Exploitation of Transparent Conductive Oxides in the Implementation of a Window-Integrated Wireless Sensor Node

Exploitation of transparent conductive oxides (TCOs) to implement an energy-autonomous sensor node for a wireless sensor network is studied and a practical solution presented. In the practical implementations, flexible and rigid substrates, i.e., polyimide and glass, are coated with TCO, namely, aluminum-doped zinc oxide (AZO). AZO-coated flexible substrates are used to form thermoelectric generators (TEGs) that produce electricity for the sensor electronics of the node from thermal gradients on a window. As the second solution to utilize AZO, its conductive properties are exploited to implement transparent antennas for the sensor node. Antennas for a UHF RFID transponder and the Bluetooth radio of the node are implemented. A prototype of a flexible transparent TEG, with the area of 67 cm² when folded, was measured to produce power of 1.6μW with a temperature difference of 43 K. A radiation efficiency of -9.1 dB was measured for the transparent RFID antenna prototype with the center frequency of 900 MHz. Radiation efficiencies between -3.8 and -0.4 dB, depending on the substrate, were obtained for the 2.45 GHz Bluetooth antenna.