Flexible Capacitive Pressure Sensor Research Articles

Sensitivity enhanced flexible capacitive pressure sensor microstructure optimization for biomedical applications

Abstract This paper explores the design and optimization of Flexible Capacitive Pressure Sensors (FCPS) using microfabrication technology for applications in the emerging field of flexible electronics, with a particular focus on measuring bio-signals characterized by lower pressure ranges. Sensitivity, a critical parameter for effective FCPS performance, is investigated through a comprehensive series of simulation analyses employing finite element modeling. The study involves varying geometrical and mechanical parameters that influence FCPS performance, individually adjusting each parameter while keeping others constant. Microstructures such as cuboids, truncated pyramids with an aspect ratio of 0.5, cylinders, pyramids, and cones are modeled on the dielectric material surface. The parameters considered include inter-space, base length, height, and elastic modulus, to enhance FCPS sensitivity and linearity. Among the different shapes modeled, the cone exhibits the highest sensitivity, followed by the pyramid structure. Comparative analysis indicates that the cone and pyramid shapes demonstrate 15- and 10-times higher sensitivity, respectively, compared to the cuboid structure under an applied pressure of 10 Pa. Simulation results suggest that sensitivity can be finely tuned, with higher inter-space and microstructure height, as well as lower base length and Young's modulus of the dielectric material, contributing to increased sensitivity. However, it is noted that these conditions may lead to decreased capacitance in the absence of applied pressure due to air occupation relative to the dielectric material. The findings are further compared with existing literature, and the FCPS response analysis provides valuable insights for the future design of FCPS, particularly in the context of biomedical applications requiring precise low-pressure signal measurements. This research contributes to advancing the understanding of FCPS performance optimization and lays the groundwork for the development of sensors with enhanced sensitivity for bio-medical applications.

Gait Pattern Analysis: Integration of a Highly Sensitive Flexible Pressure Sensor on a Wireless Instrumented Insole.

Gait phase monitoring wearable sensors play a crucial role in assessing both health and athletic performance, offering valuable insights into an individual's gait pattern. In this study, we introduced a simple and cost-effective capacitive gait sensor manufacturing approach, utilizing a micropatterned polydimethylsiloxane dielectric layer placed between screen-printed silver electrodes. The sensor demonstrated inherent stretchability and durability, even when the electrode was bent at a 45-degree angle, it maintained an electrode resistance of approximately 3 Ω. This feature is particularly advantageous for gait monitoring applications. Furthermore, the fabricated flexible capacitive pressure sensor exhibited higher sensitivity and linearity at both low and high pressure and displayed very good stability. Notably, the sensors demonstrated rapid response and recovery times for both under low and high pressure. To further explore the capabilities of these new sensors, they were successfully tested as insole-type pressure sensors for real-time gait signal monitoring. The sensors displayed a well-balanced combination of sensitivity and response time, making them well-suited for gait analysis. Beyond gait analysis, the proposed sensor holds the potential for a wide range of applications within biomedical, sports, and commercial systems where soft and conformable sensors are preferred.

Lantern-inspired capacitive pressure sensor with wide linear measuring range

In the field of pressure sensing, high sensitivity and linearity are two critical performance indicators, but striking a balance between them remains a prominent challenge for sensors. Existing solutions typically involve the structural design of electrodes or dielectric layers, often requiring complex and expensive techniques for designing microstructures. This study presents a novel flexible capacitive pressure sensor characterized by its low-cost nature, ease of manufacture, and scalability in design. The lantern accordion-like structure inspires the design of the dielectric layer and the porous structure is designed using thermally expandable microspheres (TEM). The synergy of surface microstructures and internal microstructures results in a high sensitivity of 3.07 × 10−3 kPa−1 within a wide linear response range of 0–100 kPa. The developed sensor is also evaluated for its weight detection capabilities, highlighting its promising weight and pressure data acquisition.

A highly-sensitive wearable capacitance pressure sensor based on calcium copper titanate/polydimethysiloxane/graphene oxide and polydimethysiloxane/silver nanowires sanwich strustures combination for human body monitoring

