Flexible Capacitive Pressure Sensor Research Articles

Customized flexible iontronic pressure sensors: Multilevel microstructures by 3D-Printing for enhanced sensitivity and broad pressure range

Flexible capacitive pressure sensors stand out for their energy efficiency, rapid responsiveness, and exceptional durability, with their performance hinging on the intricate design of microstructures and the strategic selection of dielectric materials. However, creating cost-effective and practical fabrication methods for these components continues to pose a significant challenge. This study unveils an innovative iontronic flexible pressure sensor that integrates an ionic layer with sophisticated multilayer microstructures, setting new benchmarks in pressure sensing technology. The sensor operates within an expansive pressure range, achieving sensitivities as high as 92.14 kPa−1 at pressures from 0 to 50 kPa, and 22.96 kPa−1 at pressures ranging from 50 to 800 kPa, demonstrating extraordinary sensitivity. It also achieves an exceptionally low detection limit of 6.67 Pa and features swift response times of 56 ms to activate and 18 ms to deactivate. Enhanced by the addition of CuSO4, the sensor not only withstands freezing conditions but also significantly boosts sensitivity. Moreover, this sensor is capable of detecting human joint movements and subtle pressure fluctuations under high-pressure conditions, suggesting a breakthrough in the field. This research presents a simple, reliable, and cost-efficient method for developing flexible iontronic pressure sensors, poised to revolutionize applications in wide-ranging pressures and adverse temperature environments.

Enhancing sensitivity in wireless capacitive pressure sensors via highly flexible LC circuits utilizing porous polydimethylsiloxane dielectric layer

In this study, we introduce a highly flexible LC circuit-based wireless capacitive pressure sensor (CPS) that utilizes porous polydimethylsiloxane (PDMS) as a dielectric layer, demonstrating its transformative potential in tactile sensing, physiological monitoring, and flexible electronics. To optimize sensor performance, various porous PDMS thin films (100 μm) with different porosities (ranging from 0 % to 75 %) were prepared using a novel steaming method, and their properties were thoroughly analyzed using field emission scanning electron microscopy (FE-SEM) and capacitance measurements. Remarkably, the sensor with a 75 % porous PDMS film demonstrated enhanced sensitivity up to 11 times compared to the 0 % porous (pristine) PDMS film when subjected to a 300 g weight. High sensitivities of 0.046 kPa^-1, 0.036 kPa^-1, and 0.028 kPa^-1 were attained for the pressure sensor in the pressure ranges of 0–9.8 kPa, 0–19.6 kPa, and up to 29.4 kPa, respectively. Additionally, a real-time resonance frequency analysis was conducted using a network analyzer, allowing the detection of tiny pressure changes in an artificial blood vessel. Finally, the flexibility of the wireless CPS was investigated by studying various parameters, including body temperature, facial expressions such as smiling, selected speech characters (M, N, T, L), and swallowing actions.

Cleanroom-free fabrication of flexible capacitive pressure sensors using paintable silver electrodes on stationery paper and random microstructured polydimethylsiloxane dielectric layer

Abstract In this work, we propose a facile, low-cost, and cleanroom-free approach for fabricating flexible capacitive pressure sensors based on paintable Ag electrodes on stationery paper substrates (Ag–paper electrodes) and a random microstructured polydimethylsiloxane (PDMS) dielectric layer transferred from emery paper. COMSOL Multiphysics simulations and experimental investigations suggest that the pressure sensor with random microstructured PDMS dielectric layer performs better than the sensor with ordered micropyramidal dielectric layer. The developed Ag–paper electrode and random microstructured PDMS dielectric layer-based pressure sensors are workable in a wide pressure range (up to 630 kPa) and exhibit a high sensitivity of 0.132 kPa−1 up to 1 kPa, low hysteresis (6.6%) with loading–unloading of ∼500 kPa pressure, high stability during a ∼5250 cyclic test, and the ability to sense a low pressure of ∼27 Pa. The developed sensor also successfully transduces arterial pulse wave forms when it is properly attached to the wrist. Using the proposed process, a flexible capacitive pressure sensor matrix of 4 × 4 array is also successfully developed for single- and multiple-point pressure mapping with minimal cross-talk. The proposed sensor process is simple and inexpensive to implement, and offers spatial pressure mapping for e-skin applications.

