• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.191-191
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• 2008

강유전성 세라믹스 재료로써는 PZT계열의 세라믹재료가 널리 쓰이고 있다. 이는 우수한 유전 및 압전특성을 가지고 있으나, PbO을 다량 함유하고 있어 $1000^{\circ}C$이상에서 PbO가 급격하게 휘발되는 성질 때문에 조성의 변동이 생겨 재현성이 어려우며 이를 방지하기 위하여 PbO를 과잉 첨가시키기 때문에 PbO휘발로 인한 강한 독성이 인체에 유해하고, 비환경 친화적인 물질로 최근에는 환경문제가 대두됨에 따라 대체 또는 보완 할 수 있는 방안에 검토되고 있다. 본 연구는 그 해결책의 한 방안으로 압전특성이 우수한 $(Pb_{0.94}Sr_{0.06})[(Ni_{1/2}W_{1/2})_{0.02}(Mn_{1/3}Nb_{2/3})_{0.07}(Zr_{0.51}Ti_{0.49})_{0.91}]O_3$계 조성을 설계하고 Glass frit(0~1.1 wt%)를 소량 첨가하여 액상 소결 특성을 부여하고 $1000^{\circ}C$ 이하의 저온에서 소결하여 유전 및 압전 특성을 평가하였다. 실험방법은 일반적인 세라믹스 제조공정으로 24시간 ball milling하고 $850^{\circ}C$에서 2시간 하소 후 Glass frit를 소결조제로 소랑 첨가하여 $1000^{\circ}C$ 이하 온도에서 소결을 진행하여 각 소결온도에 따른 유전 및 압전 특성을 평가하였다. 최종 소결된 시편의 밀도와 수축율을 분석하여 최적의 소결온도를 확립하였으며 XRD분석을 통해 perovskite구조를 확인하고 미세구조확인을 위해 SEM으로 관찰하였다. 압전 특성을 평가하였다.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.466-472
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• 2016

In this work, a medical linear array ultrasonic transducer working in the range of 20 MHz has been developed for high-resolution ultrasonic imaging. After devising the structure of the transducer suitable for the transmission of high-frequency waves, we optimized the dimension of constituent components. Then, the process to fabricate the transducer was developed to realize the designed structure, and a prototype of the transducer was fabricated and characterized. The center frequency of the fabricated transducer was measured to be 19 MHz, and the fractional bandwidth to be 84.5 %, and the standard deviation of the sensitivity over the entire channels to be 0.74 dB. These measurement results showed good agreement with design data, which confirmed the validity of the high frequency ultrasonic transducer structure developed in this work. It was confirmed that the developed transducer with new structure had wider frequency bandwidth and uniform sensitivity than a conventional 20 MHz transducer.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.135-138
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• 2004

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride­trifluoroethylene) (P(VDF-TrFE)) copolymer have been used as a sensor. The advantages of polymer sensor are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. Polymer sensor can be directly embedded in a structure. In this study, nondestructive damage sensitivity of single basalt fiber/epoxy composites was investigated with sensor type and thermal damage using AE and oscilloscope. And AE waveform for epoxy matrix with various damage types was compared to each other. The damage sensitivity of two polymer sensors was rather lower than that of PZT sensor. The damage sensitivity of PVDF sensor did not decrease until thermal damage temperature at $80^{\circ}C$ and they decreased significantly at $110^{\circ}C$ However, the damage sensitivity of P(VDF-TrFE) sensor at $110^{\circ}C$ was almost same in no damage sensor. For both top and side impacts, the difference in arrival time increased with increasing internal and surface damage density of epoxy matrix.

• Korean Journal of Materials Research
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• v.25 no.10
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• pp.566-570
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• 2015

$Bi_{0.5}Na_{0.5}TiO_3$ (BNT) based ceramics are considered potential lead-free alternatives for $Pb(Zr,Ti)O_3$(PZT) based ceramics in various applications such as sensors, actuators and transducers. However, BNT-based ceramics have lower electromechanical performance as compared with PZT based ceramics. Therefore, in this work, lead-free bulk $0.99[(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}]_{(1-x)}La_xTiO_3-0.01SrZO_3$ (BNBTLax-SZ, with x = 0, 0.01, 0.02) ceramics were synthesized by a conventional solid state reaction The crystal structure, dielectric response, degree of diffuseness and electric-field-induced strain properties were investigated as a function of different La concentrations. All samples were crystallized into a single phase perovskite structure. The temperature dependent dielectric response of La-modified BNBT-SZ ceramics showed lower dielectric response and improved field-induced strain response. The field induced strain increased from 0.17%_for pure BNBT-SZ to 0.38 % for 1 mol.% La-modified BNBT-SZ ceramics at an applied electric field of 6 kV/mm. These results show that La-modified BNBT-SZ ceramic system is expected to be a new candidate material for lead-free electronic devices.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.187-190
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• 2002

