FREQUENCY MODULATION STUDY AND DEVELOPMENT FOR HF CW SPECTROMETERY

高频连续波谱仪的调频研究与开发

• 批准号: 8363991
• 负责人: CURT R DUNNAM
• 金额: $ 0.26万
• 依托单位: CORNELL UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8363991
• 关键词: Biological; Circular Dichroism; Detection; Development; Frequencies; Funding; Grant; Heating; Literature; Methods; Motion; National Center for Research Resources; Noise; Performance; Principal Investigator; Proteins; Reading; Research; Research Infrastructure; Resources; Sampling; Scheme; Solutions; Source; Spin Labels; System; Techniques; Technology; United States National Institutes of Health; Width; cost; design; detector; improved; magnetic field; operation

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. All ACERT c.w. spectrometers currently utilize conventional ca 100KHz magnetic field modulation for ESR spectral line detection. However, for high-field detection of moderately broad spectral linewidths the utility of this detection technique is severely constrained. Detection of moderately broad HF spectra corresponding to, e.g., spin-labeled proteins in the intermediate slow-motion regime, becomes relatively inefficient when Bmod << Hpp, necessitating operation of field modulation components at the extreme limit of power input capability, corresponding to a maximum field modulation of only 5 - 10Gpp. At field values exceeding this modulation level, coil-induced Lorentz forces become an increasingly significant microphonic noise source, and the coil power dissipation rapidly becomes a significantly perturbing heat source. Ideally, modulation widths of ca 100G would be available for a majority of HF samples, in particular biological samples at low concentrations,; however, this value is clearly out of reach of conventional direct magnetic field modulation techniques. An alternative modulation solution we have previously investigated is the circular-dichroism scheme described in the 2006 ACERT grant renewal proposal, Core Project III, at (F). For spectra that are not too broad, however, source frequency modulation (FM), a simpler and more easily implemented method of broad ESR line detection, seems possible (Hyde et al., 2007). Our initial task will be to evaluate the performance of a wide-band FM line detection system of at least 280 MHzpp (100Gpp) maximum modulation capability which may be adapted to our existing 170/240 GHz c.w. spectrometer. Because this HF spectrometer utilizes a bolometer power detector rather than a typical hetrodyne conversion and detection scheme as described elsewhere in the literature, our FM line detection system will differ in key design aspects with respect to FM systems described elsewhere. We believe, for example, that it is likely FM detection SNR in a bolometer (or other baseband power detection) system can be greatly enhanced by subtracting out the frequency- (i.e., field-) dependent baseline prior to synchronous demodulation. We have assigned this project a very high priority since improved HF c.w. ESR sensitivity is a critical factor in reading biological samples of low concentration.

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 所有Acert C.W.光谱仪目前使用常规的CA100 KHZ磁场调制来进行ESR谱线检测。然而，对于中等宽谱线宽的高场检测，这种检测技术的实用性受到严重限制。对应于例如在中间慢动作区域中的自旋标记蛋白质的中等宽的HF谱的检测在Bmod；HPP时变得相对低效，这需要场调制组件在功率输入能力的极端极限下操作，对应于仅5-10Gpp的最大场调制。当场值超过该调制水平时，线圈感生的洛伦兹力成为越来越重要的微音噪声源，线圈功率耗散迅速成为显著扰动热源。 理想情况下，对于大多数HF样品，尤其是低浓度的生物样品，大约100G的调制宽度是可用的；然而，这个值显然超出了传统的直接磁场调制技术的范围。 我们先前研究过的另一种调制解决方案是在2006年Acert授权续展提案，核心项目III，AT(F)中描述的圆二向色性方案。然而，对于不太宽的频谱，源频率调制(FM)似乎是一种更简单、更容易实现的广泛ESR线检测方法(Hyde等人，2007年)。 我们的首要任务将是评估至少280兆赫(100Gpp)最大调制能力的宽带调频线路检测系统的性能，该系统可能适用于我们现有的170/240 GHz C.W.分光计。由于这款高频光谱仪使用的是测辐射热计功率探测器，而不是文献中其他地方描述的典型异差转换和检测方案，因此我们的调频线路检测系统在关键设计方面将与其他地方描述的FM系统有所不同。例如，我们认为在测辐射热计(或其他基带功率检测)系统中，通过在同步解调之前减去与频率(即，场)相关的基线，可以极大地提高FM检测SNR。自从改进HF C.W.以来，我们对这个项目给予了非常高的优先级。ESR灵敏度是读取低浓度生物样品的关键因素。