Abstract-High-Tc Superconducting Fourth-Harmonic Mixer Using a Dual-Band Terahertz On-Chip Antenna of High Coupling Efficiency

Xiang Gao, Jia Du, Ting Zhang,  Y. Jay Guo

https://ieeexplore.ieee.org/document/8534418

This paper presents a dual-band on-chip antenna-coupled high-Tc superconducting (HTS) Josephson-junction subterahertz (THz) fourth-harmonic mixer. The antenna utilizes a couple of different structured twin slots to enable the resonant radiations at two frequencies, and integrates a well-designed coplanar waveguide network for achieving good radiation coupling and signal isolation characteristics. The electromagnetic simulations show that coupling efficiencies as high as -4 and -3.5 dB are achieved for the 160- and 640-GHz operating frequency bands, respectively. Based on this dual-band antenna, a 640-GHz HTS fourth-harmonic mixer is developed and characterized in a range of operating temperatures. The mixer exhibits a measured conversion gain of around -18 dB at 20 K and -22 dB at 40 K, respectively. The achieved intermediate frequency bandwidth is larger than 23 GHz. These are the best results reported for HTS harmonic mixers at comparable sub-THz frequency bands to date.

Abstract-An Electrically Tunable Terahertz Plasmonic Device Based on Shape Memory Alloys and Liquid Metals

Hui Zhou, Ting Zhang, Sivaraman Guruswamy, Ajay Nahata,

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700684/full

An electrically tunable terahertz (THz) plasmonic device is designed and fabricated using liquid metals (eutectic gallium indium) and shape memory alloy wires (Flexinol). The liquid metal is injected into the voids of a poly(dimethyl) siloxane microfluidic mold forming a periodic array of subwavelength apertures, while the wires are inserted into the elastomer below the metal plane. When a DC voltage is applied to the wires, they contract via Joule heating, reducing the aperture periodicity and blueshifting the transmission resonances of the device. When the voltage is removed, the wires cool and elongate back to their original length, allowing the transmission spectrum to return to its original state. The magnitude of this change depends upon the applied voltage. The device is shown to thermally cycle between the relaxed state and the fully contracted state reproducibly over at least 500 thermal cycles. The asymmetric geometry of the device and the contraction process yield transmission properties that are unexpected: two closely spaced resonances, where both resonances correspond to the same scattering indices, and an increase in the transmission amplitude of the lowest order resonance upon contraction. Numerical simulations are used to understand these features.

Abstract-Experimental Investigation of a Broadband High-Temperature Superconducting Terahertz Mixer Operating at Temperatures Between 40 and 77 K

• Xiang Gao, Jia
•  Du, 
• Ting Zhang, 
• Y. Jay Guo, 
• Cathy P. Foley

https://link.springer.com/article/10.1007%2Fs10762-017-0422-x

This paper presents a systematic investigation of a broadband thin-film antenna-coupled high-temperature superconducting (HTS) terahertz (THz) harmonic mixer at relatively high operating temperature from 40 to 77 K. The mixer device chip was fabricated using the CSIRO established step-edge YBa2Cu3O7-x (YBCO) Josephson junction technology, packaged in a well-designed module and cooled in a temperature adjustable cryocooler. Detailed experimental characterizations were carried out for the broadband HTS mixer at both the 200 and 600 GHz bands in harmonic mixing mode. The DC current-voltage characteristics (IVCs), bias current condition, local oscillator (LO) power requirement, frequency response, as well as conversion efficiency under different bath temperatures were thoroughly investigated for demonstrating the frequency down-conversion performance.

Abstract-Bistable Physical Geometries for Terahertz Plasmonic Structures Using Shape Memory Alloys

http://onlinelibrary.wiley.com/doi/10.1002/adom.201601008/full

Shape memory alloy foils that are appropriately patterned are cycled between two different metal foil geometries resulting in two different terahertz (THz) plasmonic responses. This is accomplished by using patterned foils of a nickel–titanium alloy (Nitinol) that switches between the martensite phase below 31 °C, yielding one physical geometry, and the austenite phase, when the foil is heated above 51 °C, yielding a second physical geometry. In order to enable this reproducible switching, the sample is initially put through a two-way training procedure, through which the two different desired physical geometries are imprinted. Specifically, the metal foils are trained to switch between a sinusoidal corrugation, either 1D or 2D, at close to room temperature and a flat metal sheet above the austenite phase transition temperature. The foils are found to switch reproducibly between geometries over at least 100 thermal cycles. Using THz time-domain spectroscopy, the transmission properties of the foils are measured as a function of incident polarization and foil geometry. The changes in spectrum are explained qualitatively and through numerical simulation.