Electron Spin Resonance Spectrometer Research Articles

Understanding the Reaction Mechanism and Kinetics of Mediated Li-O2 Batteries Using Flow Set-Ups and Cyclic Voltammetry

Li-O2 batteries are very promising candidates for electromobility because of their very high theoretical energy density. Moreover, they are composed of abundant materials, as opposed to Li-ion batteries, which would make them a greener and cheaper alternative. The principal reaction in Li-O2 batteries is the formation of lithium peroxide during discharge via the oxygen reduction reaction (ORR), that is then oxidised during the charge by the oxygen evolution reaction (OER). One of the major challenges of Li-O2 batteries is related to the insulating nature of their discharge product, that significantly limits the capacity and hinders performance. A strategy to overcome this is by using redox mediators (RMs), which shuttle electrons from the electrode surface to the solution and thus facilitate a solution-based mechanism for the formation of large crystals. Understanding the reaction kinetics of these RMs can therefore aid in increasing the battery performance.Quinones, specifically 2,5-Di-tert-butyl-1,4-benzoquinone (DBBQ),is a commonly used discharge RM in this type of batteries. However, their reaction kinetics and how these vary with different electrolyte conditions are not yet well understood. DBBQ undergoes two single electron reductions, whose potentials and kinetics vary with salt concentrations and solvent having a direct effect on its ability to mediate the ORR.In this work, we have developed a Li-O2 flow cell to study the reaction mechanism and kinetics of DBBQ, and performed cyclic voltammetry (CV) studies to better understand how these vary with changing solvent and salt conditions. In the Li-O2 flow set-up the battery is positioned outside the nuclear magnetic resonance (NMR) magnet and plastic tubing then runs through the NMR and electron paramagnetic resonance (EPR) spectrometers. In this way, the reduction of the DBBQ can be monitored while the battery is cycling. In the proton NMR, the neutral DBBQ signals disappear on discharge as the singly reduced DBBQ semiquinone monoanion is a radical. The fast electron exchange between the neutral and radical species broaden out the NMR signals on discharge as the EPR signal grows. On charge, the neutral DBBQ signal reappears and the EPR signal disappears. The Li-O2 flow set-up is very sensitive to air and moisture exposure as the tubing is not perfectly impermeable to them. Therefore, having the CVs as a complementary method to study the reaction mechanisms and kinetics is very useful.We have developed a theoretical framework of Li-coupled electron transfer reactions that can predict the electrochemical kinetics in the presence of high and low donor number solvents and used to quantify thermodynamic and kinetic parameters. We define E0 app and k0 app as the apparent thermodynamic and kinetic parameters that describe the overall system and can be derived from the Nernst equation and Butler Volmer kinetics. These overall descriptors depend on the pathway the reaction takes (Figure 1). The different pathways in different solvents/salts are due to changes in the Li+ solvation strength as well as the competing ionic association of the counter anion.Experimentally, we have shown that in three different solvents, DME, tetraglyme and DMSO the behaviour of DBBQ can be explained by this theoretical framework. In DME, the DBBQ behaviour is most reminiscent of pathway 1 where the kinetics slow down with increasing Li+ concentration. In DMSO the kinetics present a maximum at Li+ concentrations around 1M. Simulations and fitting of the CV experiments in DMSO for the first reduction are in good agreement with pathways 2 and 3, while in tetraglyme it is harder to explain the trends as they do not fit into just one of the pathways.In conclusion we have studied the mechanism and kinetics of DBBQ as a RM for Li-O2 batteries with an in-situ flow set up and CVs and build a theoretical framework to understand how these vary in different electrolyte conditions. This method can be extended to study both the second reduction of DBBQ and other discharge and charge RMs for Li-O2 batteries. Figure 1

First magnetic and spectroscopic constraints on attenuated space weathering at the Chang'e-5 landing site

