Radiometric Imaging for Monitoring and Surveillance Issues

This paper deals with the recent advances performed by State Research Center “Iceberg” (SRC) in the field of the passive imaging at millimeter wavelengths. In particular, first the paper describes the design and the realization of two systems working in 3 mm and 8 mm wave bands, respectively. Second, the measurements collected by the two systems are enhanced by means of simple data processing strategies developed by the Institute for Electromagnetic Sensing of the Environment (IREA-CNR)

Indoor Full-Body Security Screening: Radiometric Microwave Imaging Phenomenology and Polarimetric Scene Simulation

The paper discusses the scene simulation of radiometric imagers and its use to illustrate the phenomenology of full-body screening of people for weapons and threats concealed under clothing. The aperture synthesis technique is introduced as this offers benefits of wide field-of-views and large depths-of-fields in a system that is potentially conformally deployable in the confined spaces of building entrances and at airport departure lounges. The technique offers a non-invasive, non-cooperative screening capability to scrutinize all human body surfaces for illegal items. However, for indoor operation, the realization of this capability is challenging due to the low radiation temperature contrasts in imagery. The contrast is quantified using a polarimetric radiometric layer model of the clothed human subject concealing threats. A radiation frequency of 20 GHz was chosen for the simulation as system component costs here are relatively low and the attainable half-wavelength spatial resolution of 7.5 mm is sufficient for screening. The contrasts against the human body of the threat materials of metal, zirconia ceramic, carbon fiber, nitrogen-based energetic materials, yellow beeswax, and water were calculated to be ≤7 K. Furthermore, the model indicates how some threats frequency modulate the radiation temperatures by ~ ±1 K. These results are confirmed by experiments using a radiometer measuring left-hand circularly polarized radiation. It is also shown using scene simulation how circularly polarized radiation has benefits for reducing false alarms and how threat objects appear in canyon regions of the body, such as between the legs and in the armpits

Millimeter wave imaging : a historical review

The SPIE Passive and Active Millimeter Wave Imaging conference has provided an annual focus and forum for practitioners in the field of millimeter wave imaging for the past two decades. To celebrate the conference's twentieth anniversary we present a historical review of the evolution of millimeter wave imaging over the past twenty years. Advances in device technology play a fundamental role in imaging capability whilst system architectures have also evolved. Imaging phenomenology continues to be a crucial topic underpinning the deployment of millimeter wave imaging in diverse applications such as security, remote sensing, non-destructive testing and synthetic vision.Publisher PD

Millimeter-wave and terahertz imaging techniques

This thesis presents the development and assessment of imaging techniques in the millimeterwave (mmW) and terahertz frequency bands. In the first part of the thesis, the development of a 94 GHz passive screener based on a total-power radiometer (TPR) with mechanical beamscanning is presented. Several images have been acquired with the TPR screener demonstrator, either in indoor and outdoor environments, serving as a testbed to acquire the know-how required to perform the research presented in the following parts of the thesis. In the second part of the thesis, a theoretical research on the performance of near-field passive screeners is described. This part stands out the tradeoff between spatial and radiometric resolutions taking into account the image distortion produced by placing the scenario in the near-field range of the radiometer array. In addition, the impact of the decorrelation effect in the image has been also studied simulating the reconstruction technique of a synthetic aperture radiometer. Guidelines to choose the proper radiometer depending on the application, the scenario, the acquisition speed and the tolerated image distortion are given in this part. In the third part of the thesis, the development of a correlation technique with optical processing applicable to millimeter-wave interferometric radiometers is described. The technique is capable of correlating wide-bandwidth signals in the optical domain with no loss of radiometric sensitivity. The theoretical development of the method as well as measurements validating the suitability to correlate radiometric signals are presented in this part. In the final part of the thesis, the frequency band of the imaging problem is increased to frequencies beyond 100 GHz, covering the THz band. In this case the research is centered in tomographic techniques that include spectral information of the samples in the reconstructed images. The tomographic algorithm can provide detection and identification of chemical compounds that present a certain spectral footprint in the THz frequency band.Postprint (published version

