Tham khảo tài liệu 'wave propagation part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Microwave Sensor Using Metamaterials 27 Fig. 16. Transmission coefficient S21 versus frequency for different dielectric materials in the detecting zone Huang et al 2009 To quantify the sensitivity of the evanescent mode for dielectric sensing the performance of the metamaterial-assisted microwave sensor is compared with the traditional microwave cavity. We closed both ends of a hollow waveguide with metallic plates which forms a conventional microwave cavity flxbx and computed the resonant frequency of the cavity located with dielectric sample. Table 1 shows a comparison between the relative frequency shift . AfN fN Sj - fN sr of the waveguide filled with coupled metamaterial particles and that of the conventional microwave cavity . Afc fc Sj - fc sr . Where Sj and sr denotes the relative permittivity of the air and the dielectric sample respectively. It indicates that minium respectively maximum frequency shift of the waveguide filled with đi-shape coupled metamaterial particles is 360 times respectively 450 times that of the conventional microwave cavity. As a consequence the waveguide filled with đi-shape coupled metamaterial particles can be used as a novel microwave sensor to obtain interesting quantities such as biological quantities or for monitoring chemical process etc. Sensitivity of the metamaterial-assisted microwave sensor is much higher than the conventional microwave resonant sensor. a 2 3 4 5 txr 144 288 432 558 684 810 918 1026 n 360 411 393 429 428 450 417 410 Table 1. Comparison of the relative frequency shift MHz between the waveguide filled with coupled metamaterial particles and the conventional cavity In addition the microwave sensor can also be constructed by filling the other type of coupled metamaterial particles into the rectangular waveguide. For example the meander line and split ring resonator coupled metamaterial particle Fig. 17 a the metallic wire and split ring .
