서지주요정보
2차원 유전체의 초고주파 영상을 위한 Improved born 역산란 = Improved born inversion for microwave imaging dielectric cylinder
서명 / 저자 2차원 유전체의 초고주파 영상을 위한 Improved born 역산란 = Improved born inversion for microwave imaging dielectric cylinder / 김상기.
저자명 김상기 ; Kim, Sang-Ki
발행사항 [대전 : 한국과학기술원, 1992].
Online Access 제한공개(로그인 후 원문보기 가능)원문

소장정보

등록번호

8003125

소장위치/청구기호

학술문화관(문화관) 보존서고

DEE 92045

SMS전송

도서상태

이용가능

대출가능

반납예정일

초록정보

In the electromagnetic inverse diffraction problem, the first order Born approximation in the integral equation for the scattered field may be used. It gives a well-known Fourier transform relation eliminating the nonlinearity between the scattered fields and the physical properties of objects by replacing the total field inside the integral by the incident field. In the last decade, this linearizing approximation has been intensively studied in the medical imaging and nondistructive evaluation of materials since it offers numerically efficient and stable inversion algorithm. However, it is limited in the weakly scattering object. In this dissertation, the limitation of the first order Born approximation is explicitly shown by using the reconstruction by projection, and an improved Born inversion for dielectric profile reconstruction of dielectric cylinder is suggested. It improvess the validity of the first order Born approximation up to about ten times in the multiplication of the size of the object and the square root of the relative dielectric constant minus one. One may introduce a projection function defined as the one dimensional inverse Fourier transform of the scattered far fields measured for multi-frequency incident waves. Then the convolution back-projection scheme, well-known in the X-ray computerized tomography, may be used to obtain the cross-sectional images or the quantitative distribution of the relative dielectric constants in the cross-section. The projection function obtained from the inverse Fourier transform is larger than the real size since the propagation velocity of the electromagnetic wave inside the dielectric object is slow due to higher dielectric constant. The projection may be deformed from the refraction and diffraction of the wave within the object. In the case of weak scattering objects, the slowness and deformation is sufficiently small and may be neglected. However, for the strong scattering objects, this phenominon is pronounced and the projection function deviates from the original one, which limits the validity of the first order Born approximation. The projection obtained through the inverse Fourier transform of the time-harmonic fields is basically equal to the range profile due to the irradiation of the impulse plane wave on the objects, since impulse is consisted of infinitely many time-harmonic fields. Therefore, one may find the starting points of the object and the external boundary of the object by rotating the object. One may correct the extended projection obtained from the direct inverse Fourier transform of the scattered fields by the measured external boundary. It is shown via this correction that the reconstructed image closely predicts the original up to about 10 times strong scatterer than the ordinary Born inversion. Numerical examples and the X-band microwave measured reconstruction through this improved Born inversion are presented to compared with the ordinary Born inversion. Furthermore, it is shown that the similar improvent may also be possible for the first order Rytov inversion that is compared with the first order Born inversion. The actual inversion system such as the water-immersed imaging system and the subsurface radar is operated in the dissipated medium and the effects of the dissipativeness of the background medium and scatterer are investigated by using the concept of the point spread function in the band-limited system. Bi-static scheme is also included in its Fourier transformation formulation and its improved Born reconstruction is tested numerically.

서지기타정보

서지기타정보
청구기호 {DEE 92045
형태사항 v, 136 p. : 삽도 ; 26 cm
언어 한국어
일반주기 저자명의 영문표기 : Sang-Ki Kim
지도교수의 한글표기 : 나정웅
지도교수의 영문표기 : Jung-Woong Ra
학위논문 학위논문(박사) - 한국과학기술원 : 전기 및 전자공학과,
서지주기 참고문헌 : p. 126-136
주제 Diffractive scattering.
Microwave imaging.
Dielectrics.
Bistatic radar.
역 산란법. --과학기술용어시소러스
유전체. --과학기술용어시소러스
마이크로파 진단. --과학기술용어시소러스
레이터 화상. --과학기술용어시소러스
전자파 회절. --과학기술용어시소러스
Inverse scattering transform.
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