Biomimetic-inspired highly sensitive flexible capacitive pressure sensor with high-aspect-ratio microstructures

Porous conductive electrode for highly sensitive flexible capacitive pressure sensor over a wide range

Large scale production of highly sensitive and flexible pressure sensor has aroused widely interest for their high potential use in real-wearable electronics and e-textiles. In this work, a flexible and wearable capacitive pressure sensor has been fabricated based on the unique honeycomb weave architecture, conferring the sensor with an extreme synchronization between output capacitance and input pressure, as well as the high sensitivity of 0.045 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> under 10 kPa, large workable pressure range of 40 kPa, good durability and stability over 1000 cycles, fast response time of 135 ms and comparable stability under diverse pressures. The sensor can be used for various pressure detections such as finger pressing, tape loading and handshaking. Moreover, the self-made sensor has good ability in monitoring spatial distribution, showing its promising application in flexible and wearable devices.

A highly sensitive and wide-range pressure sensor based on orientated and strengthened TPU nanofiber membranes fabricated by a conjugated electrospinning technology

Flexible capacitive pressure sensors with a simple structure and low power consumption are attracting attention, owing to their wide range of applications in wearable electronic devices. However, it is difficult to manufacture pressure sensors with high sensitivity, wide detection range, and low detection limits. We developed a highly sensitive and flexible capacitive pressure sensor based on the porous Ecoflex, which has an aligned airgap structure and can be manufactured by simply using a mold and a micro-needle. The existence of precisely aligned airgap structures significantly improved the sensor sensitivity compared to other dielectric structures without airgaps. The proposed capacitive pressure sensor with an alignment airgap structure supports a wide range of working pressures (20–100 kPa), quick response time (≈100 ms), high operational stability, and low-pressure detection limit (20 Pa). Moreover, we also studied the application of pulse wave monitoring in wearable sensors, exhibiting excellent performance in wearable devices that detect pulse waves before and after exercise. The proposed pressure sensor is applicable in electronic skin and wearable medical assistive devices owing to its excellent functional features.

Skin mountable flexible pressure sensors are crucial for the next generation technologies. Capacitive pressure sensors bring several advantages and hence, they have been preferred over piezoelectric and piezoresistive alternatives. Flexible electrode and dielectric material are the fundamental components of the capacitive flexible pressure sensors. Hence, solution processable silver nanowires (AgNWs) are highly promising as electrode material or filler material in dielectric layer, owing to their superior inherent conductivity and flexibility. This article reviews recent progress on fabrication of flexible capacitive pressure sensors with AgNWs used as electrode and dielectric material. Performance of the sensors based on AgNWs is comprehensively discussed and emerging applications, as well as future outlook, are presented in detail.

Flexible capacitive pressure sensors are crucial for applications in electronic skin, artificial intelligence, and wearable medical devices. Despite their potential, conventional sensors often suffer from low pressure sensitivity, particularly in high‐pressure environments, and complex microstructure construction methods. This study addresses these limitations by developing a novel flexible capacitive pressure sensor based on a composite dielectric layer consisting of carbon nanotubes (CNTs), thermally expandable microspheres (TEMs), and polydimethylsiloxane (PDMS), with a 3D direct ink writing (DIW) technology. The CNTs‐TEMs synergy modulates both mechanical and dielectric response in capacitive sensors, achieving a two‐order‐of‐magnitude enhancement in sensitivity compared to that of CNT‐only filler system. The groove‐like microstructure on the surface of the dielectric layer enables rapid and stable air expulsion to boost dielectric constant change and sensitivity under pressure. The proposed sensor exhibits a maximal sensitivity as high as 3.09 kPa −1 in the wide pressure range of 0–500 kPa, and a detection limit as low as 16.7 Pa. Furthermore, the sensor shows excellent pressure resolution of 0.3%, cycling stability over 40 000 cycles, and can accurately monitor various human activities, demonstrating its potential for applications in health monitoring and flexible electronics.

This paper successfully prepares a polyacrylonitrile (PAN) fiber-based flexible film electrode by combining electrospun and immersion methods. It also assembles a capacitive flexible pressure sensor, characterizing the structure and properties of the material. The results demonstrate that adding carbon nanotubes (CNTs) to the spinning solution alters the morphology and fiber diameter of the electrospun membrane, and the incorporation of CNTs increases the loading rate of CNTs in the electrospun membrane. The CNT loading rate is the highest when the weight ratio of PAN to CNT powder is 12:2, which reaches 151%. The film electrode enables the preparation of a highly sensitive capacitive flexible pressure sensor, making it suitable for wearable monitoring applications such as finger pressure and finger bending.

Capacitive pressure sensors based on bioinspired structured electrode for human-machine interaction applications.

