Research Tasks and Future Prospects

Another open question concerns the actual long-term behaviour of surface-applied or embedded strain/deformation sensors. Future research work should be more intensively focused on optimal design of the interface zone sensor -coating - host material. In adaptronic systems, reliable data must be delivered from sensors over a long period of time. The user has to pay attention to three main points  

It has been experienced that coating materials usually used can fail under raw environmental conditions. The load transfer characteristics can be perturbed or a long-term bonding to the measuring object cannot be reached. Alternative paths must be trodden. 

Worldwide research activities focusing on these problems have been carried out. The next steps should concentrate the worldwide research experience on the still open application-related problems, e.g. establishing of user-friendly evaluation techniques and validation methods to know the longterm sensor characteristics, development of guidelines as well as standards for practical use of available sensors. Fruitful output is expected from current European COST actions, e.g. COST 270 (reliability of optical components and devices in communication networks) [75] and COST 299 (op- 

The direct piezoelectric effect, via mechanical deformation of the piezo crystal lattice, causes an electric polarization by charge displacement. Vice versa, the effect of an electric field will cause a deflection of the crystal lattice and 

Piezoelectricity appears in natural crystals such as quartz, tourmaline, rochelle salt as well as in artificially produced ceramics and polymers such as e. g. nylon or copolymers of vinylidenefluoride (VDF) with trifluoroethylene (TrFE) or with tetrafluorethylene (TeFE). Most of the piezoelectric materials used for commercial sensor applications are synthetically produced polycrystalline ferroelectric ceramics such as e.g. lead-zirconate-titanate (PZT). 

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