Fiber-Optic Sensor for Aircraft Lightning Current Measurement

Abstract

An electric current sensor based on Faraday rotation effect in optical fiber was developed for measuring aircraft lightning current. Compared to traditional sensors, the design has many advantages including the ability to measure total current and to conform to structure geometries. The sensor is also small, light weight, non-conducting, safe from interference, and free of hysteresis and saturation. Potential applications include characterization of lightning current waveforms, parameters and paths, and providing environmental data for aircraft certifications. In an optical fiber as the sensing medium, light polarization rotates when exposed to a magnetic field in the direction of light propagation. By forming closed fiber loops around a conductor and applying Ampere's law, measuring the total light rotation yields the enclosed current. A reflective polarimetric scheme is used, where polarization change is measured after the polarized light travels round-trip through the sensing fiber. The sensor system was evaluated measuring rocket-triggered lightning over the 2011 summer. Early results compared very well against a reference current shunt resistor, demonstrating the sensor's accuracy and feasibility in a lightning environment. While later comparisons show gradually increasing amplitude deviations for an undetermined cause, the overall waveforms still compared very well.

Lightning current measurement with fiber-optic sensor

“…The measurements were performed at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, U.S.A. facility [10]. The measurements were similar to an earlier (2011) successful effort that used twisted single-mode sensing fiber [3] at 850nm wavelength.…”

“…Of three systems constructed and tested operating at 850nm [3], 1310nm and 1550nm, the 1310nm system is chosen for future aircraft installations. This wavelength provides slightly better sensitivity than the 1550nm (300 A vs. 400 A) while offers adequate measurement ceiling at 300 kA.…”

“…The measurement range achieved is approximately 300 A -300 kA for the 1310nm system or 400 A -400 kA for the 1550nm system, a 60 dB range. Both systems are less sensitive but otherwise similar to a 850nm system that successfully measured rocket-triggered lighting [3].…”