• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.54-62
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• 2013

In this study, a wireless and non-power SAW (surface acoustic wave) temperature sensor was developed. The single inter-digital transducer (IDT) of SAW temperature sensor of which resonance frequency is 434 MHz was fabricated on $128^{\circ}$ rot-X $LiNbO_3$ piezoelectric substrate by semiconductor processing technology. To find optimal acoustic reflector for SAW temperature sensor, various kinds of acoustic reflectors were fabricated and their reflection characteristics were analyzed. The IDT type acoustic reflector showed better reflection characteristic than other reflectors. The wireless temperature sensing system consisting of SAW temperature sensor with dipole antenna and a microprocessor based control circuit with dipole antenna for transmitting signal to activate the SAW temperature sensor and receiving the signal from SAW temperature sensor was developed. The result with wireless SAW temperature sensing system showed that the frequency of SAW temperature sensor was linearly decreased with the increase of temperature in the range of 40 to $80^{\circ}C$ and the developed wireless SAW temperature sensing system showed the excellent performance with the coefficient of determination of 0.99.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.219-222
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• 1996

수열법은 밀폐용기중에서 10$0^{\circ}C$이상의 가열, 가압된 수용액이 반응에 관여하는 것으로써, 수정, CaCO3, AlPO4, GaPO4 등과 같은 단결정의 육성 뿐만 아니라 균일분산계로부터 균일한 결정성의 미립자 합성에도 폭넓게 이용되고 있다. 세라믹분말의 합성에 있어서, 이 방법은 특히 형상, 입자크기의 제어가 용이할 뿐만 아니라 고상법, 졸-겔법, 공침법에서와 같은 열처리, 분쇄과정이 필요없기 때문에 고순도의 초미립자를 얻을 수 있는 장점이 있다. 근년 미국, 일본에서는 수열법을 이용한 유전, 압전체 등 세라믹분말의 일부가 공업적인 규모로 대량 생산되고 있다. 그러나 이에 대한 국내 기술은 아직 초기단계에 이르고 있는 실정이다. 따라서 본 연구실에서는 수열법에 의한 단결정 육성 (예; 자수정, CaCO3, AlPO4, GaPO4, KTP, Emerald 등), 박막제조 (예; GaP, PbTiO3, BaTiO3 등), 정제 (고령토, 장석, 도석 등), 원석처리 (진주, 인공 emerald, 비취 등) 그리고 각종 세라믹분말의 합성 등과 같은 다양한 기반기술의 축적과 동시에 공업화에 대응한 수열장치를 위하여 반응용기의 대형화, 엄밀한 밀폐방식, 실용적인 수열조건 등을 개발해 오고 있다. 본 발표에서는 현재까지의 연구개발 내용 중에서 결정성 미립자에 관련한 세라믹분말의 합성에 대한 일부의 결과들을 보고한다. 일반적으로 수열장치는 전기로, 반응용기, 온도 및 압력제어계 등을 기본으로 하고 있으며 시판용의 대부분이 교반기가 부착된 수직형 (vertical type)이다. 이와 같은 방식에 있어서는 엄밀한 밀폐가 곤란, 반응온도의 한계성 (25$0^{\circ}C$ 이하), 증진율의 한계성 (소량생산) 등과 같은 점이 있기 때문에 본 연구실에서는 개폐식 전기로내에 엄밀한 밀폐가 가능한 수평식(horizontal type)의 반응용기를 채택한 뒤 이를 회전 또는 시이소(seesaw)식으로 움직일 수 있도록 하여 연속공정화, 온도구배의 자율조절 그리고 보다 저온에서도 인위적인 이온의 확산을 효율적으로 유도할 수 있도록 하였다. 이와 같은 방식은 기존의 방식과 비교하여 반응용기 내에 응집현상과 미반응물이 존재하지 않으며 또한 단분산으로 결정성 미립자를 대량적으로 얻을 수 있는 장점이 있었다. 다음은 이상과 같이 본 연구실에서 자체 개발한 수열장치를 이용하여 PbTiO3, (Pb,La)TiO3Mn, BaTiO3, ZnSiO4:Mn, CaWO4 등과 같은 세라믹분말에 대한 합성 실험의 결과이다. 압전성, 초전성이 우수한 PbTiO3 및 (Pb,La)TiO3:Mn 분말의 수열합성은 PbO, TiO2, La2O3 등의 분말을 출발원료로 하여 합성도도 25$0^{\circ}C$부근의 알카리성 용액중에서 결정성 PbTiO3 및 (Pb,La)TiO3:Mn 미립자를 단상으로 얻었으며 입자의 형상 및 크기는 합성온도와 수열용매의 종류에 의존하였다. 유전체로서 폭넓게 응용되고 있는 BaTiO3 분말은 Ba(OH)2.8H2O, TiO2와 같은 최적의 출발원료를 선택함으로써 15$0^{\circ}C$ 부근의 저온영역에서도 용이하게 합성할 수 있었다. 특히 본 연구에서는 수용성인 Ba(OH)2.8H2O를 사용함으로써 host-guest적인 반응을 유도시키는데 있어 물의 가장 실용적이고 효과적인 수열용매임도 알았다. ZnSiO4:Mn, CaWO4, MgWO4와 같은 형광체 분말은 공업적으로 고상반응 또는 습식법에 의해 얻어지고 있으나 이들 방법에 있어서는 분쇄공정으로 인한 형광특성의 저하와 같은 문제점이 있다. 따라서 본 연구에서는 수열법을 이용하여 이들 화합물의 합성을 시도하였으며 그 결과 합성온도 30$0^{\circ}C$ 부근의 알칼리성 용액중에서 수열적으로 얻어짐을 알았다. 여기서의 합성분말을 이용하여 실제 조명램프로 제조한 결과 녹색, 청색 발광용 형광체로서 우수한 형광특성을 나타내었다. 천연에서 소량 산출되고 있는 고가의 (Li,Al)MnO2(OH)2:Co 분말은 도자기의 전사지용 청색안료로써 이용되고 있다. 본 연구실에서는 LiOH.H2O, Al(OH)3, MnO2 등의 분말을 출발원료로 하고 24$0^{\circ}C$ 온도 부근 그리고 물을 수열용매로 하여 천연산에 필적하는 (Li,Al)MnO2(OH)2:Co 분말을 인공적으로 합성하였다.

