Battery-Free Antenna Sensors for Strain and Crack Monitoring: Technical Report

This project studies a wireless patch antenna as a novel strain/crack sensing technique for structural health monitoring (SHM). The strain/crack induced resonance frequency shift of the antenna can be wirelessly detected and utilized to estimate the surface strain and crack propagation. However, temperature fluctuation can generate some unwanted changes in resonance frequency and introduce significant noises in measurement. This project studies a thermally stable patch antenna sensor through both numerical simulations and laboratory experiments. Using a substrate material with a steady dielectric constant, a patch antenna sensor is designed to perform reliably under temperature fluctuations. In addition, a dual-mode patch antenna sensor is designed to achieve long interrogation distance. Various types of materials used in substrate are investigated through laboratory tests. Strain/crack sensing performance has been validated through multi-physics simulations and experiments. The patch antenna sensors are demonstrated to be effective in wireless strain/crack measurements and have potential for large-scale monitoring of structures

A Study of Microfluidic Reconfiguration Mechanisms Enabled by Functionalized Dispersions of Colloidal Material for Radio Frequency Applications

Communication and reconnaissance systems are requiring increasing flexibility concerning functionality and efficiency for multiband and broadband frequency applications. Circuit-based reconfiguration mechanisms continue to promote radio frequency (RF) application flexibility; however, increasing limitations have resulted in hindering performance. Therefore, the implementation of a "wireless" reconfiguration mechanism provides the required agility and amicability for microwave circuits and antennas without local overhead. The wireless reconfiguration mechanism in this thesis integrates dynamic, fluidic-based material systems to achieve electromagnetic agility and reduce the need for "wired" reconfiguration technologies. The dynamic material system component has become known as electromagnetically functionalized colloidal dispersions (EFCDs). In a microfluidic reconfiguration system, they provide electromagnetic agility by altering the colloidal volume fraction of EFCDs - their name highlights the special considerations we give to material systems in applied electromagnetics towards lowering loss and reducing system complexity. Utilizing EFCDs at the RF device-level produced the first circuit-type integration of this reconfiguration system; this is identified as the coaxial stub microfluidic impedance transformer (COSMIX). The COSMIX is a small hollowed segment of transmission line with results showing a full reactive loop (capacitive to inductive tuning) around the Smith chart over a 1.2 GHz bandwidth. A second microfluidic application demonstrates a novel antenna reconfiguration mechanism for a 3 GHz microstrip patch antenna. Results showed a 300 MHz downward frequency shift by dielectric colloidal dispersions. Magnetic material produced a 40 MHz frequency shift. The final application demonstrates the dynamically altering microfluidic system for a 3 GHz 1x2 array of linearly polarized microstrip patch antennas. The parallel microfluidic capillaries were imbedded in polydimethylsiloxane (PDMS). Both E- and H-plane designs showed a 250 MHz frequency shift by dielectric colloidal dispersions. Results showed a strong correlation between decreasing electrical length of the elements and an increase of the volume fraction, causing frequency to decrease and mutual coupling to increase. Measured, modeled, and analytical results for impedance, voltage standing wave ratio (VSWR), and radiation behavior (where applicable) are provided

Low Velocity Impact and RF Response of 3D Printed Heterogeneous Structures

Three-dimensional (3D) printing, a form of Additive manufacturing (AM), is currently being explored to design materials or structures with required Electro-Mechanical-Physical properties. Microstrip patch antennas with a tunable radio-frequency (RF) response are a great candidate for 3D printing process. Due to the nature of extrusion based layered fabrication; the processed parts are of three-layer construction having inherent heterogeneity that affects structural and functional response. The purpose of this study is to identify the relationship between the anisotropy in dielectric properties of AM fabricated acrylonitrile butadiene styrene (ABS) substrates in the RF domain and resonant frequencies of associated patch antennas and also to identify the response of the antenna before and after a low velocity impact. In this study, ANSYS high frequency structure simulator (HFSS) is utilized to analyze RF response of patch antenna and compared with the experimental work. First, a model with dimensions of 50 mm x 50 mm x 5 mm is designed in Solidworks and three separate sets of samples are fabricated at three different machine preset fill densities using an extrusion based 3D printer LulzBot TAZ 5. The actual solid volume fraction of each set of samples is measured using a 3D X-ray computed tomography microscope. The printed materials appeared to exhibit anisotropy such that the thickness direction dielectric properties are different from the planar properties. The experimental resonant frequency for one fill-density is combined with ANSYS-HFSS simulation results to estimate the bulk dielectric constant of ABS and the equivalent dielectric properties in planar and thickness directions. The bulk dielectric properties are then used in HFSS models for other two fill densities and the simulated results appear to match reasonably well with experimental findings. The similar HFSS modeling scheme was adopted to understand the effect of material heterogeneity on RF response. In addition, a hybrid structure with dimensions of 50 mm x 50 mm x 20 mm is designed with the first 15 mm thickness being a cellular BCC structure and the other 5 mm being a solid cuboid. These samples are printed on an extrusion based 3D printer Stratasys uPrint using ABS. A patch antenna is embedded at the interface of the solid and the cellular structure. Both ABAQUS finite element modeling and experimental methods are used to understand the load-displacement and the energy absorption behavior of the hybrid structure under low velocity impact loadings. The hybrid structure is impacted on both sides to investigate the damage tolerance capabilities of embedded electronic components

