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Combined MEMS Acoustic Emission and Strain Sensors for On Chip Data Fusion



The complexity of the damage evolution in structures requires redundant measurements from different sensing methods in order to increase the reliability of the Structural Health Monitoring (SHM) outcome for real time damage detection. MicroElectro- Mechanical Systems (MEMS) allow designing multiple sensors on the same device due to the diversity in the materials and manufacturing methods. In this study, acoustic emission (AE) and strain sensors are combined on the same device. The passive nature of the AE method is ideal for real time damage detection and location triangulation for inaccessible areas on large scale structures. Unfortunately the AE method is highly influenced by background noise. The presence of the strain sensor on the same device can be utilized as trigger for AE sensing when the structure is loaded higher level, which is the expected initiation condition of damage. The MEMS AE sensors rely on the capacitance change of two electrodes made of doped polysilicon and nickel, and are manufactured using MetalMUMPs. The sensitivities of the MEMS AE sensors operating in the range of 50 kHz to 200 kHz are comparable with the similar frequency piezoelectric sensors. The MEMS strain sensors are based on the piezoresistive property of polysilicon, which nominally may lead to more than 70 times higher gauge factor (sensitivity) than conventional metal strain sensors. However, the substrate and insulation layers as well as any packaging and adhesive material reduce the strain level transferred to the sensing element which is compensated by the higher gauge factor. In this paper, the modeling, design and characterization of two sensor types are presented. The sensors are tested on an aluminum plate when the substrate is directly attached to the plate using an adhesive layer. The sensor responses to the simulated acoustic emission signals and the static strain through introducing deflection to the plate are compared with the conventional piezoelectric AE sensors and metal gauges. The obtained results illustrate the advantages of MEMS sensors over the conventional sensors.

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