Development of 3D-Printed Embedded Temperature Sensor for Both Terrestrial and Aquatic Environmental Monitoring Robots

Abstract

A linear resistive temperature sensor has been 3D printed through fused deposition modeling using a conductive filament based on polylactic acid (PLA) and graphene nano rods (GNR) composite. The sensor is capable of measuring temperature variations based on the change in resistance of the printed pattern. As PLA is insensitive to and insoluble in water, the sensor can be used both in air and under water without any need of encapsulation. Graphene nanorods give the printed patterns a conductive property, while the PLA acts as a binder matrix. When the temperature rises, there is physical expansion of the polymer matrix at microscopic level that reduces the contact between the conductive GNRs and the resistance increases. On cooling down, the physical properties are retained and the resistance drops again. The sensors show excellent linearity and stability when tested both in air and under water up to 70°C. Beyond this temperature, the deformation in the polymer matrix is permanent and the resistance does not return to its initial value. To minimize hysteresis, the recommended operation temperature is up to 60°C. The effect of pattern width and length has also been investigated that shows a direct relationship of resistance with the length, while an inverse relationship with the width as expected. The sensitivity of the linear sensors was calculated to be ∼13 Ω/°C, while the response and recovery times were 6 and 14 s, respectively. Based on their performance, the sensors can be efficiently used for general aquatic and terrestrial environmental monitoring.