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음향 매질의 추가질량 효과를 고려한 광음향 영상용 초소형 압전 기반 초음파 트랜스듀서의 개발
안홍민 ( Hongmin Ahn ),문원규 ( Wonkyu Moon ) 한국센서학회 2020 센서학회지 Vol.29 No.1
Typically, photoacoustic images are obtained in water or gelatin because the impedance of these mediums is similar to that of the human body. However, these acoustic mediums can have an additional mass effect that changes the resonance frequency of the transducer. The acoustic radiation impedance in air is negligible because it is very small compared to that of the transducer. However, the high acoustic impedance of mediums such as the human body and water is quite large compared to that of air, making it difficult to ignore. Specifically, in a case where the equivalent mass is very small, such as with a micro-machined ultrasound transducer, the additional mass effects of the acoustic medium should be considered for an accurate resonance frequency design. In this study, a piezoelectric micro-machined ultrasonic transducer (pMUT) was designed to have a resonance frequency of 10 MHz in the acoustic medium of water, which has similar impedance as the human body. At that time, the resonance frequency of the pMUT in air was calculated at 15.2 MHz. When measuring the center displacement of the manufactured pMUT using a laser vibrometer, the resonance frequencies were measured as 14.3- 15.1 MHz, which is consistent with the finite element method (FEM) simulation results. Finally, photoacoustic images of human hair samples were successfully obtained using the fabricated pMUT.
Design of ferromagnetic shims for an HTS NMR magnet using sequential search method
Hongmin Yang,SangGap Lee,Minchul Ahn 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4
This study deals with the ferromagnetic shims design based on the spherical harmonic coefficient reduction method. The design method using the sequential search method is an intuitive method and has the advantage of quickly reaching the optimal result. The study was conducted for a 400 MHz all-REBCO magnet, which had difficulty in shimming due to the problem of SCF (screening current induced field). The initial field homogeneity of the magnet was measured to be 233.76 ppm at 20 mm DSV (Diameter Spherical Volume). In order to improve the field homogeneity of the magnet, the ferromagnetic shim with a thickness of 1 mil to 11 mil was constructed by a design method in which sequential search algorithm was applied. As a result, the field homogeneity of the magnet could be significantly improved to 0.24 ppm at 20 mm DSV and 0.05 ppm at 10 mm DSV.
Optimal Design Methodology of Multiwidth HTS Magnet for Minimum Wire Consumption
Ahn, Min Cheol,Yang, Hongmin,Kim, Kyungmin,Jang, Jae Young,Lee, SangGap,Hahn, Seungyong Institute of Electrical and Electronics Engineers 2018 IEEE transactions on applied superconductivity Vol.28 No.3
<P>This paper investigates an optimal design methodology for multiwidth (MW) high-temperature superconductor (HTS) magnets, where pancake coils wound with the narrowest tapes were placed at and near the magnet center and those with progressively wider tapes toward the top and bottom of the magnet. For a given design, target of field strength and winding bore, input parameters include tape width, number of grading tapes, and number of pancakes coils, while the main objective is to minimize the magnet volume, i.e., essentially the stored energy and thus the cost. A magnet with a single-width tape is also designed as a control sample for comparison. A case study on a design of 3-T 240-mm HTS magnet was carried out. In that case, MW magnets save 40% wire consumption of single-width magnets. The results are expected to be beneficial to determine the practical level of HTS tape grading and estimate a volume of an MW magnet.</P>
Furbee, Brittany,Ahn, Hongmin The International Promotion Agency of Culture Tech 2019 International Journal of Advanced Culture Technolo Vol.7 No.4
In this study, we attempted to identify the personality traits that influence one's likelihood to stalk an ex-partner on Facebook. Specifically, we focused on self-concept-related traits, given that the motivations for using social network sites (SNS) are highly associated with the concept of self. These include self-esteem, narcissism, and self-efficacy. To assess these factors, we controlled for extraneous variables while assessing the predictive power of personality traits, such as Facebook usage, length of the relationship, and time since the break-up. The results of a self-administered, web-based survey (N=207) showed that self-esteem, narcissism, and self-efficacy are all traits that can predict the stalking of an ex-partner on Facebook. More specifically, we showed a negative association between self-esteem and one's likelihood to stalk an ex-partner on Facebook, while it showed positive relationships between Facebook stalking and both narcissism and self-efficacy.