Fibre-meshed Textile Electromagnetic Structures

This thesis investigated novel textile electromagnetic structures fabricated by a commercial computerized knitting machine. Different electronics such as elliptical waveguides, slotted waveguide antennas (SWA) and frequency selective surfaces (FSS) working at microwave band had been realized with fully textile materials. Knitted polyester was used as a dielectric and silver embedded yarn was knitted to create conducting patterns. Most of the textile electromagnetic structures in this thesis were the first time proposed to the public. Their performances were studied in both simulation and measurement

An investigation of nanoscale materials and their incorporation in patch antenna for high frequency applications

The rapid development in the polymer-based electronic contribute a strong determination for using these materials as substitute to the high-cost materials commonly used as medium substrate in the fabrication of Microstrip Patch Antenna (MPA). Antenna technology can strongly gain from the utilisation of low-cost, flexible, light weight with suitable fabrication techniques. The uniqueness of this work is the use of variety of common but unexplored different polymer materials such as Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride, (PVC) Polystyrene (PS), Polystyrene fibre (PSF) as the substrates for the design and fabrication of different MPAs for communication and sensing applications in millimetre wave (MMW)region. Electrospinning (ES) technique is used to reconstruct PS and produced PSF material of low dielectric constant. A co-solvent vehicle(comprising 50:50 ratio) of Dichloromethane (DCM) and acetone was utilised with processing condition of solution infusion flow-rate of 60μL/min and an applied voltage of 12± kV yielded rigid PSF substrates. The PSF Produced has complex permittivity of 1.36±5% and a loss tangent of 2.4E-04±4.8E-04 which was measured using Spilt-Post Dielectric Resonators (SPDR) technique at National Physics Laboratory, Teddington, London. A diamond-shaped MPAs on RT Duriod material were simulated and fabricated using photo-lithography for different inner lengths to work in the frequencies range from (1-10 GHz). The resonant frequency is approximated as a function of inner length L1 in the form of a polynomial equation. The fabricated diamond-shaped MPA more compact (physical geometry) as compared with a traditional monopole antenna. This MPAs experimentally measured and have a good agreement with the simulated results. The coplanar waveguide (CPW) diamond-shaped MPA working in the MMW region was designed and fabricated with polymer materials as substrates using thermal evaporation technique and the RF measurement was carried out using Vector Network Analyser (VNA). The resonant frequencies of the CPW diamond shaped MPAs for (PE, PP, PVC, PS and PSF) were found to be 67.5 GHz, 72.36 GHz, 62.41 GHz, 63.25 GHz and 80.58 GHz, respectively. The antenna fabricated on PSF were resonating at higher frequency when compared to the other polymers materials. In adding an air-bridge to the CPW diamond-shaped MPA the resonating frequency increased from ≈55 GHz to≈ 62 GHz. Three different shaped nano-patch antennas (Diamond shaped, diamond shaped array and T-shaped) have been designed, simulated and fabricated on Silicon substrate with DLC deposition using focused Ion Beam (FIB) technique, these antennas were found to resonate at 1.42 THz with (-19 dB return loss), 2.42 THz with (-14 dB return loss) and 1.3 THz with (-45 dB return loss) respectively

New solutions for directive antennas and components for millimeter wave-band applications

