80 J. N. Satme et al. Fig . 8. 7 Benchtop experimental setup for the sensor package network deployment Fig . 8. 8 Frequency domain analysis of the beam impulse response test with the first three modes annotated used to initiate all sensors within an acceptable tolerance. The beam was then excited with an impulse response using a hammer at various positions on the beam. This ensured that all mode shapes are excited. With the data of interest being the frequencies of the first three mode shapes, the time domain data extracted from the test is converted to the frequency domain using the Fast Fourier Transform (FFT). In Fig. 8.8, the first three frequency peaks are observed. The peaks at 32.74 Hz, 126.62 Hz, and 281.50 Hz are of the first three modes, respectively. This was compared to the FEA model presented prior. A maximum error margin of 11% was found between modal frequencies extracted from the model when compared to experimental results. This is attributed to boundary conditions and material property inconsistencies. Using mode shapes from the simulation, the sensor packages were positioned at the mode’s antinodes where the vibration signal was at its highest. For mode 1, it was shown that the three sensors peak together as they all experience vibration in the same direction at 32.7 Hz. When observing mode 2 at 126.6 Hz, it is shown that sensor node 2 (middle package) does not detect any peak which correlates to a node of mode 2. Finally, peaks are observed as mode 3 at a frequency of 281.5 Hz indicating that all three sensors are on antinodes of the third mode. 8.4 Conclusion In this work, an embedded system-based high-mobility sensor network is examined. During system characterization tests, the network has shown the potential to be a reliable tool in structural health monitoring and experimental modal analysis applications. The ease of use and compact footprint, along with the magnetic mounting capability, makes these sensors optimal for UAV deployment where human access is challenging or dangerous. For rapid assessment of infrastructure following extreme weather conditions, such systems can be widely deployed in a very short time providing the first
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