Gapped cantilever for the enhancement of strain sensitivity and energy efficiency

Cantilever structures have been widely used in a large variety of transducer applications. For cantilever based transducers, piezoresistive/piezoelectric mechanisms has always been a popular choice due to the advantages of being low cost, simple structure and portability. However, low sensitivity is recognized as a major disadvantage of these transducers compared with optical based measurement. In this research, a gapped cantilever structure is proposed to potentially increase the sensitivity by orders of magnitude. In order to guide the design, an advanced analytical model is developed, and the increased strain sensitivity is theoretically demonstrated. In addition, optimizations with this model interestingly reveal that the gapped cantilever is much more efficient than conventional cantilever from energy perspective as well. Applications of gapped cantilever structure including piezoresistive accelerometer, vibration energy harvester and resonant mass sensor are carefully investigated in this work. Multiple prototypes of these applications both in meso-scale and micro-scale are designed, manufactured and characterized. The testing results show good agreement with theoretical expectation, and demonstrate a good potential of gapped cantilever structure for the enhancement of strain sensitivity and energy efficiency

Flexible bond wire capacitive strain sensor for a vehicle tyre

This thesis reports a novel flexible wire bond structured capacitive sensor design that can measure the strain in the tyres stably and reliably without any influence or disturbance to the tyre material during the measurement. An industry achievable fabrication method based on the design has been also investigated and it is also believed that there is a possibility of introducing the sensor into mass production. Bond wire technology, laser machining technology and photolithography technology are adopted to fabricate the strain sensor, in which the wire bonding technology is the most significant process for this design. An array of 25 micrometer bond wires that are normally employed for electrical connections in integrated circuits is built to create an interdigitated structure and generating approximately 10pF capacitance. The array that in an approximately 8*8 mm area consists of 50 wire loops and creates 49 capacitor pairs. The aluminium wires are bonded to a flexible PCB which is specially finished to allow direct bonding to copper surface. The wire array is finally packaged and embedded in a flexible and compliant material, polydimethylsiloxane (PDMS), which acts as the structural material that is strained. The implementations of the bond wire, the flexible PCB and PDMS embedding minimize the stiffness of the strain sensor while the PDMS can also prevent the sensor from any potential damage. When a tensile strain occurs, the wires are stretched further apart reducing the capacitance. On the contrary, the wires move closer and increase the capacitance if the strain sensor is compressed. Different from the traditional interdigital capacitor, the capacitance of the device is almost in a linear relationship with respect to the strain, which can measure the strain up to at least ±60000 micro-strain (±6%) with the resolution of 111 micro-strain (0.01%)

Desenvolvimento de uma matriz de sensores piezoresistivos baseados em técnicas de impressão

Dissertação de mestrado em Técnicas de Caracterização e Análise QuímicaA implementação de materiais inteligentes nomeadamente piezoresistivos, numa grande variedade de aplicações que vão desde componentes para automóveis a dispositivos médicos, é uma prática cada vez mais comum. De uma forma particular, a utilização de matrizes poliméricas reforçadas com materiais condutores tem-se vindo a tornar uma opção interessante para o desenvolvimento de sensores mais eficientes que aumentam a aplicabilidade dos mesmos. No entanto, a remoção de solventes tóxicos no fabrico destes materiais e o desenvolvimento de estratégias para a produção em larga escala são problemas para os quais são necessárias soluções urgentes e inovadoras. A utilização de solventes “verdes” permite resolver o primeiro problema e as técnicas de impressão solucionar o segundo. Desta forma, este trabalho propõe o desenvolvimento de três tipos de nanocompósitos piezoresistivos de base polimérica reforçados com diferentes concentrações de nanotubos de carbono, utilizando uma abordagem “verde”. Isto é, pretende-se substituir o solvente tóxico (tolueno) presente num desses nanocompósitos por um solvente “verde”, o metoxiciclopentano. Pretende-se ainda desenvolver outro nanocompósito com base aquosa, pois a água é o solvente menos tóxico e mais seguro. Após a caraterização estrutural, morfológica, mecânica, elétrica, eletromecânica e reológica de todos os nanocompósitos, escolheu-se um de base “verde” e um de base aquosa, cujas propriedades mais se adequassem ao desenvolvimento de um sensor piezoresistivo. Estes dois nanocompósitos permitiram obter uma boa linearidade entre a deformação mecânica e a variação da resistência elétrica e ainda um Gauge Factor cujos valores variam entre 1,1 e 2,8. Através da adaptação da viscosidade de ambos os nanocompósitos para impressão por spray (142-407 cP) e serigrafia (774-1490 cP) imprimiram-se quatro sensores piezoresistivos de deformação. Os sensores impressos permitiram obter linearidade e sensibilidade próximas daqueles obtidos através de técnicas de produção em pequena escala.The smart materials implementation, particularly the piezoresistive ones, are increasingly present in a wide variety of applications ranging from automotive components to medical devices. Particularly, the use of a polymeric matrix reinforced with conductive materials has become an interesting option to develop more efficient sensors, which increases their applicability. Further, the removal of toxic solvents in the manufacture of these materials and the development of large scale production techniques are issues which require urgent and innovative solutions. The use of “green” solvents allows to solve the first problem and the printing technologies the second one. Thus, this work proposes the development of three types of piezoresistive polymer based nanocomposites reinforced with different concentrations of carbon nanotubes, using a “green” approach. The main objective is to replace the toxic solvent (toluene) present in the nanocomposite by a “green” solvent, the cyclopentyl methyl ether. It is also intended to develop a water-based nanocomposite, since water is the less toxic and safer solvent. After the structural, morphological, mechanical, electrical, electromechanical and rheological characterization of all nanocomposites, it was chosen a green-based and a water-based nanocomposite, whose properties were more suitable for the development of a piezoresistive sensor. These nanocomposites allowed to obtain a good linearity between the mechanical deformation and the variation of the electrical resistance and also a Gauge Factor between 1.1 and 2.8. By adjusting nanocomposites viscosities for spray printing (142-407 cP) and screen printing (774-1490 cP), four piezoresistive strain sensors were printed. The printed sensors allowed to achieve a linearity and sensibility close to the ones obtained through small scale production techniques

Polymers and Their Application in 3D Printing

Dear Colleagues, Fused filament fabrication, also known as 3D printing, is extensively used to produce prototypes for applications in, e.g., the aerospace, medical, and automotive industries. In this process, a thermoplastic polymer is fed into a liquefier that extrudes a filament while moving in successive X–Y planes along the Z direction to fabricate a 3D part in a layer-by-layer process. Due to the progressive advances of this process in industry, the application of polymeric (or even composite) materials have received much attention. Researchers and industries now engage in 3D printing by implementing numerous polymeric materials in their domain. In this Special Issue, we will present a collection of recent and novel works regarding the application of polymers in 3D printing

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018