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

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 for a sample was opened. Thus, a large sample could be placed at the end of the resonator without much limitation on the size. For an application 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.     

L波段三维ESR成像系统的研制（Ⅱ）——L波段三维ESR成像系统

叙述了一个L波段（1.05 GHz）用于ESR和ESR成像的装置，用这套自制装置实现了3D ESR成像. 该装置由L波段ESR谱仪、三组梯度场线圈及控制单元和PC机数据采集系统组成. 样品腔是一个3-环2-缝再进入式谐振腔，可放入直径为20 mm、 长30 mm的H₂O样品，空谐振腔的频率是1.05 GHz. 微波振荡频率用自动频率控制（AFC）的方法自动锁在有载腔的频率上. 梯度场线圈沿X-，Y-和Z-轴产生线性梯度场，在中心40 mm球形范围内梯度场强度为2 mT/cm. 依照Lauterbur's方法进行3D ESR 图像重建. 用该系统检测了样品中TEMPO氮氧自由基的3D空间分布. 得到了TEMPO的2D、3D ESR图像、用像素灰度表示的自旋密度分布图及3D ESR-CT图像.     

Bench-Top Type In Vivo EPR Spectrometer for Estimating the Renal Reducing Ability of a Rat

A main electromagnet optimized for electron paramagnetic resonance (EPR) measurements of rats by using a surface loop resonator with a loop diameter of 10?mm was designed. The fabricated main electromagnet was ca. 420?mm in diameter, ca. 240?mm in width, and ca. 60?kg in weight. When a static magnetic field of 25?mT was generated at the center of the main electromagnet, its deviation in a sphere space with a diameter of 10?mm was <0.02?mT. In this condition, the temperature elevation on the surface of the magnet was negligible for the measurement time assumed for in vivo study. Using this magnet, a bench-top type in vivo EPR spectrometer could be obtained, which made it possible to perform EPR measurements for estimating the renal reducing ability of a rat.     

A longitudinally detected high-field ESR spectrometer for the measurement of spin-lattice relaxation times

We describe a high-field longitudinally detected electron spin resonance (LOD-ESR) spectrometer operating at 35 and 75 GHz. The lack of resonant microwave circuits facilitates operation at different microwave frequencies without changing the probehead. A very low noise radio frequency detection compensates partially the resulting low sensitivity. The major elements of the LOD-ESR spectrometer are commercially available and may be adapted to usual high frequency spectrometers. The instrument allows field and frequency dependent spin lattice relaxation time (T1) studies. T1 in the range of 2-80 ns can be determined from the phase sensitively detected LOD-ESR spectra. We demonstrate the performance of the apparatus by the measurement of T1 in the normal state of RbC60, an electrically conducting alkaline fulleride polymer.     

L波段三维ESR成像系统的研制（Ⅲ）——L波段谐振腔的研制

描述了一个用于生物样品L波段ESR成像用的谐振腔,讨论了在制作、设计过程中几个值得注意的问题，该腔为3-环2-裂缝再进入式谐振腔，可检测直径为20 mm长30 mm的H₂O样品. 空腔的共振频率为1.05 GHz. 腔的Q值是样品中水含量的函数，无载Q大于1 000. 用插入侧臂的耦合环得到谐振腔与微波桥之间的匹配，确定了耦合环直径的最佳值，对无载腔其值约为腔臂直径的1/3，而对有载腔其值约等于腔臂的直径. 用该腔检测了样品中TEMPO氮氧自由基的空间分布.     

New Cavity Design for Broad-Band Quasi-Optical HF-EPR Spectroscopy

The design and performance of two new devices adapted for high-frequency electron paramagnetic resonance (HF-EPR) in a broad frequency range are described. Both systems, a Fabry–Pérot resonator and a rotating sample holder, rely on similar construction schemes and on the use of submicrometer piezoelectric positioners. A study of a single crystal of graphite allows illustrating the operation of these two new systems associated with our quasi-optical HF-EPR spectrometer.     

NMR永磁体精密温度控制器的设计与实现

低场核磁共振（low-field NMR）谱仪常采用钕铁硼（NdFeB）永磁体提供静磁场.NdFeB对温度非常敏感，磁体温度变化会引起磁场漂移，影响NMR实验的可靠性.为提高低场磁共振谱仪的稳定性，本文提出了一种基于双回路控制算法的磁共振永磁体精密温度控制方案，并在0.06 T磁共振谱仪上进行验证.结果表明：24 h内控温精度达到±0.005℃；相比无温控时，质子共振频率0.5 h内漂移量由255 Hz减小至15 Hz，24 h内漂移量由4 950 Hz减小至145 Hz，有效提高了低场磁共振谱仪永磁体的稳定性.     

