  This paper reports a method to design highly coupled piezoelectric energy
harvesters with frequency tuning capabilities using nonlinear electrical
techniques. A cantilever beam with two PMN-PT patches has been optimized thanks
to both analytical modelling and Finite Element Methods (FEM). The built
prototype exhibits a strong electromechanical coupling (k${}^2$=17.6%) and a
figure of merit (km${}^2$Q=12.4) which allow a bandwidth corresponding to 22%
of the resonant frequency value.
