## 4 Effect Evaluation of Electromagnetic Environment on Equipment
### Effects Mechanism Methods
#### 4.2.1 Sensitivity Criteria  
The effect mechanism method establishes the effect's evaluation model by analyzing the interference weighting of different interference components on the equipment. Hence, it first determines the sensitivity threshold of the equipment, both in-band and out-of-band. Subsequently, the reliability of the model is verified by the effect evaluation results of the critical interference. It means that the sensitivity criterion is of great significance to the electromagnetic environmental effects evaluation using this mechanism's method. It is also a primary problem to be solved in future research. Generally, the interference margin [65] can be employed as the sensitivity criterion for most electronic equipment. Digital communication systems always use the interference level [66] or bit error rate [67] as the sensitivity criterion. UAV (Unmanned Aerial Vehicle) information link [68] adopts AGC voltage and bit error rate as its sensitivity criteria to analyze the electromagnetic interference effect of a data link. In the sensitivity criterion of communication radios [69], the work damage level can be used as the sensitivity criterion for the voice communication system, and 10% of the fixed bit error rate can be adopted for the digital communication system. However, in the following research on digital communication radio [70], it was found that a fixed bit error rate can no longer be taken as the sensitivity criterion of communication radio under electromagnetic pulse-string interference. Their findings show that the proportional relationship between the sensitive bit error rate and the pulse repetition rate is more accurately taken as the sensitivity criterion. Therefore, it is necessary to take the type of interference signal into account to obtain a more precise sensitivity criterion. The radar uses the peak echo level compression of the measured target [71] as the sensitivity criterion. The compression amount varies with the interference threshold. To solve the universality problem of the radar sensitivity criterion, the researcher conducted a further experimental study [72] on it. They found that using an effective interference probability of 40-60% as the radar sensitivity criterion could be better. For the research on the sensitivity criterion of the navigation receiver, [PERSON] [73] took the satellite's CNR of 30 dB-Hz as the sensitivity criterion of the navigation receiver. However, we carried out dozens of experiments [74] to prove that it is unreliable to take the CNR as the sensitivity criterion of the navigation receiver. In experiments, the CNR of each satellite without interference and that under critical interference are disparate. It shows that taking 30 dB-Hz as the sensitivity criterion is not the best choice. We verified that taking the continuous loss of positioning for 30 s as the sensitivity criterion is more accurate when the navigation receiver is subjected to critical interference. The sensitivity research is shown in Table 6.  
Figure 6: The research design of effect mechanism methods.  
According to the literature analysis and experiments, we can see that the sensitivity criteria used are also diverse for different equipment. Even the same equipment has distinct sensitivity criteria due to the disparate experiment methods. In the current studies, the single-frequency continuous wave is mainly used as the interference signal to build the electromagnetic environmental effect test platform. Injection and radiation methods are always used to generate interference signals. In theory, they could obtain the same testing results. However, the test results of the former are more theoretical due to the pure injection signal. That is to say, the test results of the latter are closer to the actual working of the equipment. In brief, the most precise sensitivity criterion should be determined through the experiment. It is also necessary to have further studies on sensitivity criteria to obtain consistent sensitivity testing results for the same equipment.