Preparation And Performance Study Of Flexible Printed Sensors Based On Surface Modification

Skin-interfaced,wearable electronics have attracted significant attention because of their unique role from preventative monitoring and diagnostic confirmation to convenient therapeutic options.The ultimate application of these bio-integrated devices for practical and convenient applications hinges on the seamless integration of on-body sensors with wireless transmission modules.Multifunctional on-body sensors can precisely and continuously monitor the health conditions of the human body,whereas the wireless transmission modules can wirelessly power up the sensors and transmit the data generated from them to the cloud for the healthcare professionals.As a promising direction toward this class of integrated systems,the soft body area sensor network includes on-body sensors for physiological signal monitoring and flexible printed circuit boards(FPCBs)for signal conditioning/readout and wireless transmission.Compared with other wearable devices,the on-body sensors that pliably laminate on the skin surface can precisely capture the clinically relevant data for health monitoring.Realization of the soft body area sensor network currently relies on various sophisticated fabrication approaches from lithography and transfer printing to direct printing,especially when stretchable sensors are separated from readout circuits(e.g.,FPCBs).In particular,extensive efforts have been devoted to exploring the integration of wearable electronics on paper/fabric or human skin.However,there lacks a simple yet universal approach to fabricate all of the modules relevant to the soft body area sensor network,due to the challenging requirements of low-temperature processing on textured surfaces with easy removal capabilities.This dissertation investigates the ultralow-temperature sintering of large-sized silver nanoparticles(Ag NPs)by laser modification of the substrate surface.Ag NPs in conductive ink were sintered at only 60?.Designing the appropriate size of modified regions,the sintered Ag layer exhibits a sheet resistance of only 0.274?and withstands 10000 folding cycles.In this dissertation,we report a simple yet universally applicable fabrication technique with the use of a novel sintering aid layer to enable direct printing and room-temperature sintering of various metal inks for constructing paper-/fabric-based FPCBs and on-body sensors.Consisted of the polyvinyl alcohol(PVA)paste and functional nanoadditives(e.g.,Ti O₂ or Ca CO₃,among others),the sintering aid layer reduces the surface roughness of various substrates to allow printing of an ultrathin layer of metal patterns with improved electromechanical performance against bending and folding.More importantly,the metal NPs printed on the sintering aid layer have significantly decreased sintering temperature to form an FPCB on paper/textile or on-body sensors directly on the skin surface.Various on-body sensors integrated with an FPCB illustrate a system-level example of this technology.In the field of wireless transmission,we report a body NET system composed of stretchable sensors attached on multiple skin locations to gather human physiological and movement signals,which are wirelessly operated by silicon readout circuits attached to textiles.The physically separated stretchable sensors and silicon readout circuit communicate via passive radiofrequency identification(RFID)technology.The stretchable sensor tags are fabricated by printing intrinsically stretchable materials on elastic substrates,and are completely free from rigid silicon chips and batteries to avoid potential stress-concentrated regions and improve system robustness.The main technical challenge encountered here is dealing with the strain-induced changes of the sensor antenna inductance and resistance,which can affect readout effectiveness.We address this by adapting an unconventional detuned RFID tag design and verify its appropriateness through simulation and experiments.Our design enables the body NET system to maintain full functionality even when the on-skin sensors are stretched to 50%strain.Our body NET system is demonstrated by connecting multiple sensor nodes and a smartphone through Bluetooth.Our hands-free body NET could continuously,simultaneously and accurately monitor a person's respiration,pulse and body movements.The platform offers a powerful tool for analysing relevant human activities and physiological signals,and could potentially be used for real-time physiological studies.