High-temperature Superconducting Resonators Research Articles

Implementing High Q-Factor HTS Resonators to Enhance Probe Sensitivity in 13C NMR Spectroscopy

Nuclear magnetic resonance spectroscopy (NMR) probes using thin-film high temperature superconducting (HTS) resonators provide exceptional mass sensitivity in small-sample NMR experiments for natural products chemistry and metabolomics. We report improvements in sensitivity to our 1.5 mm 13C-optimized NMR probe based on HTS resonators. The probe has a sample volume of 35 microliters and operates in a 14.1 T magnet. The probe also features HTS resonators for 1H transmission and detection and the 2H lock. The probe utilizes a 13C resonator design that provides greater efficiency than our previous design. The quality factor of the new resonator in the 14.1 T background field was measured to be 4,300, which is over 3x the value of the previous design. To effectively implement the improved quality factor, we demonstrate the effect of adding a shorted transmission line stub to increase the bandwidth and reduce the rise/fall time of 13C irradiation pulses. Initial NMR measurements verify 13C NMR sensitivity is significantly improved while preserving detection bandwidth. The probe will be used for applications in metabolomics.

Application of Counter-wound Multi-arm Spirals in HTS Resonator Design.

Significant sensitivity improvements have been achieved by utilizing high temperature superconducting (HTS) resonators in nuclear magnetic resonance (NMR) probes. Many nuclei such as 13C benefit from strong excitation fields which cannot be produced by traditional HTS resonator designs. We investigate the use of double-sided, counter-wound multi-arm spiral HTS resonators with the aim of increasing the excitation field at the required nuclear Larmor frequency for 13C. When compared to double-sided, counter-wound spiral resonators with similar geometry, simulations indicate that the multi-arm spiral version develops a more uniform current distribution. Preliminary tests of a two-arm resonator indicate that it may produce a stronger excitation field.

Very large group delay in VHF band using coupled high temperature superconducting resonators

Storing a very high frequency (VHF) band (30–300 MHz) electromagnetic wave has many potential applications, such as phase modulation, buffering, and radio frequency memory. It can be effectively achieved by applying coupled resonator-based electromagnetically induced transparency (EIT) due to its slow light effect. However, the wavelength in the VHF band is too long to design resonators, and the group delay is limited by the high resistive loss of metal. The practical application of EIT in the VHF band is still a big challenge. In this work, we propose and experimentally demonstrate EIT response in a high-temperature superconducting (HTS) microwave circuit with coupled-resonator-induced transparency. The chip size of the HTS circuit is only 34 mm × 20 mm with a very low transparency frequency of 198.55 MHz. In addition, we implement very large group delay higher than 12.3 μs and 16.2 μs with working temperatures of 65 K and 50 K separately, which is much longer than the previous reported works on slow wave. The fabricated circuit is planar with working temperature about 65 K, and thus can be easily integrated into other microwave devices under the cryogenic conditions provided by a commercial portable Stirling cryocooler. Our proposed method paves a way for studying EIT in the microwave region due to the high quality factor of the HTS resonator, which has great potential use for radio-frequency memory in the future.

Progress Towards a Higher Sensitivity 13C-Optimized 1.5 mm HTS NMR Probe.

Nuclear magnetic resonance (NMR) probes using thin-film high temperature superconducting (HTS) resonators offer high sensitivity and are particularly suitable for small-sample applications. We are developing an improved 1.5 mm HTS NMR probe designed for operation at 14.1 T and optimized for 13C detection. The total sample volume is about 35 μL and the active sample volume is 20 μL. The probe employs HTS resonators for 13C and 1H transmission and detection and the 2H lock. We examine the interactions of multiple superconducting resonators and normal metal tuning loops on coil resonance frequency and probe sensitivity. We test a recently introduced 13C resonator design, engineered to significantly increase 13C detection sensitivity over previous all-HTS probes. At zero field, we observe a 13C quality factor of 6000 which is several times higher than previous resonators. In this work the coil design considerations and probe build-out procedure are discussed.

