Nanocomposite functional paint sensor for vibration and noise monitoring

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<ul><li><p>Sensors and Actuators A 149 (2009) 233240</p><p>Contents lists available at ScienceDirect</p><p>Sensors and Actuators A: Physical</p><p>journa l homepage: www.e lsev ier .co</p><p>Nanoco rat</p><p>Osama J.a Mechanical Eb Design &amp; Prodc Mechanical E 2, Uni</p><p>a r t i c l</p><p>Article history:Received 4 FebReceived in reAccepted 28 OAvailable onlin</p><p>Keywords:Functional paiCarbon black nConducting poVibration &amp; noise monitoringStructural health monitoring</p><p>ionalmakeerstasis inmetenanoo preed tctrossens</p><p>to validate the piezoresistance model. Finally, the predictions of the electromechanical model areexperimentally veried by examining the dynamic response of the sensor system under cyclic load-</p><p>1. Introduc</p><p>Paints arproviding psesses a senRecently, sesmart painthealth monpaints are cFor exampletric powderof electrodethe sensingtion processexpensive coutput signsensitive sma repeatablspheric oxy</p><p> CorresponE-mail add</p><p>(W.N. Akl), baz</p><p>0924-4247/$ doi:10.1016/j.sing.The ultimate goal of this study is to demonstrate the feasibility of the proposed nanocomposite</p><p>functional paint as a sensor for monitoring the vibration, acoustics, and health of basic structural sys-tems.</p><p> 2008 Elsevier B.V. All rights reserved.</p><p>tion</p><p>e commonly applied as lms on structures surfaces forrotective and decorative functions.When the paint pos-sing capability, the paint becomes functional or smart.veral attempts have resulted in the development ofs which can be used as sensors for vibration, noise, anditoring applications. The currently available functionalomplex and very expensive for practical applications., smart composite paints which are made of piezoelec-immersed in epoxy resin must be coated with layerss and then poled using very high voltage to impartcapability to the paint [13]. Such a complex prepara-esmake this type of paint very expensive. Furthermore,harge ampliers are needed to monitor the capacitiveals of the smart paint sensor. Alternatively, the pressureart paints which modulate the light intensity through</p><p>e chemical interaction of the sensing layer with atmo-gen require the use of an expensive photo-detector such</p><p>ding author. Tel.: +966 1 4670166.resses: (O.J. Aldraihem), (A.M. Baz).</p><p>as a CCD camera or photomultiplier tube for interrogation of thepaint [4].</p><p>Carbon black (CB) composite is another class of functionalmate-rial that nds wide applications, e.g., in deformation sensing. Thecomposite consists basically of electrically conductive CB aggre-gates embedded in a polymer matrix. The composite conductivitynoticeably changes with the applied mechanical deformation.</p><p>Extensive research effort has been put forth to studying the per-colation theory which is often used to describe the relationshipbetween CB contents and the direct current (DC) conductivity [5].However, investigation of the sensing ability of CB composites isfocused on the detection of quasi-static effect. For example, thework of Shevchenko et al. [6] focused on graphite lled polypropy-lene composites, which possess smart properties, such as a positivetemperature coefcient of resistance and strain dependent conduc-tivity. Along a similar direction, Kimura et al. [7] experimentallyillustrated the linear relationship between the logarithms of theresistance and elongation. Furthermore, they developed a modelbased on the tunneling junction model. Flandin et al. [8] evaluatedthe DC electrical and mechanical properties of composites com-posed of conductive llers impeded into elastomermatrices. Zhanget al. [9] presented a systematic work on the piezoresistance effectsof electrically conducting compositeswhich are subject to uni-axialpressure. The investigation experimentally veried the theoretical</p><p>see front