Microdome Structures Research Articles

3D printing for capacitive flexible pressure sensors of small pressure high sensitivity with microdome-labyrinth structure

Abstract Capacitive flexible pressure sensors have excellent sensing characteristics such as ductility and high sensitivity, and are capable of accurately detecting small pressures generated by human movement and human-computer interaction. However, small pressure sensors fabricated using most conventional preparation methods (e.g., stencil molding) do not provide high enough resolution for small pressure measurements. Therefore, in this paper, capacitive flexible pressure sensors that can be applied to motion signal detection and motion sensing are prepared using digital light processing (DLP) printing technology. Elastomers with microdome and labyrinth composite structures are prepared using polyurethane acrylate (PUA) materials. At the same time, the sensor is capable of detecting minute pressures as low as 1pa and has a wide detection range with a sensitivity S of 0.037kPa-1 in the 0-20kPa stress range and 0.007kPa-1 in the 300kPa-400kPa stress range.

Flexible pressure sensor based on CNTs/CB/PDMS sponge with porous and microdome structures for sitting posture discrimination

The application fields of flexible pressure sensors are constantly expanding benefiting from their characteristics of being lightweight, flexible, easy to install, etc. Various structures have been developed for the purpose of improving the sensing performances of these sensors. However, the traditional structure designs typically enhance only a single aspect of performance. In this study, a flexible pressure sensor based on carbon nanotubes (CNTs)/carbon black (CB)/polydimethylsiloxane (PDMS) conductive sponge (CCPS) with both porous and microdome dual microstructures is prepared through the double template and swelling ultrasound methods. The introduction of two microstructures leads to the synergistic effect of dual sensing mechanisms, and the dual sensing mechanisms have been discussed according to the changes in microstructure morphology and finite element analysis results. Thanks to the synergistic effect of dual sensing mechanisms, CCPS exhibits comprehensive pressure sensing performances including a wide pressure sensing range of more than 350 kPa, high sensitivity under low pressure (7.10 kPa−1 over 0–25 kPa, 2.96 kPa−1 over 25–135 kPa, 1.09 kPa−1 over 135 kPa), and satisfactory long-term using performance of over 2000 cycles. CCPS is finally demonstrated for applications such as human motion detection, Morse code, and sitting position discrimination, indicating its broad application possibilities.

High-Resolution Total Internal Reflection-Based Structural Coloration by Electrohydrodynamic Jet Printing of Transparent Polyethylene Glycol Microdomes.

Total internal reflection (TIR)-based structural coloration is a brilliant strategy to overcome the need for periodic nanostructures and complex fabrication processes. Light entering the microdome structure undergoes TIR, and owing to varying reflection paths, it exhibits a color that changes with the microdome size. Although solution-based printing techniques have been proposed to achieve this effect, they fall short of full-color realization owing to resolution limitations. Herein, we achieved 3628 dpi of full-color and high-resolution structural color images by printing transparent microdome structures with 1.2-9.9 μm diameter using electrohydrodynamic (EHD) jet printing. Additionally, high-resolution EHD jet-printed structural color images display complex encoded information, enhancing the anticounterfeiting effectiveness through their fabrication simplicity and precise control over the microdome size. Because of these advantages, this TIR-based structural coloration technique with EHD jet printing is highly suitable for anticounterfeiting applications.

Neuron-Inspired Flexible Phase Change Materials for Ambient Energy Harvesting and Respiration Monitoring.

