High-Resolution and High-Sensitivity Flexible Capacitive Pressure Sensors Enhanced by a Transferable Electrode Array and a Micropillar-PVDF Film.

Flexible pressure sensors have attracted increasing attention because they can mimic human skin to sense external pressure; however, for mimicking human skin, the sensing of a pressure point is far from sufficient. To realize fully biomimetic skins, it is crucial for flexible sensors to have high resolution and high sensitivity. We conducted simulations and experiments to determine the relationship between the sensor sensitivity and physical parameters, such as the effective relative permittivity and air ratio of the dielectric layer. According to the results, a micropillar-poly(vinylidene fluoride) (PVDF) dielectric layer was designed to achieve high sensitivity (0.43 kPa-1) in the low-pressure regime (<1 kPa). An 8 × 8 pixel sensor matrix was prepared based on a micropillar-PVDF (MP) film and electrode array (MPEA) to detect the pressure distribution with high resolution (13 dpi). Each pixel could reflect the point of applied pressure through an obvious change in the relative capacitance; moreover, objects with various geometries could be mapped by the pixels of the flexible sensor. A counterweight, a plastic flag, and pine leaves were placed on the flexible sensor, and the shapes were successfully mapped; in particular, the mapping of the ∼0.005 g ultra-lightweight pine leaves with a length of 7 mm and a width of 0.6 mm shows the high sensitivity and high resolution of our flexible pressure sensor.

A Supersensitive, Multidimensional Flexible Strain Gauge Sensor Based on Ag/PDMS for Human Activities Monitoring.

For more comprehensive monitoring human state of motion, it is necessary to sense multidimensional stimulus information. In this paper, we reported a supersensitive flexible sensor based on Ag/PDMS composites with sensing abilities of strain and force. The fabrication method is simple and rapid, which only need physically grinding the silver particles and mixing with liquid PDMS. The flexible sensor has excellent performances in multidimensional detection. The strain gauge factor can reach as high as 939 when it was stretched to 36%, and the minimum resolution for force detection is 0.02 N. The sensing characteristic of the sensors with different filling fraction and thickness were analyzed from the microscopic point of view. Multidimensional sensing abilities of flexible sensor have greatly expands its applications. We experimentally verified the Ag/PDMS based sensor in human body dynamic monitoring and sound detecting in real-time, which has shown great potential in motion recognition, haptic perception and soft robotics.

Printable, Highly Sensitive Flexible Temperature Sensors for Human Body Temperature Monitoring: A Review.

In recent years, the development and research of flexible sensors have gradually deepened, and the performance of wearable, flexible devices for monitoring body temperature has also improved. For the human body, body temperature changes reflect much information about human health, and abnormal body temperature changes usually indicate poor health. Although body temperature is independent of the environment, the body surface temperature is easily affected by the surrounding environment, bringing challenges to body temperature monitoring equipment. To achieve real-time and sensitive detection of various parts temperature of the human body, researchers have developed many different types of high-sensitivity flexible temperature sensors, perfecting the function of electronic skin, and also proposed many practical applications. This article reviews the current research status of highly sensitive patterned flexible temperature sensors used to monitor body temperature changes. First, commonly used substrates and active materials for flexible temperature sensors have been summarized. Second, patterned fabricating methods and processes of flexible temperature sensors are introduced. Then, flexible temperature sensing performance are comprehensively discussed, including temperature measurement range, sensitivity, response time, temperature resolution. Finally, the application of flexible temperature sensors based on highly delicate patterning are demonstrated, and the future challenges of flexible temperature sensors have prospected.

Superelastic, Sensitive, and Low Hysteresis Flexible Strain Sensor Based on Wave-Patterned Liquid Metal for Human Activity Monitoring.

Flexible strain sensors have been widely used in wearable electronic devices for body physical parameter capturing. However, regardless of the stretchability of the sensing material, the resolution of small strain changes or the hysteresis between loading/unloading states has always limited the various applications of these sensors. In this paper, a microfluidic flexible strain sensor was achieved by introducing liquid metal eutectic gallium indium (EGaIn) embedded into a wave-shaped microchannel elastomeric matrix (300 µm width × 70 µm height). The microfluidic sensor can withstand a strain of up to 320%, and the hysteresis performance was also improved from 6.79 to 1.02% by the wave-patterned structure which can restrain the viscoelasticity of the elastomer effectively. Moreover, an enhanced wave-shaped strain sensor was fabricated by increasing the length of the microfluidic channel; it has high sensitivity (GF = 4.91) and resolution, and even as low as 0.09% strain change could be detected, which is capable of resolving microdeformation; besides, the enhanced wave-shaped strain sensor exhibits quick response time (t = 116 ms), long-term stability, and durability under periodic dynamic load. As an example of potential applications, the enhanced flexible sensor showed excellent mechanical compliance and was successfully applied as a conceptual wearable device for distinctively monitoring various kinds of human body and robot activities, such as the different states of the finger, neck, breathing chest, robot's joint, and so forth. The flexible wave-shaped strain sensor has great promising applications for wearable electronics, motion recognition, healthcare, and soft robotics.