EMP/HEMP filter technologies designed to mitigate EMI threats

Article By : Jeff Cherseon

Electromagnetic threats have been known for almost a century, but a new breed of EMP/HEMP filters have been designed to ensure that electrical systems benefit from not only survivability, but suppression of harmful EMI.

Electromagnetic threats have been known, and to a degree understood, for almost a century. Nevertheless, it is only in the past couple of decades that governments and military organizations have come to realize the extent of the threat that intentional/unintentional electromagnetic interference (IEMI/UEMI) pose to critical facilities, infrastructure, aerospace, and land mobile electronic systems. Most nations’ electrical infrastructure and utilities have been identified as vulnerable to sabotage and intentional disruption using IEMI, the threat to these systems has been a known entity for many years. What is an emerging unknown, and possibly equally as disruptive, is the new threat to digital and communications network infrastructure (data centers and internet systems) that the world’s banking, transportation, and resource allocation now relies on.

The threat of IEMI, and even UEMI and natural EMI, on every level of a modern society only grows, as people become more dependent on electrical systems to enhance efficiency, reduce expenditures, speed processes, and raise profits. Additionally, the most recent electronics are built with low power ICs and other sensitive active and passive devices whose economics depend on miniaturization, power reduction, and feature integration. Unfortunately, few non-governmental/military organizations have come to recognize this threat, and fewer have taken action to ensure their essential systems, for which many other organizations and individuals depend, are robust toward IEMI, or EMI in general.

Notwithstanding the general blind eye, there are a few organizations that have been studying and developing technologies to protect critical and sensitive electronic systems from the dangers of IEMI and EMI. Where most prior efforts have been in the protection of buildings and racks of electronic equipment, a new breed of EMI filters, electromagnetic pulse/high altitude electromagnetic pulse (EMP/HEMP) or IEMI filters are now available. EMP/HEMP filters are designed to protect specific electrical assemblies, or sub-assemblies, from IEMI and ensure that these susceptible electrical systems benefit from not only survivability, but suppression of harmful EMI.

Overview of electronic threats

The term EMI broadly applies to any unwanted signals that degrade or disrupt the desired performance of electrical equipment. EMI can be further broken down into three categories, intentional, unintentional, and natural, all of which can be destructive to electronics. Natural and unintentional EMI can be produced by naturally occurring sources, such as geomagnetic storms caused by weather patterns and the interaction of the Earth’s electro magnetosphere and space weather (solar coronal mass ejections), or by a number of poorly planned/designed or damaged electronic systems. As the effects of several EMI generators can be cumulative, even several relatively weak EMI generators could pose a hazard if in close proximity to a EMI sensitive system.

Natural and unintentional EMI are outside of the scope of this work. However, the methods of protecting electronics from IEMI can also provide some protection from natural and unintentional EMI sources.

The potential threat of IEMI is hard to gauge, as malicious, or even ignorant, parties could produce EMI that could affect different electrical systems in a variety of ways. IEMI is a risk to electrical systems which is only increasing as access to EM weapons is becoming easier. There are several countries, namely Russia and China, who are actively developing EM weapons designed to disable even protected electrical systems and infrastructure. Though nuclear weapons are destructive enough in their immediate blast radius, there is also an EMP component of a nuclear blast that can be destructive toward electronics over a much wider area than what was affected by the nuclear blast.

Even nuclear weapons detonated in space can emit severe and damaging radiation, known as HEMP, which can even affect ground based electrical systems, aircraft, and vehicles. This is why nuclear EMP is used as a basis for the development of standards and EMP protection systems. Nuclear EMP/HEMP threats are classified by the International Electrotechnical Commission (IEC) as E1, E2, and E3 components, and have a dominant energy distribution from 1 MHz to 300 MHz. Each component classification comes with a description of the type of EMI that is generated and guidelines on how to protect against it.

The E1 component
The E1 pulse, or short pulse, component of nuclear EMP is a result of electrons being ejected from atoms in the upper atmosphere due to the huge initial surge of gamma radiation from a nuclear explosion. A product of the interaction of these highly accelerated electrons and the Earth’s magnetic field, the stray electrons are predominantly directed toward the Earth over a large affected area. The E1 pulse acts as a very intense, but short duration, blast of relativistic speed electrons, which are capable of interacting with conductors and producing high voltages in those conductors. These voltages can easily exceed the electrical breakdown voltages of the conductors and connected electronic components, devices, and interconnects.

Typically, the E1 pulse is too brief for traditional lightning protection to be effective, and only transient protection that can respond to extremely fast rise-time pulses is capable of mitigating E1 EMP. The E1 pulse has a typical rise time of 20 nanoseconds, and reaches 50% of its peak value in 500 nanoseconds, and by the IEC’s definition, completely occurs within 1 microsecond. The critical frequency range for the E1 pulse is between 1 MHz and 300 MHz. The electric field strength of the E1 pulse peaks at roughly 50,000V per meter, with peak power densities reaching 6.6 MW per square meter. Depending on a variety of factors, the peak current induced into an electrical system from an E1 pulse could reach 2500A. The E1 pulse is the most dangerous of the HEMP pulses toward smaller electronics and electrical system not connected to long conductor lines, still damaging integrated circuits.

[Continue reading on EDN US: Components and standards]

Jeff Chereson is the Director of Technology at API Technologies.

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