Soft eSkin: distributed touch sensing with harmonized energy and computing

An overview of critical applications of resistive random access memory

The rapid advancement of new technologies has resulted in a surge of data, while conventional computers are nearing their computational limits. The prevalent von Neumann architecture, where processing and storage units operate independently, faces challenges such as data migration through buses, leading to decreased computing speed and increased energy loss. Ongoing research aims to enhance computing capabilities through the development of innovative chips and the adoption of new system architectures. One noteworthy advancement is Resistive Random Access Memory (RRAM), an emerging memory technology. RRAM can alter its resistance through electrical signals at both ends, retaining its state even after power-down. This technology holds promise in various areas, including logic computing, neural networks, brain-like computing, and integrated technologies combining sensing, storage, and computing. These cutting-edge technologies offer the potential to overcome the performance limitations of traditional architectures, significantly boosting computing power. This discussion explores the physical mechanisms, device structure, performance characteristics, and applications of RRAM devices. Additionally, we delve into the potential future adoption of these technologies at an industrial scale, along with prospects and upcoming research directions.

Neuromorphic Nanoionics for Human-Machine Interaction: From Materials to Applications

Human-machine interaction (HMI) technology has undergone significant advancements in recent years, enabling seamless communication between humans and machines. Its expansion has extended into various emerging domains, including human healthcare, machine perception, and biointerfaces, thereby magnifying the demand for advanced intelligent technologies. Neuromorphic computing, a paradigm rooted in nanoionic devices that emulate the operations and architecture of the human brain, has emerged as a powerful tool for highly efficient information processing. This paper delivers a comprehensive review of recent developments in nanoionic device-based neuromorphic computing technologies and their pivotal role in shaping the next-generation of HMI. Through a detailed examination of fundamental mechanisms and behaviors, the paper explores the ability of nanoionic memristors and ion-gated transistors to emulate the intricate functions of neurons and synapses. Crucial performance metrics, such as reliability, energy efficiency, flexibility, and biocompatibility, are rigorously evaluated. Potential applications, challenges, and opportunities of using the neuromorphic computing technologies in emerging HMI technologies, are discussed and outlooked, shedding light on the fusion of humans with machines.

Spike timing-based coding in neuromimetic tactile system enables dynamic object classification

Rapid processing of tactile information is essential to human haptic exploration and dexterous object manipulation. Conventional electronic skins generate frames of tactile signals upon interaction with objects. Unfortunately, they are generally ill-suited for efficient coding of temporal information and rapid feature extraction. In this work, we report a neuromorphic tactile system that uses spike timing, especially the first-spike timing, to code dynamic tactile information about touch and grasp. This strategy enables the system to seamlessly code highly dynamic information with millisecond temporal resolution on par with the biological nervous system, yielding dynamic extraction of tactile features. Upon interaction with objects, the system rapidly classifies them in the initial phase of touch and grasp, thus paving the way to fast tactile feedback desired for neuro-robotics and neuro-prosthetics.

Emerging Iontronic Neural Devices for Neuromorphic Sensory Computing

Living organisms have a very mysterious and powerful sensory computing system based on ion activity. Interestingly, studies on iontronic devices in the past few years have proposed a promising platform for simulating the sensing and computing functions of living organisms, because: 1) iontronic devices can generate, store, and transmit a variety of signals by adjusting the concentration and spatiotemporal distribution of ions, which analogs to how the brain performs intelligent functions by alternating ion flux and polarization; 2) through ionic-electronic coupling, iontronic devices can bridge the biosystem with electronics and offer profound implications for soft electronics; 3) with the diversity of ions, iontronic devices can be designed to recognize specific ions or molecules by customizing the charge selectivity, and the ionic conductivity and capacitance can be adjusted to respond to external stimuli for a variety of sensing schemes, which can be more difficult for electron-based devices. This review provides a comprehensive overview of emerging neuromorphic sensory computing by iontronic devices, highlighting representative concepts of both low-level and high-level sensory computing and introducing important material and device breakthroughs. Moreover, iontronic devices as a means of neuromorphic sensing and computing are discussed regarding the pending challenges and future directions.