Flexible Tactile Sensors with Gradient Conformal Dome Structures.

The trade-off between high sensitivity and wide detection range remains a challenge for flexible capacitive pressure sensors. Gradient structure can provide continuous deformation and lead to a wide sensing range. However, it simultaneously augments the distance between two electrodes, which diminishes the variation in the relative distance and results in a decreased sensitivity. Herein, a conformal design is introduced into the gradient structure to construct a flexible capacitive pressure sensor. The gradient conformal dome structure is fabricated by a simple reverse dome adsorption process. Taking advantage of the progressive deformation behavior of the gradient dielectric, and the significant improvement of relative distance variation between two electrodes from the conformal design, the sensor achieves a sensitivity of 0.214 kPa-1 in an ultrabroad linear range up to 200 kPa. It maintains high-pressure resolution under the preload of 10 and 100 kPa. Benefiting from the rapid response and excellent repeatability, the sensor can be used for physiological monitor and human motion detection, including arterial pulse, joint bending, and motion state. The gradient conformal design strategy may pave a promising avenue to develop pressure sensors with high sensitivity and wide linear range.

Highly Sensitive and Flexible Capacitive Pressure Sensors Combined with Porous Structure and Hole Array Using Sacrificial Templates and Laser Ablation.

Flexible, wearable pressure sensors offer numerous benefits, including superior sensing capabilities, a lightweight and compact design, and exceptional conformal properties, making them highly sought after in various applications including medical monitoring, human-computer interactions, and electronic skins. Because of their excellent characteristics, such as simple fabrication, low power consumption, and short response time, capacitive pressure sensors have received widespread attention. As a flexible polymer material, polydimethylsiloxane (PDMS) is widely used in the preparation of dielectric layers for capacitive pressure sensors. The Young's modulus of the flexible polymer can be effectively decreased through the synergistic application of sacrificial template and laser ablation techniques, thereby improving the functionality of capacitive pressure sensors. In this study, a novel sensor was introduced. Its dielectric layer was developed through a series of processes, including the use of a sacrificial template method using NaCl microparticles and subsequent CO2 laser ablation. This porous PDMS dielectric layer, featuring an array of holes, was then sandwiched between two flexible electrodes to create a capacitive pressure sensor. The sensor demonstrates a sensitivity of 0.694 kPa-1 within the pressure range of 0-1 kPa and can effectively detect pressures ranging from 3 Pa to 200 kPa. The sensor demonstrates stability for up to 500 cycles, with a rapid response time of 96 ms and a recovery time of 118 ms, coupled with a low hysteresis of 6.8%. Furthermore, our testing indicates that the sensor possesses limitless potential for use in detecting human physiological activities and delivering signals.

A Flexible Capacitive Pressure Sensor with Adjustable Detection Range Based on the Inflatable Dielectric Layer for Human-Computer Interaction.

As an essential component in wearable electronic devices and intelligent robots, flexible pressure sensors have enormous application value in fields such as healthcare, human-computer interaction, and intelligent perception. However, due to the complex and ever-changing pressure loads borne by sensors in different application scenarios, this also puts great demands on the flexible response and adjustment ability of a sensor's detection range. Therefore, developing a flexible pressure sensor with a wide and adjustable detection range, which can be applied flexibly under different pressure loads, is also a major challenge in current research. In this paper, we propose a flexible pressure sensor with a wide and adjustable detection range based on an inflatable adjustable safety airbag as the dielectric layer. This sensor uses inflatable airbags prepared using 3D printing technology and silicone reverse molding technology as the dielectric layer and achieves high sensitivity (0.6 kPa-1 to 1.19 kPa-1), wide detection range (220-1500 kPa), and flexible performance applicability by adjusting the air pressure inside the dielectric layer. At the same time, its simple production process, convenient production, fast response time (100 ms), and good stability provide the possibility for the flexible application of sensors in different pressure detection. The experimental results indicate that the sensor has enormous potential for applications in wearable devices, healthcare, human-computer interaction, and intelligent perception recognition.

