Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Low Scattering Photodiode-Modulated Probe for Microwave Near-Field Imaging 91 Zon and Zp Zoff see . In fact if a simple capacitor model is assumed for the short dipole in free-space resonance frequencies of GHz and GHz can be calculated for the ON and OFF states respectively. Results from a simulation done with the thin-wire method of moment are also shown in the figure. In the simulation the probe is illuminated with a uniform plane wave in free space. This shows the normalized difference between the squared scattered field taken 1 cm away from the dipole in the two states. The results also exhibit a double peak response. In the measurement the resonance observed in the waveguide are shifted to lower frequencies. This shift is thought to be due to imperfections in the construction and uncertainty in the substrate s constitutive material parameters. Furthermore the value of Zp in free-space is not the same as in the waveguide where the dipole is interacting with the metallic walls. Finally as these reflection differences are obtained by subtracting very similar measured values the results are susceptible to measurement and simulation inaccuracies. Both curves exhibits a maximum sensitivity near the design frequency of GHz. Finally the waveguide measurement process described above was simulated in HFSS. The reflection coefficient difference shown in Fig. 13 exhibits peaks near GHz and 3 GHz. It should be noted that this curve is derived from differences between S11 values with a variation smaller than 5 X 10 5 in magnitude. Therefore the frequency shift compared to the other two curves may be partly due to simulation inaccuracies. Fig. 13. Difference of frequency response for the OMS probe in ON and OFF states solid line is the measured reflection coefficient dashed line is the simulated scattered field dotted line is simulated reflection coefficient. 8. OMS probe performance validation In order to verify the performance of the developed OMS
