Photovoltaic enhanced UHF RFID tag antennas for dual purpose energy harvesting

The most significant barrier to improving passive RFID tag performance for both fixed function ID tags and enhanced RFID tags is the limitation on the amount of power that can be harvested for operation. This paper presents a novel approach for incorporating solar harvesting capability into existing passive RFID tags without increasing the parts count or changing the tag assembly process. Our approach employs the tag's antenna as a dual function element in which the antenna simultaneously harvests RF energy, communicates with the RFID reader, and harvests solar energy for auxiliary power. This is accomplished by using low cost, printable photovoltaics deposited on flexible substrate to form part of the antenna's radiating structure. Several prototype UHF RFID antennas are demonstrated using commercially available thin film, amorphous solar cells. To quantify the improvement in tag performance, Intel's WISP was used as an initial test vehicle. The effective read range of the tag was increased by six times and exceeded the reader's sensitivity limitations. Additionally, the new antenna allowed for sensing and computing operations to take place independent of the RFID reader under typical office lighting conditions.