Application of paraelectric to a miniature capacitive energy harvester realizing several tens micro watt — Relationship between polarization hysteresis and output power

We previously proposed a vertical type vibratory energy harvester using polymer electret and dielectric. A proof mass consists of counter electrode and dielectric beneath it, which faces with electret on base electrode fabricated on a substrate. A narrow gap between mass and electret is feasible, since dielectric prevents discharge from electret to counter electrode. The narrow gap leads to large output power. In this article, we propose to use paraelectric as the dielectric material instead of previously used ferroelectric, taking account that ferroelectric has a severe hysteresis on polarization-electric field (PE) characteristics, which may cause energy loss. We experimentally prove the superiority of paraelectric (compounded TiO₂-BaO, ε_r: 100) to ferroelectric (Pb(Zr, Ti)O₃, ε_r: 2,600) in terms of output power. A miniature harvester with paraelectric employing double swastika-shaped springs for suppressing unwanted vibration modes generated 45 μW for free vibration at 20 Hz/0.8 mm amplitude (acceleration: 1.3 g).