Bridge12 in Action

Bridge12 products are used in a variety of applications in academic and industrial research. Below is a selected list of publications in which customers use our products in their research.

13. Introducing adaptive cold atmospheric plasma: The perspective of adaptive cold plasma cancer treatments based on real-time electrochemical impedance spectroscopy

Lin, Li, Zichao Hou, Xiaoliang Yao, Yi Liu, Jagadishwar R. Sirigiri, Taeyoung Lee, and Michael Keidar. “Introducing Adaptive Cold Atmospheric Plasma: The Perspective of Adaptive Cold Plasma Cancer Treatments Based on Real-Time Electrochemical Impedance Spectroscopy.” Physics of Plasmas 27, no. 6 (June 2020): 063501.

Following the understanding of the cold atmospheric plasma jet control, the optimization of plasma parameters for biomedical applications has become an important area of research in the field of plasma-based cancer treatment. A real-time feedback signal is usually required by a control algorithm, such as a self-adaptive plasma jet, which is designed to automatically self-optimize its parameters to adapt to a variety of biomedical applications and situations. In this paper, we introduce the potential of replacing the cell viability or cell stress assay with electrochemical impedance spectroscopy (EIS) to provide a real-time feedback signal for a model predictive control (MPC) method aided by machine learning. The EIS frequency is in the kHz to GHz regime. Therefore, the MPC method is not only designed for minimizing the cancer cell viability, but also considered to optimize cell membrane behaviors and other chemical species dialing. Since these signals are in the range of GHz, we introduce alternatives for the impedance analyzer to measure the impedance spectrum, including a Fabry–Perot resonator and one of its scanning-array variations.

12. High-Resolution Overhauser Dynamic Nuclear Polarization Enhanced Proton NMR Spectroscopy at Low Magnetic Fields

Keller, Timothy J., Alexander J. Laut, Jagadishwar Sirigiri, and Thorsten Maly. “High-Resolution Overhauser Dynamic Nuclear Polarization Enhanced Proton NMR Spectroscopy at Low Magnetic Fields.” Journal of Magnetic Resonance, March 2020, 106719.

Dynamic nuclear polarization (DNP) has gained large interest due to its ability to increase signal intensities in nuclear magnetic resonance (NMR) experiments by several orders of magnitude. Currently, DNP is typically used to enhance high-field, solid-state NMR experiments. However, the method is also capable of dramatically increasing the observed signal intensities in solution-state NMR spectroscopy. In this work, we demonstrate the application of Overhauser dynamic nuclear polarization (ODNP) spectroscopy at an NMR frequency of 14.5 MHz (0.35 T) to observe DNP-enhanced high-resolution NMR spectra of small molecules in solutions. Using a compact hybrid magnet with integrated shim coils to improve the magnetic field homogeneity we are able to routinely obtain proton linewidths of less than 4 Hz and enhancement factors > 30. The excellent field resolution allows us to perform chemical-shift resolved ODNP experiments on ethyl crotonate to observe proton J-coupling. Furthermore, recording high-resolution ODNP-enhanced NMR spectra of ethylene glycol allows us to characterize the microwave induced sample heating in-situ, by measuring the separation of the OH and CH2 proton peaks.

11. Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron

Gao, Chukun, Nicholas Alaniva, Edward P. Saliba, Erika L. Sesti, Patrick T. Judge, Faith J. Scott, Thomas Halbritter, Snorri Th. Sigurdsson, and Alexander B. Barnes. “Frequency-Chirped Dynamic Nuclear Polarization with Magic Angle Spinning Using a Frequency-Agile Gyrotron.” Journal of Magnetic Resonance 308 (November 2019): 106586.

We demonstrate that frequency-chirped dynamic nuclear polarization (DNP) with magic angle spinning (MAS) improves the enhancement of nuclear magnetic resonance (NMR) signal beyond that of continuous-wave (CW) DNP. Using a custom, frequency-agile gyrotron we implemented frequencychirped DNP using the TEMTriPol-1 biradical, with MAS NMR at 7 Tesla. Frequency-chirped microwaves yielded a DNP enhancement of 137, an increase of 19% compared to 115 recorded with CW. The chirps were 120 MHz-wide and centered over the trityl resonance, with 7 W microwave power incident on the sample (estimated 0.4 MHz electron spin Rabi frequency). We describe in detail the design and fabrication of the frequency-agile gyrotron used for frequency-chirped MAS DNP. Improvements to the interaction cavity and internal mode converter yielded efficient microwave generation and mode conversion, achieving >10 W output power over a 335 MHz bandwidth with >110 W peak power. Frequency-chirped DNP with MAS is expected to have a significant impact on the future of magnetic resonance.

