Optical Detection Of Bending Modes Of Micro-nano Cantilever Beam Mechanical Sensor

For the small size and low mass,the micro-nano cantilever beam mechanical os-cillator is a good sensor for detecting the minute environmental change,and it is the core device of many scanning probe microscopes,including atomic force microscope and magnetic force microscope.The micro-nano cantilever structure has developed into a multipurpose and powerful platform for detecting physical quantities of mechan-ical vibration.Since the invention of atomic force microscope,great progress has been made in the fundamental research and application of micro-nano cantilever beam me-chanical oscillators.In the study of magnetic resonance force microscope,micro-nano cantilever beam is also an important part,which is used in cross-disciplinary studies such as molecular adsorption and biophysics of nanoelectromechanical systems.Recent developments have shown that more environmental detection capabilities and sensitiv-ities,such as mass spectrum imaging and experimental detection of two-dimensional vector force fields,can be obtained by using multiple vibration modes of micro-nano cantilever beams to participate in the sensing process.One of the challenges for detect-ing the micro-nano cantilever beam is to measure and determine their bending vibration modes.Among the parameters of the bending vibration mode,the direction of vibration,that is,the angle of the vibration direction of the mechanical oscillator relative to the optical axis or the measuring direction,is one of the important factors affecting the sub-sequent analysis of the whole measurement system.Vector force microscopy is a uni-versal technique for characterizing the morphology of samples and probe-sample force signals.The two-dimensional vector force field diagram can be obtained by monitoring the frequency change and vibration direction of the vibration mode while scanning the sample surface to provide more information.In the light of the home-built micro-lens fiber interferometer,the two physical effects of light interference and light scattering in the optical detection of micro-nano cantilever beam mechanical oscillator are analyzed.In this paper,the study is divided into the following three parts-1.It is found that the detection of the displacement of the micro-nano cantilever beam in and out of the focused light spot plane can be realized by combining the inter-ference effect formed by two reflections of light on the fiber end and cantilever beam and the backscattering effect of light on the micro-nano cantilever beam.In particular,for the in-plane displacement detection,our home-built micro-lens optical fiber inter-ferometer does not require a four-quadrant photodetector compared with the traditional optical scattering instrument,which greatly reduces the complexity of the optical path.The optical devices that need for collimation are reduced from 3 to 2,facilitating the interferometer to be used in very low temperature systems.2.We theoretically analyze the optimization of the optimum working point of detecting mechanical oscillator's vibration in any direction by using the micro-lens op-tical fiber interferometer.And the cantilever beam vibrating along different directions is detected experimentally,which proves our analysis.Based on the above results,the thermal vibration of two cantilevered microwires are detected and the vibration direc-tions are analyzed.Our results provide a new experimental method for the study of the bending vibration mode of mechanical oscillators and lay a solid foundation for its application in vector force measurement.3.An experimental method for determining the vibration direction of the bending mode of micro-nano cantilever beam is presented.The method does not require prior knowledge of the micro-nano cantilever beam,nor does it require simultaneous detec-tion of a pair of nearly degenerated bending vibration modes.Using our micro-lens optical fiber interferometer,by selecting different working points,that is,two different vibration projection directions,we have experimentally determined the vibration direc-tions of the first-three-order bending modes.Our results provide a new experimental method for the study of the bending vibration mode of mechanical oscillator and lay a solid foundation for its application in vector force measurement.