Ratio of absorption efficiencies Q_⊥/Q_‖(top) and absorption efficiency (bottom) of an oblate spheroid as a function of radius of an equal volume sphere. This figure shows an axis ratio of the spheroid of 1/1.5 and a wavelength of radiation of 3 mm. The absorption efficiency Q_‖is the efficiency along the minor grain axis, that is, the axis of alignment. If a/λ ≥ 1, we assume a spherical particle, thus, Q_⊥ = Q_‖. See Sect. 2.3 for details.