Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR

Strangeway, Robert A.; Hyde, James S.; Camenisch, Theodore G.; Sidabras, Jason W.; Mett, Richard R.; Anderson, J. R.; Ratke, Joseph J.; Subczynski, Witold K.

doi:10.1007/s12013-017-0804-7

Cited by 6 publications

(8 citation statements)

References 27 publications

(48 reference statements)

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“…In addition, use of low-noise amplifiers greatly reduces receiver noise. The fundamental rationale for use of 100 kHz field modulation was re-examined in a recent study at W-band (19). Use of lower field modulation frequencies will not lead to a decrease in the signal-to-noise ratio in many experiments, which alleviates one of the main difficulties in construction of self-designed resonators.…”

Section: Discussionmentioning

confidence: 99%

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Uniform Field Resonators for EPR Spectroscopy: A Review

Hyde

Sidabras

Mett

2018

Cell Biochem Biophys

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Cavity resonators are often used for electron paramagnetic resonance (EPR). Rectangular TE and cylindrical TE are common modes at X-band even though the field varies cosinusoidally along the Z-axis. The authors found a way to create a uniform field (UF) in these modes. A length of waveguide at cut-off was introduced for the sample region, and tailored end sections were developed that supported the microwave resonant mode. This work is reviewed here. The radio frequency (RF) magnetic field in loop-gap resonators (LGR) at X-band is uniform along the Z-axis of the sample, which is a benefit of LGR technology. The LGR is a preferred structure for EPR of small samples. At Q-band and W-band, the LGR often exhibits nonuniformity along the Z-axis. Methods to trim out this nonuniformity, which are closely related to the methods used for UF cavity resonators, are reviewed. In addition, two transmission lines that are new to EPR, dielectric tube waveguide and circular ridge waveguide, were recently used in UF cavity designs that are reviewed. A further benefit of UF resonators is that cuvettes for aqueous samples can be optimum in cross section along the full sample axis, which improves quantification in EPR spectroscopy of biological samples.

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Section: Discussionmentioning

confidence: 99%

“…LGR was much higher. The high bandwidth enabled the frequency sweep studies of Hyde et al (18) and led to a full paper on broadband W-band (19).…”

Section: Uniform Field Loop-gap Resonatorsmentioning

confidence: 97%

Uniform Field Resonators for EPR Spectroscopy: A Review

Hyde

Sidabras

Mett

2018

Cell Biochem Biophys

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“…Although the rectangular TE U02 cavity has no modulation slots, continuous-wave experiments can be performed using a low frequency (433 Hz) field modulation with little degradation to the continuous-wave EPR signal [15]. The uniformity of the field modulation was simulated to be 70% uniform over the region-of-interest.…”

Section: Discussionmentioning

confidence: 99%

“…EPR measurements were performed on a home-built W-band spectrometer [15]. Measurements were made at room temperature, with a 2.5 mT sweep width over 90 seconds and a receiver time constant of 10 ms.…”

Section: Methodsmentioning

confidence: 99%

Uniform field loop-gap resonator and rectangular TE U02 for aqueous sample EPR at 94 GHz

Sidabras

Sarna

Mett

et al. 2017

Journal of Magnetic Resonance

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In this work we present the design and implementation of two uniform-field resonators: a seven-loop–six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94 GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3 mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0.81 mm O.D.; 0.25 mm I.D.) for aqueous samples. Additionally, field modulation slots are designed for uniform 100 kHz field modulation incident at the sample. Experiments using a point sample of lithium phthalocyanine (LiPC) were performed to measure both the uniformity of the microwave magnetic field and 100 kHz field modulation, and confirm simulations. The rectangular TEU02 cavity resonator employs over-sized end-sections with sample shielding to provide an 87% uniform field for a 0.1 × 2 × 6 mm3 sample geometry. An evanescent slotted window was designed for light access to irradiate 90% of the sample volume. A novel dual-slot iris was used to minimize microwave magnetic field perturbations and maintain cross-sectional uniformity. Practical EPR experiments using the application of light irradiated rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) were performed in the TEU02 cavity. The implementation of these geometries providing a practical designs for uniform field resonators that continue resonator advancements towards quantitative EPR spectroscopy.

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“…Additional phase noise observations were made in a custom-designed W-band spectrometer [30][31][32]. In this instrument, low phase noise 35 and 59 GHz sources are mixed to generate low phase noise 94 GHz incident power.…”

Section: W-bandmentioning

confidence: 99%

Dispersion EPR: Considerations for Low-Frequency Experiments

2021

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The hypothesis is made that the dispersion electron paramagnetic resonance (EPR) spectrum can yield a higher signal-to-noise ratio than the absorption spectrum in diagnostic examinations if phase noise in the bridge is under control. The rationale for this hypothesis is based on the observation that the dispersion spectrum becomes more intense than the absorption spectrum at high incident powers. The rationale is dependent on optimization of high microwave efficiency (Λ; mT/W1/2) and low-quality factor (Q-value) sample resonators as well as the use of microwave sources with reduced phase noise. Microwave frequencies from 1.2 to 94 GHz are considered. Although the dispersion display appears to be observable with an adequate signal-to-noise ratio for most EPR research initiatives, a weakness of microwave bridges for studies at high incident microwave power was identified. Spurious leakage of incident microwave power through the circulator, thereby bypassing the probe leading to the resonator, can result in a decreased signal-to-noise ratio in both absorption and dispersion because of phase noise. For dispersion EPR with low Q-value sample resonators, this leakage is the primary contributor to phase noise at the receiver. In this work, we focus on the design of microwave reflection bridges and discuss possible methods to ameliorate this source of noise.

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Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR

Cited by 6 publications

References 27 publications

Uniform Field Resonators for EPR Spectroscopy: A Review

Uniform Field Resonators for EPR Spectroscopy: A Review

Uniform field loop-gap resonator and rectangular TE U02 for aqueous sample EPR at 94 GHz

Dispersion EPR: Considerations for Low-Frequency Experiments

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