| In recent years,domestic mobile intelligent terminal devices and related industries have maintained rapid development,and the market scale of the intelligent wearable devices has grown quickly.The Cisco Vision Network Index predicts that there will be more emerging wearable devices in 2021 with 1.75 devices per capita.The device used in the Internet medical industry can monitor the health status of the users by the sensors integrated in it.And as a result,the efficiency of medical services can be improved as well as people's health.Antenna plays the role of information transmission in the intelligent wearable device and its performance directly determines the quality of information transmission.Compared with traditional antenna which has a rigid structure,the wearable antenna made of flexible textile material is more ergonomic and can be integrated into clothing,making it more flexible and comfortable to wear.It can be also used to measure strain.When wearing the clothing integrated with antenna,the force received on the human body can be transferred to the antenna along the clothing in the form of strain.The strain will change the size and the current distribution of the antenna,resulting in the deviation of the resonant frequency of the antenna.By measuring the change of this parameter with a vector network analyzer,the value of the strain can be determined.This paper aims to design an aperturecoupled dual-band antenna based on textile materials,and the strain sensing properties of the antenna will be studied.Specifically,the influences of bending,compression,and stretching on the resonance frequency of the antenna are studied.The specific researches and results are as follows:Firstly,the polyester felt fabric was selected as the substrate of the antenna based on the principle of the microstrip antenna.The dielectric constant of the fabric at 2.45 GHz was 1.25,measured by backward induction.An aperture-coupled single-band microstrip antenna and a dualband microstrip antenna were designed in HFSS electromagnetic simulation software.The size of the single-band antenna was 150 mm 150mm 6mm,the resonance frequency of the antenna was 2.45 GHz.It worked in 2.36~2.54 GHz with a total gain of 7.23 dBi.The size of the dual-band antenna was 100 mm 100mm 6mm,slots were designed on its radiation patch to realize the dual band work at Wireless Local Area Network(WLAN)frequency.At 2.4GHz WLAN band,the resonance frequency of the antenna was 2.52 GHz,it worked in 2.37~2.59 GHz with a total gain of 6.78 dBi.At 5.2GHz WLAN band,the resonance frequency of the antenna was 5.16 GHz,it worked in 5.06~5.27 GHz with a total gain of 7.22 dBi.The performance above meets the relevant requirements of the WLAN frequency band.Secondly,the aperture-coupled single-band microstrip antennas were made by the bonding of copper foil,conductive cloth,and screen printing,respectively.The measured resonance frequency of the three antennas were 2.47,2.37,and 2.45 GHz,individually.It was proved that the performance of the antenna made by screen printing was similar to that bonded with copper foil,and its degree of integration,as well as wearability,was better.As for the dual-band microstrip antenna,screen printing method was used in the manufacturing process The resonant frequencies measured were 2.64 and 5.20 GHz,furthermore,the working frequency of the antenna were 2.58~2.75 GHz and 5.05~5.45 GHz,respectively.Finally,the sensing performances of the aperture-coupled dual-band microstrip antenna under bending,compression and tensile conditions at 2.45 GHz were studied based on finite element analysis and practical measurements.The simulated and measured sensitivity of the antenna to bending strain were 0.376 and 0.332,respectively.Its sensitivity to compression strain was 0.144,which was corresponded to 0.36KHz/??.Its sensitivity to tensile strain was 0.260.which was corresponded to 0.65KHz/??.The overall results showed that the aperture-coupled dual-band microstrip antenna is sensitive to the three strains and can be used to detect the strain. |
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