## 3 Data Set  
The characteristics of the measured signals for different scenarios are defined in this section. The features of individuals, including age, height, and weight are summarized in Table 1. Henceforth, these participants will be referred to as subjects. Five women and 15 men took part in the measurements as the subjects inside the corrugated pipe. Time-dependent measurements were conducted on the real debris model in the laboratory environment. Measurements of each subject were completed for six different angular positions depending on the \(\phi\) angle demonstrated in Figure 1. When \(\phi=0^{\circ}\), the subject faced towards the x-axis. For each \(\phi\) orientation, signal variation for three different respiration-movement states was recorded. External noise was minimized during the measurements by keeping the measurement setup in a movement-free zone. In addition, recordings of the empty debris were made under various environmental noises generated due to external movements. Details of the recorded signals are as follows:  
* Twenty seconds of respiration of the subject in the debris with environmental noise;
* Twenty seconds of respiration of the subject in the debris;
* Twenty seconds of movement of the subject in the debris. Measurements were taken for the environment analysis at the three distinct highest frequencies--210 MHz, 332.5 MHz, and 405 MHz--where signal transmission was achieved with the highest gain. Measurement at each frequency lasted 20 s for each \(\phi\) orientation (\(\phi\in\{0^{\circ},45^{\circ},90^{\circ},135^{\circ},180^{\circ},270^{\circ}\}\)). The sampling frequency was set to 80 Hz. Thus, each recorded signal contains 1600 samples. The recording duration was approximately 45 min to 1 h for each subject. DC components were removed from the signals to expose variations in amplitude and phase. Table 2 demonstrates the main features of the entire data set. As a demonstration of the signal characteristic recorded from the measurement setup, phase and magnitude variations of the signal at 405 MHz frequency are given in Figure 3 as a function of the recording time. The solid blue line represents the case in which the corrugated pipe placed inside the debris was empty, whereas the red dashed and black dotted lines represent the case in which the subject inside the corrugated pipe inspired or moved. If the magnitude and phase responses are compared, it can be concluded that the movement of the chest or body affects the phase signal more predominantly than the magnitude signal. The respiration signal follows a sinusoidal characteristic, the maximum value of which is much lower than the maximum of the signal derived from the movement of the body. Figure 2: Physically constructed debris model in our laboratory. **(a)** Front view. **(b)** Side view. To assess the impact of various parameters on detection performance, we conducted measurements at different frequencies (210 MHz, 332.5 MHz, and 405 MHz) and subject orientation angles (\(0^{\circ}\), \(90^{\circ}\), and \(180^{\circ}\)). Our results show that the lowest frequency (210 MHz) provides more stable STFT results in noisy environments, while higher frequencies exhibit greater variation. Similarly, when the subject is oriented at 180\({}^{\circ}\), the amplitude of the STFT signal significantly decreases, leading to lower detection rates. These findings underscore the importance of carefully selecting both frequency and orientation to achieve robust respiratory monitoring. Figure 4a illustrates the magnitude of the FT of the phase of the \(S_{21}\) signals measured at 405 MHz for different subject orientation angles within the debris. The magnitude of this signal is denoted by \(|S(f)|\), providing insights into how orientation affects the detected signal strength.