Investigation on Stray-Capacitance Influences of Coaxial Cables in Capacitive Transducers for a Space Inertial Sensor

Abstract

Ultra-sensitive inertial sensors are one of the key components in satellite Earth’s gravity field recovery missions and space gravitational wave detection missions. Low-noise capacitive position transducers are crucial to these missions to achieve the scientific goal. However, in actual engineering applications, the sensor head and electronics unit usually place separately in the satellite platform where a connecting cable is needed. In this paper, we focus on the stray-capacitance influences of coaxial cables which are used to connect the mechanical core and the electronics. Specially, for the capacitive transducer with a differential transformer bridge structure usually used in high-precision space inertial sensors, a connecting method of a coaxial cable between the transformer’s secondary winding and front-end circuit’s preamplifier is proposed to transmit the AC modulated analog voltage signal. The measurement and noise models including the stray-capacitance of the coaxial cable under this configuration is analyzed. A prototype system is set up to investigate the influences of the cables experimentally. Three different types and lengths of coaxial cables are chosen in our experiments to compare their performances. The analysis shows that the stray-capacitance will alter the circuit’s resonant frequency which could be adjusted by additional tuning capacitance, then under the optimal resonant condition, the output voltage noises of the preamplifier are measured and the sensitivity coefficients are also calibrated. Meanwhile, the stray-capacitance of the cables is estimated. Finally, the experimental results show that the noise level of this circuit with the selected cables could all achieve 1–2 × 10−7 pF/Hz1/2 at 0.1 Hz.

Research on High-Precision Resonant Capacitance Bridge Based on Multiple Transformers

“…e un = 2u AMP NG (18) where NG ≈ 1 + 2 Z FB Z BR . The real part of the complex TIA feedback impedance is represented by R Z FB .…”

“…Ke Li conducted an analysis on the differential capacitive displacement sensor, focusing on how the stability of the carrier signal and the phase difference and fluctuations between the demodulation signals can restrict the modulation–demodulation process and reduce capacitive sensitivity. He proposed a novel modulation–demodulation scheme based on a step-sine carrier wave, which can effectively mitigate these impacts [ 18 ]. Jianbo Yu investigated the influence of coaxial cables employed in inertial sensors on stray capacitance.…”

Development and experimental investigation of a high-precision capacitive displacement transducer of the inertial sensor for TianQin

“…In the experiment, the circuits were connected to each other by coaxial cables. For final engineering applications, the performance of the cables between the sensor head and the transducer circuits, and in particular the parasitic capacitance effects introduced by the cables, must be considered [15].…”

“…The capacitive sensor developed mainly by ETH Zürich was successfully verified on the LISA Pathfinder mission, with a performance better than 1.8 × 10 −6 pF Hz −1/2 in the frequency range 1 mHz − 0.1 Hz [7]. At Huazhong University of Science and Technology, a pre-scanning and tuning method [13], the stability effect of the excitation frequency [14], and the influence of the stray-capacitance of the coaxial cables [15] were investigated, respectively. And the prototype with a noise level of 1.6 × 10 −7 pF Hz −1/2 above 10 mHz was achieved [16].…”

Bias Stability Investigation of a Triaxial Navigation-Compatible Accelerometer with an Electrostatic Spring

“…The stability of the position offset relies on the capacitive position sensor. The output stability of the position sensor could achieve tens of pico-meters under the micro-meter level range [ 22 , 23 , 24 ]. So, the accelerometer bias contribution by could be designed below 1 g by coupling suitable equivalent electrostatic stiffness.…”