An effect, due to Poisson's ratio, that transforms axial motion into motion that is transverse to the stud axis. The Poisson-coupled transverse motion is largest in the nodal_region (i.e., the nodal region "breathes" as the resonator vibrates).
Poisson coupling also causes nonuniform amplitude at the resonator's face and stud surfaces. The Poisson-coupling effect increases with Poisson's ratio and with the transverse dimensions of the resonator.
Slots are used to reduce the Poisson-coupling effect in resonators with large lateral dimensions.