Broadband GaN HEMT power amplifier with shunt feedback and push-pull technique is presented. Shunt-feedback and push-pull realization provide the robust broad bandwidth covering VHF and low-frequency UHF bands. The benefit due to the feedback presented in the form of shunt-shunt network on power amplifier module provides the linear and broadband frequency amplification. The push-pull topology provides enhanced efficiency and high power generation along with the cancellation of the second-order distortions and thus helps to compensate for the efficiency degradation from the feedback. These techniques are realized with the help of in-house designed GaN HEMT transistor, which provides high power, good efficiency, and high reliability (bandgap). The prototype was realized in 0.25μm GaN HEMT, operates from 30 to 520 MHz, and dissipates 650mA of quiescent current from 28V supply. The power amplifier delivered a saturated output power of > 43 dBm and < 1 dB gain flatness with > 40% PAE at 20W output power. The linearity of the amplifier was characterized by the two-tone injection test. The measurement result shows that the 3rd-order intermodulation distortion tones are below -35 dBc at 35 dBm output power.

This study aimed to develop an accelerated concrete curing method based on induction heating (IH) technology. The proposed curing method provides improved heating efficiency and safety since it directly heats only the metallic forms in a non-contacting manner. It also has the advantage of being capable of heating the concrete according to a desirable heating scenario. The effects of several parameters on its performance were evaluated using a finite element method (FEM)-based thermal analysis and heating performance tests. The FEM analysis revealed the steel form to be appropriate for the IH system. The analysis also revealed that equally spaced three-turn coils yielded increased temperature uniformity in the steel form, which was verified by results of the steel form heating experiments. Furthermore, the minimum temperature generated in the form was sufficient for concrete curing. The efficiency of the use of IH for concrete curing and the effects of curing parameters were further investigated through compression tests after applications of various curing methods and by examining the temperature distributions during curing. The test results revealed early strength development even under water freezing conditions. This demonstrated the effectiveness of IH for concrete curing in cold weather. However, the efficiency decreased when the cross-sectional dimension of the specimen increased. The test results also verified that the maximum temperature and duration of induction heat curing affect the early age strength of concrete.

The objective of this study is to develop a new vibration-free excavation method based on vermiculite expansion for rock cracking and to evaluate the performance of the heating system via elastic wave monitoring. Natural vermiculites expand rapidly in volume when heated above 800 °C. MgO powder is used to evenly transmit the surface temperature of a heater rod, which can attain high temperatures rapidly, to the vermiculites. The insertion direction of the heater rod greatly affects the expansion pressure. Three cuboid rock specimens are prepared and equipped with the heating system at different hole-to-face distances. Crack propagation is monitored by a pair of disk-shaped piezoelectric transducers. For short hole-to-face distances, the wave velocity and maximum amplitude rapidly decrease after certain time. For the greatest hole-to-face distance, the shear wave velocity remains constant during the test, while the maximum amplitude decreases after a certain time. The time taken for the velocity and amplitude of the shear waves to decrease reasonably corresponded to that taken for detectable crack propagation to occur on the surface of the rock specimen. The proposed method and materials may be useful from the viewpoints of rapid expansion, economy, and crack control.

Multiple exciton generation solar cells exhibit low power conversion efficiency owing to non-radiative recombination, even after the generation of numerous electron and hole pairs per incident photon. This paper elucidates the non-idealities of multiple exciton generation solar cells. Accordingly, we present mathematical approaches for determining the quantum yield to discuss the non-idealities of multiple exciton generation solar cells by adjusting the delta function. We present the use of the Gaussian distribution function to present the occupancy status of carriers at each energy state using the Dirac delta function. Further, we obtained ideal and non-ideal quantum yields by modifying the Gaussian distribution function for each energy state. On the basis of this approach, we discuss the material imperfections of multiple exciton generations by analyzing the mathematically obtained quantum yields. Then, we discuss the status of radiative recombination calculated from the ratio of radiative to non-radiative recombination. Finally, we present the application of this approach to the detailed balance limit of the multiple exciton generation solar cell to evaluate the practical limit of multiple exciton generation solar cells.

Integrated process and device simulations were used to predict sub-45nm Strained-Si/Si_0.8Ge_0.2 device performance. Physically-based process models, generalized from Si to strained-Si and SiGe, describe dopant implantation and diffusion, including amorphization, defect interactions and evolution, as well as dopant-defect interactions. The models are used within a unique simulation tool to reproduce the electrical characteristics of Si/SiGe devices.

In this paper, we propose an innovative, environmentally friendly, and efficient technology for concrete curing through induction heating. This technology is complemented by a comprehensive design methodology aimed at achieving uniform heating across the formwork surface. Induction heating concrete curing is a new approach based on the principle of electromagnetic induction for the purpose of concrete curing, and it offers improved heating efficiency and safety in formwork heating. However, the heating range of the formwork surface is limited depending on the induction heating coil. Thus, we introduce a coil structure derived from evaluations of formwork’s surface temperature distribution through finite element analysis simulations. Heating experiments were conducted on formwork without concrete and formwork with concrete, using a coil designed through simulation. In the experiment without concrete, a uniform temperature distribution was confirmed with a small temperature deviation of 4.28°C. For the experiment with concrete, induction heating experiments and steam curing experiments were conducted at low and room temperatures to compare surface temperature distribution, power consumption, and concrete strength. The experimental results show that room temperature induction heating has 11.39% higher strength and 41.86% less power consumption than low temperature induction heating curing. It also shows 3.51% higher strength and 30.56% less power consumption than steam curing. Room temperature induction heating curing is superior to steam curing in terms of strength and power consumption. Also, although low temperature induction heating curing has lower performance than steam curing, the difference is not significant, so it can be a feasible alternative.