Around the same time in 2003, researchers from the Army Research Laboratory (ARL) tested the Biefeld–Brown effect by building four different-sized asymmetric capacitors based on simple designs found on the Internet and then applying a high voltage of around 30 kV to them. According to their report, the researchers wrote that the effects of ion wind was at least three orders of magnitude too small to account for the observed force on the asymmetric capacitor in the air. Having proposed that the Biefeld–Brown effect could theoretically be explained using ion drift instead of ion wind due to how the former involves collisions instead of ballistic trajectories, they noted these were only "scaling estimates" and more experimental and theoretical work was needed.