石墨烯材料在天线技术中的应用

Graphene-based materials for antenna applications

电子信息产业是全球产业中重要的组成部分,通讯产业是电子信息产业的基础,而天线技术更是通讯产业的基础.石墨烯被预言是下一代逻辑器件的主要材料,同时由于其优异的透光性和柔韧性,有望实现普通硅基材料所不能实现的透明、弯折功能,从而成为智能可穿戴材料的重要组成部分.为满足5G技术的超高频波段响应、不同地区手机电磁波谱吸收频段不同、物联网追踪以及透明防伪等技术需求,本课题组成功制备出世界首款柔性透明石墨烯射频天线,实现了柔性和透明的结合,展现出优异的性能和稳定性.利用石墨烯带隙可调特性和宽光谱吸收的特点,实现不同频段电磁波谱吸收,以满足天线对多频谱的适用性.通过改变石墨烯的层数、构型以及导电性实现天线多个频谱的调节,避免通过不同物理开关调控频段所造成的复杂性,从而将不同天线整合在一个石墨烯天线系统内,大大降低天线占用器件内部的体积并减少功耗.同时,本课题组开发了可打印石墨烯墨水,设计并制备可调谐缝隙天线,通过外加电压的方式,可以达到带宽和谐振频率的调节.本文基于本课题组的研究,对石墨烯材料在柔性透明天线和可调谐天线领域的进展进行了总结.

Internet of Things(IoT) has become one of the trending technologies in recent years. With the wide applications and rapid development of wireless communication and IoT, there are growing number of requirements on novel device design, such as flexible antennas and tunable antennas. The demand of transparent and flexible wireless communicational devices is ever-increasing for a wide range of scenarios, such as noninvasive healthcare, real-time wearable electronics, etc. Besides,a highly integrated antenna with tunable bandwidth and low energy consumption is in pressing demands in order to reduce the number of antennas and achieve better signal strength and higher speed signal transmission. Graphene materials have drawn much attention due to its extraordinary optical properties, high electrical and thermal conductivity, and excellent mechanical properties. All of these properties underline that graphene can be considered as a highly competitive material for wearable communication devices. Moreover, the electrical resistance of graphene and graphene oxide could be simply changed by external electric fields, applied strain and environment, which alters the electrical characteristics of the graphene-based microwave devices. Accordingly, graphene materials have a great potential in various reconfigurable or tunable devices.Our group fabricated the first graphene-based flexible and transparent wireless antenna with 2D large single-crystalline graphene and 1D Ag NW hybrid material based on the features of graphene, such as high carrier mobility, transparency and flexibility, etc. The antenna exhibited a 75% light transmittance and an ultrawide bandwidth ranging from 5.6 to 12.8 GHz,combining with outstanding durability and stability with an almost negligible variation of reflection coefficients over 1000 bending cycles. Further research confirmed that the existence of graphene harmonized the compatibility between antenna and integrated chips, hence improved the total performance of the radio frequency identification(RFID) tags. Graphene/Ag NW-based RFID tag was fabricated with an operating UHF band of 850–960 MHz and a reading distance of 130 cm,showing a great commercial potential. The excellent performance and unique properties of graphene/Ag NW-based antenna and RFID tag came from the synergistic effect between 1D and 2D nanomaterials, providing a new vision for the design of next generation wireless electronics. Meanwhile, a slot antenna with tunable bandwidth was proposed. The antenna consisted of a planar slot antenna with graphene ink printed at the gap between the ground and a small patch. The graphene ink was made from the mixture of graphene powder and graphene oxide aqueous dispersion. Graphene oxide sheets functioned as effective surfactants rendering assistance to form uniform printable inks, displayed alterable electrical resistance by optimization of mixing proportions between graphene and graphene oxide. Dried graphene inks displayed tunable electrical resistance under applied DC voltages. The variation in the resistance of graphene ink affected radiation of the slot antenna, resulting in a shift of operating bandwidth. The proposed antenna achieved a shifting bandwidth of 0.54 from 6 to 5.46 GHz after applying DC voltage less than 15 V. Such cost-effective, easily acquired, and printable graphene inks integrated the dual advantages of graphene and graphene oxide. It could be further applied in many other fields of printable electronic devices.