A flexible capacitive pressure sensor with dual-layer microstructure for health monitoring

Flexible pressure sensors have gained increasing acceptance in recent decades due to their stability, low power consumption, and portability. However, compared to traditional sensors, the linearity of flexible sensors still needs improvement. In this study, we designed and prepared a double-layer micro-structured flexible capacitive pressure sensor with a simple structure, low cost, excellent linearity and high sensitivity. The chemical raw materials used in our experiments are inexpensive, and the overall preparation method is simple. The sensor exhibits excellent linearity (0.993, <10 kPa; 0.978, 10～130 kPa) and combines high sensitivity (0.399 kPa−1, <10 kPa) with a wide detection range (0～130 kPa). The sensor can accurately and stably detect certain sound signals and throat movements. We designed and prepared a sensor array to monitor human sitting posture by identifying pressure distribution, thus avoiding irreversible damage caused by poor posture. This demonstrates the potential of the sensor in health monitoring.

Flexible capacitive pressure sensor based on electrically assisted micro-nanoimprinting

Flexible capacitive pressure sensor based on electrically assisted micro-nanoimprinting

One-Step process of wrinkle microstructured iontronic pressure sensor with all fabric wearable electrode

The advancement of pressure sensors featuring high sensitivity, wide detection ranges, and linear response characteristics is important for advancing tactile sensing technologies for robots and human health monitoring. However, conventional preparation suffers from nonlinear signal output, non-environmental friendliness, and poor comfort, which affects the sensor’s ability to accurately detect different pressure levels, which is critical for subtle haptic feedback systems. To overcome these challenges, our research introduces a breakthrough in flexible capacitive pressure sensors by ingeniously integrating thermal stress-induced microstructured ionic gels with textile electrodes within a band-aid-like form factor. This method prevents the requirement for external templates or intricate manufacturing procedures, streamlining the production process while enhancing the sensor’s performance. The pivotal role of the ionic gel lies in its ability to form an efficient electric double layer (EDL), which adeptly transforms ion–electron interface interactions into measurable pressure-sensing outputs. Notably, this band-aid-based iontronic sensor showcases exceptional performance metrics. It exhibits an extraordinarily high sensitivity, reaching 5652.41 kPa−1, and demonstrates a broad pressure detection range (from 0-400 kPa). Additionally, the sensor responds rapidly to pressure changes, maintains robust long-term cycle stability, and boasts an impressively low detection threshold. Its potential applications, particularly in the precise monitoring of human muscle movements, open exciting new avenues for both health monitoring and the broader field of flexible electronic devices. This showcases the potential of everyday materials in advanced technological applications.

A gait phase recognition method for obstacle crossing based on multi-sensor fusion

The analysis of human motion patterns and gait phase detection holds significant importance for both human motion analysis and precise control of exoskeleton devices. Presently, research on gait during obstacle crossing primarily focuses on the medical rehabilitation domain, with limited studies concerning gait phase analysis during obstacle crossing. This study conducts a detailed analysis of gait data during obstacle crossing and proposes a CNN-PCA-LSTM algorithm that fuses multi-sensor data to accurately identify gait phases when crossing obstacles in the horizontal direction. A wearable multi-sensor data acquisition system was designed, utilizing flexible capacitive pressure sensors to collect pressure data from the soles of both feet and IMUs to gather foot motion data. Kinematic simulation analyses of human obstacle-crossing motions were performed using Anybody software to determine various gait phases, validating the efficacy of the simulation model. Subsequently, one-dimensional and two-dimensional convolutional neural networks were separately employed to extract features from sole pressure data and foot motion data. Principal Component Analysis (PCA) was utilized to reduce the dimensionality of these feature datasets, which were then inputted into LSTM networks. Finally, the Softmax function was employed for the classification and recognition of gait phases when crossing obstacles in the horizontal direction. The experimental results indicate that employing the CNN-PCA-LSTM algorithm integrating multiple sensor data achieves a recognition accuracy of 97.91 % for identifying gait phases during horizontal obstacle crossing.

