This thesis presents a theoretical description and experimental testing of two polarimetric fiber-optic strain sensors. 'The first .of these is an intrinsic sensor in which a single mode optical fiber acts as the sensing element. This sensor exhibited low strain sensitivity and high cross-sensitivity to temperature. The second sensor was of the extrinsic type, A single polarization maintaining fiber was used to deliver and collect light from the sensing element, which a was piece of photoelastic sheet PS-1. This type of sensor exhibited large dynamic range of 1:1350, resolution of 0.59ps, and strain sensitivity of the normalized signal of0.00219pe+1. / Thesis / Master of Engineering (ME)

The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

Innovation on human-machine interfacing technologies is critical for the development of smart, multifunctional and efficient electronic/optoelectronic systems. The effect of piezotronics is a newly started field of study, which utilizes piezoelectric polarization that is mechanically induced inside a piezoelectric semiconductor to regulate electron transport across electronic contact interfaces. With the concept coined in 2006, many efforts have been contributed to studying the underlying physical mechanism of this effect as well as demonstrating various applications based on single nanowire piezotronic devices. This thesis selects ZnO as the material foundation and was started by firstly studying flexible, controllable and scalable synthesis methods for ZnO nanowires array and thin film. By replacing the use of random, individual nanowires with these materials, novel piezotronic and piezophototronic devices were designed, fabricated and tested to achieve the function of strain sensing, tactile imaging, piezo-enhanced photodetection and solar energy harvesting. The adoption of nanowires array and thin film materials over single nanowires leads to significant advantages in terms of scalable fabrication, industrial compatibility and broader functionality. By consistently going down this route, we believe that the field of piezotronics will eventually make revolutionary impact on MEMS, optoelectronics, multifunctional sensor networks, human-machine interfacing and so on.

Health monitoring is an important field as small failures can build up and cause a catastrophic failure. Monitoring the health of a structure can be done by measuring the motion of the structure through the use of strain sensors. The limitations of current strain sensing technology; cost, size, form could be improved. This research intends to improve current strain sensing technology by creating a conductive polymer composite that can be used monitor health in structures. Conductive polymer composites are a viable candidate due to the low costs of manufacturing, tailorable mechanical and electrical properties, and uniform microstructure. This work will focus on determining if a all-polymer composite can be used as a strain sensor, and investigating the effects of filler, doping and latex effect the electrical and strain sensing properties. Strain sensors were prepared from polyaniline (PANI)-latex composites, the morphology, mechanical, electrical and strain sensing properties were evaluated. These strain sensors were capable of repeatable measuring strain to 1% and able to measure strain until the substrates failure at 5% strain, with a sensitivity (measured by gauge factor) of between 6-8 (metal foil strain sensors have a gauge factor of 2). The best performing strain sensor consisted of 4 wt.% polyaniline. This composition had the best combination of gauge factor, linearity, and signal stability. Further experiments were conducting to see if improvements could be made by changing the polymer used for the matrix material, the molecular weight and the level of doping of the polyaniline. Results indicate through differences in strain sensing response; lower hysteresis and unrecoverable conductivity, that polyaniline latex composites can be adjusted to further improve their performance. The polyaniline-latex composites were able to repeatable measure strain to 1%, as well as strain until failure and with gauge factor between 6-8, and a 70% increase in signal at failure. These properties make these composites viable candidates to monitor health in structures, buildings, bridges, and damns.

The thesis deals with the design and implementation of broadband and narrowband antennas and their applications in practical environment. In this thesis, a new concept for designing the UWB antenna is proposed based on the CRLH metamaterials and this UWB antenna covers a frequency range from 2.45 GHz to 11.6 GHz. Based on the design of the UWB antenna, another antenna is developed that can cover a very wide bandwidth i.e from 0.66 GHz to 120 GHz. This antenna can not only be used for UWB applications but also for other communication systems working below the UWB spectrum such as GSM, GPS, PCS and Bluetooth. The proposed antenna covering the bandwidth from 0.66 GHz to 120 GHz is by far the largest bandwidth antenna developed based on metamaterials. Wide band antennas are not preferred for sensing purpose as it is difficult to differentiate the received signals. A multiband antenna which can be used as a strain sensor for structural health monitoring is proposed. The idea is to correlate the strain applied along the length or width with the multiple resonant frequencies. This gives the advantage of detecting the strain applied along any direction (either length or width), thus increasing the sensing accuracy. Design and application of a narrow-band antenna as a temperature sensor is also presented. This sensor can be used to detect very high temperature changes (>10000C). This sensor does not require a battery, can be probed wirelessly, simple and can be easily fabricated, can withstand harsh environmental conditions.

No description available.

Over the 1980’s, the introduction of Additive Manufacturing (AM) technologies has provided alternative methods for the fabrication of complex three-dimensional (3D) synthetic bone tissue implant scaffolds. However, implants are still unable to provide post surgery feedback. Implants often loosen due to mismatched mechanical properties of implant material and host bone. The aim of this PhD research is to fabricate an integrated strain gauge that is able to monitor implant strain for diagnosis of the bone healing process. The research work presents a method of fabricating electrical resistance strain gauge sensors using rapid and mask-less process by experimental development (design of experiment) using the nScrypt 3Dn-300 micro dispensing direct write (MDDW) system. Silver and carbon electrical resistance strain gauges were fabricated and characterised. Carbon resistive strain gauges with gauge factor values greater than 16 were measured using a proven cantilever bending arrangement. This represented a seven to eight fold increase in sensitivity over commercial gauges that would be glued to the implant materials. The strain sensor fabrication process was specifically developed for directly fabricating resistive strain sensor structures on synthetic bone implant surface (ceramic and titanium) without the use of glue and to provide feedback for medical diagnosis. The reported novel approach employed a biocompatible parylene C as a dielectric layer between the electric conductive titanium and the strain gauge. Work also showed that parylene C could be used as an encapsulation material over strain gauges fabricated on ceramic without modifying the performance of the strain gauge. It was found that the strain gauges fabricated on titanium had a gauge factor of 10.0±0.7 with a near linear response to a maximum of 200 micro strain applied. In addition, the encapsulated ceramic strain gauge produced a gauge factor of 9.8±0.6. Both reported strain gauges had a much greater sensitivity than that of standard commercially available resistive strain gauges.