An underwater parametric array source transducer composed of PZT/thin-polymer composite
Hwang, Yonghwan,Ahn, Hongmin,Nguyen, Duc-Nam,Kim, Wonho,Moon, Wonkyu Elsevier 2018 Sensors and actuators. A, Physical Vol.279 No.-
<P><B>Abstract</B></P> <P>The source transducers for parametric array (PA) sound are required to radiate the primary wave with high intensity and directivity so as to generate nonlinear interactions between strong acoustic waves at different frequencies effectively, resulting in so-called PA sound. Thickness-mode piezoelectric transducers using 1–3 lead zirconate titanate (PZT) polymer composites were used to produce wide-bandwidth PA sound due to their ability to generate high-intensity, high-frequency sound beams over a relatively wide frequency band. The small mechanical quality factor of 1–3 PZT polymer composites results in high damping of the polymer matrix leading to a transducer with relatively flat frequency response but yet decreased-power efficiency. A PZT polymer composite that can enhance the power efficiency of a PA source transducer over a wide frequency bandwidth was proposed. This is achieved by adopting thinner polymer matrix layers and PZT rods with dual resonance frequencies. A transducer demonstrated ultrasonic sound up to 197 and 203 dB (re = 1 μP) at 98 and 135 kHz, respectively. The power efficiencies were 50% at 98 kHz and 33% at 135 kHz. PA sound was successfully generated up to 150 dB (re = 1 μP) at 30 kHz with a half-power beam width of 3.4°.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Source transducer was suggested for parametric array in underwater. </LI> <LI> The source transducer is PZT/thin-polymer composite. </LI> <LI> The transducer has characteristics of wide frequency bandwidth and high radiation efficiency. </LI> </UL> </P>
원자력발전소 시뮬레이터 데이터의 패턴인식을 이용한 압력경계기기 고장 진단 연구
안홍민,최현우,강성기,채장범,Ahn, Hongmin,Choi, Hyunwoo,Kang, Seongki,Chai, Jangbom 한국압력기기공학회 2017 한국압력기기공학회 논문집 Vol.13 No.1
We diagnosed the defect using the data obtained from the nuclear power plant simulator. In this paper, we diagnosed faults in the nuclear power plant system for discovery instead of the traditional single-component or device unit. We created the six fault scenarios and used a fault simulator to obtain the fault data. It was extracted pattern from acquired failure data. Neural network model was trained and simple pattern matching algorithm was applied. We presented a simulation result and confirmed that the applied algorithm works correctly.
한류 아이돌 굿즈 구매의도의 예측변수에 관한 연구 : 애착유형에 따른 효과를 중심으로
총효위(Cong, Xiaowei),안홍민(Ahn, Hongmin) 계명대학교 사회과학연구소 2021 한국사회과학연구 Vol.40 No.3
본 연구의 목적은 K-pop 해외 팬들의 아이돌 굿즈 구매의도에 영향을 미치는 원인을 구체적으로 탐구하며 이들의 영향 관계를 파악하는 데 있다. 이를 위해 발달 심리학에서 발전한 개념인 애착유형이 굿즈 구매에 미치는 영향에 따른 효과를 검증하였다. 애착유형 이외에도 아이돌 관련 SNS 이용정도, 한류 콘텐츠의 선호도, 아이돌 팬덤 활동에 대한 태도에 따른 한류 아이돌 굿즈의 구매의도에 관한 가설을 제시하였다. 가설 검증을 위해 중국에 거주 중인 10-40대 남녀 297명을 대상으로 온라인 설문을 실시한 결과, 몰두형 애착 유형은 아이돌 굿즈 구매의도에 유의미한 정(+) 영향을 미치지만, 안정형 애착 유형은 영향이 없는 것으로 나타났다. 이 외에도 아이돌 관련 SNS 이용정도, 한류 콘텐츠 선호도는 아이돌 굿즈 구매의도에 유의미한 정(+) 영향을 미치는 것으로 나타났다. 또한 몰두형 애착유형과 굿즈 구매의도의 관계에 대한 매개분석 결과, 아이돌 팬덤 활동에 대한 태도가 매개변수의 역할을 하는 것으로 확인되었다. 본 연구는 학술적으로 아이돌 팬덤이라는 특정 소비층에 애착이론을 확대 적용하고 독립변수와 종속변수 간의 관계 탐색에 더해 매개변수를 규명하여 구매의도의 예측 변인을 다각도로 탐색하였다는 데 의의가 있다. 또한 실무적으로 아이돌 굿즈 마케팅에 대한 이해를 넓히고 향후 홍보 가이드라인을 제시하여 효과적인 마케팅 전략의 방안을 제시하고자 하였다. This paper attempts to identify factors affecting purchase intentions for K-pop idol goods, based on the attachment theory and previous studies on fandom culture. The results of the online survey among K-pop fans in China show that the preoccupied attachment has positive effects on purchasing intention for idol goods whereas secure attachment has no influence. In addition to the attachment type, SNS usage and preference of Korean content have positive influence on fans’ purchasing intention of idol goods. Moreover, this study suggests that attitudes toward idol fandom behaviors mediate the relationship between attachment type and purchase intentions for K-pop idol goods. By applying the attachment theory in fandom culture, this study provide a better understanding of factors affecting purchase intentions for K-pop idol goods. In practice, promotional guidelines for effective idol marketing are also presented through research results.