matter 2008 Elsevier B.V. All rights functional paint sensor for vib</p><p>Aldraihema,, Wael N. Aklb, Amr M. Bazc</p><p>ngineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabiauction Engineering Department, Ain Shams University, Cairo, Egypt</p><p>ngineering Department, University of Maryland, 2137 Eng. Bldg., College Park, MD 2074</p><p>e i n f o</p><p>ruary 2008vised form 20 October 2008ctober 2008e 27 November 2008</p><p>nt sensoranocompositelymer</p><p>a b s t r a c t</p><p>A new class of nanocomposite functwith carbon black nanoparticles tohensive analysis is presented to undthis class of paint sensors. The analythe sensor system as a lumped-paralized to model the behavior of thea simple amplier circuit in order tsor. Several experiments are performsensor system. First, impedance speColeCole models and to obtain them/locate /sna</p><p>ion and noise monitoring</p><p>ted States</p><p>paint sensor is proposed, whereby an epoxy resin is mixedthe sensor sensitive to mechanical excitations. A compre-nd the underlying phenomena governing the operation ofcludes developing an electromechanical model which treatsr system. The Debye and the ColeCole equations are uti-composite paint. The sensor equations are integrated withdict the current and voltage developed by the paint sen-o assess the validity of the proposed models of the paintcopy is employed to verify the validity of the Debye andor electrical parameters. Then, experiments are carried out</p></li><li><p>234 O.J. Aldraihem et al. / Sensors and Actuators A 149 (2009) 233240</p><p>model for the piezoresistance. In another work, Zhang et al. [10]extended their former investigation to study the time dependenceof the piezoresistance. Knite et al. [11] proposed the use of car-bon black nanocomposites as tensile strain and pressures sensor.The investigmodel baseal. [12] studimpedanceposed for thgroup of inof graphitefocused onber compo</p><p>In this wepoxy resinact as a funcapable offrequency oused to meaby the pain</p><p>It is alsoeasily applicontinuoussurfaces. Thcations ranglaunching vcritical stru</p><p>In the prmodel of thmonitoringobtain the ptions are ppaint sensoemployed todevelopedthe impeda</p><p>Thepaperizes the liteof the functequations. Tobtained frmodel is deprinciple. Ttion whichsystem. Theple electricand voltagepresents exoped modeperformancsummarizepresent stu</p><p>2. Model d</p><p>2.1. Nanopa</p><p>The propin Fig. 1, whmake it elec</p><p>The geofrom nanosis assumed</p><p>To facilithe sensorgates consi</p><p>Fig. 1. Sample of a paint sensor.</p><p>med to form a continuum phase of a spherical shape. More-ach Cctivitmedprinsch</p><p>reme. A vothe ssticrenttionates tat cacem</p><p>uiva</p><p>paincanf thewithd-paingelempertmpise tFurtanducersacouhatused</p><p>Fig. 2. Schematic circuit of the sensor.ation included experimental results and a theoreticald on that of Zhang et al. [9]. In a recent work, Wang etied the conduction mechanism in CB composites usingspectroscopy. Three equivalent-circuit models are pro-e various regions of percolation theory curve. Another</p><p>vestigators [13,14] studied the piezoresistive behaviorscomposites under static pressures. Das et al. [15] isthe variation of the resistivity of CB and short carbonsites with the degree of strain at constant strain rate.ork, a nanocomposite paint is proposed whereby anis mixed with carbon black nanoparticles to make it</p><p>ctional composite. The paint sensor is very simple andmonitoring vibration and noise down to a quasi-staticf 0Hz. Accordingly, simple electrical circuits can besure the changes in the current and voltage developedt sensor.important to mention that the proposed paint can beed to structures of complex shapes and can act as aly distributed sensor over very large areas of structurale proposed paint sensor can be used in numerous appli-ing frommonitoring infrastructures, payload fairings ofehicles, exible space structures, as well as many otherctures that are