Research On Flexible Textile Antennas For Wearable Smart Clothing Applications

Motivated by the emerging 5G and the promising Internet of Things（Io T）,wearable smart terminals have ushered in new incentives and trends.“Internet of everything”requires wearable devices to be integrated into objects that people usually wear,but not confined to those traditional things,such as mobile phones,watches,and headphones.As an essential component of these wireless facilities,wearable antennas have to be portable,lightweight,and comfortable.The integration of wearable antennas and garments takes a critical role in wireless body area network（WBAN）applications and novel wearable Io T devices.This dissertation was supported in part by the Science and Technology Planning Projects of Guangdong Province under Grants 2015B010101006,2014A010103014,and 2017xm057,and in part by the National Natural Science Foundation of China（NSFC）under Grant 61372008,the following work is carried out mainly about the design of flexible textile antennas for wearable applications:（1）Epaulet/wristband-like tri-band dual-mode antenna.The additional TM₀₀ mode with omnidirectional pattern is excited by the use of short-ended stubs,and the corresponding principles are investigated.On this basis,a broadside array composed of 1×2 patch antennas is developed to be integrated into an epaulet or wristband.This array is compactly placed with a short-ended microstrip antenna to achieve a frequency/pattern diversity antenna,covering2.45/5.8 GHz WBAN and 3.5 GHz Wi MAX bands.The proposed antenna demonstrates bidirectional,directional,and directional radiation patterns with linear polarizations at 2.45,3.5,and 5.8 GHz,respectively.The experimental results verify the proposed design.The suitability of the proposed antenna is ensured by evaluating the communication links and analyzing the wearable issues.Due to the fact that wearable antennas are prone to suffer from performance degradations caused by deformation,human body gestures,and various uncertainties,the aforementioned antenna with narrow bandwidth may undergo frequency detuning,leading to unavailable coverage of the required band.Therefore,the following two wideband wearable antennas are investigated.（2）Wearable wideband tightly coupled array antenna with circular polarization.To address the issue that most of the reported wearable circularly polarized antennas have narrow bandwidth,an approach to improving the axial ratio bandwidth by using the mutual coupling effect is proposed.The coupling effects between elements in different layouts are characterized.Then,the additional resonance generated by the coupling can contribute to the enhancement of bandwidth through a sequential-phase feeding network.Moreover,considering the strong interaction between the conventional microstrip feed line and the human body,a modified stripline-based feeding structure is presented for better coupling efficiency and antenna gain.Experiments were carried out on a proof-of-concept prototype with the dimensions of 40 mm×40 mm×4 mm（0.73λ₀×0.73λ₀×0.07λ₀）.The measured|S₁₁|<–10 d B bandwidth of 43%（4.25–6.63 GHz）and the tested 3 d B axial ratio bandwidth of 34%（4.71–6.67 GHz）cover the required 5-GHz band（5.15–5.825 GHz）.In addition,the broad operational bandwidth allows the antenna to be robust under the conditions of bending,deforming,etc.The quality of indoor off-body communications is also evaluated.Wearable devices mounted on the human body are not only capable of communicating with distant base stations/routers,but also guarantee the on-body links like wireless data exchange between nodes distributed on the human body.To address this issue,a wearable wideband antenna for concurrent on-/off-body communications is developed.（3）Wearable dual-mode wideband antenna using metasurface.In view of the narrow bandwidths of the reported dual-mode wearable antennas and few solutions to the narrowband antennas with omnidirectional patterns,a pattern-switchable antenna with a shared-metasurface radiator is proposed.First,a wideband metasurface-loaded patch antenna realizes a directional radiation pattern.Second,a stripline-fed patch-loaded monopole antenna incorporated with the metasurface contributes to a wide bandwidth in on-body mode.The experimental results show that the 10 d B impedance bandwidths are 35.7%（4.6–6.6 GHz）and 31%（4.63–6.35 GHz）for off-body mode and on-body mode,respectively.In this research,antenna array and metasurface techniques are adopted in the design of wearable antennas.Solutions based on the proposed design guidelines facilitate the achievement of circularly polarized and multi-mode wearable antennas.