Zhang Xinwang, Schemm Nathan, Balkır Sina
Department of Electrical Engineering, 209N SEC-0511, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
Rev Sci Instrum. 2011 Mar;82(3):034707. doi: 10.1063/1.3571298.
Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)-based chemical analysis systems have been widely utilized in various areas such as medicine, security, and academic research. In these applications, the power amplifier stage plays a key role in generating the required oscillating magnetic fields within a radio frequency coil that serves as the probe. However, the bulky size and relatively low efficiency of the traditional power amplification schemes employed present a bottleneck for the realization of compact sized and portable NMR and NQR systems. To address this problem, this work presents a class D voltage-switching power amplification scheme with novel fast-start and fast-stop functions that are suitable for generating ideal NMR and NQR excitation signals. Compared to the traditional analog power amplifiers (PAs), the proposed switched-mode PA can achieve significant improvement on the power efficiency as well as the physical volume. A PA circuit for portable NQR-based explosive detection systems has been designed and built using the proposed scheme with 1 kW possible maximum output power and 10 MHz maximum operating frequency. Test results show that the presented PA achieves more than 60% measured efficiency within a highly compact volume while sustaining fast start and stop of excitation signals in the order of microseconds.
基于核磁共振（NMR）和核四极共振（NQR）的化学分析系统已在医学、安全和学术研究等各个领域得到广泛应用。在这些应用中，功率放大器阶段在作为探头的射频线圈内产生所需的振荡磁场方面起着关键作用。然而，所采用的传统功率放大方案体积庞大且效率相对较低，这成为实现紧凑型便携式NMR和NQR系统的瓶颈。为了解决这个问题，本文提出了一种具有新颖快速启动和快速停止功能的D类电压开关功率放大方案，适用于生成理想的NMR和NQR激励信号。与传统模拟功率放大器（PA）相比，所提出的开关模式PA在功率效率和物理体积方面都能实现显著提升。采用该方案设计并构建了用于便携式基于NQR的爆炸物检测系统的PA电路，其最大输出功率可达1kW，最大工作频率为10MHz。测试结果表明，所呈现的PA在高度紧凑的体积内实现了超过60%的实测效率，同时能在微秒级维持激励信号的快速启动和停止。