The global energy crisis and climate change pose unprecedented challenges. Wearable devices with personal thermoregulation and energy harvesting hold great promise for achieving energy savings and human thermal comfort. Here, inspired by neurons, a novel phase change material (PCM) is reported for efficient energy harvesting and respiratory monitoring via a self-assembly strategy. The use of gum arabic (GA) enabled the encapsulation of polyethylene glycol (PEG) and the targeted distribution of carboxylated multi-walled carbon nanotubes (cMWCNTs) simultaneously in poly (ethylene vinyl acetate) (EVA) matrix. The material exhibits an outstanding toughness value of 14.88MJ m-3 and high elongation at a break of 565.67%, exhibiting remarkable flexibility. The material with sufficient melting enthalpy (71.11 J g-1) demonstrates high photothermal conversion efficiency (95.27%) under 808nm laser irradiation (105mW cm-2). In addition, due to the synergistic effect of GA and PEG, especially the formation of microdome structures on the surface, the material demonstrates ultrasensitive humidity responsiveness for respiratory monitoring with high precision, excellent repeatability, and fast response/recovery time (50.4/50.5ms). Notably, it shows great potential for moisture-electric generators (MEGs) with the function of non-contact sensing. This material opens the path toward next-generation wearable devices in energy conversion and health monitoring.

Efficient Fabrication of Bioinspired Flexible Pressure Sensors via Electrohydrodynamic Jet Printing Method.

Bioinspired microdevices have made significant strides in various applications including human motion and health detection. However, facile and highly efficient fabrication approach of flexible pressure sensors remains a great challenge. Herein, inspired by the gecko's foot structure, a flexible pressure sensor with microdomes structure is fabricated by tip-assisted on-demand electrohydrodynamic jet (EHD-jet) printing method. Ascribed to the interlocking electrodes with microdome structure, 3Ddeformation rates are substantially enlarged. When the microdromes structure is under pressure, the resistivity of carbon nanotubes film coated on the surface of microdomes structure will change remarkably. By using the combined effect of assisted tip and ring focusing electrode, the influence and constraints on microstructure fabrication caused by substrate material and morphology are minimized. The desired uniform structures can be adjusted rapidly by changing the printing parameters and liquid properties. High length-height ratio (0.64) of microdomes enhances sensitivity, with minimum detection limit is 2Pa and response time is 40ms. Finally, the bionic flexible sensor indicated excellent performance in capable of detecting pressure, sound vibrations and human motion. This work presents a new method for high-efficiency fabrication micro-nano patterns for flexible sensors inspired, which could be used in wearable tech and health monitoring.

An iontronic flexible pressure sensor based on a multistage gradient micro-dome structure with a broad sensing range for wearable devices

The sensing principles, performance, and applications of the iontronic sensor in posture assessment in this work.

Anisotropic Piezoresistive Sensors Made with Magnetically Induced Vertically Aligned Carbon Nanotubes/Polydimethylsiloxane.

A piezoresistive material consisting of internal vertically aligned carbon nanotubes acting in concert with an external microdome structure is prepared to obtain a flexible piezoresistive sensor with high anisotropy. Here, we first obtained flexible piezoresistive composites (VCP) with anisotropic properties by inducing the vertical alignment of multiwalled carbon nanotubes in the pressure direction under a weak magnetic field of 0.6 T. Then, the composite with a microdome structure on the surface (m-VCP) was fabricated by a mold with a microstructure to further increase the anisotropy of the composite. The m-VCP microstructure was docked with VCP and placed between two layers of copper foil. With the synergistic effect of vertically aligned carbon nanotubes and the microdome structure, the sensitivity of the flexible sensor in the pressure direction was dramatically increased. In the low-strain range (0-6%), the sensitivity of m-VCP (GF = 9.208) is improved by 49% compared to m-CP and by 86% compared to VCP. The sensor has high anisotropy in the piezoresistive direction and retains good fatigue resistance under fatigue testing for 2000 cycles. This means that the sensor can be used in emerging fields such as human health monitoring, wearable electronics, and intelligent human-computer interaction.

Highly Sensitive Soft Pressure Sensors for Wearable Applications Based on Composite Films with Curved 3D Carbon Nanotube Structures.

