Abstract: A system for reducing temporal fluctuations in a powered magnet. The system includes a magnetic field generator that generates a magnetic field with temporal fluctuations and a power supply having an AC/DC converter that delivers electric current to the magnetic field generator. A cascade compensator having an inner control loop that outputs an inner loop signal and an outer control loop that outputs an outer loop signal is included. The inner control loop has a pickup coil and an analog integrating preamplifier and the outer control loop has a magnetic resonance field estimator. The inner control loop senses fluctuations of the magnetic field over 1 Hz and the outer control loop senses fluctuations of the magnetic field from DC to 20 Hz. The cascade compensator generates a correcting magnetic field that cancels the fluctuations based on the inner loop signal and the outer loop signal.

Abstract: A system for reducing temporal fluctuations in a powered magnet. The system includes a magnetic field generator that generates a magnetic field with temporal fluctuations and a power supply having an AC/DC converter that delivers electric current to the magnetic field generator. A cascade compensator having an inner control loop that outputs an inner loop signal and an outer control loop that outputs an outer loop signal is included. The inner control loop has a pickup coil and an analog integrating preamplifier and the outer control loop has a magnetic resonance field estimator. The inner control loop senses fluctuations of the magnetic field over 1 Hz and the outer control loop senses fluctuations of the magnetic field from DC to 20 Hz. The cascade compensator generates a correcting magnetic field that cancels the fluctuations based on the inner loop signal and the outer loop signal.

Abstract: Apparatus and methods for locating a nuclear quadrupole resonance are described. In an example method, a search frequency is adjusted using a blind search until a resonance absorption of an analyte is detected, and then an extremum seeking search to be used to locate an extremum frequency.

Abstract: This invention relates to a method for improving the performance of a nuclear quadrupole resonance detection system by reducing, during reception, the coupling between one or more excitation coils that provide a radio frequency magnetic field that excites quadrupole nuclei, and one or more high temperature superconductor receive coils that detect the resulting nuclear quadrupole resonance signal.

Abstract: Narrowband quadrupole resonance (QR) probes were developed from thin-film high-temperature superconducting (HTS) resonators. The QR probes are useful in analyte-detection systems, in particular for the detection of nitrogen-containing compounds. Embodiments of the invention provide greater than an order of magnitude improvement in sensitivity and the ability to reject RF interference sources located outside the pass-band of a superconducting QR probe. Methods and apparatus are described for analyte detection and resonance frequency adjustment.

Abstract: The use of a superconducting resonator with continuous-wave (CW) excitation allows low-noise quadrupole resonance (QR) detection without the need for a lock-in amplifier. This allows detection times to be greatly reduced. Hence, for the first time, a CW QR spectrometer using a superconducting resonator can be used in a portable device, such as a hand-held wand for detecting explosives.

Abstract: Apparatus and methods for locating a nuclear quadrupole resonance are described. In an example method, a search frequency is adjusted using a blind search until a resonance absorption of an analyte is detected, and then an extremum seeking search to be used to locate an extremum frequency.

Abstract: This invention relates to a method for improving the performance of a nuclear quadrupole resonance detection system by reducing, during reception, the coupling between one or more excitation coils that provide a radio frequency magnetic field that excites quadrupole nuclei, and one or more high temperature superconductor receive coils that detect the resulting nuclear quadrupole resonance signal.

Abstract: The use of a circuit to adjust the resonance frequency of a high temperature superconductor self-resonant transmit, receive, or transmit and receive coil results in improved performance. The circuit is useful in a frequency detection system, especially in a nuclear quadrupole resonance detection system.