In recent years, highly sensitive pressure sensors that are flexible, biocompatible, and stretchable have attracted significant research attention in the fields of wearable electronics and smart skin. However, there has been a considerable challenge to simultaneously achieve highly sensitive, low-cost sensors coupled with optimum mechanical stability and an ultralow detection limit for subtle physiological signal monitoring devices. Targeting aforementioned issues, herein, we report the facile fabrication of a highly sensitive and reliable capacitive pressure sensor for ultralow-pressure measurement by sandwiching MXene (Ti 3 C 2 T x )/poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) composite nanofibrous scaffolds as a dielectric layer between biocompatible poly-(3,4-ethylenedioxythiophene) polystyrene sulfonate /polydimethylsiloxane electrodes. The fabricated sensor exhibits a high sensitivity of 0.51 kPa −1 and a minimum detection limit of 1.5 Pa. In addition, it also enables linear sensing over a broad pressure range (0−400 kPa) and high reliability over 10,000 cycles even at extremely high pressure (>167 kPa). The sensitivity of the nanofiber-based sensor is enhanced by MXene loading, thereby increasing the dielectric constant up to 40 and reducing the compression modulus to 58% compared with pristine PVDF-TrFE nanofiber scaffolds. The proposed sensor can be used to determine the health condition of patients by monitoring physiological signals (pulse rate, respiration, muscle movements, and eye twitching) and also represents a good candidate for a next generation human−machine interfacing device.
The rapid development
of pressure sensors with distinct functionalities,
notably, with increased sensitivity, fast response time, conformability,
and a high degree of deformability, has increased the demand for wearable
electronics. In particular, pressure sensors with an excellent sensitivity
in the low-pressure range (<2 kPa) and a large working range simultaneously
are strongly demanded for practical applications in wearable electronics.
Here, we demonstrate an emerging class of solid polymer electrolyte
obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride-co-hexafluoropropylene) as a high-capacitance dielectric
layer for interfacial capacitive pressure sensing applications. The
solid polymer electrolyte exhibits a very high interfacial capacitance
by virtue of mobile ions that serve as an electrical double layer
in response to an electric field. The randomly distributed microstructures
created on the solid electrolyte help the material to elastically
deform under pressure. Moreover, the interfacial capacitance is improved
by utilizing a highly conductive porous percolated network of silver
nanowires reinforced with poly(dimethylsiloxane) as the electrodes.
An ultrahigh-pressure sensitivity of 131.5 kPa–1, a low dynamic response time of ∼43 ms, a low limit of detection
of 1.12 Pa, and a high stability for over 7000 cycles are achieved.
Finally, we demonstrate the application of the sensor for international
Morse code detection, artery pulse detection, and eye blinking. Owing
to the ultrahigh sensitivity, the as-fabricated sensor will have great
potential for wearable devices in health status monitoring, motion
detection, and electronic skin.
Recently, flexible capacitive pressure
sensors have received significant
attention in the field of wearable electronics. The high sensitivity
over a wide linear range combined with long-term durability is a critical
requirement for the fabrication of reliable pressure sensors for versatile
applications. Herein, we propose a special approach to enhance the
sensitivity and linearity range of a capacitive pressure sensor by
fabricating a hybrid ionic nanofibrous membrane as a sensing layer
composed of Ti3C2T
x
MXene and an ionic salt of lithium sulfonamides in a poly(vinyl
alcohol) elastomer matrix. The reversible ion pumping triggered by
a hydrogen bond in the hybrid sensing layer leads to high sensitivities
of 5.5 and 1.5 kPa–1 in the wide linear ranges of
0–30 and 30–250 kPa, respectively, and a fast response
time of 70.4 ms. In addition, the fabricated sensor exhibits a minimum
detection limit of 2 Pa and high durability over 20 000 continuous
cycles even under a high pressure of 45 kPa. These results indicate
that the proposed sensor can be potentially used in mobile medical
monitoring devices and next-generation artificial e-skin.
Advancement
of sensing systems, soft robotics, and point-of-care
testing requires the development of highly efficient, scalable, and
cost-effective physical sensors with competitive and attractive features
such as high sensitivity, reliability, and preferably reversible sensing
behaviors. This study reports a highly sensitive and reliable piezoresistive
strain sensor fabricated by one-step carbonization of the MoS2-coated polyimide film to obtain MoS2-decorated
laser-induced graphene. The resulting three-dimensional porous graphene
nanoflakes decorated with MoS2 exhibit stable electrical
properties yielding a reliable output for longer strain/release cycles.
The sensor demonstrates high sensitivity (i.e., gauge factor, GF ≈1242),
is hysteresis-free (∼2.75%), and has a wide working range (up
to 37.5%), ultralow detection limit (0.025%), fast relaxation time
(∼0.17 s), and a highly stable and reproducible response over
multiple test cycles (>12 000) with excellent switching
response.
Owing to the outstanding performances of the sensor, it is possible
to successfully detect various subtle movements ranging from phonation,
eye-blinking, and wrist pulse to large human-motion-induced deformations.
Smart electronic skin (e‐skin) requires the easy incorporation of multifunctional sensors capable of mimicking skin‐like perception in response to external stimuli. However, efficient and reliable measurement of multiple parameters in a single functional device is limited by the sensor layout and choice of functional materials. The outstanding electrical properties of black phosphorus and laser‐engraved graphene (BP@LEG) demonstrates a new paradigm for a highly sensitive dual‐modal temperature and strain sensor platform to modulate e‐skin sensing functionality. Moreover, the unique hybridized sensor design enables efficient and accurate determination of each parameter without interfering with each other. The cationic polymer passivated BP@LEG composite material on polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) substrate outperforms as a positive temperature coefficient material, exhibiting a high thermal index of 8106 K (25–50 °C) with high strain sensitivity (i.e., gauge factor, GF) of up to 2765 (>19.2%), ultralow strain resolution of 0.023%, and longer durability (>18 400 cycles), satisfying the e‐skin requirements. Looking forward, this technique provides unique opportunities for broader applications, such as e‐skin, robotic appendages, and health monitoring technologies.
In this study, a flexible and highly sensitive capacitive pressure sensor has been fabricated by coating a microporous polydimethylsiloxane (PDMS) elastomeric dielectric onto conductive fibers.
Pressure sensors with highly sensitive and flexible characteristics have extensive applications in wearable electronics, soft robotics, human–machine interface, and more. Herein, an effective strategy is explored to enhance the sensitivity of the capacitive pressure sensor by fabricating a dielectric hybrid sponge consisting of calcium copper titanate (CaCu3Ti4O12, CCTO), a giant dielectric permittivity material, in polyurethane (PU). An ultrasoft CCTO@PU hybrid sponge is fabricated via dip‐coating the PU sponge into surface‐modified CCTO nanoparticles using 3‐aminopropyl triethoxysilane. The overall results show that the –NH2 functionalized CCTO attributes proper adhesion of CCTO with the –OCN group of the PU to enhance interfacial polarization leading to a high dielectric permittivity (167.05) and low loss tangent (0.71) beneficial for flexible pressure sensing applications. Moreover, the as‐prepared CCTO@PU hybrid sponge at 30 wt% CCTO concentration exhibits excellent electromechanical properties with an ultralow compression modulus of 27.83 kPa and a high sensitivity of 0.73 kPa−1 in a low‐pressure regime (<1.6 kPa). Finally, pressure and strain sensing performance is demonstrated for the detection of human activities by mounting the sensor on various parts of the human body. The work reveals a new opportunity for the facile fabrication of high performance CCTO‐based capacitive sensors with multifunctional properties.
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