## 5 Discussion  
For the battery-free multi-node sensor system [1; 4], the system was designed using SSAIL technology [2; 3] and validated for harsh environment implementation scenarios. For the energy-harvesting technique [4], research challenges on topologies and the energy management system [6; 13], and the proposed system optimization, would increase the system reliability and scalability. Our discussion stresses the classification of coverage [5; 6; 7; 8], practical challenges in the deployment of WSNs [8; 9; 10], QoS support [15; 16; 17], sensing models, and research issues in WSNs [11; 12].  
The sensor node architecture suggested for the system consists of a base station in communication with multiple slave nodes. The slave node should be equipped with a sensing unit that contains sensors, a modified processing unit that supports the idea of enabling RF energy-harvesting circuits, Wi-Fi for communication with the master node, and the power source. In addition, a simulation model was used to investigate and compare the improved LEACH protocol's lifetime of sensor nodes, total energy dissipated, and the throughput of 100 sensor nodes with the standard LEACH protocol. The sensor transmits five bytes of data to the Wi-Fi module operating in deep sleep mode each time it  
Figure 13: Sensor readings in real-time charts in web server accessed by web client.  
is activated. This is the first demonstration of a multi-node sensor system designed using SSAIL technology. In contrast to solutions relying on various energy sources [14; 7; 8; 9; 11], the power unit RF harvesting itself is integrated and designed as a component of the system, ensuring full control over the amount of available energy and the continuous operation of the wireless sensor nodes.  
As a result of S\({}_{11}\) fractal antenna [20] simulation and measurement, we succeeded in finding a design with the measured bandwidth that entirely covers the lower Wi-Fi frequency band. The antenna resonates at five distinct frequencies, resulting in more energy gathering features. Unlike [21], additional investigation into the working frequencies of the fractal antenna depending on the size of the largest triangle and the edge ratio of other triangles was performed. At the \(-10\) dB level, the measured bandwidth is 2.40 GHz to 2.49 GHz. From Figure 12, clearly, the increase in the size of the triangles or the ratio between the triangle edges decreases the antenna resonance frequency in both bands. The dependences are close to linear. The ratio between the two frequency bands increases from 2.24 to 2.41 when \(A\) increases, and from 2.29 to 2.53 when the ratio between the triangle edges increases. This allows us more precise control of the resonance frequencies of both bands by choosing the proper dimensions of the antenna and the separate tuning of both resonance frequencies.  
Our estimations show that if a WSN of ten nodes sends one piece of information in an hour, it consumes 65.31 mW/day in total for the selected operation regime. However, the energy consumption of every node during different duty cycles in conditions such as traffic types, packet loss during data transfer, and accuracy of the data are major concerns for future work.