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Pressure response capabilities of the capacitive pressure sensor. (a) Relative capacitance change-pressure curve of the microstructure capacitance sensor (red) and non-structure sensor (black); (b) Capacitance-time curve with loading and unloading of a red bean (corresponding
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As the core component of the sense of touch, flexible pressure sensors are critical to synchronized interactions with the surrounding environment. Here, we introduce a new type of flexible capacitive pressure sensor based on a template of electrodes, with a one-dimensional pyramid micropatterned structure on a Polydimethylsiloxane (PDMS) substrate...
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The development of special wearable/portable electronic devices for health monitoring is rapidly growing to cope with different health parameters. The emergence of wearable devices and its growing demand has widened the scope of self-powered wearable devices with the possibility to eliminate batteries. For instance, the wearable thermoelectric ener...
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... Delightedly, the unique micro-pyramidal microstructure endows the sensor with high sensitivity (64.56 kPa −1 ) and wide sensing range (4.9 Pa-98 kPa). More importantly, benefiting from the good stability characteristics of the angular cone structure, [30][31][32] the prepared pressure sensor could output stable signal output and exhibit long-time service life (18 000 cycles). Based on the remarkable sensing characteristics, the resulting pressure sensor was further applied to real-time detection of human physiological signals and recognition of facial subtle expressions, demonstrating its broad application prospect in future flexible intelligent wearable electronic devices. ...
With the advent of smart era, constructing high‐quality flexible electronic devices is urgently demanded. In this contribution, a flexible and wearable pressure sensor with high stability is tactfully designed and prepared based on pyramid‐like MXene film. The investigated pyramid‐like MXene film is fabricated by a simple and low‐cost substrate shrinkage method. Owing to the conical pyramid structure, the resulting pressure sensor can output continuous and stable electrical signal under stress, and has good cycling stability and long working life (18 000 cycles). Specifically, the sensitivity of the sensor can reach up to 64.56 kPa⁻¹ under small stress, and the sensing range is 4.9 Pa–98 kPa. Moreover, the response and recovery time under small stress is 59 and 15 ms, respectively. The sensing mechanism of the pressure sensor is explored. The prepared flexible wearable sensor shows great application potential in human motion and health monitoring.
... Strain sensors principally measure external forces in planar or longitudinal direction, while pressure sensors function in perpendicular and transverse direction. Based on different working principles, diverse flexible force-responsive sensing materials have been reported via introducing functional nanomaterials in the supporting polymer substrate with specific micro/nano-structure design [2,37,38]. Generally, these nanomaterials cover low-dimensional carbons (e.g., carbon blacks (CBs), carbon nanotubes (CNTs), graphene, MXenes) [39], metal-based conductive fillers (e.g., silver nanowires (Ag NW), gold nanoparticles, liquid metal) [40], conducting polymer-based fillers (e.g., polyaniline (PANI), polypyrrole (PPY), polythiophene, poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS)) [41] and their hybrid conductive fillers (CNTs/graphene hybrid filler) [42]. As for flexible and stretchable supporting polymer matrix, elastic rubbers, fibers, fabrics, and foams are the popularly used ones for flexible force-sensitive sensors [5,9,11]. ...
Wearable electronic skin (e-skin) has provided a revolutionized way to intelligently sense environmental stimuli, which shows prospective applications in health monitoring, artificial intelligence and prosthetics fields. Drawn inspiration from biological skins, developing e-skin with multiple stimuli perception and self-healing abilities not only enrich their bionic multifunctionality, but also greatly improve their sensory performance and functional stability. In this review, we highlight recent important developments in the material structure design strategy to imitate the fascinating functionalities of biological skins, including molecular synthesis, physical structure design, and special biomimicry engineering. Moreover, their specific structure-property relationships, multifunctional application, and existing challenges are also critically analyzed with representative examples. Furthermore, a summary and perspective on future directions and challenges of biomimetic electronic skins regarding function construction will be briefly discussed. We believe that this review will provide valuable guidance for readers to fabricate superior e-skin materials or devices with skin-like multifunctionalities and disparate characteristics.
... In the past few years, various polymer materials for highly flexible capacitive membranes have been studied by many researchers [1][2][3][4][5][6][7] to replace typical silicon membranes. This vast interest is because most polymers have low elastic modulus, which produces a large displacement in response to pressure variation and produces higher mechanical sensitivity [8]. ...
