(Color online) Dynamical patterns of the planar wave trains propagating through a circular defect (radius R = 15 △ x with three different pacing frequencies ω, i.e., ω=0.81ω₀ in (a), ω=0.9ω₀ in (b), and ω=0.93ω₀ in (c), at t = 300. The arrow shows the direction of the propagating wave trains.