A solar powered 24 GHz RFID sensor node for industrial applications

The fundamental construction of a sensor node working in the 24 GHz Industrial, Scientific and Medical band (ISM) is presented. A brief overview of the electrical and technological design ideas is given. A small high efficiency solar cell is used for continuously powering the system allowing nonstop data logging of sensor data. The wireless read out procedure is accomplished by back scatter modulation of the reader signal, a communication principle which is well known from traditional Radio Frequency Identification (RFID) systems [1]. For the mechanical design a stacked structure is used which combines the digital circuit, the analog radio frequency (RF) circuit and the solar cell in a molded interconnect device (3D-MID). The radio frontend is placed above the solar cell and is optically transparent due to a lattice structure of the microstrip lines and the antenna. The overall dimensions of the sensor node which can be integrated into a metallic object too, are 13 × 13 × 4 mm
³
.