To further reveal the physical mechanism of the metadevice, we calculate the electric field and power loss density distribution at operating frequency (9.702 GHz). Only the x-polarized incident waves are analyzed here. The individual part A loaded on-state diodes are transparent for the EM waves. For state-1, the metadevice acts as an inductive equivalent circuit [25,29]. Both sides of the surface with on-state diodes do not resonate and the surface is transparent to the EM incident waves. The x-z plane electric field distribution at 9.702 GHz is shown in Figure 3a. Due to the driving of a strong electric field around part B, the electron oscillations generate strong induced currents, causing the electric field to radiate in the same direction and transmit EM wave energy as much as possible. In contrast, the metadevice behaves as a perfect electric conductor (PEC) when diodes correspond to state-2. As a result, the EM incident waves cannot pass through the metadevice. Figure 3b shows the electric field distribution in the x-z plane at 9.702 GHz. Almost no electric field components pass through part B, while the EM incident waves are reflected in the form of co-polarization. The above analysis shows that part B can be used as an EM switch by changing the external DC bias voltages of the diodes. According to impedance matching theory, EM waves will almost completely enter the absorber when the impedance is matched. Coupled EM wave energy will be eventually dissipated by the ohmic loss [34] and dielectric loss [34]. Here, the absorption is mainly caused by the ohmic loss, with almost no dielectric loss. Power loss distribution on the metadevice is mainly concentrated around PIN diode-1, and energy is dissipated in the form of joule heat, as shown in Figure 3c. Moreover, the absorption is not affected by the reduction in the loss tangents of dielectric (even if Rogers RO4003C is loss free), which also means that the absorption depends essentially on the ohmic loss, as shown in Figure 3d. The normalized complex impedance is derived from the complex reflection coefficient and complex transmission coefficient in Formula (1), as shown in Figure 3e. A range between 0.5 and 2 for the real part of relative impedance in transmission and absorption bands is marked in the diagram, indicating that an acceptable impedance match can be achieved in this area for either transmission or absorption. The impedance mismatch is severe when Re(Z) is less than 0.1, and a nearly total reflection can be achieved. The imaginary part of the relative impedance is close to zero at 9.702 GHz, and the real part is approximated to unity simultaneously, which eventually achieves perfect absorption. In other words, the equivalent impedance of the proposed absorber perfectly matches the free space, and the effect of absorption on this metadevice is superior.
Electromagnetic field theory by bakshi pdf
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