A solar pumped laser system with 7%–9% slope efficiencies has been developed. A Fresnel lens (2×2 m, f=2000 mm) is mounted on a two-axis sun tracker platform and focuses solar radiation toward laser cavity, which embraces Cr:Nd:yttrium aluminum garnet ceramic rod. The maximum emitted laser power is 80 W corresponding to maximum total area performance of 20 W/m2 for the Fresnel lens area. This solar laser system would be used as a section of power plant in a magnesium energy cycle as a cost-efficient solar energy converter. Using direct solar radiation into laser, 4.3% net conversion efficiency has been achieved.
We propose a propulsion concept to drive a microairplane by laser that can be used for observation of climate and volcanic eruption. Since it does not have to develop thrust for vertical takeoff, and it has no engine in the normal sense, the microairplane can be very light, with its payload consisting only of observation and communication equipment. In order to demonstrate the concept, we succeeded in flying a paper microairplane driven by a 590 mJ, 5 ns pulse yttrium–aluminum–garnet laser that impinges on a double-layer “exotic target.” The coupling efficiency agrees well with simulations and with experiments.
Long-range (LoRa) wireless communication technology has been widely used in many Internet-of-Things (IoT) applications in industry and academia. Radio wave propagation characteristics in forested areas are important to ensure communication quality in forest IoT applications. In this study, 920 MHz band propagation characteristics in forested areas and tree canopy openness were investigated in the Takakuma experimental forest in Kagoshima, Japan. The aim was to evaluate the performance of the LoRa 920 MHz band with spreading factor (SF12) in a forested hilly area. The received signal strength indicator (RSSI) was measured as a function of the distance between the transmitter antenna and ground station (GS). To illustrate the effect of canopy openness on radio wave propagation, sky view factor (SVF) and a forest canopy height model were considered at each location of a successfully received RSSI. A positive correlation was found between the RSSI and SVF. It was found that between the GS and transmitter antenna, if the canopy height is above 23 m, the signal diffracted and RSSI fell to −120 to −127 dBm, so the presence of the obstacle height should be considered. Further research is needed to clarify the detailed tree density between the transmitter and ground station to propose an optimal propagation model for a forested environment.
We have succeeded in drilling a crack-free high-aspect-ratio hole through glass using a YAG laser of 1 µm wavelength, 5 ns pulse width and 30–630 mJ/pulse. The hole is 25.5 mm long with 500 µm radius and no crack is observed even under atmospheric conditions. This success is due to the use of a translucent adhesive tape pasted on the glass surface in which the temperature is controlled and thermal stress is reduced. Computer simulation revealed the mechanism of the phenomena.
Due to the massive fossil fuel consumption, the increasing CO2 concentration seriously brings about the global warming. The decomposition of metal oxide to metal and oxygen is an attractive process for energy storage. We succeeded in dissociating magnesium oxide by using continuous wave (cw) CO2 laser radiation. Starting from magnesium oxide, magnesium was produced by laser-induced vaporization. The ablated vapor temperature was measured approximately 5000 k, where the MgO was dissociated to Mg and O atom thermally. A copper plate was placed to collect the high-temperature vapors, accumulating Mg as solid deposit. Unfortunately, the gaseous products reacts together to reform MgO when temperature is lowered. As vapors cool, it is necessary to quench the gaseous products fast enough to avoid recombination. The reducing agents, Zr, Si and C and Ar gases were employed to prevent magnesium re-combination with Oxygen. In these experiments, the reduction efficiency dependence on the carbon mole ratio (MgO:C=1:0-3) was measured when carbon was used as a reducing agent. The results show the reduction efficiency improves with increasing carbon molar ratio, which reachs the maximum at 54 wt% when the ratio of MgO:C is 1:2. This ratio is lower than 1:3 (MgO:C) in industrial process of Carbothermic (Reduction efficiency is 53 wt%). Consequently, utilizing the solar pumped laser in Mg production will reduce the carbon oxide emission efficiently.
In previous papers, we reported the laser propulsion using water for micro airplane. In order to apply this concept in high altitude like Stratosphere, we need to insulate the water layer from low pressure, otherwise water begins to evaporate and finally freezes because of latent heat. For this purpose, we here propose an "air curtain" using a high-speed air flow to insulate. We have done simulation and experiments on this concept. Especially, the result of simulations based on C-CUP Method show that both density and speed of the flow influences the ability to sustain the pressure of the cell. The result shows that Air-Curtain is effective for the laser propulsion in Stratosphere.