only limited by our imagination.esent study, the objective is to develop a comprehensivee paint sensor system for vibration, noise, and healthapplications. A lumped-parameter approach is used toaint sensor equations. Furthermore, impedance equa-</p><p>resented to estimate the electrical parameters of ther. Hamiltons principle for electromechanical systems isderive thedynamicequationsof the sensor system.The</p><p>models are veried experimentally by examination ofnce spectrum, piezoresistance, and dynamic response.r is organized in four sections. Section 1 briey summa-rature review. In Section 2, the equivalent circuitmodelional paint is developed using the Debye and ColeColehen, estimates of the paint electrical components areom the impedance equations. An electromechanicalrived for the paint sensor system using the Hamiltonshe model is based on an equivalent circuit representa-treats the real sensor system as a lumped-parametersensor system equations are integrated with a sim-</p><p>al circuit to enable the measurement of the currentdeveloped by the functional paint sensor. Section 3</p><p>perimental validations of the predictions of the devel-ls and provides assessments of the static and dynamice characteristics of the paint sensor system. Section 4s the major conclusions and recommendations of thedy.</p><p>evelopment</p><p>rticle paint sensor</p><p>osed paint sensor is a conductive composite, as shownereby a polymer resin is mixed with CB aggregates totrically conducting and functional.metric scale of the aggregate can, in general, rangecale to microscale. Furthermore, the composite sensorto be homogeneous on the macroscale.tate modeling formulation, the real microstructure ofis simplied as illustrated in Fig. 2. The primary aggre-st of many CB nanoparticles, where each CB aggregate</p><p>is assuover, econduis assu</p><p>Theing themeasusensorto biasor acouthecurproporillustratem th(displa</p><p>2.2. Eq</p><p>Thewhichtions oalonglumpegovernwhosecal proand dathe sentation.modeltransdelectro</p><p>In wwill beB aggregate possesses high-structure of high electricaly. Theweight fraction loading of the carbon black phaseto be within the percolation region.ciple of sensing can be best understood by consider-ematic circuit shown in Fig. 2. This circuit enables thent of the current and/or voltage developed by the paintltage source, uin, along with a series resistor, R0, is usedensor. When the sensor is subject to external vibrationexcitations, its electrical properties arealteredandsoareandvoltageof thebias resistor. The resultingchangesarel to the external excitations. The representation of Fig. 2he basic conguration of the sensor measurement sys-n be used as load (force, pressure) and/or deformationent, strain, velocity, etc.) sensor.</p><p>lent lumped-parameter models</p><p>t sensor is basically an electromechanical transducerbe described by the constitutive (characteristic) equa-sensor and the equations of motion of sensor structurethe associated boundary conditions. The equivalent</p><p>rameter approach can be used to replace the systemequations with a lumped-parameter electrical circuitents physically represent the sensor electromechani-</p><p>ies such as the capacitance, resistance, mass, stiffness,ng [16]. The equivalent circuit method is attractive inhat the sensor system can be cast in a single represen-hermore, the equivalent circuit method is often used toanalyze coupled domain devices including electrostatic[17], piezoelectric devices [18], ionic polymer [19], andstic devices [20].follows, the equivalent lumped-parameter approachto obtain the paint sensor equations.</p></li><li><p>O.J. Aldraihem et al. / Sensors and Actuators A 149 (2009) 233240 235</p><p>Fig.