• Composites Research
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• v.31 no.2
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• pp.51-56
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• 2018

A new study was carried out to utilize a pencil drawing paper sensor (PDPS), which drew a line using a pencil on the paper, as a sensor. The sensing effect on 3 different papers based on the properties of PDPS was compared. The specimens were prepared by drawing 4B pencils on plain (A4), Hwasun, and Han papers. The silver paste was used to give good electrical contacts of the copper wires and the pencil drawn line. The chemical structures of 3 papers for PDPS by FT-IR spectrum analysis were similar and the comparative compact states of each paper were observed by optical microscope. From statistical evaluation of tensile strength using 3 papers, plain paper was chosen to be best for the PDPD. The optimum drawing number of PDPD was determined by changing the thickness of the paper with the drawing number. Electrical resistance (ER) with graphite on 3 different papers were compared. The changes in compression was observed through cyclic compressive test of composite materials, it was possible to predict the degree of strain sensing under compressive test. It leads to expectation of properties.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.11
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• pp.779-789
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• 2014

Cognitive radio (CR) technology based on geo-location database access approach and/or wideband spectrum sensing approach is absolutely vital in order to recognize available frequency bands in white spaces (WSs), and efficiently utilize shared spectrums. This paper presents a new structure for the TVWS database access protocol implementation based on Internet Engineering Task Force (IETF) Protocol to Access WS database (PAWS). A wideband compressive spectrum sensing (WCSS) scheme using a modulated wideband converter is also proposed for the TVWS utilization. The developed database access protocol technology which is adopted in both the TV band device (TVBD) and the TVWS database operates well in the TV frequency bands. The proposed WCSS shows a stable performance in false alarm probability irrespective of noise variance estimation error as well as provides signal detection probabilities greater than 95%. This paper also investigates Federal Communications Commision (FCC) regulatory requirements of TVWS database as well as European Telecommunications Standards Institute (ETSI) policy related to TVWS database. A standardized protocol to achieve interoperability among multiple TVBDs and TVWS databases, which is currently prepared in the IETF, is discussed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.62-69
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• 2023

This study investigated the electromechanical properties of cement based smart repair materials (SRMs) according to the different amounts of fine steel slag aggregates (FSSAs). SRMs can self-diagnose the quality of repairing and self-sense the damage of repaired zone. The replacement ratios of FSSAs to sand for SRMs were 0% (FSSA00), 25% (FSSA25), and 50% (FSSA50) by sand weight. The electrical resistivity of SRMs generally decreased as the compressive stress of SRMs increased: the electrical resistivity of FSSA25 at the age of 7 hours decreased from 78.16 to 63.68 kΩ-cm as the compressive stress increased from 0 to 22.37 MPa. As the replacement ratio of FSSAs by weight of sand increased from 0% to 25%, the stress sensitivity coefficient (SSC) of SRM at the age of 7 h increased from 0.471 to 0.828 %/MPa owing to the increased number of partially conductive paths in the SRMs. However, as the replacement ratio of FSSAs further increased up to 50%, the SSC decreased from 0.828 to 0.649 %/MPa because some of the partially conductive paths changed to continued conductive ones. SRMs are expected to self-sense the quality and future damage of repaired zone only by measuring the electrical resistivity of the repaired zone in addition to fast recovery in the mechanical resistance of structures.

• Composites Research
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• v.26 no.3
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• pp.201-206
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• 2013

The electrical resistance measurement was investigated as a damage monitoring method. In this study, 0.5 wt% Carbon nanotube reinforced polypropylene (CNT/PP) composites were evaluated under compressive fatigue loading. The shape of specimens was $20^{\circ}$ curved round type. Compression strength and electrical resistance were measured at different sections of specimen during compression. The microcracks of CNT/PP composites were detected based on the changing ratio of electrical resistance. Micro-damage during compressive fatigue test could be detected by electrical resistance measurements. The reason is that the contact points of CNTs in composites decreased under fatigue loading. During compressive fatigue test, larger change of electrical resistance was detected at the microcrack sections. It was proved that microcracks could be detected by electrical resistance measurement under compression test, whereas the real delamination parts were consistent with the predicted results by electrical resistance measurement.

