• Current Optics and Photonics
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• 제7권1호
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• pp.28-32
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• 2023

Frequency characteristics of gain-saturated erbium-doped fiber amplifier (EDFA) are experimentally evaluated to mitigate the optical signal fluctuation induced by atmospheric turbulence in terrestrial freespace optical communication systems. Here, an acousto-optic modulator (AOM) is used to emulate optical signal fluctuations induced by atmospheric turbulence. The waveform which is generated in proportion to the refractive-index structural parameters is used to drive the AOM at various periodic frequencies. Thus, the dependence of the signal fluctuation suppression on the frequency is evaluated. The experiment is conducted using a periodic frequency sweep of the AOM driving voltage waveform and signal input power variation of the amplifier. It is observed that a low periodic frequency and high input signal power effectively suppress the optical signal fluctuation. This study evaluates the experimental results from the high-pass filter and gain-saturation characteristics of the EDFA.

• 비파괴검사학회지
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• 제27권6호
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• pp.541-549
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• 2007

This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations.

• 한국정보통신학회논문지
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• 제24권1호
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• pp.83-90
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• 2020

현재 상용화되어 있는 유량 측정 레이더 센서는 표면 유속을 이용하여 유량을 측정하는 방법을 사용한다. 이러한 방식으로는 표면 유속만으로 유량을 추정하는 것이기 때문에 단위 시간당 흐르는 물의 양을 정확하게 측정할 수 없다. 보다 정확한 측정을 위해서는 수위와 유속 정보 모두가 필요하며, 이에 따라 일부 상용 계측기는 수위와 유속을 각각 측정하는 두 개의 센서를 이용하여 유량을 산정하는 방식을 채택하고 있다. 본 논문에서는 하나의 FMCW 레이다 센서를 이용하여 수위와 유속을 동시에 측정할 수 있는 방법에 대하여 제안하고, 이를 위한 FMCW 레이다 송신 파형을 설계한다. 또한, 송신 파형을 기반으로 수신 신호를 모델링하여 수위 및 유속 측정 시 발생할 수 있는 문제점들에 대해 고찰하고자 한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.572-577
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• 2011

The acoustic emission (AE) technique is a well-known non-destructive test technique, both in research and for industrial applications. It is mainly used to monitor the onset of cracking processes in materials and components. Predicting and preventing the crack phenomenon has attracted the attention of many researchers and has continued to provide a large incentive for the use of condition monitoring techniques to detect the earliest stages of cracks. In this research, goal is in grasping features of AE signal caused by crack growth. The envelope analysis with discrete wavelet transform (DWT) is used to find the characteristic of AE signal. To estimate feature of divided into three by crack length, the time waveform and the power spectrum were generated by the raw signals and the transferred signal processed by envelope analysis with DWT.

• 동력기계공학회지
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• 제14권6호
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• pp.41-46
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• 2010

Acoustic emission (AE) technique is a well-known non-destructive test technique. Fatigue crack growth test was performed using SM53C to check up the AE signal occurred by crack growth, so AE system was used to detect the crack signal. Features calculated by the AE signals were analyzed to evaluate the steps divided the crack growth into three. The steps, initiation, growth and breaking, were separated by velocity of the crack growth. Time waveform and power spectrum were created by the AE signal of each one of the steps and compared. In the feature domains, it was found that AE values changed rapidly as the velocity of the crack increasing.

• 한국전자파학회논문지
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• 제13권7호
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• pp.641-648
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• 2002

The study on the chip waveform design to minimize multiple-access interference (MAI) and its performance evaluation are very important since chip waveform decides the signal quality and system capacity of the direct-sequence CDMA wireless communication system. This paper suggests the analytical chip waveform to minimize the MAI. The BER and throughput performances achieved by the proposed analytical optimum chip waveform are compared with those of the conventional chip waveforms in the Nakagami-m distribution frequency selective channel when the differential phase shift keying (DPSK) is employed in DS-CDMA system. From the numerical results, capacity and throughput are improved about 2 times and 1.4 times respectively when it is compared with the Kaiser chip waveform that is considered as one of the best in the conventional ones.