• Proceedings of the Korean Ceranic Society Conference
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• 2005.06a
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• pp.1-112
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• 2005

This report is results of a research on recent R&D trends in electroceramics, mainly focusing on the papers submitted to the organizing committee of the International Conference on Electroceramics 2005 (ICE-2005) which was held at Seoul on 12-15 June 2005. About 380 electroceramics researchers attended at the ICE-2005 from 17 countries including Korea, presenting and discussing their recent results. Therefore, we can easily understand the recent research trends in the field of electroceramics by analyses of the subject and contents of the submitted papers. In addition to the analyses of the papers submitted to the ICE-2005, we also collected some informations about domestic and international research trends to help readers understand this report easily. We analysed the R&D trends on the basis of four main categories, that is, informatics electroceramics, energy and environment ceramics, processing and characterization of electroceramics, and emerging fields of electroceramics. Each main category has several sub-categories again. The informatics ceramics category includes integrated dielectrics and ferroelectrics, oxide and nitride semiconductors, photonic and optoelectronic devices, multilayer electronic ceramics and devices, microwave dielectrics and high frequency devices, and piezoelectric and MEMS applications. The energy and environment ceramics category has four sub-categories, that is, rechargable battery, hydrogen storage, fuel cells, and advanced energy conversion concepts. In the processing and characterization category, there exist domain, strain, and epitaxial dynamics and engineering sub-category, innovative processing and synthesis sub-category, nanostructured materials and nanotechnology sub- category, single crystal growth and characterization sub-category, theory and modeling sub-category. Nanocrystalline electroceramics, electroceramics for smart sensors, and bioceramics sub-categories are included to the emerging fields category. We hope that this report give an opportunity to understand the international research trend, not only to Korean ceramics researchers but also to science and technology policy researchers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.113-116
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• 2010

We report on the growth and characteristics of the structural and optical properties of InGaN nano-structures doped with antimony (Sb) as a catalyst. The use of catalyst has been explored to modify the growth and defect generation during strained layer heteroepitaxial growth. We performed the growth of the InGaN nano-structures on c-sapphire substrates using mixed-source hydride vapor phase epitaxy (HVPE). The characteristic of samples was measured by scanning electron microscope (SEM) and photoluminescence (PL). The aligning direction of c-axis of the InGaN nano-structures was changed from vertical to parallel or inclined to the surface of substrates when the Sb was added as a catalyst. The indium composition was estimated about 3.2% in both cases of with or without the addition of Sb in the InxGal-xN structures. From the results of InGaN nano-structures formed with the addition of Sb, we can expect the performance of optical devices would be more improved by reduced piezo-electric field if we use the InGaN nano-structures of which c-axes are aligned parallel to the substrates as an active layer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.317-325
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• 2020

The development of a technique that can monitor the cracks, which is one of the typical types of damage, is necessary to secure the structural safety of elastically restrained cantilever-type beams with a tip mass that is used widely in infrastructure. Impedance techniques have been actively researched to detect cracks, and the cracks were estimated mainly by experimentally investigating the relationship between the crack and impedance signal. This study examined the correlation between the change in the impedance signals due to the crack, and the natural frequency obtained analytically. After updating the analysis model for the intact beam, the impedance signal was measured while gradually inflicting cracks in the cantilever-type beam, and the damage index was obtained. The results were compared with the natural frequencies calculated from the updated analysis model to investigate the correlation. A close correlation was observed between the experimentally obtained impedance damage index, and the analytically calculated natural frequency. Using this correlation, the structural characteristics could be evaluated more accurately from the damage estimation results, and the behavior of the structure could be predicted effectively using the analysis model.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.2
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• pp.112-119
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• 2015