Highly Sensitive Flexible Capacitive Pressure Sensor Based on a Multicross-Linked Dual-Network Ionic Hydrogel for Blood Pressure Monitoring Applications.

Flexible capacitive pressure sensors based on ionic hydrogels (IHs) have garnered significant attention in the field of wearable technology. However, the vulnerability of traditional single-network hydrogels to mechanical damage and the complexity associated with preparing double-network hydrogels present challenges in developing a highly sensitive, easily prepared, and durable IH-based flexible capacitive pressure sensor. This study introduces a novel multicross-linked dual-network IH achieved through the physical and chemical cross-linking of polymers polyvinyl alcohol (PVA) and chitosan (CS), ionic solution H3PO4, and cross-linking agent gum arabic. Flexible capacitive pressure sensors, characterized by high sensitivity and a broad pressure range, are fabricated by employing mesh as templates to design cut-corner cube microstructures with high uniformity and controllability on the IHs. The sensor exhibits high sensitivity across a wide pressure range (0-290 kPa) and with excellent features such as high resolution (∼1.3 Pa), fast response-recovery time (∼11 ms), and repeatable compression stability at 25 kPa (>2000 cycles). The IHs as a dielectric layer demonstrate long-term water retention properties, enabling exposure to air for up to 100 days. Additionally, the developed sensor shows the ability to accurately measure the pulse wave within the small pressure range. By combining the pulse wave acquired by the sensor with a trained neural network model, we achieve successful blood pressure (BP) prediction, meeting the standards set by the Association for the Advancement of Medical Instrumentation and the British Hypertension Society. Ultimately, the sensor proposed in this study holds promising prospects for broad applications in high-precision wearable medical electronic devices.

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

Integrated surface microstructure and enhanced dielectric constant for constructing simple, low-cost, and high-performance flexible capacitive pressure sensor

Designing microstructure surface or enhancing the dielectric constant of functional layer is a common useful strategy to improve the pressure sensing performances of flexible capacitive pressure sensors, but it usually involves complex preparation processes (such as artificial microstructure and preparation of composite materials). Considering the limitations of a single strategy in improving the pressure sensing performance of capacitive pressure sensor, herein, we propose a simple strategy that integrates surface microstructure and enhanced dielectric constant of functional layer for constructing a high-performance flexible capacitive pressure sensor. Specifically, the polyester fiber conductive tape and filter paper with intrinsic rough surfaces are selected as microstructure electrodes and dielectric layer, respectively. Meanwhile, by introducing the daily carbon ink into filter paper, the moderate conductivity of the carbon ink is utilized to enhance the dielectric constant of the filter paper dielectric layer. The results show that the proposed the pressure sensor has wide pressure detection range of 0.1−100 kPa, high sensitivity (1.47 kPa−1, 0.1−10 kPa) and good durability (4000 cycles at 20 kPa). Taking the pressure range of 10−100 kPa as an example, the sensitivity of carbon ink paper-based sensor is 60 times higher than that of sensor without carbon ink. The enhanced working mechanism of the sensor is clarified by combining testing and characterization. In addition, the proposed pressure sensor has potential applications in wrist pulse, respiratory rate, walking record, morse code transmission，and stoma bag detection. This work provides a useful reference for constructing simple, low-cost and high-performance flexible capacitive pressure sensor.

