Translational magnetic damping of a square wire loop

A square wire loop partly in a uniform field has linear drag $B^2{a}^{2}v/R$, giving velocity-relaxation time ${\tau }_t=mR/(B^2{a}^2)$. For uniform wire of mass density ${\rho }_m$ and resistivity ${\rho }_e$, ${\tau }_t=16{\rho }_m{\rho }_e/B^2$, independent of wire dimensions.