Soft pressure sensors based on 3D microstructures exhibit high sensitivity in the low-pressure range, which is crucial for various wearable and soft touch applications. However, it is still a challenge to manufacture soft pressure sensors with sufficient sensitivity under small mechanical stimuli for wearable applications. This work presents a novel strategy for extremely sensitive pressure sensors based on the composite film with local changes in curved 3D carbon nanotube (CNT) structure via expandable microspheres. The sensitivity is significantly enhanced by the synergetic effects of heterogeneous contact of the microdome structure and changes of percolation network within the curved 3D CNT structure. The finite-element method simulation is used to comprehend the relationships between the sensitivity and mechanical/electrical behavior of microdome structure under the applied pressure. The sensor shows an excellent sensitivity (571.64 kPa-1 ) with fast response time (85ms), great repeatability, and long-term stability. Using the developed sensor, a wireless wearable health monitoring system to avoid carpel tunnel syndrome is built, and a multi-array pressure sensor for realizing a variety of movements in real-time is demonstrated.

Self-powered ultra-flexible infrared sensor based on PVA-PEDOT: PSS/Ti3C2Tx composite film

Flexibility and power supply needless are two demands of the emerging electronics, including sensor, processer and so on. Wearable infrared sensor is an important part of intelligent and medical sensing. In this work, a self-powered flexible infrared sensor with photo-thermo-electric energy conversion is designed based on the composite film of polyvinyl alcohol (PVA)/poly-(3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT: PSS)/Ti3C2Tx. Appropriate content of Ti3C2Tx nanoflakes improves the Seebeck coefficient and greatly enhances light absorption simultaneously. Bionic micro-dome structure is employed to the surface of the film to further enhance the light absorption for better photo-thermal conversion. As results, the composite film with 5 mg Ti3C2Tx shows a Seebeck coefficient up to 37.57 μV K−1, a response time <0.75 s and great stretchability (up to 200 %). At 2 mW cm−2 power density of an 850 nm laser, the film generates 220 μV thermal voltage, which is 44 times of that of the film without Ti3C2Tx. An infrared sensor array based on this composite film is designed for the successful imaging of a human palm. This self-powered infrared sensor shows great application prospects in the fields of wearable non-visual perception and intelligent sensing.

Room-temperature self-healing polysiloxane networks for highly sensitive piezoresistive pressure sensor with microdome structures

Soft piezoresistive pressure sensor is an important component for next generation flexible electronics. Micropatterning of such sensors significantly improves the pressure sensitivity, however, the short device lifetime due to scratches and motions limits the translation to industrial applications. Herein, we report a novel poly(ODMS-co-MAA) for self-healing piezoresistive sensor to effectively overcoming such shortcoming. Self-healing capability was achieved by incorporating dynamic Fe(III)-carboxylate linkages in the polymer networks. These linkages work as sacrificial bonds and dissipate energy caused by mechanical damage. The bonds subsequently reform and functionality of the sensor can be restored. The poly(ODMS-co-MAA)-based self-healing polymer networks (SPN) were effectively healed from damages showing the recovery of electrical resistance (>95%) within 10 hrs. SPN was fabricated with microdome structures and exhibited a superior pressure sensitivity (2 kPa−1) as well as stability compared to planar features (9.13 × 10−3 kPa−1), demonstrating its excellent potential as pressure sensor. Combined results demonstrate the potential of the self-healing networks for next generation piezoresistive pressure sensors.

Hierarchical Asymmetric Complementary Bionic Structure for Highly Sensitive Pressure Sensor

AbstractBionic structures are widely concerned in flexible sensors. However, there is a lack of research on the optimization of structure to improve the performance. Herein, two types of plant leaves with quite different surface structures, rose petal (RP) and paper mulberry (PM) leaf, are used to fabricate an asymmetric complementary structure. Under pressure, the microcones of PM can insert into the grooves of the RP microdome structures and can be bended under high pressure. Compared to that of PM–PM and RP–RP structures, the space for increasing the internal contact area of PM–RP structure is greatly enhanced, which improves the sensitivity and detection range of the sensor simultaneously. The hierarchical combination of stacked Ti3C2Tx MXene film with nanoscale surface roughness and the micro PM–RP structure further improves the performance. The prepared sensor shows a sensitivity up to 84.79 kPa−1 (0–10 kPa), a wide pressure detection range of 0–100 kPa, and a short response time of 11 ms. It shows great application potential in wearable electronics. Meanwhile, a universal principle for the design of micro‐structure in pressure sensors is proposed, that is, reducing the initial contact resistance and enriching the approach for increasing the contact area.

