Electromagnetic Pulse Coupling Analysis of Electronic Equipment

High-intensity nuclear explosion caused by high-altitude nuclear electromagnetic pulse through the antenna, metal cables, holes and other channels, coupled with very high energy into the electronic device, and cause serious threats. In this paper, the mechanism, waveform, coupling path and damage effect of nuclear electromagnetic pulse is analyzed, and the coupling mechanism of nuclear electromagnetic pulse is studied.


Electromagnetic Pulse
The electromagnetic pulse (EMP) has a short duration and a bandwidth. Electromagnetic pulse is usually caused by the explosion (especially nuclear explosion) and other conditions of electromagnetic radiation, acting on electronic materials, blasting equipment or the surrounding medium of electromagnetic shock wave. Any form of nuclear explosion can produce electromagnetic pulse, but the form is different, high altitude nuclear explosion caused by electromagnetic pulse greater damage, nuclear electromagnetic pulse intensity, high frequency components rich, covering a wide area. For more than 100km high altitude nuclear explosion, the resulting high field strength in the ground coverage of up to thousands of kilometers. Therefore, this paper mainly discusses the high-altitude nuclear explosion electromagnetic pulse (HEMP). Electromagnetic radiation environment produced by high altitude nuclear explosion, early (0 <t <1μs), medium (1μs <t <1s) and late (t> 1s) from time to time. Which early nuclear electromagnetic pulse on the destruction of electronic systems plays a major role. At present, there are many kinds of description of HEMP radiation environment at home and abroad, mostly in the form of double exponent as the mathematical expression of radiation waveform, the time domain expression is [1] : Where k is the correction coefficient, E 0 is the peak field strength, generally 50kV/m, β, α is the characterization of the pulse before and after the parameters. The figure1 shows the waveform of the electromagnetic pulse when the parameter is k = 1.3, E 0 = 50kV/m, α = 4 × 10 7 , β = 6 × 10 8 . Electromagnetic pulse mainly through the energy of the conduction coupling, radiation coupling mode, the damage mode can be summarized as the following four aspects:

Thermal effect
The thermal effect of electromagnetic pulses is usually done in nanoseconds or microseconds, and is an adiabatic process. This effect can be used as ignition source and detonating source, instantaneous cause flammable, explosive gas and other items burning explosion; Can also make the communication system in the microelectronic devices, electromagnetic sensitive circuit overheating or input protection resistance burned, resulting in local thermal damage, resulting in deterioration of circuit performance or failure, and even lead to inventory burning explosion.

Interference and "surge" effects
The transient over-voltages or "surge" effects of electromagnetic pulses can also cause hard damage to the communication system. The performance of the device or circuit may deteriorate or completely fail, mainly for the semiconductor device open circuit, short circuit, current gain drop, leakage current increases, metal melting, and oxide breakdown; May also form a cumulative effect, buried the potential harm, so that the reliability of the circuit or equipment to reduce, resulting in malfunction.

Strong electric field effect
The strong electric field formed by the electromagnetic pulse source can not only cause the dielectric breakdown between the gate oxide layer and the metallization line of the metal oxide semiconductor (MOS) circuit in the communication device, so that the circuit fails, and the system self-test instrument and the sensitive device. hole coupling to the inside of the system [2] .

Front door coupling
Electromagnetic pulse coupling to the electronic Even if the current is not introduced from the leader of the transmission cable core, but in the outer shield on the induction, through the transfer impedance will be coupled to the core, directly into the electronic device system [3] .
There must be more than one module The center-fed dipole antenna shown in Fig. 2 is taken as an example.
Its structural parameters are: Where: χ for the antenna structure parameters, l for the antenna length (m), r antenna radius (m).
The resonant frequency of the antenna is: Where: f c for the antenna resonant frequency The damping coefficient of the center feed dipole antenna Q= χ/3.6. According to, the maximum induced current of the antenna in free space is [4] : Where: I max is the maximum induced current (A), H is the incident wave magnetic field (A/m).
From the above formula, the induced current waveform for the attenuation of oscillation, the cycle is about 2l c , where l is the length of the wire. c is the speed of light in free space. As the length of the wire increases, the magnitude of the induced current increases [5] .

Backdoor coupling
In order to facilitate the monitoring of Internet and printed circuit board can receive all kinds of electromagnetic pulse, into the sensitive circuit will damage the components, affecting the entire system. Take the seam as an example: Where ω is the electromagnetic wave The transfer impedance of the joint is related to the direction of the surface current. When the current is perpendicular to the joint, the transfer impedance is the largest, and when the surface current is parallel to the joint, the transfer impedance is very small [6]. According to the literature, the coupling electric field perpendicular to the joint direction is larger than the coupling electric field parallel to the joint direction [4] .

Concluding remarks
In summary, the coupling of electromagnetic pulse is mainly for front door coupling and backdoor coupling. The electromagnetic pulse enters into the interior of the electronic device by coupling and causes a degree of damage to it.
To study how the electromagnetic pulse on the electronic equipment, electrical system damage, so as to study the corresponding protection methods, we must first clear the electromagnetic pulse coupling path. Different electromagnetic pulse coupling path due to different frequencies, coupling, the way is also different.
Electromagnetic pulse through the front of the electronic equipment coupling or back door coupling into the system will cause serious damage to electronic equipment.