Fig. 1: Principle of measuring ΔV using a silicon photonic waveguide.
From: Compact potential sensor for spacecraft based on a silicon photonic waveguide
a Illustration of the potential difference between a spacecraft and the surrounding plasma, ΔV. As the metallic components of a satellite are typically connected to the negative terminal of the solar panels, ΔV is negative in general. b Illustration of plasma in the Earth’s plasmasphere and high-energy particles from the Sun, which can cause spacecraft electrification. c Definitions of the considered potential differences: the potential difference between the silicon layer (light blue) and the surrounding plasma, ΔVSi, and the potential difference between the base metal plate (brown) and the surrounding plasma, ΔV. In the case that ΔV (and ΔVSi) is negative, positive ions in the plasma are pulled toward the metal plate and the silicon layer, and thus positive charges are also transferred to the silicon layer. Due to the insulating layer (gray), the transferred charges accumulate in the silicon layer, and this charging process continues until ΔVSi reaches zero. d Diagram of an FCA process in a semiconductor, where a hole absorbs a photon propagating through the semiconductor. e, f Light attenuation due to FCA in the silicon photonic waveguide in the case of small and large negative ΔV values, respectively.