TERASENSE: THz device technology laboratory

The use of THz frequencies, particularly W and G band allows reaching higher resolution and deeper penetration in emerging applications like imaging, sensing, etc. The development of those new applications lays on reliable technologies, background of expertise and know-how. The CDS2008-00068 TERASENSE CONSOLIDER project has given the opportunity to extent upwards in frequency the previous background of the microwaves research group partners. This article summarizes the developments of the TERASENSE work package “THz Device Technology Laboratory”

Merged simulation procedure for W-band imaging systems

This article presents and discusses a unifying simulation procedure aimed at providing more realistic performance prediction of basic imaging systems, combining 3D EM (3 Dimensions Electro-Magnetic) simulations and nonlinear receiver circuit simulation. New methods are proposed to emulate the radiated emissivity profile of a target body and to use harmonic balance simulation to emulate nonlinear circuit/system response to a broadband noisy stimulus. The procedure focuses mainly on passive imaging, but active imaging including illuminated passive imaging is dealt with and some elemental experiments are presented and discussed for comparisons. The method enables the extrapolation of the frequency response of a single pixel detector to an array with more elements suitable for providing a complete set of pixels and can help in evaluating the most suitable bandwidth according to the operation mode (passive/active), frequency range of operation, desired resolution, and the pixel number-image resolution tradeoff.Spanish Ministry of Economy Science and Innovation, CONSOLIDER‐INGENIO CSD2008‐00068 (TERASENSE), Excellence network SPATEK, Project TEC2014‐58341‐C4‐1‐R., Project TEC2017‐83343‐C4‐1‐R,; University of Cantabria Industrial Doctorate programme 2014, Project: “Estudio y Desarrollo de Tecnologías para Sistemas de Telecomunicación a Frecuencias Milimétricas y de Terahercios con Aplicación a Sistemas de Imaging en la Banda 90 GHz‐100GHz

Passive Millimeter-Wave Imaging Based on Subharmonic Self-Oscillating Mixing

RÉSUMÉ Le sujet général de la thèse de doctorat présentée réside dans la recherche sur des nouvelles méthodes dans le domaine de l’imagerie aux micro-ondes, en particulier l’imagerie passive aux ondes millimétriques, qui est aussi connue sous le nom d’imagerie radiométrique. Cette dernière technique est utilisée pour former une image d’une scène particulière en capturant la radiation électromagnétique émise naturellement par chaque objet à la bande de fréquence des micro-ondes / ondes millimétriques, similaire à la façon dont une photographie est prise en capturant la radiation aux fréquences optiques. De cette façon, une image d’ondes millimétriques peut être formée et utilisée pour tracer différentes caractéristiques de la scène ou de l’objet, qui sont implicites à la bande de fréquences des micro-ondes / ondes millimétriques. L’imagerie à ondes millimétriques représente un des sujets d’actualité des plus prometteurs dans le domaine de la conception des capteurs à haute fréquence. L’utilité de cette technique réside surtout dans les particularités des phénomènes de l’atténuation atmosphérique permettant aux ondes millimétriques de pénétrer à travers une grande variété de conditions de mauvaise visibilité, comme par exemple la brume, le brouillard, les nuages, la fumée et les tempêtes de sable, ainsi que la capacité de se propager à travers des vêtements et certains autres matériaux. Outre ces avantages par rapport aux systèmes infrarouges ou optiques, les systèmes à ondes millimétriques surpassent les systèmes micro-ondes à plus basse fréquence par leurs longueurs d’ondes plus petites permettant d’atteindre une plus haute résolution. Pour leur mise en application, des fenêtres de propagation à 35, 77, 94, 140 et 220 GHz ont été assignées. Les domaines d’application présents et futurs sont principalement associés aux infrastructures militaires et commerciales. Ceux-ci englobent la surveillance, la navigation et la technologie automobile, ainsi que l’atterrissage des avions et le suivi de la circulation dans le brouillard sur les autoroutes. De plus, la demande de plus en plus grande en systèmes de détection de sécurité aux aéroports et d’autres lieux publics crée une demande toujours plus grande en scanners automatisés en temps réel dotés des caractéristiques suivantes : ne présenter aucun risque pour la santé, générer un nombre réduit de fausses alertes et permettre la détection des armes cachées ou des objets dangereux à travers les vêtements.----------ABSTRACT The broad topic of the presented Ph.D. thesis consists in the research on novel methods in the field of microwave imaging, in particular the so-called passive millimetre-wave imaging, which is also referred to as radiometric imaging. This latter technique is used to form an image of a particular scene by means of sensing the natural electromagnetic radiation emitted by any object at microwave / millimetre-wave wavelengths, similar to the way in which a photograph is captured by sensing the radiation occurring at optical wavelengths. In this way, different characteristics of the observed scene or object, which are inherent to the microwave / millimetre-wave frequency range, can be mapped in the form of an image. Millimetre-wave imaging represents one of today’s most promising research topics in the field of high frequency sensor design. The usefulness of this technique lies in particular in the peculiarities of atmospheric attenuation phenomenologies allowing millimetre-waves to penetrate through a variety of low-visibility conditions such as haze, fog, clouds, smoke, and sandstorms and furthermore in the ability to propagate through clothing and a number of other materials. Together with these advantages over infrared and optical systems, moreover, millimetre-wave systems outperform imagers at the lower microwave frequency range due to their smaller wavelengths and the thus achievable higher resolution. For their implementation, propagation windows at 35, 77, 94, 140, and 220 GHz are generally allocated. Present and future applications consist in both military and commercial infrastructure fields such as in surveillance, navigation, and automotive technology, as well as aircraft landing or highway traffic monitoring in fog. Moreover, the ever increasing demand for security screening systems at airports and other public environments creates a growing need for health-hazardless automated real-time scanners with minimized false alarms, and millimetre-wave imaging offering the ability to detect concealed weapons or hazardous objects through clothing material represents an excellent choice for this purpose. Furthermore, millimetre-wave imaging is applied to biomedical imaging such as the location of hot spots, tumours, or other anomalies in the body. Additional applications consist in non-destructive material testing and geological examinations such as the sensing of the Earth’s atmosphere, oil spill detection, research on volcano activity, or meteorology