In contrast to conventional electromagnetic motor, USM(Ultrasonic Motor), as piezoelectric ceramic applying ultrasonic mechanical vibration and as frictional-movement type motor, get rotational torque by elastic friction between stator and rotator, The USM, which is small motor without iron cores and coil as a simple structure, has little load weight, has character of high torque at low speed, and can apply a direct drive type without deceleration gear as low speed type. A response of USM from control input is satisfactory, and also generates much torque in low speed driving, and holding torque is much without supplying power. In this study, I designed and made Ultrasonic motor-digital multi controller(USM- DMC) using FPGA chip, A54SX72A made in Actel Corporation. By the minute, USM-DMC can control frequency, duty ratio, and phase difference of USM by llbit digital input from Pc. Therefore, when we use this controller, we can apply to typical parameter, frequency, phase difference, and voltage parameter, to control as well as we can do mixing control like phase-frequency, phase-voltage, frequency-voltage, frequency-phase-voltage, What is more, the strongest point is that it can trace frequency based on optimized frequency because we can input optimized resonant frequency while in motoring.

• Journal of Sensor Science and Technology
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• v.5 no.3
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• pp.25-31
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• 1996

Steel wires are made by elongating hot billets. If the billets have internal or surface defects, the wire can be broken during elongation process. After testing surface defect, we are testing internal defect by ultrasonic transducers. POSCO is producing two kinds of billets, hot rolled billet and cast billet. Hot rolled one is denser than cast billet. Because of the low density and rough surface, ultrasonic testing is difficult for the cast billet. Size of the transducer was related with the size and density of the billet. A transducer having 21mm long, 8.5mm wide and 0.95mm thick piezoelectric ceramic plate was best for $160mm\;{\times}\;160mm$ cast billet. Center frequency of the transducer was 2.25MHz and the focus distance was 70mm.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.313-320
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• 2007

Recently, a new class of single-crystal piezoelectric materials such as lead metanibobate doped with lead titanate (PMN-PT) has been synthesized and were found to further enhance the electro-mechanical coupling factor compared to piezo-ceramic materials. This paper describes fabrication and evaluation of PMN-PT single crystal ultrasonic transducers for contact measurement of stainless steel that is one of the highly attenuative materials. The design conditions for ultrasonic transducer such as front matching layer between test materials and piezo-material and backing materials were investigated based on the simulation results by KLM model. The PMN-PT single crystal ultrasonic transducers with centre frequencies at 1 and 2.25 MHz were fabricated and their performances were evaluated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.4
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• pp.407-411
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• 2022

Bulk-sized PbTiO₃ (PT), which is widely known as a high-performance ferroelectric oxide but cannot be fabricated into a monolithic ceramic due to its high c/a ratio, was successfully prepared with a high tetragonality by partially substituting Ni ions for Pb ions using a solid-state reaction method. We found that Ni-doped PT was well-fabricated as a bulk monolith with a significant c/a ratio of ~1.06. X-ray diffraction on as-sintered and crushed samples revealed that NiTiO₃ secondary phase was present at the doping level of more than 2 at.%. Scanning electron microscopic study showed that NiTiO₃ secondary phase grew on the surface of PT specimens regardless of the doping level possibly due to the evaporation of Pb during sintering. We demonstrated that an unconventional introduction of Ni ions into A-site plays a key role on the fabrication of bulk PT, though how Ni ion functions should be studied further. We expect that this study contributes to a further development of displacive ferroelectric oxides with a high c/a ratio.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.505-512
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• 2023

This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bi-based lead-free ferroelectric/relaxor composites. Bi_1/2Na_0.82K_0.18)_1/2TiO₃ (BNKT) as a ferroelectric material and 0.78Bi_1/2(Na_0.78K_0.22)_1/2TiO₃-0.02LaFeO₃ (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (S_max) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest S_max/E_max value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.526-526
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• 1996

The single crystal of LiTaO3 is well known eletro-optic material as well as the piezoelectric one applied to SAW filter. LiTaO3 has large electro-optic effects, so applied to optical switch, acosto-optic deflector, and optical memory device using photorefractive effects. The crystal growth of SAW-grade LiTaO3 has been studied many aspects, but there is no detail research about optic-grade crystal growth. The conditions of optic-grade LiTaO3 single crystal are as below. The optical transmittance must be over 75%, and axial and radial concentratiom uniformity below 1%. The variation of Curie temperature depending on Li/Ta ratio must be also below 2$^{\circ}C$ and no internal no internal cracks and defects. Because of the limitation of crystal quality, the growing of optic-grade LiTaO3 single crystal is very difficult compared with the growing of SAW-grade. In this research, upper conditions of optic-grade single crystal was investigated after growing of 1 inch diameter and 1.5 inch length LiTaO3 single crystal having no internal cracks and defects using Czochralski method. Curie temperature was determined with DSC and measuring capacitance and lattice parameter was calculated about the grown crystal and ceramic powder samples of various Li/Ta ratio. The result of Tc variation was below 1.2$^{\circ}C$ all over the grown crystal, so it is confirmed that LiTaO3 was grown under congruent melting composition having optical homogeniety. Also, the optical transmittance was about 78%, which was sufficient for optical device.