Ali Molaei

Consensus-based imaging using ADMM for a Compressive Reflector Antenna

This paper describes a novel norm-one-regularized, consensus-based imaging algorithm, based on the Alternating Direction Method of Multipliers (ADMM), that can be used by a high-sensing-capacity Compressive Reflector Antenna (CRA). The proposed method outperforms current state of the art iterative reconstruction algorithms in terms of computational cost; and it ultimately enables the use of a CRA in quasi-real-time, compressive sensing imaging applications.

Miniaturized UWB Antipodal Vivaldi Antenna for a mechatronic breast cancer imaging system

Digital Breast Tomosynthesis (DBT) can be fused with microwave Nearfield Radar Imaging (NRI) in order to improve breast cancer detection. This paper presents the design of a new miniaturized ultra-wideband Antipodal Vivaldi Antenna (AVA), which can be used in such a hybrid DBT/NRI mechatronic imaging device. The antenna is miniaturized by using a coupling media and a substrate that have a high effective dielectric constant. Preliminary results show that the designed antenna has a return loss above 9 dB in a 2.5 GHz frequency band.

Active imaging using a metamaterial-based compressive reflector antenna

This paper presents a new high-sensing-capacity system for active imaging. The proposed system consists of a Compressive Reflector Antenna (CRA) coated with Metamaterial Absorbers (MMA). The Compressive Reflector Antenna creates a spatial codification in the imaging domain, while the MMA creates a frequency codification in the spectral domain. To solve the inverse problem, we built the sensing matrix using a high frequency method based on Physical Optics; and an iterative Compressive Sensing algorithm (ADMM) is used to perform the inversion. Numerical simulations consisting on PEC targets in the reconstruction domain are carried out. The performance of the proposed system is compared to that of the Compressive Reflector Antenna without metamatrial absorbers. Preliminary results show that a better imaging performance and higher channel capacity is achieved for the metamaterial-based CRA than the CRA configuration.

Norm-1 Regularized Consensus-based ADMM for Imaging with a Compressive Antenna

This letter presents a novel norm-1-regularized, consensus-based imaging algorithm, based on the alternating direction method of multipliers (ADMM). This algorithm is capable of imaging metallic targets by using a limited amount of data. The distributed capabilities of the algorithm enable a fast imaging convergence. Recently, a compressive reflector antenna (CRA) has been proposed as a way to provide high sensing capacity with a minimum cost and complexity in the hardware architecture. The ADMM algorithm applied to the imaging capabilities of the CRA outperforms current state-of-the-art iterative reconstruction algorithms, such as Nesterov-based methods, in terms of computational cost, enabling the use of the CRA in quasi-real-time, compressive sensing imaging applications.

Preliminary imaging results and SAR analysis of a microwave imaging system for early breast cancer detection

Currently X-ray-based imaging systems suffer from low contrast between malignant and healthy fibrous tissues in breast. Microwave Near-field Radar Imaging (NRI) shows a higher contrast between the aforementioned tissues and therefore can enhance tumor detection and diagnosis accuracy. In this work, we present the first imaging results of our developed NRI system that is equipped with a pair of Antipodal Vivaldi Antennas. We used a metal bearing ball immersed in oil as our object of interest, to keep the first measurement configuration simple. Moreover, to demonstrate the safety of our system for human subject tests, we simulated the Specific Absorption Rate (SAR) in a realistic breast tissue model and compared the resulted values with both the USA and Europe standards. The results show that firstly the imaging results from the measurements and simulations are comparable, and secondly the antennas radiations meet the SAR criteria.

Holey-Cavity-Based Compressive Sensing for Ultrasound Imaging

The use of solid cavities around electromagnetic sources has been recently reported as a mechanism to provide enhanced images at microwave frequencies. These cavities are used as measurement randomizers; and they compress the wave fields at the physical layer. As a result of this compression, the amount of information collected by the sensing array through the different excited modes inside the resonant cavity is increased when compared to that obtained by no-cavity approaches. In this work, a two-dimensional cavity, having multiple openings, is used to perform such a compression for ultrasound imaging. Moreover, compressive sensing techniques are used for sparse signal retrieval with a limited number of operating transceivers. As a proof-of-concept of this theoretical investigation, two point-like targets located in a uniform background medium are imaged in the presence and the absence of the cavity. In addition, an analysis of the sensing capacity and the shape of the point spread function is also carried out for the aforementioned cases. The cavity is designed to have the maximum sensing capacity given different materials and opening sizes. It is demonstrated that the use of a cavity, whether it is made of plastic or metal, can significantly enhance the sensing capacity and the point spread function of a focused beam. The imaging performance is also improved in terms cross-range resolution when compared to the no-cavity case.

