Screen-Printed Remotely Readable Environmental Sensor Pair

In this paper, we present the fabrication methods and the characterization results of a remotely readable flexible temperature/humidity sensor pair. The sensor pair has been fabricated with a screen printing technology, and it consists of a polymer-based capacitor as a temperature and humidity sensitive component added to the antenna coil for remote reading purposes. The sensor pair relays its operation to the double sensor structure in order to produce the environmental temperature and relative humidity readings. The resonance frequency of the sensor (i.e., the formed LC network designed to 13.56 MHz) is measured as a function of temperature and relative humidity. Temperature is sensed with the reference sensor with full lamination and the relative humidity with the active sensor with a lamination opening over the polymer capacitor. The sensor has been characterized in the temperature and humidity ranges of 0 °C-70 °C and 45%RH-95%RH, respectively. The simple data-analysis algorithm developed enables the calculation of both temperature and relative humidity from the corresponding measured resonance frequencies. The relative humidity sensitivity (ΔfRES/%RH) of the sensor was between 3.6-5.3 kHz/%RH in the temperature range of 30 °C-50 °C. The temperature sensor in the sensor pair had the sensitivity of 9 kHz/°C in the applied temperature range. In addition, the temperature compensation of the polymer humidity sensor is considered, based on the data-analysis algorithm. Finally, the calibration and the effect of the installation medium of such a sensor pair are discussed.