Multi-scale Structure Design Of Self-powered Skin-like Flexible Sensor System And Application

The self-powered "skin-like" flexible sensor systems with specific multi-scale structure design for its indispensable component enable novel devices with deformability and stretchability.Skin-like flexible sensor systems have drawn much attention from researchers and have been intensively studied in many fields such as health information monitoring,chronic disease management,and intelligent rehabilitation.However,there are still some critical scientific and technical issues in the design of the indispensable critical functional component,and further related multiscale structure design strategies are urgently demanded.From the perspective of sensor components,the stretchability analysis methods of serpentine network planar structure are incomplete because the influence caused by different mesh distributions is ignored,and it’s necessary to further construct relevant theoretical analysis models;Laserinduced graphene(LIG)with the porous structure is widely used in strain,electrophysiology,and chemical sensing.However,the gage factor(GF)with small deformation is still lower than that with large deformation,it’s a fatal demerit for the collection of weak physiological signals of the human body.At the same time,we note that it’s important to reduce the skin contact impedance to improve the signal-to-noise ratio of the ECG and EMG signal by enhancing the conductivity of LIG.As another indispensable component,the stretchable antenna with the potential use in wireless communication and RF energy harvesting can provide future wearable electronics with a low profile and integrated functions.However,mechanical deformations applied to stretchable antennas often lead to a shift of their resonant frequency(i.e.,the detuning effect),which limits their applications to strain sensing.Additionally,the meshed ground plane in the structure-engineering stretchable microstrip patch antenna leads to a relatively large back lobe in radiation patterns and degraded on-body performance which reduces the efficiency of ambient RF energy harvesting.In this thesis,several studies focusing on these issues are presented as follows.The concept of "stretching angle" and "limited distance" which has a great influence on the distribution of serpentine mesh structure was proposed,and the stretchability calculation model of serpentine mesh structure with different stretching angles under ideal conditions was obtained.Meanwhile,a newly invented "Laser cut and paste" method based on water-soluble adhesive materials has been proposed for the fabrication of serpentine mesh structures.Based on the versatile,cost-and timeeffective method,the skin-like electrophysiology sensor was fabricated and applied on human skin to measure ECG and EMG.At the same time,a serpentine mesh wireless strain sensor with different stretching angles was prepared to investigate the influence of stretching angles on the performance of strain sensing,which can be used to collect information of human motion.Especially,we focus on the influence of different stretching angles on the linearity of the wireless strain sensor,and the wireless strain sensor with the orientation of 30° showcase a value of 0.999.In addition,the LIG strain sensor was fabricated with 25%power with the ability of high sensitivity to small deformation and showcased the fiber/porous structure,which can be used to collect information about human micro-vibration(i.e.,pulse).The LIG-Ag composite with improved conductivity(3 orders of magnitude)and mechanical stability/robustness was prepared to measure high-quality ECG,EMG,and EOG.The LIG was also modified by GOx to gain sensing ability for glucose with the sensitivity of 19.5μA/mM.As the key component of wireless data transmission and powering,stretchable antennas play an indispensable role in flexible/stretchable electronics.In this research,a hierarchically structured stretchable microstrip antenna with meshed patterns arranged in an arched shape showcases tunable resonance frequency upon deformations with improved overall stretchability.The nearly constant resonance frequency(<2%)during deformations enables robust on-body wireless communication and RF energy harvesting.The stretchable microstrip antenna proposed by this research was demonstrated to communicate wirelessly with a transmitter(input power of-3 dBm)efficiently(i.e.,the receiving power higher than-100 dBm over a distance of 90 m)on human bodies even upon 25%stretching.Furthermore,the stretchable microstrip antennas with varying 3D configurations for excellent on-body radiation performance were prepared.In particular,the optimized peak gain(3.52dB)from the stretchable asymmetric 3D microstrip antenna allows it to wirelessly transmit the energy and data at a further distance(～120m),as well as a higher charging rate(43 μJ/s)from the harvested RF energy.More importantly,the integration of stretchable antenna and rectenna with stretchable sensing and energy storage units can yield a self-powered"skin-like" flexible sensor system for health monitoring of humans and structures.