Noise and thermal performance of a sub-attofarad capacitance sensor for precision measurements, with applications in gravitational wave detectors.
Rev Sci Instrum
; 95(3)2024 Mar 01.
Article
em En
| MEDLINE
| ID: mdl-38552176
ABSTRACT
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/âHz 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/âHz. 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/âHz, 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/âHz, 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/âHz 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/âHz. 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.
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01-internacional
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MEDLINE
Idioma:
En
Ano de publicação:
2024
Tipo de documento:
Article