Printing Flexible Multi-channel Sensing Circuit And System Design

The multi-functional flexible sensor system is composed of flexible sensor,hardware circuit and data receiving terminal.At present,there are three main problems in the construction of flexible sensing system: One is how to integrate multiple sensors into a flexible substrate,all sensors share a hardware system,so that electronic devices have a smaller size and lower power consumption.The second is how to reduce the manufacturing deviation of the flexible sensor in the system and improve the adaptability of the flexible sensor and the hardware part.The third is how to ensure the accuracy of data acquisition when the sensor system is applied in bad environment.A multi-channel signal acquisition system is developed in this paper.By printing process controls the size of the resistance value resistor matching with resistance strain gauge,strain bridge forming low zero drift,strain bridge resistance signal into a voltage signal transmission to the hardware system,and through the Bluetooth module,will process after the sensing signal transmission to the android APP,real-time display and save the size of each channel strain,At the same time,intelligent data visualization graphics are generated.The main research contents of this paper are as follows:(1)In order to improve the matching range of resistance values,PET(polyethylene terephterate)is used as a flexible substrate.After adding 30 wt% PMMA(polymethyl methacrylate)solution and high resistance carbon paste on the basis of the main carbon paste,printing resistors ranging from 76 Ω/sq to 5 kΩ/sq are obtained by screen printing.In order to improve the matching accuracy,after optimizing the line width of the printing resistor and the viscosity of the printing material,the printing deviation of the resistor is up to ±20% through experiments.In order to reduce the printing deviation,a resistance adjustment theory is proposed to reduce the printing deviation to 0%～3.33%.(2)Static and dynamic stability tests of printed resistors are carried out in this paper.The resistors are placed at room temperature for 90 days and 85 ℃/85% for 100 h to record the changes of their resistance values.The results show that the relative changes of resistance are small and the resistors have good static stability.Resistors with no PMMA addition show good dynamic stability and are suitable for strain resistors in 500 cycle bending experiments,while resistors with PMMA addition show poor dynamic stability and are suitable for fixed resistors.(3)In order to convert the resistance signal of strain gauge into voltage signal which can be recognized by computer,single-arm and double-arm Bridges are designed in this paper.Experiments verify that the zero drift of the bridge is greatly reduced after the resistance adjustment,and the temperature compensation can be effectively realized by adjusting the resistance value of the adjacent arms of the strain bridge to the same size combined with the temperature and humidity change characteristics of the resistor.The sensitivity of single arm and double arm bridge are 18.14 m V/mm/5V and 37.72 m V/mm/5V respectively.(4)Four single-arm Bridges with temperature compensation are printed on the flexible substrate to meet the demand of all-directional strain collection.The corresponding channels are selected by controlling the on/off of multiplexing switches.The strain bridge converts the strain signal into voltage signal for signal processing,and then transmits the strain signal to the mobile phone terminal through Bluetooth.In this paper,the strain gauge is affixed to the four joints of the finger for finger bending and gesture recognition.The results show that the system has good response characteristics and repeatability to strain in different scenarios.(5)The flexible strain system proposed in this paper has low cost and simple process,and the number of multiplexing switches and printed flexible strain gauges has good scalability,which can meet the needs of wearable electronic products for large-area and multi-point acquisition.To sum up,the system has broad application prospects in the field of wearable electronic devices.