• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.744-750
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• 2001

Higher directivity acoustic transducer using the self-demodulation effect was fabricated. The structure of transducer was designed such as dimension and support type of the piezoelectric element, the vibrating metal plate, and the housing case. Based on the design, the transducer was fabricated and measured its acoustic characteristics. Also, AM modulated driving circuit was designed for using the self-demodulation effect. The piezoelectric sounder with 200kHz resonant frequency and 20kHz bandwidth was designed by considering the sharp directivity and the sound pressure. The design and fabrication method worked in this study can be utilized in development of various speakers with higher directivity and broader bandwidth.

• Journal of the Optical Society of Korea
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• v.3 no.2
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• pp.64-68
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• 1999

The performance of a fiber Bragg grating strain sensor constructed with 3$\times$3 coupler is investigated. A 3$\times$3 coupler Mach-Zehnder (M/Z) interferometer is used as wavelength discriminator, interrogating strain-induced Bragg wavelength shifts. Two quadrature-phase-shifted intensities are synthesized from the as-coupled interferometer outputs, and digital arctangent demodulation and phase unwrapping algorithm are applied to extract the phase information proportional to strain. Due to the linear relation between the input strain and the output of quadrature signal processing, signal-fading problems eliminated. In the experiment, a fiber grating that was surface adhered on an aluminum beam was strained in different ways, and the photodetector signals were transferred and processed in a computer-controlled processing unit. A phase recovery fo 7.8$\pi$ pk-pk excursion, which corresponds to ~650$\mu$strain pk-pk of applied strain, was demonstrated. The sensor system was stable over the environmental intensi쇼 perturbations because of the self-referencing effect in the demodulation process.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.7
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• pp.787-793
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• 1999

A self-sensing magnetic suspension system utilizing a LC resonant circuit is proposed by using the characteristic that the inductance of the magnetic system is varied with respect to the air gap displacement. An external capacitor is added into the electric system to make the levitation system be statically stable system, which much relieves the control effort required to stabilize the magnetic suspension system of haying an intrinsic unstable nature. For the realization of the self- sensing magnetically levitated system, an amplitude modulation / demodulation method is used with a positive position feedback controller Experimental results are presented to validate the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.62-70
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• 2000

Intelligent vehicles are equipped with radar sensors for collision avoidance. We present a method of suppressing mutual interference among pulse-type radars, where all the radars are standardized. We developed a method of separating the true self-reflection from the false one by controlling the pulse emission of a radar in anorhogonal ON, OFF pattern. Interference signal identified in OFF-intervals is recorded to indicate the positions of the expected ghosts in ON-intervals. PFA and PM are derived for a radar system with I-Q demodulation scheme, where Gaussian noise alone is Rayleigh-distributed and Gaussian noise plus reflected radar pulse are Rician-distributed. The value of the threshold adaptively updated in order to prevent the deterioration of PM. In the experimental result, PFA decreases by an order of 10,000, when compared with the conventional M of N majority voting method.

• Journal of Sensor Science and Technology
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• v.27 no.1
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• pp.6-12
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• 2018

In this paper, a 32-variable pulse position modulation (32-VPPM) scheme is proposed to support a red-green-blue light-emitting-diode (RGB-LED)-based optical camera communication (OCC) system. Our proposed modulation scheme is designed to enhance the OCC data transmission rate, which is targeted for the wearable biomedical data monitoring system. The OCC technology has been utilized as an alternative solution to the radio frequency (RF) wireless system for long-term self-healthcare monitoring. Different biomedical signals, such as electrocardiograms, photoplethysmograms, and respiration signals are being monitored and transmitted wirelessly from the wearable biomedical device to the smartphone receiver. A common 30 frames per second (fps) smartphone camera with a CMOS image sensor is used to record a transmitted optical signal. Moreover, the overall proposed system architecture, modulation scheme, and data demodulation are discussed in this paper. The experimental result shows that the proposed system is able to achieve > 9 kbps using only a common smartphone camera receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.229-235
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• 2019

The implementation of an in-band full-duplex wireless communication system is demonstrated in this study. In the analog/RF domain, the self-interference(SI) signal is reduced using a separate antenna for the transmitter and receiver paths, and most of the SI signal is canceled in the digital domain. A software defined radio(SDR) is used to implement the in-band full-duplex wireless communication system. The USRP X310 device uses transmitting and receiving antennas. By adjusting the gain of the transmitting and receiving ends of the SDR device, the magnitude of the SI signal entering the receiving antenna, and the size of the received signal from the outside, are both set to -64 dB. To verify the in-band full-duplex wireless communication performance, the source data is image and orthogonal frequency-division multiplexing is used for modulation. A WiFi standard frame with a carrier frequency of 2.67 GHz and bandwidth of 20 MHz is used. In the received signal, the SI signal is canceled by digital signal processing and the SI signal is attenuated by up to 34 dB. OFDM demodulation was impossible when the SI signal was not removed. However, the bit error rate is reduced to $2.63{\times}10^{-5}$ when the SI signal is attenuated by 34 dB, and no error is detected in the 100 Mbit data output as a result of passing through the Viterbi decoder.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.1030-1038
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• 2013

The proposed Alamouti coded OFDM effectively cancels Inter Carrier Interference (ICI) due to frequency offset between distributed antennas. The conventional Alamouti coded OFDM schemes to mitigate ICI utilize N-point Inverse Fast Fourier Transform/Fast Fourier Transform (IFFT/FFT) operations for OFDM modulation and demodulation processes with total N subcarriers. However, the performance degrades because ICI is also repeated in N periods due to the property of N-point IFFT/FFT operation. In order to avoid this problem, null data are used at the subcarriers with large ICI and thus, data rate decreases. The proposed scheme employs 2N-point IFFT/FFT instead of N-point IFFT/FFT in order to increase sampling rate. By increasing sampling rate, the amount of interference significantly decreases because the period of ICI also increases. The proposed scheme increases the data rate and improves the performance by reducing amount of ICI and the number of null-data. Furthermore, the gain of the performance and data rate of the proposed scheme is significant with higher modulation such as 16-Quadarature Amplitude Modulation (QAM) or 64-QAM.