  We have investigated generation of magnetic fields associated with velocity
shear between an unmagnetized relativistic jet and an unmagnetized sheath
plasma. We have examined the strong magnetic fields generated by kinetic shear
(Kelvin-Helmholtz) instabilities. Compared to the previous studies using
counter-streaming performed by Alves et al. (2012), the structure of KKHI of
our jet-sheath configuration is slightly different even for the global
evolution of the strong transverse magnetic field. In our simulations the major
components of growing modes are the electric field $E_{\rm z}$ and the magnetic
field $B_{\rm y}$. After the $B_{\rm y}$ component is excited, an induced
electric field $E_{\rm x}$ becomes significant. However, other field components
remain small. We find that the structure and growth rate of KKHI with mass
ratios $m_{\rm i}/m_{\rm e} = 1836$ and $m_{\rm i}/m_{\rm e} = 20$ are similar.
In our simulations saturation in the nonlinear stage is not as clear as in
counter-streaming cases. The growth rate for a mildly-relativistic jet case
($\gamma_{\rm j} = 1.5$) is larger than for a relativistic jet case
($\gamma_{\rm j} = 15$).