Space weathering is a primary process altering the lunar surface, producing submicroscopic iron particles embedded in soil grains, which have diagnostic magnetic and spectroscopic effects. However, the space weathering of lunar soils from young geological units remains mysterious without solid constraints from returned samples. Chang'e-5 mission is the first lunar sample-return mission in decades. The Chang'e-5 landing and sampling unit (∼2.0 Ga) is much younger than all Apollo and Luna units (>3.0 Ga). It has provided an unprecedented opportunity to reveal the recent space weathering characteristics with both returned soil samples and in situ investigation data. In this study, magnetic approaches (Vibrating Sample Magnetometer, Electron Paramagnetic Resonance Spectrometer, Mössbauer Spectrometer) were used to characterize the Chang'e-5 lunar soil for the first time after the return of the samples, strongly supporting it is among the most immature soils on the Moon with a metallic iron abundance of 0.42% and an Is/FeO value of 14−10+6. Additional Landing Camera and Lunar Mineralogical Spectrometer (480–3200 nm) data obtained surrounding the sampling area were used to study the lateral effects of rocket exhaust. All data from soil samples and in situ observations have offered magnetic and spectroscopic constraints on the space weathering state of the Chang'e-5 site. The combined effects of rocket exhaust by removing the top highly weathered soil and the young age of the landing site with lesser degree of impact reworking may attenuate the maturity of Chang'e-5 lunar soils.

Covalent organic frameworks doped with manganese-metal organic framework for peroxymonosulfate activation

A novel N, O modified Mn3O4@porous carbon catalyst (NOC-Mn3O4) was prepared by direct carbonization using the manganese-metal organic framework (Mn-MOF) and covalent organic framework (COF) as precursors to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA) and rhodamine B (RhB). Benefiting from the N and O co-doping of COF, larger specific surface area, faster electron transfer and Mn cycling, the optimum 1NOC-Mn3O4 could significantly improve the degradation performance of BPA and RhB (92.1% and 96.9% within 30 min) as compared to C-Mn3O4 without COF doping. In addition, 1NOC-Mn3O4 showed good reusability and strong anti-interference ability. Radical quenching experiments, X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance spectrometer (EPR) and electrochemical tests showed that the 1NOC-Mn3O4/PMS system degraded BPA and RhB by both radical and non-radical pathways. Moreover, the possible degradation pathways of BPA and RhB were proposed by liquid chromatography-mass spectrometry (LC-MS). Except for that, the toxicity of BPA, RhB and their intermediates were evaluated. This study opens up a new prospect for the design of COF-doped PMS catalysts.

Enhancement of microwave fields in pulse EPR of quantum paraelectrics

The pulse electron paramagnetic resonance (EPR) is widely used in different branches of material and life sciences, including promising applications in quantum information processing and quantum sensing. Here, we study the effect of the high polarizability of KTaO3 and SrTiO3 quantum paraelectrics on local electric and magnetic field components of microwaves (MW) at Fe3+ and Mn2+ paramagnetic ions. The measurements are performed with a commercial EPR spectrometer using dielectric and split-ring resonators. It is found that the power of MW pulses used in coherent spin manipulation at nanoseconds timescale decreases to milliwatts as compared to the tens–hundreds of watts usually used for spins in conventional materials. The amplification of MW fields is related to the very high dielectric permittivity (up to 25 000 in SrTiO3) of quantum paraelectrics at GHz frequencies and temperatures below 20 K. This creates the large induced polarization and, thus, huge displacement current and in turn the secondary MW magnetic field. Numerical simulations support the observation of the enhanced magnetic MW field in the high-permittivity sample. The low MW power for excitation of spin transitions in quantum paraelectrics eliminates the requirement of expensive high-power MW equipment. This approach also allows to globally control spin qubits in tandem with integrated devices based on conventional semiconductor MW circuits working at mW powers. It is suggested that quantum paraelectrics can also be used as substrates for deposition of nanoparticles or films of other materials, which would be manipulated by the low-power MW pulses.

