Electromagnetic Pulse Test

Electromagnetic and Electrical Tests

Electromagnetic Pulse Test

The effects of electromagnetic pulses (EMP) on electronics can be serious, but they pose an even more devastating threat to the processes and infrastructures they support. Designing equipment and systems to withstand the effects of EMPs will reduce the impact of potential EMP attacks on our electronic devices in the future.

Electromagnetic Pulse Test

Direct Energy Weapons (DEW) and Security

Highly effective non-nuclear EMP technologies are being developed quite widely worldwide. These technologies are classified as "Direct Energy Weapons" and are currently used by the US armed forces, state and local police agencies. Direct energy weapons are very similar to a traditional EMP and go to the target at the speed of light. It can have gradual effects on electronics, from interrupting work to permanent damage or complete demolition.

The best example of this technology is arc discharge EMP generator. These devices use high voltage and large energy storage of capacitors released up to a thin impedance load or short circuit under a sudden conductor. The wire acts as a fuse opening at the peak of the high current discharge of the capacitor, resulting in a large release of the broadband electroma.

Another example of non-nuclear EMP technology is Flux Compression Generator (FCG). FCG was first demonstrated at the Los Alamos National Laboratories (LANL) by Clarence Fowler in the late fifties. This technology injects high energy pulses into a large conductive coil. At the highest pulse current point, a small explosive charge that quickly compresses the coil to one end of the generator comes into play, generating large amounts of electromagnetic energy. The initial designs were several meters long, but thanks to technological advances, it is reported to be roughly the size of a soda can.

With the creation of non-nuclear direct energy weapons and the current use of devices and non-war environments on the battlefield, the need to protect electronic equipment is always at the highest level. The U.S. Army has been evaluating the effects of electromagnetic pulses on equipment for the past 50 years and developing protective design guidelines and curing techniques used today.

MIL-STD-461, RS105

MIL-STD-461Gprovides test methodology and scan levels to determine the immunity of a device to EMP from a radiated and transmitted perspective. The connection modes and interconnect cables on the equipment enclosure can be complicated, so they are considered separately.

The RS461 test method specified in MIL-STD-105G eliminates the risk of exposure to an EMP event. The RS105 test generally applies to equipment installed in exposed and partially exposed environments. The U.S. Navy requires RS105 testing for almost any installation platform, surface ships, submarines and aircraft to ground applications.

The RS105 impact characteristics consist of a rapid rise time, short stroke time, and high amplitude, which resembles a true EMP. Peak field strengths of 50 kV / m are specified for the exposed equipment. However, the peak area levels need to be adapted for partially exposed installations due to the attenuated effects provided by enclosures such as deck building structure or hangar doors. For example, equipment installed near deck slot openings must meet external stress, which is reduced by the shielding effectiveness of a particular opening or 40 dB electromagnetic shielding provided by the deck building structure, whichever is lower.

RS105 test was performed with a transmission line connected to the temporary pulse generator. The remote end of the generator and transmission circuit is usually connected to the reference ground. This connection provides a return path that allows current flow, which allows the creation of electromagnetic fields. The tested equipment is then mounted under the transmission line in the predefined uniform area.

The area developed between the transmission line and the ground plane consists of large differential voltage and current fields. To ensure a smooth even distribution area, RS105 requires that the length and width of the transmission line be at least twice the height of the equipment under test and at least three times the height.

MIL-STD-461, CS116

The test method of MIL-STD-461 CS116 evaluates the coupling effects of EMP on metallic interconnection lines. The purpose of this test is to provide the equipment's ability to withstand platform switching operations, indirect effects of lightning, and damped sinusoidal transitions induced by EMP. The minimum test frequency set is 10 kHz, 100 kHz, 1 MHz, 10 MHz, 30 MHz and 100 MHz.

In accordance with MIL-STD-461F, the CS116 test applies to all installation platforms and supply agents with limited applicability for submarines. Similar to RS105, the CS116 test is not to damage the hardware, but to determine the immune threshold for the electromagnetic pulse. This is done by starting at 10% of the peak area level and gradually increasing the area until the sensitivity is determined or the specified peak area level is reached.

An important point to note about the test method is that inductive signals are inductively connected to each line. The amount of voltage and current induced in each line depends on the impedance. Higher impedance lines will allow higher voltages to be obtained at low currents where low impedance lines such as shielded wiring will obtain more current at lower voltages. To avoid excessive over-testing, the injected currents are pre-calibrated to 100 ohm loop impedance and induced currents are monitored in each line. As stated, test levels are gradually increased until equipment sensitivity is detected, the current limit is reached, or the generator setting set during the 100 ohm calibration is reached.

In summary, the effects of electromagnetic pulses on electronics can be serious, but they pose an even more devastating threat to the processes and infrastructures they support. Designing equipment and systems to withstand the effects of EMPs will reduce the impact of potential EMP attacks on our electronic devices in the future.

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