| Radio Frequency Identification(RFID),especially UHF(Ultra-High-Frequency,UHF)RFID technology is a long-distance and non-contact technology of two-way data communication through radio frequency(RF),which will connect an extremely complex Internet of Things system.It is regarded as one of the most promising information technologies of 21 st century.According to different structures,the UHF RFID tag can be divided into two categories: UHF RFID tag(with the chip)and chipless UHF RFID tag.A UHF RFID tag with the chip consists of an antenna and a silicon chip,while the chipless UHF RFID tag relies on special circuit to radiate electromagnetic signals to carry the information.The combination of RFID technology and textile/clothing will greatly improve the efficiency of clothing production and sale,save the costs and avoid human errors.At the same time,it can be widely used in areas such as unattended clothing stores,garment washing services,anti-counterfeiting and supervision and care for special groups.Up to now,the application of UHF RFID tags in the clothing market is still in its infancy,and only a small number of UHF RFID tags are used in the logistics and sales management of clothing.On the one hand,compared with the very mature and cheap tags of barcodes or QR codes,the cost of the chip(IC)in the UHF RFID tag greatly limits the commercial application in clothing market.On the other hand,during the usage of wearing and washing,the connection between the chip and the antenna is easily damaged,resulting in a failure identification of the RFID tag.The emerging fabric-based chipless UHF RFID tag consists of a fabric-based antenna and filter circuit,which can solve the above problems at the same time.Theoretically,the functional characteristics of the fabric-based chipless UHF RFID tags depend on the filter circuit.Although many scholars have done a lot of research on the antenna design and preparation for fabric-based UHF RFID tags,the technical field of the design and preparation of fabric-based filter circuits is almost blank,and there is no chipless UHF RFID tag based on common fabrics.According to the structure and working principle of fabric-based chipless UHF RFID tags,the main technical difficulties during the design and preparation are as follows:(1)Characterization technology for the dielectric properties of light and thin fabrics.The dielectric properties of the fabric determine the geometric structure and electrical length of the tags.As the dielectric properties of fabrics vary at a small range and they are light,soft and easy to deform,traditional methods are difficult to accurately measure the dielectric properties of fabrics.(2)The deposition of conductive materials on the fabric surface.Existing researches use chemical reagents to corrode copper on the surface of PCB(printied circuit board)to fabricate the conductor of UHF RFD tags.However,it cannot reach the requirements of flexible wearability and contact comfortability.However,the emerging technologies that use metal patches,conductive yarn weaving or embroidery to prepare electronic devices on the surface of the fabric are complex and have low flexibility.(3)Conductivity characterization technology for uneven film of conductive composite.Screen printing technology can deposit conductive ink on the fabric surface to achieve conductive fabric.However,the screen printing film is a conductive composite material with low conductivity compared with bulky metal and it is uniform.Therefore,the measurement of conductivity at high frequencies is very difficult.(4)The synergistic effect of non-homogeneous fabric substrate,printed conductor and circuit structure on the electromagnetic radiation characteristics of the tag.It is difficult to design circuit structure of the chipless RFID tag to carry information.Because,the porous structure of conventional fabrics lead to large dielectric loss,and the rough surface causes the uniformity of printing film.Aiming at the above technical problems,this paper proposes solutions one by one based on conventional fabrics,and completes the simulation design and experimental preparation of fabric-based microstrip multi-resonant circuits.Combining simulated and measured verification,this paper explores the influencing factors of the electromagnetic radiation performance of the microstrip multi-resonant circuit.The research content includes the following aspects: Firstly,based on the principle of the classic ring resonator,a method for measuring the dielectric properties of the fabric and the conductivity of the screen-printed film under ultra-high frequency conditions was proposed,and the accuracy was demonstrated.Then,based on the measured properties of fabric and ink,a fabric-based microstrip multi-resonant circuit was designed and prepared to evaluate its RF performance.Finally,the designed microstrip multi-resonant circuit is applied to fabricate a fabric-based chipless UHF RFID tag,and the signal transmission performance at high frequency is measured.Additionally,and the performance of information carry is evaluated,and the feasibility of fabric-based chipless UHF RFID based on the resonant circuit is initially verified.The specific contents and results are as follows:(1)In response to the measurement problem of fabric dielectric properties and conductivity of screen-printed films at high-frequency cuased by the uniformity,the classical ring resonator principle was proposed to demonstrate the measurement method of dielectric and electrical properties of conventional printed electronic materials based on textile.The accuracy of this method was verified.Then,the dielectric properties of the fabric and the high-frequency conductivity of the screen-printed film were accurately measured at a certain frequency.The research results showed that the dielectric and electrical properties of the materials were closely related to the resonance frequency and signal attenuation of the ring resonator.The position and shape of the resonance peak could be used to determine the dielectric and electrical properties of textile printed electronic materials.(2)In response to the design difficulty of resonant circuit caused by the high loss and unevenness of textile printed electronic materials,the reflection principle of impedance mismatching was adopted,and a method of symmetrical microstrip stubs was proposed to design and prepare fabric-based microstrips multi-resonators.The influence of dielectric properties of textile,electrical properties of printed conductor on the UHF signal transmission characteristics was revealed.The research results showed that the dielectric loss and thickness of the fabric,the conductivity of the printed conductor jointly determined the notch depth of the resonator.The dielectric constant and thickness of the fabric affected the resonant frequency and port impedance,thus determined the prototype geometry of the resonant unit.The notch position,notch depth and the overall trend of the fabric-based microstrip multi-resonant of experiment were in good agreement with the simulated results.Additionally,the deviation rates of the resonant frequency were 0.99%,0.88%and 2.26%,respectively.It demonstrated that the resonant circuit can effectively realize the filtering function and can be applied to fabric-based chipless UHF RFID tags.(3)In response to the impact of ununiform printed conductive film on the RF performance of printed electronic devices,a method of constructing chipless UHF RFID tag based on multi-resonant circuit was proposed.The effect of screen printing quality on the high frequency signal transmission of fabric-based chipless tags was explored.The feasibility of achieving information coding for chipless tag was preliminary explored.The research results show that the label system can work normally,and the feasibility of the fabrication techniques was initially verified with experiments.Additionally,the thickness,thickness uniformity,and printing accuracy of the screen printing film affect the electrical size of the resonant unit and change the impedance matching,and thus affect the performanceof high-frequency signal transmission.Based on the above research,the topic is based on the preparation of fabric-based microstrip multi-resonant circuits utilized screen printing technique and apply it in UHF RFID chipless tags.A method for characterizing the dielectric and electrical properties of conventional textile printed electronic materials was created.The influence of the dielectric properties of fabrics,electrical properties of the printed film and the circuit structure on the electromagnetic coupling of the multi-resonant circuits was studied.And thus the circuit structure of fabric-based chipless UHF RFID tag was determined.Finally,it was apply to initially explore the feasibility of information encoding of chipless UHF RFID tag.The research indicated that the thickness uniformity and width accuracy of the screen printing film is a key factor in improving the RF performance of the filter.This research provides certain theoretical and practical guidance for the design and preparation of flexible fabric-based RF devices,and will promote the development of smart textiles. |
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