Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

Medical Application of Ultra-Wideband Technology

This chapter deals with the applications of ultra-wideband technology, especially for medical scope, and the most features and advantages that made it useful in this scope. Also, the chapter has been included with the most important medical applications of UWB technology. Ultra-wideband radar for angiography and UWB glucometer are the main applications which will be explained in this chapter. The exposure for safety aspects, the dielectric properties of human tissues, blood dielectric properties measurement using open-ended coaxial probe experiment to improve the blood image, and the ideal ultra-wideband pulses’ shape, width, and repetition time that are used for medical applications have been illustrated. Finally, the results (figures, tables, and experiment results), conclusions, and discussions have been mentioned

Enhanced microwave imaging of the subsurface for humanitarian demining applications

© Cranfield University 2020. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright ownerThis thesis presents a theoretical analysis and applied evaluation deploying ground penetrating radar (GPR) for landmine detection. An original contribution has been made in designing and manufacturing a light-weight, low-cost, fully polarimetric antenna system for GPR, enabling easy transportation and assembly. This facilitates extensive use by various smaller communities in remote areas. By achieving the goal of supplying various smaller communities with advanced ground penetrating radar technology the technological standard of landmine detection can be improved beyond existing solutions such as metal detection or manual probing. The novel radar system itself allows detection of various subsurface targets of different shapes and sizes, metallic and non-metallic, in a number of different soils, such as sand, loam or gravel and therefore can be used in versatile environments. The GPR system has been realised by designing novel light-weight, 3D printed X-band horn antennas, manufactured from single piece plastic then copper electroplated. These antennas are 50% lighter than their commercial equivalents. They are incorporated in an antenna array as a group of four to allow full-polarimetric imaging of the subsurface. High resolution images of landmines and calibration targets were performed in the subsurface over an experimental sand test bed. For performing subsurface measurements in the near-field, four novel gradient-index (GRIN) lenses were designed and 3D printed to be incorporated in the apertures of the Xband antennas. The improved target detection from these lenses was proven by scanning the test bed and comparing the imaging data of the antenna array with and without lensesattached. A rigorous theoretical study of different decomposition techniques and their effect on the imaging and detection accuracy for polarimetric surface penetrating data was performed and applied to the gathered imaging data to reliably isolate and detect subsurface targets. Studied decomposition techniques were Pauli decomposition parameters and Yamaguchi polarimetry decomposition. It was found that it is paramount to use both algorithms on one set of subsurface data to detect all features of a buried target. A novel temporal imaging technique was developed for exploiting natural occurring changes in soil moisture level, and hence its dielectric properties. Contrary to the previously introduced imaging techniques this moisture change detection (MCD) mechanism does not rely on knowledge of the used measurement setup or deploying clutter suppression techniques. This time averaged technique uses several images of a moist subsurface taken over a period while the moisture evaporates from the soil. Each image pixel is weighted by the phase change occurring over the evaporation period and a resulting B-scan image reveals the subsurface targets without surrounding clutter. Finally, a multi-static antenna set-up is examined on its capability for suppressing surface clutter and its limitations are verified by introducing artificial surface clutter in form of pebbles to the scene. The resulting technique was found to suppress up to 30 The GPR antenna system developed in this thesis and the corresponding imaging techniques have contributed to a significant improvement in subsurface radar imaging performance and target discrimination capabilities. This work will contribute to more efficient landmine clearance in some of the most challenged parts of the world

Enhanced Microwave Imaging of the Subsurface for Humanitarian Demining Applications

