## 2 Materials and Methods
### Synchronization Validation  
The first experimental investigation focused on a 3 DOF system constructed from wood, with dimensions measuring 0.40 \(\times\) 0.30 \(\times\) 1.30 m, as depicted in Figure 4a. Wood was specifically chosen as the material for the 3 DOF structure due to its characteristics, including lower stiffness and density compared to alternative materials such as light metals. Consequently, the wood structure exhibited a lower natural frequency. Additionally, the viscoelastic nature of wood imparted inherent damping properties, enabling effective energy dissipation and vibration reduction, thereby resulting in higher damping characteristics. To ensure stability during the experiments, a 5 kg mass was added to the base floor of the 3 DOF structures as shown in Figure 4b. This precautionary measure minimized any potential motion or vibrations that could affect the accuracy of the recorded data. To facilitate data collection, three end nodes were strategically positioned on the top storey of the 3 DOF structure. The sensors were integrated onto the same breadboard, which was then securely affixed to the top of the 3 DOF structure using commercial adhesive tape. The specific coordinates of the sensor arrangement are illustrated in Figure 4c. To simulate dynamic loading conditions, several impacts were introduced to the side panel of the top storey. These impacts were carefully investigated and used to investigate time alignment between RPi0-2W sensor nodes. This allowed for the assessment of the system's performance under varying external factors, further validating its synchronization capabilities in practical scenarios. The resulting acceleration responses recorded by the three RPi0-2W sensor nodes were analyzed and explored. Figure 3: The experimental setup: The RPi0-2W sensor nodes were located on top of the 3 DOF structure, while the PRi4 gateway was connected to a monitor for investigating the.csv file. All RPi0-2W nodes and RPi4 were controlled by a personal computer through SSH. The Application of Frequency Domain Decomposition  
In the second experiment depicted in Figure 5, the study adopts a distinct approach from conventional comparative studies that aim to evaluate the accuracy of low-cost sensors compared to commercial-grade sensors, which can pose challenges in real-life practical scenarios. Instead, our investigation focuses on meticulously utilizing low-cost sensors to differentiate between structural parameters in two distinct structures with varying stiffness properties. Specifically, in the experimental setup, each RPi0-2W sensor node was carefully placed on a designated storey of the more rigid structure, which was distinguished by its full side panels (shown in Figure 5a). The sensor placement was intentionally altered at the center of each storey. Moreover, while the sensors were positioned at the same location, the partition side panel was used instead of the full side panel (shown in Figure 5b). To ensure secure attachment, commercial adhesive tape was employed to firmly affix the  
Figure 4: Three-Degree-of-Freedom (3 DOF) wood system: (**a**) 3 DOF dimensions of \(0.40\times 0.30\times 1.30\) m, (**b**) Front view of the 3 DOF structure with strategically placed end nodes, and (**c**) Top view of the 3 DOF structure illustrating the location of the sensor nodes. Figure 5: Three-Degree-of-Freedom (3 DOF) wood system: (**a**) The more rigid structure with full side panels, (**b**) The less rigid structure with partition side panels (front view and side view, respectively), (**c**) Sensor at first storey, (**d**) Sensor at second storey, and (**e**) Sensor at third storey. -headboard containing each sensor. The structural responses were captured by collecting data from the \(x\)-axis of the sensor nodes, as depicted in Figure 5c-e.  
During the experimental sessions, the wood 3D structure was subjected to several impact loadings.