Online proceedings - EDA Publishing Association

11-13 May 2011, Aix-en-Provence, France
Fig. 4. Equivalent Circuit of MEMS Piezoelectric Energy Harvester
III.
SIMULATION RESULT AND DISCUSSION
The simulation results indicate that the displacement at z
direction of fundamental mode 1 provides highest
displacement as shown in Fig. 5. A total of 30 harmonic
frequency steps within range of 220 to 290 Hz were
generated. Fig. 6 to 8 show the graph of displacement, output
voltage and output power versus frequency applied
respectively. The graphs show the expected sharp change and
the peak as the frequency approach the fundamental
resonance Mode 1 value that is 233 Hz.
It is essential for the MEMS piezoelectric inertial generator
to operate at the resonance frequency to harvest optimum
power. Resonant frequency of 233 Hz provides the maximum
displacement of vibration, output voltage and power. Fig. 6
and 8 illustrate maximum displacement of 420µm and
maximum output power of 3.02µW at mode 1 resonance
frequency of 232 Hz. It shows that the device needs to
operate at resonance mode to harvest optimum output power.
Fig. 7. Output voltage produced versus frequency
Fig. 8. Output power produced versus frequency
A. The effect of various volume of the cantilever beam
to its natural frequency
Low resonant frequency is essential in MEMS
piezoelectric inertial generator because most of the ambient
vibrations are at very low frequencies [1]. The power output
will only be optimized if the miniature devices are operated
at the resonance mode. Table III and Fig. 9 illustrate the
volume increment of the cantilever beam decreases the
resonant frequency and increases the peak output power
produced. The larger the volume of the cantilever beam, the
lower the resonant frequency.
Fig. 5. Mem Mech Piezoelectric Analysis
B. The effect of resonant frequency to the peak output
power
Output power of the system will be optimized when it is
operated at the ambient resonance frequency. MEM PZE
piezoelectric analysis was done to compute the output power
produced at the resonance frequency. To obtain resonance
TABLE III
Fig.6. Displacement of vibration versus frequency
SIZES, RESONANT FREQUENCY AND OUTPUT POWER OF PIEZOELECTRIC INERTIAL
GENERATOR
Design
Number
Wbeam Lbeam Resonant
Frequency
Peak Output
Power ( R L=50
ohm)
1 722 2044 1542.00 0.7260
2 442 3018 976.40 0.5765
3 166 3288 620.87 0.8350
4 1010 4299 463.50 1.8216
5 672 5039 232.0 3.0560
87