Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields

The effect of high magnetic fields on the current carrying properties of both MgB2 bulks and Fe-sheathed tapes was investigated following different thermal sequences. It is found that application of a large magnetic field during processing results in the quite uniform microstructure and the better connectivity between the MgB2 grains. As a result, the Jc of these samples has shown much higher value than that of the MgB2 samples in the absence of magnetic field. The possible mechanism of the Jc enhancement under an external magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio

Integrating Li-Fi Wireless Communication and Energy Harvesting Wireless Sensor for Next Generation Building Management

Wireless sensors have been increasingly utilized in the design of next generation high performance buildings. When deploying wireless sensors, energy supply and data communication are the major concerns. Although energy harvest wireless sensors could automatically feed themselves by harvesting ambient energy, the presence of reliable energy sources to support dependable wireless transmission is a great challenge. The emerging Li-Fi technology is promising to fundamentally solve this problem. Li-Fi stands for Light-Fidelity, which is a new kind of wireless communication systems using light as a medium instead of traditional radio-frequency electromagnetic radiation. Li-Fi technology provides harvested energy to power wireless sensors with a unique advantage of power generation from the lighting system being controlled. The combination of Li-Fi and energy harvesting wireless sensor technologies could enable attractive features and bring in great benefits in the design of next generation high performance buildings because: (i) energy harvest sensors do not face the short-of-energy problem; (ii) Li-Fi enables much higher transmission speed compared to the existing RF electromagnetic technologies, thus, energy harvest sensors could easily deliver environmental parameters quickly for control purposes; (iii) energy harvest sensors could assist the building management team to understand the coverage area of the lighting system; (iv) the communication of sensor aggregated information can be naturally encrypted due to the combination of both technologies

Modelling and Design of Efficient Photomixer Based Terahertz Antennas

The lack of unoccupied and unregulated bandwidth for wireless communication vanished at lower frequency spectrum and the increasing demand of high data transmission rate leads to an intensive interest in the research of THz technologies at 0.3THz to 30THz spectrum. However, the limitation of the low output power and low efficiency of current THz devices obstacles the utilization of THz technologies. Also, compared with microwave antenna, the signal generation and excitation of THz antenna require new simulation approach. Therefore, the motivation of this thesis is theoretically analyse the reason that cause the inefficiency of THz antenna, from which, the performance of such antennas is improved from the aspects of THz source with low efficiency, THz antenna with low match efficiency and THz antenna with low gain. These investigations are necessary for the development of the THz photomixer antenna in various applications . First of all, an new equation of the generated THz power from photomixer is developed from the equivalent circuit of photomixer fed antenna. Through this equation, various factors that affect the behaviour of photomixer is examined. Furthermore, a computational simulation process that solving both optoelectronic and electromagnetic problem in a full wave electromagnetic solver. This is a prerequisite for the analysis of improving the optical to THz conversion efficiency of photomixer. After that, the optical to THz conversion efficiency of the photomixer has been gradually improved through three different aspects, by optimizing photomixer electrodes, by utilizing reflectors underneath photomixer and by implementing superstrate. As a result, the highest enhancement factor of optical to THz conversion efficiency achieved is 494. Moreover, instead of exciting planar antenna with photomixer, the concept of truncating the photoconductive substrate of photomixer to form a dielectric resonator antenna is proposed. Such design eliminated the substrate effect to improve the radiation efficiency and to avoid using bulky lens. In addition, choke filter network and dielectric superstrate are used to improve the matching and radiation of these DRAs. The proposed DRA improved the matching efficiency and antenna gain by 10 times and 3dBi, respectively. Finally, a realization design that provide physically support to the dielectric superstrate and replace central feeding slot with coplanar waveguide is presented