In this work, a 230 GHz all-NbN superconductor-insulator-superconductor (SIS) mixer was designed and analyzed. The NbN/AlN/NbN tunnel junctions (with an energy gap of 5.7 meV) and NbN/MgO/NbN tuning circuits were utilized. Full-height waveguides and bow-tie waveguide probes were adopted. The signal coupling circuit was designed and optimized to be transmissible to the given band. The quantum mixing characteristics of the all-NbN mixers were optimized with different-size SIS junctions. The mixer with a junction diameter of 1 μm achieves a conversion gain close to 0 dB and a noise temperature close to 40 K. The proposed design and analysis will provide technical support for the recovery and upgrade of the heterodyne receiver for the Leighton Chajnantor Telescope (LCT).
Carbon-based materials, such as graphene and carbon nanotubes, have emerged as a transformative class of building blocks for state-of-the-art metamaterial devices due to their excellent flexibility, light weight, and tunability. In this work, a tunable carbon-based metal-free terahertz (THz) metasurface with ultrabroadband absorption is proposed, composed of alternating graphite and graphene patterns, where the Fermi level of graphene is adjusted by varying the applied voltage bias to achieve the tunable ultrabroadband absorption characteristics. In particular, when the Fermi level of graphene is 1 eV, the absorption coefficient exceeds 90% from 7.24 through 16.23 THz, and importantly, the absorption bandwidth reaches as much as 8.99 THz. In addition, it is polarization-insensitive to incident waves and maintains a high absorption rate at an incident angle of up to 50 deg. This carbon-based device enjoys higher absorption bandwidth, rates, and performance compared to conventional absorbers in the THz regime and can be potentially applied in various fields, including THz wave sensing, modulation, as well as wearable health care devices, and biomedicine detection.
The propagation properties of terahertz (THz) wave propagating along conical metal wire have been investigated. The
effects of composed materials, metal wire diameter and temperature on waveguide characteristics have been shown and
discussed. The numerical calculation agrees well with the experimental results and predicts that metal wire waveguide shows
better propagation properties at lower temperature. The energy concentration at the end-tip increases with the decreasing of
frequency, end-tip diameter and temperature. The conical metal wire tip can be used to measure the changes of temperature
accurately because the energy density is very sensitive to temperature, showing great potential in the field of THz
spectroscopy, imaging and sensing.
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