Research On Magnetohydrodynamics Angular Rate Sensor Based On Magnetic Induction Modulation

The Magnetohydrodynamics(MHD)angular sensor has the characteristics of wide frequency band,low loss,and ability to work in extreme environments.It is especially suitable for the measurement of wide-frequency micro-angle vibration in spacesensitive loads.Bandwidth and noise levels are the main technical indicators of the MHD angular sensor.Current research has focused on improving its low frequency signal-to-noise ratio to improve low frequency performance and further reducing passband noise for higher resolution.Therefore,this paper proposes an MHD angular sensor based on magnetic field modulation,which modulates low-frequency noise interference through modulation and demodulation,thereby improving the output signal-to-noise ratio and improving the measurement resolution.First,this paper analyzes the voltage noise spectral density of the pre-processing circuit of the constant magnetic field MHD angular sensor.It is found that the 1/f noise of the operational amplifier accounts for the main component of noise and contains power frequency interference.In order to solve the above problems,an MHD angular sensor using AC magnetic source is proposed to design an overall angular velocity measurement system,and its sensing and measurement principles are analyzed.Secondly,this paper designs the AC magnetic source and structure of the sensor,and proposes the solenoid which is driven by the alternating current as the AC magnetic source of the sensor,and theoretically calculates the magnetic field.Select the core housing material and design the closed magnetic circuit structure and the corresponding sensor mechanical structure.In order to verify the rationality of the structural design and analyze the magnitude and uniformity of the magnetic induction at the fluid ring,the sensor structure is simplified,the simplified structure is simulated in Maxwell,and the problems to be paid attention to during the sensor assembly process are discussed.Finally,this paper designs an extraction scheme for the sensor output weak amplitude modulation voltage signal.In order to realize signal amplification and filtering,a signal preprocessing circuit is designed,which consists of a low noise amplifier circuit,a second-order band-pass filter and a single-ended to differential circuit.In order to realize the demodulation of the signal,a digital phase sensitive detection system based on embedded system is designed.The reference signal and the amplitude modulation signal are synchronously acquired,and the signal is demodulated in the DSP chip.After the demodulation system is tested,The relative error of the frequency of the signal is less than 0.6%,and the relative error of the amplitude is less than 0.15%,which can effectively extract the modulated signal.Through the measurement and analysis of the noise floor of the signal extraction system,the results show that low frequency noise interference can be avoided by modulation and demodulation.