Frequency-Selective Surfaces for Microwave and Terahertz Spectra

FREQUENCYselective surfaces (FSSs) made of subwavelength periodic structures have been broadly applied in various electromagnetic applications. Their main function is to tailor the frequency response to incident waves, or to obtain electromagnetic (EM) properties that do not exist in homogeneous natural materials. When increasing the design complexity to enhance performance, however, the computation cost hikes dramatically in analysis and synthesis as additional design variables are introduced. In contrast to such complexity increase, this thesis aims at systematically developing effective and efficient design and optimization approaches for FSS-based structures adopting fundamental unit-cell patterns, such as rectangular patches, rings and grids. Additionally, impedance matching to free space is thoroughly investigated and adapted as a means towards performance improvement in both absorbers and filters. Hereby, multiple designs are demonstrated with realizations from the microwave to the terahertz (THz) frequency spectrum. In spite of their simplicity, the proposed designs outperform the state-of-the-art counterparts in the literature by fully exhausting the potentials of their spatial structures and material attributes. Specifically, Chapter 3 challenges a common belief that adding an impedance matching superstrate to an absorber will broaden its operation bandwidth at the cost of increased total thickness profile. This Chapter proves that it is possible to increase the bandwidth-to-thickness ratio. The concept is firstly demonstrated at the circuit level, and then verified by full-wave simulations. The optimization process can be illustrated with an admittance Smith chart. The distinctive performance of the proposed single- FSS-layer absorber is justified with a figure of merit (FoM) which comprehensively involves the relative bandwidth, the normalized thickness and the level of reflectivity. In Chapter 4, a semi-analytical approach for absorber design is developed by systematically combining analytical, empirical and numerical techniques. The optimization space can be simplified from millions of exhaustive search cases to merely a few hundreds of seed simulations, by exploiting insights into the linearity, scalability and independence regarding the major components of an absorber. For any specified level of absorption and operation bandwidth, the obtained semi-analytical algorithm enables fast synthesis of an absorber with a minimal thickness. Both absorbers proposed in the above chapters have been realized using patterned resistive layers and experimentally validated under oblique angles of incidence for transverse-electric (TE) and transversemagnetic (TM) modes. The design methods can be readily expanded for structures of multiple FSS layers. In the terahertz frequency range, common microfabrication technologies do not accommodate those resistive inks used for silk-printing lossy FSS patterns. As an alternative, a sub-skin-depth metal layer with nanoscale thickness is proposed in Chapter 5 to meet this requirement. The Drude model is adopted to simulate the ultra-thin metallic FSS, as it satisfactorily describes the frequency dependent properties of noble metals. The proposed absorber is robust to dimensional tolerance in fabrication and attains a stable absorption bandwidth under oblique impinging waves. In Chapter 6, a frequency reconfigurable terahertz bandpass filter is proposed and experimentally verified. It includes two identical double-layer FSSs separated by an air spacer which can be mechanically tuned. The filter allows a highly selective transmission sweeping across a wide spectrum. The underlying mechanism can be explained from two perspectives, namely through interpretation as Fabry-Perot resonant cavity and through consideration of the admittance Smith chart. The designed device is insensitive to fabrication tolerances and stable to oblique angle of incidence. The fabricated filter confirms a 40% tuning range and less than 1 dB insertion loss. This design is among the first few practical reconfigurable terahertz bandpass filters reported in the literature. Overall, the research outcomes suggest that developing complicated FSS patterns with a large number of degrees of freedom is unnecessary in many cases if the potential of fundamental geometries is fully exploited through rigorous algorithmic optimization methods. The design approaches illustrated in this thesis are generic to all FSS-based structures and can potentially be extended to multi-FSS layers and impedance surfaces, to satisfy performance requirements in specific applications.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

Experimental and numerical study on self-sustaining performance of a 30-kW micro gas turbine generator system during startup process

