• 한국음향학회지
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• 제16권3호
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• pp.45-50
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• 1997

쐐기각이 다른 4종류의 쐐기형 수중음파 흡수타일을 설계, 제작하고 각각의 흡음타일에 대한 반사음장의 크기를 측정하였다. 흡음타일의 정면에서 측정한 반사음장의 크기는 실험한 4개의 타일중 쐐기의 꼭지각이 30$^{\circ}$일 때 최소값을 갖고 120$^{\circ}$일 때 최대값을 가졌다. 쐐기형 흡음타일의 꼭지각이 클수록 그 반사계수가 증가되는 것을 확인하였다. 또한 본 실험에 사용된 10kHz~30kHz 주파수 범위에서 쐐기각이 같은 흡음판에 의한 반사음장의 크기는 주파수와 무관하였다. 그리고 쐐기형 흡음타일 후면에서 측정한 반사음장의 크기는 흡음판의 형태와 실험에 사용된 주파수들에 무관한 일정한 값을 가졌다. 쐐기형 흡음타일의 반사음장에 대한 측정값과 수치모델에 의한 계산값은 대체로 잘 일치하였다.

• 한국해양공학회지
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• 제1권1호
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• pp.138-143
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• 1987

Friction welding has emerged as a reliable process for high-production commercial applications with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristcs of the pulse echo effects according to various change in welding conditions. This paper presents an attempt to determine the relationship between the varios welding conditions and the coefficients of reflection using the ultrasonic pulse echo method in dissibilar metals friction weld. The new approach of calculating the coefficients of reflection based on measured amplitudes of the echoes is applied in this paper. These coefficients provides a single quantitative measurement which involves both acoustic energy reflected at the welded interface as well as transmitted across the interface. As a result, it was known that the quantitave relationship between welding conditions and the coefficients of reflection using the ultrasonic pulse echo exists in dissimilar metals friction weld.

• 비파괴검사학회지
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• 제33권3호
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• 한국세라믹학회지
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• 제38권11호
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• pp.980-986
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• 2001

5.2GHz 중심 주파수를 갖는 Bragg reflector형 FBAR를 제작하여 주파수 응답 특성을 측정하고, 공진기 구조에서 각 층의 탄성 손실(acoustic loss)을 고려한 주파수 응답의 수치적 계산을 통해서 그 특성을 분석하였다. W과 $SiO_2$쌍을 선택하여 RF sputtering법으로 총 9층의 Bragg reflector를 제작하였고, 공진기의 압전층으로 pulsed dc 전원에 의한 sputtering법으로 AlN과 Al 전극을 증착하여 제작하였다. 제작된 공진기의 반사손실( $S_{11}$)은 중심주파수 5.38GHz에서 12dB이었고 직렬 공진 주파수( $f_{s}$)는 5.376GHz, 병렬 공진 주파수 ( $f_{p}$)는 5.3865GHz로 관찰되었다. 공진기의 성능지수인 유효 전기기계결합계수( $K_{ef{f^2}}$)값이 약 0.48%, 품질계수 ( $Q_{s}$) 값이 411이었다. 수치적으로 계산된 주파수 응답 특성으로부터 AlN 박막의 acoustic 상수들과 Bragg reflector의 반사계수를 도출한 결과 AlN 박막의 material acoustic impedance와 wave velocity는 AlN 고유의 값보다 감소되었으며, AlN 박막의 전기기계 결합계수( $K^2$)값은 c축 배향성 저하에 의해 매우 작은 값(0.49%)을 가졌다. 주파수 대역에서 Bragg reflector의 반사계수는 약 0.99966으로 계산되었으며 약 2.5 GHz에서 9.5 GHz까지의 넓은 반사대역을 나타내었다.다.었다.

• 한국음향학회지
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• 제25권1호
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• pp.1-6
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• 2006

천해에서의 수중음장 계산에서 음향 임피던스를 해저면 입력인자로서 도입하는 방안의 가능성을 고찰하였다. 먼저 탄성 해저면에서의 음파반사 특성을 고찰한 결과, 임계 접지각 이하에서 음향 임피던스는 접지각이 거의 $0^{\circ}$에 가까울 때의 임피던스 $Z_0$ 1개 값으로 근사가 가능함을 나타내었다. 이러한 특성과 'effective depth' 개념을 접목시켜 전달손실을 계산한 결과, 수중음장 계산에서 임피던스를 해저면 음향 특성을 나타내는 입력인자로 사용하는 것이 가능성이 있음을 확인하였다.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1143-1148
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• 2002