The LC-MEMS pressure sensor is an attractive option for an implantable sensor. It senses pressure wirelessly through an LC resonator, eliminating the requirement for electrical wiring or a battery system. However, the sensitivity of LC-MEMS pressure sensors is still comparatively low, especially in biomedical applications, which require a highly-sensitive sensor to measure low-pressure variations. This study presents the microfabrication of an LC wireless MEMS pressure sensor that utilizes a PMMA-Graphene (PMMA/Gr) membrane supported on a silicon trench as the deformable structure. The (PMMA/Gr) membrane was employed to increase the sensor’s sensitivity due to its very low elastic modulus making it easy to deform under extremely low pressure. The overall size of the fabricated sensor was limited to 8 mm × 8 mm. The experimental results showed that the capacitance value changed from 1.64 pF to 12.32 pF when the applied pressure varied from 0 to 5 psi. This capacitance variation caused the frequency response to change from 28.74 MHz to 78.76 MHz. The sensor sensitivity was recorded with a value of 193.45 kHz/mmHg and a quality factor of 21. This study concludes that the (PMMA/Gr) membrane-based LC-MEMS pressure sensor has been successfully designed and fabricated and shows good potential in biomedical sensor applications.
... Research is focusing on improving the sensitivity of pressure sensors for low pressure ranges by developing polydimethylsiloxane (PDMS) based micro-structured dielectric layers to increase its deformation and contact area [30]- [32]. Various micro-structures including micro-cones [33], micro-sphere [34], micro-pyramids [35], micro-pillars [36], porous structures [37], nanoparticles [38], microspheres [39] and micro-array structures [40] have been widely studied. Among these, micro-pyramids have shown excellent sensitivity owing to its structural deformation compared to other structures [41], [42]. ...
A novel capacitive pressure sensor based on micro-structured polydimethylsiloxane (PDMS) dielectric layer was developed for wearable E-skin and touch sensing applications. The pressure sensor was fabricated on a flexible polyethylene terephthalate (PET) substrate, using PDMS and silver (Ag) as the dielectric and electrode layers, respectively. A set of PDMS films with pyramid shaped micro-structures were fabricated using a laser engraved acrylic mold. The electrodes (top and bottom) were fabricated by depositing Ag on PET films using additive screen-printing process. The pressure sensor was assembled by attaching the top and bottom Ag electrodes to the smooth side of pyramid shaped micro-structured PDMS (PM-PDMS) films. The top PM-PDMS was then placed on the bottom PM-PDMS. The capability of the fabricated pressure sensor was investigated by subjecting the sensor to pressures ranging from 0 to 10 kPa. A sensitivity of 0.221% Pa
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, 0.033% Pa
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and 0.011% Pa
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along with a correlation coefficient of 0.9536, 0.9586 and 0.9826 was obtained for the pressure sensor in the pressure range of 0 Pa to 100 Pa, 100 Pa to 1000 Pa, and 1 kPa to 10 kPa, respectively. The pressure sensor also possesses a fast response time of 50 ms, low hysteresis of 0.7%, recovery time of 150 ms and excellent cycling stability over 1000 cycles. The results demonstrated the efficient detection of pressure generated from various activities such as hand gesture and carotid pulse measurement. The PM-PDMS based pressure sensor offers a simple and cost-effective approach to monitor pressure in E-skin applications.
... As shown in Fig. 2, the triangular wrinkle structures were fabricated using the MEMS technology, which have been reported in our previous work [19]. First, a positive photoresist was spin-coated on the silica wafer at 3000 rad/min and baked at 105°C for 90 s. ...
... And the size of sample was about 4 mm × 4 mm. Desired periodicity was achieved by tuning the size of mask structures and etch parameters, which can be calculated as introduced in our previous studies [19]. ...
Abstract We demonstrate a novel infrared stealth structure consisting of SiO2/TiO2 film, which was manufactured as the highly stretchable triangular wrinkle structures. The triangular wrinkle structures have firstly been transferred to the flexible substrate from the surface of Si-substrate, which was manufactured by the MEMS technology. Then, the infrared reflective film have been manufactured to be the triangular wrinkle structures by depositing the materials (noble metal (Ag or Au) or multilayer oxide (SiO2/TiO2)) on the surface of flexible substrate. Due to the lower reflection effect of curved surface, the infrared reflectivity of these structures has been tuned down to 5%. And, compared to the flat surface, the reflection-to-diffuse ratios improved approximately one order of magnitude. These structures can adapt to the environment by changing the reflectivity of triangular wrinkle structures under stretching. Finally, an Au-modified infrared stealth structure has been fabricated as the array structures, which disappeared and then display by stretching the triangular wrinkle structures at room temperature. It features high reflection-to-diffuse ratios, stable repeatability, low-cost, and easy to manufacture. It may open opportunities for infrared camouflage for military security and surveillance field application.
