Sensors and Actuators A 149 (2009) 233–240 Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna Nanocomposite functional paint sensor for vibration and noise monitoring Osama J. Aldraihem a,∗ , Wael N. Akl b , Amr M. Baz c a Mechanical Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia b Design & Production Engineering Department, Ain Shams University, Cairo, Egypt c Mechanical Engineering Department, University of Maryland, 2137 Eng. Bldg., College Park, MD 20742, United States article info Article history: Received 4 February 2008 Received in revised form 20 October 2008 Accepted 28 October 2008 Available online 27 November 2008 Keywords: Functional paint sensor Carbon black nanocomposite Conducting polymer Vibration & noise monitoring Structural health monitoring abstract A new class of nanocomposite functional paint sensor is proposed, whereby an epoxy resin is mixed with carbon black nanoparticles to make the sensor sensitive to mechanical excitations. A compre- hensive analysis is presented to understand the underlying phenomena governing the operation of this class of paint sensors. The analysis includes developing an electromechanical model which treats the sensor system as a lumped-parameter system. The Debye and the Cole–Cole equations are uti- lized to model the behavior of the nanocomposite paint. The sensor equations are integrated with a simple amplifier circuit in order to predict the current and voltage developed by the paint sen- sor. Several experiments are performed to assess the validity of the proposed models of the paint sensor system. First, impedance spectroscopy is employed to verify the validity of the Debye and Cole–Cole models and to obtain the sensor electrical parameters. Then, experiments are carried out to validate the piezoresistance model. Finally, the predictions of the electromechanical model are experimentally verified by examining the dynamic response of the sensor system under cyclic load- ing. The ultimate goal of this study is to demonstrate the feasibility of the proposed nanocomposite functional paint as a sensor for monitoring the vibration, acoustics, and health of basic structural sys- tems. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Paints are commonly applied as films on structures surfaces for providing protective and decorative functions. When the paint pos- sesses a sensing capability, the paint becomes functional or smart. Recently, several attempts have resulted in the development of smart paints which can be used as sensors for vibration, noise, and health monitoring applications. The currently available functional paints are complex and very expensive for practical applications. For example, smart composite paints which are made of piezoelec- tric powder immersed in epoxy resin must be coated with layers of electrodes and then poled using very high voltage to impart the sensing capability to the paint [1–3]. Such a complex prepara- tion processes make this type of paint very expensive. Furthermore, expensive charge amplifiers are needed to monitor the capacitive output signals of the smart paint sensor. Alternatively, the pressure sensitive smart paints which modulate the light intensity through a repeatable chemical interaction of the sensing layer with atmo- spheric oxygen require the use of an expensive photo-detector such ∗ Corresponding author. Tel.: +966 1 4670166. E-mail addresses: odraihem@ksu.edu.sa (O.J. Aldraihem), waelakl@gmail.com (W.N. Akl), baz@eng.umd.edu (A.M. Baz). as a CCD camera or photomultiplier tube for interrogation of the paint [4]. Carbon black (CB) composite is another class of functional mate- rial that finds wide applications, e.g., in deformation sensing. The composite consists basically of electrically conductive CB aggre- gates embedded in a polymer matrix. The composite conductivity noticeably changes with the applied mechanical deformation. Extensive research effort has been put forth to studying the per- colation theory which is often used to describe the relationship between CB contents and the direct current (DC) conductivity [5]. However, investigation of the sensing ability of CB composites is focused on the detection of quasi-static effect. For example, the work of Shevchenko et al. [6] focused on graphite filled polypropy- lene composites, which possess smart properties, such as a positive temperature coefficient of resistance and strain dependent conduc- tivity. Along a similar direction, Kimura et al. [7] experimentally illustrated the linear relationship between the logarithms of the resistance and elongation. Furthermore, they developed a model based on the tunneling junction model. Flandin et al. [8] evaluated the DC electrical and mechanical properties of composites com- posed of conductive fillers impeded into elastomer matrices. Zhang et al. [9] presented a systematic work on the piezoresistance effects of electrically conducting composites which are subject to uni-axial pressure. The investigation experimentally verified the theoretical 0924-4247/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2008.10.017