The safe startup of micro gas turbine (MGT) generator system is the premise of normal operation. The whole start-up process contains motor startup, ignition, speed acceleration, motor switching to generator and power acceleration. Motor switching to generator happens at the self-sustaining state, which is significant to safe start-up process. However, characteristics of MGT generator system at self-sustaining state are hardly to investigate due to the lack of performance maps and complete experiments. Therefore, this work analyzed start-up schedule and presented a theoretical and experimental study on the self-sustaining performance of MGT generator system, based on the self-designed 30 kW MGT generator system built in Jiangjin Turbocharger Plant, China. The self-sustaining speed boundary and fuel consumption area is determined from the aspects of safe startup. A novel principle for determining the self-sustaining point (SSP) is proposed. Results show that the self-sustaining state can be achieved only when speed is over 26,750 rpm, and the SSP is determined at the speed of 30,750 rpm based on the proposed principle. Finally, the self-sustaining TIT and natural gas flow are compared with the experimental data, with two relative errors both almost within 4%. This method is instructive to the MGT generator system startup process

Hydrogen Production Characteristic of Diesel Reforming under Ship SOFC-GT Operation Environment

SOFC/GT hybrid system is proposed as one of the advanced power systems of future ships due to its high efficiency, low emission and fuel flexibility. However, how to efficiently reform marine diesel into H2 is the key to maintaining the operation of SOFC/GT. This paper studies the influence of operating parameters such as S/C, temperature and pressure of ship SOFC/GT hybrid system on H2 production characteristics of marine diesel reforming through numerical simulation and experimental analysis. The results show that under the variable working conditions, the H2 production increases with temperature and the carbon deposition decreases. The increase of S/C promotesthe increase of H2 yield and inhibits carbon deposition. Pressure has a negative effect on H2 production. The research results can provide basic technical support for the safe and efficient operation of the SOFC-GT hybrid power system on ships and the continuous supply of fuel

AI based Robot Safe Learning and Control

Introduction This open access book mainly focuses on the safe control of robot manipulators. The control schemes are mainly developed based on dynamic neural network, which is an important theoretical branch of deep reinforcement learning. In order to enhance the safety performance of robot systems, the control strategies include adaptive tracking control for robots with model uncertainties, compliance control in uncertain environments, obstacle avoidance in dynamic workspace. The idea for this book on solving safe control of robot arms was conceived during the industrial applications and the research discussion in the laboratory. Most of the materials in this book are derived from the authors’ papers published in journals, such as IEEE Transactions on Industrial Electronics, neurocomputing, etc. This book can be used as a reference book for researcher and designer of the robotic systems and AI based controllers, and can also be used as a reference book for senior undergraduate and graduate students in colleges and universities

Evaluation of the Ecological Quality of the Taishan Region Based on Landsat Series of Satellite Images

The deterioration of ecological environment has seriously restricted regional sustainable development. Taishan region is one of the ecological protection and restoration of life community of mountains-rivers-forests-farmlands-lakes-grasslands in China. Its ecological quality changes are directly related to the overall layout of ecological restoration and protection projects. In this study, the Taishan region of China was taken as study area, and the grade change, spatial distribution, and spatial temporal fluctuation of the ecological environment quality were quantified. Based on the ENVI platform, the Landsat series of three images of the Taishan region in 2005, 2013, and 2017 serve as the data source, and the remote sensing ecological index model (RSEI) was used. According to the change characteristics of land use types, the driving factors of ecological environmental quality change were analyzed. The results showed that: (1) The area ratio of the ecological environment quality above the middle level was in order from large to small: 2005 (97.37%) > 2017 (91.46%) > 2013 (84.64%). (2) The overall quality of the ecological environment declined during the period of 2005-2013. (3) The overall change ranges from 2013 to 2017 are smaller than those from 2005 to 2013. The area of the deteriorating area decreased by 44.90%, and the area of the constant area and the area of the area that improved increased by 16.17% and 28.72%, respectively. During 2013-2017, the general trend is getting better and better. The improved areas were mainly concentrated in the main urban areas (Taishan District, Daiyue District), eastern Ningyang County, and western Xintai City. The research results can provide a scientific basis for the scientific evaluation of the ecological environment quality during the development and construction of the region, and have important value in the design and application of the ecological environment quality optimization path

Determination of safe operation zone for an intermediate-temperature solid oxide fuel cell and gas turbine hybrid system

