## 2 The Mechanism of EMA and Flame Retardant  
### EMA  
The EMA performance of materials is typically assessed by measuring their electromagnetic parameters, including the complex permittivity (\(\varepsilon_{\text{r}}=\varepsilon^{\prime}-\text{j}\varepsilon^{\prime\prime}\)) and complex permeability (\(\mu_{\text{r}}=\mu^{\prime}-\text{j}\mu^{\prime\prime}\)) [33; 34; 35]. These parameters reflect the material's dielectric loss and magnetic loss capabilities, which are key to understanding its EMA mechanisms. One of the most commonly used methods for measuring these electromagnetic parameters is the coaxial transmission line method, widely employed for its accuracy and reproducibility. The coaxial transmission line method involves using a vector network analyzer (VNA) to measure the scattering parameters (S-parameters) of samples. The materials under study are typically fabricated into toroidal samples and placed within a coaxial transmission line fixture. S-parameters (S11 and S21) are measured over a specific frequency range, and these values are used to calculate the material's \(\varepsilon_{\text{r}}\) and \(\mu_{\text{r}}\). Based on the measured S-parameters, analytical models such as the Nicholson-Ross-Weir (NRW) algorithm [36; 37] can be used to extract the material's \(\varepsilon_{\text{r}}\) and \(\mu_{\text{r}}\). By analyzing these electromagnetic parameters, further calculations can be performed to determine the material's microwave reflection loss (RL), a key performance indicator of EMA. RL is typically calculated using the following equation [38; 39; 40]:  
\[Z_{\text{in}}=Z_{0}\sqrt{\frac{\mu_{\text{r}}}{\varepsilon_{\text{r}}}}\text {tanh}\text{j}[\frac{2\pi\text{fd}}{\text{c}})\sqrt{\mu_{\text{r}}\varepsilon _{\text{r}}}] \tag{1}\]  
\[\text{RL}=20\text{lg}[\frac{Z_{\text{in}}-Z_{0}}{Z_{\text{in}}+Z_{0}}] \tag{2}\]  
Figure 1: Development of MOF-based dual-functional composites with EMA and flame retardant in recent years (until January 2025). where \(Z_{\text{in}}\) and \(Z_{0}\) are the material and air impedances, respectively; f is the microwave frequency; d is the absorber thickness; and c is the speed of light. The RL value is an important metric for evaluating the EMA performance of materials since it represents the degree of attenuation of the incident microwave on the material's surface and within. RL \(<-10\) dB means 90% absorption efficiency. EAB refers to the frequency range when RL is less than \(-10\) dB. Materials with a broad frequency absorption range are often more useful for practical applications [41]. Most research on EMA materials has focused on the 2-18 GHz range, which is particularly interesting because it aligns with the operational frequencies of many modern radar systems, satellite communications, and wireless networks [42]. Achieving high EMA performance within this range is critical for both civilian and military applications, including electromagnetic compatibility and stealth technology [43]. MOF-based composite materials have significant potential in EMA, owing to their distinctive porous structure and variable chemical composition. Controlling the synthesis conditions of MOFs allows for exact adjustment of their pore size distribution, specific surface area, and framework structure to fulfill the various demands of EMA [44]. MOFs' flexible binding sites on the surface enable hybridization with a variety of materials, resulting in synergistic effects of dielectric and magnetic loss that lead to wideband and efficient EMA performance. The main mechanisms of EMA are dielectric loss and magnetic loss [45,46]. The primary way energy is dissipated is through dielectric loss. The coordination bonds formed between metal elements and organic ligands in MOF materials will be polarized under the action of an alternating electric field. This polarization process consists of electronic polarization, ionic polarization, orientational polarization, and interfacial polarization.