Modified Dual Piezo Configuration for Improved Structural Health Monitoring Using Electro-Mechanical Impedance (EMI) Technique S. Adhikari 1,2 & S. Bhalla 2 Received: 3 December 2016 /Accepted: 17 April 2018 # The Society for Experimental Mechanics, Inc 2018 Abstract This paper presents a new variant of the electro-mechanical impedance (EMI) technique encompassing sensor-actuator dual configuration for improved damage assessment. In this arrangement, called as dual piezo configuration (DPC), an outer piezo- electric ring acts as the actuator and an inner piezoelectric disc as the sensor. The configuration yields better results than the conventional EMI configuration employing the same piezo patch as the sensor as well as the actuator. This paper presents a more practical and modified version of DPC entailing a group of normal commercially available PZT patches. The piezo sensor configurations evaluated in the paper are: (a) single piezo configuration (SPC), which is conventionally employed in the EMI technique; (b) dual piezo configuration (DPC), which consists two different patches in ring type configuration; and (c) modified dual piezo configuration (MDPC), which uses four outer piezo patches for the actuation and a centrally located piezo patch for the sensing purpose. The paper first covers the comparison of the three configurations through finite element method (FEM), using an aluminum block of dimensions 48 × 48 × 10 mm as the host structure and lead zirconate titanate (PZT) patches of size 10 × 10 × 0.3 mm, analyzed through coupled field analysis. The simulation study is followed by an experiment on the aluminum block of the same size and finally on a prototype steel plate of dimensions 1200 × 970 × 8 mm. Simulation results and experimental data prove that the proposed MDPC is much more sensitive to the occurrence than the conventional SPC. Also, MDPC ensures much larger zone of influence as compared to the conventional SPC as well as the DPC and it commands higher sensitivity. Hence, it can be employed on the large structures to detect damage, which is not possible by using the SPC which may warrant very large number of sensors. Thus, the proposed MDPC approach can be practically employed to detect the damage in large civil, mechanical and aerospace structures. Keywords Structural health monitoring (SHM) . Lead zirconate titanate (PZT) . Electro-mechanical impedance (EMI) technique . Dual piezo configuration (DPC) . Modified dual piezo configuration (MDPC) . Sensors . Actuators Introduction Structural health monitoring (SHM) deals with the evaluation of the structures to determine their current status of perfor- mance form the point of strength, stability and serviceability. SHM encompasses a reliable system of sensors to acquire the signals and an algorithm to interpret the sensor data for identification and location of damage [1]. Alternately, SHM can be defined as the acquisition, validation and analysis of technical data to derive life cycle management decisions [2]. Among the various techniques used for the SHM, the EMI technique is considered very suitable for detecting incipient damage in structures ranging from civil engineering to aero- space. In recent years, several techniques have come up to detect various types of damages on the real-life structures. The global dynamic technique, which uses the changes in nat- ural frequencies and the mode shape of the structure, is very popular but its major limitation is that it cannot detect the lo- calized incipient damage. Other tests, which are local in nature and are commonly used to detect the damage are the dye pen- etration test, the magnetic particle test, the impact echo test and the X ray radiography. They are most suitable for surface crack detection but unsuitable for the continuous monitoring of the structures. Acoustic emission (AE) tests are suitable for locating * S. Bhalla sbhalla@civil.iitd.ac.in S. Adhikari sailesh.adk@gmail.com 1 Presently Lecturer, IOE Pashchimanchal Campus, Tribhuvan University, Pokhara, Nepal 2 Department of Civil Engineering, Indian Institute of Technology (IIT) Delhi, Hauz Khas, New Delhi 110 016, India Experimental Techniques https://doi.org/10.1007/s40799-018-0249-y