  This paper proposes a novel vibration energy harvesting strategy based on an
extension of the Synchronous Electric Charge Extraction (SECE) approach,
enabling both the maximization of the harvested power and a consequent
bandwidth enlargement in the case of highly coupled/lightly damped
piezoelectric energy harvesters. The proposed strategy relies on the tuning of
the frequency of the energy extraction events, which is either N times greater
than the vibration frequency (Multiple SECE case, N > 1) or 1/N times smaller
(Regenerative SECE, N < 1). We first prove analytically than increasing or
decreasing N both lead to a damping reduction. While N has no impact on the
system's resonance frequency in the Regenerative case (N < 1), we show that
this resonant frequency becomes a function of N in the Multiple SECE case (N >
1). Experimental results on a highly coupled/lowly damped piezoelectric
harvester (k^2= 0.44, Q_m = 20) demonstrates the potential of this strategy,
leading to 257% harvested power improvement compared to SECE (N = 1). and the
possibility to tune the resonant frequency on a range as large as 35% of the
short-circuit resonant frequency of the harvester.
