOS technology. The modulator is verified by introducing nonlinear factors such as DC gain and slew rate in system model that determines the transfer function in S-domain and in time-domain. Dynamic range is more than 110 dB and the peak SM is 102.6 dB at a clock rate of 2.8224 MHz for voiceband signal. The structure of a ∑-$\Delta$ modulator is a modified fourth-order ∑-$\Delta$ modulator using direct feedback loop method, which improves performance and consumes less power. The transmission zero for noise is located in the first-second integrator loop, which reduces entire size of capacitors, reduces the active area of the chip, improves the performance, and reduces power dissipation. The system is stable because the output variation with respect to unit time is small compared with that of the third integrator. It is easy to implement because the size of the capacitor in the first integrator, and the size of the third integrator is small because we use the noise reduction technique. This paper represents a new design method by modeling that conceptually decides transfer function in S-domain and in Z-domain, determines the cutoff frequency of signal, maximizes signal power in each integrator, and decides optimal transmission-zero frequency for noise. The active area of the prototype chip is 5.25$\textrm{mm}^2$, and it dissipates 10 mW of power from a 5V supply.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3C
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• pp.398-407
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• 2004

In this paper, a blind watermarking method which is suitable to the video compression using 2-D discrete wavelet transform was proposed and implemented into the hardware using VHDL(VHSIC Hardware Description Language). The goal of the proposed watermarking algorithm is the authentication about the manipulation of the watermark embedded image and the detection of the error positions. Considering the compressed video image, the proposed watermarking scheme is unrelated to the quantization and is able to concurrently embed or extract the watermark. We experimentally verified that the lowest frequency subband(LL4) is not sensitive to the change in the spatial domain, so LL4 subband was selected for the mark space. And the combination of the bitplanes which has the properties of both the minimum degradation of the image and the robustness was chosen as the embedded Point in the mark space in LL4 subband. Since we know the watermark embedded positions and the watermark is embedded by not varying the value but changing the value, the watermark can be extracted without the original image. Also, for the security when exposing the watermark embedded position, we embed the encrypted watermark by the block cipher. The proposed watermark algorithm shows the robustness against the general image manipulation and is easily transplanted into the image or video compressor with the minimal changing in the structure. The designed hardware has 4037 LABs(24％) and 85 ESBs(3％) in APEX20KC EP20K400CF672C7 FPGA of Altera and stably operates in 82MHz clock frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.1
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• pp.60-68
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• 2016

This paper presents a 6~18 GHz 7-bit digital-controlled attenuator. The proposed attenuator is based on switched-T architecture, but no inductor is used for minimum chip size. The designed attenuator was fabricated using $0.18{\mu}m$ CMOS process, and characterized using on-wafer testing setup. The resolution(minimum attenuation step) and the maximum attenuation range of the attenuator were measured to be 0.22 dB and 28 dB, respectively. The measured RMS attenuation error and the RMS phase error for 6~18 GHz were less than 0.26 dB and $3.2^{\circ}$, respectively. The reference state insertion loss was less than 12.4 dB at 6~18 GHz. The measured input and output return losses were better than 9.4 dB over all frequencies and attenuation states. The chip size is $0.11mm^2$ excluding pads.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6C
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• pp.502-511
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• 2012

As the importance of GNSS system increases, the necessity of independent system is increased also. When the independent GNSS system is required, GNSS signal design is necessary with requirement definition. This paper suggests the design method of GNSS signal using the analysis result of receiver performance. First, the candidates are defined based on the design elements. Then the receiver performance of the candidates is analyzed based on the performance evaluation parameters. The weights of performance evaluation parameter are defined in order to consider the receiver performance in a various aspects. Finally, the calculation of normalized performance evaluation parameters and weights are derived to obtain the compared value for signal selection. Spreading code, modulation method and carrier frequency are considered as design parameters. Also, correlation width, DLL PLL thermal noise jitter, frequency bandwidth and side lobe peak ratio are considered as performance evaluation parameters. And positioning performance, robustness to noise, bandwidth efficiency are considered as the performance aspects. This paper analyzes the performance of each candidate using software based simulator and suggest the method to compare objectively the performance of each candidates.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6C
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• pp.476-482
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• 2012

In this paper, we analyze and compare several co-channel interference mitigation algorithms for WBAN application in 2.4 GHz ISM frequency bands. ML (Maximum Likelihood), OC (Optimal Combining) and MMSE (Minimum Mean Square Error) has been considered for the possible techniques for interference cancellation in view of the trade off between the performance and the complexity of implementation. Based on the channel model of IEEE 802.15.6 standard, simulation results show that ML and OC attains the lower BER performance than that of MMSE if we assume the perfect channel estimation. But, ML and OC have the additional requirement of implementation for his own and other users's channel estimation process, hence, besides the BER performance, the complexity of implementation and the sensitivity to channel estimation error should be considered since it requires the simple and small sized equipment for WBAN system application. In addition, the gap of detection BER performance between ML, OC and MMSE is much decreased under the imperfect channel estimation if we adopt real channel estimation process, therefore, in order to apply to WBAN system, the trade off between the BER performance and complexity of implemetation should be seriously considered to decide the best co-channel interference cancellation for WBAN system application.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5C
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• pp.393-402
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• 2012

In this study, we propose a signal processing algorithm to measure the arousal level of a human subject using a PPG(Photoplethysmography) sensor. From the measured PPG signals, the arousal level is determined by PPI(Pulse to Pulse Interval) and discrete-time signal processing. We ran psychophysical experiments displaying visual stimuli on TV display while measuring PPG signal from a finger, where the nature landscape scenes were used for restorative effect, and the urban environments were used to stimulate the stress. However, the measured PPG signals may include noise due to subject movement and measurement error, which results in incorrect detections. In this paper, to mitigate the noise impact on stimulus detection, we propose a detecting algorithm using digital signal processing methods and statistics of measured signals. A filter is adopted to remove a high frequency noise and adaptively designed taking into account the statistics of the measured PPG signals. Moreover we employ a hysteresis method to reduce the distortion of PPI in decision of emotional. Via experiment, we show that the proposed scheme reduces signal noise and improves stimulus detection.