Sketch of the phenomenological model of the dust polarized emission. The observer is represented by the central star, and the polarized emission is assumed to arise from a small number of layers (here N = 3) in which the total magnetic field B = B₀ + B_t is the sum of a uniform field B₀ and an isotropic turbulent field B_t that is taken, in each layer, as a different realization of a Gaussian random field in three dimensions.