Humidity Sensors Printed on Recycled Paper and Cardboard

Abstract

Research, design, fabrication and results of various screen printed capacitive humidity sensors is presented in this paper. Two types of capacitive humidity sensors have been designed and fabricated via screen printing on recycled paper and cardboard, obtained from the regional paper and cardboard industry. As printing ink, commercially available silver nanoparticle-based conductive ink was used. A considerable amount of work has been devoted to the humidity measurement methods using paper as a dielectric material. Performances of different structures have been tested in a humidity chamber. Relative humidity in the chamber was varied in the range of 35%–80% relative humidity (RH) at a constant temperature of 23 °C. Parameters of interest were capacitance and conductance of each sensor material, as well as long term behaviour. Process reversibility has also been considered. The results obtained show a mainly logarithmic response of the paper sensors, with the only exception being cardboard-based sensors. Recycled paper-based sensors exhibit a change in value of three orders of magnitude, whereas cardboard-based sensors have a change in value of few 10s over the entire scope of relative humidity range (RH 35%–90%). Two different types of capacitor sensors have been investigated: lateral (comb) type sensors and modified, perforated flat plate type sensors. The objective of the present work was to identify the most important factors affecting the material performances with humidity, and to contribute to the development of a sensor system supported with a Radio Frequency Identification (RFID) chip directly on the material, for use in smart packaging applications. Therefore, the authors built a passive and a battery-supported wireless module based on SL900A smart sensory tag's IC to achieve UHF-RFID functionality with data logging capability.

Evaluation of the Sheet Resistance of Inkjet-Printed Ag-Layers on Flexible, Uncoated Paper Substrates Using Van-der-Pauw’s Method

“…An example would be the capacitive sensing of humidity, where the porous paper serves as a dielectric material. When the paper absorbs humidity from its environment, the dielectric constant of the capacitor alters accordingly, and those changes can be measured [12][13][14][15]. Additionally, wireless readout-options for such sensors have frequently been reported [16][17][18] paving the way for truly low-cost, sustainable and smart packaging solutions of the future [19,20].…”

Towards low-cost, wireless blood anomaly sensing: An RFID-based anemia detection sensor

“…The latter approach often uses electromagnetically responsive smart materials or background changes to an RFID tag to cause a controlled change in tag signal parameters such as backscatter signal strength [9] or response frequency [10]. There have been several case studies where researchers have developed RFID devices to sense parameters like temperature alarms [11], humidity [12], volatile organics [13], and pH [14].…”

Humidity Sensing Properties of Paper Substrates and Their Passivation with ZnO Nanoparticles for Sensor Applications

“…However, only a few concrete examples of humidity sensors using paper substrate as the sensing element can be found in the literature. For instance, a fully printed chip-less radio frequency identification sensor for humidity monitoring applications was reported in [17]. Another example presents a capacitive-type humidity sensor using silver interdigitated electrodes printed on paper substrate.…”