The flexible strain sensor is of significant importance in wearable electronics, since it can help monitor the physical signals from the human body. Among various strain sensors, the foam-shaped ones have received widespread attention owing to their light weight and gas permeability. However, the working range of these sensors is still not large enough, and the sensitivity needs to be further improved. In this work, we develop a high-performance foam-shaped strain sensor composed of Ti 3 C 2 T x MXene, multiwalled carbon nanotubes (MWCNTs), and thermoplastic polyurethane (TPU). MXene sheets are adsorbed on the surface of a composite foam of MWCNTs and TPU (referred to as TPU/MWCNTs foam), which is prefabricated by using a salt-templating method. The obtained TPU/ MWCNTs@MXene foam works effectively as a lightweight, easily processable, and sensitive strain sensor. The TPU/MWCNTs@MXene device can deliver a wide working strain range of ∼100% and an outstanding sensitivity as high as 363 simultaneously, superior to the state-of-the-art foam-shaped strain sensors. Moreover, the composite foam shows an excellent gas permeability and suitable elastic modulus close to those of skin, indicating its being highly comfortable as a wearable sensor. Owing to these advantages, the sensor works effectively in detecting both subtle and large human movements, such as joint motion, finger motion, and vocal cord vibration. In addition, the sensor can be used for gesture recognition, demonstrating its perspective in humanmachine interaction. Because of the high sensitivity, wide working range, gas permeability, and suitable modulus, our foam-shaped composite strain sensor may have great potential in the field of flexible and wearable electronics in the near future.
Transparent e-skin that can fully
mimic human skin with J-shaped
mechanical-behavior and tactile sensing attributes have not yet been
reported. In this work, the skin-like hydrogel composite with J-shaped
mechanical behavior and highly transparent, tactile, soft but strong,
flexible, and stretchable attributes is developed as structural strain
sensing element for e-skin. Piezo-resistive polyacrylamide (PAAm)
hydrogel is used as supporting matrix to endow high transparency,
softness, flexibility, stretch-ability and strain sensing capability
desired for e-skin. Ultrahigh molecular weight polyethylene (UHMWPE)
fiber with a wavy configuration is designed as reinforcement filler
to provide the tunable strain-limiting effect. As a result, the as-prepared
UHMWPE fiber/PAAm composite e-skin presents unique “J-shape”
stress–strain behavior akin to human skin. And the PAAm composite
can switch from supersoft to highly stiff in the designed strain range
up to 100% with a prominent tensile strength of 48.3 MPa, which enables
it to have the high stretch-ability and excellent load-bearing ability,
simultaneously. Moreover, finite element model is developed to clarify
the stress distribution and damage evolution for the UHMWPE fiber/PAAm
composite during the tensile process. The PAAm composite exhibits
not only an excellent strain sensing performance with a long-term
reliability up to 5000 loading–unloading cycles but also an
extraordinary softness and mechanical strength with a low initial
modulus of 6.7 kPa, which is matchable with soft human epidermis.
Finally, the e-skin is used for demonstrations in monitoring various
human activities and protecting structural integrity in designed strain
ranges. The strategy for reinforcing piezo-resistive hydrogel with
wavy-shaped UHMWPE fibers proposed here is promising for the development
of transparent, flexible, soft but strong e-skin with a tunable strain-limiting
effect akin to human skin.
Pseudo mechanical impedance, as one of frequency response functions, characterizes the dynamic behavior of a mechanical system and is useful for applications for applications such as modal testing, mechanical design, vibration monitoring and control, structural coupling and theoretical model modifications. Dynamic measurement of impedance, iii ACKNOWLEDGEMENT I would like to express my sincere appreciation to my doctoral supervisor, Professor Dr Ling Shih-Fu, for his invaluable advice and guidance and constant support and encouragement throughout my study and research.
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