Monday, July 15, 2019
Limei Qi, Chang Liu, Syed Mohsin, Ali Shah
A switchable graphene-based terahertz metamaterial absorber is proposed by using nonstructured graphene loaded with simple dielectric resonators, which can achieve both the broad and dual-band absorption with polarization-independent and wide-angle characteristics. The relative bandwidth of the two bands above 80% absorption reaches 97.8% and 31% in the frequency range of 0.473-1.407 THz and 2.273-3.112 THz, respectively. By changing the chemical potential of graphene, the state of the absorber can be switched from absorption (>80%) to reflection (>91%) over the two broad bands. Physical mechanisms of the broad dual-band switchable absorber are investigated by the impedance matching theory and the coupled-mode theory. The dual bands are caused by the Fabry-Perot resonance of dielectric substrate, the broad and high absorption originates from the appropriate impedance match between the absorber and free space. As the absorber is based on a monolayer nonstructured graphene loaded with simple dielectric resonators, the processing difficulty will be reduced greatly and it is easy to tune it through the bias voltage. This structure provides a new perspective to design broad multi-band absorbers and would have promising applications in multiple amplitude modulators, imaging and sensing.
Ruiqiang Zhao, Zheng Zhu, Guohua Dong, Tingting Lv, Yuxiang Li, Chunying Guan, Jinhui Shi, and Han Zhang
Minoru Fujishima, Shuhei Amakawa,
Communications technology at a frequency range into Terahertz (THz) levels has attracted attention because it promises near-fibre-optic-speed wireless links for the 5G and post-5G world. Transmitter and receiver integrated circuits based on CMOS, which has the ability to realize such circuits with low power consumption at a low cost, are expected to become increasingly widespread, with much research into the underlying electronics currently underway. This book describes recent research on terahertz CMOS design for high-speed wireless communication. The topics covered include fundamental technologies for terahertz CMOS design, amplifier design, physical design approaches, transceiver design, and future prospects. This concise source of key information, written by leading experts in the field, is intended for researchers and professional circuit designers working in RFIC and CMOS design for telecommunications.
Sunday, July 14, 2019
Abstract-Characterization and Water Content Estimation Method of Living Plant Leaves Using Terahertz Waves
Adnan Zahid, Hasan T. Abbas, Muhammad A. Imran, Khalid A. Qaraqe, Akram Alomainy. David R. S. Cumming, Qammer H. Abbasi,
An increasing global aridification due to climate change has made the health monitoring of vegetation indispensable to maintaining the food supply chain. Cost-effective and smart irrigation systems are required not only to ensure the efficient distribution of water, but also to track the moisture of plant leaves, which is an important marker of the overall health of the plant. This paper presents a novel electromagnetic method to monitor the water content (WC) and characterisation in plant leaves using the absorption spectra of water molecules in the terahertz (THz) frequency for four consecutive days. We extracted the material properties of leaves of eight types of pot herbs from the scattering parameters, measured using a material characterisation kit in the frequency range of 0.75 to 1.1 THz. From the computed permittivity, it is deduced that the leaf specimens increasingly become transparent to the THz waves as they dry out with the passage of days. Moreover, the loss in weight and thickness of leaves were observed due to the natural evaporation of leaf moisture cells and change occurred in the morphology of fresh and water-stressed leaves. It is also illustrated that loss observed in WC on day 1 was in the range of 5% to 22%, and increased from 83.12% to 99.33% on day 4. Furthermore, we observed an exponential decaying trend in the peaks of the real part of the permittivity from day 1 to 4, which was reminiscent of the trend observed in the weight of all leaves. Thus, results in paper demonstrated that timely detection of water stress in leaves can help to take proactive action in relation to plants health monitoring, and for precision agriculture applications, which is of high importance to improve the overall productivity.
Abstract-Characteristics of terahertz waves from laser-created plasma with an external electric field
T. Fukuda, T. P. Otsuka, T. Kobayashi, T. Asai, Y. Yoshida, K. Yamamoto, T. Nagami, H. Yamanaka, S. Endo, N. Yugami
We investigated the terahertz radiation from laser-created plasma in the presence of an external electric field parallel to the laser direction in the frequency range 0.14 to 0.33 THz. A narrow cone radiation pattern was observed by measuring the angular distribution, and polarizations were quasi-radial polarization. The terahertz intensities depended on the square of the electric field in the range 2 to 5 kV cm.