| Wearable devices have the functions of sensing,communication,energy collection and storage,providing solutions for the ubiquitous personal monitoring needs in the fields of sports and fitness,medical rescue,leisure and entertainment,etc.Textile antenna based on fabric is a new type of antenna component that combines fabric and communication system,which can complete the signal transmission function while ensuring conformal comfort with the human body.The substrate is an important part of the antenna,and its characteristics are critical to the performance of the antenna.In this paper,five kinds of wool/polyester woven fabrics with different contents were selected as the antenna substrates.The influence of different fabric parameters on the dielectric properties of the substrates was studied,and a coplanar waveguide broadband textile antenna was designed and fabricated.In addition,the effects of bending and human domain environment on antenna performance were also investigated.The specific work of the paper is as follows:(1)Five kinds of wool/polyester woven fabrics with different contents were selected as the antenna substrates,and the structural performance parameters of the five kinds of fabrics were tested.The dielectric constants and dielectric loss tangents of the five substrates were obtained by inverse inference,and were correlated with the fabric structural parameters.The influence of fabric structure and fabric warp and weft density on dielectric constant and dielectric loss tangent.(2)Using HFSS electromagnetic simulation software,a printed monopole antenna fed by coplanar waveguide was designed.The combination of semicircle and inverted isosceles trapezoid formed the radiation patch of the antenna.Using the aforementioned five kinds of wool/polyester woven fabrics as antenna substrates,by optimizing the feeder width S,the gap g between the feeder and the ground plate,and the value of the symmetrical chamfer a on the lower edge of the radiation patch,all five antennas could reach the simulation bandwidth of 2?7 GHz,and obtain approximately omnidirectional radiation directions.The peak gain of the antenna was close to 4d Bi.(3)The conductive layer of the antennas were prepared by screen printing.Antennas with small size and low profile were easy integrated into clothing.The measured return loss of the antennas were basically consistent with the simulation.The return loss values of the optimal resonance point were far less than-10 d B.The relative bandwidths were 114.3%,115.0%,111.5%,41.4%,and 111.8%,respectively.The bandwidth was greater than 25% of the requirement.(4)Four kinds of textile coplanar waveguide broadband antennas with the best performance were selected for simulation and test in the bending environment.The radius of curvature was set to 50 mm and 150 mm to simulate the placement of the antenna in the forearm and chest respectively.The measured results showed that after bending,the resonance frequency and return loss of the four antennas were in good agreement with the simulation,and still met the requirements of antenna return loss.The bending slightly reduced the bandwidth of the antenna,but it still met the requirement that the relative bandwidth is greater than 25%.At the 4 GHz frequency point,the maximum gain of the curved antenna could reach 5.6 d B.Finally,in the wireless body network area,the specific absorption ration(SAR)with its change response to the distance between the antenna and human body was discussed,and it was concluded that under typical frequencies,10 mm was effective for obtaining SAR value lower than 2 W/kg. |
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