Terahertz narrow bandstop, broad bandpass filter using double-layer S-shaped metamaterials

Abstract In this study, double-layer S-shaped metamaterials （MMs） are analyzed by terahertz time-domain spectroscopy. These materials exhibit narrow bandstop and broad bandpass transmission properties at both horizontal and vertical electric-field polarizations. A 117% increase in the unloaded quality factor is experimen- tally observed for these materials. The center frequency is approximately 0.45 THz, with a 3-dB bandwidth of 0.52 THz from 0.20 to 0.72 THz at normal incidence. The measured average insertion loss is 0.5 dB with a ripple of 1 dB. These results show that double-layer S-shaped MMs are effective in designing tunable terahertz devices.     

Terahertz detectors based on superconducting hot electron bolometers

Low noise terahertz(THz)heterodyne detectors based on superconducting niobium nitride(NbN) hot electron bolometers(HEBs)have been studied.The HEB consists of a planar antenna and an NbN bridge connecting across the antenna’s inner terminals on a high-resistivity Si substrate.The double sideband noise temperatures at 4.2 K without corrections have been characterized from 0.65 to 3.1 THz.The excess quantum noise factor β of about 4 has been obtained,which agrees well with the calculated value.Allan variance of the HEB has been measured,and Allan time up to 20 s is obtained using a microwave feedback method.Also,the intermediate frequency gain bandwidth(GBW)was measured using two dierent methods,resulting in same GBW value of about 3.5 GHz.     

Iron diffusivity into superconducting YBa2Cu3O7−δ at oxygen-assisted sintering: structural,magnetic, and transport properties

Optimization of materials exhibiting high-temperature superconductivity for producing controllable nano-devices is crucial for industrial applications. Herein we report a comprehensive study of the diffusion process between YBa₂Cu₃O_7−δ (YBCO) and iron particles. Fe diffusion into the YBCO matrix could be fundamental for multilayer systems with YBCO/Fe-alloy interfaces. We have found that the orthorhombic YBCO structure adopts to 3 wt% Fe, while for higher Fe content, a formation of BaFeO_3−δ and iron oxides was observed. Complementary measurements confirmed the strong superconductivity suppression in YBCO-Fe materials containing more than 7 wt% Fe. The YBCO with diffused Fe material retain the unit cell orthorhombicity (max. 3 wt% Fe), and their superconducting properties follow the principle of critical scaling with different exponents (γ). The critical current density (J_c), pinning fields (H_P) exhibit γ = 1, the first critical field (H_c1) shows γ = 1/2, and critical temperature (T_c) demonstrates γ = 7/4.     

A single-photon fault-detection method for nanocircuits that use GaN material

As the complexity of nanocircuits continues to increase,developing tests for them becomes more difficult.Failure analysis and the localization of internal test points within nanocircuits are already more difficult than for conventional integrated circuits.In this paper,a new method of testing for faults in nanocircuits is presented that uses single-photon detection to locate failed components(or failed signal lines)by utilizing the infrared photon emission characteristics of circuits.The emitted photons,which can carry information about circuit structure,can aid the understanding of circuit properties and locating faults.In this paper,in order to enhance the strength of emitted photons from circuit components,test vectors are designed for circuits’components or signal lines.These test vectors can cause components to produce signal transitions or switching behaviors according to their positions,thereby increasing the strength of the emitted photons.A multiple-valued decision diagram(MDD),in the form of a directed acrylic graph,is used to produce the test vectors.After an MDD corresponding to a circuit is constructed,the test vectors are generated by searching for specific paths in the MDD of that circuit.Experimental results show that many types of faults such as stuck-at faults,bridging faults,crosstalk faults,and others,can be detected with this method.