• Journal of IKEEE
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• v.22 no.1
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• pp.201-204
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• 2018

We know that the piezoelectric constant d, the dielectric constant, and the electric-mechanical coupling coefficient affect the output for piezoelectric ceramics used in ultrasonic welders. Therefore, in this study, the characteristics of ceramics according to the changes of additives to the components of PZT-PMN-PZW were examined. When the addition amount of $MnO_2$ was 2 wt%, the most excellent properties were shown, which suggested the applicability as a material for fusion welding.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.167-170
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• 1999

초음파 변환기의 음향 특성 평가항목으로는 주파수에 따른 출력특성, 입력 전압에 대한 출력의 선형성(방사컨덕턴스), 방사음장의 지향성 및 대칭성 등을 들 수 있다. 평면 주사기법은 교정된 하이드로폰을 이용하여, 초음파 변환기에서 방사된 음파가 형성하는 음장의 분포를 측정하는 기법이다. 본 연구에서는 이들을 측정할 수 있는 장치로 DC servo모터를 장착한 3 축 이송 장치와 가로 400 mm, 세로 800 mm, 높이 400 m를 갖는 수조를 제작하고 제어프로그램을 개발하여 상온의 증류수에 형성된 초음파 음장의 공간 분포를 실험하여, 이론적 예측값과 비교하였다.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.17-24
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• 2002

The objective of the present research is to evaluate the wave propagation velocity and attenuation characteristics of kaolin clay specimens using ultrasonic testing. Test specimens with known initial micro-fabric were prepared using a two-stage slurry consolidation technique. For a known state of stress conditions, initial void ratio, and micro-fabric, a series of experiments were conducted to evaluate the longitudinal wave propagation velocity and associated damping behavior. The effects of major variables involved in ultrasonic testing of cohesive soil were considered in this study. Ultrasonic velocity was not correlated to the microfabric structure under the given consolidated pressure whereas ultrasonic attenuation was affected by the microstructural properties of the specimen.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1213-1215
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• 2008

분산능력은 나노콤포지트의 제반적인 물성에 큰 영향을 준다. 그러나 유기용매를 사용한 분산능력은 전기적 절연특성에 불순물케리어로 작용되는 경우가 있어 오히려 절연성능 즉, 결합이 약하게 작용되는 결과를 가져오게 된다 이런 이유로 물리적인 분산법인 강력초음파법을 이용하여 Epoxy/Organoclay_93A 나노콤포지트를 제조하였다. 최적의 초음파 적용시간을 연구하기위해 강력초음파를 15,30,60,120분 각각에 대해 적용하였다. 적용시간은 기계적,전기적인 물성에 독립적인 특성을 나타내었다. 그러나 전반적인 물성의 비교에서 최적의 초음파 적용시 60분의 경우가 가장 양호한 결과를 얻었다. 기계적, 전기적인 물성에서 1차경화만으로 측정자료로 최적의 2차 경화를 가져가하면 더욱 높은 물성을 가져오게 될 것이다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.80-85
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• 2000

The rheology of alumina slurries with maltodextrin was studied with different processing routes using experimental design and statistical analysis. Different processing routes include maltodextrin addition, different ultrasonication intensity applied to the slurries before or after adding maltodextrin, and shaking time. Viscosities of the slurries showed shear thinning behavior and were correlated with the Ostwald-de-Weale model. The viscosities of alumina slurries decreased with the addition of maltodextrin and increased with ultrasonication intensity. There were little differences in the viscosities of the slurries depending on whether maltodextrin was added before or after ultrasonication.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.628-631
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• 2017

An experimental study of the combustion characteristics according to the equivalence ratio of hydrocarbon fuel/air premixture excited by ultrasonic standing wave are presented. The image of the propagating flame was acquired using a high-speed camera, and the combustion characteristics of each fuel were closely observed through image processing. it was conformed that ultrasonic standing wave has been found to stimulate the combustion reaction in the stoichiometric ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.282-283
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• 2007

압전소자의 초음파 진동을 구동원으로 하는 초음파 모터의 토오크 특성을 개선하기 위하여 양면 Teeth 구조를 가지는 진행파 여진용 고정자를 설계하고, 이를 유한요소해석 프로그램 ATILA-GID를 이용하여 변위분포를 해석하였다. 한 면에만 Teeth 구조를 가지는 기존의 고정자를 이용한 초음파 모터가 소형화, 제한된 토오크 응용분야에 있어서 Direct drive actuation을 위한 발판을 마련해 주었다면, 본 연구에서 제안하는 양면 Teeth 구조의 고정자는 토오크와 효율, 출력특성의 개선과 함께 구조적인 특성에서 기인하는 온도 안정성에 의하여 그 응용분야의 확대를 기대할 수 있다.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.99-104
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• 2021

The characteristics of wind sensors were experimentally analyzed and compared for purposes of application in multicopter type drones. For rotating wind sensors, the dynamics effect causes measurement errors, while manufacturing errors and signal processing errors were found to constitute significant errors in ultrasonic sensors. In the ultrasonic sensor, the errors decrease as the distance of the transducer increases. These characteristics were experimentally confirmed, and it was established that ultrasonic sensors capable of outputting voltage or data of 10 Hz or more are suitable for use in multicopters.

• Food Science and Preservation
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• v.23 no.5
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• pp.660-665
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• 2016

The effects of ultrasound-assisted extraction (UAE) on the physicochemical and sensory characteristics of coffee beverage were investigated. Coffee powder (4 g) was soaked into 80 mL distilled water and extracted for 15, 30, 60, 120, 180, 240, or 300 sec at $60^{\circ}C$ in an ultrasonic bath (40 kHz, 300 W). Hot-water extraction (HE) at $80^{\circ}C$ for 300 sec was used as a control. Content of soluble solids in coffee beverage prepared by UAE (60~300 sec) was same or higher than those of HE, however, no significant differences were observed among the four beverages extracted for more than 120 sec. Clarity and browning index of beverage prepared by UAE (15 sec) and by HE were significantly higher and lower, respectively, compared to those of the other. Content of phenolic compounds was lower and higher respectively, in beverage prepared by UAE (15 sec, 30 sec) and UAE (60~300 sec) than by HE. DPPH radical scavenging activity was highest in beverage prepared by UAE (15 sec) and HE. Sensory evaluation showed that color, aroma, taste, and overall acceptability were rated with the best score for beverage prepared by UAE (15 sec) and the worst score for beverage prepared UAE (120~300 sec). Therefore, ultrasound-assisted extraction can be used for improving quality of coffee beverage.

• Korean Journal of Food Science and Technology
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• v.49 no.5
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• pp.507-512
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• 2017

The physicochemical properties of maize starch sonicated at various amplitudes (100, 200, and 300 W) and times (10, 30, and 50 min) were examined. The amount of enzyme-susceptible starch increased marginally after sonication. Sonication increased the amount of oil absorbed in the starch although the degree of oil absorption decreased with an extension of the sonication time, implied that different types and extent of damages occurred. Scanning electron microscopy revealed that ultrasound sonication did not form pores on the surfaces, but caused damages such as depression and erosion. Pasting viscosity of starch decreased with an increase in the severity of sonication conditions because of the weakened polymer network. X-ray diffraction suggested that the crystalline domains in starch were not susceptible to sonication and were more resistance to degradation. Sonicated starch formed more pin-holes on the surfaces in the initial glucoamylase reaction; subsequently, as the reaction proceeded, porous starch with enlarged pores was formed and finally, disrupted granular fragments were observed.