The Effect of Humidity on Microwave Characteristics of Screen Printed Paper-Based Electronics

This paper addresses one of the key issues in using paper electronics at
microwave frequencies. As paper is hygroscopic, the varying moisture content
can lead to differing dielectric and even conductive properties of paper
electronics and must be taken into consideration in any device design. In this
work, coplanar waveguides (CPWs) have been screen printed using silver ink
on matt paper. Increasing the relative humidity between 40 and 90% is
shown to increase the losses, decrease the propagation velocity and decrease
the characteristic impedance of CPWs. The effect of water on both silver flake
ink and the matt paper used in this work are considered, and it is shown
that the change in permittivity of the substrate as a result of absorbed water
within paper is the most dominant factor on the microwave characteristics.
The reported findings should be considered in paper-based applications at
microwave frequencies, as the changes in transmission-line parameters can
lead to drastic variations in device and system operation.