10. Thermo-mechanical analysis of a probe for electron paramagnetic resonance spectroscopy operating at cryogenic temperatures

Dev, Bodhayan, Charan Raj Gujjala, and Thorsten Maly. “Thermo-Mechanical Analysis of a Probe for Electron Paramagnetic Resonance Spectroscopy Operating at Cryogenic Temperatures.” Review of Scientific Instruments 90, no. 4 (April 2019): 045123.

In this article, we present the thermo-mechanical analysis of an electron paramagnetic resonance (EPR) probe operating at cryogenic temperatures using finite element analysis. Thermo-mechanical analysis plays a key role in the mechanical design evaluation process as EPR probes are often subjected to large stresses under such extreme conditions. For simplification, we assume thermal conduction to be the dominant mode of heat transfer over convection and radiation. The simulation model consists of a cryostat-probe assembly with appropriate thermal and structural boundary conditions. The predicted temperature distributions from the steady-state thermal analysis is then used for the stress analysis of the EPR probe. The stress analysis indicated that stresses in the EPR probe are below the ultimate strengths of each component, and thus safe for running EPR experiments. Furthermore, the simulation results were confirmed experimentally, and we found that the predicted heat losses for the EPR probe assembly and the sample holder are in excellent agreement with the experimental measurements.

9. Magic angle spinning NMR with metallized rotors as cylindrical microwave resonators

Scott, Faith J., Erika L. Sesti, Eric J. Choi, Alexander J. Laut, Jagadishwar R. Sirigiri, and Alexander B. Barnes. “Magic Angle Spinning NMR with Metallized Rotors as Cylindrical Microwave Resonators.” Magnetic Resonance in Chemistry, May 16, 2018.

We introduce a novel design for millimeter wave electromagnetic structures within magic angle spinning (MAS) rotors. In this demonstration, a copper coating is vacuum deposited onto the outside surface of a sapphire rotor at a thickness of 50 nanometers. This thickness is sufficient to reflect 197 GHz microwaves, yet not too thick as to interfere with radiofrequency fields at 300 MHz or prevent sample spinning due to eddy currents. Electromagnetic simulations of an idealized rotor geometry show a microwave quality factor of 148. MAS experiments with sample rotation frequencies of ωr/2π = 5.4 kHz demonstrate that the drag force due to eddy currents within the copper does not prevent sample spinning. Spectra of sodium acetate show resolved 13C J-couplings of 60 Hz and no appreciable broadening between coated and uncoated sapphire rotors, demonstrating that the copper coating does not prevent shimming and high-resolution NMR spectroscopy. Additionally, 13C Rabi nutation curves of ω1/2π = 103 kHz for both coated and uncoated rotors indicate no detrimental impact of the copper coating on radiofrequency coupling of the nuclear spins to the sample coil. We present this metal coated rotor as a first step towards an MAS resonator. MAS resonators are expected to have a significant impact on developments in electron decoupling, pulsed DNP, room temperature DNP, DNP with low power microwave sources, and EPR detection.

8. Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization

Scott, F. J., E. P. Saliba, B. J. Albert, N. Alaniva, E. L. Sesti, C. Gao, N. C. Golota, et al. “Frequency-Agile Gyrotron for Electron Decoupling and Pulsed Dynamic Nuclear Polarization.” J Magn Reson 289 (April 2018): 45–54.

We describe a frequency-agile gyrotron which can generate frequency-chirped microwave pulses. An arbitrary waveform generator (AWG) within the NMR spectrometer controls the microwave frequency, enabling synchronized pulsed control of both electron and nuclear spins. We demonstrate that the acceleration of emitted electrons, and thus the microwave frequency, can be quickly changed by varying the anode voltage. This strategy results in much faster frequency response than can be achieved by changing the potential of the electron emitter, and does not require a custom triode electron gun. The gyrotron frequency can be swept with a rate of 20MHz/mus over a 670MHz bandwidth in a static magnetic field. We have already implemented time-domain electron decoupling with dynamic nuclear polarization (DNP) magic angle spinning (MAS) with this device. In this contribution, we show frequency-swept DNP enhancement profiles recorded without changing the NMR magnet or probe. The profile of endofullerenes exhibits a DNP profile with a <10MHz linewidth, indicating that the device also has sufficient frequency stability, and therefore phase stability, to implement pulsed DNP mechanisms such as the frequency-swept solid effect. We describe schematics of the mechanical and vacuum construction of the device which includes a novel flanged sapphire window assembly. Finally, we discuss how commercially available continuous-wave gyrotrons can potentially be converted into similar frequency-agile high-power microwave sources.

