Consider a rectangular coordinate system (x, y, z) with unit vectors a_x, a_y and a_z. A plane wave travelling in the region z ≥ 0 with electric field vector E = 10cos(2 × 10⁸t + βz)a_y is incident normally on the plane at z = 0, where β is the phase constant. The region z ≥ 0 is in the free space and the region z < 0 is filled with a lossless medium (permittivity ε = ε₀, permeability µ = 4µ₀, where ε₀ = 8.85 × 10¹² F/m and µ₀ = 4π × 10^-7 H/m).
The value of the reflection coefficient is