© Cranfield University 2020. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright ownerThis thesis presents a theoretical analysis and applied evaluation deploying ground penetrat ing radar (GPR) for landmine detection. An original contribution has been made in designing and manufacturing a light-weight, low-cost, fully polarimetric antenna system for GPR, enabling easy transportation and as sembly. This facilitates extensive use by various smaller communities in remote areas. By achieving the goal of supplying various smaller communities with advanced ground pene trating radar technology the technological standard of landmine detection can be improved beyond existing solutions such as metal detection or manual probing. The novel radar system itself allows detection of various subsurface targets of different shapes and sizes, metallic and non-metallic, in a number of different soils, such as sand, loam or gravel and therefore can be used in versatile environments. The GPR system has been realised by designing novel light-weight, 3D printed X-band horn antennas, manufactured from single piece plastic then copper electroplated. These an tennas are 50% lighter than their commercial equivalents. They are incorporated in an an tenna array as a group of four to allow full-polarimetric imaging of the subsurface. High resolution images of landmines and calibration targets were performed in the subsurface over an experimental sand test bed. For performing subsurface measurements in the near-field, four novel gradient-index (GRIN) lenses were designed and 3D printed to be incorporated in the apertures of the X band antennas. The improved target detection from these lenses was proven by scanning the test bed and comparing the imaging data of the antenna array with and without lenses attached. A rigorous theoretical study of different decomposition techniques and their effect on the imaging and detection accuracy for polarimetric surface penetrating data was performed and applied to the gathered imaging data to reliably isolate and detect subsurface targets. Studied decomposition techniques were Pauli decomposition parameters and Yamaguchi polarime try decomposition. It was found that it is paramount to use both algorithms on one set of subsurface data to detect all features of a buried target. A novel temporal imaging technique was developed for exploiting natural occurring changes in soil moisture level, and hence its dielectric properties. Contrary to the previously intro duced imaging techniques this moisture change detection (MCD) mechanism does not rely on knowledge of the used measurement setup or deploying clutter suppression techniques. This time averaged technique uses several images of a moist subsurface taken over a period while the moisture evaporates from the soil. Each image pixel is weighted by the phase change occurring over the evaporation period and a resulting B-scan image reveals the subsurface targets without surrounding clutter. Finally, a multi-static antenna set-up is examined on its capability for suppressing sur face clutter and its limitations are verified by introducing artificial surface clutter in form of pebbles to the scene. The resulting technique was found to suppress up to 30 The GPR antenna system developed in this thesis and the corresponding imaging tech niques have contributed to a significant improvement in subsurface radar imaging perfor mance and target discrimination capabilities. This work will contribute to more efficient landmine clearance in some of the most challenged parts of the world.Ph

M-sequenze based ultra-wideband radar and its application to crack detection in salt mines

