## 4 Discussion  
The analysis of the experiments in this study improves our understanding of the empirical frequency selection for different materials, specifically copper and resin in EIT. The discussions of each experiment collectively provide valuable insight into the frequency-dependent contrast behavior of these materials, guiding the identification of empirical frequency ranges. For copper, Experiment I focused on revealing a distinct trend in frequency-dependent conductivity imaging. The reconstructed conductivity cross-section and profile line consistently demonstrated high contrast in the frequency range of 2-40 kHz. Normalized contrast, sharpness, and CNR supported this finding, indicating that the frequency window of 15-38 kHz is most advantageous for a higher contrast in EIT imaging for copper. The high contrast of copper in this range can be attributed to its favorable electrical conductivity properties, which enhance the impedance contrast with that of its surroundings. EIT captures variations in electrical conductivity particularly well within this frequency window, contributing to the observed high contrast. In Experiment II, the influence of adjacent aluminum on the contrast behavior of copper was explored. Despite the presence of another conductive material, both copper and aluminum maintained a significant contrast in the frequency range identified from 18 to 36 kHz. This result helps understand the potential interference of nearby conductive materials and reaffirms the effectiveness of the chosen frequency range for the high-contrast EIT imaging of copper. This suggests that the mechanism driving the contrast is robust and resilient to the influence of neighboring conductive elements, which is crucial for anticipating and mitigating potential interference in real-world applications. Experiments III and V, conducted in heterogeneous environments using a ground meat environment, provided valuable information on the frequency-dependent contrast behavior of copper and resin. With some deviation, the frequency range of 14-37 kHz provides an understanding of the better imaging parameters for EIT in complex environments with multiple conductive materials. Experiment V reinforced the trends observed in Experiment I.1 for copper and Experiment IV.1 for resin, highlighting the consistency of the empirical frequency range for contrast. This provides insight into the adaptability of the imaging system to complex conditions, underscoring the resilience of EIT and its potential for application in scenarios with varying material compositions. For acrylic resin, Experiment IV, focusing on the resin in a homogeneous environment (salt water), revealed minimal changes in object contrast within the frequency range of 45-75 kHz. The normalized profile and analyses confirmed that this frequency window is used to achieve high contrast in the EIT imaging of the resin. This finding expands our understanding of frequency-dependent contrast characteristics in EIT imaging of non-conductive materials. Minimal changes in contrast within the identified empirical frequency range for resin suggest a consistent behavior of non-conductive materials. The mechanism underlying this behavior may involve the interaction of the electric field with the molecular structure of the resin, resulting in detectable but limited variations in impedance. This study acknowledges specific limitations that merit discussion. First, the use of cylindrical samples may introduce considerations about the generalizability of the findings to more complex geometries. Cylindrical objects represent a simplified model, and the behavior of conductive and non-conductive materials in more intricate shapes may exhibit variations not captured in this study. Furthermore, the study focused on specific materials (copper and acrylic resin), and the results may not be universally applicable to a wider range of materials with diverse electrical properties.