Flexible pressure sensor based on graphene/PS microsphere/PDMS composite dielectric layer and activated carbon non-woven fabrics

• Fabrication of ultra-thin dielectric layers with surface microstructures and filler doping. • Offering new ideas for improving the sensitivity of flexible capacitive sensors. • Activated carbon non-woven fabrics are used to make flexible electrodes. • New dielectric layer fabrication process developed. • A number of dynamic tests have been completed using this sensor. With the widespread application of wearable devices, the demand for high-performance sensors has increased dramatically. This study proposes a novel capacitive sensor. By using polystyrene (PS) microspheres and the sacrificial layer method, the ultrathin dielectric layer with surface micro-dome structure and uniform graphene doping are fabricated. In addition, the activated carbon non-woven fabrics (ACNWF) electrode was prepared, and the device characteristics of the sensor were investigated. The sensor has a good capacitive response in a wide pressure range (0–150 kPa) and a sensitivity of 0.209 kPa −1 in the low-pressure range. The short response time (<25 ms) is suitable for real-time dynamic monitoring. Meanwhile, the sensor has good stability (3500 cycles) and performs well in mouse double-click, muscle contraction and arm swing. This sensor has great potential in wearable electronics and human-computer interaction.

Two-birds-one-stone: Flexible PANI film with bionic microstructures for multifunctional sensing of physical and chemical stimuli

Flexible and wearable electronic multifunctional sensors have promising applications in healthcare detection, electronic skins (e-skins) and motion detection. However, it remains a great challenge to manufacture eco-friendly sensors that are versatile, flexible, transparent, comfortable to wear and suitable for mass production. A special flexible transparent polyaniline (PANI) film with a bionic rose micro-dome structure was designed via an eco-friendly and scalable manufacturing approach. Benefiting from the special micro-structure modification, the multifunctional flexible sensor presents high sensitivity to different stimuli, including pressure and VOC gases. Taking advantages of the construction of the rose micro-dome structure, the structured PANI (s-PANI) film exhibits high sensitivity (1.104 kPa−1), ultra-low detection limit (0.64 Pa), and it can accurately monitor small movements of the human body. Moreover, due to the high moisture resistance of s-PANI film and the increased contact area with NH3, it has increased sensitivity in response to NH3 and can reach detection limit as low as 10 ppb. This novel and cost-effective strategy for the simple preparation of high-performance, multifunctional and flexible PANI film offers the opportunity to develop environmentally friendly devices on a large scale.

Irregular Microdome Structure‐Based Sensitive Pressure Sensor Using Internal Popping of Microspheres (Adv. Funct. Mater. 27/2022)

Flexible Pressure Sensors In article number 2201147, Inkyu Park, Hanchul Cho, and co-workers develop a new strategy for generating 3D and irregular micro-dome structures with a design and manufacturing flexibility by internal popping of microspheres. This method allows controllable microscale 3D surface morphology without using micro-patterned molds for flexible pressure sensors with excellent sensing performances. A health monitoring system and human–computer interaction system are demonstrated using the fabricated flexible pressure sensor.

A high-performance flexible triboelectric nanogenerator based on cellulose acetate nanofibers and micropatterned PDMS films as mechanical energy harvester and self-powered vibrational sensor