</p><p>2.2.1. IdealThe sim</p><p>electricallyequation. Ttance, Ra, cas shown iaggregatesbon black agThese paraland capacitcomponentand are estifrequency d</p><p>ZDebye = Ra</p><p>with</p><p> = RgCg,where (=2time of theDebye impe</p><p>Z Debye = Ra</p><p>Z Debye = 1The ideal coof Z Debye anRa +Rg, howWhen themaximum vfrequency,via Cg = (1/(</p><p>2.2.2. FrequThe Deb</p><p>in describinquency indesensor is mquency depobtained by</p><p>ZCC = Ra +</p><p>where isthe range,sin(/2), t</p><p>ZCC = Ra +</p><p>Letting = R1/g Cg , the impedance (5) is reduced to</p><p>ZCC = Ra +1</p><p>(1/Rg) + (1/r) + jc(6)</p><p>equency dependent resistor and capacitor given by</p><p>1Cg cos(/2)</p><p>Cg sin(/2)</p><p>(7)</p><p>Ra, Rg and Cg are frequency independent elements. The realaginary parts take form similar to those of the Debye modelare given, respectively, as</p><p>Ra + Re1 + (w)2</p><p> Re1 + ( )2</p><p>(8)</p><p>ec,</p><p>uivald gr</p><p>eterse nuRa, Ror es an.</p><p>vern</p><p>senThisnicalhownn. Detake</p><p>echatiffnesort x(turrey chasureen the beectedactiv3. Equivalent electrical circuit of the ideal, Debye, model.</p><p>components, Debye modelplest equivalent circuit mimicking the impedance ofconducting composites can be modeled by a Debyehe equivalent circuit of this model consists of a resis-onnected in series with parallel RgCg elements [12],n Fig. 3. The resistance Ra is the overall carbon blackresistance of the composite. The gaps between the car-gregates are equivalent to resistorcapacitor elements.lel elements Rg and Cg are the overall gaps resistanceance of the composite, respectively. The Ra, Rg and Cgs are considered ideal, that is frequency independent,mated from the impedance spectrum of the sensor. Theependent impedance of this composite sensor is</p><p>+ Rg1 + j (1)</p><p>j =</p><p>1 (2)f) is the angular frequency and is the characteristicequivalent circuit. The real and imaginary parts of thedance (1) can be extracted, respectively, as</p><p>+ Rg1 + ()2</p><p>Rg</p><p>+ ()2(3)</p><p>mponentsRa,Rg andCg canbeestimated fromthevaluesd Z Debye. At low frequency, the value of the real part isever, this value reduces to Ra at very high frequency.frequency reaches (1/), the imaginary part attains aalue of Z max = Z Debye(max = (1/)) = (Rg/2). At thismax, the capacitance of the composite can be calculated</p><p>Rgmax)).</p><p>ency dependent components, ColeCole modelye model presented in the previous section is usefulg a composite sensor with impedance possessing fre-pendentparameters.When thematrixof thecomposite</p><p>with fr</p><p>r =</p><p>c = </p><p>whereand im(3) and</p><p>Z CC =</p><p>Z CC =</p><p>where</p><p> = R</p><p>The eqresenteparampositivnentsZ CC. Fvanishmodel</p><p>2.3. Go</p><p>TheFig. 5.mechacuits sdomaican beThe malent sthe senamountrical ctherebas mea</p><p>Whdistancis subjan attrade of polymer, the impedance parameters become fre-endent. For such a case, a good representation can bethe ColeCole empirical equation:</p><p>Rg</p><p>1 + (j) (4)</p><p>a dimensionless positive parameter with values in10. Using De Moivre identity, j = cos(/2) + jhe impedance (4) is expanded as</p><p>Rg1+ cos(/2) + j((/) sin(/2)) (5) Fiw</p><p>Re =Rgr</p><p>Rg + r (9)</p><p>ent circuit of the ColeCole impedance (6) can be rep-aphically, as shown in Fig. 4. In ColeCole model, fourshouldbeestimated;Ra,Rg,Cg and. Thedimensionlessmber is obtained from tting the data. The compo-g and Cg can be estimated from the values of Z CC and=1, it should be clear that the resistor term in (6), 1/r ,d the capacitor, c , becomes Cg leading to the Debye</p><p>ing equations of the sensor system</p><p>sor system depicted in Fig. 2 is modeled as shown inmodel is a lumped-parameter model which treats thedomain as a single degree of freedom system. The cir-in Figs. 3 and 4 are adopted for the sensor electrical</p><p>pending on the model used, the sensor impedance, Zs,n from the Debye (1) or the ColeCole (6) equation.nical elements are the equivalent mass, m, the equiv-ss, K, and the equivalent damping coefcient, b. Whenis disturbed by a force F(t), the mass is displaced by an). The mechanical disturbance is converted into elec-nt signal which ow...</p></li></ul>