As shown in Fig. 1, the proposed energy
harvesting device consists of a bimorph PZT bender
and an asymmetric inertial mass. The inertial mass
located at the end of PZT bender helps to generate
electrical power from the one-dimensional vibration
which is applied through the thickness direction of
PZT bender, z-axis [1-3]. The motion of vibration is
coupled to generator by means of the inertia of total
mass. This mass (m) is modeled as being suspended by
a spring with spring constant (k), while its motion is
damped by a parasitic damping (bm). This mass also
damped by the generator (Pg). Fig. 2 (a) shows a
schematic drawing of vibration energy harvester. The
displacement of total mass is θ(t) and the displacement
in z-axis of this system is represented by z(t). Fig. 2 (b)
shows the equivalent circuit of vibration energy
harvester. The piezoelectric coupling at between
electrodes is modeled as a transformer. The dielectric
and piezoelectric losses are neglected in this analysis.
The mechanical part in Fig. 2 (b) can be obtained by
applying Kirchhoff’s law as