A Highly Sensitive and Flexible Capacitive Pressure Sensor Based on a Porous Three-Dimensional PDMS/Microsphere Composite

In recent times, polymer-based flexible pressure sensors have been attracting a lot of attention because of their various applications. A highly sensitive and flexible sensor is suggested, capable of being attached to the human body, based on a three-dimensional dielectric elastomeric structure of polydimethylsiloxane (PDMS) and microsphere composite. This sensor has maximal porosity due to macropores created by sacrificial layer grains and micropores generated by microspheres pre-mixed with PDMS, allowing it to operate at a wider pressure range (~150 kPa) while maintaining a sensitivity (of 0.124 kPa−1 in a range of 0~15 kPa) better than in previous studies. The maximized pores can cause deformation in the structure, allowing for the detection of small changes in pressure. In addition to exhibiting a fast rise time (~167 ms) and fall time (~117 ms), as well as excellent reproducibility, the fabricated pressure sensor exhibits reliability in its response to repeated mechanical stimuli (2.5 kPa, 1000 cycles). As an application, we develop a wearable device for monitoring repeated tiny motions, such as the pulse on the human neck and swallowing at the Adam’s apple. This sensory device is also used to detect movements in the index finger and to monitor an insole system in real-time.

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A Soft Pressure Sensor Array Based on a Conducting Nanomembrane

Micromachines ◽

10.3390/mi12080933 ◽

2021 ◽

Vol 12 (8) ◽

pp. 933

Author(s):

Daekwang Jung ◽

Kyumin Kang ◽

Hyunjin Jung ◽

Duhwan Seong ◽

Soojung An ◽

...

Keyword(s):

Pressure Sensor ◽

High Performance ◽

Sensor Array ◽

Pressure Sensors ◽

Strain Range ◽

High Sensitivity ◽

Critical Issue ◽

Mechanical Stimuli ◽

Highly Sensitive ◽

Accumulated Strain

Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft pressure sensors, but such a nonlinearity issue still exists and the sensors are only effective within a very narrow strain range. Herein, we fabricated a highly sensitive multi-channel pressure sensor array by using a simple thermal evaporation process of conducting nanomembranes onto a stretchable substrate. A rigid-island structure capable of dissipating accumulated strain energy induced by external mechanical stimuli was adopted for the sensor. The performance of the sensor was precisely controlled by optimizing the thickness of the stretchable substrate and the number of serpentines of an Au membrane. The fabricated sensor exhibited a sensitivity of 0.675 kPa−1 in the broad pressure range of 2.3–50 kPa with linearity (~0.990), and good stability (>300 Cycles). Finally, we successfully demonstrated a mapping of pressure distribution.

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Self-Restoring Capacitive Pressure Sensor Based on Three-Dimensional Porous Structure and Shape Memory Polymer

Polymers ◽

10.3390/polym13050824 ◽

2021 ◽

Vol 13 (5) ◽

pp. 824

Author(s):

Byunggeon Park ◽

Young Jung ◽

Jong Soo Ko ◽

Jinhyoung Park ◽

Hanchul Cho

Keyword(s):

Porous Structure ◽

Shape Memory ◽

Pressure Sensor ◽

Shape Memory Polymer ◽

Three Dimensional ◽

Pressure Sensors ◽

Capacitive Pressure Sensor ◽

Practical Applications ◽

Flexible Pressure Sensor ◽

Sensing Performance

Highly flexible and compressible porous polyurethane (PU) structures have effectively been applied in capacitive pressure sensors because of the good elastic properties of the PU structures. However, PU porous structure-based pressure sensors have been limited in practical applications owing to their low durability during pressure cycling. Herein, we report a flexible pressure sensor based on a three-dimensional porous structure with notable durability at a compressive pressure of 500 kPa facilitated by the use of a shape memory polymer (SMP). The SMP porous structure was fabricated using a sugar templating process and capillary effect. The use of the SMP resulted in the maintenance of the sensing performance for 100 cycles at 500 kPa; the SMP can restore its original shape within 30 s of heating at 80 °C. The pressure sensor based on the SMP exhibited a higher sensitivity of 0.0223 kPa−1 than a typical PU-based sensor and displayed excellent sensing performance in terms of stability, response time, and hysteresis. Additionally, the proposed sensor was used to detect shoe insole pressures in real time and exhibited remarkable durability and motion differentiation.

