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

Roadmap on measurement technologies for next generation structural health monitoring systems

Structural health monitoring (SHM) is the automation of the condition assessment process of an engineered system. When applied to geometrically large components or structures, such as those found in civil and aerospace infrastructure and systems, a critical challenge is in designing the sensing solution that could yield actionable information. This is a difficult task to conduct cost-effectively, because of the large surfaces under consideration and the localized nature of typical defects and damages. There have been significant research efforts in empowering conventional measurement technologies for applications to SHM in order to improve performance of the condition assessment process. Yet, the field implementation of these SHM solutions is still in its infancy, attributable to various economic and technical challenges. The objective of this Roadmap publication is to discuss modern measurement technologies that were developed for SHM purposes, along with their associated challenges and opportunities, and to provide a path to research and development efforts that could yield impactful field applications. The Roadmap is organized into four sections: distributed embedded sensing systems, distributed surface sensing systems, multifunctional materials, and remote sensing. Recognizing that many measurement technologies may overlap between sections, we define distributed sensing solutions as those that involve or imply the utilization of numbers of sensors geometrically organized within (embedded) or over (surface) the monitored component or system. Multi-functional materials are sensing solutions that combine multiple capabilities, for example those also serving structural functions. Remote sensing are solutions that are contactless, for example cell phones, drones, and satellites. It also includes the notion of remotely controlled robots

Development of a chipless RFID based aerospace structural health monitoring sensor system

Chipless Radio Frequency Identification (RFID) is modern wireless technology that has been earmarked as being suitable for low-cost item tagging/tracking. These devices do not require integrated circuitry or a battery and thus, are not only are cheap, but also easy to manufacture and potentially very robust. A great deal of attention is also being put on the possibility of giving these tags the ability to sense various environmental stimuli such as temperature and humidity. This work focusses on the potential use of chipless RFID as a sensor technology for aerospace Structural Health Monitoring. The project is focussed on the sensing of mechanical strain and temperature, with an emphasis placed on fabrication simplicity, so that the final sensor designs could be potentially fabricated in-situ using existing printing technologies. Within this project, a variety of novel chipless RFID strain and temperature sensors have been designed, fabricated and tested. A thorough discussion is also presented on the topic of strain sensor cross sensitivity, which places emphasis on issues like, transverse strain, dielectric constant variations and thermal swelling. Additionally, an exploration into other key technological challenges was also performed, with a focus on challenges such as: accurate and reliable stimulus detection, sensor polarization and multi-sensor support. Several key areas of future research have also been identified and outlined, with aims related to: Enhancing strain sensor fabrication simplicity, enhancing temperature sensor sensitivity and simplicity and developing a fully functional interrogation system

Miniaturized RF Components With A Novel Tunable Engineered Substrate For Wireless Communication Systems