Die vorliegende Dissertation beschreibt einen innovativen ultra-breitband (UWB)elektromagnetischen Sensor basierend auf einem Pseudo-Rauschverfahren.Der Sensor wurde für zerstörungsfreies Testen in zivilen Anwendungen entwickelt.Zerstörungsfreies Testen entwickelt sich zu einem immer wichtiger werdenden Bereich in Forschung und Entwicklung. Neben unzähligen weiteren Anwendungen und Technologien, besteht ein primäres Aufgabenfeld in der Überwachung und Untersuchung von Bauwerken und Baumaterialien durch berührungslose Messung aus der Ferne.Diese Arbeit konzentriert sich auf das Beispiel der Auflockerungszone im Salzgestein.Der Hintergrund und die Notwendigkeit, den Zustand der oberflächennahen Salzschichten in Salzminen kennen zu müssen, werden beleuchtet und die Messaufgabe anhand einfacher theoretischer Überlegungen beschrieben. Daraus werden die Anforderungen für geeignete UWB Sensoren abgeleitet. Die wichtigsten Eigenschaften sind eine sehr hohe Messband breite sowie eine sehr saubere Systemimpulsantwort frei von systematischen Gerätefehlern. Beide Eigenschaften sind notwendig, um die schwachen Rückstreuungen der Auflockerungen trotz der unvermeidlichen starken Oberflächenreflexion detektieren zu können.Da systematische Fehler bei UWB Geräten technisch nicht von vorne herein komplett vermeidbar sind, muss der Sensor eine Gerätekalibrierung erlauben, um solche Fehler möglichst gut zu unterdrücken.Aufgrund der genannten Anforderungen und den Nebenbedingungen der Messumgebung unter Tage, wurde aus den verschiedenen UWB-Technologien ein Prinzip ausgewählt, welches pseudozufällige Maximalfolgen als Anregungssignal benutzt. Das M-Sequenzkonzept dient als Ausgangpunkt für zahlreiche Weiterentwicklungen. Ein neues Sendemodul erweitert dabei die Messbandbreite auf 12~GHz. Die äquivalente Abtastrate wird um den Faktor vier auf 36~GHz erhöht, ohne den geringen Abtastjitter des ursprünglichen Konzepts zu vergrössern.Weiterhin wird die Umsetzung eines Zweitormesskopfes zur Erfassung von S-Parametern sowie einer automatische Kalibriereinheit beschrieben. Etablierte Kalibrierverfahren aus dem Bereich der Netzwerkanalyse werden kurz rekapituliert und die Adaption des 8-Term Verfahrens mit unbekanntem Transmissionsnormal für das M-Sequenzsystem beschrieben. Dabei werden Kennwerte vorgeschlagen, die dem Bediener unter Tage einfach erlauben, die Kalibrierqualität einzuschätzen und Hinweise auf mögliche Gerätefehler oder andere Probleme zu bekommen. Die Kalibriergenauigkeit des neuen Sensors im Labor wird mit der eines Netzwerkanalysators verglichen. Beide Geräte erreichen eine störungsfreie Dynamik von mehr als 60~dB in den Systemimpulsantworten für Reflexion und Transmission.Der neu entwickelte UWB Sensor wurde in zahlreichen Messungen in Salzminen in Deutschland getestet. Zwei Messbeispiele werden vorgestellt - ein sehr alter, kreisrunder Tunnel sowie ein ovaler Tunnelstumpf, welcher kurz vor den Messungen erst aufgefahren wurde. Messaufbauten und Datenverarbeitung werden beschrieben. Schließlich werden Schlussfolgerungen und Vorschläge für zukünftige Arbeiten mit dem neuen M-Sequenzsensor sowie der Messung von Auflockerungen im Salzgestein diskutiert.This dissertation describes an innovative ultra-wideband (UWB) electromagnetic sensor device based on a pseudo-noise principle developed in the context of non-destructive testing in civil engineering.Non-destructive testing is becoming a more and more important fieldfor researchers and engineers alike. Besides the vast field of possibleapplications and testing technologies, a prime and therefore typical topic is the inspection and monitoringof constructions and materials by means of contactless remote sensing techniques.This work focuses on one example the assessment of the disaggregation zone in salt rock tunnels.The background and relevance of knowing the state of salt rock layers near a tunnel's surface are explainedand simple theoretical considerations for requirements of suitable UWB sensor devices are shown. The most important sensor parameters are a very large measurement bandwidth and a very clean impulse response. The latterparameter translates into the mandatory application of calibration techniques to remove systematic errors of the sensor system itself. This enables detection of weak scattering responses from near-surface disaggregation despite the presence of a strong surface reflection.According to the mentioned requirements and other side conditions in salt mine environments an UWB sensor principlebased on pseudo-noise stimuli namely M-Sequences is selected as a starting point for system development. A newtransmitter frontend for extending the stimulus bandwidth up to 12~GHz is presented. Furthermore, a technique for increasing the (equivalent) sampling rate while keeping the stable and low-jitter sampling regime of the M-Sequencesapproach is introduced and its implementation is shown. Moreover, an automatic calibration unit for full two-port coaxial calibration of the new UWB sensor has been developed. Common calibration techniques from the area of vector network analysers are shortly reviewed and a reasonablealgorithm the 8-term method with an unknown line standard - is selected for the M-Sequences device. The 8-term method is defined in the frequency domain and is adapted for use with time domain devices. Some performance figures and comparisonwith calibration results from network analysers are discussed to show the effectiveness of the calibration.A spurious-free dynamic range of the time domain impulse responses in excess of 60~dB has been achieved for reflection as well as transmission measurements.The new UWB sensor was used in various real world measurements in different salt mines throughout Germany. Two measurementexamples are described and results from the disaggregation zone of a very old and a freshly cut tunnel will be presented. Measurement setup and data processing are discussed and finally some conclusions for future work on this topic are drawn