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A new strategy for the fabrication of a flexible and highly sensitive capacitive pressure sensor

Microsystems & Nanoengineering ◽

10.1038/s41378-021-00327-1 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Ruzhan Qin ◽

Mingjun Hu ◽

Xin Li ◽

Te Liang ◽

Haoyi Tan ◽

...

Keyword(s):

Pressure Sensor ◽

Pressure Sensors ◽

High Sensitivity ◽

Capacitive Sensor ◽

Capacitive Pressure Sensor ◽

Interdigital Electrode ◽

Interdigital Electrodes ◽

Highly Sensitive ◽

New Strategy ◽

Application Prospects

AbstractThe development of flexible capacitive pressure sensors has wide application prospects in the fields of electronic skin and intelligent wearable electronic devices, but it is still a great challenge to fabricate capacitive sensors with high sensitivity. Few reports have considered the use of interdigital electrode structures to improve the sensitivity of capacitive pressure sensors. In this work, a new strategy for the fabrication of a high-performance capacitive flexible pressure sensor based on MXene/polyvinylpyrrolidone (PVP) by an interdigital electrode is reported. By increasing the number of interdigital electrodes and selecting the appropriate dielectric layer, the sensitivity of the capacitive sensor can be improved. The capacitive sensor based on MXene/PVP here has a high sensitivity (~1.25 kPa−1), low detection limit (~0.6 Pa), wide sensing range (up to 294 kPa), fast response and recovery times (~30/15 ms) and mechanical stability of 10000 cycles. The presented sensor here can be used for various pressure detection applications, such as finger pressing, wrist pulse measuring, breathing, swallowing and speech recognition. This work provides a new method of using interdigital electrodes to fabricate a highly sensitive capacitive sensor with very promising application prospects in flexible sensors and wearable electronics.

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Flexible and Transparent Pressure Sensor Based on CNTs Film Microstructure

10.21203/rs.3.rs-1078880/v1 ◽

2021 ◽

Author(s):

Liangliang Liu ◽

Xin Yan

Keyword(s):

Pressure Sensor ◽

Production Cost ◽

Composite Electrode ◽

Pressure Sensors ◽

Wearable Devices ◽

Capacitive Pressure Sensor ◽

Detection Range ◽

Electronic Skin ◽

Film Microstructure ◽

Flexible Pressure Sensors

Abstract In recent years, capacitive flexible pressure sensors have been widely studied in electronic skin and wearable devices. The traditional capacitive pressure sensor has a higher production cost due to micro-nano machining technology such as lithography. This paper presents a flexible transparent capacitive pressure sensor based on a PDMS/CNT composite electrode, simple, transparent, flexible, and arrays without lithography. The sensitivity of the device has been tested to 0.0018 kpa -1 with a detection range of 0-30 kPa. The sensor is capable of rapidly detecting different pressures and remains stable after 100 load-unload tests.

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Ultra-Sensitive Flexible Pressure Sensor Based on Microstructured Electrode

Sensors ◽

10.3390/s20020371 ◽

2020 ◽

Vol 20 (2) ◽

pp. 371 ◽

Cited By ~ 5

Author(s):

Mengmeng Li ◽

Jiaming Liang ◽

Xudong Wang ◽

Min Zhang

Keyword(s):

Pressure Sensor ◽

Dielectric Layer ◽

Pressure Sensors ◽

High Sensitivity ◽

Capacitive Sensor ◽

Duty Ratio ◽

Capacitive Pressure Sensor ◽

Element Analysis ◽

Sequential Coupling ◽

Flexible Pressure Sensors

Flexible pressure sensors with a high sensitivity in the lower zone of a subtle-pressure regime has shown great potential in the fields of electronic skin, human–computer interaction, wearable devices, intelligent prosthesis, and medical health. Adding microstructures on the dielectric layer on a capacitive pressure sensor has become a common and effective approach to enhance the performance of flexible pressure sensors. Here, we propose a method to further dramatically increase the sensitivity by adding elastic pyramidal microstructures on one side of the electrode and using a thin layer of a dielectric in a capacitive sensor. The sensitivity of the proposed device has been improved from 3.1 to 70.6 kPa−1 compared to capacitive sensors having pyramidal microstructures in the same dimension on the dielectric layer. Moreover, a detection limit of 1 Pa was achieved. The finite element analysis performed based on electromechanical sequential coupling simulation for hyperelastic materials indicates that the microstructures on electrode are critical to achieve high sensitivity. The influence of the duty ratio of the micro-pyramids on the sensitivity of the sensor is analyzed by both simulation and experiment. The durability and robustness of the device was also demonstrated by pressure testing for 2000 cycles.