Triboelectric nanogenerators are emerging mechanical energy harvesting devices in the era of the Internet of Things (IoT) for powering small-scale electronic devices or functioning as state-of-the-art self-powered sensors. Furthermore, observing vibration patterns from different electronic gadgets helps in assessing the health of the gadgets and also allows to detect the downtime as well as faults pre-emptively. Here, a triboelectric nanogenerator based on electrospun cellulose acetate nanofibers and surface modified PDMS is fabricated for powering commercial sensors. In addition, the effect of surface patterning on PDMS film such as arrays of micropyramid and microdome structures on the output characteristics of TENG has been systematically investigated. The PDMS with micropyramidal arrays in combination with electrospun cellulose acetate nanofibers showed a massive enhancement (~180 times) in the power density of TENG, as compared to the flat PDMS film-based device. The fabricated facile and flexible TENG with micropyramidal surface modification on PDMS can generate an output voltage of 400 V, short circuit current of 3 mA/m2 and peak power density of 0.9 W/m2 respectively. In addition, with a little tweak in the structure, the same cellulose acetate nanofiber-PDMS based TENG is transformed into an active self-powered vibration sensor. Utilizing this, the vibration profile of an electric-sewing machine is mapped under various frequencies of operation. Additionally, anomalous vibrational behaviours from different electronic gadgets such as hard disks and computer fans, as a result of mechanical imbalances, are also detected using the self-powered triboelectric vibrational sensor.

Irregular Microdome Structure‐Based Sensitive Pressure Sensor Using Internal Popping of Microspheres

AbstractModifying the surface morphology of an elastomer surface into 3D microstructures is crucial for various soft sensor applications. However, processes based on typical mold microfabrication and elastomer casting remain the dominant methodologies. This study demonstrates a novel strategy for generating 3D and irregular microdome structures for flexible pressure sensors through the internal popping of microspheres. When thermal treatment is applied to a composite film composed of microspheres and an elastomer matrix, the microspheres expand, and irregular microdome structures are generated. This composite film with an irregular microdome structure is utilized as a piezoresistive pressure‐sensing film. The sensor shows high sensitivity (−50.45 kPa−1) owing to the heterogeneous contact change between the irregular microdome structure and a laser‐induced graphene electrode; it also exhibits a short response time (τ10‐90% ≈ 39 ms), excellent repeatability, and high reliability. The sensor is applied in a fingertip‐shaped pressure sensor to detect the blood pulse on the index finger and on electronic skin to recognize soft objects. Furthermore, a pressure sensor array that enables various functions such as drawing, multitouch, and deep learning‐based motion control, is demonstrated.

Wireless Rehabilitation Training Sensor Arrays Made with Hot Screen-Imprinted Conductive Hydrogels with a Low Percolation Threshold.

Herein, we propose a highly sensitive wireless rehabilitation training ball with a piezoresistive sensor array for patients with Parkinson's disease (PD). The piezoresistive material is a low percolation threshold conductive hydrogel which is formed with polypyrrole (PPy) nanofibers (NFs) as a conductive filler derived from a polydopamine (PDA) template. The proton acid doping effect and molecular template of PDA are essential for endowing PPy NFs with a high aspect ratio, leading to a low percolation threshold (∼0.78 vol %) and a low Young's 004Dodulus of 37.69 kPa and hence easy deformation. The piezoresistive sensor exhibited a static and dynamic stability of 10,000 s and 15,000 cycle times, respectively. This stability could be attributed to the increased hydrophilicity of conductive fillers, enhancing the interfacial strength between the conductive filler and the matrix. The interaction between the PDA-PPy NFs and the hydrogel matrix endows the hydrogel with toughness and ensures the stability of the device. Additionally, the microdome structure of the conductive hydrogel, produced by hot screen-imprinting, dramatically improves the sensitivity of the piezoresistive sensor (∼856.14 kPa-1). The microdome conductive hydrogel can distinguish a subtle pressure of 15.40 Pa compared to the control hydrogel without a microstructure. The highly sensitive piezoresistive sensor has the potential to monitor the hand-grip force, which is not well controlled by patients with PD. The rehabilitation training ball assembled with a sensor array on the surface and a wireless chip for communication inside is built and used to monitor the pressure in real time through the WeChat applet. Thus, this work has significantly broadened the application of hydrogel-based flexible piezoresistive sensors for human activity monitoring, which provides a promising strategy to realize next-generation electronics.

An ultra-thin flexible wearable sensor with multi-response capability prepared from ZIF-67 and conductive metal-organic framework composites for health signal monitoring.

