IEEE SENSORS 2006, EXCO, Daegu, Korea / October 22-25, 2006 A Self-contained Active Sensor System for Health Monitoring of Civil Infrastructures Seunghee Park and Chung-Bang Yun Department of Civil and Environmental Engineering Korea Advanced Institute of Science and Technology Daejeon 305-701 Korea Abstract- A self-contained active sensor system is proposed for the practical use of an electro-mechanical impedance-based structural health monitoring (SHM) technique for civil infrastructures. This system, which consists of a miniaturized impedance measuring chip (AD5933) and a self-sensing macro- fiber composite (MFC) patch, can be a powerful tool for a variety of in-situ SHM applications in civil, mechanical, and aerospace systems, since (1) the AD5933 is low-cost, portable, and readily combined with a wireless telemetry and (2) the MFC patch can be permanently attached to a structure and provide meaningful information regarding the structure's integrity through its self-sensing function. In this study, the effectiveness of the proposed active sensor device has been verified through a series of experimental studies: (a) inspecting loosening bolts in a bolt-jointed structure and (b) detecting corrosion in an aluminum beam. I. INTRODUCTION Civil infrastructures such as buildings, bridges, dams, water supply lines, tunnels, and off-shore platforms are suffering the damage caused by fatigues, large earthquakes, strong winds, and environmental effects or traffic impact. Early detection of the structural damage or deterioration prior to local failure can prevent catastrophic failure of the structures. Sensors to monitor the structures have special requirements. They must be 1) inexpensive as many are required, 2) rugged as they are exposed to the strong elements of nature, 3) preferably wireless with some data processing capabilities, and 4) minimal power requirement or which can work with the harvested power. The large and complex civil infrastructures necessitate low cost but high effect smart sensors and appropriate technologies for data acquisition/reduction for rational health monitoring applications. The sensor systems should also be able to automatically detect, locate and assess damage anywhere within the structures, and to communicate the status to responsible authorities. In this context, this study proposes a self-contained active sensor system for impedance-based health monitoring of the civil infrastructures. The final goal of this research is to develop an intelligent multi-functional Daniel J. Inman Department of Mechanical Engineering Virginia Polytechnic Institute and State University Blacksburg VA 24061 USA sensor which will utilize energy harvested from the ambient environment, analyze the sensing data on a single chip, and wirelessly provide the status of the structure to an end user. II. ELECTRO-MECHANICAL IMPEDANCE-BASED STRUCTURAL HEALTH MONITORING Recent advances in the structural health monitoring (SHM) and nondestructive evaluation (NDE) field have led to the development of novel techniques such as smart sensors /sensor networks, on-line health monitoring and wireless telemetry. As one of the typical examples, an automated electro-mechanical impedance-based SHIM technique using piezoelectric materials has been investigated with keen interest as a powerful and innovative NDE method for local damage detection of a variety of structures, including civil, mechanical, and aerospace systems [1-9]. The electro- mechanical impedance-based SHlM technique utilizes small piezoelectric ceramic (PZT) patches attached to a structure as self-sensing actuators to simultaneously excite the structure with high-frequency excitations, and monitor changes in the patch electrical impedance signature. Since the PZT is bonded directly to the structure of interest, it has been shown that the mechanical impedance of the structure is directly correlated with the electrical impedance of the PZT. Thus, by observing the electrical impedance of the PZT, assessments can be made about the integrity of the host structure. Conventionally, the electro-mechanical impedance method has required the use of impedance analyzers, including HP4194A. Such analyzers are bulky and expensive, and are not suited for permanent placement on a structure. With the current trend of SHM heading towards unobtrusive self- contained sensors, the first step in meeting the low-cost, portable, and readily combined with a wireless telemetry requirements resulted in an active sensing device which consists of a miniaturized impedance measuring chip (AD5933) and a self-sensing macro-fiber composite (MFC) patch [10]. The on-board sensor system is active sensing system which interrogates a structure utilizing a self-sensing MFC patch and the low-cost impedance method, and all the Smart Infra -Structure Technology Center (SISTeC), KAIST and Center for Intelligent Material Systems and Structures (CIMSS), Virginia Tech 1-4244-0376-6/06/$20.00 }2006 IEEE 798