Fig. 4.4 Relationship between electromagnetic susceptibility and electromagnetic vulnerability. a Electromagnetic susceptible frequency points; b electromagnetic vulnerable points

4.1.3 Electromagnetic Vulnerability

Electromagnetic vulnerability (EMV) refers to the electromagnetic susceptibility that causes serious failures, degraded performance, and safety threats to personnel or equipment. Typically, it refers to more serious problem that might affect personnel or system safety or might be exploitable by enemy forces. A system is said to be vulnerable if its performance is degraded below a satisfactory level as a result of exposure to the stress of an operational electromagnetic field or transient. EMV can be considered a special subset of the susceptibility side of EMI which is defined in Sect. 4.1.1, and it is also an inherent attribute of the system. The root cause of EMV is the oversusceptibility of the system.

Our readers can better understand the relationship between EMV and electromagnetic susceptibility (EMS) by comparing Figs. 4.1 and 4.4. EMS frequency points that cause system and personnel safety problems are referred to as EMV frequency points (the frequency points corresponding to and ♦ in Fig. 4.4b); thus, EMV is a special subset of electromagnetic susceptibility. However, it should be noted that not all EMV frequency points are marked in the EMS test report (the frequency point corresponding to in Fig. 4.4b). In practice, it is possible that certain EMV frequency point occurs outside the susceptible frequency marked in the electromagnetic susceptibility test report (the frequency point corresponding to ♦ in Fig. 4.4b). The main reason is that the frequency points of EMS test are not dense enough.

EMV is directly related to the safety of the system and personnel, so it is necessary to add a sufficient safety margin to the tested product at the vulnerable frequency, as shown in Fig. 4.5. The current military standard has a safety margin requirement of 6 dB for non-pyrotechnics and a safety margin requirement of 16.5 dB for pyrotechnics.

Fig. 4.5 Safety margin

4.1.4 Electromagnetic Environment

Electromagnetic environment (EME): The distribution of electromagnetic emission energy in a range of frequency changes over time, i.e., the various conduction and radiation emissions that may be encountered by an electronic information system when performing its assigned mission in its predetermined operational environment.

According to different electromagnetic emission characteristics, the EME can be divided into two kinds: electromagnetic environment involved in EMC research (which is called background environment) and electromagnetic environment involved in electronic warfare research (which is called threat environment).

The EME in this book mainly refers to the background environment, since this book focuses on EMC research.

From the definition of the electromagnetic environment, we can see that the electromagnetic environment function is a function of frequency, time, and electromagnetic emission power, i.e.,

EME function( f, t, P)

where f represents frequency, t represents time, and P is electromagnetic emission power.

Complexity can be used to describe how complex electromagnetic environment is. This book will give a description of EME complexity from the perspective of the EME’s impact on the electronic information system (i.e., from the perspective of EMC).

For a certain equipment, if it is susceptible due to a certain kind of electromagnetic emission, the emission is called effective EMI. And we can say that the EME containing such electromagnetic emission signal has a certain degree of complexity. On the other hand, regardless of the EME situation, it is not complex as long as it does not produce significant EMI toward susceptible equipment. Therefore, the EME complexity

(HERO), and volatile materials such as fuel (HERF)), lightning, and precipitation static (p-static) are explained below.

(1)Electromagnetic pulse (EMP): Electromagnetic radiation from a nuclear explosion caused by Compton recoil electrons and photoelectrons from photons scattered. Once the radiation is picked up by the electronic system or equipment, sudden voltage and current changes will occur, which will cause temporary or permanent damage to the electronic system or equipment. Since the damage range of EMP can be hundreds of kilometers, EMP weapons are a method of electromagnetic attack.

(2)Electronic protection (EP): Used to be called electronic protection means (EPM) or electronic counter-countermeasure (ECCM). It refers to measures for protecting people, equipment, and facilities from electromagnetic spectrum produced by an enemy or one’s own that reduces, suppresses, and destroys one’s the combat effectiveness. EP includes various technologies and measures such as antielectron interference, anti-reconnaissance, and anti-destruction.

(3)Electromagnetic radiation hazard (RADHAZ): When humans, equipment, ordnance, or fuel are exposed to dangerous electromagnetic radiation environment, the electromagnetic energy density will be sufficient to cause ignition, combustion of volatile materials, harmful biological effects of human, false triggering of electrically initiated devices (EIDs), failure or gradual degradation of critical safety circuits. These phenomena are usually referred to as electromagnetic radiation hazards on people (HERP), electromagnetic radiation hazards on ordnance (HERO), and electromagnetic radiation hazards on fuels (HERF).

(4)Lightning: The impact of lightning on electrical and electronic systems has become an important issue for systems with composite materials such as aircraft and ships. On the one hand, lightning strikes directly on aircraft and ships can instantly produce extremely high electromagnetic energy, causing catastrophic disasters to the system; on the other hand, currents generated by lightning on the surface of the system will have secondary effects, which will cause destruction to the critical equipment in the system.

(5)Precipitation static (P-static): It is an EM disturbance caused by a random ESD buildup as a result of the flow of air, moisture, or airborne particles over the structure or components of a vehicle moving in the atmosphere, such as an aircraft or spacecraft [13].

4.1.6 Electromagnetic Environment Adaptability

Electromagnetic environment adaptability (EEA) refers to the system’s ability to achieve its intended function, performance, and/or malfunction in the expected EME, and its ability to not produce unacceptable electromagnetic emissions to its environment.