Sensor Nodes for Continuous Monitoring of Structures Through Accelerometric Measurements

Design and Field Validation of a Low Power Wireless Sensor Node for Structural Health Monitoring

“…21, x FOR PROOF16 of 18 to 0.4 g, as it can be appreciated inFigure 12b[1]. In accordance with the explained physics of the problem, the higher amplitude values correspond to low frequencies, while for relatively high frequencies(30-50 Hz range) the lowest amplitude values are observed.…”

“…Since a few acquisitions with different input acceleration amplitudes were performed for each tested frequency, the standard uncertainty uc was estimated as the standard deviation for each of these amplitudes. Then, the expanded uncertainty was determined according to (2): In (1), S represents the Discrete Fourier Transform amplitude while i max is the spectrum line corresponding to the maximum amplitude. This equation allows one to take into account, following an energetical interpretation, the energy spread due to leakage on spectrum lines adjacent to the one corresponding to the maximum amplitude detected.…”

“…The device chosen to perform this task is the Fanstel 2.4 GHz BT840F RF Transceiver (based on Nordic nRF52840) which is able to support BLE and transmit data, using this communication protocol, in the range of a few hundred meters as it will be shown in Section 3.1.4 . A 3D rendering of the designed board and an external view of the first prototype of WindNode are visible respectively in Figure 3 a,b [ 1 ].…”

“…The transfer function between the sensor node and reference accelerometer was evaluated by performing the FFT and by taking the spectrum lines corresponding to the forcing frequency. In Figure 6 a–c the transfer functions of x, y, and z axes are represented [ 1 ]. The expected value is unitary over the whole frequency range tested and is represented by the black line.…”

“…The shift of the research in the SHM field from traditional wired systems towards the use of Wireless Smart Sensors (WSS) has also been motivated by other attractive features, such as the wireless communication, on-board computation, low cost, small size, and performances nearly equivalent to wired sensors. Furthermore, the reduction in cost and size of wireless sensors allows an important measurement redundancy, with the deployment of several nodes in the structure subject to monitoring [ 1 , 2 , 3 , 4 , 5 , 6 ]. In this framework, the sensor node object of the present work has been developed at the Mechanical Department of Politecnico di Milano, named “WindNode”, since it has been created with the aim of performing SHM through acceleration measurements on structures mainly subject to wind-induced vibrations.…”