Structural Health Monitoring Using Smart Sensors - ideals ...

7.1.4 Complex matrix inverse
A complex matrix inverse function is developed based on the Gauss-Jordan matrix
inverse method described in Numerical Recipes in C (Press et al., 1992). The accuracy of
the algorithm is examined by calculating the matrix product of the inverse and original
matrices. The identity matrix was obtained as the output.
The complex matrix inverse algorithm for an n n complex matrix needs
n + n B of memory. n B is first used to store the original matrix and then
replaced with the matrix inverse. n B is internally used. The necessary memory space,
n + n , exceeds 256 kB when n = .
7.1.5 Sort
A quick sort algorithm is developed based on Numerical Recipes in C (Press et al.,
1992). One application example requiring two vectors be sorted simultaneously is the
ordering of natural frequencies in ascending order and the corresponding reordering of
multiple modal parameters. This function is implemented using floating point operations.
The memory size required to run this function is approximately n B, where n is the
length of the vector to be sorted; the size of floating type variable is 4 B. Sorting of more
than 30,000 data points can be achieved with 256 kB memory. This function is not
considered to be expensive in terms of memory usage.
7.2 DCS implementation
Components of DCS (i.e. Sensing, NExT, ERA, DLV methods, and DCS logic) are
implemented on the Imote2s. The outputs of each step of the DCS algorithm on Imote2s is
compared with reference values calculated on the PC using MATLAB. Sensing is
examined by comparing signals from the Imote2s with those from conventional reference
accelerometers. To check the validity of the various DCS components, acceleration data is
injected from the PC, instead of acceleration measured on the Imote2, and used for the
numerical evaluation. The Imote2 is shown to perform DCS calculations as designed.
7.2.1 Sensing
The middleware service developed in section 5.3 is implemented on the Imote2, and
the sensing capability investigated. The sensing capability is first calibrated against
reference sensors. In anticipation of the damage detection experiment with Imote2s in the
next chapter, the Imote2s and reference sensors are placed on the three-dimensional truss
structure, and the measured acceleration signals are examined. Synchronization of the
measured signals is considered by sensing acceleration responses of the truss and
comparing the phase characteristics of the signals.
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