Frequency Tuning of the Elementary Base of Microwave Electronics Using Structured Htsc Films

Abstract—A study of the current–voltage characteristics of structured high-temperature superconducting (HTSC) films based on YBa2Cu3O7 – x–YBa2Cu3O7 – x showed that the critical current of the film structure with an area of 10.0 × 10.0 mm2 can be reduced from 10 A up to 100 mA. By the example of an HTSC resonator, it is shown that in the millimeter wavelength range, with a resonance response width of 2∆f = 20–30 MHz at a level of 0.5 of its amplitude, a structured film used as an “grounded” plane permits tuning of the resonator in a band of at least 300 MHz.

Inductively-coupled Frequency Tuning and Impedance Matching in HTS-based NMR Probes.

Nuclear Magnetic Resonance (NMR) probes based on High Temperature Superconducting (HTS) resonators have demonstrated significant gains in detection sensitivity. However, the widespread acceptance of this technology has been limited by some unresolved issues including the mechanical unreliability of the moveable inductive loops used to adjust tuning and matching. In order to improve reliability, we propose to implement frequency tuning and impedance matching of HTS resonators using fixed inductively coupled loops and variable capacitors. By analyzing the loss mechanisms associated with inductive loops, we predict that using a superconducting inductive loop for tuning and matching will not only improve the reliability of HTS probes, but also provide improvements in sensitivity.

Design Considerations of Superconducting Wireless Power Transfer for Electric Vehicle at Different Inserted Resonators

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electrical vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. However, there are challenges in its commercialization, such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using high-temperature superconducting (HTS) resonance coil in the WPT system, which is called superconducting wireless power transfer for electric vehicle (SUWPT4EV) system. Since the superconducting wire has merits, i.e., a larger current density and a higher Q value than normal conducting wire, the HTS antenna coil enables to deliver a mass amount of electric energy in spite of a small-scale antenna, as well as is possible to keep much stronger magnetic fields out in the peripheral regions. Thus, the SUWPT4EV system has been expected as a reasonable option to improve the transfer efficiency of large electric power. In this study, as an advanced approach, we proposed the advanced SUWPT4EV system with inserted resonator using noncooled copper, cooled copper, and HTS resonators, respectively, in order to expand the transfer distance and improve the transfer ratio. In this paper, we presented operating characteristics of the advanced SUWPT4EV system and achieved the improvement and effects of transmission power for inserted resonators within 40-cm distance under radio frequency power of 370 kHz below 600 W.

Development of a <sup>1</sup>H-<sup>13</sup>C Dual-Optimized NMR Probe Based on Double-Tuned High Temperature Superconducting Resonators

Nuclear magnetic resonance (NMR) spectroscopy is a very powerful technique to study molecular structure and dynamics because of the rich chemical information it can extract. However, low inherent sensitivity is the Achilles' heel of NMR. The use of high temperature superconducting (HTS) resonators as pick-up coils in NMR probes can significantly improve the detection sensitivity of NMR and expand the use of NMR for dilute and mass-limited samples. In previously proposed HTS-based probes, the resonators for the various channels are nested orthogonally around the sample region. With this configuration, optimal sensitivity can be achieved only by the single innermost channel, which has its coils closest to the sample. We report here a new configuration in which the NMR probe has been simultaneously optimized for detection sensitivity of two channels, namely, hydrogen and carbon. The probe employs novel double-tuned HTS resonators that generate strong, uniform, and mutually orthogonal magnetic fields at the hydrogen and carbon NMR frequencies. The resonator is designed for optimal magnetic field homogeneity and minimal electric field in the sample region. Design considerations for the resonators and probe performance in NMR tests are presented.

Phase noise of an HTS resonator operated in the nonlinear regime

Nonlinear properties of high-temperature superconducting (HTS) strongly coupled resonators at different input power have been investigated by measurements of the quality factor as a function of input power as well as by generation of the intermodulation distortion (IMD). The double-sided YBCO films on CeO/sub 2/ buffered sapphire demonstrate advanced performance with the microwave surface resistance of /spl sim/0.3 m/spl Omega/ at 8.5 GHz at 77 K and an IMD third-order interception point estimated at P/sub circ//spl ap/70 W. A parallel feedback oscillator was assembled using a transmission type HTS resonator cooled with liquid nitrogen and a room temperature low noise amplifier. Results on the phase noise investigation of the 2.3 GHz oscillator based on HTS resonator operated in the nonlinear regime demonstrated a deviation from the simple model of the phase noise, which predicts an up-conversion of 1/f noise of the amplifier to oscillator phase noise. The latter can be explained by the phase noise introduced additionally due to the nonlinear response of the HTS resonator.

