Publicação
Development of a high sensitivity FBG-based accelerometer
| Resumo: | Accelerometers are widely used in monitoring the structural integrity of many constructions, such as buildings and bridges. In this application, the sensor must have a high sensitivity and resonant frequency, both inversely proportional. Its working principle is based on the energy conversion of a stimulated mass (usually a cantilever) in a magnitude that allows signal acquisition. Typically, a sensor based on fibre Bragg gratings (FBG) technology translates the mechanical signals into wavelength shifts. The FBG-based accelerometers are highly efficient and have numerous advantages, such as easy multiplexing, minimised cabling and immunity to electromagnetic interference. This internship report aims to describe the developing process of an FBG-based accelerometer with high sensitivity (1000 pm/g) and resonant frequency (200 Hz) from the conceptual stage to prototype development and testing. The internship was carried out at HBK FiberSensing, in Porto, Portugal. The accelerometer developed consists of two masses connected by a main frame through flexures, configuring a symmetrical push-pull design. These flexures make the cantilever-based structure flexible. The use of two suspended gratings doubled the sensitivity and guaranteed temperature compensation. When comparing the simulated and experimental values, the resonant frequency computed an error of 3.65% and sensitivity was tested at different frequencies and accelerations, with the highest error value being 13.13%. However, the sensitivity and resonant frequency achieved with the prototype were respectively 24.10% and 74.10% higher than the requirements. The experimental tests have shown that the application of damping will be necessary for future improvement. Regarding the cross-sensitivity to temperature variation, the tests showed a value of 0.01 nm/°C, which is very low compared to the accelerometer’s sensitivity. The fatigue test allowed us to conclude that, considering the 100 million cycles applied, the accelerometer can have an infinite life. The proof of concept was validated with only one prototype modelling/manufacturing iteration. Some optimisations are still necessary to reach a minimum viable product (MVP), although the experimental results highlight the great potential of this solution. |
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| Autores principais: | Batista, Vinícius Campos de Oliveira |
| Assunto: | Accelerometer Fibre bragg gratings High sensitivity High eesonant frequency Structure health monitoring Dynamic simulation |
| Ano: | 2022 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso embargado |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Accelerometers are widely used in monitoring the structural integrity of many constructions, such as buildings and bridges. In this application, the sensor must have a high sensitivity and resonant frequency, both inversely proportional. Its working principle is based on the energy conversion of a stimulated mass (usually a cantilever) in a magnitude that allows signal acquisition. Typically, a sensor based on fibre Bragg gratings (FBG) technology translates the mechanical signals into wavelength shifts. The FBG-based accelerometers are highly efficient and have numerous advantages, such as easy multiplexing, minimised cabling and immunity to electromagnetic interference. This internship report aims to describe the developing process of an FBG-based accelerometer with high sensitivity (1000 pm/g) and resonant frequency (200 Hz) from the conceptual stage to prototype development and testing. The internship was carried out at HBK FiberSensing, in Porto, Portugal. The accelerometer developed consists of two masses connected by a main frame through flexures, configuring a symmetrical push-pull design. These flexures make the cantilever-based structure flexible. The use of two suspended gratings doubled the sensitivity and guaranteed temperature compensation. When comparing the simulated and experimental values, the resonant frequency computed an error of 3.65% and sensitivity was tested at different frequencies and accelerations, with the highest error value being 13.13%. However, the sensitivity and resonant frequency achieved with the prototype were respectively 24.10% and 74.10% higher than the requirements. The experimental tests have shown that the application of damping will be necessary for future improvement. Regarding the cross-sensitivity to temperature variation, the tests showed a value of 0.01 nm/°C, which is very low compared to the accelerometer’s sensitivity. The fatigue test allowed us to conclude that, considering the 100 million cycles applied, the accelerometer can have an infinite life. The proof of concept was validated with only one prototype modelling/manufacturing iteration. Some optimisations are still necessary to reach a minimum viable product (MVP), although the experimental results highlight the great potential of this solution. |
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