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Superconductor Science and Technology

A tunable superconducting LC-resonator with a variable superconducting electrode capacitor bank for application in wireless power transfer

Yingda He, Yu Wang, Zhongming Yan

Published Oct 8, 2019• 8 citations
Publisher

Abstract

Abstract The frequency alignment of resonators is essential for wireless power transfer (WPT) systems to achieve strongly coupled magnetic resonances. Here, we present a novel tunable superconducting resonator for WPT applications. The tunable resonator is composed of a high-temperature superconducting (HTS) coil and a variable HTS electrode capacitor bank based on two series YBa 2 C 3 O 7− x –SrTiO 3 –YBa 2 C 3 O 7− x thin films. The HTS coil serves as a wireless transmitting tool for power delivery, while the HTS electrode capacitor bank provides a frequency-tuning element for the resonator. At 77 K, the HTS materials cause low loss and thus achieve a high quality factor, while the incipient ferroelectric SrTiO 3 substrate with HTS electrodes has a nonlinear capacitance dependence on the applied electric field with no hysteresis. A voltage supply applies a continuous DC bias to both capacitors synchronously via the coil, adjusting the total capacitance and thus the resonant frequency. Our results indicate that the tunable resonator can achieve a tuning range of 12% from 775 kHz, offering a frequency-tuning functionality to superconducting WPT technology.