High temperature superconducting (HTS) C-band oscillator with phase noise of ?134 dBc/Hz

A high Q HTS cavity resonator with resonating frequency f0= 5.624 GHz was fabricated using high quality HTS film and high purity sapphire. The unloaded quality factor of the HTS resonator was as high as Q u= 1.09xl06 at the nitrogen temperature, 77 K. A HTS local oscillator combining the high Q cavity resonator with a C-band low noise GaAs HEMT amplifier was then designed and constructed. The phase noise of the oscillator, measured by a HP 3048A noise measurement system, is −134 dBc/Hz at 10 kHz offset when the temperature is 77 K. This result is close to the best level reported by other groups in the world.

Modulated optical reflectance characterization of high temperature superconducting thin film microwave devices

The modulated optical reflectance (MOR) technique is shown to provide a room temperature, noncontact, nondestructive and high spatial resolution means of assessing high temperature superconducting (HTS) thin film quality. Room temperature MOR characterizations of a number of 8 GHz planar HTS resonators indicating a range of property variations and local degradations in HTS film performance are shown to be consistent with results obtained at low temperatures by the electron beam induced voltage contrast technique. The microwave performances of some of the resonators are found to exhibit nonlinear characteristics that can be explained by HTS defects revealed by the MOR technique.

Two-dimensional resonators for local oscillators

The expedited globalization of satellite technology has brought about a rapid boost in satellite competition and increased utilization of wireless communications remote data devices. In space communications receivers, there is an expanding demand for higher performance from local oscillators. The determining conditions are high Q values, high circulating power and low amplifier noise figures. In spite of their low insertion loss, conventional one-dimensional high-temperature superconducting (HTS) resonator-feedback oscillators suffer from high peak current densities inside the resonator and thus have a limited power-handling characteristics. To achieve higher-power oscillators, it is possible to introduce a two-dimensional microstrip resonator to balance the internal current distribution. To this end, 3 GHz two-dimensional resonators have been fabricated from TBCCO 2212 thin films deposited by RF sputtering onto 2 cm square LaAlO3 substrates. This paper demonstrates the frequency stabilizer role and the frequency response of the two-dimensional resonator. The considerable improvement for the performance of resonator-feedback oscillators constructed using such HTS resonators will also be presented.

Electrical tuning of passive HTS microwave devices using single crystal strontium titanate

Over the last few years several groups have fabricated High Temperature Superconducting (HTS) thin film microwave devices which have included a ferroelectric thin film layer in their design. The electric field dependence of the ferroelectric promises desirable in-situ tuning of the frequency response. Here we present the results of our experiments on the tuning of a coplanar HTS resonator using single crystal strontium titanate (STO). We have patterned a simple coplanar resonator device onto Y-Ba-Cu-O thin films deposited on [100] magnesium oxide substrates. Careful consideration of the size, position and biasing of these high permittivity STO crystals with respect to the planar device allows us to minimise the perturbance to the plain resonators response whilst at the same time maximising the degree to which we are able to tune the device. We have also performed a series of capacitance measurements on our STO crystals to obtain reliable data for the dependence of the permittivity on temperature, applied bias and crystallographic orientation.

Microwave Characteristics of YBaCuO Coplanar Waveguide Resonators Fabricated by the Sol–Gel Process on Polycrystalline MgO

High temperature superconducting (HTS) Y–Ba–Cu–O (YBCO) films were prepared on MgO polycrystal substrates by the sol–gel process. The resistivity at DC and the surface resistance (R s) at a microwave frequency of the films were measured. R s was found to be highly dependent on the thickness of the films and the temperature, and the optimal value obtained for R s was 4.2 mΩ at 40 K and 10 GHz. We also fabricated a YBCO coplanar waveguide (CPW) half-wavelength resonator around 2 GHz and compared its RF property with that of a normal metal. The incident power dependence of the transmission characteristics was observed to examine the power handling capability of the HTS resonator. As the temperature and the input power decreased, the quality factor (Q0) of the YBCO CPW resonator improved significantly, as opposed to hardly any change of that of a normal metal.