8. A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument

Siaw, T. A., A. Leavesley, A. Lund, I. Kaminker, and S. Han. “A Versatile and Modular Quasi Optics-Based 200GHz Dual Dynamic Nuclear Polarization and Electron Paramagnetic Resonance Instrument.” J. Magn. Reson. 264 (March 2016): 131–53.

Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3T) and cryogenic temperatures ( approximately 2-90K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the “DNP power curve”, i.e. the microwave (MW) power dependence of DNP enhancement, the “DNP spectrum”, i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201GHz and outputs up to 140mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW bridge will provide an efficient means to collect DNP data that is crucial for understanding the relationship between experimental and sample conditions, and the DNP performance. The modularity of this instrumental platform is suitable for future upgrades and extensions to include new experimental capabilities to meet contemporary DNP needs, including the simultaneous operation of two or more MW sources, time domain DNP, electron double resonance measurements, pulsed EPR operation, or simply the implementation of higher power MW amplifiers.

7. Advanced instrumentation for DNP-enhanced MAS NMR for higher magnetic fields and lower temperatures

Matsuki, Y., T. Idehara, J. Fukazawa, and T. Fujiwara. “Advanced Instrumentation for DNP-Enhanced MAS NMR for Higher Magnetic Fields and Lower Temperatures.” J Magn Reson 264 (March 2016): 107–15.

Sensitivity enhancement of MAS NMR using dynamic nuclear polarization (DNP) is gaining importance at moderate fields (B0<9T) and temperatures (T>90K) with potential applications in chemistry and material sciences. However, considering the ever-increasing size and complexity of the systems to be studied, it is crucial to establish DNP under higher field conditions, where the spectral resolution and the basic NMR sensitivity tend to improve. In this perspective, we overview our recent efforts on hardware developments, specifically targeted on improving DNP MAS NMR at high fields. It includes the development of gyrotrons that enable continuous frequency tuning and rapid frequency modulation for our 395GHz-600MHz and 460GHz-700MHz DNP NMR spectrometers. The latter 700MHz system involves two gyrotrons and a quasi-optical transmission system that combines two independent sub-millimeter waves into a single dichromic wave. We also describe two cryogenic MAS NMR probe systems operating, respectively, at T approximately 100K and approximately 30K. The latter system utilizes a novel closed-loop helium recirculation mechanism, achieving cryogenic MAS without consuming any cryogen. These instruments altogether should promote high-field DNP toward more efficient, reliable and affordable technology. Some experimental DNP results obtained with these instruments are presented.

6. The Development of 460 GHz gyrotrons for 700 MHz DNP-NMR spectroscopy

Idehara, T., Y. Tatematsu, Y. Yamaguchi, E. M. Khutoryan, A. N. Kuleshov, K. Ueda, Y. Matsuki, and T. Fujiwara. “The Development of 460 GHz Gyrotrons for 700 MHz DNP-NMR Spectroscopy.” Journal of Infrared, Millimeter, and Terahertz Waves, March 15, 2015, 1–15.

Two demountable gyrotrons with internal mode converters were developded as sub-THz radiation sources for 700 MHz DNP (Dynamic Nuclear Polarization) enhanced NMR spectroscopy. Experimental study on the DNP-NMR spectroscopy will be carried out in Osaka University, Institute for Protein Research, as a collaboration with FIR UF. Both gyrotrons operate near 460 GHz and the output CW power measured at the end of transmission system made by circular waveguides is typically 20 to 30 watts. One of them named Gyrotron FU CW GVI (we are using “Gyrotron FU CW GO-1” as an official name in Osaka University) is designed to have a special function of high speed frequency modulation δf within 100 MHz band. This will expand excitable band width of ESR and increase the number of electron spins contributing to DNP. The other gyrotron, Gyrotron FU CW GVIA (“Gyrotron FU CW GO-II”) has a function of frequency tunability Δf in the range of wider than 1.5 GHz, which is achieved in steady state by changing magnetic field intensity. This function should be used for adjusting the output frequency at the optimal value to achieve the highest enhancement factor of DNP.

5. Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

Hoff, D. E., B. J. Albert, E. P. Saliba, F. J. Scott, E. J. Choi, M. Mardini, and A. B. Barnes. “Frequency Swept Microwaves for Hyperfine Decoupling and Time Domain Dynamic Nuclear Polarization.” Solid State Nuclear Magnetic Resonance 72 (November 2015): 79–89.

