Optical Fibres and Their Role in Smart Structures

Abstract

The term “smart structures’’ crept into the technical vocabulary more than a decade ago.1-3 Since then a significant amount of philosophical debate as to what the term might mean has occupied the more academic amongst us wondering whether or not our smart structure should seek to emulate a biological organism or whatever. Yet others will point out that smart structures are nothing more than a sensible approach to integrated engineering (Figure 1.). The debate over the benefits and disadvantages of incorporating “smartness” into structural entities will continue. There is little doubt that the smart structure will be more costly at the outset than its less intellectually endowed ancestors. However whether this smartness costs more in the long term remains open for debate and frequently depends upon how the accountants do the accounting and who is spending from which budget and when. Equally there is little doubt that major infrastructure investments such as bridges, highways, pipelines, ships, trains, motor vehicles and all the rest could be significantly improved by incorporating as needed rather than panic measure maintenance using structural smartness as the trigger. All the better if the structure could react and adjust or heal itself. Further all agree that the first stage in the smart structure is to find out how it feels -which means sensors. Indeed it means usually a very large array of sensors since to know how our structure feels we really need inputs from its most personal parts. This requirement for sensor arrays imposes new demands on not only sensing systems but also on the capability to process the data which is produced by such systems. Sensor technologies are many and range from observing ground movements through satellite radar speckle interferometry, to precision GPS, to nanoprobes addressing cellular chemistry, to tunnelling microscopes for detecting individual atoms. Sensing is a niche oriented activity, the domain where the small specialised company can compete effectively with lumbering multinationals. The niche for sensing in smart structures has its own well defined characteristics. First and foremost the sensors must be compatible with the structural environment, which means in particular for advanced structural materials such as fibre reinforced composites the sensor must