초음파 SPI 기초물리 및 기초원리

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1. Normal Incidence (Perpendicular Incidence)

정상 입사(수직 입사)는 음파 빔이 두 매질 사이의 경계면에 0°의 입사각으로 만나는 경우를 말한다. 이 경우 반사음은 입사음과 같은 방향으로 돌아오고, 투과음은 입사음과 같은 방향으로 계속 진행한다. 굴절은 일어나지 않는다.
2. Oblique Incidence

사선 입사는 음파 빔이 두 매질 사이의 경계면에 0°가 아닌 각도로 만나는 경우를 말한다. 이 경우 반사각은 입사각과 같고, 투과음은 굴절되어 진행한다. 굴절각은 매질의 음속 차이에 따라 달라진다. 사선 입사에서는 구조물의 가시화가 감소할 수 있다.
3. Refraction

굴절은 경계면에서 음파 빔의 진행 방향이 바뀌는 현상을 말한다. 이는 두 매질의 음속 차이로 인해 발생한다. 매질 2의 음속이 매질 1보다 크면 굴절각이 입사각보다 크고, 매질 2의 음속이 매질 1보다 작으면 굴절각이 입사각보다 작다.
4. Acoustic Impedance (z)

음향 임피던스는 매질의 밀도와 음속의 곱으로 정의되는 물리량으로, 음파가 매질을 통과할 때 겪는 저항을 나타낸다. 임피던스 차이가 클수록 반사가 크게 일어나며, 임피던스가 같으면 반사가 거의 일어나지 않는다. 이는 초음파 영상에서 중요한 요소이다.
5. Intensity Reflection Coefficient (IRC)

반사 강도 계수는 입사 강도에 대한 반사 강도의 비율을 나타내는 값으로, 임피던스 차이에 비례한다. 임피던스 차이가 크면 IRC가 크고, 임피던스가 같으면 IRC가 0이 된다.
6. Intensity Transmission Coefficient (ITC)

투과 강도 계수는 입사 강도에 대한 투과 강도의 비율을 나타내는 값으로, IRC와 관계가 있다. ITC = 1 - IRC이며, IRC와 ITC의 합은 항상 1이 된다.
7. Scattering

산란은 거친 표면에 부딪힌 음파가 여러 방향으로 퍼져나가는 현상을 말한다. 그중 backscatter는 입사 방향과 반대 방향으로 산란되는 것을 의미한다.

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1. Normal Incidence (Perpendicular Incidence)

Normal incidence, also known as perpendicular incidence, occurs when a wave, such as light or sound, strikes a surface at a 90-degree angle. This is an important concept in wave physics as it simplifies the analysis of the wave's behavior at the interface between two different media. When a wave encounters a surface at normal incidence, the angle of reflection is equal to the angle of incidence, and the wave is reflected back into the original medium without any change in direction. This is known as specular reflection. Additionally, at normal incidence, the intensity reflection coefficient (IRC) and intensity transmission coefficient (ITC) can be easily calculated using the acoustic impedance of the two media. Normal incidence is a fundamental principle in various fields, including optics, acoustics, and electromagnetic wave propagation, and is widely used in the design and analysis of various devices and systems.
2. Oblique Incidence

Oblique incidence refers to the situation where a wave, such as light or sound, strikes a surface at an angle other than 90 degrees. This is in contrast to normal incidence, where the wave strikes the surface perpendicularly. When a wave encounters a surface at oblique incidence, the angle of reflection is no longer equal to the angle of incidence, and the wave is reflected at a different angle. Additionally, the intensity reflection coefficient (IRC) and intensity transmission coefficient (ITC) are more complex to calculate, as they depend on the angle of incidence, the properties of the two media, and the polarization of the wave. Oblique incidence is a more general case and is commonly encountered in various applications, such as in the design of optical devices, the analysis of radar systems, and the study of wave propagation in the atmosphere or underwater. Understanding the behavior of waves under oblique incidence is crucial for many fields, including optics, acoustics, and electromagnetics.
3. Refraction

