Microwave Metamaterial Applications using Complementary Split Ring Resonators and High Gain Rectifying Reflectarray for Wireless Power Transmission

In the past decade, artificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in mobile communications, medical, and optoelectronics applications. To realize this potential, more research on metamaterials is needed. In this dissertation, new bandpass filter and diplexer as microwave metamaterial applications have been developed. Unlike the conventional complementary split ring (CSRR) filters, coupled lines are used to provide larger coupling capacitance, resulting in better bandpass characteristics with two CSRRs only. The modified bandpass filters are used to deisgn a compact diplexer. A new CSRR antenna fed by coplanar waveguide has also been developed as another metamaterial application. The rectangular shape CSRRs antenna achieves dual band frequency properties without any special matching network. The higher resonant frequency is dominantly determined by the outer slot ring, while the lower resonant frequency is generated by the coupling between two CSRRs. The proposed antenna achieves about 35 percent size reduction, compared with the conventional slot antennas at the low resonant frequencies. As a future alternative energy solution, space solar power transmission and wireless power transmission have received much attention. The design of efficient rectifying antennas called rectennas is very critical in the wireless power transmission system. The conventional method to obtain long distance range and high output power is to use a large antenna array in rectenna design. However, the use of array antennas has several problems: the relatively high loss of the array feed networks, difficultiy in feeding network design, and antenna radiator coupling that degrades rectenna array performance. In this dissertation, to overcome the above problems, a reflectarray is used to build a rectenna system. The spatial feeding method of the reflectarray eliminates the energy loss and design complexity of a feeding network. A high gain rectifying antenna has been developed and located at the focal point of the reflectarray to receive the reflected RF singals and genterate DC power. The technologies are very useful for high power wireless power transmission applications

Experimental Field Tests and Finite Element Analyses for Rock Cracking Using the Expansion of Vermiculite Materials

In the previous research, laboratory tests were performed in order to measure the expansion of vermiculite upon heating and to convert it into expansion pressure. Based on these test results, this study mainly focuses on experimental field tests conducted to verify that expansion pressure obtained by heating vermiculite materials is enough to break massive and hard granite rock with an intention to excavate the tunnel. Hexahedral granite specimens with a circular hole perforated in the center were constructed for the experimental tests. The circular holes were filled with vermiculite plus thermal conduction and then heated using the cartridge heater. As a result, all of hexahedral granite specimens had cracks in the surface after 700-second thermal heating and were finally spilt into two pieces completely. The specimen of larger size only requires more heating time and expansion pressure. The material properties of granite rocks, which were obtained from the experimental tests, were utilized to produce finite element models used for numerical analyses. The analysis results show good agreement with the experimental results in terms of initial cracking, propagation direction, and expansion pressure

The HIF-1/glial TIM-3 axis controls inflammation-associated brain damage under hypoxia.

Inflammation is closely related to the extent of damage following cerebral ischaemia, and the targeting of this inflammation has emerged as a promising therapeutic strategy. Here, we present that hypoxia-induced glial T-cell immunoglobulin and mucin domain protein (TIM)-3 can function as a modulator that links inflammation and subsequent brain damage after ischaemia. We find that TIM-3 is highly expressed in hypoxic brain regions of a mouse cerebral hypoxia-ischaemia (H/I) model. TIM-3 is distinctively upregulated in activated microglia and astrocytes, brain resident immune cells, in a hypoxia-inducible factor (HIF)-1-dependent manner. Notably, blockade of TIM-3 markedly reduces infarct size, neuronal cell death, oedema formation and neutrophil infiltration in H/I mice. Hypoxia-triggered neutrophil migration and infarction are also decreased in HIF-1α-deficient mice. Moreover, functional neurological deficits after H/I are significantly improved in both anti-TIM-3-treated mice and myeloid-specific HIF-1α-deficient mice. Further understanding of these insights could serve as the basis for broadening the therapeutic scope against hypoxia-associated brain diseases

