Textronic Capacitive Sensor with an RFID Interface.

This article presents an innovative combination of textile electrical circuits with advanced capabilities of electronic RFID sensors, indicating the revolutionary nature of the development of textronics, which is used in various areas of life, from fashion to medicine. A review of the literature relating to the construction of textronic RFID identifiers and capacitive textronic sensors is performed. Various approaches to measuring capacity using RFID tags are discussed. This article focuses on presenting the concept of a capacitive sensor with an RFID interface, consisting of a microelectronic part and a textile part. The textile part is based on the WL4007 material, where antennas and capacitive sensors are embroidered using SPARKFUN DEV 11791 conductive thread. The antenna is a half-wave dipole designed to operate at a frequency of 860 MHZ. The microelectronic part is sewn to the textile part and consists of a microcontroller, an RFID-integrated circuit and a coupling loop, placed on the PCB. The embroidered antenna is coupled with a loop on the microelectronic module. This article focuses on presenting various designs of textronic electrodes, enabling various types of measurements. Article presents capacitance measurements of individual sensor electrodes, made using a measuring bridge and a built RFID tag. The sensors' capacity measurement results are shown.

Investigation of Factors Affecting the Performance of Textronic UHF RFID Transponders.

The aim of this paper is to demonstrate progress in textronic UHF RFID transponder (RFIDtex tag) technology. The fundamental idea behind the RFIDtex tag design involves galvanic separation between circuits of the sewn antenna and the chip, which are electromagnetically coupled through a system of inductive loops. To advance the development of this concept, it is crucial to detect factors affecting the performance of the transponders. To achieve this goal, a mathematical model of the textronic UHF RFID transponder was developed. It involves relationships that describe the impedance of each element, the mutual inductance of the loops, and the chip voltage, and it enables the exploration of the influence of these variables on general parameters such as impedance matching and read range. Various analytical and numerical approaches were considered to obtain the value of the mutual inductance of the loops. The dimensions and geometry of the antenna, as well as the matching circuit in the microelectronic module, were taken into account. Based on the mathematical model, it was determined that mutual inductance strongly affects the chip voltage for frequencies higher than 800 MHz. The calculations from the mathematical model were compared with numerical simulations. Experimental studies were also conducted to investigate how the transponder performance is affected by either the distance between the centers of the loops or the conductivity of the threads used to embroider the antenna. The measurement results allowed us to conclude that even small imperfections in the manufacturing of the transponder, which slightly increase the vertical or horizontal distance between the centers of the loops, cause a dramatic decrease in the mutual inductance and coupling coefficient, significantly impacting the transponder's performance.

Textronic UHF RFID Transponder.

In order to respond the growing interest towards radio frequency identification textile transponders, the authors propose a new approach to design radio frequency identification (RFID) devices by introducing the RFIDtex concept. The coupling system of inductive loops is implemented in the textronic structure with the RFID interface in order to split the transponder into two independently manufactured components. Then both modules can be easily integrated into the RFIDtex tag. The presented simulation and measurement results prove the concept of manufacturing a relatively small antenna in the form of a meandered dipole sewn in with a single thread, and further, that can be connected to the RFID chip through the coupling system without galvanic junctions. The achieved parameters clearly indicate that the tag can correctly communicate with the read/write device as well as the coupling between its both parts works properly, and the impedance matching is possible in this case. The possibility of confectioning products with electronic identification tags at the textile factory site and improved resistance to the impact of environmental conditions are the main advantage of the proposed approach to the RFID devices designing. The RFIDtex transponder idea proposed by the authors was restricted in the patent no PL 231291 B1.