Hui Xu

Columbia University, New York City, New York, United States

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Publications (4)5.46 Total impact

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    ABSTRACT: A number of recent reports in the MRI literature have established that substantial signal-to-noise ratio (SNR) gains can be achieved with small samples or low resonance frequencies, through the use of high-quality factor high-temperature superconducting (HTS) RF receive coils. We show the application of HTS coils to the imaging of human subjects with improved SNR compared with copper coils. HTS coils were constructed from 7.62-cm YBa2Cur3O7-delta thin films on LaAlO3 substrate and cooled in a liquid nitrogen cryostat. Human and phantom images were acquired on a 0.2-T scanner. The SNR improvements compared with equivalent-sized copper coils are reported. SNR gains of 2.8-fold and 1.4-fold were observed in images of a phantom acquired with an HTS coil versus a room temperature copper coil and a liquid nitrogen-cooled copper coil, respectively. Preliminary results suggest higher image quality can be obtained in vivo with an HTS coil compared with copper coil imaging. Images of human orbit, brain, temporomandibular joint, and wrist are presented. The experimental results show that benefits can be expected from application of HTS surface coils in human MR imaging with low-field scanners. These potential benefits justify the continued development of practical HTS coil imaging systems despite the considerable technical difficulties involved in cryostat and coil design.
    Full-text · Article · Oct 2003 · Academic Radiology
  • Hui Xu · EH Gao · Q.Y. Ma
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    ABSTRACT: In this paper, we present a new electromechanical approach of active control of high temperature superconducting (HTS) resonator and filter center frequency. The design of the tunable devices incorporates piezoelectric bender or tube actuator, which acts as a varactor of the resonance circuit, with YBCO thin film on LAO substrate. The resonator has an unloaded Q of over 18,000 at 77 K and a center frequency of 362 MHz and a tuning range of over 20% with unloaded Q over 10,000. By applying different voltages to the piezoelectric bender, we have tuned the resonance frequency over 30% with a good linearity and high Q. Based on this structure, a two-pole HTS bandpass filter was designed, fabricated and tested. The filter has a tunable center frequency from 17 to 20 MHz while maintaining a 2.5% 3dB bandwidth, and an insertion loss of less than 0.5 dB at 77 K
    No preview · Article · Apr 2001 · IEEE Transactions on Applied Superconductivity
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    EZ Gao · S. Sahba · Hui Xu · Q.Y. Ma
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    ABSTRACT: We report a new RF resonator that operates at high frequency (HF, 3-30 MHz) of electromagnetic spectrum. The resonator is fabricated on a double-sided HTS (YBCO) thin film on a single 2" LAO substrate. The resonator is of smaller size and has a higher Q-value than conventional copper resonators. At temperatures below 77 K the Q-value of the resonator is above 40,000. A 3-pole filter is made by using 3 of this resonator which demonstrates a low insertion loss. This report will discuss the design, fabrication, RF characteristics (return and insertion loss), and the Q-value of the devices in detail. The simulated model of the RF characteristics of the devices will also be given
    Preview · Article · Jul 1999 · IEEE Transactions on Applied Superconductivity
  • Hui Xu · EZ Gao · S. Sahba · J.R. Miller · Q.Y. Ma · J.M. Pond
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    ABSTRACT: We have designed a three-pole bandpass filter operating at 15 MHz. The parameters of the filter include high Q, narrow band, low insertion loss and a return loss of 20 dB. The filter was fabricated from double-sided YBCO thin film on a two inch LAO substrate. The design utilizes individual HTS lumped elements (interdigital capacitors and meander line inductors) to realise the poles of the filter. The design and modeling of the filter are discussed in detail. Experimental results from the S-parameter measurements will be presented. Good agreement has been found between the simulation results and experimental data
    No preview · Article · Jul 1999 · IEEE Transactions on Applied Superconductivity