Photoacoustic microscopy is capable of providing high-resolution molecular images, and its spatial resolution is typically determined by ultrasonic transducers used to receive the photoacoustic signals. Therefore, ultrasonic transducers for photoacoustic microscopy (PAM) should have a high operating frequency, broad bandwidth, and high signal-reception efficiency. Polyvinylidene fluoride (PVDF) is a suitable material. To take full advantage of this material, the selection of the backing material is crucial, as it influences the center frequency and bandwidth of the transducer. Therefore, we experimentally determined the most suitable backing material among EPO-TEK 301, E-Solder 3022, and RTV. For this, three PVDF high-frequency single-element transducers were fabricated with each backing material. The center frequency and -6 dB bandwidth of each transducer were ascertained by a pulse-echo test. The spatial resolution of each transducer was examined using wire-target images. The experimental results indicated that EPO-TEK 301 is the most suitable backing material for a PAM transducer. This material provides the highest signal magnitude and a reasonable bandwidth because a large portion of the energy propagates toward the front medium, and the PVDF resonates in the half-wave mode.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.134-141
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• 2011

There have been increased economic and societal demands to continuously monitor the integrity and long-term deterioration of civil infrastructures to ensure their safety and adequate performance throughout their life span. However, it is very difficult to continuously monitor the structural condition of the pipeline structures because those are placed underground and connected each other complexly, although pipeline structures are core underground infrastructures which transport primary sources. Moreover, damage can occur at several scales from micro-cracking to buckling or loose bolts in the pipeline structures. In this study, guided wave measurement can be achieved with a self-sensing circuit using a piezoelectric active sensor. In this self sensing system, a specific frequency-induced structural wavelet response is obtained from the self-sensed guided wave measurement. To classify the multiple types of structural damage, supervised learning-based statistical pattern recognition was implemented using the damage indices extracted from the guided wave features. Different types of structural damage artificially inflicted on a pipeline system were investigated to verify the effectiveness of the proposed SHM approach.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.170-178
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• 2011

In this paper, a research was performed to develop a wireless measurement system for bridge monitoring using MEMS sensor and bluetooth wireless communication module. First, in order to prove the suitability of MEMS sensor for the bridge measurement, its ranges of measuring acceleration and of frequency response were experimented. Also, the quality of wireless communication was tested by an experiment on long-distance communication for the knowledge of maximum communication distance, and also by an experiment on the data transmit-receive capability both inside and outside of a steel box bridge. Later, placing the wireless acceleration sensor system that had been developed in our lab on a bridge in public service, we acquired vibration data from the bridge under traffic load and analyzed its dynamic characteristics in realtime. For the analysis of the data, NExT & ERA algorithm were employed. The result of analysis was compared to the FE analysis of the same bridge, and the comparison made it possible to evaluate the performance of wireless acceleration sensor system. As a result, it was proven that the wireless acceleration sensor system developed with the use of MEMS sensor and bluetooth wireless communication module could be effectively applied to the measurement of structure whose vibration feature was low frequency like a bridge.

• Journal of the Korean Magnetics Society
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• v.20 no.6
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• pp.222-227
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• 2010

$BiFeO_3$ (BFO) thin films were deposited on Pt/Ti/$SiO_2$/Si(100) substrates by RF magnetron sputtering method at room temperature. The influence of the flow rate of $O_2$ gas on the preparation of $BiFeO_3$ thin films was studied. XRD results indicate that the $BiFeO_3$ thin films were crystallized to the perovskite structure with the presence of small amount of impurity phases. The flow rate of $O_2$ gas has great affect on the microstructures and magnetic properties of $BiFeO_3$ thin films. As flow rate of $O_2$ gas increased, roughness and grain size of the thin films increased. $BiFeO_3$ thin films exhibited weak ferromagnetic behavior at room temperature. The PFM images revealed correlation between the surface morphology and the piezoresponse, indicating that the piezoelectric coefficient is related to microstructure.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.3-10
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• 1993

Polycrystalline CdS thin films were grown on ceramic substrate using a chemical bath deposition method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdS polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdS samples annealed in $N_{2}$ gas at $550^{\circ}C$ it was found hexagonal structure whose lattice constants $a_{o}$ and $c_{o}$ were $4.1364{\AA}$ and $6.7129{\AA}$, respectively. Its grain size was about $0.35{\mu}m$. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility defending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33K and 150k and by polar optical scattering at temperature range of 150K and 293K. We measured also spectral response, sensitivity (${\gamma}$), maximum allowable power dissipation and response time on these samples.