Mención Internacional en el título de doctorEn las últimas décadas se ha producido un avance tecnológico exponencial en el área de las telecomunicaciones. Cada pocos años surgen sistemas de comunicaciones de nueva generación, siendo el 5G el que, hoy en día, se va implementando y ofreciendo progresivamente a los usuarios de todo el mundo. Los sistemas de comunicaciones 5G permiten tasas de datos mucho más altas, una velocidad ultrarrápida y un mayor ancho de banda que el 4G no soportaba debido a las bandas excesivamente utilizadas por debajo de los 6 GHz. Sin embargo, este aumento de la frecuencia introduce retos que no existen en frecuencias inferiores, como la absorción ambiental. Además, los obstáculos físicos que se interponen en el trayecto entre el emisor y el receptor también son un problema a estas frecuencias y las pérdidas inherentes a la propagación en el espacio libre son muy elevadas. El objetivo de esta tesis ha sido desarrollar e introducir nuevos e innovadores diseños de antenas que puedan ser utilizados en las bandas de frecuencia de las comunicaciones 5G y superiores así como en otras aplicaciones de ondas milimétricas. Los diseños que se presentan tienen como principal objetivo conseguir una alta directividad, manteniendo bajas pérdidas. Estos diseños se pueden agrupar en dos categorías principales: antenas Fabry-Pérot, y antenas gap waveguide. En la primera parte de esta tesis se han desarrollado tres diseños de antena Fabry-Pérot, incluyendo una metodología innovadora para el diseño de una metasuperficie que permite un funcionamiento en doble banda con control de directividad y que también puede ser utilizada también para implementar arrays de antenas en bandas de ondas milimétricas. Además, se muestra que este concepto de antenas Fabry-Pérot, implementado en un rango de frecuencias mucho más bajas, puede utilizarse también en aplicaciones de sistemas radar. En la segunda parte, se han desarrollado e implementado diseños innovadores de antenas y arrays usando la tecnología gap waveguide en particular su versión groove. En ellos, se han diseñado novedosas redes de alimentación y sistemas de corrección de fase que proporcionan bajas pérdidas y alta eficiencia.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: José Luis Masa Campos.- Secretario: Óscar Quevedo Teruel.- Vocal: Guido Valeri

Passive low frequency RFID for non-destructive evaluation and monitoring

Ph. D ThesisDespite of immense research over the years, defect monitoring in harsh environmental conditions still presents notable challenges for Non-Destructive Testing and Evaluation (NDT&E) and Structural Health Monitoring (SHM). One of the substantial challenges is the inaccessibility to the metal surface due to the large stand-off distance caused by the insulation layer. The hidden nature of corrosion and defect under thick insulation in harsh environmental conditions may result in it being not noticed and ultimately leading to failures. Generally electromagnetic NDT&E techniques which are used in pipeline industries require the removal of the insulation layer or high powered expensive equipment. Along with these, other limitations in the existing techniques create opportunities for novel systems to solve the challenges caused by Corrosion under Insulation (CUI). Extending from Pulsed Eddy Current (PEC), this research proposes the development and use of passive Low Frequency (LF) RFID hardware system for the detection and monitoring of corrosion and cracks on both ferrous and non-ferrous materials at varying high temperature conditions. The passive, low cost essence of RFID makes it an enchanting technique for long term condition monitoring. The contribution of the research work can be summarised as follows: (1) implementation of novel LF RFID sensor systems and the rig platform, experimental studies validating the detection capabilities of corrosion progression samples using transient feature analysis with respect to permeability and electrical conductivity changes along with enhanced sensitivity demonstration using ferrite sheet attached to the tag; (2) defect detection using swept frequency method to study the multiple frequency behaviour and further temperature suppression using feature fusion technique; (3) inhomogeneity study on ferrous materials at varying temperature and demonstration of the potential of the RFID system; (4) use of RFID tag with ceramic filled Poly-tetra-fluoro-ethyulene (PTFE) substrate for larger applicability of the sensing system in the industry; (5) lift-off independent defect monitoring using passive sweep frequency RFID sensors and feature extraction and fusion for robustness improvement. This research concludes that passive LF RFID system can be used to detect corrosion and crack on both ferrous and non-ferrous materials and then the system can be used to compensate for temperature variation making it useful for a wider range of applications. However, significant challenges such as permanent deployment of the tags for long term monitoring at higher temperatures and much higher standoff distance, still require improvement for real-world applicability.Engineering and Physical Sciences Research Council (EPSRC) CASE, National Nuclear Laboratory (NNL)