SOFI - indirect lightning test strike system

SOFI, “Système d’Onde Foudre Indirecte”, developed for the Direction Générale de l’Armement

With its new high pulsed power generator: SOFI, ITHPP once again demonstrates its appetite and capacity for innovation. SOFI (Système d’Onde Foudre Indirecte in French) is a generator designed to simulate the indirect effects of lightning on structures such as aircrafts. 

On average, an aircraft is struck by lightning every 1500 hours of flying time. In order to lighten the weight of aircrafts to improve their performances, lighter composite materials replace metallic fuselage parts. The result is a decrease in the "faraday cage"^[1] effect. It is therefore essential to assess the vulnerability of such devices to the effects of lightning.

When an aircraft is struck, strong currents run out through the fuselage which can provoke direct effects, i.e. mechanic damages (destruction of elements, hole in the structure of the aircraft etc.) but also indirect effects (electromagnetic disturbances in electronic equipment of the aircraft).

ITHPP designed the SOFI generator to assess the indirect effects of lightning. It does this by applying pulsed power to simulate the indirect effects of a current flow into an aircraft. ITHPP developed SOFI for the DGA (Direction Générale de l’Armement, a French government defence agency). This system is a significant technological achievement for several reasons:

• Ecologically: this generator does not use SF6. SF6 is an extremely potent greenhouse gas, commonly used in the high power systems due to its excellent insulating properties. ITHPP replaced SF6 with ambient air. More over the system only requires 100L of dielectric oil to insulate parts of the system which are under heavy electrical stressed.
• Technically:  SOFI is a three-in-one system, designed to deliver an A-wave, it can also generate two other standard waveforms used to assess the vulnerability of a system to lightning.
• Logistically: A portable system, which can be stored and transported in two containers. Only two people are required to assemble and disassemble the system.

Once deployed, the total structure measures 6x5.5x8 meters.

SOFI can be used to assess various aircraft structures (planes, helicopters, UAVs etc.). It can also be exploited to assess the vulnerability to lightning of land based vehicles and heavy weapon systems.

^[1] Faraday cage: metallic shielding which protects from electromagnetic disturbances and thus prevents the disturbance of the internal electrical systems of a device. In this case, it is the hull of the aircraft, which plays the role of cage de faraday. As the fuselage of aircraft is mainly in foil, -a good conductor of electricity-, in case of lightning strike the current runs along the hull and continues its course in the air. However, with the use of composite materials, the current flow is not as good and can potentially interfere with the on-board electrical systems and cause serious disturbances.