Visualizing HIRF

Visualizing HIRF Fields Inside Aircraft

By Jennifer Kitaygorsky

High intensity radiated fields (HIRF) can come at an aircraft from any direction, and enter the aircraft through apertures, seams and gaps. Some aircraft systems may be susceptible to this type of EM radiation, and visualizing HIRF fields can further our understanding about what’s happening inside an aircraft. Here, we use EMA3D®, a FDTD based solver, to visualize HIRF fields inside a medium size business jet modeled with and without absorption losses.

For this problem, the incident electric field is a broadband plane wave coming in broadside, as can be seen from the animation of surface currents on the aircraft skin:

Aircraft HIRF surface currents simulation animation

Click on the image to view a larger size. This is a false color image of surface currents, with red being the highest current density (see scale on the right of the image). The plane wave comes in from the right and propagates along the x-axis, creating surface current patterns seen above. Note that the plane wave propagates much faster than it takes for the surface currents to stop ringing: because the skin is metallic, the Ohmic losses are very small, and it takes a while for the surface currents to dampen. In fact, the surface currents are still ringing by the end of the animation. (It is worth mentioning that at higher frequencies the skin depth effect should help with the damping).

When the aircraft is empty, with apertures and seams being the only loss mechanisms, a similar situation occurs inside the aircraft with EM fields. Adding absorption losses, such as seats, bulkheads, aircraft harnesses and avionics boxes, will increase the aircraft shielding effectiveness and decrease the ringing time. The animation below shows electric fields inside the aircraft longitudinal cross section without absorption losses, while the one below that shows the aircraft with absorption losses added. Click on the images to view the animations. Note the lower field amplitudes and ringing time inside the aircraft in the animation for an aircraft with losses.

Visualizing HIRF fields inside aircraft

Visualizing HIRF fields inside aircraft

The fields penetrate the aircraft cockpit and cabin mainly through the windows. Also note that the fields penetrate underneath the floor through the modeled seams. However, no fields penetrate through the aft bulkhead to the tail end of the aircraft. That’s because no seams were added to the bulkhead in the model, and there is no way for the fields to penetrate into that region.

For a more rigorous treatment of computational electromagnetics for HIRF analysis, see our HIRF Analysis Tutorial.

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