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The magnetron, a vacuum tube, is currently the usual high-power microwave power source used for microwave heating. However, the oscillating frequency and output power are unstable and noisy due to the low quality of the high-voltage power supply and low Q of the oscillation circuit. A heating system with enhanced reliability and the capability for control of chemical reactions is desired, because microwave absorption efficiency differs greatly depending on the object being heated. Recent studies on microwave high-efficiency power amplifiers have used harmonic processing techniques, such as class-F and inverse class-F. The present study describes a high-efficiency 100 W GaN-HEMT amplifier that uses a harmonic processing technique that shapes the current and voltage waveforms to improve efficiency. The fabricated GaN power amplifier obtained an output power of 50.4 dBm, a drain efficiency of 72.9%, and a power added efficiency (PAE) of 64.0% at 2.45 GHz for continuous wave operation. A prototype microwave heating system was also developed using this GaN power amplifier. Microwaves totaling 400 W are fed from patch antennas mounted on the top and bottom of the microwave chamber. Preliminary heating experiments with this system have just been initiated. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ

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A photosensing circuit using thin-film transistors (TFTs) for a retinal prosthesis has been developed. First, the TFTs that are low-temperature polycrystalline silicon (poly-Si) TFTs are fabricated on a transparent substrate, which enables us to build an epiretinal implantation system without using any extracorporeal cameras. Then, the photosensing circuit is fabricated by connecting a p/i/n-type phototransistor and a ring oscillator, which provides stimulating current pulses with an oscillation frequency dependent on light illuminance. In particular, the device structure of the p/i/n-type phototransistor is designed well on the basis of device physics, and the configuration of the photosensing circuit on the basis of device characteristics. Subsequently, a wireless power transfer system is architected by magnetic resonance coupling. Finally, a retinal prosthesis is produced by assembling the photosensing circuit and wireless power transfer system, and the stimulating performance is confirmed in an in vitro experiment, which suggests a future possibility of this retinal prosthesis.