Characterization and Comparison of Biodegradable Printed Capacitive Humidity Sensors

Abstract

Flexible and biodegradable sensors are advantageous for their versatility in a range of areas from smart packaging to agriculture. In this work, we characterize and compare the performance of interdigitated electrode (IDE) humidity sensors printed on different biodegradable substrates. In these IDE capacitive devices, the substrate acts as the sensing layer. The dielectric constant of the substrate increases as the material absorbs water from the atmosphere. Consequently, the capacitance across the electrodes is a function of environmental relative humidity. Here, the performance of polylactide (PLA), glossy paper, and potato starch as a sensing layer is compared to that of nonbiodegradable polyethylene terephthalate (PET). The capacitance across inkjet-printed silver electrodes is measured in environmental conditions ranging from 15 to 90% relative humidity. The sensitivity, response time, hysteresis, and temperature dependency are compared for the sensors. The relationship between humidity and capacitance across the sensors can be modeled by exponential growth with an R2 value of 0.99, with paper and starch sensors having the highest overall sensitivity. The PET and PLA sensors have response and recovery times under 5 min and limited hysteresis. However, the paper and starch sensors have response and recovery times closer to 20 min, with significant hysteresis around 100%. The PET and starch sensors are temperature independent, while the PLA and paper sensors display thermal drift that increases with temperature.

Integrated Capacitive- and Resistive-Type Bimodal Relative Humidity Sensor Based on 5,10,15,20-Tetraphenylporphyrinatonickel(II) (TPPNi) and Zinc Oxide (ZnO) Nanocomposite

“…The sensor’s transient, capacitive, and resistive responses to step input between low (45%) and high (85%) ambient % RH values are depicted in Figure a,b. It is pertinent to mention that the response time is defined as the time required for the capacitive humidity sensor to accomplish 90% of the saturated capacitance value across the high % RH region; similarly, the recovery time is defined as the time required by capacitance of the device to alter from a local maximum to within 10% of the average minimum value across the low % RH region . From Figure a, it is observed that at constant 45% RH value, the response is quite stable up to 50 s for TPPNi-ZnO nanocomposite-based capacitive sensors but increases to its maximum with an average response time of ∼30 s when % RH changes from 45 to 85%.…”

Silver Conductive Threads-Based Embroidered Electrodes on Textiles as Moisture Sensors for Fluid Detection in Biomedical Applications

“…The percentage hysteresis at different volumes of water is summarized in Table 3. The percentage value of hysteresis is calculated from Equation (8) [25].…”

“…Numerous sensors based on various principles and substrates are available for the detection and monitoring of humidity and moisture [9,[24][25][26][27]. These are capacitive, resistive (inductive) LC resonators or optical sensors.…”

Sustainable Printed Chitosan-Based Humidity Sensor on Flexible Biocompatible Polymer Substrate

“…Such sensors can be realized on numerous sustainable and even biodegradable substrates [10]. The relationship between humidity dependent permittivity and capacitance is commonly modeled by a second order polynomial growth, which makes this type of sensors rather sensitive in a higher humidity range [11].…”