A novel noncontact stress/strain measurement method has been developed for monitoring dynamic strain on the surface of various structures under operation. The change of electrical properties of carbon nanotubes (CNT)-dispersed resin was investigated to evaluate the possibility of its application to a highly sensitive and remote strain sensor without interconnections. It was validated that the electrical impedance of the CNT-dispersed resin changes drastically at frequencies higher than 500 kHz under strain. Application of microwave showed the possibility of the non-contact measurement of the change of electrical impedance of the resin under dynamic load by measuring the change of its reflectivity obtained from the surface of the resin. A theoretical method to estimate the change of the intensity of the microwave reflected from the resin was discussed based on the microwave theory. The change of the reflectance under tensile strain of 20% was calculated by the method using the measured change of the impedance of the resin under the frequency range between 1Hz and 10MHz. As a result, the maximum change of the reflectance was estimated as 1.2% at 630 kHz. Therefore, it is possible to realize remote monitoring of the strain field on the surface of various products under operation by applying the CNT-dispersed resin.

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