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김철기(C. G. Kim),김호철(H. C. Kim),윤석수(S. S. Yoon),박덕근(D. G. Park),홍준화(J. H. Hong),지세환(S. H. Jee) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.2
The complex magnetic susceptibility of as-quenched and proton irradiated amorphous ribbons of Fe_(81)B_(13.5)Si_(3.5)C₂ was measured in the frequency range 10 ㎑ ~ 10 ㎒. The frequency spectra of real and imaginary parts of susceptibility showed a typical Debye-type relaxation. Relatively high relaxation frequency, ~3 ㎒ observed in the present work suggested that domain rotation is involved in the relaxation process. The susceptibility at the low frequency decreased with the irradiation, while that at high frequency increased due to the increasing defect density. The relaxation frequency of domain rotation shifted toward higher frequency. due to the increasing pinning force against domain motion by the irradiation.
두상 혼합체의 유전 반응에 대한 deterministic fractal circuit 모델
윤석수,권성덕 안동대학교 기초과학연구소 1996 基礎科學 硏究論文集 Vol.7 No.1
일반적인 형태의 fractal two phases mixtures의 유전반응을 deterministic fractal circuit(DFC)모델을 통해 해석적으로 다룬다. 열의 수가 2로 한정된 Dissado-Hill에 의해 고려된 모델이 일반적인 열의 수를 포함하는 경우로 확장된다. 일반적인 DFC model로부터 얻어지는 교류 impedance spectrum은 fractal mixture의 기하학적인 형태에 의존하는 지수를 가지는 fractional power-law response를 보여준다. 특히 impedance의 실수부와 허수부가 같이 주파수에 대해 fractional power-law 의존성을 가지는 constant-phase-angle response의 존재 조건이 유도된다. A deterministic fractal circuit(DFC) model for the dielectric response of general fractal mixture is analytically investigated. The Dissado-Hill`s model, where the number of row in the fractal mixture was confined to two, is generalized to include arbitrary number of rows. The impedance spectrum by DFC model shows fractional power-law dependence with the exponent depending on the structure of fractal mixture. Specially the condition for the existence of constant-phase-angle response is derived.
Directional Dependence of Magneto-impedance and Phase Angle in Co-based Amorphous Ribbon
윤석수,권성덕 안동대학교 기초과학연구소 2000 基礎科學 硏究論文集 Vol.11 No.1
The spectra of the absolute value of impedance and phase angle Φ were investigated in the amorphous Co66Fe4NiB14Si15 ribbons of various cutting angles with respect to the ribbon axis in as-quenched state. The profile for the magneto-impedance and -phase angle, |Z(H)| and Φ(H), at the frequency of 10 MHz showed a sensitive dependence on the cutting angle during continuous sweeping of external magnetic field H. The magnitudes of the dips for |Z(H)|and Φ(H) obtained from the profiles showed a broad maximum at α= 60℃. The magnitude of magneto-impedance showed a maximum at α= 0℃ and decreased as a increases, and the magnitude of magneto-phase angle also showed a maximum at α= 60℃ , and negligible at α= 90℃ . These results suggest that the magnetic anisotropy plays an important role in the magneto-impedance and the magneto-phase angle can be used as a phase value.
윤석수,권성덕 안동대학교 기초과학연구소 1997 基礎科學 硏究論文集 Vol.8 No.1
Impedance spectrum of a general scaled transmission line was analytically investigated as a model for the fractally rough electrode. The impedance spectrum showed constant phase-angle (CPA) response with the exponent depending on the fractal structure. The conditions for the existence of CPA response were derived and compared with the spectra obtained by numerical calculation.
권성덕,이승희,윤석수 韓國非破壞檢査學會 1999 한국비파괴검사학회지 Vol.19 No.5
액체/고체 경계면에 표면파가 발생할 때 나타나는 최소반사 및 후방복사 현상을 이용하여 brass와 aluminum 시편 그리고 copper/stainless steel, nickel/brass, nickel/aluminum 도금시편에 대한 표면 탄성파 속도의 주파수 의존성이 측정되었다. 측정된 속도의 분산관계는 일반화 램 표면파의 분산 특성과 잘 일치하였다. 시편들의 분산 특징에 따라 최소반사와 후방복사에 의해 결정된 속도 차이의 경향이 다르게 나타났다. 이러한 대응 관계는 두 현상의 생성 메커니즘과 군속도의 도입으로 설명되었다. Minimum reflection and backward radiation methods on liquid/solid interface were used to determine the velocity dispersion relation of acoustical surface wave for brass and aluminum substrates and copper/stainless steel, nickel/brass, and nickel/aluminum layered substrates. Dispersion data agreed to dispersion characteristics of a generalized Lamb wave. The difference between velocities determined by two phenomena was closely related to the dispersion characteristics. This correspondence was explained by considering the generation mechanism of surface waves and the concept of group velocity.
권성덕,윤석수,송성진,이영제 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.2
레일리(Rayleigh) 표면탄성파의 속도와 산란의 주파수 의존성을 이용하여 마모로 인해 열화된 AISI 1045강 시편의 깊이방향 잔류응력 분포(열화 기울기)의 비파괴적인 평가가 시도되었다. 액체/고체 경계면에 초음파가 특정각도로 입사할 때 발생한 표면탄성파의 산란과 복사로 인해 나타나는 후방복사 프로파일의 오른쪽 반치폭과 크기 그리고 발생각으로 잔류응력 분포의 해석도 가능하였으며 평균법에 의한 복사파의 세기 및 스펙트럼의 변화는 잔류응력 분포의 열화로 인해 발생한 미세 결함 밀도와의 연관성을 보여주었다. The frequency dependency of the Rayleigh surface wave was investgated indirectly by measuring the angular dependency of the backward radistion of the incident ultrasonic wave in the abrasion specimens, which was explained in view of the residual stress distribution. The peak intensity of the backward radiation profile decreased and the right halt width of the profile increased with an increase of the variational rate of residual stress for the scuffing specimen. The peak intency was also affected by the surface wave scattering during the propagation around the micro damages. The peak angle might depend on not only the amount of residual stress but also the micro-structure. The result observed in this study demonstrates the high potential od the backwatd radiated ultrasound as a tool for the nondestructive evaluation of the subsurface gradients of materials.