Ao longo dos últimos anos, redes de Bragg em fibras ópticas (FBG, do inglês Fiber Bragg Gratings) vêm sendo frequentemente utilizadas como sensores de deformação e de temperatura. O problema da indistinguibilidade entre esses dois parâmetros físicos, presente durante medidas realizadas por esse tipo de sensor, tem sido bem resolvido com o uso de duas FBGs com comprimentos de onda distintos. Muito embora esse artifício tenha apresentado bons resultados, ele também oferece algumas desvantagens, sendo uma delas a necessidade de duas fontes de luz para diferentes comprimentos de onda. Em virtude disto, este trabalho apresenta um sistema capaz de realizar medidas de temperatura e deformação, simultaneamente, utilizando apenas uma fonte de luz. O método baseia-se na inscrição de duas redes de Bragg com comprimentos de onda próximos (no caso, 810 e 860 nm) na mesma posição da fibra óptica. Apesar de a separação entre os comprimentos de onda das FBGs ser aparentemente pequena (cerca de 50 nm), o sistema respondeu precisamente a variações de deformação e temperatura. Dessa forma, a utilização de apenas uma fonte de luz no sistema é corretamente justificada, uma vez que, com essa alteração, o custo do sistema é substancialmente reduzido. Ademais, o uso de comprimentos de onda em torno de 800 nm também barateia o sistema, pois os CCDs usados neste intervalo espectral são menos onerosos do que aqueles tradicionalmente usados em comprimentos de onda de comunicações ópticas (1,55 &mu;m). / In recent years, fiber Bragg gratings (FBGs) have been frequently used as strain and temperature sensors. Several studies have tackled the problem of distinguishing between these two physical parameters using a dual-wavelength sensor. Although these sensors have shown good results, they have a few drawbacks, one of them being the need for two light sources with different wavelengths. We present an approach for simultaneous strain and temperature sensing which uses only one light source. The method relies on writing FBGs with nearby wavelengths (for instance, at 810 and 860 nm) at the same section of the fiber. Even though the Bragg wavelengths are separated by just a few nanometers (about 50 nm), it is possible to accurately measure variations in strain and temperature. One of the major advantages of this approach is the use of a unique light source, what reduces substantially the system cost. Another advantage is the lower cost of array detectors at 800 nm when compared to those of telecom wavelengths (1,55 &mu;m).

Tecnologias para o monitoramento de componentes estruturais, como strain gauges e fibra ótica, são comumente utilizadas quando deseja-se obter informações sobre o estado de deformação. Ambas as técnicas exigem cabeamento, produzindo diversas adversidades em suas aplicações. Assim, novas tecnologias sem fio vem ganhando espaço, buscando monitoramento remoto e versátil. Sensores sem fio, utilizando a tecnologia de identificação por radiofrequência (RFID), se mostram atrativos meios de contornar estas adversidades. Estes sensores são formados por uma antena e um componente integrado de identificação RFID. O conceito de funcionamento do sensor é que ao ser fixado no componente que deseja ser monitorado, irá sofrer esforços mecânicos semelhantes aos esforços sofridos pelo componente e irá se deformar. Esta deformação conduzirá a uma alteração sua frequência de ressonância. Dessa forma, dependendo do tipo de esforço uma resposta será obtida. Para construção do sensor foi utilizado o material NY9220 para o corpo de prova uma chapa de alumínio de 2 mm de espessura. Para validação do sensor, incialmente foi realizado um estudo numérico pelo método de elementos finitos. Posteriormente uma etapa experimental foi realizada onde o sensor foi fixado através de resina ao corpo de prova. À medida que deslocamentos eram aplicados os dados da frequência de ressonância e deformação são coletados e estes correlacionados. Uma correlação linear entre frequência de ressonância e deformação foi verificada no modelo numérico e na parte experimental. O sensor se mostrou capaz de detectar e monitorar deformações em estruturas metálicas. / Technologies for the monitoring of structural components, such as strain gauges and fiber optic, are commonly used when information on the state of deformation is desired. Both techniques require cabling, producing various adversities in their applications. Thus, new wireless technologies have been gaining space, seeking remote and versatile monitoring. Wireless sensors, using Radio Frequency Identification (RFID) technology, are attractive means of getting around these adversities. These sensors consist of an antenna and an integrated identification component RFID. The concept of operation of the sensor is that when attached to the component it wishes to be monitored, it will undergo similar stresses to the stresses suffered by the component and will deform. This strain will lead to a change in its resonant frequency. In this way, depending on the type of effort, a response will be obtained. For the construction of the sensor was used the material NY9220 for the specimen a sheet of aluminum of 2 mm of thickness. For the validation of the sensor, a numerical study was initially carried out by the finite element method. Subsequently an experimental stage was performed where the sensor was fixed through resin to the specimen. As displacements were applied, the resonance and strain frequency data were collected and correlated. A linear correlation between resonance frequency and strain was verified in the numerical model and in the experimental part. The sensor was able to detect and monitor deformations in metal structures.