A High-Sensitivity and Low-Noise Thermal Gas Flow Sensor Based on Silicon-Doped Thermocouples

The detection of gravitational waves in space requires microthrusters that can respond quickly to compensate for nonconservative forces on the satellite with low thrust noise. Flow measurement plays a crucial role in cold gas microthrusters (CGMTs), directly determining the control accuracy of thrust adjustment and the upper limit of thrust noise. It is a challenge to achieve high-resolution and low flow measurement noise for flow measurement to obtain sub-micro-Newtonian thrust resolution and thrust noise. A high-sensitive temperature differential flow sensor has been developed using pairs of doped silicon thermocouples as the key temperature sensing elements. Aiming at reducing the noise at low-frequency band of mHz-Hz, which is the concern of space gravitational waves, the thermal noise of the internal resistance of the thermocouple, the fluctuation noise of the heating power, and the low-frequency noise of the amplifier circuit are carefully handled to achieve a flow measurement noise better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1~\mu $ </tex-math></inline-formula>g/s/Hz1/2 @ 1 mHz–10 Hz. Through the design of the flow channel, the flow conduction of the system exceeds <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu $ </tex-math></inline-formula>g/s/Pa, with a response time of about 10.2 ms, ensuring the rapid response capability. It holds promise for integration into CGMT systems for space-based gravitational wave detection.