Structural Health Monitoring Using Smart Sensors - ideals ...

structural vibration is considered relatively small. Providing ample power to the smart
sensors from these energy sources is not likely to happen soon. Power consumption at
smart sensors, therefore, needs to be well-managed.
9.2.4 Power management and scheduling
Although the realized SHM system manages power consumption, the management
still has room for improvement. The system does change the CPU speed depending on the
tasks to be performed, and the system does prepare to enter a sleep mode when all of the
tasks are performed. However, the change in CPU speed is only between two of four
available speeds, and the Imote2 does not actually enter a sleep mode. By addressing these
problems, power consumption can be further reduced.
In the future, DCS for SHM can be performed periodically. For example, the
measurement and data processing can take place once every few days. While not active,
the Imote2 can be in a sleep mode, only checking its clock. When the monitoring time
approaches, the Imote2 can wake up and perform the necessary monitoring.
9.2.5 Monitoring of occasional events such as earthquakes
For monitoring of occasional events such as earthquakes, a scheme to wake up
networks of smart sensors in a sufficiently short time is needed. Assigning one sensor
node to monitor possible earthquakes continuously and to disseminate wake-up signals to
all of the other nodes is one approach. However, the radio is turned off to save power in
the sleep mode. Therefore, waking up all of the smart sensors by a wake-up command sent
through the radio is not straightforward. Periodically turning on the radio to listen to a
wake-up preamble is one possible solution, though such periodic usage of the radio
consumes power. The interval of the periodic radio listening can be shortened to improve
the response time in system wake-up at the expense of power consumption. If the start of
an earthquake can be predicted, for example by measuring primary waves of an
earthquake near the epicenter, the response time need not be so short, allowing relatively
long intervals between the periodic radio listening. Another approach is to equip all of the
sensor nodes with a mechanism to detect large motion and trigger sensing. A mechanism
to detect large motion mechanically without power is preferable. Thus, system wake-up at
the beginning of a rare event is a key issue.
9.2.6 Multihop
SHM systems to monitor full-scale structures may need multihop communication,
while the SHM system realized in this research is based on single-hop communication. A
sensor community for full-scale structures can be physically larger than the
communication range for a smart sensor. Multihop communication is necessary in such
cases. The unicast and multicast protocols need to be extended for multihop
communication.
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