Temperature/light sensing using carbon fiber polymer-matrix composite

A polymer (epoxy)-matrix composite with the top two laminae of continuous carbon fibers in a crossply configuration was found to be a temperature sensor. Each junction between crossply fiber tow groups of adjacent laminae is a sensor, while the fiber groups serve as electrical leads. A junction array provided by two crossply laminae allows sensing of the temperature/light distribution. The contact electrical resistivity of the junction decreases reversibly upon heating (whether using light or hot plate to heat), due to the activation energy involved in the jump of electrons across the junction. The contact resistivity decreases with increasing pressure during composite fabrication, due to the increase in pressure exerted by fibers of one lamina on those of the other lamina. The absolute value of the fractional change in contact resistivity per degree C increases with increasing pressure during composite fabrication, due to decrease in composite thickness, increase in fiber volume fraction and consequent increases in interlaminar stress and activation energy. A junction between unidirectional fiber tow groups of adjacent laminae is much less effective for temperature/light sensing, due to the absence of interlaminar stress.