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High sensitivity and broad detection range flexible capacitive pressure sensor based on rGO cotton fiber for human motion detection

Smart Materials and Structures ◽

10.1088/1361-665x/ac3c07 ◽

2021 ◽

Author(s):

Rongliang Zheng ◽

Youyuan Wang ◽

Zhanxi Zhang ◽

Yanfang Zhang ◽

Jinzhan Liu

Keyword(s):

Pressure Sensor ◽

Cotton Fiber ◽

Pressure Sensors ◽

High Sensitivity ◽

Human Motion ◽

Superior Performance ◽

Capacitive Pressure Sensor ◽

Joint Movement ◽

Process Technology ◽

Flexible Pressure Sensors

Abstract Recently, flexible pressure sensors have attracted considerable interest in electronic skins, wearable devices, intelligent robots and biomedical diagnostics. However, the design of high sensitivity flexible pressure sensors often relies on expensive materials and complex process technology, which greatly limit their popularity and applications. Even worse, chemical-based sensors are poorly biocompatible and harmful to the environment. Here, we developed a flexible capacitive pressure sensor based on reduced graphene oxide (rGO) cotton fiber by a simple and low-cost preparation process. The environmentally friendly sensor exhibited a comprehensive performance with not only ultra-high sensitivity (up to 15.84 kPa-1) and a broad sensing range (0-500 kPa), but also excellent repeatability (over 400 cycles), low hysteresis (≤11.6%), low detection limit (<0.1 kPa) and wide frequency availability (sensitivity from 19.71 kPa-1 to 11.24 kPa-1, frequency from 100 Hz to 10 kHz). Based on its superior performance, the proposed sensor can detect various external stimuli (vertical stress, bending and airflow) and has been successfully applied for facial expression recognition, breathing detection, joint movement and walking detection, showing great potential for application in artificial electronic skin and wearable healthcare devices.

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Improving the performance and stability of flexible pressure sensors with an air gap structure

RSC Advances ◽

10.1039/c7ra09392f ◽

2017 ◽

Vol 7 (76) ◽

pp. 48354-48359 ◽

Cited By ~ 5

Author(s):

Xiongbang Wei ◽

Lun Xiao ◽

Wen Huang ◽

Jiaxuan Liao ◽

Zhi David Chen

Keyword(s):

Pressure Sensor ◽

Pressure Sensors ◽

Air Gap ◽

Highly Sensitive ◽

Flexible Pressure Sensors ◽

Gap Structure

A highly sensitive flexible resistive pressure sensor based on an air gap structure was presented.

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A theoretical model of flexible capacitive pressure sensor with microstructured electrode for highly sensitive electronic skin

Journal of Physics D Applied Physics ◽

10.1088/1361-6463/ac34a9 ◽

2021 ◽

Author(s):

Weidong Yang ◽

Wenxuan Ding ◽

Menglong Liu ◽

Jun Yang ◽

Mao Li

Keyword(s):

Pressure Sensor ◽

Electromechanical Coupling ◽

Present Model ◽

Pressure Sensors ◽

Compressive Force ◽

Contact Radius ◽

Capacitive Pressure Sensor ◽

Electronic Skin ◽

Highly Sensitive ◽

Theory Framework

Abstract Electronic skin (E-skin) has attracted much attention in smart wearables, prosthetics, and robotics. The capacitive-type pressure sensor is generally regarded as one good option to design tactile sensing devices owing to its superior sensitivity in low-pressure region, fast response time and convenient manufacturing. Introducing microstructures on electrode surface is an effective approach to achieve highly sensitive capacitive pressure sensors. In this work, an electromechanical model is proposed to build the relationship between capacitance change and compressive force. The present model can predict the sensitivity of capacitive pressure sensor with microstructured electrodes, where each cellular microstructure is modeled using the contact mechanics theory. It is the first time in the literature that based on Hertz theory framework, one rigorous electromechanical theory framework is established to model flexible capacitive pressure sensor, and the model can be extended to other microstructures, such as micro-pyramid, micro-pillar, and micro-dome array. The validation indicates that the analytical results well agree with the experimental data from our previous work and other literatures. Moreover, the present model can well capture the sensitivity of pressure sensor on the beginning range of small pressure. The sensitivity on this range is the most significant for the E-skin due to its robust linearity for one pressure sensor. Besides, we analyzed the compressive force-displacement relationship, the compressive force-contact radius relationship and the influences of the geometrical and material parameters on the electromechanical coupling effect. The results show that the height and the Young’s modulus of the soft dielectric layer are regarded as the dominant influencing factors in the sensitivity of capacitive pressure sensors.

