Denys S. Shumakov
McMaster University
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Featured researches published by Denys S. Shumakov.
Inverse Problems | 2015
Sheng Tu; J J McCombe; Denys S. Shumakov; Natalia K. Nikolova
A quantitative imaging method is proposed based on microwave measurements where a direct inversion in real space is employed. The electrical properties of penetrable objects are reconstructed using a resolvent kernel in the forward model, which is extracted from calibration measurements. These measurements are performed on two known objects: the reference object (RO) representing the scatterer-free measurement and the calibration object representing a small scatterer embedded in the RO. Since the method does not need analytical or numerical approximations of the forward model, it is particularly valuable in short-range imaging, where analytical models of the incident field do not exist while the fidelity of the simulation models is often inadequate. The experimentally determined resolvent kernel inherently includes the particulars of the measurement setup, including all transmitting and receiving antennas. The inversion is fast, allowing for quasi-real-time image reconstruction. The proposed technique is demonstrated and validated through examples using simulated and experimental data. Its performance with noisy data is also examined. The concept of experimentally determined resolvent kernel in the forward model may be valuable in other imaging modalities such as ultrasound, photonic imaging, electrical-impedance tomography, etc.
IEEE Transactions on Microwave Theory and Techniques | 2017
Alexander S. Beaverstone; Denys S. Shumakov; Natalia K. Nikolova
A rigorous frequency-domain forward model of scattering is derived that relates any desired complex-valued scalar response to the vectors of the electromagnetic field. The model is valid in any reciprocal medium. The S-parameter forward model is derived as a special case. The forward model for the open-circuit voltage at the terminals of a receiving antenna is also given. The proposed model is useful in microwave imaging since it eliminates the need to employ inadequate approximations of: 1) Green’s dyadic function and 2) the relation between the field in the antenna vicinity and its response. As a validation, the magnitude and phase distributions of fields are mapped using a small scattering probe in reflection-coefficient measurements. The maps contain both the magnitude and the phase distributions. The application of the proposed model in imaging is also demonstrated.
international microwave symposium | 2017
Daniel Tajik; Denys S. Shumakov; Natalia K. Nikolova
Microwave holography is a direct inversion algorithm that shows promise for use in real-time near-field tissue imaging. However, the methodology depends on the linearization of the scattering problem which, in reality, is nonlinear. Therefore, the choice of the linearization method significantly impacts the reconstruction output of holography. Two linearization strategies, the Born and the Rytov approximations, are explored. To analyze their fidelity, the approximations are applied to a tissue-imaging problem. Results suggest that the Rytov approximation is advantageous in tissue imaging.
international symposium on antennas and propagation | 2016
Denys S. Shumakov; Alexander S. Beaverstone; Daniel Tajik; Natalia K. Nikolova
The performance of the recently proposed axial-null illumination scheme for microwave imaging has been experimentally investigated in comparison with the conventional axial-peak illumination. The axial-null scheme is implemented as an array of four simultaneously transmitting X-band waveguides physically oriented to produce zero field along the array axis. Two independent direct inversion algorithms - scattered-power mapping and microwave holography - are used for processing the respective data. It is shown that axial-null illumination provides reconstruction of better quality in comparison with the axial-peak illumination.
Progress in Electromagnetics Research-pier | 2016
Denys S. Shumakov; Alexander S. Beaverstone; Natalia K. Nikolova
Axial-null illumination (ANI) is proposed to simplify the calibration of microwave imaging systems. The illumination also enhances the spatial resolution. ANI can be achieved with various array configurations, but a minimum of two transmitting antennas are required, which is a well-known form of differential illumination. Here, ANI is achieved with four transmitting antennas, and its implementation is investigated in a planar scanning scenario. The receiving antenna resides at the radiation null of the ANI array. Back-scattered reception requires an antenna at the center of the ANI array whereas forward-scattered reception requires an antenna aligned with the ANI axis, but on the opposite side of the imaged volume. The most important advantage of the proposed imaging setup is that it eliminates the need for background (or baseline) measurements, thus simplifying the system calibration. Also, it is proven that at least two-fold improvement in the spatial resolution can be achieved in near-field imaging scenarios compared to the conventional single-source illumination.
Archive | 2018
Denys S. Shumakov; Daniel Tajik; Alexander S. Beaverstone; Natalia K. Nikolova
Direct inversion methods, also known as linear inversion methods, such as holography and diffraction tomography are the working horses of microwave imaging. They provide fast qualitative estimates of an object’s shape and electrical contrast. However, these traditional methods cannot be used as linearized solvers at the core of nonlinear iterative reconstruction schemes because of their inability to provide a quantitative estimate of the electromagnetic constitutive parameters. In the past decade, advances have led to two powerful approaches to linear quantitative inversion, specifically developed for microwave imaging based on scattering-parameter data. These two approaches, quantitative microwave holography (QMH) and scattered-power mapping (SPM), provide quantitative images in real time. Thus they add new capability to real-time microwave imaging and offer new linearized core solvers for nonlinear reconstruction schemes. The performance of QMH and SPM is compared utilizing three different strategies of acquiring the resolvent kernel in the forward model: analytical, simulated, and measured. The results ascertain that the quantitative reconstruction is attainable only with experimentally acquired resolvent kernel.
The Journal of Engineering | 2017
Denys S. Shumakov; Alexander S. Beaverstone; Natalia K. Nikolova
european conference on antennas and propagation | 2016
Denys S. Shumakov; Alexander S. Beaverstone; Justin J. McCombe; Natalia K. Nikolova
IEEE Transactions on Microwave Theory and Techniques | 2018
Denys S. Shumakov; Natalia K. Nikolova
european conference on antennas and propagation | 2017
Daniel Tajik; Denys S. Shumakov; Alexander S. Beaverstone; Natalia K. Nikolova