Research Of Feedbcak Measurement System Of Micro Resonant Sensor

Resonant sensor outputs internal resonant frequency signals.Here,measured parameters change the equivalent mass,stiffness and damping of resonator and cause changes of the resonant frequencies.The frequency signals can be picked up easily and have good anti-noise ability.They can be transformed into digital signals and transmitted to the long distance easily.High resolution of the resonant mass sensors relies on its high resonant frequency which requires tiny resonator size and high quality factor of the detection system.It gives a great challenge to the sensor processing and detecting.In this paper,a dual closed-loop feedback mass detection system is proposed.The equivalent mass and damping coefficient can be adjusted simultaneously so that the atomic/molecular level resolution and high quality factor is obtained with a micron scale resonator.The resonant sensor with nanometer gap between the pole plates is developed.Micro electroforming process technology is used to deposit nickel material and the cantilever beam resonance sensor is produced.Here,the clearance between pole plates is 7?m.A new crystalline silicon etching process is designed and a micron size resonator is fabricated to obtain 200 nm clearance between pole plates.The closed loop detection system based on phase locked loop(PLL)is proposed.To decrease the equivalent mass of the resonator and increase its resonant frequency,a 180° feedback loop is applied in the detection system.Reverse Lock-In Amplifier(RLIA)is used to replace the high frequency band pass filter(BPF)and shift useful frequency signals,so the signal noises are filtered out.An accurate movement control system is designed to regulate the number of metal atom or gas molecule deposited on the resonator.By adjusting the detection system to achieve fairly high resonant frequency,and then the mass of single metal atom or gas molecule are exactly measured in vacuum environment.The dual feedback detection system is proposed.To decrease the equivalent damping factor of resonator and get high quality factor,another 90° feedback loop is used.For the dual feedback detection system,the relationship between resonant frequency,quality factor,detection resolution,and noise is investigated.Based on it,the best gain factors of the dual feedback detection system are determined.Compared with the single feedback system,the noise levers of dual feedback system are decreased significantly.Using the detection system,the mass of single H2 molecule is detected in air.The dual feedback detection system is used in micro gas sensor to increase resolution of the gas sensor.Here,the low and middle frequency detection systems are designed and produced.Using the gas sensors produced by electroforming and wet etching technique,H2,ethanol and NH3 concentration are measured at ambient temperature and pressure conditions.For the gas sensors,180° and 90° feedback loops are added to their detection system so that the quality factor and resolution of the sensors are increased and the signal noise is decreased significantly.Thus,the universal property of the dual feedback detection system is illustrated.