| Wearable radio frequency identification(RFID)tags are widely concerned for their potential applications in identification,monitoring and sensing.The ideal way is to realize the function of RFID tags based on the fabric materials of the textile products,while the fabrication technology needs to be compatible with mature modern textile technology.Among them,embroidery technology is tried to be applied in the fabrication of tag antenna,and a lot of scholars have conducted research.In order to avoid the discontinuity of multiple conductive yarns and to achieve the simplicity of the process,some scholars propose to use a single conductive yarn to embroider the antenna topology,and they make some progress.However,few scholars pay attention to the impact of embroidery process deviations and the industrialized inverse packaging technology of embroidery antenna-chip bridging on the performance of tags when embroidering the antenna topology with a single conductive yarn.Aiming at the research and development of fabric-based tag antenna embroidery process deviation and packaging technology,this subject used a single conductive yarn to fabricate fabricbased dipole tag antenna by embroidery technology.Two sets of UHF RFID tag antennas were made by changing the main embroidery parameters,such as the structure of the conductive thread and the length of the stitch,and the influence of embroidery deviation on the performance of the tag antenna was analyzed.Then,around the embroidery antenna-chip bridge reverse packaging technology,from the packaging method and the location of the chip and antenna bridged two aspects to explore.Specific research contents were as follows:(1)The influence of the main embroidery fabrication technology of the antenna on the performance of the tag antenna was studied,and it was found that compared with the metal wire as the embroidery thread,the wire-wrapped yarn could enhance the performance of the label antenna,and the setting of the stitch length needed to consider the embroidery deviation of the antenna geometric structure.According to the geometry of the antenna,the stitch length was changed to explore the deviation between the actual structure and the design structure of the embroidery antenna,and the electrical performance,gain and reading distance of the tag under different stitch lengths were tested.The research showed that when the stitch length increased from 0.9mm to 5mm,the stitch length had a certain influence on the tag performance.When the stitch length was 1.7mm,the impedance matching and gain of the tag were optimal,and the maximum read range was 17.5m,which was more than 100% of the results of earlier research.At this time,there was no deviation in the antenna structure.In the range of 1.9mm-5mm,the antenna's geometric structure gradually deviated from 5-30 °.When the length of the stitch was 5mm,the deviation of the antenna structure was serious,and the deviation angle was 30 °.At this point,the antenna had a high energy loss and the minimum read range was 13.85 m.Therefore,when the deviation Angle of antenna structure was more than 30°,the performance of the tag will be greatly affected.(2)Investigate the embroidery tag antenna-chip inversion packaging method.The printed contact was used to bridge the antenna and the chip and the thickness of the conductive contact was related to the diameter of the yarn.In order to solve the problem that the package of embroidery antenna-chip cannot be industrialized,this paper adopted reverse packaging technology.First,an intermediate "bridge",a conductive contact,was introduced.The specific method was to print two conductive contacts at the antenna port of the embroidery tag,and then used an inverse packaging process to connect the chip and the conductive contacts,so as to bridge the antenna to the chip.It was found that the conductive contacts printed by screen printing could not form an effective path.In order to overcome the problem that the thickness of the conductive contact printed by the screen printing method was too thin,the production and optimization of the packaging mask will be performed.The thickness of the printed conductive contacts should exceed the diameter of the conductive yarn(0.31mm)to ensure the formation of conductive paths.The thickness of the printed conductive contacts in this article was 0.39 mm.(3)Study the impact of different bridge chip port positions on the reading performance of UHF RFID tags.By changing the distance between the port and the coupling ring,it was found that the closer the port is to the coupling ring,the greater the reading range of the tag.The results showed that because of the uneven current distribution of the antenna,when the bridging position is closer to the position of the coupling loop,the tag obtained the largest amount of energy with the induced current and the largest read range was 17.5m.In summary,first of all,when controlling the geometrical deviation of the antenna produced by the embroidery process,a suitable conductive yarn structure and stitch length should be selected.Compared with the linear structure,the spiral structure of the metal fiber blended yarn is beneficial to achieve the maximum energy transfer.Secondly,in the antenna-chip inverted package experiment,the thickness of the printed contacts should be slightly larger than the diameter of the conductive yarn.And the conductive contacts should be printed at the port position closer to the coupling ring.The energy obtained by the current is the largest,and the read range is also the largest.The research results clarify the selection basis of conductive yarns,stitch lengths and tag antenna-chip connections for tag antenna embroidery.These research conclusions supplement and improve the fabrication technology and evaluation method of UHF RFID embroidery tags for fabric-based silk mesh,laying a foundation for the application and promotion of tags.At the same time,the conclusions of the study are also useful for the fabrication of fabric-based flexible embroidery electronic devices. |
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