Experimental strain sensor uses cuts to combine range and sensitivity

With the rapid development of wearable medical devices [one], [ii], [3], [4], [5], electronic skin and high-performance sensors [6], [7], [eight], [9], sensors are increasingly needed to mensurate strain (stress) signals with large deformation and high sensitivity [ten]. Nevertheless, although micrometer-thick metals [11], [12] or semiconductor materials [thirteen], [14] are mostly used as sensitive materials for metal foil strain gauges and piezoresistive sensors, measuring large strains (>5%) is also difficult and challenging. Therefore, studies on the high sensitive and large deformation flexible strain sensors for article of clothing devices, medical health monitoring and bio-robotics applications have attracted considerable interest.

Many studies already produced high-operation flexible strain sensor, using various types of sensitive materials, such as carbon nanotubes [15], [16], [17], graphene [xviii], [19], ZnO nanowires [20], [21], and C-fibers [22], [23], which are combined with flexible polymer (PDMS, Ecoflex or epoxy resin) substrates to realize large strain range and high sensitivity coefficient. However, this method has special sensitive materials, complex training processes and high costs. Besides, micro/nano cracks [24], [25], [26], [27] were applied to heighten the sensitivity of flexible sensors in some references while the existence of cracks influenced the measurement range of flexible sensors. A flexible nano-scale-cracks sensor [26] with a sensitivity ratio of every bit high as 2000 and strain measurement limit of only 1%. To increase the measurement range of the sensor, some researchers [28], [29], [30] have made strain sensors with regular micro/nano folds by using micro/nano fabrication techniques, of which the ultimate strain tin can reach up to 100%. However, the beingness of micro/nano folds results in low sensitivity coefficient in small deformation measurements. Therefore, it is important that using a simple and low-price method to fabricate flexible and high sensitivity strain sensors which can work under either small-scale or large deformation.

Harmless metals such as Cu and Au are the most commonly used and the oldest sensitive fabric in strain sensors [31], [32] because is stable, simple, inexpensive, and convenient and exhibit reliable functioning and capacity for mature processes. Thus, information technology is used for fabricating sensitive structures on various substrates mostly past common processes of sputtering, evaporation, machining and welding, as shown in Fig. 1(b). However, the usually used bulk metal only has a limited elastic strain range and is hard to employ in large deformation measurements. Another unremarkably used polymer material is polyurethane (PU), which has a large elastic range, is inexpensive, and has skillful biological compatibility [33], [34], [35]. It has been widely used in clinical bandage dressing equally shown in Fig. one(a). Therefore, the two materials are combined in this study. Specifically, we use PU picture with micron thickness equally the substrate to achieve large strain deformation, and utilize nano metallic sparse film as strain sensing material to accomplish loftier sensitivity, where we utilise a combination of micro/nano cleft and micro/nano structure with bulges to obtain high-sensitivity strain sensing in the condition of the big deformations. The schematic diagram of the strain sensor is shown in Fig. 1(c). The structure of the strain sensor is simple, and the major part is only composed of a flexible substrate material and nano metallic thin films with micro/nano bulges and micro/nano cracks, which makes the strain sensor realize large measurement range and highly sensitive. And the specific analysis and explanation can be observed in the sensor’s conductive model in minor and big strains, as shown in Fig. 1(d) and (e). The mechanism of the flexible sensor could state as follows. The loftier sensitivity of the flexible sensor is due to the meaning resistance change of the AU nano-moving picture acquired by the cracks disconnection-reconnection process. The large measurement range is due to the bugles which blocked the expansion of micro/nano cracks and formed many brusque cracks.