Infrared imaging as a means of visually characterizing the thermoacoustic onset process influenced by a Helmholtz resonator

A Helmholtz resonator can be used as a transmission part to connect the thermoacoustic engine (TE) with its load. However, the resonator can significantly influence the performance of the TE. In order to investigate the impact of a Helmholtz resonator on the onset process of a TE, infrared (IR) imaging is firstly used as a visualization method to characterize the onset mechanism. The influence of dimensions of the Helmholtz resonator on the onset process are analyzed experimentally and theoretically. Results show that the Helmholtz resonator reduces the pressure amplitude at the onset moment and increases the onset temperature of the TE, both of which depend on the acoustic power absorbed from the TE. Onset without a sudden increase of pressure amplitude is observed with the Helmholtz resonator at resonance length. This paper shows that IR imaging is an effective way to characterize the temperature distribution in a TE study.     

Three dimensional magnetic resonance imaging by magnetic resonance force microscopy with a sharp magnetic needle

An electropolished magnetic needle made of Nd(2)Fe(14)B permanent magnet was used for obtaining better spatial resolution than that achieved in our previous work. We observed the magnetic field gradient |G(Z)|=80.0G/microm and the field strength B=1250G at Z approximately 8.8 microm from the top of the needle. The use of this needle for three dimensional magnetic resonance force microscopy at room temperature allowed us to achieve the voxel resolution to be 0.6 microm x 0.6 microm x 0.7 microm in the reconstructed image of DPPH phantom. The acquisition time spent for the whole data collection over 64 x 64 x 16 points, including an iterative signal average by six times per point, was about 10 days.     

High-frequency EPR applications of open nonradiative resonators

A new class of open single-mode cavities, the nonradiative (NR) resonators, has recently been proposed in order to overcome the limitations of standard cylindrical cavities and Fabry-Perot resonators at millimeter wavelengths. This paper presents the first applications of a NR resonator in W-band pulsed electron paramagnetic resonance spectroscopy. It consists of a cylindrical cavity having a lateral aperture that represents about 35% of its total height. Electron-spin-echo measurements performed on different samples show that the signal-to-noise ratio and the optimal pulse length obtained with the proposed device are comparable to those obtained with the closed cavity used in the commercial W-band spectrometer, at both cryogenic and room temperature. Similar results have been obtained for paramagnetic species optically activated by means of an optical fiber inserted in the aperture of the resonator. The insertion losses estimated for the probe employed with the NR resonator are higher than those of the commercial probe, hence, demonstrating that the proposed cavity holds the promise of improved resonator performance.     

A far-infrared laser magnetic resonance spectrometer for the investigation of radicals of atmospheric relevance

A far-infrared laser magnetic resonance spectrometer is described. A superconducting magnet is used for the tuning of the energy levels. Pressure broadening measurements of OH and NO have been performed. The measurements demonstrate that the laser magnetic resonance technique is well suited for this kind of measurements. Based on this results the design and expected performance of a compact laser magnetic resonance spectrometer is presented. The sensitivity as well as the mechanical ruggedness of this spectrometer is sufficient in order to be used aboard an aircraft for the in situ detection of OH and HO₂ in the lower stratosphere and upper troposphere.     

Microwave frequency modulation in continuous-wave far-infrared ESR utilizing a quasi-optical reflection bridge

We report the development of the frequency-modulation (FM) method for measuring electron spin resonance (ESR) absorption in the 210- to 420GHz frequency range. We demonstrate that using a high-frequency ESR spectrometer without resonating microwave components enables us to overcome technical difficulties associated with the FM method due to nonlinear microwave-elements, without sacrificing spectrometer performance. FM was achieved by modulating the reference oscillator of a 13GHz Phase-Locked Dielectric Resonator Oscillator, and amplifying and frequency-multiplying the resulting millimeter-wave radiation up to 210, 315 and 420GHz. ESR spectra were obtained in reflection mode by a lock-in detection at the fundamental modulation frequency, and also at the second and third harmonic. Sensitivity of the setup was verified by conduction electron spin resonance measurement in KC60.     

Electronically tunable surface-coil-type resonator for L-band EPR spectroscopy

The automatic frequency control (AFC) circuit in conventional electron paramagnetic resonance (EPR) spectrometers automatically tunes the microwave source to the resonance frequency of the resonator. The circuit works satisfactorily for samples stable enough that the geometric relations in the resonance structure do not change in a significant way. When EPR signals are measured during in vivo experiments with small rodents, however, the distance between the signal source and the surface-coil detector can change rapidly. When a conventional AFC circuit keeps the oscillator tuned to the resonator under those conditions, the resultant frequency change may exceed +/-5 MHz and markedly shift the position of the EPR signal. Such a shift results in unacceptable effects on the spectra, especially when the experimenter is dealing with narrow EPR lines. The animal movement also causes a mismatching of the resonator and the 50-ohm transmission line. Direct results of this mismatching are increased noise; shifts in the position of the baseline; and a high probability of overdriving the signal preamplifier with consequent loss of the EPR signal. We therefore designed, built, and tested a new surface-coil resonator using varactor diodes for tuning the resonance frequency to the fixed frequency oscillator and for capacitive matching of the resonator to the 50-ohm transmission line. The performance of the automatic matching system was tested in vivo by measuring EPR spectra of lithium phthalocyanine implanted in rats. Stability and sensitivity of the spectrometer were evaluated by measuring EPR spectra with and without the use of the automatic matching system. The overall experimental performance of the spectrometer was found to significantly improve during in vivo experiments using the automatic matching system. Excellent matching between the 50-ohm transmission line and the resonator was maintained under all experimental circumstances that were tested. This should allow us now to carry out experiments that previously were not possible.     

