Tham khảo tài liệu 'wave propagation 2010 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 22 Wave Propagation resonant peaks. The low-frequency peak is red shifted with the increase of sample permittivity while the high-frequency peak keeps unchanged. Dielectric properties of the testing sample can be inversed by measuring the position of the low-frequency peak. When increasing the length L of the waveguide results show that the high-frequency peak can be red shifted. It means that the high-frequency peak is mainly dependent on the Fabry-Perot resonance. Fig. 8. a Model of the dumbbell -shaped coaxial metallic waveguide. b Cross-section of the model. Red region ENZ metamaterials Yellow region testing sample Grey region metallic conductor R 20mm r L 30mm L1 L2 ach R 20 1mm . 15 Wu et al 2008 Fig. 9. Transmission coefficient for a variation of sample permittivity Wu et al 2008 Fig. 10. The power flow distribution a and the electric field distribution b at the low-frequency transmission peak Wu et al 2008 Microwave Sensor Using Metamaterials 23 To investigate the working principle of the ENZ metamaterial-assisted microwave sensor the power flow and the electric field distribution inside the waveguide are calculated as shown in Fig. 10. It is seen that the the power flow is squeezed through waveguide filled with ENZ metamaterials and perfectly recovered to original status at the output port. The electric field is confined into the detection zone and as a consequence this region will be rather sensitive to any slight change in sample permittivity. The above simulation results show that the electromagnetic wave can be tunnelled and squeezed through 3D coaxial waveguide filled with ENZ metamaterials. The effects are similar to literature results of other guidewave structure Silveirinha Engheta 2006 Alù Engheta 2008 . The ENZ metamaterial-assisted wave guide have potential applications in microwave sensor. 5. Microwave sensor using metamaterial particles Microwave sensor based on a single metamaterial particle The model of the waveguide filled .