• 한국전자파학회논문지
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• 제26권11호
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• pp.999-1011
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• 2015

전자전(Electronic Warfare) 상황에서 레이다는 재머에 의해 전파교란공격(ECM: Electronic Counter Measures)을 받게 된다. Linear-FM 신호는 도플러 특성이 우수하고, 신호의 구현이 용이하여 레이다에서 주로 사용되어 왔지만, 반복된 패턴에 의해 피탐 확률이 높고, 신호 특성변수 추정이 가능하여 기만재밍에 취약하다. 최근 제안된 APCN(Advanced Pulse Compression Noise) 신호는 랜덤 진폭과 랜덤 위상코드로 이루어진 신호로서, 저피탐 성능이 우수한 신호이다. 하지만, APCN 신호를 비롯한 일반적인 위상코드 신호는 도플러 특성이 좋지 않으므로, 주파수 천이에 의해 신호수신 성능이 저하될 수 있다. 따라서 본 논문에서는 도플러 특성을 개선하기 위한 방안으로 랜덤 위상천이 및 부호율 천이(RPCR: Random Phase and Code Rate transition) 레이다 신호 파형을 제안하고, 도플러 성능과 저피탐 성능을 분석하였다. Ambiguity 함수를 이용하여 부호율 천이에 의한 도플러 특성 개선을 제시하며, WHT(Wigner-Hough Transform)을 이용한 신호 특성 변수 추정 실험을 통해 RPCR 신호의 저피탐 성능을 분석하고, 전파교란대응책(ECCM: Electronic Counter Counter Measures)으로의 가능성을 확인한다.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.868-874
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• 2018

In this paper, we propose a new jammer suppression algorithm that uses orthogonal waveform space projection (OWSP) processing for a multiple input multiple output (MIMO) radar system exposed to a jamming signal. Generally, a conventional suppression algorithm based on adaptive beamforming (ABF) needs a covariance matrix composed of the jammer and noise only. By exploiting the orthogonality of the transmitting waveforms of MIMO, we can construct a transmitting waveform space (TWS). Then, using the OWSP processing, we can build a space orthogonal to the TWS that contains no SOI. By excluding the SOI from the received signal, even in the case that contains the SOI and jamming signal, the proposed algorithm makes it possible to evaluate the covariance matrix for ABF. We applied the proposed OWSP processing to suppressing the jamming signal in bistatic MIMO radar. We verified the performance of the proposed algorithm by comparing the SINR loss to that of the ideal covariance matrix composed of the jammer and noise only. We also derived the computational complexity of the proposed algorithm and compared the estimation of the DOD and DOA using the SOI with those using the generalized likelihood ratio test (GLRT) algorithm.

• 한국컴퓨터정보학회논문지
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• 제27권2호
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• pp.163-170
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• 2022

현재 반려동물과 함께 사는 가정이 매우 늘어나면서 반려동물의 건강 상태에 대해서 알고 싶어하는 요구가 늘었다. 이에 대한 요구의 증가에 따라 반려동물에게서 호흡과 맥박을 측정하는 방법이 필요한데 반려동물의 특성상 털이 있다는 것을 고려하여 흡착식의 심전도와는 다른 방법인 심탄도 방식을 이용하여 호흡과 맥박 신호를 측정하고자 한다. 이 심탄도 방식은 호흡과 맥박 신호가 하나의 신호에 섞여 만들어지기 때문에 하나의 신호 파형에서 호흡 신호 파형과 맥박 신호 파형을 분리할 필요가 있다. 본 논문에서는 심탄도 측정을 위한 웨어러블 기기를 구현하여 신호를 측정할 수 있게 하고, 이 심탄도 웨어러블 장치로부터 입력된 신호를 호흡 신호와 맥박 신호로 분리하는 방법을 제안하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1992년도 춘계학술대회
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• pp.184-185
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• 1992

This paper investigates the EEG waveform distortions caused by the transient responses of the various types of signal conditioning filters, which are generally introduced for the automated EEG analysis. This study explicitly simulates the filter responses to the typical EEG waveform models, and compares the distortions.