In recent years, flexible pressure sensors, with their high sensitivity, low detection limit, wide working pressure range and fast response speed, have been playing an important role in the development of wearable artificial devices, human-computer interaction and healthcare systems, and have attracted wide attention. However, the pressure sensors face challenges related to the weak tightness of bipolar materials, low charge density, and limitation in dielectric layers. In this paper, we present a novel configuration of flexible capacitive pressure sensors, utilizing a polydimethysiloxane (PDMS) thin film covered by silver nanowires (PDMS/SN, PSN) as the electrode materials and a porous material composed of calcium copper titanate (@CCTO), PDMS and graphene oxide (GO)(@CCTO/PDMS/GO, @CPG) as the positive electrode material. The sacrificial material, sugar, is employed to create dense internal pores within the substrate material, @CPG, leading to the formation of a profoundly porous substrate. The integration of the flexible capacitive pressure sensor using @CPG/PSN results in enhanced output performance. The modified sensors achieves a sensitivity of 0.22 kPa−1, which is 7 times higher than that of a pure PDMS dielectric layer sensor. Moreover, the sensors has a response time of 87 ms, a low detection pressure of 5 Pa with an extensive detection range from 0 to 150 kPa, and are capable of enduring 7200 cycles without sustaining damage. To validate the practical performance of the @CPG/PSN sensor, various human body activities are detected, including swallowing, coughing, neck bending, wrist bending, elbow bending, finger flexing, and holding objects like cups using a digitally designed glove capable of accommodating different materials. The pressure sensor based on @CPG/PSN demonstrates significant promise in detecting both low and high pressures, thus expanding the potential applications of capacitive pressure sensors.

A Flexible Capacitive Pressure Sensor Based on Thermoplastic Polyurethane Porous Films by Non-Solvent Induced Phase Separation

A Flexible Capacitive Pressure Sensor Based on Thermoplastic Polyurethane Porous Films by Non-Solvent Induced Phase Separation

A novel self-powered sensitive porous ZnO NWs/PDMS sponge capacitive pressure sensor

The demand for flexible sensors has increased due to the explosive expansion of flexible electronic applications, but there are concerns that the development of high-precision measurement is limited. Capacitive pressure sensors are extensively utilized among diverse sensors due to their simple structure, high resolution, and outstanding dynamic response characteristics. Therefore, by sandwiching a porous ZnO NWs PDMS (PZP) sponge dielectric layer between two ITO/PET electrodes, a flexible capacitive pressure sensor with high sensitivity, short response time, and wide working range was prepared. The porous PDMS sponge was prepared utilizing the salt particle as a template, then ZnO NWs in different precise proportions were added to it. The sensitivity of PZP sponge capacitive pressure sensors with different salt particle sizes and ZnO NWs dosages were compared. The research results indicate that when salt particle sizes less than 150 μm, and the amount of ZnO NWs in PZP sponge is increased to 200 mg, the sensor sensitivity is highest in the pressure range of 2.5-7.5 kPa, reaching 0.1279 kPa-1, response time less than 70 ms. When the PZP sponge sensor is used as a self-powered source, it achieves the best output of 1.2 V and 6.8 nA at 5.74 kPa pressure. It provides a new way to tackle the challenge of low sensitivity of flexible sensors to capacitive signal and lays a foundation for expanding the application scenarios of ZnO NWs.

A flexible pressure sensor with wide detection range and high sensitivity based on glycerol@phosphoric acid nanofibers for human posture recognition applications

Flexible pressure sensors are widely used in wearable devices, especially in the field of human–computer interaction. Hence, the development of flexible pressure sensors with excellent sensitivity and detection range is essential. This paper introduces a flexible capacitive pressure sensor based on glycerol@phosphoric acid nanofibers, showcasing remarkable properties, including high sensitivity (53.97 kPa−1), an exceptionally wide detection range (1800 kPa), faster response/recovery time than human skin (14.4/9.6 ms), an extremely low detection limit (5 Pa), outstanding stability (>10,000 fatigue tests), and excellent biocompatibility. In addition, the sensor was seamlessly integrated with deep learning algorithms, embedded systems, and internet technologies to develop a comprehensive human posture recognition system, which can adeptly capture and identify intricate human movements with an accuracy rate over 98 %. This system establishes a diagnostic channel between home patients and rehabilitation experts. Owing to its excellent sensitivity and detection range, the developed sensor presents promising prospects for future advancements in human–computer interaction.

Novel flexible capacitive pressure sensor with a wide detection range enabled by carboxyl iron particle-paraffin wax/silicone composite

The emergence of flexible capacitive pressure sensors has prominently accelerated the development of flexible electronics. However, most capacitive pressure sensors reported so far have limited detection ranges, which greatly restricts their application scenarios. In this work, a novel flexible capacitive pressure sensor with a wide detection range was produced by employing the carboxyl iron particle-paraffin wax (CIP-PW)/silicone composite as the dielectric layer. Due to the introduction of phase-changing PW and magnetic CIPs, the resultant CIP-PW/silicone composite exhibits magnetism and temperature-controllable mechanical properties, which therefore provides the capacitive pressure sensor with a tunable effective detection range in the frequency range of 0.1–5 Hz. To be specific, the sensor could achieve an effective detection range of 0.2–350 kPa, much wider than other capacitive sensors reported. This merit is further demonstrated by monitoring finger and arm movements as well as walking status. In addition to the physical contact sensing, the sensor exhibits a contactless sensing capacity, and could be used to monitor finger movements without direct contact. In virtue of the wide detection range and bimodal sensing capacity, the current capacitive pressure sensor shows greatly promising in the fields of wearable devices, e-skin, robotics and so on.

