Automatic Coupling Control of a Loop–Gap Resonator by a Variable Capacitor Attached Coupling Coil for EPR Measurements at 650 MHz

Yokoyama, Hidekastu; Sato, Toshiyuki; Ogata, Toru; Ohya, Hiroaki; Kamada, Hitoshi

doi:10.1006/jmre.2000.2268

Cited by 30 publications

(13 citation statements)

References 9 publications

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“…Even if a trimmer capacitor C M is adjustable, critical coupling of the resonator could only be achieved when the other capacitors were appropriately adjusted. For several EPR resonators, remote tuning and matching circuits with varactor diodes have been reported [28][29][30][31]. Since the varactor diodes are usually used in applications with small signals, e.g., tuning of RF oscillators and radio/television receivers, non-linearity of the varactor diodes will appear in high-power applications.…”

Section: Resonator Designmentioning

confidence: 99%

“…Since AFC was operating in this measurement, a dominant cause of this periodic noise could be related to impedance mismatching of the resonator. This could be further suppressed with automatic matching control, also called automatic coupling control [28][29][30][31]. Figure 6B shows an EPR image of the bottle phantom in the ZY-plane (Fig.…”

Section: Sensitivity Distribution In the Loopmentioning

confidence: 99%

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A loop resonator for slice-selective in vivo EPR imaging in rats

Hirata

Deng

et al. 2008

Journal of Magnetic Resonance

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A loop resonator was developed for 300-MHz continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy and imaging in live rats. A single-turn loop (55 mm in diameter) was used to provide sufficient space for the rat body. Efficiency for generating a radiofrequency magnetic field of 38 µT/W 1/2 was achieved at the center of the loop. For the resonator itself, an unloaded quality factor of 430 was obtained. When a 350 g rat was placed in the resonator at the level of the lower abdomen, the quality factor decreased to 18. The sensitive volume in the loop was visualized with a bottle filled with an aqueous solution of the nitroxide spin probe 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (3-CP). The resonator was shown to enable EPR imaging in live rats. Imaging was performed for 3-CP that had been infused intravenously into the rat and its distribution was visualized within the lower abdomen.

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Section: Resonator Designmentioning

confidence: 99%

Section: Sensitivity Distribution In the Loopmentioning

confidence: 99%

A loop resonator for slice-selective in vivo EPR imaging in rats

Hirata

Deng

et al. 2008

Journal of Magnetic Resonance

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“…The RF source is a synthesizer on the basis of a PLL-locked VCO. The RF homodyne detection circuits were similar to the circuits designed in our institute [4,5]. The RF source and homodyne detection circuits were controlled by the personal computer via a digital-to-analog converter and parallel port.…”

Section: Epr Spectrometermentioning

confidence: 99%

Open-type EPR spectrometer to measure electron spins of a sample located outside a resonator

et al. 2003

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An open-type electron paramagnetic resonance (EPR) spectrometer to measure a sample located outside a resonator was fabricated. As the resonator, the field modulation coils, and the main magnet were integrated on the resonator side in the sensor head, the space fora sample was opened. Thus, a large sample could be placed at the end of the resonator without much limitation on the size. For ah apptication of this apparatus, various coal masses were placed on the resonator of the sensor head and EPR measurements were performed nondestructively. It was found that the EPR signal intensity of coals showed a good correlation with the carbon-to-hydrogen ratio, one of the parameters for classifying coal.

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“…A possible solution to this is to use automatic control techniques, such as automatic tuning control (ATC) and automatic matching control (AMC), also known as automatic coupling control. [1][2][3][4][5][6][7] In conventional CW-EPR spectroscopy, automatic frequency control (AFC) has been used. [8][9][10] An AFC system adjusts the microwave carrier frequency to the resonance frequency of the resonator.…”

Section: Introductionmentioning

confidence: 99%

Decoupling of automatic control systems in a continuous‐wave electron paramagnetic resonance spectrometer for biomedical applications

et al. 2004

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This article describes a systematic approach to decoupling automatic tuning control (ATC) and automatic matching control (AMC) systems in continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy for animal experiments. This technique enables us to improve the stability of CW-EPR spectroscopy even if the animal is moving during the data acquisition of EPR spectra. The control systems are formulated to allow the behavior of interference between them to be investigated, since they are generally coupled due to the characteristics of the microwave resonator. The stability of the entire control system in a 1.1 GHz CW-EPR spectrometer is evaluated with the generalized Nyquist stability criterion. We compare the EPR spectra of a triarylmethyl (TAM) radical that is dosed in anesthetized mice in terms of the signal-to-noise ratio (SNR) to test the precompensator for decoupling the ATC and AMC systems. The experimental findings suggest that the present technique is useful for improving the SNR of EPR spectra in animal experiments. The SNR of the measured EPR spectra was improved by about 50% with the precompensator.

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Automatic Coupling Control of a Loop–Gap Resonator by a Variable Capacitor Attached Coupling Coil for EPR Measurements at 650 MHz

Cited by 30 publications

References 9 publications

A loop resonator for slice-selective in vivo EPR imaging in rats

A loop resonator for slice-selective in vivo EPR imaging in rats

Open-type EPR spectrometer to measure electron spins of a sample located outside a resonator

Decoupling of automatic control systems in a continuous‐wave electron paramagnetic resonance spectrometer for biomedical applications

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