Simulation of somatosensory systems in human skin with electronic devices has broad applications in the development of intelligent robots and wearable electronic devices. Here, we give an account of a new biomimetic flexible dual-mode pressure sensor, which is based on the first developed sea dandelion-like conductive metal-organic framework (cZIF-67@Cu-CAT) and the self-synthesized mechanically luminescent zinc sulfide nanoparticles and cleverly combines the microdome structure of the lotus leaf. According to finite element simulation analysis (FEA), the deformation behavior and pressure distribution of the contact interface with dandelion-like nanostructures cause the contact area of the sensor to increase rapidly and steadily with the load. It is for this reason that the piezoresistive pressure sensor has a high sensitivity of 71.74 kPa-1 over a wide range of 0.5 to 80 kPa. More importantly, it can roughly perceive stress changes in the external environment through mechanoluminescence materials without a power supply. The ultra-thin flexible pressure sensor is suitable for sensitive monitoring of small vibrations, including wrist pulse and joint motion. Combined with Bluetooth data transmission, it is not difficult to see that the high-sensitivity ultra-thin sensor designed in this study has broad potential in the applications of bio-wearable electronics and will play an immeasurable role in various sports training and joint protection in the future.

Hierarchically Microstructure-Bioinspired Flexible Piezoresistive Bioelectronics.

The naturally microstructure-bioinspired piezoresistive sensor for human-machine interaction and human health monitoring represents an attractive opportunity for wearable bioelectronics. However, due to the trade-off between sensitivity and linear detection range, obtaining piezoresistive sensors with both a wide pressure monitoring range and a high sensitivity is still a great challenge. Herein, we design a hierarchically microstructure-bioinspired flexible piezoresistive sensor consisting of a hierarchical polyaniline/polyvinylidene fluoride nanofiber (HPPNF) film sandwiched between two interlocking electrodes with microdome structure. Ascribed to the substantially enlarged 3D deformation rates, these bioelectronics exhibit an ultrahigh sensitivity of 53 kPa-1, a pressure detection range from 58.4 to 960 Pa, a fast response time of 38 ms, and excellent cycle stability over 50 000 cycles. Furthermore, this conformally skin-adhered sensor successfully demonstrates the monitoring of human physiological signals and movement states, such as wrist pulse, throat activity, spinal posture, and gait recognition. Evidently, this hierarchically microstructure-bioinspired and amplified sensitivity piezoresistive sensor provides a promising strategy for the rapid development of next-generation wearable bioelectronics.

Bioinspired Gradient Conductivity and Stiffness for Ultrasensitive Electronic Skins.

Hierarchical and gradient structures in biological systems with special mechanical properties have inspired innovations in materials design for construction and mechanical applications. Analogous to the control of stress transfer in gradient mechanical structures, the control of electron transfer in gradient electrical structures should enable the development of high-performance electronics. This paper demonstrates a high performance electronic skin (e-skin) via the simultaneous control of tactile stress transfer to an active sensing area and the corresponding electrical current through the gradient structures. The flexible e-skin sensor has extraordinarily high piezoresistive sensitivity at low power and linearity over a broad pressure range based on the conductivity-gradient multilayer on the stiffness-gradient interlocked microdome geometry. While stiffness-gradient interlocked microdome structures allow the efficient transfer and localization of applied stress to the sensing area, the multilayered structure with gradient conductivity enables the efficient regulation of piezoresistance in response to applied pressure by gradual activation of current pathways from outer to inner layers, resulting in a pressure sensitivity of 3.8 × 105 kPa-1 with linear response over a wide range of up to 100 kPa. In addition, the sensor indicated a rapid response time of 0.016 ms, a low minimum detectable pressure level of 0.025 Pa, a low operating voltage (100 μV), and high durability during 8000 repetitive cycles of pressure application (80 kPa). The high performance of the e-skin sensor enables acoustic wave detection, differentiation of gas characterized by different densities, subtle tactile manipulation of objects, and real-time monitoring of pulse pressure waveform.