Study On Compact Flexible And Implantable RF Antenna

Flexible electronics presents the advantages of foldability, thinness, lightweight, small volume, conformability and simple manufacturing process, etc. The flexible circuit board such as polyester, polyethylene, plastic or paper can be obtained at relatively low prices. In recent years, many researchers have done a lot of researches on flexible electronics. In the applications of implantable flexible electronics, compared with the antenna based on the rigid substrate the antenna based on the soft substrate can better conform to the surface of the biological tissue because the biological tissue is often curved. So researches on the flexible and implantable antenna and rectenna have great significance for the development of flexible electronics. Flexible and implantable antenna and rectenna have become one of the hot topics of flexible electronics in the world. In this dissertation, the miniaturization, broadband design technology and biocompatibility of flexible and implantable monopole antenna and rectenna are studied. The main work of this dissertation is as follows:1. Compact design of flexible broadband monopole antenna based on the meandered patch structureThe meandered patch structure on the polyimide film and the Parylene C film protecting method are proposed in order to reduce the size of the broadband flexible monopole antenna and make the antenna have the characteristics of biocompatibility. The meandered patch structure is used to extend the current path, thereby the resonant frequency and the volume of the antenna are reduced. The bendability of the antenna is improved because of its thin organic substrate. Because Parylene C film has the characteristics of both biocompatibility and resistance to chemical erosion, the antenna coated with Parylene C film has the features of good biocompatibility and strong ability to suit to harsh environment. The flexible broadband monopole antenna coated with Parylene C film is fabricated using thin film process technology. Experimental results of the 10 μm Parylene C film coated flexible monopole antenna(size: 32 mm × 18 mm) based on the meandered patch structure showed that the antenna can operate in the bandwidths of 2.4 – 2.484 GHz and 3.5 – 10.6 GHz. The coating and bending(radius 20 mm) do not have much effects on the return loss of the flexible antenna. The 2.44, 5.8 and 10.6 GHz associated gain of the bent antenna are-2.4 d Bi,-0.3 d Bi and 2.4 d Bi separately. Experimental results of the flexible broadband monopole antenna based on the meandered patch structure showed that it can operate under the bent condition.2. Design of flexible broadband monopole antenna loaded by the plate capacitor between the layers of substrateBased on the theory that the capacitive load can reduce the size of the antenna, a method of using U radiation element loaded by circular plate capacitor between the layers of the thin substrate to design a compact flexible broadband monopole antenna is proposed, which is in order to further reduce the volume of the flexible broadband monopole antenna. A second order impedance transformer is inserted between the feeding microstrip and the radiator of the antenna, which makes the antenna have good input matching in broadband frequency range. A flexible monopole antenna with the size of 28 mm × 18 mm is designed on the polyimide film according to the proposed method and the antenna is coated with 10 μm Parylene C protective film. Experimental results showed that flexible broadband monopole antenna loaded by the circular plate capacitor can operate in the bandwidths of 2.4 – 2.484 GHz and 3.8 – 10.6 GHz. The return loss of the flexible antenna does not change much when the antenna is coated or bent(radius of 20 mm). The 2.44, 5.8 and 10.6 GHz associated gain of the bent antenna are-4.0 d Bi,-1.0 d Bi and-1.3 d Bi separately. It can be seen that the size of the capacitively loaded flexible monopole antenna is smaller than the size of the meandered patch monopole antenna.3. Design of an implantable antenna for WLAN applicationsA method of improving the implantability of the flexible broadband monopole antenna through reducing the length of radiation element is proposed. Based on the capacitively loading technique, a flexible WLAN monopole antenna loaded by the rectangular plate capacitor was designed. Experimental results showed that the flexible monopole antenna has good omnidirectional radiation characteristics in the two bands of WLAN. The implantable characteristics of the WLAN antenna had been intensively studied. The experimental results showed that the resonant frequency and the gain of the antenna embedded in the pork were significantly decreased. The length of the U radiation element is reduced according to the proposed method in order to improve the return loss and radiation gain of the implanted antenna. The experimental results showed that the gain of the antenna was increased from-12.9 d Bi to 0.8 d Bi and the return loss was increased from 14 d B to 18 d B. The improved antenna has become an implantable antenna with good characteristics.4. Design of a compact implantable rectennaA design method of compact flexible rectenna based on ultra-thin liquid crystal polymer(LCP) laminate is proposed. The rectenna was fabricated on 50 μm thick double copper clad laminate using conventional photolithography technique which greatly reduces the difficulty of the manufacturing process. Furthermore, the thickness of the antenna is reduced through using the ultra-thin substrate. Experimental results showed that the power transmission efficiency of the flexible rectenna was reduced when it was under different bending conditions. However, the integrated blue light-emitting diode(LED) was still successfully lit by the flexible rectenna. A 2.4- 2.484 GHz compact implantable rectenna for optogenetic technology applications was realized on the ultrathin LCP laminate according to the proposed design method. The research results of power transmission efficiency of the rectenna embedded in the pork showed that the integrated blue LED can be lit wirelessly under the maximum permissible human exposure limit.