FREQUENCY MODULATION STUDY AND DEVELOPMENT FOR HF CW SPECTROMETERY

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可在其他CRISP条目中表示。所列机构为 中心，但不一定是研究者所在的机构。 所有ACERT c.w.光谱仪目前利用常规的约100 KHz磁场调制用于ESR谱线检测。然而，对于中等宽光谱线宽的高场检测，这种检测技术的实用性受到严重限制。检测中等宽的HF光谱，例如，自旋标记蛋白质在中间慢动作制度，变得相对低效， Bmod << Hpp，需要在功率输入能力的极限下操作场调制组件，对应于仅5 - 10 Gpp的最大场调制。在超过该调制水平的场值处，线圈感应的洛伦兹力成为越来越显著的颤噪噪声源，并且线圈功率耗散迅速成为显著扰动的热源。 理想情况下，约100 G的调制宽度可用于大多数HF样品，特别是低浓度的生物样品;然而，该值显然超出了传统直接磁场调制技术的范围。 我们以前研究过的另一种调制方案是在2006年ACERT资助更新提案，核心项目III中描述的圆二色性方案。然而，对于不太宽的光谱，源频率调制（FM），一种更简单且更容易实现的宽ESR谱线检测方法，似乎是可能的（Hyde等人，2007年）。 我们最初的任务是评估宽带FM线路检测系统的性能，该系统至少具有280 MHzpp（100 Gpp）的最大调制能力，可适用于我们现有的170/240 GHz c.w.。光谱仪因为该HF光谱仪利用测辐射热计功率检测器，而不是文献中其他地方描述的典型外差转换和检测方案，所以我们的FM线检测系统在关键设计方面与其他地方描述的FM系统不同。我们相信，例如，很可能通过减去频率（即，在同步解调之前依赖于场的基线。自从改进HF c.w.以来，我们已将该项目列为非常高的优先级。ESR灵敏度是低浓度生物样品阅读的关键因素。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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.