A Flexible Pressere Sensor Based On A Multiple-Contact Mechanism And A Discrete Structure

Pressure sensors,as a kind of tactile sensors,are paid great attention to potential applications for intelligent robots,healthcare and human-computer interaction.Recently,with the development of materials science and nano technology,high-sensitivity pressure sensos based on smart materials and microstructures are attached importance.Generally,high sensitivity depends on the rapid cut-off/connection between the conductive pathways of sensitive elements,but wide measure range benefits from the good stability of active materials with large external force loaded.Therefore,there is trade-off between sensitivity and measurement range for the pressure sensors to the disadvantage of reliability of the pressure sensor in different application scenarios.So,there is a challenge for preparing a high-performance pressure sensor with extensive applicability.Herein,a flexible pressure sensor based on a discrete structure and a multiple-contact mechanism（DSMM）is proposed.A DSMM mathematical model is established.The structure of the DSMM pressure sensor is optimized and the functional material is also analyzed.Based on the optimization and deepness development of non-silicon micro fabrication technology,DSMM pressure sensors are prepared and tested on performance and application.The main contents and research results of this thesis are explained in further detail below.First,a discrete structure and a multiple-contact mechanism for pressure sensing is proposed,of which the emphasis is discretizing the single contact between conductive units into the discrete contact between electrode and discrete pixels array.And the electrical response comes from pixels orderly connected with free electrode in parallel nor the change of contact resistance between conductive elements.Because the contact conditions of pixels are only on or off,it is not the change of the contact resistance between pixels and electrode but the number of pixels contacted（k）.So,the rapid saturation of contact resistance can be avoided in sensing mechanism,and the foundations of preparing pressure sensos with both high sensitivity and wide range are paid.On this basis,a multiple-contact mechanism mathematical model is established to optimize sensitivity,accuracy of measurement and linearity of the pressure sensor through the modification of pixels density and distribution pattern.Therefore,high sensitivity can be achieved with wide measurement range.Second,the core structure of DSMM pressure sensors are optimized through finite element simulation methods on the calculation and analysis of their force conditions.The force conditions of discrete structure are definitively affected by the thickness,patterning and height of free electrode,which have an important influence for gravity deformation,reactive force and threshold force.The gravity deformation,error of reactive force and threshold force can be limited to<0.55μm,<5.6%and<17.3 m N respectively after optimization,when both the thickness and height of free electrode are 20μm.And the measurement accuracy can be improved.Third,for the requirement of functional materials of the DSMM pressure sensor,the in-situ synthesis technology and micromachining technology of graphite nanosheets/Polyimide materials are researched systematically.The performance of GNS/PI materials is tested for verifying the rationality of GNS/PI materials on pixels materials.The GNS/PI composite materials have advantages of good dispersibility and film-forming properties.With external pressure applying,the variation of resistance is less than 0.05%and the contact resistance between pixels and electrode easily becomes saturated,showing the good electrical stability to meet the requirements of the active materials of DSMM pressure sensors.Fourth,based on in-situ synthesis technology and micromachining technology,several process difficulties are overcome to design the integrated manufacturing process of the DSMM pressure sensor.The DSMM pressure sensors are prepared and several performances are tested for verifying the feasibility of the multiple-contact sensing mechanism.The current response curves are piecewise when the density of pixels is 100/cm².But based on 225/cm² density of pixels,the current response curves are smooth with expectations,and high sensitivity（0.79/k Pa）and wide measurement range（～410 k Pa）of the pressure sensor are also established.Ultralow limit of detection is established（15 mg）based on the free electrode prepared with micro serpentine springs.The stability of the flexible pressure sensor is tested after 800 pressure cycles,and the current response is still stable.Fifth,on the basis of the verification of the multiple-contact sensing mechanism and according to the testing results,optimum proposals are proposed to optimize the sensitivity and linearity of the DSMM pressure sensors.After optimization,as to a pressure sensor with square pixels,high sensitivity（3.06/k Pa）is established corresponding to wide measurement range（～230 k Pa）,when the density of pixels is 900/cm².And for the orthohexagonal pixels,high sensitivity（5.16/k Pa）is established corresponding to wide measurement range（～230k Pa）with 1183/cm² density of pixels.This shows advantages of the DSMM pressure sensors in both high sensitivity and wide measurement.It is non-linearity when the distance between pixels is uniform,but the linearity can be optimized after adjusting the pixels spacing.According to the experimental results,when the distance between pixels increases according to Fibonacci sequence,the linearity of I/I₀-pressure can be improved,,showing high linearity.Finally,for enhancing the abilities of the DSMM pressure sensor for information extraction,the addressable DSMM pressure sensors are prepared to accurately detect the contact status of each pixel.The DSMM pressure sensor not only has good applications for press actions detections but also can be integrated in a robotic arms system to control its motions,showing the potential application for intelligent robots tactile sensing.