Abstract
A new type of flexible sensor, which could maintain the deformation consistency and achieve the real-time detection of the variation in load of the measured object, was proposed in this work. According to the principle of forced assembly, PDMS was used as the substrate of sensitive components and electrodes, while carbon fiber was added as a conductive medium to prepare a polymer-based flexible sensor, which effectively overcame the deformation limitation and output instability of conventional flexible sensors due to different substrates of sensitive components and the electrode. Combined with the sensor structure and the forced assembly method, a theoretical analysis of its conductive measurement mechanism was carried out. Meanwhile, an experimental test device was designed to test and analyze the output characteristics of the flexible sensor under a static and dynamic alternating load. The results show that the flexible sensor exhibited linear output under the dynamic alternating load of 10 kN to 60 kN and frequency of 3 Hz. Peak and valley value had the same phase with the load extremes. The dynamic and static experiments show that the resistance output signal and the sensitivity was in the range of 310~624.15 Ω and 171–183 N/Ω respectively. However, due to the hysteresis of the elastic recovery of the polymer, the output repeatability of the flexible sensor under the dynamic alternating load was 5.03% and 0.78% lower than that of the static load, respectively. Combined with the static and dynamic experiments, it was verified that the polymer-based flexible sensor can maintain the same deformation characteristics with the measured object, and at the same time outputted a resistance signal with a certain mapping relationship with the applied load. The repeatability of the output signal under dynamic and static experiments was within ±7%, which can meet the measurement requirements of the fatigue life of the measured body during periodic load.
Highlights
With the development of information technology, electronic technology and polymer synthesis processing technology, as a new type of sensor, the polymer-based flexible sensors have been widely used in the detection of human motion states [1], physiological parameters detection on skin [2,3], environmental signal monitoring [4] and other complex situations that the shape of measured objects would change with variation forces, attributed to their superior flexibility, malleability, portability and wearability [5,6,7]
The electrodes were usually made of carbon nanotubes (CNTs), graphene (GN), carbon fiber (CF) and nano-metal materials as the main conductive medium, prepared by different molding methods [8,9,10]
The flexible sensor was composed of an upper flexible sensing film 2 and a lower flexible sensing film 3 made of the same process recipe, wherein the surface of the lower flexible sensing film 3 was formed into a microstructure groove
Summary
With the development of information technology, electronic technology and polymer synthesis processing technology, as a new type of sensor, the polymer-based flexible sensors have been widely used in the detection of human motion states [1], physiological parameters detection on skin [2,3], environmental signal monitoring [4] and other complex situations that the shape of measured objects would change with variation forces, attributed to their superior flexibility, malleability, portability and wearability [5,6,7].Polydimethylsiloxane (PDMS), Poly(ethylene terephthalate) (PET), polyimide (PI) and parylene, which has superior flexibility, malleability, were often used as the substrate for the flexible sensor.Sensors 2019, 19, 1403; doi:10.3390/s19061403 www.mdpi.com/journal/sensorsThe electrodes were usually made of carbon nanotubes (CNTs), graphene (GN), carbon fiber (CF) and nano-metal materials as the main conductive medium, prepared by different molding methods [8,9,10].JS et al [11] from Seoul National University made a super thin flexible sensor with a thickness of about1/6 of human skin using poly(vinylidene fluoride) (PVDF) as the substrate and zinc oxide (ZnO) as the electrode. With the development of information technology, electronic technology and polymer synthesis processing technology, as a new type of sensor, the polymer-based flexible sensors have been widely used in the detection of human motion states [1], physiological parameters detection on skin [2,3], environmental signal monitoring [4] and other complex situations that the shape of measured objects would change with variation forces, attributed to their superior flexibility, malleability, portability and wearability [5,6,7]. Baek et al [12] from Korea University made oxygen ion treatment on the surface of PDMS film with 3 mm thick protrusion structure, and bonded with PDMS film containing copper metal layer to make flexible sensor for electrocardiogram (ECG) signal detection. Ruan X et al [13]
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