Fibre-reinforced composite materials are increasingly being used in the construction of advanced aircraft structures. The detection of damage in such materials is critical to ensure safe application. An in-situ structural health monitoring (SHM) system, either embedded in the composite structure or surface-mounted, would permit the timely detection of damage in such structures. There has been much work reported on the application of, for example, piezoelectric and optical fibre sensing technology for the detection of composite damage. In this paper we outline our approach using silicon microsystem (MEMS) technology. Silicon micromachining offers the potential for fabricating a range of microsensors for structural applications including load, vibration and damage. Such microsensors are extremely small, they can be embedded into CFRP materials, can be mass-produced and are therefore potentially cheap. Additionally a range of sensor types can be integrated onto a single chip with the signal processing electronics, providing a low power microsystem. Micromachined ultrasonic transducers have been designed, fabricated and evaluated for their application in detecting damage parameters such as impact and acoustic emissions in fibre-composite materials. The transducer comprises a deflectable thin-film membrane, typically 1mm(2) and 1 mu m thick, which is fabricated using a low temperature, CMOS-compatible process. Device sensitivity, resonant frequency and bandwidth can all be accurately controlled in the micromachining process. Results indicate that these devices exhibit high sensitivity, excellent SNR and wide operating bandwidth. Transducers have been surface-mounted to CFRP panels and evaluated for their response to both low energy impacts and acoustic emissions signals, these results are presented.
