| In recent years,with the continuous development of communication technology,human centered wireless body area networks have begun to be applied in military,medical,and daily life,showing an extremely broad application prospect.As a key device for wireless body area network systems to achieve signal transmission and reception,wearable antennas are one of the important features and key technologies of wireless body area networks,and their communication performance has a decisive impact on data transmission in wireless body area networks.As a new type of antenna,the application scenario and usage environment of wearable antennas are far more complex and harsher than traditional antennas.Parameters such as bending angle,the distance between the antenna and the human body,and the wearing position can affect the communication performance of wearable antennas,resulting in characteristic migration.In order to improve the tolerance of wearable antennas to these unconventional factors,this paper proposes various new structures and methods for the design robustness requirements of wearable antennas with off-body,in-body,on-body three different radiation modes,and designs a variety of antennas with high robustness,mainly including:(1)A microstrip antenna for off-body radiation mode is proposed.The antenna adopts a microstrip patch structure to realize off-body mode radiation;adopts a complete copper foil as the ground of the antenna,which improves the robustness of the antenna;adopts the coupled feeding and slotting technology to increase the impedance bandwidth of the antenna.In order to verify the robustness of antenna communication,the antenna is further fabricated.The reflection coefficient and radiation gain of the antenna in free space,after loading the human body and after changing the external environment,as well as the link margin and the specific absorption rate of the human body after loading the human body are tested.The results show that the reflection coefficient and radiation gain of the antenna is insensitive to the change of external environment,demonstrating that the proposed antenna has high robustness.And the robust off-body communication between the wearable device and the base station in the wireless body area networks is realized without harming the human body.(2)A flexible slot antenna for in-body radiation mode is proposed.Hexagonal microstrip monopole structure with ultra-wideband characteristics is adopted to improve the robustness of the in-body mode antenna;The parasitic reflector is placed on the top of the substrate,which effectively improves the antenna radiation gain and directivity.The impedance characteristics of the antenna in the WLAN frequency band and the communication ability with the Implantable device are tested on the human body simulation model.Compared with the same type of design,the antenna has the characteristics of high gain,ultra-wideband and low SAR.The antenna is printed on the flexible substrate,and the coplanar waveguide side feed structure with low profile characteristics is used,which is easy to be integrated into clothing,and can effectively solve the problem of wearing comfort.The bending of the base plate will not greatly affect the design.(3)A modular antenna with switchable in-body/off-body radiation characteristics is proposed.The modular antenna is composed of a common antenna base and a removable reconfigurable module.The common antenna base consists of two layers of base plates,including adjacent coupling feed structure,off-body radiation patch and in-body radiation circular slot.The detachable reconstruction module uses conductive cloth to reduce the height and weight of the antenna,and can be fixed on the common base with insulating screws to achieve the reconstruction of antenna radiation characteristics.The advantage and uniqueness of this modular antenna design is that the in vivo/in vitro mode not only shares a common feed structure,but also shares the radiation part of in-body and off-body antennas,which greatly reduces the occupied area of the antenna and reduces the complexity of switching.Moreover,both in-body and off-body working modes of the antenna have high robustness.(4)A flexible microstrip quasi-yagi antenna for on-body directional communication is proposed.The microstrip quasi-yagi microstrip structure is adopted to improve the directivity of the antenna and reduce the section height of the antenna;The monopole antenna is used as the active dipole of the quasi-yagi antenna,which reduces the size of the antenna;The traditional AMC structure is placed on the back of the guide dipole,which improves the robustness of the quasi-yagi antenna.Further,the real antenna is made,and the reflection coefficient and radiation gain results of the quasi-yagi antenna after loading the human body,the reflection coefficient and radiation gain results after the external environment of the antenna is changed,and the SAR situation after loading the human body are tested. |
