Kimiaki Kashiwagi

Low-Resonant-Frequency Micro Electret Generator for Energy Harvesting Application

A vibration-driven electret generator has been developed for energy harvesting applications. By using parylene as the spring material, a low-resonant-frequency MEMS generator is realized. Electrostatic levitation is adopted for the gap control. Large in-plane amplitude of 0.5 mm at the resonant frequency as low as 21 Hz has been achieved. We also demonstrate electret-powered operation of LED using a low-power-consumption impedance conversion circuit.

Nano-cluster-enhanced high-performance perfluoro-polymer electrets for energy harvesting

Development of high-performance electret materials is required to obtain a large power output of the electrostatic vibration-driven energy harvesters. In this study, by introducing aminosilane derivatives into CYTOP-based perfluorinated polymer film, we have successfully formed nano-clusters containing the organic siloxanes in the polymer electrets. Using small-angle x-ray scattering, tapping mode AFM and SEM analysis, the existence of such nano-clusters has been directly observed in the CYTOP film. It is suggested that the observed nano-clusters serve as the charge trap site and enhance the surface charge density and the thermal stability of the trapped charges. As a polymer electret, an extremely high surface charge potential of −1.6 kV with the 15 µm thick film has been obtained under the optimum condition of corona charging.

Diethynyl naphthalene derivatives with high ionization potentials for p-channel and n-channel organic field-effect transistors

We have developed and characterized diethynyl naphthalene derivatives with high ionization potentials, 2,6-bis [(naphthalen-2-yl)ethynyl]-naphthalene (BH-202) and 2,6-bis[(heptafluoronaphthalen-2-yl)ethynyl]-naphthalene (BF-202) for new organic semiconductors. Using x-ray diffraction, we have found that thin films of the two organic semiconductors have a high degree of molecular order. Organic field-effect transistors (OFETs) with BH-202 films showed p-type characteristics. By the optimization of the fabrication process, the device exhibited a high field-effect hole mobility up to 0.12 cm2 V−1 s−1 and a high on/off current ratio of 3.3 × 105. On the other hand, OFETs with BF-202 films showed n-type characteristics. The field-effect electron mobility was calculated to be 3.4 × 10−3 cm2 V−1 s−1 and the on/off current ratio was 5.4 × 103.

Oil droplet manipulation using liquid dielectrophoresis on electret with superlyophobic surfaces

We propose a novel low-voltage droplet manipulation method “liquid dielectrophoresis on electret (L-DEPOE)” with superlyophobic surfaces (SLS), which enable high contact angle and low flow friction for water and oil. Charge stability of electret in liquid is much improved with new polymer coating, and SLS with electrodes are successfully fabricated, showing high mechanical robustness and extreme repellence for hexadecane droplets even with fast droplet motion. Low adhesion and contact angle hysteresis of SLS for oil droplets are experimentally demonstrated, indicating low motion resistance of droplet on SLS.

Liquid-crystalline behavior and ion transport properties of block-structured molecules containing a perfluorinated ethylene oxide moiety complexed with a lithium salt

AbstractThe liquid-crystalline behavior of fluorinated block-structured molecules and the ion transport properties of their complexes with a Li salt have been examined. The block-structured molecules comprise a perfluorinated oligo (ethylene oxide) moiety containing a terminal methyl carbonate or a terminal hydroxyl group and an octadecyl moiety. These molecules exhibit highly ordered smectic phases. The fluorinated molecule with a terminal methyl carbonate possesses an isotropization temperature lower than that of the analogous non-fluorinated molecule. The fluorinated molecule complexed with a Li salt shows ionic conductivities on the order of 10−6 S cm−1 in the smectic phase formed at ambient temperature, while conductivities on the order of 10−5 S cm−1 are observed in the isotropic phase.A perfluorinated oligo (ethylene oxide) monoalkyl ether containing a terminal methyl carbonate has been developed for potential application as quasi-solid-state electrolytes for Li-ion batteries. The fluorinated block-structured molecule self-assembles to form nanosegregated bilayer structures, which can be used for anisotropic Li ion transport when complexed with a Li salt. The complex shows ionic conductivities on the order of 10−6 S cm−1 in the ordered smectic phase formed at ambient temperature.

Nano-cluster-enhanced high performance perfluoropolymer electrets

In conclusion, we have proposed a new strategy for improving performance of polymer electrets using aminosilane based nano clusters. By adding animosilane into CYTOP electrets, nano clusters of about 20 nm are formed in the film. It is clearly shown that the nano clusters are critically important to obtain higher surface charge density and better thermal stability of electrets.

Micro power generator with high-performace polymer electret

Vibration-driven electret generator has been developed with the aid of MEMS technologies. Parylene high-aspect-ratio spring is successfully microfabricated to support an in-plane seismic mass. Resonant frequency as low as 37Hz has been achieved with a large in-plane amplitude of 1 mm. With our early prototype, we have obtained 21 Vp-p voltage output.