Smart Sensor Systems for Structural and Health Monitoring

Over the last decades monitoring of engineering structures has become more and more important. Besides traditional sensor systems, Smart Sensor Systems, which inmany cases are put into practice by embodying active materials into the structures to be monitored, have gained an ever increasing attention for Structural and Health Monitoring. The proper distribution of the active materials, which constitute the sensing authority, over the structure, is of fundamental importance in order to gain specific information concerning the state of the monitored structure. In particular, sensing mechanisms, which enable the direct measurement of strains (e.g. piezoelectric sensors) have proven to be suitable sensing authorities for distributed sensing.

Moreover, embodied smart sensor systems eliminate the need for additional external sensor systems and they may as well be used as actuator systems; this further enables passive/active control using embodied sensors and actuators. The first part of the present talk is focussed on the development of novel easy-to-use methods for computing the distribution of smart sensor systems to measure kinematically relevant structural entities (e.g. the relative displacement between two points or the slope of the displacement field of a structure). A simple solution for this Sensor Design Problem is presented and different types of practically important distributed smart sensor systems are discussed; e.g. modal sensors and nilpotent sensors. Based on these findings, practical implementations utilizing piezoelectric sensors are introduced and numerically and

experimentally verified. A specific problem, to which the design methods are applied, is discussed in detail in the second part of the talk – Structural Health Monitoring of frame structures using piezoelectric sensor networks. These networks are designed to be highly sensi tive to damage by using nilpotent sensor networks, which result into a trivial signal, if the structure is undamaged. For damaged frames this particular type of sensor network facilitates the detection, localisition and quantification of damage. Analytical, numerical and experimental results are presented for a three-storey frame structure.

In the last part of the talk extensions to using the smart piezoelectric sensor systems as actuators as well are introduced; in particular, methods such as Self-Sensing Actuators and passive Shunt Damping, for which no additional physical actuator system is needed. Practical problems concerned with active health monitoring of frame structures and with noise reduction for thin plates complete the present talk.

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