Time-synchronized wireless strain and damage measurements at multiple locations in CFRP laminate using oscillating frequency changes and spectral analysis

Wireless monitoring of the health of CFRP structures reduces the cost and time of inspections and can be usefully applied for continuous monitoring. In a previous study, we presented a wireless sensor for detection of internal delamination in a CFRP laminate. The method utilizes a simple electrical resistance change in CFRP and so monitors delamination at only one location. For monitoring of large-scale structures, however, many sensors have to be distributed to cover the structure. A major problem for using many sensors is time synchronization among sensors. To overcome the problem and enable strain/damage to be monitored at multiple locations with time synchronization, we develop a simple wireless strain/damage sensor that consists of a bridge circuit, voltage-controlled oscillator and amplifiers. Since the sensor does not need A/D conversion procedures or memory storing, there is no time delay. Each sensor has an original basic frequency that changes in accordance with the electrical resistance. The frequencies from the multiple sensors are transmitted to a receiver. Using a short-time maximum entropy method, the received waves are converted to multiple electrical resistance data. The proposed method is applied to CFRP laminates and oscillating frequencies are measured in real time. The results show that the system successfully measures applied strain and detects fiber breakage at multiple locations in CFRP laminates with time synchronization.

[1]  Hoon Sohn,et al.  Wavelet-based active sensing for delamination detection in composite structures , 2004 .

[2]  Darryll J. Pines,et al.  Conceptual framework of a remote wireless health monitoring system for large civil structures , 1998 .

[3]  Liang Cheng,et al.  A study on the optimal time synchronization accuracy in wireless sensor networks , 2005, Comput. Networks.

[4]  Stephan Olariu,et al.  A simple and robust virtual infrastructure for massively deployed wireless sensor networks , 2005, Comput. Commun..

[5]  Ajay D. Kshemkalyani,et al.  Clock synchronization for wireless sensor networks: a survey , 2005, Ad Hoc Networks.

[6]  Xia Zhao,et al.  Distributed structural health monitoring system based on smart wireless sensor and multi-agent technology , 2006 .

[7]  Akira Todoroki,et al.  Wireless Strain Monitoring of CFRP Laminates Using Electric Resistance Change with Oscillating Circuit , 2006 .

[8]  Jerome P. Lynch,et al.  Algorithms for time synchronization of wireless structural monitoring sensors , 2005 .

[9]  Håkan L. Wettergren,et al.  Delamination in composite rotors , 1997 .

[10]  Charles Chien,et al.  Wireless Sensor Networks for Area Monitoring and Integrated Vehicle Health Management Applications , 1999 .

[11]  Evgeny V. Morozov,et al.  Impact damage tolerance of laminated composite helicopter blades , 2003 .

[12]  Jerome P. Lynch,et al.  Embedding damage detection algorithms in a wireless sensing unit for operational power efficiency , 2004 .

[13]  A. Todoroki,et al.  Wireless detection of internal delamination cracks in CFRP laminates using oscillating frequency changes , 2006 .

[14]  Stephan Olariu,et al.  Group key management scheme for large-scale sensor networks , 2005, Ad Hoc Networks.

[15]  Wan-Young Chung,et al.  Remote monitoring system with wireless sensors module for room environment , 2006 .

[16]  Hideo Kobayashi,et al.  Detection of Matrix Cracking of CFRP Using Electrical Resistance Changes , 2005 .