A continuous-wave and pulsed electron spin resonance spectrometer operating at 275 GHz

An electron paramagnetic resonance (EPR) spectrometer is described which allows for continuous-wave and pulsed EPR experiments at 275 GHz (wavelength 1.1 mm). The related magnetic field of 9.9 T for g approximately 2 is supplied by a superconducting solenoid. The microwave bridge employs quasi-optical as well as conventional waveguide components. A cylindrical, single-mode cavity provides a high filling factor and a high sensitivity for EPR detection. Even with the available microwave power of 1 mW incident at the cavity a high microwave magnetic field B1 is obtained of about 0.1 mT which permits pi/2-pulses as short as 100 ns. The performance of the spectrometer is illustrated with the help of spectra taken with several samples.     

Magneto-optical measurements with a hybrid magnet

An FFT spectrometer has been constructed to measure magneto-optical spectra in the far-infrared region (3 to 40 cm^–1) with a hybrid magnet system. The magneto-absorption was studied in the spin-Peierls cuprate CuGeO₃ at various magnetic fields. Coil constants of superconducting magnet and resistive one, of which a hybrid magnet consists, were calibrated by ESR spectra at the constant field.     

A CW and pulse EPR spectrometer operating at 122 and 244 GHz using a quasi-optical bridge and a cryogen-free 12 T superconducting magnet

A high-field continuous-wave (CW) and pulse electron paramagnetic resonance spectrometer operating at 122 and 244 GHz is described. The instrument is based on a millimeter-wave bridge built from quasi-optical components. To improve the sensitivity, a cryo-cooled detector/mixer is used. The magnetic field is generated using a cryogen-free superconducting 12 T magnet (warm bore, 88 mm) equipped with a helium-flow cryostat for sample cooling. The advantages of this spectrometer are described and first results (obtained in CW mode) on different types of samples at 122 and 244 GHz are presented. The extensions to pulse operation as well as double resonance techniques (electron-electron and electron-nuclear) are briefly discussed.     

ESR spectrometer with a wide frequency range using a gyrotron as a radiation power source

The development of a high frequency electron spin resonance (ESR) spectrometer with a wide frequency range using a gyrotron as the radiation power source is described.GYROTRON FU-E, optimized for use in an ESR spectrometer in the millimeter wave range, was developed in Fukui University. In order to test the normal operation of the spectrometer, the ESR of two standard samples, single crystal and polycrystalline DPPH, has been measured, in the pulsed mode over the frequency range from 65 GHz to 135 GHz.     

Magnetic resonance imaging of isolated single liposome by magnetic resonance force microscopy

Magnetic resonance imaging (MRI) is very useful spectroscopy to visualize a three-dimensional (3D) real structure inside the sample without physical destruction. The spatial resolution of the readily available MRI spectrometer is, however, limited by a few ten to hundreds of microns due to a technological boundary of generating larger magnetic field gradient and to the insensitivity inherent to the inductive signal detection. Magnetic resonance force microscopy (MRFM) is new alternative MRI spectroscopy which is anticipated to significantly surpass the conventional MRI in both resolution and sensitivity. We report two imaging experiments on our MRFM spectrometer operated at room temperature and in vacuum approximately 10(-3)Pa. One is for approximately 20 microm liposome membrane labeled entirely by a nitroxide imaging agent and the other for approximately 15 microm DPPH particles, both are nearly the same size as that of human cell. The reconstructed images at spatial resolution approximately 1 microm were in satisfactory agreement with the scanning electron microscope images. The potential capability of visualizing intrinsic radicals in the cell is suggested to investigate redox process from a microscopic point of view.     

Active resonators for sound control in narrow pipes

A method of active sound control by a local device, namely, an active resonator that provides a resonance absorption or scattering of sound in a broad frequency band, is proposed. The active resonator is modeled as a sound source with an acoustoelectric feedback, which allows the correction of its motion depending on the sound field measured in the vicinity of the resonator. The performance of the method is demonstrated by two examples.     

新型X波段多功能EPR谱仪的设计与性能

本文设计和研制了一款新型X波段多功能电子顺磁共振（electron paramagnetic resonance,EPR）谱仪,并为其开发一款新的控制和读出系统（control and readout system,CRS）来操控微波脉冲的产生和信号的采集,提高了系统的集成度和可扩展性. 该谱仪可实现常规的连续波EPR（continuous-wave EPR,cw-EPR）、脉冲EPR（pulsed EPR）和瞬态EPR（transient EPR,trEPR）实验,并装配了6~300 K的无液氦变温装置,以及兼具平行模式与垂直模式的新型双模连续波谐振腔和用于脉冲EPR及trEPR的介质腔. 针对新型EPR谱仪和新谐振腔,本文利用双模连续波、脉冲和瞬态三个不同方式的EPR实验,对其功能进行了验证.