| With the rapidly development and progress of smart textiles,more and more fabric-based electronic devices are used in radio transmission.Electronic device flexibility has become an irresistible trend.As the main component of RF devices,micro-strip resonant circuit has a series of advantages such as small volume,light weight,good performance,and easy to match with other integrated circuits,which is in line with the development direction of today's circuit design.The transmission performance of the resonant circuit is the most important parameter of radio transmission,which determines the application of the resonant circuit.It is not only related to the design of the resonant circuit,but also to the base material.At present,most of the research on transmission performance of micro-strip resonant circuit is based on hard plate.As a kind of typical flexible fiber material,the fabric is in line with the development direction of the intelligent textiles for the requirements of the required electronic devices.Based on this,the special flexible material of fabric was chosen as the substrate of micro-strip resonant circuit,printing the micro-strip resonant circuit on the surface of the fabric to study the influence of material property and structure parameters on the RF transmission performance of the printed circuit.In order to fulfill this purpose,different fabric samples with different material parameters such as fiber material,yarn count,warp density,weft density and structure were selected to study the effect of fabric parameters on UHF dielectric properties.And studied the influence of the fabric structure parameters on the reflection and transmission of radio frequency signal of micro-strip resonant circuit printed on the surface of fabric.The research contents in details were followed.(1)The influence of yarn material and fabric structure parameters on dielectric properties under ultra-high frequency is studied.The results show that the dielectric permittivity and dielectric loss of modal fabric was significantly higher than that of other materials,and the permittivity and loss of polyester fabric is the lowest,which proved the higher the crystallinity(or degree of polymerization)of the fiber is,the lower the dielectric constant and loss.The closer the fabric's structure is,the higher its dielectric constant and loss.Different fabric with different fiber material,yarn count,warp density,weft density and structure were selected to be tested.The experiment use control variable method to test the fabric dielectric properties of several groups of samples in the same condition.(0.7~1.3GHz).Then an ANOVA analysis on dielectric properties of textiles was performed to find the significant factors from fabric structure,materials,yarn fineness and yarn density according to the test results.The results show that the increasing density and count of weft yarns in woven fabric nearly lead to a significant change of the dielectric constants,while the change of warp yarn has not significant effect.And also,the fabric with more interweaving points and compact structure has a larger dielectric permittivity and a higher dielectric loss.When either yarn density or yarn count changes,the pore size and the fiber volume fraction will change to some degree.The dielectric permittivity of air is approximately 1.0,and that of textile fibers is generally larger than air.Therefore,the woven fabric with larger fiber volume fraction has larger dielectric permittivity.Concerning the yarn material,the result shows that the permittivity and loss of the modal fabric are the greatest,followed by the silk fabric,then the blended fabric and the cotton fabric.Generally,the crystallinity,orientation,and degree of polymerization of cotton fibers are higher than the Modal fibers.Due to the composite structure of silk,the degree of crystallinity of silk fibers is litter lower than cotton fibers and higher than the modal fibers.The high crystallinity of cotton fiber makes the molecule chains difficult to appreciably rotate in response to the applied fields,therefore,little relaxation polarizing response is observed and the permittivity is low.On the other hand,the difference of crystallinity and the molecular group polarity of these fibers leads to the varieties of moisture regain,and they can contribute to the dielectric properties of woven fabric with different yarn constitutions.Generally,the hygroscopicity of fibers in order is:modal > silk > cotton.At the same relative humidity and air temperature,the fiber ensembles with high moisture regain will trap or absorb a higher content of water.The higher the moisture regain,the greater the dielectric permittivity.(2)Study on the influence of fabric material and structural parameters on the quality and electrical properties of printed micro-strip resonant circuit.The results show that the higher the tightness of the fabric,the better the quality of printing conductive film,the smaller the resistance and the lower the impedance.The substrate material and screen printing process for the micro-strip resonant circuit are prepared according to research results above.Then,we need to identify the ink for screen printing,the design of micro-strip resonant circuit and the parameters of the base fabric.After screen printing,the adhesion and penetration of printed circuit ink and the integrity and uniformity of printed film were observed by SEM.The resistance and impedance characteristics of printed transmission line were tested.The results show that,as a printing substrate,the fabric surface should to be smooth to meet the good performance of the printed conductive film.Compared with PET and PCB,the fabric surface has a special texture structure,and there are many holes in the interior.Therefore,the structure of the fabric should be as close as possible to meet the uniform and uniform conductive film.However,based on the study of the dielectric properties of fabric,the fabric with tight constructions makes the lager dielectric loss,which is not conducive to the transmission of electrical signals.Therefore,the close degree of base fabric should be reasonable,it can't be too tight or too loose.And the resistance of the conductive layer is closely related to the quality of the printing.The better printing quality makes the smaller resistance.Transmission line impedance decreases with increasing of frequency at UHF(860-960 MHz).The impedance values of the transmission line are different when printed on different fabric at the resonant frequency.It indicated that the substrate has an impact on the impedance characteristics of the printed conductive layer.(3)The influence of substrate material on the transmission performance of printed micro-strip resonant circuit was studied.It was found that the less the permittivity of the fabric is beneficial to the transmission efficiency and modulation of the signal.And the fabric with tight structure has small printed film impedance and strong signal modulation ability.The network analyzer was used to test the S parameters of the resonant circuit printed on fabrics of different structural parameters.The effects of the dielectric properties,electrical properties and the apparent morphology of the printed conductive layer on the transmission reflection properties are analyzed.The results show that the performance of micro-strip resonant circuit to signal radio frequency transmission mainly depends on two aspects,the performance of modulation for signals and transmission loss.And the modulation effect of circuit have on signal are mainly related to permittivity and the printing quality.The smaller the permittivity leads to the higher the efficiency of transmission.And good printing quality can make the modulation of the signal more accurate.The dielectric loss of substrate and the impedance of printed conductive layer affect the transmission loss.The larger dielectric loss leads to the greater the impedance and the more transmission loss,which is not conducive for signal to the transmission of the electrical signal in the fabric.In summary,the influence of the fabric properties of the printed micro-strip resonant circuit electrical performance characteristics were studied,the following conclusions are drawn.For the part of material,the dielectric permittivity and dielectric loss of modal fabric was significantly higher than that of other materials,and the permittivity and loss of polyester fabric is the lowest,which proved the higher the crystallinity(or polymerization degree)of the yarn material cause the lower the dielectric constant and loss.The permittivity affects the resonance frequency offset.In terms of fabric structure,it was found that the higher the tightness makes the better quality of printing film.And the fabric with tight structure has small printed film impedance and strong signal modulation ability.However,the higher the dielectric permittivity and loss are not conducive to the transmission of electrical signals. |
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