This paper proposes a novel approach to determine the safe zone for an intermediate-temperature solid oxide fuel cell and gas turbine hybrid system. The approach first ensures the compressor safety and then determines the overall system safe zone by analyzing the unsafe characteristics of main components. Safe performance of the hybrid system fueled with biomass gas at all operations is analyzed. Finally, the map of safe zone is obtained to avoid component malfunctions and system performance deterioration. Results show that the hybrid system can achieve a high efficiency 60.78%, which is an interesting reference for distributed power stations. Under all operations, two unbalanced energy zones exist, which may cause the short supply of O2 or fuel for electrochemical reaction. The lower the rotational speed of gas turbine, the narrower the zone of carbon deposition takes place in the reformer or turbine inoperation caused by too low inlet temperature. However, the phenomenon of fuel cell thermal cracking due to over-temperature will be exacerbated. System layout also affects component safety especially for the fuel cell. In the safe zone, the system has a characteristic of high efficiency and low load with low rotational speed, vice versa. In other words, the powers and load adjustment ranges both decrease with decreasing rotational speed whereas the efficiency increases, which peaks at 63.43%.</p

Effect of gasified biomass fuel on load characteristics of an intermediate-temperature solid oxide fuel cell and gas turbine hybrid system

This work uses the mathematical model of an intermediate-temperature solid oxide fuel cell and gas turbine (IT-SOFC/GT) hybrid system to study the effects of gasified biomass fuels on system load characteristics. The system performance is investigated by using four types of fuels in each adjusting mode. The relation between the fuel type and load adjusting mode is obtained for users and designers to select the appropriate fuel for reasonable operation modes. Results show that the hybrid system of 182.4 kW has a high electric efficiency of 60.78% by using wood chip gas (WCG). If cotton wood gas (CWG) and corn stalk gas (CSG) are used, both boundary values of steam to carbon ratio (S/Cbv) and system power are higher, but system efficiencies decrease to 57.36% and 57.87% respectively. In the designed three load adjusting modes, the system can reach maximum efficiency over 59% with four types of biomass gases. If high efficiency and a wide range of load adjustment are required, users can select Case B to use fuels like WCG and GSG. When higher efficiency and low load is expected, Case A is more desirable. With fuels like CWG and CSG, the system has good safety performance in Case C.</p

Effect of QiShenYiQi Pill on Myocardial Collagen Metabolism in Rats with Partial Abdominal Aortic Coarctation

This study investigated the effect of QiShenYiQi pill (QSYQ) on myocardial collagen metabolism in rats with partial abdominal aortic coarctation and explored its mechanism of action. A series of assays were used to detect the effect and mechanism of QSYQ on systolic blood pressure, heart mass index, left ventricle mass index, HYP, expression of PICP, PIIINT, and CTX-I in serum, MMP-1, and TIMP-1 expression in myocardium. We observed that QSYQ can reduce the rate of myocardial collagen synthesis and increase the rate of myocardial collagen degradation. It also effectively improved the degree of myocardial fibrosis in partial abdominal aortic rats and it had a tendency to have a greater effect with longer treatment duration, which is related to the mechanism of regulation of MMP-1 and TIMP-1 expression in the myocardial rat

A miniature multi-functional photoacoustic probe

Photoacoustic technology is a promising tool to provide morphological and functional information in biomedical research. To enhance the imaging efficiency, the reported photoacoustic probes have been designed coaxially involving complicated optical/acoustic prisms to bypass the opaque piezoelectric layer of ultrasound transducers, but this has led to bulky probes and has hindered the applications in limited space. Though the emergence of transparent piezoelectric materials helps to save effort on the coaxial design, the reported transparent ultrasound transducers were still bulky. In this work, a miniature photoacoustic probe with an outer diameter of 4 mm was developed, in which an acoustic stack was made with a combination of transparent piezoelectric material and a gradient-index lens as a backing layer. The transparent ultrasound transducer exhibited a high center frequency of ~47 MHz and a −6 dB bandwidth of 29.4%, which could be easily assembled with a pigtailed ferrule of a single-mode fiber. The multi-functional capability of the probe was successfully validated through experiments of fluid flow sensing and photoacoustic imaging