Study On Mass Sensing Mechanism Of Coupled Cantilevers Based On Mode Localization

In recent years,with the rapid development of human society and industrial production,issues such as haze and flu in the fields of environmental monitoring and biochemical medicine have become increasingly prominent,seriously threatening people's life.Therefore,high-sensitivity detection of toxic substances such as harmful gases,bacteria,and viruses is of great significance in preventing diseases and improving the quality of people's life.With the widespread application of MEMS technology in the field of sensing and detection,micro-cantilever sensors have great advantages on detecting tiny substances such as high sensitivity,small size,simple structure,low cost,and easy integration.Traditional methods of mass sensing with cantilevers use frequency shifts as an output,which is difficult to meet the high sensitivity detection requirements for the tiny mass.Therefore,this paper studies the mechanism of mass sensing based on mode localization with coupled cantilevers.We propose a new method of sensitivity evaluation based on amplitude change,which achieves high-sensitivity mass detection on pico-gram level.A spring-mass-damping model of a coupled cantilever structure was established to analyze the mode-localized vibration characteristics of the whole system.Besides,the mechanism of the external perturbation on the system's resonant characteristics was studied.A new sensitivity evaluation method based on amplitude change was proposed.Moreover,analytical results show that the smaller the coupling factor?(=k_c/k)of the system is,the higher the sensitivity is.A mode localization parameter that can reflect the uneven distribution of vibration energy of the coupled cantilever structure is proposed,and a quantitative analysis of the degree of mode localization is achieved.The relationship between the coupling factor and the steering curve was studied under the condition that the coupled cantilever structure was disturbed by mass.It was found that the smaller the coupling factor is,the more severe the mode shape in the turning point area are,and the more obvious the amplitude change of the cantilever is.The conclusion contributed to the enhancement on the sensitivity of detecting small mass.By designing and optimizing the size parameters of the coupled cantilever structure,the weak coupling of the system is achieved.By analyzing the influence of the mass perturbation on the resonant characteristics of the coupled cantilever structure,we studied the mechanism of the sensing cantilever's amplitude change.The side cantilever(No.3)was determined as the sensing cantilever to increase the amplitude variation.We explored the mechanism of two sorts of excitation ways on the mode localization and the vibration response of the system,including excitation on the non-disturbed cantilever and excitation on all three cantilevers.The influence of different excitation ways on the system resonance frequency,vibration mode and amplitude change is analyzed.Finally we determine excitation on all three cantilevers as an experimental excitation scheme to improve sensitivity.The coupled cantilever structure was designed and fabricated with MEMS techniques.An experimental test platform was set up at the same time.Two polystyrene micro-particles of 8.8 pg were successfully applied as the disturbing mass at the free end of the sensing beam.By experimental analysis,the detection of mass change on the pico-gram level was achieved.Furthermore,by numerous simulations,the law of the resonant characteristics of the coupled cantilever structure with mass perturbation was explored.The sensitivity and linear range based on the amplitude change were studied.Compared to the sensitivity of traditional mass sensing method based on frequency shifts,the sensitivity of the proposed structure was improved by 2~4 orders of magnitude.This paper contributes to the application of the coupled harmonic oscillator structure to realize the high-sensitivity detection on small mass.