Yuri Álvarez López

Geometry Reconstruction of Metallic Bodies Using the Sources Reconstruction Method

This letter presents a novel application of the Sources Reconstruction Method (SRM) for geometry reconstruction. Foundations of this work are based on the correspondence between the placement of the metallic objects and the highest values of the reconstructed equivalent currents. In order to improve the accuracy of the method, reconstructed equivalent currents, due to different incident waves and working frequencies, are combined. Application examples using simulated data are presented.

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.

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.

Compressed Sensing Techniques Applied to Ultrasonic Imaging of Cargo Containers

One of the key issues in the fight against the smuggling of goods has been the development of scanners for cargo inspection. X-ray-based radiographic system scanners are the most developed sensing modality. However, they are costly and use bulky sources that emit hazardous, ionizing radiation. Aiming to improve the probability of threat detection, an ultrasonic-based technique, capable of detecting the footprint of metallic containers or compartments concealed within the metallic structure of the inspected cargo, has been proposed. The system consists of an array of acoustic transceivers that is attached to the metallic structure-under-inspection, creating a guided acoustic Lamb wave. Reflections due to discontinuities are detected in the images, provided by an imaging algorithm. Taking into consideration that the majority of those images are sparse, this contribution analyzes the application of Compressed Sensing (CS) techniques in order to reduce the amount of measurements needed, thus achieving faster scanning, without compromising the detection capabilities of the system. A parametric study of the image quality, as a function of the samples needed in spatial and frequency domains, is presented, as well as the dependence on the sampling pattern. For this purpose, realistic cargo inspection scenarios have been simulated.

SAR-based technique for soil permittivity estimation

ABSTRACT A conventional synthetic aperture radar (SAR)-based technique for soil permittivity estimation is presented in this contribution. Ground penetrating radar imaging techniques are mainly based on SAR imaging algorithms that take into account the wave velocity in the soil for accurate imaging of buried objects. Reflectometers, datasheets, and indirect observation methods are commonly considered for soil characterization. However, factors such as humidity and temperature may cause some variations in the soil constitutive parameters. This contribution proposes a methodology for in situ characterization of soil permittivity, using the known position of a reference object and the application of conventional SAR imaging to recover the reflectivity image, from which the required information to calculate the complex permittivity can be extracted. Experimental validation in both controlled and realistic scenarios proves the capability of the proposed technique to recover the permittivity of different types of soil and to improve the quality of the Underground-SAR image.

Sensor network and inertial positioning hybridisation for indoor location and tracking applications

An indoor location system (ILS) for practical asset and people tracking in indoor scenarios using received signal strength (RSS) ZigBee-based sensor network and inertial sensors is presented. A novel algorithm that uses differential signal levels gathered from a set of transmitter nodes is developed for processing RSS data. These levels are introduced into a cost function whose minimum gives the asset location estimation. The use of differential field levels-based algorithm avoids the need of system calibration due to signal strength fluctuation. Moreover, position accuracy is improved by adding inertial sensor information. The method is tested in a real scenario, demonstrating practical indoor positioning when combining ZigBee-based sensor network and inertial sensors information. The influence of the number of ZigBee nodes on the position estimation accuracy has been analysed.

RFID Technology for Management and Tracking: e-Health Applications

Radio frequency identification (RFID) has become a key technology in the logistics and management industry, thanks to distinctive features such as the low cost of RFID tags, and the easiness of the RFID tags’ deployment and integration within the items to be tracked. In consequence, RFID plays a fundamental role in the so-called digital factory or 4.0 Industry, aiming to increase the level of automatization of industrial processes. In addition, RFID has also been found to be of great help in improving the tracking of patients, medicines, and medical assets in hospitals, where the digitalization of these operations improves their efficiency and safety. This contribution reviews the state-of-the-art of RFID for e-Health applications, describing the contributions to improve medical services and discussing the limitations. In particular, it has been found that a lot of effort has been put into software development, but in most of the cases a detailed study of the physical layer (that is, the characterization of the RFID signals within the area where the system is deployed) is not properly conducted. This contribution describes a basic RFID system for tracking and managing assets in hospitals, aiming to provide additional details about implementation aspects that must be considered to ensure proper functionality of the system. Although the scope of the RFID system described in this contribution is restricted to a small area of the hospital, the architecture is fully scalable to cover the needs of the different medical services in the hospital. Ultra high-frequency (UHF) RFID technology is selected over the most extended near-field communication (NFC) and high-frequency (HF) RFID technology to minimize hardware infrastructure. In particular, UHF RFID also makes the coverage/reading area conformation easier by using different kinds of antennas. Information is stored in a database, which is accessed from end-user mobile devices (tablets, smartphones) where the position and status of the assets to be tracked are displayed.

An Ultrasonic Approach for Sensing and Imaging Shielding Containers of Nuclear Threats

A new guided wave imaging application for fast, low-cost ultrasound-based cargo scanning system is presented. The goal is the detection of high-atomic-number, shielding containers used to diminish the radiological signature of nuclear threats. This ultrasonic technology complements currently deployed X-ray-based radiographic systems, thus enhancing the probability of detecting nuclear threats.An array of acoustic transceivers can be attached to the metallic structure of the truck to create a guided acoustic wave. Guided medium thickness and composition variation creates reflections whose placement can be revealed by means of an imaging algorithm. The knowledge of the reflection position provides information about the shielding container location inside the truck.Reflected waves in the guided domain bounds may limit the performance of imaging methods for guided media. This contribution proposes a solution based on Fourier domain analysis, where plane wave components can be filtered out, thus removing non-desired contributions from bounds. Apart from this, the imaging algorithm can be used to recover information about material composition. Simulation-based examples are used for algorithm validation.Copyright

Antenna diagnostics using phaseless NF information

An extension of the Sources Reconstruction Method (SRM) for antenna diagnostics using phaseless information is presented. The aim of this work is to extend the methods capabilities from planar field acquisition domains to arbitrary ones. To achieve this goal, the SRM capabilities for handling with arbitrary-geometry domains are combined with phase retrieval technique. The consideration of the radiation inverse problem with a general integral equation formulation using arbitrary-geometry field and currents domains, and field phaseless information, supposes a challenging ill-posed problem that is solved using iterative minimization techniques for non-linear problems. An application example is presented, comparing the proposed methods performance with amplitude and phase results.