arXiv subjects

C. Y. Lui

Publications and source records attributed to C. Y. Lui.

3 recordsLinked to original sources

arXiv2024

Performance Variance of Low Noise Resonant Capacitance Bridges While Replacing their Ungapped MnZn Ferrite Cores

Precision AC resonant capacitance bridges, with a planar printed circuit board transformer using an ungapped MnZn ferrite core, have shown excellent noise performance in high-precision measurements. As many applications use an ensemble of bridges, consistency of performance is critical to the functionality of the systems. If part of the same manufacturing batch and scaled to the same frequency, the noise performance of the ferrite cores at 293 K has a weighted mean variance of <0.3%, with all the cores within a +/- 1% band. At 140 K the weighted mean variance is <0.6% and the 90% inclusion band is +/- 1.5%. Ten cores of SIFERRIT Material N41, from TDK Ferrites Accessories, were tested at room temperature, 293 K, and in a liquid nitrogen dewar at 140 K. Fitted to a parabolic function, to + 3dB on both frequency sides, the weighted mean of the noise minima at 293 K was 0.3027 aF/rtHz, with a variance of 0.0012 aF/rtHz spanning a frequency range of 85.0 +/- 2.7 kHz. Scaled to 100 kHz, the weighted mean and variance were 0.2788 aF/rtHz and 0.0008 aF/rtHz. Corresponding noise values at 140 K were 0.1815 aF/rtHz with a variance of 0.0016 aF/rtHz for the range of 152.7 +/- 6.3 kHz, and 0.1835 aF/rtHz with a variance of 0.0011 aF/rtHz when scaled to 150 kHz. Scaled for resonant frequency and temperature these results are consistent with a previous measurement of another ungapped core (same supplier and type, different manufacturing batch) to within 9% and 6% at 293 K and 140 K respectively.

physics.space-ph↗

arXiv2023

Noise and Thermal Performance of a Sub-Attofarad Capacitance Sensor for Precision Measurements, with Applications in Gravitational Wave Detectors

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/rtHz, 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/rtHz. We compare the ungapped configuration to five different RCBs; three with a core gap of 65 um and two with a core gap of 130 um. Their average room temperature short term noise sensitivities are 0.30 +/- 0.01 aF/rtHz and 0.45 +/- 0.01 aF/rtHz, while the cryogenic operation of these transformers at 120 K resulted in averaged sensitivities of 0.23 +/- 0.01 aF/rtHz and of 0.36 +/- 0.01 aF/rtHz 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 aF/rtHz, 0.338 +/- 0.009 aF/rtHz, and 0.435 +/- 0.010 aF/rtHz for the ungapped (40-hour duration) and the 65 um and 130 um (28-hour duration) cores respectively. At 0.1 mHz, a critical frequency for space gravitational wave detectors, the respective sensitivities are 0.25 +/- 0.02 aF/rtHz, 0.35 +/- 0.02 aF/rtHz, and 0.53 +/- 0.07 aF/rtHz. Measurements with the ungapped transformer configuration for temperatures from 325 K to 349 K further validate the dependence of the noise model on the 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 of two or more compared with capacitance bridges developed for similar applications. A further factor of about two noise reduction is achieved by cooling to 120 K.

physics.ins-det↗

arXiv2022

Flight and ground demonstration of reproducibility and stability of photoelectric properties for passive charge management using LEDs

Charges as small as 1 pC degrade the performance of high precision inertial reference instruments when accumulated on their test masses (TMs). Non-contact charge management systems are required for the most sensitive of these instruments, with the TMs free-floating, and their charges compensated by photoelectrons in a feedback loop with a TM charge measurement. Three space missions have successfully demonstrated this technique: GP-B, LPF, and the UV-LED mission. Charge management techniques that eliminate the charge measurement and feedback systems, referred henceforth as passive, reduce the complexities and disturbance effects introduced by these systems, and are thus the subject of active research and development work. Passive charge management depends critically on the stability and reproducibility of the photoemission properties of a given system. In support of this work, we present comprehensive flight characterization data for a suite of 16 UV-LEDs in various configurations and 255+/-1 nm center wavelength. Flight data was acquired between December 2014 and December 2015 with the UV-LED instrument flown on SaudiSat 4. We back up our results with ground-based measurements performed in configurations comparable to the flight one between September 4, 2020, and October 8, 2020. All results confirm the excellent reliability of the UV-LEDs in the space environment, are fully consistent with the findings of ground studies, and support the approach of using LEDs for passive charge management. We find that the equilibrium potential of the TM, under illumination by the 255 nm LEDs, is independent of the UV intensity and reproduceable to about +/- 6 mV, or +/-6 fC/pF, over periods of up to six months. The value of the equilibrium potential is dependent on the geometry of the electric field between the TM and its enclosure, and thus on the exact configuration of the instrument.

physics.space-ph↗