Design of Miniaturized Antipodal Vivaldi Antennas and a Microwave Head Imaging System for the Detection of Blood Clots in the Brain

Traditional brain imaging modalities, for example, MRI, CT scan, X-ray, etc. can provide precise and high-resolution images of the brain for diagnosing lesions, tumors or clots inside the brain. However, these modalities require bulky and expensive test setups accessible only at specialized diagnostic centers, and hence may not be suitable or affordable to many patients. Furthermore, the inherent health risks limit the usability of these modalities for frequent monitoring. Microwave imaging is deemed a promising alternative due to its being cost-effective, portable, non-ionizing, non-intrusive. Therefore, this work aims to design an effective microwave head imaging system for the detection of blood clots inside the brain. Two miniaturized antipodal Vivaldi antenna designs are proposed which can provide wideband operation covering the low microwave frequency range (within 1 - 6 GHz) while having electrically small dimensions, directional radiation pattern with reasonable gain, and without requiring immersion in any matching/ coupling liquid. A head imaging system is presented which utilizes a quarter-head scanning approach, to reconstruct four images of the brain by scanning four quarters of the head, using the designed antipodal wideband Vivaldi antenna. A numerical brain model, with and without the presence of blood clot, is simulated using the proposed head-imaging system. At each quarter, the antenna is placed at nine different positions for scanning. The reflected signal at each position is processed and using confocal microwave imaging technique four images of the brain are reconstructed. A comparison is made among the four images in terms of their intensities, for the detection and approximate location of the blood clot inside the brain. The presence of higher intensity regions in any specific quarter of the head demonstrates the presence of a clot and its location and validates the feasibility of the proposed head imaging system using the low frequency wideband Vivaldi antenna

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

UWBレーダのための多偏波散乱データ学習に基づく高精度立体画像外挿法

UWB(Ultra -wideband)レーダは，高い距離分解能を有し，光学センサが適用困難な暗闇や濃煙環境下での計測が可能であるため，救助ロボットやセキュリティーシステム，高齢者等の見守りシステムに搭載する近距離立体イメージングセンサとして有望である．同レーダを用いた高精度画像化技術として，合成開口処理(Synthetic Aperture Radar :SAR)やRPM(Range Points Migration)法などがこれまでに提案されている．　一般に，レーダ画像化では素子可動領域が十分に確保できない状況下では，特に遠方にある目標物体の画像再現領域を十分に確保することが難しいという問題を有する．上記問題を解決するため，人体や目標形状を近似的に楕円体の集合とみなし，楕円外挿法を適用することで目標形状を外挿する手法が提案されている．同手法は，観測データから直接的に抽出される距離点群を用いた楕円当てはめを採用しており，目標形状推定点群の推定誤差の影響を受けないため，高精度に外挿可能である．しかし，同手法は楕円体近似に基づくため，楕円体と大きく異なる目標形状に対しては外挿精度が著しく劣化する問題がある．　本論文では，上記の問題点を解決すべく，多偏波散乱データ解析により，RPM法で再現される各推定点に楕円体の一部を当てはめる手法を提案する．本手法では様々な楕円体目標に対する多偏波散乱データを解析・学習し，RPM法による推定点を点の集合ではなく，楕円体の一部の集合で表現する．一般に，各偏波情報には，目標境界の散乱中心位置付近の局所的情報だけではなく，目標形状全体の大局的な情報が含まれており，形状推定に有用である．提案法では，様々な楕円体目標からの多偏波散乱データをFDTD(Fnite Difference Time Domain)法で生成し，形状推定に有用な特徴量をNeural Network（NN と呼称）で学習させる．次に，RPM法で得られた目標推定点に対して，NNから楕円体パラメータを推定し，その一部をRPM法の推定点に当てはめる．また，距離減衰による振幅補正を考慮する距離補正法を導入する．多様な目標形状に対して，FDTD法により生成されたデータを用いて，提案法の有効性を示す．電気通信大学201