Structural Health Monitoring Using Smart Sensors - ideals ...

Integration of different types of information obtained from smart sensors has the
possibility of improving damage detection capabilities. For example, smart sensors
measuring acceleration, strain, wind velocity, temperature, and humidity may use four
types of sensors to detect damage more reliably than smart sensors employing only
accelerometers. Each measurand has its own characteristics. Acceleration responses
reflect global motion of a structure and have particularly rich information at higher
frequencies; on the other hand, strain is a local physical quantity, with its information
concentrated at lower frequencies. Wind velocity affects the input force, damping, and
stiffness. Temperature and humidity change at slower rate, affecting structural
characteristics. Integration of different types of information may result in more reliable
damage detection.
Furthermore, the applicability of the algorithms to nontruss structures needs to be
examined and experimentally verified. The applicability has been studied mainly for truss
structures. For DCS for SHM to be more widely used in monitoring civil infrastructure,
the applicability to a wide range of structure types should be demonstrated.
9.2.3 Power harvesting
The three AAA batteries powering the Imote2 have a limited life. For some
applications needing only a few samples taken infrequently, the batteries may last for
months or even years. However, data-intensive applications such as SHM consume
significant power, shortening the battery life. A battery life of years using only a few AAA
batteries is not likely to be achieved in the near future. Using larger batteries is one
practical solution when a small form factor is not required. The life of a smart sensor can
be lengthened by increasing the battery capacity. Alternatively, power harvesting at the
smart sensor nodes is a promising approach to achieve semipermanent monitoring of
structures using nonplugged-in smart sensors.
Several energy sources can be identified for development of SHM power harvesting
strategies. Wind energy is a potential energy source. Bridges are most likely constructed
over a river, street, or railroad tracks where obstacles to block the wind are limited. Wind
velocities at bridge cites are expected to be relatively high, making power harvesting with
wind energy promising. Solar power is another candidate, though available energy
depends on the climate at the site and sunlight availability of sensor locations. As opposed
to wind power, solar power harvesting does not have any moving parts; therefore,
vibration originating from solar power harvesting will not contaminate measurement of
structural vibration signals. Another energy source, structural vibration energy, can
conceptually be converted to electrical energy. Considering that vibration of civil
infrastructure is normally in the low frequency range, power harvesting from such
vibration might be difficult. Devices to capture small sources of energy and condition
stored energy for smart sensor use have also been reported (Advanced Linear Devices,
Inc., 2007). Further study is required to use these energy sources reliably for smart
sensors.
Even when power harvesting is realized, power consumption on the smart sensor
should be kept moderate. The amount of energy available from wind, solar power, or
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