Bamboo-Inspired, Environmental Friendly PDMS/Plant Fiber Composites-Based Capacitive Flexible Pressure Sensors by Origami for Human–Machine Interaction

Bamboo-Inspired, Environmental Friendly PDMS/Plant Fiber Composites-Based Capacitive Flexible Pressure Sensors by Origami for Human–Machine Interaction

Design and Analysis of Porous Elastomeric Polymer Based on Electro-Mechanical Coupling Characteristics for Flexible Pressure Sensor.

Elastomeric polymers have gained significant attention in the field of flexible electronics. The investigation of the electro-mechanical response relationship between polymer structure and flexible electronics is in increasing demand. This study investigated the factors that affect the performance of flexible capacitive pressure sensors using the finite element method (FEM). The sensor employed a porous elastomeric polymer as the dielectric layer. The results indicate that the sensor's performance was influenced by both the structural and material characteristics of the porous elastomeric polymer. In terms of structural characteristics, porosity was the primary factor influencing the performance of sensors. At a porosity of 76%, the sensitivity was 42 times higher than at a porosity of 1%. In terms of material properties, Young's modulus played a crucial role in influencing the performance of the sensors. In particular, the influence on the sensor became more pronounced when Young's modulus was less than 1 MPa. Furthermore, porous polydimethylsiloxane (PDMS) with porosities of 34%, 47%, 67%, and 72% was fabricated as the dielectric layer for the sensor using the thermal expansion microsphere method, followed by sensing capability testing. The results indicate that the sensor's sensitivity was noticeably influenced within the high porosity range, aligning with the trend observed in the simulation.

A High-Performance Flexible Capacitive Pressure Sensor With 3-D Printed Hemispherical Graded Microstructures

A High-Performance Flexible Capacitive Pressure Sensor With 3-D Printed Hemispherical Graded Microstructures

An intelligent insole based on wide-range flexible pressure sensor

In this paper, an intelligent insole that contains five wide-range flexible capacitive pressure sensors is developed. The output signal of these five sensors is collected and processed by a portable microprocessor system, which is then transmitted to a cloud platform via a Wi-Fi module. The ensuing data visualization is constructed with a WeChat mini-program. The wide-range flexibility is achieved by employing composition materials with a high pressure-sensitive effect. A novel approach is proposed to fabricate flexible pressure-sensitive dielectrics, thereby significantly enhancing the sensitivity and detection range of pressure sensors. The fabrication process involves utilizing polydimethylsiloxane (PDMS) as a flexible substrate, incorporating nano-iron powder and polyvinylidene fluoride as sensitizing materials, and applying an external magnetic field to control the distribution of iron nanoparticles during the curing process of PDMS. Furthermore, a motion detection system tailored for these flexible sensors is developed. By integrating sensor networks with Internet of things technology, the application potential of wide-range flexible pressure sensors in kinematics and medical rehabilitation fields can be effectively realized.

3D Printing of Capacitive Pressure Sensors with Tuned Wide Detection Range and High Sensitivity Inspired by Bio-Inspired Kapok Structures.

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.

Flexible capacitive pressure sensor with synergistic effect between double-sided pyramid sponge structure dielectric layer and fiber structure electrode layer

Flexible capacitive pressure sensors have a wide range of applications in wearable applications. This paper prepares a double-sided pyramidal foam sponge doped with barium titanate particles as the sensor dielectric layer by template method, and the flexible electrode layer prepared by electrostatic spinning technique. Benefiting from the excellent compressibility of the dielectric layer under stress and the good deformability of the electrode layer, the sensors with a synergistic effect between the electrode layer and the dielectric layer have been assembled. The sensor has high sensitivity (0.44 kPa−1) and a wide range (0–300 kPa), fast response (90 ms), ultra-low detection limit of 0.01 kPa, and reliable durability (>2000 cycles). The excellent performance of the sensor can realize the detection of human body signals and assembled into a data glove and combined with a host monitor to enable real-time monitoring of signal changes during grasping, and it shows enormous potential in intelligent wearable device applications.

Flexible capacitive pressure sensors and their applications in human-machine interactions

Flexible pressure sensors offer more significant advantages than rigid sensors in various applications, including human-computer interaction, medical health, and robot touch. However, this also places more stringent demands on the materials used. For example, the materials must be thin and soft enough to fit onto the surface of the human skin or be implanted into the body while also exhibiting good biocompatibility and matching the mechanical properties of biological tissues. Regarding device performance, flexible pressure sensor design primarily focuses on enhancing sensitivity, response time, detection limit, and stability. Researchers have recently been expanding these sensors' pressure response range, pressure resolution, spatial resolution, and tensile performance, which will further broaden their potential applications. This review provides an overview of the recent classification of flexible pressure sensors, covering their sensing principle, sensing performance, and future application prospects.