DOI
10.1088/1361-6668/ab4c1d

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Abstract The frequency alignment of resonators is essential for wireless power transfer (WPT) systems to achieve strongly coupled magnetic resonances. Here, we present a novel tunable superconducting resonator for WPT applications. The tunable resonator is composed of a high-temperature superconducting (HTS) coil and a variable HTS electrode capacitor bank based on two series YBa 2 C 3 O 7− x –SrTiO 3 –YBa 2 C 3 O 7− x thin films. The HTS coil serves as a wireless transmitting tool for power delivery, while the HTS electrode capacitor bank provides a frequency-tuning element for the resonator. At 77 K, the HTS materials cause low loss and thus achieve a high quality factor, while the incipient ferroelectric SrTiO 3 substrate with HTS electrodes has a nonlinear capacitance dependence on the applied electric field with no hysteresis. A voltage supply applies a continuous DC bias to both capacitors synchronously via the coil, adjusting the total capacitance and thus the resonant frequency. Our results indicate that the tunable resonator can achieve a tuning range of 12% from 775 kHz, offering a frequency-tuning functionality to superconducting WPT technology.
We present a design and implementation of a frequency-tunable superconducting resonator. The resonance frequency tunability is achieved by flux-coupling a superconducting LC loop to a current-biased feedline; the resulting screening current leads to a change of the kinetic inductance and shift in the resonance frequency. The thin-film aluminum resonator consists of an interdigitated capacitor and thin line inductors forming a closed superconducting loop. The magnetic flux from the nearby niobium current feedline induces Meissner shielding currents in the resonator loop leading to a change in the kinetic part of the total inductance of the resonator. We demonstrate continuous frequency tuning within 160 MHz around the resonant frequency of 2.7 GHz. We show that: (1) frequency up-conversion is achieved when a kilohertz ac modulation signal is superimposed onto the dc bias resulting in sidebands to the resonator tone; (2) three-wave mixing is attained by parametrically pumping the nonlinear kinetic inductance using a strong rf pump signal in the feedline. The simple architecture is amenable to large-array multiplexing and on-chip integration with other circuit components. The concept could be applied in flux magnetometers, up-converters, and parametric amplifiers operating above 4 K when alternative high-critical-temperature material with high kinetic inductance is used.
Frequency-tunable microwave resonators are in great demand especially in hybrid systems where precise frequency alignment of resonances is required. Here, we present frequency-tunable high-Q superconducting resonators fabricated from thin niobium nitride and niobium titanium nitride films. The resonant frequency is tuned by applying a magnetic field perpendicular to the hole structures in the resonator's inductor wire, whose kinetic inductance is modified by wirelessly induced DC supercurrents. A continuous in situ frequency tuning of over 300 MHz is achieved for a 10 GHz resonator with a moderate magnetic field of 1.2 mT. The planar resonator design and the noncontact tuning scheme greatly ease the fabrication complexity and can be widely applied in many hybrid systems for coupling microwave modes with other forms of excitations such as optical photons, phonons, magnons, and spins.
Wireless power transfer (WPT) technology has received much attention due to its flexibility and safety, becoming an important area of research and development for various applications. However, conventional WPT systems are often constrained by the inherent properties of physical circuit components, leading to limitations in power density and transmission efficiency. The advent of high-temperature superconducting (HTS) materials offers a promising pathway to significantly enhance WPT performance by leveraging the nearly zero resistance and higher current-carrying capacity of HTS materials. This review comprehensively examines the state-of-the-art in HTS devices and HTS-based wireless power transfer (HTS-WPT) technology. By systematically analyzing the theoretical and experimental advances in HTS-WPT systems, this review aims to provide a comprehensive understanding of their advantages and limitations, offering insights for future research and practical implementations in various promising applications. • Superconducting materials and circuit components are thoroughly surveyed and discussed. • Research on HTS-WPT systems is comprehensively reviewed and evaluated. • Potential applications of HTS-WPT systems based on their characteristics are recommended. • Future research directions and limitations of HTS-WPT systems are revealed.
We have designed, fabricated, and tested a frequency-tunable high-Q superconducting resonator made from a niobium titanium nitride film. The frequency tunability is achieved by injecting a DC through a current-directing circuit into the nonlinear inductor whose kinetic inductance is current-dependent. We have demonstrated continuous tuning of the resonance frequency in a 180 MHz frequency range around 4.5 GHz while maintaining the high internal quality factor Qi > 180 000. This device may serve as a tunable filter and find applications in superconducting quantum computing and measurement. It also provides a useful tool to study the nonlinear response of a superconductor. In addition, it may be developed into techniques for measurement of the complex impedance of a superconductor at its transition temperature and for readout of transition-edge sensors.
Frequency tuning enables both high-sensitivity and wide-bandwidth detection in the resonator. Potassium tantalate (KTO) is a quantum paraelectric with tunable permittivity and low microwave loss at cryogenic temperature, making it promising for tunable devices. Here, we demonstrate a superconducting microwave resonator on a KTO substrate. The resonant frequency can be tuned by ∼40 MHz using a 9 V bias at 20 mK, with no observable hysteresis. The absence of hysteresis is a key metric for practical devices, addressing one of the major obstacles in other paraelectric-based tunable resonators. More interestingly, we observed that the quality factor oscillates during voltage tuning, arising from the competition between phonon hardening and charge injection. Therefore, our work provides a practical tunable resonator platform and offers a potential approach to study energy-loss characteristics in quantum paraelectrics.
Superconducting coplanar waveguide (CPW) resonators are powerful and versatile tools used in areas ranging from radiation detection to circuit quantum electrodynamics. Their potential for low intrinsic losses makes them attractive as sensitive probes of electronic properties of bulk materials and thin films. Here we use superconducting MoRe CPW resonators to investigate the high-frequency (up to 0.3 GHz) and low-temperature (down to 3.5 K) permittivity of SrTiO3{\mathrm{SrTiO}}_{3}SrTiO3​, a nonlinear dielectric on the verge of a ferroelectric transition (quantum paraelectricity). We perform a quantitative analysis of its dielectric properties as a function of external dc bias (up to $\ifmmode\pm\else\textpm\fi{}15\phantom{\rule{0.16em}{0ex}}\mathrm{V}$), rf power, and mode number and discuss our results within the framework of the most recent theoretical models. We also discuss the origin of a fatigue effect that reduces the tunability of the dielectric constant of SrTiO3{\mathrm{SrTiO}}_{3}SrTiO3​, which we relate to the presence of oxygen vacancies.