This paper analyses the transient response of a spherical elastic shell located near fee surface and impinged by spherical step-exponential acoustic shock waves. The problem is solved through extension of a method (Huang, 1969) previously formulated for the excitation in an infinite domain, which employs the classical separation of variables, series solutions, and Laplace transform technique The effect of the free surface reflection is taken into account using the image source method. The reflection of the incident wave has been treated by the same image formulation. If the reflection of the pressure field scattered and radiated by the shell is considered, the problem becomes that of multiple scattering by two spheres. However, this is in general negligible considering errors inherent from other sources and that the scattered and radiated pressure waves emanating from the shell are small. Thus, the problem is reduced to that of a structure immersed in an infinite fluid and impinged upon the origin and the image incident.

• 전기학회논문지
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• 제56권8호
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• pp.1430-1435
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• 2007

We developed a 440MHz surface acoustic wave (SAW) microsensor integrated with pressure-temperature sensors and ID tag. Two piezoelectric substrates were bonded, in which ${\sim}150\;{\mu}m$ cavity was structured. Four sides were completely sealed by JSR photoresist (PR). Pressure sensor was placed on the top substrate, whereas ill tag and temperature sensor were placed on the bottom substrate. Using network analyzer, the developed microsensor was wirelessly tested. Sharp reflection peaks with high S/N ratio, small signal attenuation, and small spurious peaks were observed. All the reflection peaks were well matched with the coupling of mode (COM) simulation results. With a 10mW RF power from the network analyzer, a ${\sim}1$ meter readout distance was observed. Eight sharp ON reflection peaks were observed for ID tag. Temperature sensor was characterized from $20^{\circ}C$ to $200^{\circ}C$. A large phase shift per unit temperature change was observed. The evaluated sensitivity was ${\sim}10^{\circ}/^{\circ}C$.

• 한국항행학회논문지
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• 제27권4호
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• pp.469-472
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• 2023

If temperature management is required in factory or environmental monitoring, temperature can be measured by connecting various sensors wired or wirelessly. Surface acoustic wave sensors measure temperature using changes in acoustic waves on the sensor surface according to temperature, and are useful for wireless networks. In this paper, in order to build a wireless temperature measurement system in the 900 MHz frequency band, the temperature characteristics of the passive SAW sensor were measured, and the analysis and removal of multipath reflection wave effect inside the high temperature chamber were conducted. The resonant frequency of the SAW sensor was measured, and radio transmission/reception and multipath reflected wave removal techniques were proposed in the shielded chamber.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.1044-1049
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• 2007

The construction of concrete slab track system is increased because the system has advantages which are maintenance free and so on, the other side, the system has weak points such as increase of the cost of the early stage construction and noise levels. The increment of noise is due to the reflection of generated noise on the slab tracks. Therefore the acoustic-absorptive materials are considered to reduce noise level. It has been made clear that acoustic-absorptive materials are effective for reducing the wheel/rail noise on slab tracks. The important performance of the acoustic-absorptive material is absorption rates and absorption rates are verified for the considered absorber elements using acoustic duct method. In addition, the required provisons for installing acoustic-absorptive block on slab tracks are considered.

• 한국음향학회지
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• 제25권5호
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• pp.246-256
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• 2006

평면파 반사 계수는 수중에서의 음파에너지에 관한 해저 바닥의 모든 정보를 담고 있고 음향 해석 모델의 입력 값으로도 사용할 수 있는 음향학적 물리량이다. 본 연구에서는 실험실 수조 환경에서 입자 매질 ( 세 종류의 유리구슬, 모래 )의 평면파 반사 계수, 음속 및 감쇠계수를 측정했다. 반사 실험은 수조의 한계를 고려해 $28{\sim}53^{\circ}$의 입사각과 중심 주파수 100kHz의 협대역 신호를 이용해 수행했다. 자기 교정법 (Self-calibration method)을 이용해 측정된 자료로부터 반사 계수를 계산했고 측정된 반사 계수의 경향 및 실험의 불확실성을 서술했다. 입자 매질의 음속 및 감쇠계수는 거리 수신 신호간의 회귀분석을 통해 계산했다. Biot 이론을 이용해 측정된 음속과 감쇠계수로부터 다공율과 침투율을 추정하고 실제 지질학적 측정값과의 유사성을 확인했다. 최종적으로 추정된 다공율, 침투율을 이용해 이론적 인 반사 계수를 계산하고 반사 실험의 측정값과 비교했다. 본 실험 결과는 Biot 이론으로 일관성 있게 입자 매질의 음향학적 물성을 설명할 수 있음을 입증한다.