Sensitive, Robust, Wide-Range, and High-Consistency Capacitive Tactile Sensors with Ordered Porous Dielectric Microstructures.

Flexible capacitive tactile sensors show great promise in personalized healthcare monitoring and human-machine interfaces, but their practical application is normally hindered because they rarely possess the required comprehensive performance, that is, high pressure sensitivity and fast response within a broad pressure range, high structure robustness, performance consistency, etc. This paper aims to engineer flexible capacitive pressure sensors with highly ordered porous dielectric microstructures and a 3D-printing-based fully solution-processable fabrication process. The proposed dielectric layer with uniformly distributed interior microporous can not only increase its compressibility and dynamic response within an extended pressure range but also enlarge its contact area with electrodes, contributing to a simultaneous improvement in the sensitivity, response speed, detection range, and structure robustness. Meanwhile, owing to its superior abilities in complex structure manufacturing and dimension controlling, the proposed 3D-printing-based fabrication process enables the consistent fabrication of the porous microstructure and thus guarantees device consistency. As a result, the prepared pressure sensors exhibit a high sensitivity of 0.21 kPa-1, fast response and relaxation times of 112 and 152 ms, an interface bonding strength of more than 455.2 kPa, and excellent performance consistency (≤5.47% deviation among different batches of sensors) and tunability. Encouraged by this, the pressure sensor is further integrated with a wireless readout circuit and realizes wireless wearable monitoring of various biosignals (pulse waves and heart rate) and body movements (from slight finger touch to large knee bending). Finally, the influence law of the feature parameters of the porous microstructure on device performance is established by the finite element method, paving the way for sensor optimization. This study motivates the development of flexible capacitive pressure sensors toward practical application.

Highly sensitive flexible capacitive pressure sensor with structured elastomeric dielectric layers

Sensitive yet stable, robust yet flexible and accurate yet energy efficient pressure sensors are required for variety of purposes. While a large variety of designs and dielectric materials have been explored for this purpose, there is still need of a flexible pressure sensor that will allow easy scale up and inexpensive fabrication. To this end, we have presented here the design of a flexible capacitive pressure sensor using copper coated paper as flexible electrodes and soft Ecoflex layers decorated with cylindrical micro-pillars as the dielectric. While microscopic construct of the sensor allows its easy manufacturability, softness of the layer imparts sensitivity to it. In contrast to many conventional sensors, this design yields sensitivity as high as ∼5 kPa−1 at pressure <1 kPa and somewhat smaller sensitivity as pressure exceeds 1 kPa. We have varied systematically pillar diameter, skin thickness of dielectric layer and pitch of the pillar array to optimise the design and demonstrate its easy tunability. We have presented a model based on buckling of the pillars to predict the response of the sensor. We have explored also a specific design that minimises the hysteresis.

Broad detection range of flexible capacitive sensor with 3D printed interwoven hollow dual-structured dielectric layer

Flexible pressure sensors play a pivotal role in the realm of smart wearable devices. Despite extensive exploration into methods for creating dielectric layers with microstructures, the associated complex fabrication processes and challenges of mass production remain pressing issues. This study introduces an innovative approach to crafting flexible capacitive pressure sensors. We utilize interwoven hollow dual-structured materials as the dielectric layer of the sensor through photocurable 3D printing, simplifying production steps and achieving the one-piece molding of the dielectric layer. Due to the abundant air within the dielectric layer and the inherent resilience of the flexible photocurable material, the resulting sensors exhibit exceptional responsiveness and durability, with a measurement range extending to at least 600 kPa. Furthermore, we evaluate the effectiveness of sensors employing the interwoven hollow structure by comparing them with other structural designs. The dual-structured sensors demonstrate a sensitivity approximately ten times higher than that of flat structures, particularly in the wide pressure range of 200–600 kPa. In practical applications, our designed sensors can detect various human activities, such as finger presses, wrist bending, and object grasping. They are also well-suited for monitoring plantar pressure distribution, signifying their potential for integration into smart wearable devices, health monitoring systems, and human-computer interaction interfaces.

Mantis leg-inspired flexible capacitive pressure sensor with high sensitivity and fast response for wearable devices and human–machine interaction

Mantis leg-inspired flexible capacitive pressure sensor with high sensitivity and fast response for wearable devices and human–machine interaction

Laser speckle grayscale lithography: a new tool for fabricating highly sensitive flexible capacitive pressure sensors

Laser speckle grayscale lithography: a new tool for fabricating highly sensitive flexible capacitive pressure sensors