Alteration in the molecular structure of the adenine base exposed to gamma irradiation: An ESR study

Abstract Adenine polycrystals were obtained from their powder form under effective crystallization conditions by adjustment of the concentration of chemical solutions. The adenine samples were irradiated with a 60Co gamma-ray source at room temperature for 12, 24, 48, and 72 h, and then these samples were investigated between 240 and 400 K using an electron spin resonance (ESR) spectrometer. No signals were observed in the non-irradiated samples irradiated for 12, 24, and 48 h; however, when irradiated for 72 h, the samples exhibited complex ESR spectra. The analysis indicated the presence of a radical structure, NH ̇ \dot{{NH}} . The hyperfine splitting and g-values were calculated from the spectra by simulation programs. Also, during the measurements, it was observed that the shapes of the ESR lines changed slightly with the temperature.

Highly effective degradation of ibuprofen by alkaline metal-doped copper oxides via peroxymonosulfate activation: Mechanisms, degradation pathway and toxicity assessments

Redox ratios of Cu2+/Cu+ and adsorbed oxygen species (Oads) have shown great activity toward radical generation by activating peroxymonosulfate (PMS). Herein, different alkaline metal oxides (CaO, MgO and BaO) and various amounts of CaO are incorporated into CuO, which could tune the main active sites of redox ratios of Cu2+/Cu+ and Oads. The results show that CaO-CuO-5% exhibits the outstanding performance of PMS activation toward ibuprofen (IBF) degradation with excellent kinetics (k = 0.812 min−1). The X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation show that the CaO-CuO-5% has the higher electron density with superior electron transfer ability and lower PMS adsorption energy. Based on radical scavengers and electron paramagnetic resonance spectrometer (EPR), a nonradical process is proposed to play the dominant role. The degradation pathway and the corresponding toxicity of degraded intermediates with residue PMS after reaction is evaluated by LC-MS/MS and bioassay experiments, indicating the lower antagonistic influence on human hormone receptors after advanced oxidation process. Mitigation of the Cu leaching with cyclic stability can be achieved. This study provides a facile method to optimize high-performance catalysts to activate PMS and offer practical environmental applications in the remediation of emerging contaminants.

Ultrasonic assisted activation of persulfate for the treatment of spent porous biochar: Degradation of adsorbed PFOA and adsorbent regeneration

In this work, the regeneration of spent biochar adsorbent and the degradation of adsorbed PFOA by the system of ultrasonic assisted activation of persulfate were explored. The effects of ultrasound, persulfate and biochar on PFOA removal were investigated through a series of regeneration and degradation experiments. Meanwhile, the degradation mechanism and reaction pathways of PFOA were investigated with electron paramagnetic resonance (EPR) and high-resolution quadrupole orbitrap mass spectrometer. The results showed that PFOA adsorbed by biochar could be degraded efficiently with the synergistic effect of ultrasound and persulfate. The degradation of PFOA in biochar could be finished in 4 h, while the defluorination took longer, with a defluorination efficiency of 50.6% after 4 h and 99.6% after 10 h. In this process, PFOA was degraded and defluorinated gradually by thermal decomposition caused by cavitation bubbles and degradation caused by the attack of SO4•ˉ and •OH. Two different free radicals controlled different degradation pathways, with SO4•ˉ playing a dominant role. In this system, the regeneration of the waste biochar adsorbent was achieved by eliminating PFOA, which could be recycled more than three times. The application potential of the system was evaluated using real water sample, and it was found that the removal of PFOA in real water sample was satisfactory even with the influence of inorganic ions and organic matter, indicating that it has promising application prospects. This work provided new insight into the degradation of adsorbed PFOA and adsorbent regeneration.

Insights into a Removal Mechanism of Triclosan Using an Electroactivated Persulfate-Coupled Carbon Membrane System

Triclosan (TCS), a broad-spectrum bacteriostatic agent with bactericidal and disinfectant properties, is one of the emerging pollutants of great interest. The electrically activated persulfate-coupled carbon membrane system was studied in this paper. The removal of triclosan achieved 90% within 40 min. Complete degradation can be achieved within 90 min. The electrode was characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The optimal reaction conditions were explored. The catalytic mechanism of the reaction was investigated. It was proved that hydroxyl radicals, sulfate radicals, and singlet oxygen were the main reactive oxygen species in the reaction process by the free radical quenching experiment and electron paramagnetic resonance spectrometer. The degradation path and mechanism of triclosan were investigated.