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions.

4. 263 GHz Traveling Wave Tube (TWT) amplifier for Dynamic Nuclear Polarization (DNP) and Electron Paramagnetic Resonance (EPR) spectroscopy

Fernandez-Gutierrez, S., Dennis Gautreau, and J. R. Sirigiri. “263 GHz Traveling Wave Tube (TWT) Amplifier for Dynamic Nuclear Polarization (DNP) and Electron Paramagnetic Resonance (EPR) Spectroscopy.” In 2015 40th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 1–1. Hong Kong, China: IEEE, 2015.

We present the circuit design of a 263 GHz Traveling Wave Tube (TWT) amplifier for use in Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (NMR). The circuit design achieves a linear gain of 36 dB and output power > 50 W. This work describes the design of the interaction circuit for optimal interaction with a 20 kV, 125 mA elliptical beam using 3D electromagnetic Finite Element Method (FEM) and Particle-in-Cell (PIC) solvers.

3. Corrugated transmission line systems for 395 GHz/600 MHz and 460 GHz/700 MHz DNP-NMR spectroscopy

Sirigiri, J. R., T. Maly, N. Tarricone, J. Zhou, T. Idehara, Y. Matsuki, and T. Fujiwara. “Corrugated Transmission Line Systems for 395 GHz/600 MHz and 460 GHz/700 MHz DNP-NMR Spectroscopy,” 1–1, 2014.

We present the design, initial installation and test results of two corrugated waveguide transmission line systems for coupling terahertz power from gyrotrons to two different solid-state Dynamic Nuclear Polarization – Nuclear Magnetic Resonance (DNP-NMR) spectrometers at 600 MHz and 700 MHz (1H). The first system combines the power from two different tunable 460 GHz gyrotrons to the DNP-NMR experiment while the second line couples power from a single 395 GHz tunable gyrotron to the DNP-NMR experiment. The lines are currently being installed at the Institute of Protein Research in Osaka University. Test results of individual components and system level test results will be presented.

2. Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy

Maly, T., and J. R. Sirigiri. “Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy.” Applied Magnetic Resonance 43 (July 1, 2012): 181–94

We present an alternate simplified concept to irradiate a nuclear magnetic resonance sample with terahertz (THz) radiation for dynamic nuclear polarization (DNP) experiments using the TE(01) circular waveguide mode for transmission of the THz power and the illumination of the DNP sample by either the TE(01) or TE(11) mode. Using finite element method and 3D electromagnetic simulations we demonstrate that the average value of the transverse magnetic field induced by the THz radiation and responsible for the DNP effect using the TE(11) or the TE(01) mode are comparable to that generated by the HE(11) mode and a corrugated waveguide. The choice of the TE(11)/TE(01) mode allows the use of a smooth-walled, oversized waveguide that is easier to fabricate and less expensive than a corrugated waveguide required for transmission of the HE(11) mode. Also, the choice of the TE(01) mode can lead to a simplification of gyrotron oscillators that operate in the TE(0n) mode, by employing an on-axis rippled-wall mode converter to convert the TE(0n) mode into the TE(01) mode either inside or outside of the gyrotron tube. These novel concepts will lead to a significant simplification of the gyrotron, the transmission line and the THz coupler, which are the three main components of a DNP system.

1. A 200 GHz Dynamic Nuclear Polarization Spectrometer

Armstrong, Brandon D., Devin T. Edwards, Richard J. Wylde, Shamon A. Walker, and Songi Han. “A 200 GHz Dynamic Nuclear Polarization Spectrometer.” Physical Chemistry Chemical Physics 12 (2010): 5920–26.

We present our experimental setup for both dynamic nuclear polarization (DNP) and electron paramagnetic resonance (EPR) detection at 7 T using a quasi-optical bridge for propagation of the 200 GHz beam and our initial results obtained at 4 K. Our quasi-optical bridge allows the polarization of the microwave beam to be changed from linear to circular. Only the handedness of circular polarization in the direction of the Larmor precession is absorbed by the electron spins, so a gain in effective microwave power of two is expected for circular vs. linear polarization. Our results show an increase in DNP signal enhancement of 28% when using circularly vs. linearly polarized radiation. We measured a maximum signal enhancement of 65 times that of thermal polarization for a 13C labeled urea sample corresponding to 3% nuclear spin polarization. Since the time constant for nuclear spin polarization buildup during microwave irradiation is 10 times faster than the 13C nuclear spin T1, the actual gain in detection sensitivity with DNP is much greater.

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