Design and Implementation of High Gain 60 GHz Antennas for Imaging/Detection Systems

Recently, millimeter wave (MMW) imaging detection systems are drawing attention for their relative safety and detection of concealed objects. Such systems use safe non-ionizing radiation and have great potential to be used in several applications such as security scanning and medical screening. Antenna probes, which enhance system performance and increase image resolution contrast, are primarily used in MMW imaging sensors. The unlicensed 60 GHz band is a promising band, due to its wide bandwidth, about 7 GHz (57 - 64 GHz), and lack of cost. However, at 60 GHz the propagation loss is relatively high, creating design challenges for operating this band in MMW screening. A high gain, low profile, affordable, and efficient probe is essential for such applications at 60 GHz. This thesis’s focus is on design and implementation of high gain MMW probes to optimize the performance of detection/imaging systems. First, single-element broadside radiation microstrip antennas and novel probes of endfire tapered slot high efficient antennas are presented. Second, a 57-64 GHz, 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer controlled phase shifter is presented. Then, a mechanical scanner is designed specifically to test proposed antenna probes utilizing low-power 60 GHz active monostatic transceivers. The results for utilizing proposed 60 GHz probes show success in detecting and identifying concealed weapons and explosives in liquids or plastics. As part of the first research theme, a 60 GHz circular patch-fed high gain dielectric lens antenna is presented, where the prototype’s measured impedance bandwidth reaches 3 GHz and a gain of 20 dB. A low cost, 60 GHz printed Yagi antenna array was designed, optimized, fabricated and tested. New models of the antipodal Fermi tapered slot antenna (AFTSA) with a novel sine corrugated (SC) shape are designed, and their measured results are validated with simulated ones. The AFTSA-SC produces a broadband and high efficiency pattern with the capacity for high directivity for all ISM-band. Another new contribution is a novel dual-polarized design for AFTSA-CS, using a single feed with a pair of linearly polarized antennas aligned orthogonally in a cross-shape. Furthermore, a novel 60 GHz single feed circularly polarized (CP) AFTSA-SC is modeled to radiate in the right-hand circularly polarized antenna (RHCP). A RHCP axial ratio bandwidth of < 3dB is maintained from 59 to 63 GHz. In addition, a high gain, low cost 60 GHz Multi Sin-Corrugations AFTSA loaded with a grooved spherical lens and in the form of three elements to operate as the beam steering antenna is presented. These probes show a return loss reduction and sidelobes and backlobe suppression and are optimized for a 20 dB or higher gain and radiation efficiency of ~90% at 60 GHz. The second research theme is implementing a 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer (PET) controlled phase shifter. A power divider with a triangular feed which reduces discontinuity from feed lines corners is introduced. A 1 × 16-element array is fabricated using 60 GHz AFTSA-SC antenna elements and showed symmetric E-plane and H-plane radiation patterns. The feed network design is surrounded by electromagnetic band-gap (EBG) structures to reduce surface waves and coupling between feed lines. The design of a circularly polarized 1 × 16-element beam steering phased array with and without EBG structures also investigated. A target detection investigation was carried out utilizing the proposed 60GHz antennas and their detection results are compared to those of V-band standard gain horn (SGH). System setup and signal pre-processing principle are introduced. The multi-corrugated MCAFTSA-SC probe is evaluated with the imaging/detection system for weapons and liquids concealed by clothing, plywood, and plastics. Results show that these items are detectable in clear 2D image resolution. It is believed that the 60 GHz imaging/detection system results using the developed probes show potential of detecting threatening objects through screening of materials and public

