Development Of Capacitive Extensometer With Versatility Superior To The Resistive Extensometer

The objective of this work was to develop a capacitive extensometer containing four identical capacitives sensors that went connected in the two branches of a Wheatstone Bridge. The electrodes of the capacitives sensors were made of stainless steel to avoid corrosion with the humidity that would impair the response of the extensometer. Each sensor has an immobile electrode measuring 8.0 mm in length, 5.0 mm in width and 0.1 mm in thickness by being bonded onto an insulation holder developed with PAI66 polyamide polymer. There are two identical mobile electrodes measuring 40.0 mm in length, 5.0 mm in width and 0.1mm in thickness, which are common to four capacitives sensors. These electrodes were bonded to the opposite faces of the same polyethylene polymer that moves when the extensometer undergoes stretching or shortening. It was verified that the extensometer can be stimulated with sinusoidal voltage higher than 10 Vac and frequency higher than 59 Hz, its response was linear with hysteresis of 3.0%, response time of 8.0 ms, resolution of 0.09 N. The new extensometer has higher sensitivity, 1.0 V while resistive extensometer presented 0.20 V. This capacitive extensometer has the potential to do measure several different physical magnitudes.