By Dr. Arthur Bradley author of Disaster Preparedness for EMP Attacks and Solar Storms
There is a great deal of confusion about what an electromagnetic pulse (EMP) is and how best to protect against them. This three-part tutorial is meant to help clear up some of this confusion as well as dispel a few myths that frequently circulate the internet. This first part will be a general introduction. The second will discuss building an effective Faraday cage. And the third part will answer questions that I am frequently asked on this topic.
What is an EMP?
An EMP is an intense broadband burst of electromagnetic energy. It can be the result of many things, including lightning, a nuclear explosion, or specialized EMP weaponry. Of all of these sources, the EMP that results from a high-altitude nuclear explosion has the greatest potential to cause widespread damage. When people talk about an “EMP attack,” they are almost always referring to one caused by a high-altitude nuclear detonation. Many times solar events are also described as causing an EMP, but it’s important to understand the differences between the electromagnetic disturbance resulting from the Sun and the other sources mentioned—more on that later.
EMP-generating devices can be employed in conventional, large-scale warfare, but they are more likely to be used as asymmetric weapons by a hostile state or terrorist group that strives to inflict great damage without requiring the need for military supremacy. EMP weapons offer several tactical advantages over conventional weapons, including:
- Affecting all targets in range without requiring knowledge of the specific electronic systems
- Being largely independent of weather,
- Offering a scalable area of attack, ranging from single electronic assemblies using a directed energy weapon, to an entire continent using a high-altitude nuclear detonation,
- Causing lasting effects through permanent destruction to both civilian and military electronic hardware,
- Having a damage-to-cost ratio that is much higher than conventional or “dirty bomb” weapons, and
- Not directly harming humans or animals, making full-scale retaliation politically difficult.
A high-altitude EMP (HEMP) emits gamma rays that strip electrons from atmospheric atoms. There are several unique atomic interactions that occur, including photoelectric absorption, Compton scattering, and pair production, all of which result in the generation of free electrons. Most of this ionization occurs at an altitude of 12 to 25 miles (20 to 40 km) in a region of the atmosphere known as the “Source Region.” These free electrons ultimately interact with the Earth’s magnetic field lines, resulting in an intense electromagnetic pulse that affects the surface. Saturation occurs in the Source Region as it become more and more conductive, limiting the maximum field to 50-100 kV/m – very high fields, indeed!
The area affected by the high-altitude EMP is determined by line of sight and, therefore, largely a function of altitude. The greatest threat is from a high-altitude EMP produced by a nuclear weapon detonated 25 to 250 miles above the Earth’s surface. It is reported that if even a small 1 to 2-megaton nuclear bomb was detonated 250 miles above the central states, the resultant pulse could disrupt, disable, and damage electronics across most, if not all, of the continental United States.
Fig. 1: Area affected by high-altitude EMP attack at different detonation heights
An EMP damages electronics by inducing voltages and/or currents far above the levels that the circuits were designed to withstand. This leads to overheating or electrical breakdown of components. The energy is coupled into electronic systems by three mechanisms: electrical induction (energy transferred to conducting wires or junctions), magnetic induction (energy transferred into closed conducting loops), and through transfer impedance, such as energy transferred to buried conductors. Most modern integrated circuits are susceptible to high-frequency pulses, whereas large electrical systems, including our commercial power grid, are more susceptible to low-frequency pulses. Unfortunately, an EMP has both high- and low-frequency pulse content. The Sun, however, only causes low-frequency electromagnetic disturbances, which will greatly affect how we protect against those events – coming in Part 2.
An EMP is defined by its timing, field strength, and frequency content. The precise extent of damage that a particular EMP will inflict is not easily predicted because it is dependent on many factors, including field orientation, waveform polarization, circuit geometry, filtering, and shielding. It is often taken that field levels of 10 kilovolts per meter (kV/m) or greater are sufficient to cause widespread damage to electronic systems. Note that the peak fields from a high-altitude EMP would likely be in excess of 50 kV/m.
Devices that are most susceptible to an EMP are those that use solid-state semiconductors, such as computers, alarm systems, radios and transceivers, control systems, and communications equipment. Electronic equipment designed for higher currents, such as transformers, motors, and circuit breakers are less susceptible. Batteries are not susceptible to EMP energy.
The greatest threat from an EMP is its ability to disrupt, damage, and destroy electronic hardware. Affected systems include the electrical power grid, cellular and wired communications systems, the internet, personal electronics, agricultural systems, airplanes, gasoline pumps, satellites, water purification plants, generators, automobile electronics, and nearly every other type of modern electronic device.
Due to the interdependency of systems, a cascade of failures would likely promulgate through every major infrastructure. It is estimated that a high-altitude EMP attack on the continental U.S. would cause several trillion dollars of damage in cascading failures of interdependent systems. Such a disruption would crush the economy and seriously degrade critical infrastructures, including: electrical power, telecommunications, financial, petroleum and natural gas, transportation, food, water, emergency services, space operations, and government.
Coming soon… EMPs – Part 2, Building a Faraday Cage
If you have comments or questions regarding EMPs, write the author at [email protected], consult Disaster Preparedness for EMP Attacks and Solar Storms, or watch my free videos on YouTube (search disasterprepper).
About the Author
Dr. Arthur Bradley is the bestselling author of the Handbook to Practical Disaster Preparedness for the Family, the Prepper’s Instruction Manual, the Disaster Preparedness Handbook, and Disaster Preparedness for EMP Attacks and Solar Storms. He is also the author of the bestselling post-apocalyptic series, The Survivalist. He provides free disaster preparedness information at http://disasterpreparer.com.
Dr. Bradley is an Army veteran, father of four, martial artist, weapons expert, and dedicated homeschooler. He is active in volunteer youth organizations, including the Boy and Girl Scouts of America. He holds a doctorate in engineering and currently works for NASA. Having lived all across the United States, Dr. Bradley writes from personal experience about preparing for a wide variety of disasters. He has been featured in the New York Times, Toronto Sun, Men’s Journal, Costco Connection, Popular Mechanics, and Money magazine.