Structural Health Monitoring Using Smart Sensors - ideals ...

that time synchronization error smaller than a millisecond is acceptable. SHM strategies
need to be examined against time synchronization error prior to their use.
4. Limited computational capability
Some SHM applications utilize numerical operations that require large computational
power and memory allocations. Methods requiring manipulation of large matrices, such as
ERA, fall into this category. Because memory space on smart sensors is limited, these
methods are impossible to implement on smart sensors, or the performance is limited
(Chintalapudi et al., 2006; Nagayama et al., 2004).
5. Power
Power consumption is an important issue to civil infrastructure monitoring. As
compared to other smart sensor applications (e.g., habitat monitoring), monitoring of
structures may have easier access to power sources. Buildings are equipped with power
outlets, and many long bridges have power that is used for light poles, etc. However,
wiring power to numerous sensors takes a significant amount of time and increases
installation cost, negating one of the important advantages of smart sensor. Also, sensor
installation location is not always close to a power source on a structure. Available power
may need to be transformed to an appropriate voltage and frequency. Some structures are
without power. Therefore, power source cannot be assumed to be available. Smart sensors
employing batteries are beneficial and oftentimes the only solution.
Once smart sensors are installed on civil infrastructure, their batteries may not be
easily changed. Some nodes may be installed at places with low accessibility.
Maintenance during which batteries on smart sensors can be replaced is not frequently
scheduled. Power consumption for SHM applications is, however, in general larger than
other wireless sensor applications, shortening battery life. So far, no battery-powered
smart sensor systems for SHM has been implemented on a permanent basis. Much
research effort is being devoted to resolve this issue; one promising approach is power
harvesting.
2.5 Summary
Recent technological advance in smart sensor technology offers new opportunities in
SHM for civil infrastructure. A dense array of smart sensors is expected to be a rich source
of information for SHM. Attempts toward SHM using smart sensors, however, always
encounter difficulties. Although there are reports on smart sensor usage in structural
vibration measurement, none of them has resulted in a full-fledged SHM system. Issues in
scalability, sensing capability, synchronization accuracy, etc. must still be addressed. This
research realizes a framework for SHM using smart sensors by addressing these issues.
The next chapter presents the SHM architecture employed in this report to address these
difficulties.
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