Enhancing output and durability of polymer-based piezoelectric vibration energy harvesters using mechanical metamaterials

Maintenance-free wearable energy harvesters are attracting attention as an energy source for sensors within the internet of things (IoT) landscape. The effectiveness of vibration energy harvesting uses resonance; therefore, achieving frequency matching with the vibration source is essential. However, the target vibrations in wearable environments are concentrated in the low-frequency band, making it challenging to achieve device miniaturization and frequency matching. Our previous work proposed polymer-based piezoelectric vibration energy harvesters (PVEHs) incorporating mechanical metamaterials (MMs). This allowed us to achieve low resonance alongside high output power in compact devices. However, concerns regarding decreased yield during the deposition process of the thin-film piezoelectric layer and potential compromises in the microstructure strength have been identified. In response to these challenges, this study focuses on redesigning PVEHs to improve the yield and structural integrity. Using finite element method (FEM) analysis, we examined the effects of the PVEH structure and thickness of the elastic layer on performance, leading to a design of PVEHs that optimize both output power and sufficient strength. The proposed PVEHs were fabricated through photolithography, and their performance was evaluated by vibration experiments. When subjected to a sine wave excitation of 0.2 G, equivalent to walking vibration, the proposed PVEH had a resonance frequency of 25.0 Hz and RMS output power of 11.5 µW. Compared to the conventional solid-type PVEH, this corresponds to an approximately 31% lower resonance frequency and 1.3 times higher output power.