Yolanda Rodriguez-Vaqueiro

On the Use of Compressed Sensing Techniques for Improving Multistatic Millimeter-Wave Portal-Based Personnel Screening

This work develops compressed sensing techniques to improve the performance of an active three dimensional (3D) millimeter wave imaging system for personnel security screening. The system is able to produce a high-resolution 3D reconstruction of the whole human body surface and reveal concealed objects under clothing. Innovative multistatic millimeter wave radar designs and algorithms, which have been previously validated, are combined to improve the reconstruction results over previous approaches. Compressed Sensing techniques are used to drastically reduce the number of sensors, thus simplifying the system design and fabrication. Representative simulation results showing good performance of the proposed system are provided and supported by several sample measurements.

Sparse Array Optimization Using Simulated Annealing and Compressed Sensing for Near-Field Millimeter Wave Imaging

The optimization and use of a sparse array configuration for an active three dimensional (3D) millimeter wave imaging system for personnel security screening is presented in this work. The combination of the optimization procedure with the use of Compressed Sensing techniques allows drastic reduction in the number of sensors, thereby simplifying the system design and fabrication and reducing its cost. Representative simulation results showing good performance of the proposed system are provided and supported by sample measurements.

Fourier-Based Imaging for Multistatic Radar Systems

Fourier-based methods for monostatic and bistatic setups have been widely used for high-accuracy radar imaging. However, the multistatic configuration has several characteristics that make Fourier processing more challenging: 1) a nonuniform grid in k-space, which requires multidimensional interpolation methods, and 2) image distortion when the incident spherical wave is approximated by a plane wave. This contribution presents a Fourier-based imaging method for multistatic systems, solving the aforementioned limitations: the first, by using k-space partitioning and applying interpolation in each domain; the second, by approximating the spherical wave with multiple plane waves. Both solutions are fully parallelizable, thus allowing calculation time savings. Validation and benchmarking with a synthetic aperture radar backpropagation algorithm have been performed through 2-D and 3-D simulation-based examples. Imaging results from radar measurements have been assessed.

Multispectral and Photoplethysmography Optical Imaging Techniques Identify Important Tissue Characteristics in an Animal Model of Tangential Burn Excision.

Burn excision, a difficult technique owing to the training required to identify the extent and depth of injury, will benefit from a tool that can cue the surgeon as to where and how much to resect. We explored two rapid and noninvasive optical imaging techniques in their ability to identify burn tissue from the viable wound bed using an animal model of tangential burn excision. Photoplethysmography (PPG) imaging and multispectral imaging (MSI) were used to image the initial, intermediate, and final stages of burn excision of a deep partial-thickness burn. PPG imaging maps blood flow in the skin’s microcirculation, and MSI collects the tissue reflectance spectrum in visible and infrared wavelengths of light to classify tissue based on a reference library. A porcine deep partial-thickness burn model was generated and serial tangential excision accomplished with an electric dermatome set to 1.0 mm depth. Excised eschar was stained with hematoxylin and eosin to determine the extent of burn remaining at each excision depth. We confirmed that the PPG imaging device showed significantly less blood flow where burn tissue was present, and the MSI method could delineate burn tissue in the wound bed from the viable wound bed. These results were confirmed independently by a histological analysis. We found these devices can identify the proper depth of excision, and their images could cue a surgeon as to the preparedness of the wound bed for grafting. These image outputs are expected to facilitate clinical judgment in the operating room.

A compressed sensing approach for detection of explosive threats at standoff distances using a Passive Array of Scatters

This work presents a new radar system concept, working at millimeter wave frequencies, capable of detecting explosive related threats at standoff distances. The system consists of a two dimensional aperture of randomly distributed transmitting/receiving antenna elements, and a Passive Array of Scatters (PAS) positioned in the vicinity of the target. In addition, a novel norm one minimization imaging algorithm has been implemented that is capable of producing super-resolution images. This paper also includes a numerical example in which 7.5 mm resolution is achieved at the standoff range of 40 m for a working frequency of 60 GHz.

Three-Dimensional Compressed Sensing-Based Millimeter-Wave Imaging

An extension of compressed sensing (CS)-based millimeter-wave imaging techniques from two- to three-dimensional (2-D to 3-D) is presented. The idea is to study the reduction in the minimum number of receivers with respect to standard synthetic aperture radar (SAR) imaging to accurately recover the geometry of the object-under-test. 3-D CS main drawback is the increased calculation time with respect to standard SAR algorithms. To overcome this limitation, a novel technique consisting in splitting a large problem as a combination of small ones is proposed. These small problems can be solved via parallelized 3-D CS, resulting in calculation time savings. Moreover, practical implementation of a 3-D CS-based millimeter-wave imaging system is discussed. Validation with simulations and measurements is presented.

Millimeter Wave Imaging Architecture for On-The-Move Whole Body Imaging

This paper presents a novel interrogation system that combines multiple millimeter wave transmitters and receivers to create real-time high-resolution radar images for personnel security screening. The main novelty of the presented system is that the images can be created as the person being screened continuously moves across a corridor where the transmitters and receivers, working in a fully coherent architecture, are distributed. As the person moves, the transmitters and receivers are sequentially activated to collect data from different angles to inspect the whole body. Multiple images, similar to video frames, are created and examined to look for possible anomalies such as concealed threats. Two-dimensional (2-D) and three-dimensional (3-D) setups have been simulated to show the feasibility of the proposed system. The simulation results in 2-D have been validated using measurements.

Phase Error Compensation in Imaging Systems Using Compressed Sensing Techniques

A study of the capabilities for phase error correction of compressed sensing (CS) imaging techniques is presented. The idea is to show that CS method is able to recover reflectivity images with a reduced number of sensors even if the system suffers from phase errors. A comparison to the sparsity-driven approach (SDA) technique for phase error correction is presented, analyzing SDA and CS performance with different numbers of sensors, phase error values, and sensor placement uncertainties. Validation with synthetically blurred experimental data-collected using multistatic radar-is presented.

Antenna Diagnostics and Characterization Using Unmanned Aerial Vehicles

This paper presents a compact, low-cost unmanned aerial system for antenna measurement. The proposed system overcomes existing limitations in terms of unmanned aerial vehicle positioning and data geo-referring accuracy using a real-time kinematic positioning system to achieve centimeter-level accuracy. Amplitude-only measurements acquired using a low-cost power sensor are processed by means of the phaseless sources reconstruction method. This is an iterative phase retrieval technique that allows recovering an equivalent currents distribution, which characterizes the antenna under test (AUT). From these equivalent currents, near-field to far-field transformation is applied to calculate the AUT radiation pattern. This contribution also analyzes probe antenna characterization and the impact of positioning and geo-referring accuracy on the radiation pattern. Two application examples of antenna measurement at S- and C-bands using the implemented system are presented.

Fourier-Based Imaging for Subsampled Multistatic Arrays

This contribution focuses on the limitations of Fourier-based imaging when applied to subsampled arrays used in multistatic millimeter-wave radar systems. The aim is to determine the relationship between the size of the object under test (OUT), its position with respect to the radar aperture, and the sampling requirements on the aperture so as to recover aliasing-free images. Based on the analysis results, a method for recovering spectral information is proposed, the idea of which is to replicate the plane wave spectrum, and then apply a band-pass filter defined by a priori knowledge of the OUT size. For simplicity, the analysis is done in two-dimensional (2-D; range and cross-range dimensions). A simulation-based application is presented for validation purposes.