Ultra-low-power strain SOI sensor for wind turbine applications

(eng) The development of alternatives for thermal power plants is extensively growing to face the environmental issues caused by fossil fuels. Among these alternatives, wind turbines received a large part of the attention, leading to larger structures with higher power capacity. This size increase has brought a cost increase that can be critical for competitiveness. Structural health monitoring based on sensors is then becoming an important asset to reduce the cost of wind turbine by preventing structural damage while reducing the time required for maintenance. This work aims to develop a strain sensor to monitor the deformation of the wind turbine blades. Based on the data provided by the sensor, an appropriate strategy can then be set up to prevent failure. We start by introducing the key features of structural health monitoring and sensors in order to define the specifications needed for wind turbine applications. A literature review is done to find the best solution possible for strain measurements. It has been found that the piezoresistive properties of silicon lead to a high gauge factor up to 200. This material is used to form a transistor in SOI technology that allows both high strain sensitivity and low power consumption. A current mirror configuration is realized and experimented with these transistors. This configuration allows to recover the main piezoresistive component of silicon. On top of the experimental validation of the strain performances, mismatch and noise analyses and measurements are conducted and their impacts are discussed. In order to form the transducer, the mirror is simulated with LTSpice and integrated into a complete circuit. The circuit reaches a high gauge factor of 309 and a sensitivity of 0.5 nA/με for a power consumption of 10 μW. Finally, a second design is realized to reach a gauge factor of 1000 and a sensitivity of 2.72 nA/με at the cost of higher consumption of 70 μW.