Flexible capacitive pressure sensor based on warp knitted spacer fabric

High-performance flexible pressure sensors are highly desirable in health monitoring, robotic tactile, and artificial intelligence. Construction of microstructures in dielectrics and electrodes is the dominating approach to improving the performance of capacitive pressure sensors. Herein, we have demonstrated a novel three-dimensional microconformal graphene electrode for ultrasensitive and tunable flexible capacitive pressure sensors. Because the fabrication process is controllable, the morphologies of the graphene that is perfectly conformal with the electrode are controllable consequently. Multiscale morphologies ranging from a few nanometers to hundreds of nanometers, even to tens of micrometers, have been systematically investigated, and the high-performance capacitive pressure sensor with high sensitivity (3.19 kPa-1), fast response (30 ms), ultralow detection limit (1 mg), tunable-sensitivity, high flexibility, and high stability was obtained. Furthermore, an ultrasensitivity of 7.68 kPa-1 was successfully achieved via symmetric double microconformal graphene electrodes. The finite element analysis indicates that the microstructured graphene electrode can enhance large deformation and thus effectively improve the sensitivity. Additionally, the proposed pressure sensors are demonstrated with practical applications including insect crawling detection, wearable health monitoring, and force feedback of robot tactile sensing with a sensor array. The microconformal graphene may provide a new approach to fabricating controllable microstructured electrodes to enhance the performance of capacitive pressure sensors and has great potential for innovative applications in wearable health-monitoring devices, robot tactile systems, and human-machine interface systems.

Highly sensitive and flexible wearable pressure sensor with dielectric elastomer and carbon nanotube electrodes

Flexible capacitive pressure sensors are becoming increasingly significant in wearable electronic devices. The conventional form of pressure sensors, however, focuses primarily on microstructure design. While this approach can enhance sensitivity, it can also compromise the reliability of the sensor device. Here, we present a flexible pressure sensor according to the capacitance effect using the high dielectric P(VDF-TrFE)/MXene polymer as the capacitive pressure sensor dielectric layer. The P(VDF-TrFE)/MXene film has a high dielectric constant, making it an ideal choice for the dielectric layer of the flexible capacitive pressure sensor, resulting in rapid response and high sensing sensitivity. We also examine the impact of dielectric layer thickness on the sensor’s performance and find that increasing the thickness from 0.5 to 1.5 mm leads to a continuous improvement in sensitivity, reaching a maximum sensitivity of 0.42 kPa−1 and a wide sensing amplitude (3 Pa–25 kPa). Moreover, the response time of the capacitive pressure sensor can reach 47 ms. In addition, the sensor can be utilized to monitor human physiological information such as respiration and heartbeat. Its flexibility makes it ideal for application in sports, particularly for monitoring the movement posture of football players. Our findings can drive the wider adoption of pressure sensors in football motion monitoring.

Flexible pressure sensors are crucial for E-skins to enable tactile sensing capabilities. However, flexible pressure sensors often exhibit high hysteretic response caused by internal and external mechanical dissipations in flexible materials. The hysteresis gives rise to reliability issues, especially in the presence of dynamic stress. In this letter, we report a flexible capacitive pressure sensor design with hierarchically microstructured electrodes to obtain both high sensitivity and low hysteresis. The sparsely spaced large pyramid microstructure improves the sensitivity, whereas the small pyramid reduces the hysteresis caused by interfacial adhesion. The optimized sensor shows excellent performances in terms of high sensitivity (~3.73 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ), ultralow detection limits (0.1 Pa), significantly reduced hysteresis (~4.42%), and enhanced sensing capability for pluses, which demonstrates its potential for advanced electronic skins.

Flexible pressure sensors have attracted great attention due to their extensive applications in human–computer interaction and health monitoring. So far, the development of flexible pressure sensors that balance high sensitivity and a wide measurement range remains a challenge. Herein, a double-layer dielectric structure with a surface convex structure is reported for the preparation of flexible capacitive pressure sensors. The double-layer dielectric structure, which is composed of a silicone rubber-based conductive elastomer with a surface micro-convex structure and a PVA-H-based conductive elastomer, balances the advantages and disadvantages of the two conductive elastomer dielectrics. It can form a complete micro-capacitive network under relatively large pressures, enabling the sensor to have high sensitivity at different stages (1.7 kPa−1, 0–104 kPa; 19.14 kPa−1, 104–140 kPa), thus achieving a dual enhancement of sensitivity and sensing range. Additionally, the sensor has been successfully applied to scenarios such as monitoring of human breathing, speaking, and movement, as well as mouse clicks, demonstrating its great potential in the fields of health monitoring and human–computer interaction applications.

Flexible pressure sensors have drawn considerable attention for their potential applications as electronic skins with both sensitivity and pressure response range. Although the introduction of surface microstructures effectively enhances sensitivity, the confined volume of their compressible structures results in a limited pressure response range. To address this issue, a biomimetic kapok structure is proposed and implemented for constructing the dielectric layer of flexible capacitive pressure sensors employing 3D printing technology. The structure is designed with easily deformable concave and rotational structures, enabling continuous deformation under pressure. This design results in a significant expansion of the pressure response range and improvement in sensitivity. Further, the study purposively analyses crucial parameters of the devised structure that affect its compressibility and stability. These include the concave angle θ, height ratio d1/d2, rotation angle α, and width k. As a result, the ultimate pressure sensors demonstrate remarkable features such as high sensitivity (≈2.38kPa-1 in the range of 0-10kPa), broad detection range (734kPa), fast response time (23ms), and outstanding pressure resolution (0.4% at 500kPa). This study confirms the viability of bionic structures for flexible sensors, and their potential to expand the scope of wearable electronic devices.