Structural Health Monitoring Using Smart Sensors - ideals ...

4. Battery powered
Smart sensors are frequently powered by local batteries, particularly when other
power sources are not easily reached. Even when power is available, such as in a building,
tethering a large number of smart sensors to power sources is expensive and reduces the
merits of wireless communication. There have been several attempts to harvest energy at
sensor nodes locally, for example, from mechanical vibration (Rahimi et al., 2003).
Vibration energy for civil infrastructure is, however, typically contained in the low
frequency range, where electric energy is difficult to harvest. Currently available smart
sensors rely on the local battery power supply, which has finite capacity and finite life.
Because replacing or recharging batteries in smart sensors installed on a structure may not
be a trivial task, power saving is a major concern. This finite energy source problem
imposes a strict constraint.
5. Low cost
Smart sensors primarily composed of MEMS and other integrated circuits (IC) have
the potential to be produced at a low cost as well as being small in size. This feature of
smart sensors, combined with inexpensive installation cost due to wireless
communication, enables numerous smart sensors to be densely distributed over civil
infrastructure, thus offering the potential to capture the structure's state in detail, and
drawing us closer to realizing the dream of ubiquitous sensing.
2.1.2 Smart sensors to date
Some of the first efforts in developing smart sensors for application to civil
engineering structures were presented by Straser and Kiremidjian (1996, 1998) and
Kiremidjian et al. (1997). In their work, a wireless sensor unit was constructed consisting
of a microprocessor, radio modem, data storage, and batteries. To reduce the battery
consumption, the smart sensor could be either in a waiting mode or an operational mode.
Since these first efforts, numerous researchers have developed smart sensing platforms.
Lynch and Loh (2006) cited over 150 papers on wireless sensor networks for SHM
conducted at over 50 research institutes worldwide. These platforms can be grouped into
two primary categories: proprietary and nonproprietary
Many proprietary platforms have been developed by individual research groups,
including the work of Straser and Kiremidjian. Other examples include Mason et al.
(1995), Bult et al. (1996), Agre et al. (1999), Aoki et al. (2003), Basheer et al. (2003),
Kawahara et al. (2003), Kottapalli et al. (2003), Shinozuka (2003), Wang et al. (2003),
Casciati et al. (2004), Sazonov et al. (2004), Farrar et al. (2005), and Lynch (2006), all of
whom designed their smart sensor hardware using commercial-off-the-shelf (COTS)
components. Each of these papers cited shortcomings in previously developed smart
sensors as motivation for the development of their own hardware. While the individual
researchers advanced the state-of-the-art in smart sensor technology, progress was slow
due to the lack of coordination and leveraging of efforts.
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