Thermally or Optically Powered Actuation of Liquid Crystal Elastomers

Soft actuator is a promising candidate for replacing a traditional rigid materials-based actuator when the actuating system requires human compatibility, large degree of freedom for the motion, low fabrication cost, and simple body structure. Among many soft materials, liquid crystal elastomer (LCE) is one of the most advantageous soft active material due to their large macroscopic deformability coupled with molecular level anisotropy. Patterning of LCE with precise control of molecular alignment can generate diverse actuations. In addition, different types of actuation of LCE can be induced by various external stimuli such as heat or light.In this study, we demonstrate radially patterned LCE with predesigned stretch field using a strain engineering technique which is facile, effective, and does not require any sophisticated setup. The radially patterned LCE exhibits fully reversible undulating deformation upon heating or swelling, attributed to the constrained expansion of radially patterned LCE in hoop direction. By applying the strain engineering technique, we design different LCE structures which exhibit diverse actuations like bending, rolling, crawling, or jumping. Incorporation of carbon nanotube (CNT) in the LCE allows photoresponsivity of LCE-CNT composite due to the photothermal effect of CNT. We prepare LCE-CNT rod with molecular alignment in its longitudinal direction which shows heliotropic behavior with multi-directional bending under the light irradiation rather than conventional uni- or bi-directional bending. The bending is induced by the contraction gradient of LCE-CNT rod in thickness which is maximized on the surface towards light, so the bending direction can be tuned by controlling the position of light source. Using the similar LCE or LCE- CNT rod, we show unusual rolling phenomena in which the LCE or LCE-CNT rod keeps rolling while maintaining its initial curvature in the same direction continuously induced by simply placing them on a homogeneously hot flat surface or under the visible light irradiation. Such non- intuitive autonomous rolling phenomena is induced by coupling of inhomogeneously distributed supporting force and gravity, which is triggered by continuous bending deformation of the rod during rolling. We also design a light-driven soft robot based on an arch shape LCE-CNT structure with magnet pieces on each end that performs crawling, squeezing, and jumping motions inspired by deformation traveling of inchworm locomotion and power amplification mechanism of jumping fly larva. The soft robot can perform different motions by switching its shape between arch and closed loop shape under different light irradiation modes, which enables fully reversible biomimetic motions

Investigation of Key Parameters of Rock Cracking Using the Expansion of Vermiculite Materia

The demand for the development of underground spaces has been sharply increased in lieu of saturated ground spaces because the residents of cities have steadily increased since the 1980s. The traditional widely used excavation methods (i.e., explosion and shield) have caused many problems, such as noise, vibration, extended schedule, and increased costs. The vibration-free (and explosion-free) excavation method has currently attracted attention in the construction site because of the advantage of definitively solving these issues. For such reason, a new excavation method that utilizes the expansion of vermiculite with relatively fewer defects is proposed in this study. In general, vermiculite materials are rapidly expanded in volume when they receive thermal energy. Expansion pressure can be produced by thermal expansion of vermiculite in a steel tube, and measured by laboratory tests. The experimental tests are performed with various influencing parameters in an effort to seek the optimal condition to effectively increase expansion pressure at the same temperature. Then, calibrated expansion pressure is estimated, and compared to each model. After analyzing test results for expansion pressure, it is verified that vermiculite expanded by heat can provide enough internal pressure to break hard rock during tunneling work

Multiple Exciton Generation Solar Cells: Numerical Approaches of Quantum Yield Extraction and Its Limiting Efficiencies

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

Investigation of Key Parameters of Rock Cracking Using the Expansion of Vermiculite Materia

The demand for the development of underground spaces has been sharply increased in lieu of saturated ground spaces because the residents of cities have steadily increased since the 1980s. The traditional widely used excavation methods (i.e., explosion and shield) have caused many problems, such as noise, vibration, extended schedule, and increased costs. The vibration-free (and explosion-free) excavation method has currently attracted attention in the construction site because of the advantage of definitively solving these issues. For such reason, a new excavation method that utilizes the expansion of vermiculite with relatively fewer defects is proposed in this study. In general, vermiculite materials are rapidly expanded in volume when they receive thermal energy. Expansion pressure can be produced by thermal expansion of vermiculite in a steel tube, and measured by laboratory tests. The experimental tests are performed with various influencing parameters in an effort to seek the optimal condition to effectively increase expansion pressure at the same temperature. Then, calibrated expansion pressure is estimated, and compared to each model. After analyzing test results for expansion pressure, it is verified that vermiculite expanded by heat can provide enough internal pressure to break hard rock during tunneling work

Expansion-Induced Crack Propagation in Rocks Monitored by Using Piezoelectric Transducers

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

Development of a Novel Concrete Curing Method Using Induction Heating System

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