Research On Micro Resonat Alcohol Gas Sensor

The micro resonant gas sensor uses the resonant frequency of the resonant beam to detect the gas concentration.It has the advantages of rapid response,stable operation and high sensitivity.In this paper,a micro-resonant gas sensor bases on capacitance detection and electrostatic excitation is proposed.By adding a feedback gain to the closed-loop detection circuit,the natural frequency and sensitivity of the resonantor are improved.The free vibration characteristics of the rectangular constant section cantilever and triangular variable section cantilever are analyzed,and the difference of natural frequencies between rectangular cantilever and triangular cantilever is compared.The coupling dynamics model and feedback control model of mechanical,chemical,molecular force and electric force for the rectangular constant section cantilever beam are established.The four-field coupling free vibration differential equations of the cantilever beam under feedback control and adsorption mass at the end are established.The effects of electric field force,molecular force,dimension parameter,adsorption mass and feedback gain on natural frequency are analyzed.The rectangular cantilever beam with constant section and the triangular cantilever beam with variable section are fabricated by wet etching.The end of cantilever beam is coated with copper phthalocyanine sensitive layer by vacuum evaporation,electron beam exposure and metal stripping.The excitation electrode and pickup electrode of the upper plate are fabricated by photolithography and vacuum evaporation.The rectangular beam alcohol gas sensor and triangular beam alcohol gas sensor are made.The weak signal measurement circuit of the micro resonant gas sensor is designed,and the factors affecting the sensitivity of the sensor AC bridge are analyzed.The open-loop detection circuit and the closed-loop feedback control detection circuit based on the sensor AC bridge are designed.The closed-loop feedback control detection circuit takes the sensor AC bridge,feedback control circuit and phase-locked loop as the core.The resonant frequency can be accurately and stably locked.The natural frequency measurements of the rectangular beam sensor and triangular beam sensor are completed by open loop and closed loop detection circuit.The experimental platform of ethanol gas concentration under vacuum environment is built and the experiment of the ultra-low concentration gas is completed.The effects of molecular force and feedback gain on the natural frequency and sensitivity of two cantilever structures are verified by comparing the natural frequency and output signal strength,and the quality factor is determined under standard air pressure.The detection of the ultra-low concentration of the ethanol gas in vacuum environment is realized,and the performance of the sensor is tested,which proves the closed-loop measurement system and the feedback control model.