The addition of artificial pinning centers has led to an impressive increase in the critical current density (Jc) of superconductors, enabling record-breaking all-superconducting magnets and other applications. The Jc of superconductors has reached ~0.2–0.3 Jd, where Jd is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying λ and/or ξ, the penetration depth and coherence length, respectively, we can increase Jd. For (Y0.77Gd0.23)Ba2Cu3Oy ((Y,Gd)123), we can achieve this by controlling the carrier density, which is related to λ and ξ. We can also tune λ and ξ by controlling the chemical pressure in Fe-based superconductors, i.e., BaFe2(As1−xPx)2 films. The variation in λ and ξ leads to an intrinsic improvement in Jc via Jd, allowing extremely high values of Jc of 130 MA/cm2 and 8.0 MA/cm2 at 4.2 K, consistent with an enhancement in Jd of a factor of 2 for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe2(As1−xPx)2 films, showing that this new material design is useful for achieving high critical current densities in a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached ~3.17 TN/m3 at 4.2 K and 18 T (H||c), the highest values ever reported for any superconductor.
We have designed a miniaturized high-temperature superconducting dual-band bandpass filters (DBPFs) using stubloaded meander line resonators and their applications to tri-band bandpass filters (TBPFs). The DBPF enables independent control of the center frequencies of the first and second bands. The bandwidths of the DBPF can be flexibly adjusted using a capacitance-loaded microstrip line between the resonators. The DBPF was designed and analyzed using an electromagnetic simulator and fabricated using an YBa 2 Cu 3 O y thin film on an Al 2 O 3 substrate. The center frequencies are 3.5 and 5.0 GHz; two bands have 2% bandwidth. The measured frequency responses of the DBPF were in good agreement with the simulated frequency responses. The TBPF was realized by combining the DBPF and a single-band bandpass filter (SBPF) that uses a folded stepped-impedance resonator with common input and output. The DBPF constructs the first and third bands of 3.5 and 5.0 GHz, and the SBPF forms the second band of 4.25 GHz. The frequency responses of the simulated TBPF meet the design parameters.Index Terms-Dual-band bandpass filter, HTS filter, stubloaded resonator, tri-band bandpass filter.
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