Reflectometry for structural health monitoring

Aging wiring and structural cables in buildings, aircraft and transportation systems, consumer products, industrial machinery, etc. are among the most significant potential causes of catastrophic failure and maintenance cost in these structures. Smart wire health monitoring can therefore have a substantial impact on the overall health monitoring of the system. Reflectometry is commonly used for locating faults on wire and cables. It can also be used for location of faults on structural cables, if they are electrically isolated. This chapter describes and compares several reflectometry methods -- time domain reflectometry (TDR), frequency domain reflectometry (FDR), mixed signal reflectometry (MSR), sequence time domain reflectometry (STDR), and spread spectrum time domain reflectometry (SSTDR) -- in terms of their accuracy, convenience, cost, size, and ease of use. Advantages and limitations of each method are outlined and evaluated for several types of aircraft cables, and the general equations that govern their performance are given. The impact of the fault location and size is also discussed.