Research On Micro/Nano Particles Mass Measurement Based On Micro-Cantilever Sensor With Suspended Channel

The physical properties of micro-nano particles are necessary to determine their application,especially the water-based particles with a diameter of less than 50 nm are at the core of their wide application.The conventional micro-cantilever sensor is difficult to be used for the detection of water-based particles,while the suspension channel micro-resonator has complex processing technology and small measurement particle size range.In view of the above problems,this thesis proposes to use SON structure technology to make a large-size suspension channel micro-beam（cantilever beam or double-branch beam）sensor,and combine the MPN counting method to realize the detection of the number and quality of nanoparticles in nanofluids.The combination of MPN counting method increases the minimum detection quality of the microcantilever beam and reduces the cost of manufacturing the microcantilever beam itself in the suspension channel,which is of great significance in the field of micro/nano particle weighing and counting.The main contents of this thesis are as follows:（1）The detection model of micro-cantilever in suspension channel is established.For the beam with suspended microchannels,the important parameters such as the deflection curve differential equation and the section moment of inertia in material mechanics are modified.The calculation formula between deflection and concentrated load and uniform load in static detection model is established.Then,based on Timoshenko beam theory and Euler-Bernoulli beam theory,the mathematical relationship between resonant frequency and beam size is derived,and the influence curve of beam size change on resonant frequency is drawn.The single beam and double beam are studied from static detection and dynamic detection respectively.The minimum detection quality and sensitivity of the two beams are obtained,and the change curve between the position of the concentrated load and the minimum detection quality and sensitivity is drawn.（2）Simulation analysis of suspension channel micro cantilever beam.The finite element analysis of single beam and double beam is carried out by using COMSOL Multiphysics 5.5 multiphysics simulation software.Firstly,the influence of the size change of the micro-cantilever on the resonant frequency is simulated,and the size parameter table is established according to the results of theoretical and simulation analysis.The effects of uniform load applied by micro-nano fluid and concentrated load applied by micro-nano particles on the bending deflection and resonant frequency of the beam are analyzed in detail by using fixed mechanics and fluid mechanics multi-physics coupling.Finally,the relationship between fluid with different density and particles with different mass and bending deflection and resonant frequency is simulated.Comparing the theoretical and simulation analysis results,the relative error is within 10%,which verifies the correctness of the theoretical model to a certain extent.（3）Sensor fabrication and experimental verification.The fabrication of the suspended microchannel in this thesis adopts the SON structure process.The specific dimensions of the single beam U-shaped microchannel are:length 500μm,width 100μm,thickness 10μm,microchannel width 20μm,microchannel height 4μm;then,a set of system for detecting micro-cantilever beam is built by using the principle of optical lever,and the signal acquisition and data processing program of upper computer is developed by LabVIEW.The high purity silica particles with a particle size of 50 nm were weighed and counted.The mass of a single silica particle measured by MPN counting method was 1.61×10^-162),and the error was 11.94%.The minimum detection mass of single beam with a length of 500μm a width of100μm a thickness of 10μm a microchannel width of 20μm and a microchannel height4μm combined with MPN counting method is 1.61×10^-162).After the introduction of suspension channel and MPN counting method,the mass prediction of single nanoparticle can be realized.The research method of this thesis can realize the detection of the number of particles in the nanofluids or the mass of a single nanoparticle without reducing the size of the cantilever beam.