Kazusuke Maenaka

20-μm-diameter WGM resonators that include a terfluorene emission layer and a 10-nm-thick layer of Al or Ag were investigated. The plasmon-quenching effect on amplified spontaneous emission was effectively suppressed by the resonator structure.

This paper reports on the improvement of the output power of piezoelectric energy harvesters (PEHs). A tapered thickness structure of a cantilever beam for uniform stress, tungsten proof mass, thick piezoelectric film, and series connection of the piezoelectric films are utilized for PEHs to increase the output power. The three-dimensional (3D) etching process of Si enables the formation of tapered thickness beam structure, which increases not only the output power, but the beam strength. The 3D shape allows to increase the weight of the proof mass, contributing to increase the output voltage and power. Furthermore, output voltage is enhanced by using series-connection of PZT cells to improve the circuit efficiency. The open-circuit output voltage and optimum power with resistance load of the fabricated harvesting device revealed 14.4 V0-P and 92 mu W at an acceleration of 9.8 m/s(2). The output power was improved by 8.9 times higher than that of the conventional model.

Similarly to a harmonica reed, a piezoelectric MEMS cantilever is self-excited by an airflow. An airflow-induced self-excited vibration can be utilized as an energy source for energyharvesting devices. In this study, with the aim of reducing the cut-in flow velocity, which is the lowest flow velocity required for resonant vibration, a thin MEMS structure with an intentionally warped shape was exploited in an energy harvester based on the principle of harmonica reeds. By compensating for the residual stresses of PZT and Pt electrode films, the cantilever warpage of the harvester structure can be controlled. The thin-film nature and the warped PZT/Si laminated MEMS structure enabled energy harvesting from an airflow at low flow velocities. Moreover, the cut-in flow velocity of the airflow-induced MEMS harvesting device was very low (1.2 m/s, one-tenth of that of a conventional device), and an output power of 3.84 μW was obtained at a flow velocity of 3.7 m/s.