# Zero Energy IoT Devices in Smart Cities Using RF Energy Harvesting
## 3 Materials and Methods
### Testbeds Studies
#### 3.3.6 Optimal Points/Area for Sensor Devices
Figure 10: 250\({}^{\circ}\) Sense Data from Patch Antenna. Figure 9: 150\({}^{\circ}\) Sense Data from Patch Antenna. #### 3.3.8 Experimental Setup with Dipole Antenna

The dipole antenna has a 360-degree reception angle to receive the energy from the charger, so there is no restriction on direction for the sensor device as the patch antenna has a 122-degree restriction. When the charger moves, the sensor receives the energy in all directions. We have collected the receiving data and shown them in Table 3 for observation. Consequently, these experimental data in Table 3 are the proof that the area or points shown in Figure 12 are the optimal points/area for placing the sensors, and the circular direction is the optimal charger tour point or path to provide unstoppable energy to the sensors. #### 3.3.9 Analysis of Data in Dipole Antenna

The dipole antenna can receive data from all sides because it has 360-degree reception antennas. however when the sensor devices become under the charger device, then the time differential (dT) between received packets increases, and the sensor devices gain sophisticated power for data transmission. #### 3.3.10 Analysis of RSSI of Patch Antenna in a Mobile Environment

We have equipped our charger with a moving vehicle to make it mobile, and the sensor with a path antenna was put on the ground for experimentation. The sensor send data successfully to the access point, and we used Table 4 to present all the sensed data from sensors for 100 to 360 degrees. \begin{table}
\begin{tabular}{l l l l l l l l l l} \hline \hline Point 3 (50\({}^{\circ}\)) & & & & & & & & &



#### 3.3.11 RSSI of Patch Antenna during Circular Tour of the Charger

In this section, we are going to present the charger movement on a circular and obtain the RSSI of the patch antenna. We used 100 degrees as the first point and moved to 360. The RSSI is good from 100 to 280 degrees but starts degrading after 280 (see Table 5). \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Pkt No. ** & **DT** & **RSSI** & **Temp** & **Humidity** & **Light** & **External** \\ \hline
1 & 0 & 12.71 & 71.2 & 48 & 29 & 1670 \\ \hline
2 & 1 & 12.97 & 71.2 & 48 & 33 & 1666 \\ \hline
3 & 0 & 11.5



## 4 Results

We have experimented according to our requirements. We have used circular points to check whether our problem identification is valid or not. The optimal points are decided through packet transmission. Suppose in Figure 3 that if the point is 200\({}^{\circ}\), the sensor device transmits multiple packets in seconds (because the sensor device receives enough energy), but when the charger changes its location to 0\({}^{\circ}\), the packet transmission slows down. The Powercast Company referred to this as the time differential (dT) between received packets. At optimal points, the dT will be high otherwise. In this section, we are going to present the results in a graph and discuss them in detail. Figure 13 presents the comparison with the work of [26] based on RSSI from different angles and distances. He used fixed points for sensor devices and fixed the charger up the ground, but it creates the nearest-farthest problem. It is clear that our work is better. In the figure, existing represents the work of [26], while proposed is our work. Figure 14 is based on the patch antenna receiving RSSI, which is placed at different points according to our requirements. The points could be from 0\({}^{\circ}\) to 360\({}^{\circ}\). Points 1 to

Figure 13: Patch Antenna RSSI. \begin{table}
\begin{tabular}{c c c c c} \hline
**100–150\({}^{\circ}\)** & **151–200\({}^{\circ}\)** & **201–250\({}^{\circ}\)** & **251–300\({}^{\circ}\)** & **301–360\({}^{\



4 represent RSSI within the 122-degree range, and 5 to 6 points represent outside the 122-degree range. Our optimal points for the sensor are when the optimal points of the charger go well and it receives all of the energy, but when it goes other than our points, it degrades the receiving strength.