A conclusion of these experiments is that a distributed sensor can substantially reduce the complexity of the SHM system, since the number of channels as well as the associated electronics can be greatly reduced. The distributed sensor also improves sensitivity by being closer to the damage. With a piezo-fiber composite, it may be possible to conform a long antenna type sensor over the surface of the structural component. This will enable detection of high frequency components of the AE signal occurring anywhere in the structure with a single or a small number of distributed sensors. It was demonstrated that the charge from the individual elements of the sensor bleeds into the remaining elements of the sensor. In effect, this is an increase in the capacitance of the sensor which reduces the signal output. The overall characteristic of this type of sensor is that the proximity of the distributed sensor to all possible AE locations greatly increases the signal to noise ratio corresponding to the high frequency components, but the bleeding effect reduces the amplitude of the signal. Furthermore, connecting the PZT's with alternating polarity was shown to increase the output voltage of the distributed sensor. This is thought to occur because the alternating polarity cancels the low frequency bending vibrations and improves sensitivity to the higher frequency vibrations. The experiments performed indicates that poling of the AFC can be used as a spatial filter to tune the bandwidth characteristics of the sensor. Modeling and testing are continuing to develop smart distributed sensors.
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