Order-of-magnitude SNR improvement for high-field EPR spectrometers via 3D printed quasi-optical sample holders.

Here, we present a rapidly prototyped, cost-efficient, and 3D printed quasi-optical sample holder for improving the signal-to-noise ratio (SNR) in modern, resonator-free, and high-field electron paramagnetic resonance (HFEPR) spectrometers. Such spectrometers typically operate in induction mode: The detected EPR ("cross-polar") signal is polarized orthogonal to the incident ("co-polar") radiation. The sample holder makes use of an adjustable sample positioner that allows for optimizing the sample position to maximize the 240-gigahertz magnetic field B1 and a rooftop mirror that allows for small rotations of the microwave polarization to maximize the cross-polar signal and minimize the co-polar background. When optimally tuned, the sample holder was able to improve co-polar isolation by ≳20 decibels, which is proven beneficial for maximizing the SNR in rapid-scan, pulsed, and continuous-wave EPR experiments. In rapid-scan mode, the improved SNR enabled the recording of entire EPR spectra of a narrow-line radical in millisecond time scales, which, in turn, enabled real-time monitoring of a sample's evolving line shape.

MEPROS – Modular electron paramagnetic resonance operating software for multifunctional high-frequency EPR spectrometer

We present a software solution developed in LabVIEW for a home-built High–Frequency Electron Paramagnetic Resonance (HF-EPR) spectrometer. A modular approach was applied to control the spectrometer subsystems and simplify the adaptation to hardware changes during the development. The solution implements measuring procedures for conventional Continuous Wave EPR (CW-EPR), Frequency–Swept EPR (FS-EPR), and Two-Dimensional EPR (2D-EPR) mapping, which are relevant in different cases. The software’s automation capabilities were tested in several trial measurements to obtain CW-EPR spectra of Silicon Carbide doped by vanadium (SiC + V) at various temperatures and microwave frequencies, multi-frequency spectra via 2D-EPR mapping, and dense FS-EPR data of a lithium phthalocyanine crystal rotated in a magnetic field. Several prospective modifications of the software are discussed in the conclusion. A modular character allows the easy re-use of code portions in other experimental setups. The spectrometer and the software are currently deployed and utilized in a laboratory of EPR spectroscopy at Central European Institute of Technology (CEITEC) in Brno, and data obtained by it has been already used in a number of publications.

The measurement of radiation doses in brachytherapy using an alanine dosimeter

Background: Brachytherapy involves the use of high radiation doses to treat cancer patients, making it essential to have appropriate dosimeter properties to confirm the accuracy and precision of the dose delivered to the patient. Objectives: This study was to investigate the relationship between radiation dose and electron spin resonance (ESR) signal and to evaluate the optimal conditions for the ESR technique. Additionally, the radiation dose from brachytherapy was measured in a solid phantom using alanine in combination with the ESR technique. Materials and methods: The alanine dosimeter (FWT-50-10, Steris, USA), ionization chamber (TW30013, PTW Freiburge, Germany), and transferring tube were positioned inside the solid phantom (Krieger, T9193, PTW Freiburge, Germany), with the BEBIG Co-60 source located at the center of the phantom. Dwell times were calculated to obtain a radiation dose range of 0.06-1.5 Gy. Following irradiation, the alanine derivative was measured using an ESR spectrometer, and a graph was generated to determine the relationship between radiation dose and ESR signal. The uncertainty and fading of the ESR signal were also evaluated. Results: The results indicate that there is a linear relationship (R2 = 0.877) between the radiation dose range of 0.49-1.5 Gy and ESR signal, with a microwave power of 1.5 milliwatt. The uncertainty of the ESR signal was found to be in the range of 0.12% - 3.79%. Signal fading was observed to be in the range of 7.2% - 27.4% over a period of two weeks. Conclusion: Alanine and ESR technique can be used to measure absorbed dose in brachytherapy. The dose response of alanine was linear for radiation doses above 0.49 Gy. The advantages of alanine dosimetry are that alanine is tissue equivalent, nondestructive, small in size, and has low signal uncertainty.

