學術研究•ACADEMIC RESEARCH 澳大新語•2020 UMAGAZINE 22 59 A critical drawback of the NMR, whether for the conventional type or the miniaturised type, is its inherently low throughput. Since the NMR signals from the samples are very weak – usually at the order of microvolts, a lot of experiments are required and accumulated to improve the signal-to-noise ratio (SNR) of the acquisition. Yet, after the excitation from the transmitter, the nuclei takes several seconds to return to their thermal equilibrium. This long recovery time limits the repetition rate of the acquisition and throttles down the throughput of the experiment. Depending on the type of NMR experiment, it may take a matter of hours or even days to acquire the NMR signals with the desired resolution. To tackle this limitation, we proposed different parallelisation schemes to accelerate the throughput of the measurement. The first one is the acceleration of the experiment via time‑interleaving. We placed multiple (N) samples (can be homogenous or heterogeneous) with their respective radio-frequency coils within the permanent magnet. The coils are separated from each other to prevent cross interference. These N coils are connected to a CMOS IC by an array of switches. After the first coil finished the NMR scan on its sample and the nuclei are resting to return to 數小時甚至數天以進行實驗，時間視乎 實驗種類而定。 為了克服這種限制、加大測量的通量， 我們提出了不同的並行化方案。首先是 以時間交錯方式加快實驗。具體方法是 將N個同質或異質樣本分別放在一個永 久磁鐵內，並各配置N組射頻線圈。這 些線圈分開擺放，避免交叉干擾，但都 透過繼電器連接至同一CMOS芯片。當 第一組線圈中的樣本完成一次核磁共振 掃描後，樣本內之原子核會逐漸回復至 熱平衡，這時儀器馬上會掃描另一組線 圈內之樣本，如此類推，直至完成所有 N組線圈的掃描。當第一組線圈的樣本 內的原子核回復至熱平衡，另一輪掃描 就會開始。換言之，我們利用原子核每 次掃描後回復至熱平衡的時間去進行不 同樣本之掃描。在理想情況下，這種掃 描方式能將實驗時間縮短N倍。我們在 小型化核磁共振平台上用這種時間交錯 的方式，同時間進行二維的1H關聯性磁 振頻譜實驗，以檢測甲酸乙酯和乙酸乙 酯的結構（圖四），結果需時48分鐘， 比沒有使用時間交錯方式之裝置節省一 圖三： 第一代可攜式核磁共振系統，其 CMOS芯片安裝在磁鐵內的印刷 電路板上。1 Picture 3: The system hardware of our first portable NMR system. The CMOS IC is mounted on the printed circuit boards and put inside the magnet1.
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