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相关概念视频

Linear Approximation in Frequency Domain01:26

Linear Approximation in Frequency Domain

84
Linear systems are characterized by two main properties: superposition and homogeneity. Superposition allows the response to multiple inputs to be the sum of the responses to each individual input. Homogeneity ensures that scaling an input by a scalar results in the response being scaled by the same scalar.
In contrast, nonlinear systems do not inherently possess these properties. However, for small deviations around an operating point, a nonlinear system can often be approximated as linear....
84
Linear Approximation in Time Domain01:21

Linear Approximation in Time Domain

59
Nonlinear systems often require sophisticated approaches for accurate modeling and analysis, with state-space representation being particularly effective. This method is especially useful for systems where variables and parameters vary with time or operating conditions, such as in a simple pendulum or a translational mechanical system with nonlinear springs.
For a simple pendulum with a mass evenly distributed along its length and the center of mass located at half the pendulum's length,...
59
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

721
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.
721
Linear time-invariant Systems01:23

Linear time-invariant Systems

202
A system is linear if it displays the characteristics of homogeneity and additivity, together termed the superposition property. This principle is fundamental in all linear systems. Linear time-invariant (LTI) systems include systems with linear elements and constant parameters.
The input-output behavior of an LTI system can be fully defined by its response to an impulsive excitation at its input. Once this impulse response is known, the system's reaction to any other input can be...
202
Mesh Analysis for AC Circuits01:12

Mesh Analysis for AC Circuits

332
In the domain of radio communication, the significance of impedance matching must be considered. It is crucial to ensure the efficient transmission of signals between radio transmitters and receivers. Achieving this balance involves using impedance-matching circuits, with one fundamental configuration comprising a resistor, capacitor, and inductor.
The process of harmonizing these impedances begins with a clear understanding of the input and output signals. Once these signals are known, the...
332

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Updated: May 24, 2025

High Speed Sub-GHz Spectrometer for Brillouin Scattering Analysis
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基于线性假设的射频脉冲校准框架使用布洛赫-西格特移位.

Huabin Zhang, Yufu Zhou, Yongxiang Fang

    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference
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    概括
    此摘要是机器生成的。

    精确的磁共振成像 (MRI) 校准通过新的数学模型得到了改进. 该模型量化了射频 (RF) 链的复杂性,提高了翻转角度的准确性,并使RF放大器非线性性的预补偿成为可能.

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    相关实验视频

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    科学领域:

    • 医学成像物理 医学成像物理
    • 无线电频率工程 无线电频率工程
    • 生物医学信号处理

    背景情况:

    • 可靠的磁共振成像 (MRI) 扫描取决于无线电频率 (RF) 传输链的精确校准.
    • 核磁共振的挑战包括线圈负载变化,射频非均性和射频非线性,需要先进的校准技术.

    研究的目的:

    • 提出和验证一个数学模型来描述MRI系统中的射频传输链.
    • 用Bloch-Siegert转移方法量化线圈负载,射频不均性和射频非线性的影响.

    主要方法:

    • 开发一个线性模型来描述射频传输链.
    • 使用布洛赫-西格特转移方法量化射频传输链参数.
    • 通过线性回归,线圈加载实验和B1映射测量进行验证.

    主要成果:

    • 拟议的模型有效量化了线圈负载,射频不均性和射频非线性的影响.
    • 使用非线性模型实现了翻转角度配置文件的卓越精度,显示1.5度的误差,而在160度的标称翻转角度下,线性模型的误差为8.8度.
    • 验证通过实验测量证实了模型的有效性.

    结论:

    • 开发的数学模型为模拟MRI中系统特定的射频响应提供了有价值的工具.
    • 该模型为RF放大器非线性提供了简单的预补偿,提高了MRI系统的整体性能和可靠性.
    • 这项工作有助于为先进的MRI应用提供全面的校准框架.