Large cross-effect dynamic nuclear polarisation enhancements with kilowatt inverting chirped pulses at 94 GHz

Dynamic nuclear polarisation (DNP) is a process that transfers electron spin polarisation to nuclei by applying resonant microwave radiation, and has been widely used to improve the sensitivity of nuclear magnetic resonance (NMR). Here we demonstrate new levels of performance for static cross-effect proton DNP using high peak power chirped inversion pulses at 94 GHz to create a strong polarisation gradient across the inhomogeneously broadened line of the mono-radical 4-amino TEMPO. Enhancements of up to 340 are achieved at an average power of a few hundred mW, with fast build-up times (3 s). Experiments are performed using a home-built wideband kW pulsed electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz, integrated with an NMR detection system. Simultaneous DNP and EPR characterisation of other mono-radicals and biradicals, as a function of temperature, leads to additional insights into limiting relaxation mechanisms and give further motivation for the development of wideband pulsed amplifiers for DNP at higher frequencies.

A miniaturized quintuple-band frequency selective surface based on enclosed cross slots

Abstract This article presents a low-profile quintuple-band frequency selective surface (FSS) that is designed as a sub-reflector for applications including satellite systems (C band), EPR (electron paramagnetic resonance) spectrometers, motion and traffic light crossing detectors (X band), Direct Broadcast Satellite and broadcasting satellite service (Ku band), and shortrange applications (K band). The dimensions of the miniaturized unit cell 0.08λ0×0.08λ0×0.012λ0, where, λ0 is the free-space wavelength corresponding to the lower cut-off frequency. There are five stop bands, and frequencies at which they resonate are 6.3, 7.06, 9.30, 11.2, 14.0, and 18.64 GHz. The fractional bandwidths (FBW) of these bands are 62.6, 7.5, 9.2, 11, and 11.69%, respectively. Additionally, as a result of the structure’s four-fold symmetry, it exhibits a good polarization-insensitive response as well as a stable response in both the TE and TM modes. Full-wave simulation is performed on the structure, after which an equivalent circuit model is constructed.

Time-resolved electron paramagnetic resonance spectrometer based on ultrawide single-sideband phase-sensitive detection.

A time-resolved electron paramagnetic resonance (TREPR) method with 40ns time resolution and a high sensitivity suitable for the detection of short-lived radicals under thermal equilibrium is developed. The key is the introduction of a new detection technique named ultrawide single sideband phase sensitive detection (U-PSD) to the conventional continuous-wave EPR, which remarkably enhanced the sensitivity for the detection of broadband transient signals compared with the direct detection protocol. By repeatedly triggering a transient kinetic event f(t) (e.g., by laser flash photolysis) under a 100kHz magnetic field modulation with precise phase control, this technique can build an ultrawide single sideband modulated signal. After single sideband demodulation, the flicker noise-suppressed signal f(t) with wide bandwidth is recovered. A U-PSD TREPR spectrometer prototype has been built, which integrated timing sequence control, laser flash excitation, data acquisition systems, and the U-PSD algorithm with a conventional continuous-wave EPR. It exhibited excellent performance in monitoring a model transient radical system, laser flash photolysis of benzophenone in isopropanol. Both the intense chemically induced dynamic electron polarization signals and the much weaker thermal equilibrium EPR signals of the generated acetone ketyl radical and benzophenone ketyl radical were clearly observed within a wide timescale ranging from sub-microsecond to milliseconds. This prototype validated the feasibility of the U-PSD technique and demonstrated its superior performance in studying complex photochemical systems containing various transient radicals, which complements the established TREPR techniques and provides a powerful tool for deep mechanistic understandings, such as in photoredox catalysis and artificial photosynthesis.

Electrically Detected Magnetic Resonance on a Chip (EDMRoC) for Analysis of Thin-Film Silicon Photovoltaics

Electrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments.