TERASENSE: THz device technology laboratory: final summary

The use of THz frequencies, particularly W and G band allows reaching higher resolution and deeper penetration in emerging applications like imaging, sensing, etc. The development of those new applications lays on reliable technologies, background of expertise and know-how. The CDS2008-00068 TERASENSE CONSOLIDER project has given the opportunity to extent upwards in frequency the previous background of the microwaves research group partners. This article summarizes the developments of the TERASENSE work package “THz Device Technology Laboratory”.This work was supported by the Spanish Ministerio de Ciencia e Innovación through the CONSOLIDER-INGENIO 2010 program reference CSD2008-00068 TERASENSE

Concealed Explosives Detection using Swept Millimetre Waves

The aim of this project is to develop a system for the stand-o detection (typically ten metres) of concealed body-worn explosives. The system must be capable of detecting a layer of explosive material hidden under clothing and distinguishing explosives from everyday objects. Millimetre wave radar is suitable for this application. Millimetre Waves are suitable because they are not signi cantly attenuated by atmospheric con- ditions and clothing textiles are practically transparent to this radiation. Detection of explosive layers from a few mm in thickness to a few cm thickness is required. A quasi optical focussing element is required to provide su cient antenna directivity to form a narrow, highly directional beam of millimetre waves, which can be directed and scanned over the person being observed. A system of antennae and focussing optics has been modelled and built using designs from nite element analysis (FEA) software. Using the developed system, represen- tative data sets have been acquired using a Vector Network Analyser (VNA) to act as transmitter and receiver, with the data saved for processing at a later time. A novel data analysis algorithm using Matlab has been developed to carry out Fourier Transforms of the data and then perform pattern matching techniques using arti cial neural networks (ANN's). New ways of aligning and sorting data have been found using cross-correlation to order the data by similar data slices and then sorting the data by amplitude to take the strongest 50% of data sets. The signi cant contribution to knowledge of this project will be a system which can be eld tested and which will detect a layer of dielectric at a stando distance, typically of ten metres, and signal processing algorithms which can recognise the di erence 17 between the response of threat and non-threat objects. This has partially been achieved by the development of focussing optics to acquire data sets which have then been aligned by cross-correlation, sorted and then used to train a pattern matching technique using neural networks. This technique has shown good results in di erentiating between a person wearing simulated explosives and a person not carrying simulated explosives. Further work for this project includes acquiring more data sets of everyday objects and training the neural network to distinguish between threat objects and non-threat objects. The operational range also needs increasing using either a larger aperture optical element or a similarly sized Cassegrain antenna. The system needs adapting for real time use with the data processing techniques developed in Matlab. The VNA is operated over a band of 14 to 40 GHz, future work includes moving to a stand-alone transmitter and receiver operating at w-band (75 to 110 GHz)