Saraf S, Buchman S, Lui C Y, Wang S, Lipa J
SN&N Electronics, Inc., 1846 Stone Avenue, San Jose, California 95125, USA.
Hansen Experimental Physics Laboratory, Stanford, California 95038, USA.
Rev Sci Instrum. 2024 Mar 1;95(3). doi: 10.1063/5.0198159.
We describe the design principles, fabrication, and characterization of a precision AC resonant capacitance bridge (RCB) sensor, based on a resonant differential planar printed circuit board transformer with a solid (ungapped) MnZn ferrite core, demonstrating a short-term sensitivity at 293 K of 0.225 ± 0.005 aF/√Hz at around 120 kHz resonance frequency and 1 Hz Fourier measurement frequency. At 120 K, the RCB short term noise sensitivity is 0.118 ± 0.005 aF/√Hz. We compare the ungapped configuration to five different RCBs: three with a core gap of 65 μm and two with a core gap of 130 μm. Their average room temperature short term noise sensitivities are 0.30 ± 0.01 and 0.45 ± 0.01 aF/√Hz, while the cryogenic operation of these transformers at 120 K resulted in averaged sensitivities of 0.23 ± 0.01 and 0.36 ± 0.01 aF/√Hz, respectively. Multi-hour room temperature runs, with one core of each of the three gap types, proved the stability of their long-term sensitivities of 0.234 ± 0.005, 0.338 ± 0.009, and 0.435 ± 0.010 aF/√Hz for the ungapped (40-h duration) and the 65 and 130 μm (28-h duration) cores, respectively. At 0.1 mHz, a critical frequency for space gravitational wave detectors, the respective sensitivities are 0.25 ± 0.02, 0.35 ± 0.02, and 0.53 ± 0.07 aF/√Hz. Measurements with the ungapped transformer configuration for temperatures from 325 to 349 K further validate the dependence of the noise model on temperature and permeability. The performance of our RCB with an ungapped core matches the calculated performance value and shows an improvement in signal-to-noise ratio of two or more compared with capacitance bridges developed for similar applications. A further factor of about two noise reductions is achieved by cooling to 120 K.
我们描述了一种基于带有实心（无间隙）锰锌铁氧体磁芯的谐振差分平面印刷电路板变压器的精密交流谐振电容桥（RCB）传感器的设计原理、制造和特性，展示了在293K时，在约120kHz谐振频率和1Hz傅里叶测量频率下的短期灵敏度为0.225±0.005 aF/√Hz。在120K时，RCB的短期噪声灵敏度为0.118±0.005 aF/√Hz。我们将无间隙配置与五种不同的RCB进行比较：三种磁芯间隙为65μm，两种磁芯间隙为130μm。它们在室温下的平均短期噪声灵敏度分别为0.30±0.01和0.45±0.01 aF/√Hz，而这些变压器在120K的低温运行下，平均灵敏度分别为0.23±0.01和0.36±0.01 aF/√Hz。对三种间隙类型的每种磁芯中的一个进行了数小时的室温运行，结果证明了它们的长期灵敏度的稳定性，无间隙（持续40小时）、65μm（持续28小时）和130μm（持续28小时）磁芯的长期灵敏度分别为0.234±0.005、0.338±0.009和0.435±0.010 aF/√Hz。在0.1mHz（空间引力波探测器的临界频率）时，相应的灵敏度分别为0.25±0.02、0.35±0.02和0.53±0.07 aF/√Hz。使用无间隙变压器配置对325至349K的温度进行测量，进一步验证了噪声模型对温度和磁导率的依赖性。我们的无间隙磁芯RCB的性能与计算的性能值匹配，并且与为类似应用开发的电容桥相比，信噪比提高了两倍或更多。通过冷却到120K，噪声降低了约两倍。
