Figure 2

First row: Trajectories of spiral tips movement under the influence of an ac electric field with ω e = 2ω, ϕ e = 0, and Φ = 0. Second row: Drift speed as a function of Φ with ϕ e = 0. Third row: Drift angle as a function of Φ with ϕ e = 0. In the second and the third rows, the circles represent numerical simulations and the lines represent theoretical predictions. Left column: Highly excitable medium. Right column: Weakly excitable medium.