There is an increasing demand for reliable sensor system capable of remote sensing and measuring interesting data. Although large communication range can be achieved, active wireless communication systems are still suboptimal in longtime applications due to their harmful battery supply. Inductively coupled passive devices, with the advantages in safe long-term implanting, structural simplicity, small fabrication footprint and low-cost production, are preferred in chronic monitoring, but little work has been done to optimize the performance of these systems, especially under some design constraints. The model and optimization of an inductively coupled wireless pressure sensor system is presented in this dissertation. With MEMS and semiconductor technology, the pressure sensor is designed as a miniaturized LC resonant circuit operating in 402MHz within a small footprint of 3.2 mm by 3.2 mm. An optimization approach is conducted to analyze inductive as well as pressure sensitivity. With mutually dependent geometrical parameters and performance related RF characteristics considered in the full optimization of the system, the applied design of this experiment method can reduce the large number of combined groups of values in fractional simulations with a focus on a few performance related factors. The second task of this research is to improve the limited working range of the sensing system. A half-active wireless communication system is studied as an alternative solution to this problem. Wireless power harvesting circuits and auxiliarydata-acquisition circuits are integrated in the system for long distance communication. However, physical size of system also becomes large with the added circuits. The challenges of designing compact wireless communication system are proposed to be solved in this dissertation. With the requirements of multi-band and multi-function in wireless communication systems with improved performance and reduced size, development of tunable miniaturized RF components are a promising solution to fulfill the trend. Many technologies have been investigated and applied to develop tunable devices including MEMS and semiconductor varactors, ferroelectric capacitors, and magnetically tunable inductors with ferromagnetic materials, etc. However, the tunability of reported devices using the above technologies is directly dependent on the individual design configurations, which limits the design flexibility and broader application. A unique solution is to design arbitrary tunable RF components using an engineered substrate with an embedded patterned permalloy (Py) thin film which was developed for the first time in this dissertation. With high and current-dependent permeability, an engineered substrate embedded with Py thin film is a promising and flexible approach to design compact frequency-agile RF devices. Py thin film is patterned into slim bars on an engineered substrate to improve its ferromagnetic resonant frequency (FMR) for RF and mmwave applications. Miniaturized RF components are first developed with the proposed engineered magneto-dielectric substrate in this dissertation. Permeability tunable smart substrate was also developed by integrating an array of DC bias lines to provide a tuning path of Py patterns. The design principles and factors affecting the characteristics of the engineered substrate have been fully analyzed. Design efficacy of the developed tunable substrate has been demonstrated with implemented components including a patch antenna, a phase shifter, a bandpass filter, and a three-port bandpass filtering balun. The proposed engineered substrate is feasible in implementing arbitrary RF and microwave devices with improved tuning capability and design flexibility

Microwave Devices for Wearable Sensors and IoT

The Internet of Things (IoT) paradigm is currently highly demanded in multiple scenarios and in particular plays an important role in solving medical-related challenges. RF and microwave technologies, coupled with wireless energy transfer, are interesting candidates because of their inherent contactless spectrometric capabilities and for the wireless transmission of sensing data. This article reviews some recent achievements in the field of wearable sensors, highlighting the benefits that these solutions introduce in operative contexts, such as indoor localization and microwave sensing. Wireless power transfer is an essential requirement to be fulfilled to allow these sensors to be not only wearable but also compact and lightweight while avoiding bulky batteries. Flexible materials and 3D printing polymers, as well as daily garments, are widely exploited within the presented solutions, allowing comfort and wearability without renouncing the robustness and reliability of the built-in wearable sensor

Pop-Up Stretchable Sensor Designs Using Multiphysics Modeliing

Stretchable electronic devices are critical for the future of wearable sensor technology, where existing rigid and non-flexible devices severely limit the applicability of them in many areas. Stretchable electronics extend flexible electronics one step further by introducing significant elastic deformation. Stretchable electronics can conform to curvy geometries like human skin which enables new applications such as fully wearable electronics whose properties can be tuned through mechanical deformation. Much of the effort in stretchable electronics has focused on investigation of the optimum fabrication method to make a trade-off between the manufacturing cost and acceptable performance. Here in this thesis a novel pop-up strain sensor design is introduced and tested.This technique is simple to use and can be applied to almost all available materials such as metals, dielectrics, semiconductors and different scales from centi-meter to nanoscale. Using this method three main electronic devices have been designed for different applications. The first category is pop-up antennas that are able to reconfigure their frequency response with respect to the mechanical deformation by out of plane displacement. The second category is pop-up frequency selective surface which similarly can change its frequency behaviour due to applied strain. This ability to accommodate the applied stress by three-dimensional (3D) deformation, making these devices ideal for strain sensing applications such as vapor sensing or on skin mountable sensors. Using the advantage of RFID technology in terms of wireless monitoring, the third category has been introduced which is a pop-up capacitor sensor integrating with an RFID chip to detect finger joint bending that can help those patients who are recovering after stroke. The proposed devices have been modelled using COMSOL Multiphysics and Extensive evaluations of the prototype system were conducted on purpose-built laboratory scale test rigs. Both results are in good correlation which makes them applicable for sensing purposes

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)