Microwave (MW) heating has received attention as a new heating source for various industrial processes. Some materials are expected to be a more effective absorber of MW, and graphite is observed as a possible candidate for high-temperature application. We investigated the dependence of the aspect ratio of graphite fibers on both their heating behavior and permittivity under a 2.45 GHz MW electric field. In these experiments, both loss tangent and MW heating behavior indicated that the MW absorption of conductive fibers increases with their aspect ratio. The MW absorption was found to be well accounted for by the application of a spheroidal model for a single fiber. The absorption of graphite fibers decreases with increasing aspect ratio when the long axis of the ellipsoid is perpendicular to the electric field, whereas it increases with the aspect ratio when the long axis is parallel to the electric field. The analytical model indicated that MW heating of the conductive fibers is expected to depend on both the shape and arrangement of the fibers in the electric field.
EV trucks are effective means for solving environmental problems. Microwave wireless power transmission (MWPT) solves the problems with large capacity batteries in EV trucks. MWPT present automatic car charging for moving car systems. We are focusing on rectifiers used in the receiving units of the new MWPT system. Their rectifiers should be small and high rf-dc conversion efficiency enough for installing to the EV trucks. The limitation output power is 8.7 W or more within 50 mm square. We design a 5.8 GHz single-shunt rectifier with Class-R filter which satisfies the desired requirements by using numerical simulations. The Class-R filter is a novel output filter developed in recent years, and is used in amplifiers. We achieve the size reduction and improvement of efficiency of the rectifier by this filter. The simulation result shows the maximum rf-dc conversion efficiency of 87.1 % and 16.8 W within 50 mm square.
To meet the increasing power demands of microwave industries and scientific innovations, a dual-way magnetron (MGT) power-combining system based on an asymmetric H-plane tee combined with closed-loop phase compensation (CLPC) was developed and tested. Only one external injection was used, which could lock both frequencies of the two MGTs via the port coupling of the asymmetric H-plane tee. Additionally, phase control was achieved simultaneously in both MGTs. By tuning the external frequency, the frequencies of both MGTs could be shifted to optimize the power-combining efficiency. The optimal combining efficiency was 95.7%. By adjusting the phase of the external injection, the phase for the combining output was adjusted with a control scope in the 0°-360° range. The phase noise level of the combined output was largely inhibited by implementing only one closed-loop phase compensation subsystem. The phase jitter was limited to approximately ±0.5°, and spur suppression ratios of -61.0 dBc/Hz at 10 Hz, -80.9 dBc/Hz at 100 Hz, -91.6 dBc/Hz at 1 kHz, and so on were achieved. Moreover, we deduced the corresponding power-combining theories in the asymmetric H-plane tee and noise reduction using the closed-loop compensation method. The numerical predictions qualitatively agreed with the experimental results. Additionally, this research reveals that the proposed techniques have great potential for future power-combining systems because they provide higher power output and noise reduction.
Wireless power transmission technology via microwave (microwave power transmission ; MPT) was advanced from 1960's and many researchers which had a dream to realize the space solar power satellite/station (SPS). In Japan, many kinds of the SPS were proposed and designed in recent ten years. We will show the newest Japanese SPS and its characteristics. We also show some results of the recent Japanese MPT experiments, ubiquitous power source, MPT for moving rover, wireless charging system of electrical vehicle.
This study presents a novel waveguide slot array with a code-division multiplexing function for single RF chain digital beamforming. The proposed antenna is comprised of a rectangular metallic waveguide's bottom part and a multilayer printed circuit board (PCB) with the rectangular waveguide's top wall and slot apertures. Multiple pairs of two symmetric longitudinal slots are etched on the metal surface of the PCB, and a PIN diode is mounted across each slot. The received signals of each slot pair are multiplexed in a code-division multiplexing fashion by switching the diodes' bias according to the Walsh Hadamard code, and the original signals are then recovered through a despreading process in the digital domain for digital beamforming. A prototype antenna with eight slot pairs has been fabricated and tested for proof of concept. The measured results show the feasibility of the proposed antenna.
The SPS (Space Solar Power Satellite/Station) will be clean base-load power station in space. It will be hugest space system and we need high efficient, huge, high accurate, light weight and inexpensive phased array for the SPS in order to transmit energy generated in space from space to ground. We have proposed and developed a phase controlled magnetron (PCM) with injection locking and PLL technique for the high efficient, light weight and inexpensive phased array. It has still weak points; (1) it contains approximately 10% power loss at circulator for injection locking, (2) we need phase shifter in each PCMs for the phased array. In order to solve the weak points, we propose a magnetron phased array with mutual injection locking. For the magnetron phased array, we only use two PCMs with phase shifters and the other components are self-oscillated and mutual injection locked magnetrons. In this paper, we propose new formula for the magnetron phased array with mutual injection locking. We also show experimental results of beam direction control with the magnetron phased array with mutual injection locking.
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