Hiroyuki Mitsuya

A novel vibrational energy harvester with electric double layer electrets

We propose a new type of vibrational energy harvester with an electric double layer (EDL) electrets. Instead of using any external bias-voltage source or dielectric layer on top of the metal electrode to sustain EDL, we succeed to anchor the ions to polymer network to form the EDL electrets. By changing contact area between the EDL electrets and the electrode, large electric current is generated in the circuit. Owing to extremely large capacitance of the EDL electret, vibrational energy harvesters have the unique capability to leverage the high- density charge accumulation to the electrode and obtained current density becomes as high as 200 μA/cm2 with output voltage of 1V even with low frequency vibrations as low as 1 Hz.

Electrostatic vibrational energy harvester with ionic liquid and potassium-ion-electret

This paper introduces an electrostatic vibrational energy harvester with an effective electrode distance of ~1 μm by utilizing the 1-nm-thick insulating gap that an ionic liquid forms, followed by a proof-of-concept with an AC current of 100 nA (peak-to-peak) and a voltage of 100 mV (peak-to-peak) generated from our prototype.

A Bistable Comb-Drive Electrostatic Actuator Biased by the Built-In Potential of Potassium Ion Electret

A new bistable micro-electro-mechanical systems actuator functioned by the potassium ion electret technique is presented. We utilize a three-terminal comb-drive actuator with a built-in electret potential. We first describe the operation principle of the bistable device that is driven by a pulse and/or step-function voltage. We next explain the fabrication results and the procedure of the electret polarization. Device operation is demonstrated to determine the switching characteristics from one stable state to another with a 12 V pulse voltage of 300 μs duration. We also establish bistable switching operation with a step voltage of 5 V or less, which is manageable by a battery for portable equipment. Discrepancy of switching characteristics between the theory and the experiments is discussed from a point of view on the fringe electrical fields between the comb electrodes.

Soft Electret Gel For Low Frequency Vibrational Energy Harvesters

A soft electret material was obtained by solidifying ionic liquid in a polymer network and immobilizing cations (+) on the surface. When a piece of soft electret gel is sandwiched between a pair of electrodes, a large amount of charge is induced in an electrical-double-layer capacitor (1.0-10 μF/cm2) appearing at the interface of the electrode and the ionic liquid gel without an external voltage source. By retracting the electrode repeatedly, we obtained a current output of a few μAp-p/cm2 stably.

Triboelectric energy harvesting with surface-charge-fixed polymer based on ionic liquid

Abstract A novel triboelectric energy harvester has been developed using an ionic liquid polymer with cations fixed at the surface. In this report, the fabrication of the device and the characterization of its energy harvesting performance are detailed. An electrical double layer was induced in the ionic liquid polymer precursor to attract the cations to the surface where they are immobilized using a UV-based crosslinking reaction. The finalized polymer is capable of generating an electrical current when contacted by a metal electrode. Using this property, energy harvesting experiments were conducted by cyclically contacting a gold-surface electrode with the charge fixed surface of the polymer. Control experiments verified the effect of immobilizing the cations at the surface. By synthesizing a polymer with the optimal composition ratio of ionic liquid to macromonomer, an output of 77 nW/cm2 was obtained with a load resistance of 1 MΩ at 1 Hz. This tuneable power supply with a μA level current output may contribute to Internet of Things networks requiring numerous sensor nodes at remote places in the environment.

A broad-band vibrational energy harvester utilizing symmetrical comb-drives coupled with strong charged electret

We have developed a broad-band vibrational energy harvester by utilizing symmetrical comb-drive electrodes that were coated with solid-ion electrets made of potassium-doped thermal silicon oxide film. The device was sealed in a vacuum package for high energy conversion to eliminate mechanical losses. With this device, we capture vibrations of any frequency as well as of impulse motions for power generation.

New type of energy harvester with electric double layer electrets

We demonstrated a new type of vibrational energy harvester based on an electric double layer (EDL) electret. By mechanically modulating interfacial area between vibrating electrode and the EDL electret, the electrode is electrostatically charged and discharged at different phases and electric current is generated. Owing to extremely large capacitance of the EDL electret, vibrational energy harvesters have the unique capability to electrostatically leverage the high-density charge accumulation to the electrode and obtained current density become as high as 9 μA/cm2 even with low frequency vibration as low as 1 Hz.

Design and fabrication of a high-power energy harvester based on a three-ports comb drive mechanism for large displacement

This paper presents a high-power energy-harvesting device based on a three-ports electrostatic comb-drive mechanism. A symmetric electrodes structure is used to reduce the binding electrostatic force, thereby allowing large displacement of the oscillator mass at a low acceleration. With an acceleration of 0.27 G at 125 Hz, output power of 150.3 μW was obtained, where mechanical stroke of over 209 μm was confirmed by using a high-speed camera.

A three-ports structure for electrostatic energy-harvester to lower constraint force and to enhance fast storage

In this paper, we discuss on a new method to increase the output current of energy-harvesting device by using a symmetric three-ports electrostatic comb-drive mechanism that enables fast charging of battery. A symmetric electrodes layout is used to reduce the binding electrostatic force that constraints the movable electrodes, thereby allowing a formation of a high electret potential without electrostatic collapse. The output short-circuit current is increased by 2.8 times by increasing the electret potential from the −120 V to −300 V. At the same time, the output impedance is also decreased 5 MΩ. The lowered constraint force enables energy harvester operation at a low acceleration range of 0.1 G or less.

A Frequency-Independent Vibrational Energy Harvester using Symmetrically Charged Comb-Drive Electrodes with Heavily Doped Ion Electrets

An energy harvester has been developed to efficiently earn energy from both cyclic and impulse vibrations by using a symmetric pair of comb-electrodes that are heavily doped with potassium-ions to form electrets. By equalizing the electromechanical forces on the opposing comb-drives, energy conversion efficiency is enhanced for both impulses and broad-frequency harmonic vibrations.