Mengqing Yuan

Active Microwave Imaging II: 3-D System Prototype and Image Reconstruction From Experimental Data

A 3-D microwave imaging system prototype and an inverse scattering algorithm are developed to demonstrate the feasibility of 3-D microwave imaging for medical applications such as breast cancer detection with measured data. In this experimental prototype, the transmitting and receiving antennas are placed in a rectangular tub containing a fluid. The microwave scattering data are acquired by mechanically scanning a single transmit antenna and a single receive antenna, thus avoiding the mutual coupling that occurs when an array is used. Careful design and construction of the system has yielded accurate measurements of scattered fields so that even the weak scattered signals at S21 = -90 dB (or 30 dB below the background fields) can be measured accurately. Measurements are performed in the frequency domain at several discrete frequencies. The collected 3-D experimental data in fluid are processed by a 3-D nonlinear inverse scattering algorithm to unravel the complicated multiple scattering effects and produce high-resolution 3-D digital images of the dielectric constant and conductivity of the imaging domain. Dielectric objects as small as 5 mm in size have been imaged effectively at 1.74 GHz.

Reconstruction of 3D objects from multi-frequency experimental data with a fast DBIM-BCGS method

The objective of this work is to perform image reconstruction of 3D dielectric targets from multi-frequency experimental data by using a fast DBIM-BCGS method that combines the distorted Born iterative method (DBIM) and the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) method. In this reconstruction technique, the BCGS-FFT method is used as a forward scattering method for solving the volume integral equations governing the 3D scattering problem; it provides both the predicted scattered fields due to 3D heterogeneous objects and the Frechet derivatives in the inverse scattering problem. The plane-wave source model and the point receiver model are used in the inversion procedure to invert the calibrated scattering data obtained from Institut Fresnels measurements. The multi-frequency experimental data are processed with the frequency-hopping approach to obtain high-resolution 3D images. The reconstruction of five different targets from the measured scattered fields verifies the capability and the effectiveness of the DBIM-BCGS method.

Microwave Imaging in Layered Media: 3-D Image Reconstruction From Experimental Data

A prototype microwave imaging system for imaging 3-D targets in layered media is developed to validate the capability of microwave imaging with experimental data and with 3-D nonlinear inverse scattering algorithms. In this experimental prototype, the transmitting and receiving antennas are placed in a rectangular tub containing a fluid. Two plastic slabs are placed in parallel in the fluid to form a five-layer medium. The microwave scattering data are acquired by mechanically scanning a single transmitting antenna and a single receiving antenna, thus avoiding the mutual coupling that occurs when an array is used. The collected 3-D experimental data in the fluid are processed by full 3-D nonlinear inverse scattering algorithms to unravel the complicated multiple scattering effects and produce 3-D digital images of the dielectric constant and conductivity of the imaging domain. The image reconstruction is focused on the position and dimensions of the unknown scatterers. Different dielectric and metallic objects have been imaged effectively at 1.64 GHz.

A WIDEBAND HALF OVAL PATCH ANTENNA FOR BREAST IMAGING

A simple half oval patch antenna is proposed for the active breast cancer imaging over a wide bandwidth. The antenna consists of a half oval and a trapezium, with a total length 15.1mm and is fed by a coaxial cable. The antenna performance is simulated and measured as immersed in a dielectric matching medium. Measurement and simulation results show that it can obtain a return loss less than i10dB from 2.7 to 5GHz. The scattered fleld detection capability is also studied by simulations of two opposite placed antennas and a full antenna array on a cubic chamber.

A tapered microstrip patch antenna array for use in breast cancer screening via 3D active microwave imaging

Given the measured performance of the antennas in the imaging array and the modeled scattered field data of small tumors within the human breast model, along with the known parameters associated with the other system components (e.g. losses through RF switching system and sensitivity of the measurement device), detection and screening of tumors with the clinical microwave imaging array that has been developed is certainly feasible. Since successful inversions of phantoms from previous experimental data with 3D imaging systems have already demonstrated the capability of the inversion algorithm developed at Duke, what remains is to finish implementing improvements in the hardware system (transition to MEMS based RF switching system) and to construct the Greens function from the completed forward model of the 3D prototype clinical system. From there, optimizations based on phantom imaging experiments will be performed, ultimately leading to clinical trials of the Duke 3D microwave breast imaging system.

