Wearable Strain Sensors Based On Room-temperature Liquid Metal

Flexible sensors are extensively used nowadays in the field of wearable electronics to detect the motions/parameters of human body.Flexible strain sensors are usually employed to detected body parameters and motions under the action of stress/strain.Flexible sensors are made up of composites that combine conductive materials with elastomers that's why they exhibit large hysteresis,less stretchability and resolution.Liquid metal due to its properties like high conductivity,deformability and nontoxicity,is a best candidate to manufacture highly stretchable and low hysteresis sensors.However,high surface tension of liquid metal makes it difficult and complex to build film on flexible substrate.Moreover,variation law of resistance of stretchable sensors based on liquid metal under external stress/strain is not yet known.Besides,it is difficult to mind the requirement about specificity of wearable devices and multidirectional of bending motion.Aim at these challenges,the work of this thesis is as below:(i)A new method of liquid metal transfer printing has been utilized in this research in which different wettability of liquid metal wetted to Cu/plastic board and the enhancement of oxide layer of liquid metal to wettability of liquid metal to PDMS.The thickness of liquid metal was controlled by the width of Cu,and was well-distributed.The thickness was 32 ?m when the width of liquid metal was 150 ?m.(ii)Liquid metal based flexible sensor is fabricated by the method of liquid metal transfer printing,and got characteristics under tension.Finally sensor exhibits a gauge factor of 2.3,0.995 linearity,7% hysteresis at stretch of 100%,resolution was 0.05% strain at the range from 0 to 105%,rapid response of 170 ms and stability after 8 000 strain cycles.These superior features have made it possible to monitor interactive control(finger motion)and sports/health of human body,which shows attractive application prospects in man-machine interaction,health monitoring,and motion control.(iii)3D printing bending strain sensor is also fabricated through 3D printing technology and asymmetric microchannel structure design.This sensor exhibits the opposite variation when bending outward and inward.The relative change of resistance is proportional to bending angle when bending and the sensor shows high linearity of 0.996 when bending outward.Increasing the distance from the microchannel plane to the center plane is beneficial in the enhancement of sensitivity of sensor.The sensor exhibits very good repeatability and circulation capability.The sensor demonstrates great potential in the fields of human motion monitoring,human-machine interaction,and other fields when used to measure the bending motion of wrists,necks.