Constructing BiOBr/TiO2 heterostructure nanotubes for enhanced adsorption/photocatalytic performance

The fabrication of heterostructure materials with the synergy of adsorption and photocatalysis is an effective strategy to promote the removal of organic pollutants. In this work, BiOBr/TiO2 nanotubes were successfully obtained to enhance the removal of organic pollutants from water via the synergy of adsorption and photocatalysis. The TiO2 nanotubes were prepared using waste foam as the primary raw material by impregnation calcination, and BiOBr nanosheets were grown on their surface by a simple solvothermal method. The BiOBr/TiO2 nanotubes have significantly enhanced separation efficiency of photo-generated carriers, synergistic adsorption, and photocatalytic decomposition compared with pure TiO2 nanotubes. The enhanced activity is mainly attributed to the growth of BiOBr nanosheets leading to a substantial increase of the specific surface area and the internal electric field between the heterojunction of BiOBr/TiO2. In addition, possible degradation pathways for organic pollutants are proposed based on trapping experiments, electron spin resonance spectrometer, and density functional theory calculations. Our work provides a promising strategy for combining the advantages of adsorption and photocatalytic technologies for environmental remediation, and we anticipate it will be of significant interest to researchers in environmental science, materials science, and chemical engineering.

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as MnII (3d5) or GdIII (4f7), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive “Keck” magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet’s intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet’s temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10–4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two GdIII complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.

A low-noise X-band microwave source with digital automatic frequency control for electron paramagnetic resonance spectroscopy

We report a new design of microwave source for X-band electron paramagnetic resonance spectrometer. The microwave source is equipped with a digital automatic frequency control circuit. The parameters of the digital automatic frequency control circuit can be flexibly configured for different experimental conditions, such as the input powers or the quality factors of the resonator. The configurability makes the microwave source universally compatible and greatly extends its application. To demonstrate the ability of adapting to various experimental conditions, the microwave source is tested by varying the input powers and the quality factors of the resonator. A satisfactory phase noise as low as −135 dBc/Hz at 100-kHz offset from the center frequency is achieved, due to the use of a phase-locked dielectric resonator oscillator and a direct digital synthesizer. Continuous-wave electron paramagnetic resonance experiments are conducted to examine the performance of the microwave source. The outstanding performance shows a prospect of wide applications of the microwave source in numerous fields of science.

Magnetic Profiling of Conducting, Semi-Conducting, and Insulating Nanoparticles and Their Nanofluids Possessing Potential Transformer Application

Nanofluids (NFs) with their superior electrical and thermal properties are promising alternate liquid dielectric in power transformers. Alongside the electric field, the magnetic field is also an integral part of power transformers. It accounts for power transfer through flux linkages and due to the design constraints, flux leakages exist in every transformer. This leakage flux interacts with the liquid insulation incessantly. This article aims at studying the magnetic response of the conductive, semi-conductive, and insulating nanoparticles (NPs) and their NFs prepared using mineral oil (MO) and vegetable oil (VO) as the base liquids. Quasi-static and dynamic magnetic fields are applied to the NPs and their NFs to magnetically characterize them by using a vibrating sample magnetometer (VSM) and an electron spin resonance (ESR) spectrometer. Magnetic susceptibility and resonance field are obtained from the magnetic response studies.

GalEPR: A Galvanically Coupled Electron Paramagnetic Resonance Spectrometer for Deep Tissue Hypoxia Diagnosis

This work presents a galvanically coupled electron paramagnetic resonance spectrometer (GalEPR) for deep tissue oximetry and hypoxia diagnosis. Current in vivo EPR spectroscopy directly trades between the operation frequency (equivalent to sensitivity) and the penetration depth due to tissue absorption. Prior art is limited to 1.2 GHz/15 mm and 9 GHz/2 mm. To address this issue, a 30-MHz clock is galvanically coupled through the body to minimize attenuation and up-converted to 14 GHz by a low-power subsampling phase locked loop (SSPLL). The EPR spectrum is measured by an ultrasensitive low-power inductor sensor. The proposed GalEPR spectrometer demonstrates 14 GHz/50 mm frequency/depth (10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> better) with an in vitro hypoxia detection experiment.