Flexible humidity sensor for smart agricultural applications

Abstract

The increase in food production due to the need for food brought by the increasing world population from year to year necessitates production at high quality and in much larger quantities in every season. In order to grow fruit and vegetables efficiently, sensors that measure ambient temperature and humidity are needed in greenhouses. Two different flexible and resistant textile-based humidity sensors that can measure the humidity at higher levels (80%, 90%, and 100% RH) were designed and printed directly on the four different greenhouse fabrics using silver and carbon conductive inks. Fabric thickness, weight, tensile, tear strength, elongation, abrasion, air permeability, water permeability tests for evaluating various physical and mechanical properties of specimen fabrics to be used for the sensor were carried out. In addition, depending on the humidity value in the environment, the sensor performance was tested based on sensor electrical resistance measurements with respect to repeated bending/cyclic tests, rubbing, UV exposure/ weatherability (against UV and raining) tests. Moreover, some important features of the sensors such as hysteresis, repeatability, response time have been also examined. Statistical analyses showed that the sensor designs and type of conductive inks had significant effects on the performance of the humidity sensors and the best sensor performance was obtained with the polypropylene coated fabric using design II and silver based conductive ink. The fabricated textile based flexible humidity sensors detect the change in relative humidity levels from 80%RH to 100%RH accurately and achieve good durability, and repeatability even after prolonged UV exposure and raining. Thus, the developed textile-based flexible humidity sensor might be useful for future smart agricultural applications.