Mechanism Of Wireless Sensor Using Passive Nanocomposite

The conductive composites manufactured by adding carbon nanotube(CNT)to polymer have been widely researched.It is because of their excellent mechanical,thermal,and electrical properties.CNTs possess high-aspect-ratio characteristics that enable them to form complex conductive networks in the polymer matrix.The CNTs can form different shapes such as curved or straight,separated or intersected in the polymer matrix.CNT/polymer nanocomposites possess the properties of inductors,resistors,and capacitors.Therefore,these properties make it possible to design passive wireless sensors using CNT/polymer nanocomposites.In this research,multi-walled carbon nanotubes(MWCNT)/Epoxy(EP)nanocomposite films were fabricated to test their response to electromagnetic signals.The relationships between the strains and the responses of the MWCNT/EP nanocomposite films to the electromagnetic signals were studied using experimental and theoretical methods.The wireless strain measurements were achieved by using passive MWCNT/EP nanocomposite strain sensors.The main research works are as follows:Firstly,a wireless measurement method was proposed using passive resistive sensors.It was based on the piezoresistive properties of the CNT/polymer nanocomposite.The feasibility of this method has been proved using theoretical analysis and simulation.The test system was constructed according to the theoretical and simulation circuits to experimental verifications.Based on the experimental results,a data processing method was proposed to improve the measurement accuracy of the passive resistive sensors at a fixed frequency.The 1wt%MWCNT/polydimethylsiloxane(PDMS)nanocomposite strain sensors were fabricated,and the relationship between the voltage effective value of sampling resistance and the strain of the MWCNT/PDMS nanocomposite sensors was tested using the proposed wireless measurement method.Secondly,the MWCNT/EP nanocomposite films were fabricated using the solution blending method to test their response to electromagnetic signals.The results have shown that:(1)MWCNT/EP nanocomposite films can respond to electromagnetic signals and emitted electromagnetic signals which can be received by inductance coil;(2)The MWCNT/EP nanocomposite films can resonate under the excitation of electromagnetic waves at a specific frequency,and the resonant frequency changed with the strain of the film;(3)The variation of the resonant frequency of MWCNT/EP nanocomposite films is dependent on the MWCNT content.The variation of resonant frequency with the strain of MWCNT/EP nanocomposite film was theoretically analyzed using the RLC equivalent circuit of MWCNT/EP nanocomposite film.The experimental results have shown to be in good agreement with the theoretically analyzed results.Due to this reason,it can be confirmed that the RLC equivalent circuit can effectively analyze the wireless sensing properties of MWCNT/EP nanocomposite film.Finally,the wireless measurement of MWCNT/EP nanocomposite films was achieved using the relationship between the variation of the resonant frequency and strain of MWCNT/EP nanocomposite films.This thesis provides a theoretical foundation for passive wireless sensors using CNT/polymer nanocomposites.