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相关概念视频

NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

695
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
695
Power Factor Correction01:20

Power Factor Correction

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The power transmission to a factory involves the transfer of apparent power, a combination of active and reactive power. The power factor measures how effectively electrical power is converted into useful work output. The ratio of the real power (KW) that does the work to the apparent power (KVA) supplied to the circuit.
176
MOSFET Amplifiers01:17

MOSFET Amplifiers

156
The MOSFET, when operating in its active region, functions as a voltage-controlled current source. In this region, the gate-to-source voltage controls the drain current. This principle underlies the operation of the transconductance MOSFET amplifier. The output current is directed through a load resistor to convert this amplifier into a voltage amplifier. The output voltage is then obtained by subtracting the voltage drop across the load resistance from the supply voltage. This process results...
156
Small-Signal Analysis of MOSFET Amplifiers01:23

Small-Signal Analysis of MOSFET Amplifiers

557
In small-signal analysis, a MOSFET transistor amplifier acts as a linear amplifier when operating in its saturation region. The gate-to-source voltage (VGS) of the MOSFET is the sum of the DC biasing voltage and the small time-varying input signal. This combination sets up the operating point and modulates the drain current (ID) that flows from the drain to the source. When a small AC signal is superimposed on the DC bias voltage at the gate, the instantaneous drain current comprises three...
557
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

805
A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
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相关实验视频

Updated: Jul 1, 2025

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis
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内部扫描射频功率放大器漂移校正

Ali Aghaeifar1, Dario Bosch1,2, Rahel Heule1,2,3

  • 1High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.

Magnetic resonance in medicine
|March 12, 2024
PubMed
概括
此摘要是机器生成的。

受工作周期影响的射频功率放大器 (RFPA) 漂移可以使用预测或运行时间方法进行纠正. 这些技术通过将平均漂移降低到1%以下,显著提高了MR信号稳定性.

关键词:
无线电波功率放大器的功率放大器bSSFPFP 是一个很好的方法.定向合器 定向合器漂流 漂流 漂流 漂流 漂流运行时间校正.satTFL 的时间.

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科学领域:

  • 磁共振成像 (MRI) 硬件开发 硬件开发
  • 无线电频率 (RF) 工程
  • 医学成像中的信号处理.

背景情况:

  • 射频功率放大器 (RFPA) 是MRI系统中的关键组件,负责产生射频脉冲.
  • 由于各种因素,RFPA性能随着时间的推移而降低,导致信号不稳定性和图像工件.
  • 了解和减轻RFPA漂移对于保持高质量的MRI检查至关重要.

研究的目的:

  • 评估RFPA的漂移特征,并确定关键的促成因素.
  • 建议和评估两种新的方法,以对RFPA漂移进行前性纠正.
  • 为了提高MRI中RF传输的稳定性和可靠性.

主要方法:

  • 在不同扫描参数 (翻转角度,射频长度,TR) 下,使用脉冲内和脉冲间技术分析RFPA漂移.
  • 定向合器 (DICOs) 监控RFPA输出波形,以计算传输电压的校正因数.
  • 实施了两种校正策略:一种需要校准扫描的预测方法,另一种在扫描期间运行的运行时间方法.

主要成果:

  • RFPA漂移受到RF工作周期的显著影响,在某些修订中,潜在漂移率高达41%.
  • 翻转角度 (FA) 在低传输电压场景中对RFPA漂移的影响最小.
  • 预测和运行时间校正方法都成功地将平均RFPA偏移从10.0%降低到不到1%,改善了MR信号稳定性.

结论:

  • 使用DICO记录和反机制,可以对RFPA漂移进行前性纠正.
  • 预测校正通过校准扫描提供了更简单的方法,适合许多应用.
  • 运行时间校正方法提供了增强的性能,并推用于需要最大MR信号稳定性的应用.