Fan Yin

The superresolution imaging of high-contrast objects is of great interest to many researchers. We propose a new method to achieve superresolution in inverse-scattering imaging of high-contrast dielectric objects. In the scheme of nonlinear inverse scattering, spatial superoscillatory incident fields are designed and applied in this research in order to retain the high-spatial-frequency components of the objects. The reconstruction results show that the proposed method resolves two objects with spacing 0.13λ. Compared with the orbital angular momentum (OAM)-carrying fields that compose a typical superoscillatory wave, the designed waveform is capable of achieving superresolution over the entire region of interest (ROI), while OAM possesses a limited superresolution area near the center of the ROI, which verifies the effectiveness of the proposed method.

 
@article{Yin2020SuperresolutionQI,
author = {Fan Yin and Chang Chen and Weidong Chen and Wen Qiao and Jian Guan},
title = {Superresolution quantitative imaging based on superoscillatory field.},
journal = {Optics express},
volume = {28},
number={5},
pages = {7707-7720},
year = {2020},
doi = {10.1364/OE.384866}
}
 

In the mixed boundary inverse scattering problem (ISP), conducting and dielectric scatterers coexist in the same region, which challenges the present quantitative inverse scattering methods. Moreover, to ensure the incident waves penetrating the lossy or high-contrast objects, lower wavelength is applied in most inverse scattering applications. Therefore, methods with wavelength or subwavelength resolution are required for the mixed boundary ISP. In this article, we devise a quantitative inversion scheme alternately updating the contrast of dielectric scatterers and the T-matrix of conducting scatterers. The proposed alternate parameter updating method (APUM) avoids the reconstruction deterioration from both the large imaginary parts of conducting contrasts and the limited expansion order of the T-matrix. Then, we further improve the resolution of the APUM by optimizing the incident fields, which is also a regularization strategy. In particular, we design superoscillatory incident fields to quantitatively converse the high spatial spectrum of objects into low spectrum contrast sources, which can retain the high-frequency information of objects in the low-passband of the Green function. The results with synthetic data and single-frequency Fresnel experimental data verify the effectiveness of the proposed method.

 
@article{9664466,
author = {Yin, Fan and Chen, Chang and Chen, Weidong},
title = {Resolution Enhancement for Mixed Boundary Conditions in Inverse Scattering Problems},
journal = {IEEE Transactions on Antennas and Propagation},
volume = {70},
number={5},
pages = {3643-3655},
year = {2022},
doi = {10.1109/TAP.2021.3137294}
}
 

In the ISP with mixed boundary condition, the contrast of the PEC scatterers has infinite large imaginary parts, which can disturb the reconstruction of the dielectric scatterers in the CSI. The inverse T -matrix can handle the PEC scatterers and the dielectric scatterers simultaneously. However, the quality of the reconstructed result in the inverse T -matrix method is limited by the order of the multipole expansion, which suffers from the ill-posedness of the mixed boundary ISP. In this paper, we provide a hybrid parameter model consist of the T -matrix and the contrast. The dielectric contrast and the PEC T -matrix are updated alternately, which avoids the interferences between the reconstruction of the dielectric scatterers and the PEC scatterers. The VP regularization is introduced into the cost function to constrain the solution space, of which the objects are composed of compact piecewise homogeneous materials. The minimization of the cost function is solved by Polak-Ribi`ere-Polyak conjugate gradient method, which ensure the convergence. The proposed method is verified on the synthetic data and the experimental data. The results showed that the proposed method is superior to other algorithms when regular-shaped scatterers with different boundary conditions are at hand.

 
@INPROCEEDINGS{9792757,
author = {Yin, Fan and Chen, Chang and Chen, Weidong},
title = {A Value Piking Method for Mixed Boundary Conditions in Inverse Scattering Problems}, 
booktitle = {2022 Photonics & Electromagnetics Research Symposium (PIERS)}, 
year = {2022},
volume = {},
number = {},
pages = {605-612},
doi = {10.1109/PIERS55526.2022.9792757}}
}
 

Electromagnetic inverse scattering method is based on full wave electromagnetic calculation. Therefore, compared with other microwave imaging methods, inverse scattering reconstruction has a more accurate and universal physical model and a wider application prospect. Most of the current inverse scattering methods are applied to oil exploration, building interior perspective and breast cancer diagnosis imaging, which require low-frequency waves to penetrate obstacles. Therefore, the reconstruction target scale is mostly in the order of wavelength, which pose enormous challenges to imaging and reconstruction. In addition, when metallic and non-metallic materials are mixed in the imaging area, the reconstruction of the latter is easily disturbed by the former, which brings uncertainty to the quantitative reconstruction. Finally, in these complex scenes, the reconstruction method should be able to operate stably under the non-uniform background, which tests the robustness of the reconstruction method. Therefore, this dissertation mainly focuses on three challenges in the application of inverse scattering reconstruction: first, for the problem with mixed boundary conditions, an alternating parameter updating method is proposed to realize the accurate reconstruction of conductor and dielectric targets at the same time; Secondly, aiming at super-resolution, an super-resolution method based on superoscillation effect and material sparse a priori from the perspective of physical super-resolution and mathematical super-resolution is presented respectively; Thirdly, for the case of nonuniform background disturbance, the reconstruction strategy of partition optimization is given.