Parylene C is widely used as a passivation layer due to its excellent chemical inertness, electrical insulation, biocompatibility, and flexibility. But, it is a potential piezoelectric material which can be used as a flexible pressure sensor. Herein, the parylene C is synthesized via chemical vapour deposition method. The flexible piezoelectric, piezoresistive, and capacitive pressure sensors based on parylene C are fabricated. The flexible piezoelectric pressure sensor is used for the first time. The sensing performance of these sensors is comparatively investigated, showing high sensitivities of 140 mVkPa
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, 0.046 kPa
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, and 0.080 kPa
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in the low-pressure range (<4 kPa), respectively. Furthermore, the response times (0.40 s, 0.37 s, and 0.48 s) and the relaxation times (0.21 s, 0.37 s, and 0.62 s) are achieved. This work demonstrates that parylene C, which is often used as a passivation layer, can also be used as a flexible piezoresistive and capacitive pressure sensor. It could also be a potential candidate for wearable healthcare monitoring, human-machine interfaces, and soft robotics in the low-pressure range.
When the sensor works in a limited environment, its accuracy is easily affected by unnecessary strain loss. The key to improve accuracy is to reduce the transverse strain of the dielectric layer structure. It is an innovative technology to construct zero Poisson's ratio dielectric layer to limit the lateral strain of dielectric layer under normal pressure. The porous metamaterial dielectric layer with zero Poisson's ratio is constructed based on the paper-cutting theory. The equivalent nonlinear mechanical model is established by use of Bernoulli Euler beam theory and energy method. The analytical expressions of equivalent Poisson's ratio and equivalent Young’s modulus are given, and the necessity of considering geometric nonlinear large deformation is revealed. An improved variable step iterative method is proposed in order to solve the problem of equivalent internal force analysis caused by geometric deformation nonlinearity. The key of this method is to determine the displacement at the free end under the premise of considering the nonlinear superposition of the rigid body motion of the curved bar of the metamaterial. Based on the equivalent nonlinear mechanical model, the structural deformation characteristics of the dielectric layer structure in the linear small deformation stage and the nonlinear large deformation stage are analyzed. The results of theoretical, finite element simulation and experimental research reveal the necessity of considering geometric nonlinear factors in the practical application of the structure, which means that the foundation is theoretically and experimentally laid for the design of porous elastic dielectric layer of flexible capacitive pressure sensor.
Flexible pressure sensors have broad application prospects, such as human motion monitoring and personalized recognition. However, their applicability is limited by complex structures, low output performance, low sensitivity, and narrow measurement range. In this study, we report a single-electrode spongy triboelectric sensor (SSTS) mainly composed of spongy composite multi-walled carbon nanotubes/polydimethylsiloxane (MWCNT/PDMS) film and conductive fabric, which can simultaneously generate contact electrification and electrostatic induction coupling in a single-electrode contact-separation mode. The SSTS combines the triboelectric effect, properties of doping material, and spongy porous structure (soft sugar as a sacrificial template). An SSTS with an MWCNT content of 10 wt% and a porosity of 64% exhibits high sensitivity, a wide measurement range, and excellent linearity. It also displays two sensitivity regions (slopes): 1.324 V/kPa from 1.5 to 28 kPa in the low-pressure range and 0.096 V/kPa from 28 to 316.5 kPa in the high-pressure range, with linearities of 0.980 and 0.979, respectively. Furthermore, the SSTS delivers a high-performance output and high stability, thus enhancing the monitoring of hand pressure changes, human movement, personalized spatial recognition, and other detection tasks. This new strategy for human motion monitoring shows great potential in the healthcare fields, sports rehabilitation, and human-computer interactions.
Recent advances in the field of skin patches have promoted the development of wearable and implantable bioelectronics for long-term, continuous healthcare management and targeted therapy. However, the design of electronic skin (e-skin) patches with stretchable components is still challenging and requires an in-depth understanding of the skin-attachable substrate layer, functional biomaterials and advanced self-powered electronics. In this comprehensive review, we present the evolution of skin patches from functional nanostructured materials to multi-functional and stimuli-responsive patches towards flexible substrates and emerging biomaterials for e-skin patches, including the material selection, structure design and promising applications. Stretchable sensors and self-powered e-skin patches are also discussed, ranging from electrical stimulation for clinical procedures to continuous health monitoring and integrated systems for comprehensive healthcare management. Moreover, an integrated energy harvester with bioelectronics enables the fabrication of self-powered electronic skin patches, which can effectively solve the energy supply and overcome the drawbacks induced by bulky battery-driven devices. However, to realize the full potential offered by these advancements, several challenges must be addressed for next-generation e-skin patches. Finally, future opportunities and positive outlooks are presented on the future directions of bioelectronics. It is believed that innovative material design, structure engineering, and in-depth study of fundamental principles can foster the rapid evolution of electronic skin patches, and eventually enable self-powered close-looped bioelectronic systems to benefit mankind.