Preliminary Results of a New Auxiliary Mechatronic Near-Field Radar System to 3D Mammography for Early Detection of Breast Cancer

Accurate and early detection of breast cancer is of high importance, as it is directly associated with the patients’ overall well-being during treatment and their chances of survival. Uncertainties in current breast imaging methods can potentially cause two main problems: (1) missing newly formed or small tumors; and (2) false alarms, which could be a source of stress for patients. A recent study at the Massachusetts General Hospital (MGH) indicates that using Digital Breast Tomosynthesis (DBT) can reduce the number of false alarms, when compared to conventional mammography. Despite the image quality enhancement DBT provides, the accurate detection of cancerous masses is still limited by low radiological contrast (about 1%) between the fibro-glandular tissue and affected tissue at X-ray frequencies. In a lower frequency region, at microwave frequencies, the contrast is comparatively higher (about 10%) between the aforementioned tissues; yet, microwave imaging suffers from low spatial resolution. This work reviews conventional X-ray breast imaging and describes the preliminary results of a novel near-field radar imaging mechatronic system (NRIMS) that can be fused with the DBT, in a co-registered fashion, to combine the advantages of both modalities. The NRIMS consists of two antipodal Vivaldi antennas, an XY positioner, and an ethanol container, all of which are particularly designed based on the DBT physical specifications. In this paper, the independent performance of the NRIMS is assessed by (1) imaging a bearing ball immersed in sunflower oil and (2) computing the heat Specific Absorption Rate (SAR) due to the electromagnetic power transmitted into the breast. The preliminary results demonstrate that the system is capable of generating images of the ball. Furthermore, the SAR results show that the system complies with the standards set for human trials. As a result, a configuration based on this design might be suitable for use in realistic clinical applications.

Single-pixel mm-wave imaging using 8-bits metamaterial-based compressive reflector antenna

This paper presents a single-pixel millimeter-wave (mm-wave) imaging system, capable of performing spectral coding by using a Compressive Reflector Antenna (CRA). The CRA is designed by coating the surface of a parabolic reflector with 8-bits metamaterial absorbers (MMAs). By specially designing the codes, the mutual information between successive measurements is reduced, leading to an enhanced sensing capacity. The imaging performance of the proposed mm-wave imaging system is evaluated using synthetic data. Preliminary results show that the proposed 8-bits metamaterial-based CRA system outperforms the equivalent one without MMAs in terms of imaging quality and sensing capacity.

A bilayer ELC metamaterial for multi-resonant spectral coding at mm-Wave frequencies

Metamaterial-based spectral coding is of special interest in high capacity sensing and imaging applications. This paper presents the design, fabrication and performance evaluation of a bilayer, multi-resonant ELC metamaterial that may be used for those applications at mm-Wave frequencies. The S21 response of both fabricated and simulated bilayer metamaterial are in good agreement within the used 60–90 GHz frequency range; and they show the desired narrow-band, double resonances at 78 GHz and 82 GHz.

A 2-bit and 3-bit metamaterial absorber-based compressive reflector antenna for high sensing capacity imaging

This paper describes a new coded sensing system used for imaging metallic objects in its near-field region. The presented system is composed of a compressive reflector antenna (CRA) coated with metamaterial absorbers (MMAs), in order to generate spatial and spectral codes in the imaging domain. The codes are designed to reduce the mutual information between the successive measurements, which results in a higher sensing capacity of the system. The performance of the proposed MMA-based CRA is compared to that of the traditional reflector antenna (TRA) without MMAs. Numerical examples for imaging PEC targets in the near-field of the coded system are presented. The results show that both sensing capacity and imaging performance of the MMA-based CRAs is enhanced when compared to that of the TRA.