The Design and numerical simulation of a 3D-printed flexible capacitive pressure sensor with a composite structure

Abstract Flexible pressure sensors are crucial for many areas, such as electronic skins, human motion, robot monitoring, and medical treatment. However, conventional manufacturing methods limit the speed and accuracy of manufacturing sensor dielectric layers. In this paper, a unique capacitive pressure sensor with a composite structure is introduced that can be fabricated by 3D printing technology. The structure, which has 3D hierarchical pyramids microstructures and porous substrate, can be directly fabricated by a DLP 3D printer. This allows flexible dielectric layers to be fabricated quickly while maintaining their superior performance. The dimension of the produced sensor is 10×10×4.5 mm3. The sensor’s design process, numerical simulation, and performance are provided and elucidated. The performance of the sensor is measured between 0 and 1 MPa. It has low hysteresis and high sensitivity (6.83 MPa−1 within the scope of 0 to 0.5 MPa and 2.56 MPa−1 within the scope of 0.5 to 1 MPa).

Flexible Capacitive Pressure Sensor Enhanced by Black Phosphorus-Au Nanocomposites/Ecoflex Sponge for Pressure and Proximity Detection

Flexible Capacitive Pressure Sensor Enhanced by Black Phosphorus-Au Nanocomposites/Ecoflex Sponge for Pressure and Proximity Detection

Sensitivity enhanced flexible capacitive pressure sensor microstructure optimization for biomedical applications

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.

Multimodal electrohydrodynamic jet printing-based microstructure-sensitized flexible pressure sensor

Surface modification with micro/nanostructures is a common approach for enhancing the performance of flexible pressure sensors. However, the current fabrication of the singular functionality of instruments and redundancy of processes increase the complexity of the sensor manufacturing process. In this study, we developed a multilayer microstructure-enhanced flexible capacitive pressure sensor based on the multimodal electrohydrodynamic jet (E-jet) printing technology. The experimental results demonstrate that the sensors incorporating the microstructure-sensitized electrode layer and the polyvinyl alcohol/graphene/polydimethylsiloxane dielectric layer exhibit the following characteristics: high sensitivity (0.3139 kPa−1/0–2 kPa), low limit of detection (∼100 mg), and stable performance even after 10,000 cycles. Moreover, microstructure-enhanced sensors have considerable potential for human behavior detection, such as detecting fluid flow, tracking muscle movements, and measuring pulse rates. Finally, microstructure-enhanced sensors fabricated using the E-jet printing method present a novel approach for designing sensitized structures in capacitive pressure sensors.

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

Capacitive PVC gel pressure sensors with various interlinked microstructural dielectric middle layers

Our sharp tactile sense is largely attributable to an undulating layer of microstructures between the epidermis and dermis, amplifying tactile signals. Taking inspiration from the biological template, we propose a design of flexible capacitive pressure sensors with various microstructural dielectric middle layers, fabricated using a casting-based approach. This is the first confirmed use of microstructural polyvinyl chloride (PVC) gel in dielectric layers and the first example of casting in the fabrication of capacitive sensors. Notably, on account of its flexibility, the sensor also addresses the problem of microstructure fracture and misalignment during sensor bending. These sensors can achieve a maximum sensitivity of 1.34 kPa−1 (under 10 kPa) with a fast response time (50 ms), good cyclic stability (> 1000 cycles), and a wide pressure sensing range (0 ∼ 290 kPa). When attached to a cup or balloon, this study reveals that these sensors can detect the weight and rigidity of the objects, demonstrating their potential in human-machine interaction, as well as in wearable applications.

A highly sensitive, flexible capacitive pressure sensor based on strontium alginate with crater microstructure

Electronic skin plays an important role in the age of artificial intelligence. Capacitive pressure sensors, capable of sensing pressure changes through contact, still need to improve their basic performance and comfort of use. In this paper, a flexible strontium alginate film with finely folded crater microstructure prepared by spraying method is introduced as a dielectric layer, together with PDMS film and conductive cloth as a capacitive sensor. The internal and external displacement, potential, and elastic volume ratio of the sensor were simulated using finite element analysis. The sensor has good sensitivity (R2 up to 0.99), very low response and relaxation time (≤ 50 ms), and good cyclic stability. The sensor was also used for performing several simple applications tests.