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The free-space measurement system used in this study is schematically illustrated in Fig. 1. The equipment used for the measurement comprises a pair of spot-focusing type horn antennas (transmitting and receiving), a sample holder, and a coaxial cable connected to a HP8722D network analyzer. The horn antennas were equipped with biconvex polymeric lenses, focusing the electromagnetic waves on to the sample with a spot diameter~2–3 times that of the wave under consideration. The antennas were separated by a distance measuring twice the focal length (330 mm) of the lenses. The horn antenna (I) sends an electromagnetic wave onto the surface of the sample; and the waves transmitted through and reflected from thesample were collected by horn antennas (II) and (I),respectively. In order to minimize the measurement inaccuracies in the system, a through-reflect-line (TRL) calibration was carried out,whereasatime-domain gating was used to minimize the effects of residual mismatches, such as a mismatch in the source and load impedance [21]. After calibration, the woven fabrics were attached to a square cross-sectioned cardboard frame, and were placed into the sample holder mid-waybetweentwospot-focusinghornlensantennas.The reflected and transmitted portions of the electromagnetic wave were determined for single-layer woven fabrics in the frequency range of the spot-focusing horn lens antennas(17–40 GHz). Measurements were also carried out on various double-layer combinations of fabrics,in both in their asreceived state and after heat treatment to determine theeffect of changing the electrical conductivity and sequencing of layers on electromagnetic wave absorption potential. These combinations were measured by arranging two cardboard frame sets with sample fabrics back-to-back in the sample holder. In this way, double-layer combinations with a 1-mm spacing (thickness of the cardboard) between the layers were obtained, and the electromagnetic wave reflection and transmission losses of all combinations were examined through a repetition of the above procedure. |
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研究使用的自由空间测量系统图解于图1。用于测量的设备包括一对光斑聚焦型喇叭天线（发送和接受）、样件工装、通过同轴电缆连接到HP8722D网络的分析仪。喇叭天线配备了双凸面聚合透镜，将电磁波聚焦到样件，得到波的2-3倍斑直径。天线相距2倍镜头焦距（330mm）。喇叭天线（I）发送电磁波到样件表面；穿过样件或被样件反射的电磁波分别由喇叭天线（II)和（I）接收。 为了减小系统的测量误差，进行穿透-反射-线（TRL）标定，使用时域选通减小残余失配，例如源与负载阻抗的不匹配的影响[21]。标定后，将织物贴到矩形截面的硬纸板框架，放进样件工装中2个光斑聚焦喇叭透镜天线的中间位置。对单层织物，在光斑聚焦喇叭透镜天线的频率范围（17-40GHz）探测电磁波的反射和发射部分。对不同的双层织物组合也进行测量，包括它们的收货状态和热处理后状态，以确定改变电导率和层的顺序对电磁波吸收能力的影响。 在对这些组合的测量中，2个带有织物样件的硬纸板框架背对背放置进样件工装。通过这种方式得到1mm层间距（硬纸板厚度）的双层组合，如此便可通过重复上述流程检验各种组合的电磁波反射和发射损失。 |
2楼2014-06-11 14:51:29