Dielectric loaded HTS resonators as frequency standards and low-phase noise oscillators

High-quality, high-temperature superconducting (HTS) thin-films exhibit very low losses at microwave frequencies and, as a result, allow very high Q resonators to be produced. The size of such resonators may be significantly reduced by loading with low-loss single crystal dielectric. The potential for HTS dielectric loaded resonators as practical frequency standards and reference elements for low-phase-noise oscillators is assessed, with emphasis on operation at 60 K, a temperature readily attainable with compact Stirling cycle coolers.

Microwave measurement of coplanar-type resonator fabricated with YBCO film

High temperature superconducting (HTS) Y–Ba–Cu–O (YBCO) films were prepared on MgO polycrystal substrates by the sol–gel process. The temperature dependence of the surface resistance ( R s ) of the YBCO film around 9.9 GHz was observed. YBCO coplanar waveguide (CPW) quarter-wavelength ( λ /4) resonator operating around 2 GHz was fabricated using the sol–gel film, and RF properties of the YBCO CPW resonator was compared with that of normal metal resonator. The temperature and stored energy dependence of the transmission characteristics were observed in order to examine the temperature and power handling capabilities of the HTS resonator. The quality factor ( Q 0 ) of the YBCO CPW λ /4 resonator increased significantly as the stored energy decreased, whereas the resonant frequency hardly changed. Moreover, the magnetic penetration depth at 0 K ( λ 0 ) was also estimated.

Jet Propulsion Laboratory/NASA Lewis Research Center space qualified hybrid high temperature superconducting/semiconducting 7.4 GHz low-noise downconverter for NRL HTSSE-II program

A deep space satellite downconverter receiver was proposed by Jet Propulsion Laboratory (JPL) and NASA Lewis Research Center (LeRC) for the Naval Research Laboratory's (NRL) high temperature superconductivity space experiment, phase-II (HTSSE-II) program. Space qualified low-noise cryogenic downconverter receivers utilizing thin-film high temperature superconducting (HTS) passive circuitry and semiconductor active devices were developed and delivered to NRL. The downconverter consists of an HTS preselect filter, a cryogenic low-noise amplifier; a cryogenic mixer, and a cryogenic oscillator with an HTS resonator. HTS components were inserted as the front-end filter and the local oscillator resonator for their superior 77 K performance over the conventional components. The semiconducting low noise amplifier also benefited from cooling to 77 K. The mixer was designed specifically for cryogenic applications and provided low conversion loss and low power consumption. In addition to an engineering model, two space qualified units (qualification, flight) were built and delivered to NRL. Manufacturing ,integration and test of the space qualified downconverters adhered to the requirements of JPL class-D space instruments and partially to MIL-STD-883D specifications. The qualification unit has /spl sim/50 K system noise temperature which is a factor of three better than a conventional downconverter at room temperature. Commercial applications such as intersatellite links and V-SATS are envisioned to benefit by >3 dB link margin, or a factor of 2 in antenna size, from a future hybrid HTS/semiconducting cryogenic receiver employing new InP based HEMT LNA. In a spread spectrum communication network, the number of users per beam would more than double.

Electronics for a high temperature superconducting receiver system for magnetic resonance microimaging.

We describe an MRI (magnetic resonance imaging) receiver system that incorporates a high temperature superconducting (HTS) resonator as a surface coil. Techniques for measuring the Q of the HTS resonator in a 7 Tesla field are discussed. A method for coupling a room temperature copper resonant circuit to the HTS element is covered, and it is shown that such a coupling scheme preserves the signal-to-noise (SNR) gain afforded by the HTS coil. A preamplifier with a noise figure (NF) of < 0.15 dB at 300 MHz is described.