Broadband Electromagnetic Radiation Modulated by Dual Memristors

Using dual high-speed memristors, we report on an efficient broadband electromagnetic radiation from a narrowband microstrip patch antenna. The directly modulated microstrip patch antenna system with dual memristors is calculated by using an integrated full-wave finite-difference time-domain method with an embedded SPICE3 solver. Nonlinear transient electromagnetic response is analyzed. The radiation frequency spectrum demonstrates the broadband radiation performance from the narrowband antenna system.

The Filter Diagonalization Method in Antenna Array Optimization for Pattern Synthesis

Pattern synthesis of nonuniform antenna arrays has drawn significant attention because of its wide applications. With the aim of reducing the number of elements in linear and planar arrays, this paper introduces a novel non-iterative method based on the filter diagonalization method (FDM), which was originally applied in the problem of identifying and quantifying chemical molecules with nuclear magnetic resonance (NMR) in quantum mechanical formalism. The proposed method samples the data set from the desired discrete pattern and associates the sample data with a time autocorrelation function of a fictitious dynamical system, which is described by an effective “Hamiltonian” operator that contains the array element information. The “Hamiltonian” operator can be decomposed by a set of orthonormal eigenvectors. Therefore, the original pattern synthesis is converted into solving the general eigenvalue decomposition with Krylov bases. The number of nonuniform array elements depends on the number of the Krylov bases and the sample data. The proposed method can obtain an optimized antenna array to reconstruct the desired radiation pattern with a high accuracy. Numerical examples show that proposed FDM pattern synthesis can use less prior knowledge to achieve the desired pattern with highly sparse antenna arrays.

Experimental and numerical investigations of a High-resolution 3D microwave imaging system for breast cancer detection

In this paper, we have developed a prototype 3D microwave imaging system for breast cancer diagnosis and screening. This presentation will give an overview of the hardware development, forward electromagnetic wave propagation models, nonlinear inverse scattering algorithms for this 3D microwave imaging system. This high sensitivity enables the 3D system to collect accurate scattering data from small phantom tumors.

Ultra Wide Band Response of an Electromagnetic Wave Shield Based on a Diode Grid

This paper investigates Ultra Wide Band (UWB) response of a self-actuated electromagnetic wave shield based on a diode grid both in frequency and time domain. The investigation is flrst carried out on a shield valid for an incident wave polarized at a speciflc direction only, then extended to a shield efiective for an incident wave polarized at an arbitrary direction. In the frequency domain, two linear analysis methods are used to study the properties of the diode grid over the frequency range from 0.01 to 10GHz. One method is the microwave network analysis. Another is simulating the diode grid by a linear equivalent circuit instead of a diode. In the time domain, the property of the shield is studied with respect to a broadband impulse, where the diode is described by its SPICE circuit model including the nonlinear property. The results show that the diode grid works well as a self-actuated electromagnetic power selective surface (PSS) in a certain frequency range. The diode grid is strongly frequency dependent. The operating frequency band relies on the reactive elements in the diode grid. In order to extend the operating frequency to a high band, smaller cell size and smaller junction capacitance should be employed.

Nano-scale memristor SPICE implementation using ideal operational amplifier model

The conception of memristor is becoming increasingly prevalent due to its remarkable electronic properties. In this paper, a circuit model of the memristor using simple SPICE code is presented. An ideal closed-loop operational amplifier (OP-AMP) is applied to realize the feedback-controlled integrator, which expands the hitherto methods to solve the memristor’s modeling equations presented by HP Lab. The behaviors of the proposed memristor model in SPICE are investigated. The desired excitation source and initial condition of the doped state can both be easily tuned in the memristor model. Different pinched hysteresis loop i-v curves are presented through different stimulus like sinusoidal and square-wave voltage source.