# RF Energy Harvesting
## 6 RF Energy Harvester Simulation
### Simulation  
The models presented in the above section were used to conduct simulations in all three environments. In both KiCad EDA and LT Spice, the simulation time was set to 10 ns and the simulation step was set to 10 ps. In Simscape Electrical, the simulation time was also set to 10 ns, but the simulation step was set automatically by the environment. We conducted three simulations:  
* Ideal resonator--to verify if output voltage will be boosted in comparison to the one on the antenna;
* Harvester with diode with zero internal capacitance--to provide reference results;
* Harvester with real diode model--to check the impact of the internal capacitance on the current in the diode. For an ideal resonator, results presenting both the input and output voltages and currents in the load are presented. All results were analysed in MATLAB. Figure 9 shows the results from simulation in KiCad EDA. Figure 10 presents the same relations for LT Spice, and Figure 11 presents the results for Simscape Electrical. Figure 8: RF energy harvester model designed in Simscape Electrical. Figure 6: RF energy harvester model designed in KiCad EDA. Figure 7: RF energy harvester model designed in LT Spice. Figure 11: Input and output voltages for ideal resonator as simulated in Simscape Electrical. Figure 10: Input and output voltages for ideal resonator as simulated in LT Spice. Figure 9: Input and output voltages for ideal resonator as simulated in KiCad EDA. Ideal resonator simulations were followed by simulations of a simple harvester circuit with a diode with zero internal capacitance. The simulation results are presented as graphs consisting of an axis with the simulation time and the voltage on the load and the current in the diode represented by D1 in the designs. The results of KiCad EDA are presented in Figure 15, LT Spice is in Figure 16, and Simscape Electrical is in Figure 17.  
The final simulations were done using a real diode model. Figures 18-20 show the results for KiCad EDA, LT Spice and Simscape Electrical, correspondingly. Figure 16: Results of time simulation for LT Spice. The full line shows the voltage on the load, and the dashed line shows the current in the D1 diode. Figure 15: Results of time simulation for KiCad EDA. The full line shows the voltage on the load, and the dashed line shows the current in the D1 diode. The conducted experiments shows that it is possible to analytically find a perfect impedance-matching network for an antenna-load circuit. However, adding any elements after the resonator causes the perfect match to be lost, and therefore, it is difficult to transfer all the available power from the antenna to the harvester circuit. Simulation results showed how the diode's internal capacitance influences the output voltage and current in the diode. Comparing Figures 15-17 with Figures 18-20, one can see that the presence of internal capacitance in the diode has a significant impact on the operation in the upper sub-1 GHz frequencies. It makes the diode have a slight back-current that effectively decreases the output voltage and the power available to the load of the circuit. Figure 17: Results of time simulation for Simscape Electrical. The full line shows the voltage on the load, and the dashed line shows the current in the D1 diode. Figure 6:0 Results of time simulation for KiCad EDA using a real diode. The full line shows the voltage on the load, and the dashed line shows the current in the D1 diode. Results analysis shows that simulations in all environments are comparable. The outcomes from the last simulation were imported to and presented in MATLAB based on the collected numerical values. This program allows us to easily manipulate and analyse data. It was observed that for the assumed parameters, the simulation results differed in the number of collected samples. In KiCad EDA, there were 1009 value sets; in LT Spice, there were 895 sets; in Simscape Electrical, there were 231 value sets.