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Piezoelectric energy harvesters are suitable for vibration energy harvesting due to simple design, operation and fabrication in MEMS technology. Cantilever structures fixed from one end and seismic mass at the other must tune to different resonance frequency to ensure wideband frequency operation. Adequate width to length ratio of cantilever is required to avoid curling of cantilevers (bending). Effect of increase in width of the cantilever structure on resonance frequency has been investigated and also compared analytically in this paper. An optimized design has been proposed which compensates for the increase in resonance frequency due to increase in width by changing the geometry of the seismic mass. With the change in geometry of seismic mass a shift in center of mass has been achieved towards the free end of the cantilever which reduces the resonance frequency which is desirable. The design optimization of seismic mass reported in this paper reduces the resonance frequency by 4.27 % which is appreciated as it is required to harvest ambient vibrations having low frequency. [ABSTRACT FROM AUTHOR]

This paper reports the fabrication of MEMS-based guided two-beam piezoelectric energy harvester for low-frequency operation. A highly c-axis-oriented zinc oxide thin film of 2.5- $\mu \text{m}$ thickness covered with 0.5- $\mu \text{m}$ plasma-enhanced chemical vapor deposition SiO2 is sandwiched between the aluminum electrodes to form split electrodes on the two beams. A pyramidal-shaped seismic mass that gives a higher electric potential is realized by bulk micromachining using CMOS compatible 25 wt% tetramethyl ammonium hydroxide wet etching. The thickness of the beams is optimized using deep reactive-ion etching to achieve a low-frequency operation. COMSOL Multiphysics has been used to study the stress distribution to optimize the dimension and placement of the split electrodes. The optimized split electrodes give a reduced resonance frequency by 4.2% when compared with previously used electrode pattern ensuring maximum electric potential generation for guided two-beam structure. The resonance frequency of the device measured experimentally using laser Doppler vibrometer comes to be 466 Hz. The packaged device exhibits a maximum sensitivity of 1.5089 mV/m/s2 in the frequency range from 160 to 1000 Hz. [ABSTRACT FROM AUTHOR]

MEMS devices have found applicability in remote area of operation such as temperature monitoring in extreme climates, structural health monitoring, and car tire pressure monitors etc. due to compact shape and ability to operate in low power (few microwatts). These devices are generally powered through a small battery but replacement at such remote locations is not feasible which imposes a serious challenge of powering these devices for infinitely long time. Energy harvesting provides an unending power source (few milli-watts) which is adequate to power these MEMS devices having remote area applications. Piezoelectric type energy harvesters are the most promising and efficient vibration energy harvesters that are widely used. Increased depth of cavity due to large displacement, residual stress and lower output potential are demerits of single cantilever type piezoelectric energy harvester. In this paper a new design of guided four beam cantilever type piezoelectric energy harvester is simulated, analyzed and reported. Displacement of 0.095 µm is achieved at an input acceleration of 1 g (9.8 m/s) which is 32.14 % less than displacement of single beam cantilever which has also been reported and compared with the new proposed design in this paper. Maximum stress calculated at an input acceleration of 5 g is 4.7 × 10 N/m on piezoelectric layer and 8 × 10 N/m on guided beams which is well below the fracture stress for silicon. Tensile and compressive stress generates potential of opposite polarities that can be harvested using separate set of capacitors. Potential generated ranges from 17.84 to 89.21 mV for input acceleration ranging from 1 to 5 g respectively. [ABSTRACT FROM AUTHOR]