• Composites Research
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• v.22 no.6
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• pp.1-6
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• 2009

This paper presents an experimental study on the piezoresistive behavior of nanocomposite strain sensors subjected to various loading modes and their capability to detect structural deformations and damages. The electrically conductive nanocomposites were fabricated in the form of a film using various types of thermoplastic polymers and multi-walled carbon nanotubes (MWNTs) at various loadings. In this study, the nanocomposite strain sensors were bonded to a substrate and subjected to tension, flexure, or compression. In tension and flexure, the resistivity change showed dependence on measurement direction, indicating that the sensors can be used for multi-directional strain sensing. In addition, the sensors exhibited a decreasing behavior in resistivity as the compressive load was applied, suggesting that they can be used for pressure sensing. This study demonstrates that the nanocomposite strain sensors can provide a pathway to affordable, effective, and versatile structural health monitoring.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.1
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• pp.29-33
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• 1992

A non-contact torque sensor was developed using amorphous alloy. The change of maixmum magnetic induction of C0-based amorphous alloy under the tensile and compressive stress was proportional to applied torque. For the construction of the torque sensor, a glass fiber reinforced-epoxy rod was used as shaft. The amorphous strips were attached on the epoxy shaft in the direction of $+45^{\circ}$and $-45^{\circ}$. The magnetizing coil and 2 sensing coil was installed. The static and dynamic test was carried out. The linearity and sensor hysteresis of the torque sensor was less than 1%.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.135-136
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• 2011

Sparse한 신호 복원 방법으로 underdetemined system에서 l1-minimization을 이용한 compressive sensing의 연구와 함께, l1-minimization비해 간단한 greed 알고리듬도 활발히 연구되고 있다. 이에 본 논문은 greed 알고리듬의 대표적인 orthogonal matching pursuit기법에서 iteration 마다 support 선택 개수에 따른 성능을 연구한다. 모의 실험을 통해 OMP의 iteration 단계에서 하나의 support만 선택하는 것보다 다수의 support를 선택하는 것이 더 낮은 sparsity의 신호를 복원할 수 있고 더 낮은 계산량의 이득을 가져오는 것을 확인 할 수 있다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.82-88
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• 2006

In People usually think that smart materials and smart structures have not been developed until recent years. But those kinds of sensors have already been used for sensing damage in a variety of materials and structures. Two typical examples are piezoelectric materials (e.g., PZT) and electric strain gauges. Load cell is an example that utilizes the piezoelectric property to measure the change in physical quantities occurred by applied loads, while strain gauges are used to measure the deformation of compressive and tension members. The feasibility of using smart materials is realized for a monitoring technology when those sensors are used to monitor damages at inside or outsider of the structures. In this study, a fundamental study on the development of self diagnostic smart concrete using PZT, and unsaturated polyester electric resistance sensor.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.473-474
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• 2012

Sparse한 신호 복원 방법으로 underdetermined system에서 ll-minimization을 이용한 compressive sensing의 연구와 함께, ll-minimization비에 간단한 greed 알고리듬도 활발히 연구되고 있다. 이에 본 논문은 greed 알고리듬의 대표적인 orthogonal matching pursuit기법에서 iteration 마다 후보 support를 유지하는 알고리듬을 연구한다. 모의 실험을 통해 OMP의 iteration 단계에서 하나의 support만 선택하는 것보다 후보 support를 유지하는 것이 sparse 신호를 복원하는 경우는 OMP와 비슷한 성능을 보이지만 덜 sparse한 신호복원에서는 더 좋은 성능을 보임을 확인 할 수 있다.

• The Magazine of the IEIE
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• v.38 no.1
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• pp.44-49
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• 2011

다중채널 압축센싱(multi-channel compressive sensing) 문제는 0이 아닌 성분이 공통된 위치에 분포하는 벡터들을 복원하는 방법을 다루는 문제이며 레이다의 도착방향 추정 문제, 역산란 문제, 산란광 단층촬영과 같은 많은 실용적인 문제에 응용될 수 있다. 압축 센싱 문제는 성긴(sparse) 속성을 갖는 벡터를 상당히 높은 확률로 복원시킬 수 있음이 밝혀져 있다. 이로 인해 기존의 압축 센싱 방법이 다중채널 압축센싱에서도 많이 활용되어 왔으며, 측정 벡터의 개수가 적을 때에도 높은 확률로 입력 신호를 복원할 수 있다. 그러나, 측정 벡터의 개수가 많아질수록, 기존의 압축센싱 알고리즘을 이용했을 때의 성능은 복수신호분리 (MUSIC) 알고리즘과 같이 배열신호처리(array signal processing)에서 활용되는 방법을 적용했을 때보다 더 나쁜 특성을 보인다. 이러한 기존 방법의 문제점으로 인해 우리는 새로운 다중채널 압축센싱 알고리즘을 제시하고자 하며, 이는 기존의 압축센싱 이론과 배열 신호처리 알고리즘을 개별적으로 적용할 때 가지는 한계를 극복할 수 있게 해준다.