Refraction is a fundamental phenomenon in wave physics that occurs when a wave, such as light or sound, passes from one medium to another with a different speed of propagation. When a wave encounters the boundary between two media with different refractive indices or acoustic impedances, the wave's direction of propagation changes. This change in direction is known as refraction. The degree of refraction is determined by Snell's law, which relates the angles of incidence and refraction to the refractive indices of the two media. Refraction is a crucial concept in various fields, including optics, acoustics, and geophysics. It is responsible for many natural phenomena, such as the bending of light in the atmosphere, the mirage effect, and the focusing of sound waves by the ocean. Understanding refraction is essential for the design and analysis of a wide range of devices and systems, from optical lenses and prisms to sonar and radar systems.
4. Acoustic Impedance (z)

Acoustic impedance, denoted as 'z', is a fundamental concept in the study of wave propagation, particularly in the field of acoustics. It is defined as the ratio of the sound pressure to the particle velocity at a given point in a medium. Acoustic impedance is a crucial parameter in understanding the behavior of sound waves as they interact with different materials and interfaces. The acoustic impedance of a medium is determined by its density and the speed of sound within it. When a sound wave encounters a boundary between two media with different acoustic impedances, a portion of the wave is reflected, and a portion is transmitted. The relative magnitudes of the reflected and transmitted waves are determined by the acoustic impedance mismatch between the two media. Understanding acoustic impedance is essential in various applications, such as the design of acoustic transducers, the analysis of sound propagation in buildings and underwater environments, and the development of noise-reduction technologies. Accurate knowledge of acoustic impedance is crucial for optimizing the performance of acoustic systems and predicting the behavior of sound waves in complex environments.
5. Intensity Reflection Coefficient (IRC)

The Intensity Reflection Coefficient (IRC) is a dimensionless quantity that describes the ratio of the intensity of the reflected wave to the intensity of the incident wave at an interface between two media. It is a fundamental parameter in the study of wave propagation, particularly in the fields of optics, acoustics, and electromagnetics. The IRC is directly related to the acoustic impedance mismatch between the two media and can be calculated using the acoustic impedances of the two materials. The value of the IRC ranges from 0 to 1, where 0 indicates that all the incident wave energy is transmitted, and 1 indicates that all the incident wave energy is reflected. Understanding the IRC is crucial in various applications, such as the design of optical coatings, the analysis of sound propagation in buildings and underwater environments, and the optimization of radar and sonar systems. Accurate knowledge of the IRC allows for the prediction and control of the reflection and transmission of waves at interfaces, which is essential for the efficient design and operation of many wave-based technologies.
6. Intensity Transmission Coefficient (ITC)

The Intensity Transmission Coefficient (ITC) is a dimensionless quantity that describes the ratio of the intensity of the transmitted wave to the intensity of the incident wave at an interface between two media. It is a fundamental parameter in the study of wave propagation, particularly in the fields of optics, acoustics, and electromagnetics. The ITC is directly related to the acoustic impedance mismatch between the two media and can be calculated using the acoustic impedances of the two materials. The value of the ITC ranges from 0 to 1, where 0 indicates that all the incident wave energy is reflected, and 1 indicates that all the incident wave energy is transmitted. Understanding the ITC is crucial in various applications, such as the design of optical coatings, the analysis of sound propagation in buildings and underwater environments, and the optimization of radar and sonar systems. Accurate knowledge of the ITC allows for the prediction and control of the transmission of waves at interfaces, which is essential for the efficient design and operation of many wave-based technologies.
7. Scattering

Scattering is a fundamental wave phenomenon that occurs when a wave, such as light, sound, or electromagnetic radiation, encounters an object or a medium with irregularities. When a wave encounters a scattering object or medium, the wave's direction of propagation is altered, and the wave is scattered in multiple directions. Scattering can be caused by various factors, including the size, shape, and composition of the scattering object or medium, as well as the wavelength of the incident wave. Understanding scattering is crucial in many fields, such as optics, acoustics, and atmospheric science. In optics, scattering is responsible for the blue color of the sky and the visibility of clouds and haze. In acoustics, scattering plays a role in the reverberation of sound in rooms and the propagation of sound in the atmosphere. In atmospheric science, scattering of electromagnetic radiation by particles in the atmosphere is used in remote sensing techniques, such as radar and lidar. Accurate modeling and prediction of scattering phenomena are essential for the design and optimization of various wave-based technologies and the understanding of natural phenomena.

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