This work reports the fabrication of a titanium carbide nanoparticle-based inkjet printed flexible bidirectional flow sensor. The design of the flow sensor consists of an inkjet printed titanium carbide piezoresistive strain gauge on a polyester cantilever. The sensors demonstrated a normalized flow sensitivity of 1.043/(ms-1) in the velocity range 0.15 - 0.55 m/s (for water flow). The fabrication method reported in this work potentially opens a new direction for fabrication of a class of robust, repeatable, and inexpensive flexible flow sensors.

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In this work, we report a class of fabric-like flexible and wearable capacitive sensors utilizing electrospun polyvinyl acetate (PV Ac)-graphene nanofibers for human motion monitoring applications. The sensor reported in this work features flexible PV Ac-graphene thin film sandwiched between two layers of conductive fabric and fully encapsulated in transparent adhesive films. The fabricated pressure sensor demonstrates two linear regimes with sensitivity figures of 0.0136 kPa-1 (pressure < 75 kPa) and 0.0063 kPa-1 (pressure > 75 kPa), respectively. The realized pressure sensor is flexible and apparel integrable, and the facile fabrication method will enable reliable and repeatable performance over roll-to-roll manufacturing suitable for mass production.

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During the past few decades, a significant amount of research effort has been dedicated toward developing skin-inspired sensors for real-time human motion monitoring and next-generation robotic devices. Although several flexible and wearable sensors have been developed in the past, the need of the hour is developing accurate, reliable, sophisticated, facile yet inexpensive flexible sensors coupled with neuromorphic systems or spiking neural networks to encode tactile information without the need for complex digital architectures, thus achieving true skin-like sensing with limited resources. In this work, we propose an approach entailing carbon nanofiber-polydimethylsiloxane composite-based piezoresistive sensors, coupled with spiking neural networks, to mimic skin-like sensing. The strain and pressure sensors have been combined with appropriately designed neural networks to encode analog voltages to spikes to recreate bioinspired tactile sensing and proprioception. To further validate the proprioceptive capability of the system, a gesture tracking smart glove, combined with a spiking neural network, was demonstrated. Wearable and flexible sensors with accompanying neural networks such as the ones proposed in this work will pave the way for a future generation of skin-mimetic sensors for advanced prosthetic devices, apparel integrable smart sensors for human motion monitoring, and human-machine interfaces.

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In this work, we report a class of wearable, stitchable, and sensitive carbon nanofiber (CNF)-polydimethylsiloxane (PDMS) composite-based piezoresistive sensors realized by carbonizing electrospun polyacrylonitrile (PAN) nanofibers and subsequently embedding in PDMS elastomeric thin films. Electro-mechanical tactile sensing characterization of the resulting piezoresistive strain sensors revealed a linear response with an average force sensitivity of ~1.82 kN⁻¹ for normal forces up to 20 N. The real-time functionality of the CNF-PDMS composite sensors in wearable body sensor networks and advanced bionic skin applications was demonstrated through human motion and gesture monitoring experiments. A skin-inspired artificial soft sensor capable of demonstrating proprioceptive and tactile sensory perception utilizing CNF bundles has been shown. Furthermore, a 16-point pressure-sensitive flexible sensor array mimicking slow adapting low threshold mechanoreceptors of glabrous skin was demonstrated. Such devices in tandem with neuromorphic circuits can potentially recreate the sense of touch in robotic arms and restore somatosensory perception in amputees.

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Self-powered wearable devices are gaining increasing attention to fulfil the sensing and energy harvesting needs for the next-generation wearable systems and body sensor networks. Here, we developed a wearable, flexible and lightweight nanofiber-based triboelectric nanogenearator (NF-TENG) for body motion energy harvesting. Polyvinylidene difluoride (PVDF) and nylon were electrospun into nanofiber films to form the two triboelectric materials. Under a load force of 10 N, the NF-TENG could generate an output voltage of 140 V, current of 0.5 μA and transferred charges of 50 nC. Preliminary body energy harvesting applications of the proposed NF-TENG were demonstrated, wherein the NF-TENG was able to generate an output voltage of 8 V and 10 V during typing and elbow bending, respectively.

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In this age of advanced smartphones and wearable devices, the need of unlimited power has become a basic necessity. Most of the gadgets rely on some sort of power source in the form of batteries or power adapters. For example, smart watches have become very common these days and have a huge potential for implementation of energy harvesters. In near future it will be really desirable to have self-powered smart wearable devices which meet their energy needs by scavenging mechanical energy produced by physical activities. In order to solve the problem of fast battery depletion in modern smart devices, a lot of research has been carried out in the field of energy harvesters especially using thin film technologies and polymer nanofibers. Most interesting among them are the nanogenerators using polymers with piezoelectric properties like PVDF due to their low production cost and high conversion efficiency. Polymer-based nanofiber energy harvesters are not only relevant for wearable devices and smartphones but also for biomedical energy scavenging applications primarily due to their biocompatibility. Chapter 2 particularly deals with current scenario of different types of nanofiber-based energy harvesters. A comprehensive review related to current research work going on in the field of nanofiber-based energy harvesters is presented here.@en

Chapter 3 presents a comprehensive review of the various biomimetic self-powered and low-powered MEMS pressure and flow sensors that take inspiration from the biological flow sensors found in the marine world. The sensing performance of the biological flow sensors in marine animals has inspired engineers and scientists to develop efficient state-of-the-art sensors for a variety of real-life applications. In an attempt to achieve high-performance artificial flow sensors, researchers have mimicked the morphology, sensing principle, materials, and functionality of the biological sensors. Inspiration was derived from the survival hydrodynamics featured by various marine animals to develop sensors for sensing tasks in underwater vehicles. The mechanoreceptors of crocodiles have inspired the development of slowly and rapidly adapting MEMS sensory domes for passive underwater sensing. Likewise, the lateral line sensing system in fishes which is capable of generating a three-dimensional map of the surroundings was mimicked to achieve artificial hydrodynamic vision on underwater vehicles. Harbor seals are known to achieve high sensitivity in sensing flows within the wake street of a swimming fish due to the undulatory geometry of the whiskers. Whisker inspired structures were embedded into MEMS sensing membranes to understand their vortex shedding behavior. At the outset, this work comprehensively reviews the sensing mechanisms observed in fishes, crocodiles, and harbor seals. In addition, this chapter presents an in-depth commentary on the recent developments in this area where different researchers have taken inspiration from these aforementioned underwater creatures and developed some of the most efficient artificial sensing systems.@en