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Design and Optimization of HTS SQUID based Magnetocardiography using Active Shield

Shanehsazzadeh, Faezeh | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51412 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Fardmanesh, Mehdi
  7. Abstract:
  8. In this work, we report on a developed single-channel high-Tc SQUID based MCG system for operation in unshielded environment. In brief, our system consists of a liquid Nitrogen Dewar and two high-Tc rf-SQUID capsuled in a holding probe,which is connected via coaxial cables to our multichannel rf-SQUID readout electronics.The rf-SQUIDs were patterned from about 200 nm△10 nm thick YBCO films sputtered on 1 mm thick LaAlO3 substrates. The holding probe integrates rf-SQUIDs, LC resonant circuits, and shielding coils. We have investigated the effects of the lumped element tank circuit resonator parameters on the rf-SQUID signal characteristics and based on the simulation and experimental results. we optimized the resonator structure for the maximum sensor stability in shielded as well as in unshielded environments. Using the introduced improved tank circuit configuration resulted in higher output voltage of the rf-SQUID readout electronic, which led to higher sensitivity compared to that of the conventional ones. Also, we proposed a monolayer optimum design of HTS flux concentrator integrated with resonator for strong coupling to the rf-SQUIDs. An optimized monolayer flux concentrator was obtained with pick-up and input loops chosen so that to keep their inductances as close as possible to achieve the maximum matching and coupling efficiency possible.The proposed spiral shape resonator integrated with flux concentrator had all of the optimal specifications together with having a resonance frequency at 836 MHz and the quality factor of 5900 in addition to a maximum obtained coupling coefficient value of -0.5 dB. For noise cancellation, a bi-stage active shield system is proposed, which is based on high-Tc rf-SQUID sensors in gradiometric configuration for using in MCG systems in the passively unshielded environment. The presented shielding system reduces the low and the mid-range frequency magnetic field noises by use of two separate sets of coils and their controller systems. One part of the shielding system is a feedback system, optimized for the higher frequency range, containing two small coils surrounding the SQUID holding probe. The lowfrequency part of the shielding system incorporates two large coils surrounding the Dewar. All the coils are fed by the designed control systems using the properly optimized filtering with respect to their working frequencies, and PID controllers based on their characteristics. Using the designed shielding system, the disturbing magnetic signals of the environment could be attenuated up to 50 dB. So, the artificial heart signals with 100 pT amplitude could be obtained in our noisy laboratory environment
  9. Keywords:
  10. Magnetocardiography ; Noise Removing ; Radio Frequency Superconducting Quantum Interference Device (SQUID)Sensor ; Superconducting Quantum Interference Device (SQUID) ; Superconducting Resonator ; Active Magnetic Shield

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