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Printed and Flexible Capacitive Pressure Sensor with Carbon Nanotubes based Composite Dielectric Layer

Micromachines ◽

10.3390/mi10110715 ◽

2019 ◽

Vol 10 (11) ◽

pp. 715 ◽

Cited By ~ 1

Author(s):

Zhenxin Guo ◽

Lixin Mo ◽

Yu Ding ◽

Qingqing Zhang ◽

Xiangyou Meng ◽

...

Keyword(s):

Artificial Intelligence ◽

Carbon Nanotubes ◽

Aspect Ratio ◽

Pressure Sensor ◽

Dielectric Layer ◽

Pressure Sensors ◽

Weight Fraction ◽

Capacitive Pressure Sensor ◽

Flexible Pressure Sensor ◽

Flexible Pressure Sensors

Flexible pressure sensors have attracted tremendous attention from researchers for their widely applications in tactile artificial intelligence, electric skin, disease diagnosis, and healthcare monitoring. Obtaining flexible pressure sensors with high sensitivity in a low cost and convenient way remains a huge challenge. In this paper, the composite dielectric layer based on the mixture of carbon nanotubes (CNTs) with different aspect ratios and polydimethylsiloxane (PDMS) was employed in flexible capacitive pressure sensor to increase its sensitivity. In addition, the screen printing instead of traditional etching based methods was used to prepare the electrodes array of the sensor. The results showed that the aspect ratio and weight fraction of the CNTs play an important role in improving the sensitivity of the printed capacitive pressure sensor. The prepared capacitive sensor with the CNTs/PDMS composite dielectric layer demonstrated a maximum sensitivity of 2.9 kPa−1 in the pressure range of 0–450 Pa, by using the CNTs with an aspect ratio of 1250–3750 and the weight fraction of 3.75%. The mechanism study revealed that the increase of the sensitivity of the pressure sensor should be attributed to the relative permittivity increase of the composite dielectric layer under pressure. Meanwhile, the printed 3 × 3 and 10 × 10 sensor arrays showed excellent spatial resolution and uniformity when they were applied to measure the pressure distribution. For further applications, the flexible pressure sensor was integrated on an adhesive bandage to detect the finger bending, as well as used to create Morse code by knocking the sensor to change their capacitance curves. The printed and flexible pressure sensor in this study might be a good candidate for the development of tactile artificial intelligence, intelligent medical diagnosis systems and wearable electronics.

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Hollow polydimethylsiloxane (PDMS) foam with a 3D interconnected network for highly sensitive capacitive pressure sensors

Micro and Nano Systems Letters ◽

10.1186/s40486-020-00127-8 ◽

2020 ◽

Vol 8 (1) ◽

Author(s):

Dong Hwan Kim ◽

Young Jung ◽

Kyungkuk Jung ◽

Dong Hwa Kwak ◽

Dong Min Park ◽

...

Keyword(s):

Network Structure ◽

Three Dimensional ◽

Pressure Sensors ◽

High Sensitivity ◽

High Porosity ◽

Capacitive Pressure Sensor ◽

Interconnected Network ◽

Dimensional Network ◽

Highly Sensitive ◽

Output Characteristics

AbstractWe propose a highly sensitive capacitive pressure sensor made of hollow polydimethylsiloxane (PDMS) foam with a three-dimensional network structure. The stiffness of the foam is adjusted by the viscosity of the PDMS solution. The fabricated PDMS-30 (PDMS 30 wt%) foam shows extremely high porosity (> 86%) approximately 19 times that of bare PDMS (PDMS 100 wt%) foam. Capacitive pressure sensors fabricated using the foam possess high sensitivity, good compressibility (up to 80% strain), and consistent output characteristics in a 2000-cycle test.

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