COVID-19 clinical waste reuse: A triboelectric touch sensor for IoT-cloud supported smart hand sanitizer dispenser

Earth's plastic pollution has increased due to the COVID-19 pandemic, and the world is on the doorstep of an enormous waste pandemic. The extensive use of mandatory personal protectives like masks, gloves, and PPE kits and the lack of proper waste management systems lead to a rise in the plastic pollution content of the earth. Such disposable and non-biodegradable personal protectives are thrown out to the environment after use. These distributed wastes pollute land, soil, and water bodies and effects their ecosystems. This research work establishes the concept of a waste-to-energy conversion approach to reuse COVID-19 scraps for green and sustainable development. Three-layered surgical masks and nitrile gloves were reused in this work after sterilization for energy harvesting and sensing applications by fabricating a 3D-printed contact-separation-based triboelectric nanogenerator. A piece of three-layered mask and nitrile gloves were placed inside the 3D structure as the top negative and bottom positive triboelectric materials with copper and aluminum as corresponding electrodes (MG-CS TENG). It can convert external mechanical motions into electrical energy. The maximum voltage, current, and power density obtained from the device are 50.7 V, 4.8 µA, and 6.39 µW/cm2, respectively, for a mechanical force of 9 N. The harvested energy was sufficient to power small-scale electronic devices like digital tally counters, wristwatches, lumex displays, and series connected 25 LEDs. MG-CS TENG was also performed as a pedal-operated touch sensor to dispense hand sanitizer. MG-CS TENG was pedal pressed to trigger a microcontroller and control the solenoid valve's opening and closing to regulate sanitizer flow. The setup was integrated using the internet of things (IoT) and Blynk cloud services for the remote monitoring and controlling of the sanitizer dispenser using a smartphone. This work contributes a substantial role in disaster management to suppress microplastic environmental pollution by reusing pandemic wastes for energy harvesting and sensing applications and preventing the spread of coronavirus through proper hand sanitization.

Emerging memristive neurons for neuromorphic computing and sensing

Inspired by the principles of the biological nervous system, neuromorphic engineering has brought a promising alternative approach to intelligence computing with high energy efficiency and low consumption. As pivotal components of neuromorphic system, artificial spiking neurons are powerful information processing units and can achieve highly complex nonlinear computations. By leveraging the switching dynamic characteristics of memristive device, memristive neurons show rich spiking behaviors with simple circuit. This report reviews the memristive neurons and their applications in neuromorphic sensing and computing systems. The switching mechanisms that endow memristive devices with rich dynamics and nonlinearity are highlighted, and subsequently various nonlinear spiking neuron behaviors emulated in these memristive devices are reviewed. Then, recent development is introduced on neuromorphic system with memristive neurons for sensing and computing. Finally, we discuss challenges and outlooks of the memristive neurons toward high-performance neuromorphic hardware systems and provide an insightful perspective for the development of interactive neuromorphic electronic systems.

Skin-Inspired Thermoreceptors-Based Electronic Skin for Biomimicking Thermal Pain Reflexes

Electronic systems possessing skin-like morphology and functionalities (electronic skins [e-skins]) have attracted considerable attention in recent years to provide sensory or haptic feedback in growing areas such as robotics, prosthetics, and interactive systems. However, the main focus thus far has been on the distributed pressure or force sensors. Herein a thermoreceptive e-skin with biological systems like functionality is presented. The soft, distributed, and highly sensitive miniaturized (≈700 µm2 ) artificial thermoreceptors (ATRs) in the e-skin are developed using an innovative fabrication route that involves dielectrophoretic assembly of oriented vanadium pentoxide nanowires at defined locations and high-resolution electrohydrodynamic printing. Inspired from the skin morphology, the ATRs are embedded in a thermally insulating soft nanosilica/epoxy polymeric layer and yet they exhibit excellent thermal sensitivity (-1.1 ± 0.3% °C-1 ), fast response (≈1s), exceptional stability (negligible hysteresis for >5 h operation), and mechanical durability (up to 10 000 bending and twisting loading cycles). Finally, the developed e-skin is integrated on the fingertip of a robotic hand and a biological system like reflex is demonstrated in response to temperature stimuli via localized learning at the hardware level.

Recent Advances in Transistor-Based Bionic Perceptual Devices for Artificial Sensory Systems

The sensory nervous system serves as the window for human beings to perceive the outside world by converting external stimuli into distinctive spiking trains. The sensory neurons in this system can process multimodal sensory signals with extremely low power consumption. Therefore, new-concept devices inspired by the sensory neuron are promising candidates to address energy issues in nowadays’ robotics, prosthetics and even computing systems. Recent years have witnessed rapid development in transistor-based bionic perceptual devices, and it is urgent to summarize the research and development of these devices. In this review, the latest progress of transistor-based bionic perceptual devices for artificial sense is reviewed and summarized in five aspects, i.e., vision, touch, hearing, smell, and pain. Finally, the opportunities and challenges related to these areas are also discussed. It would have bright prospects in the fields of artificial intelligence, prosthetics, brain-computer interface, robotics, and medical testing.

Neuro-inspired electronic skin for robots

Touch is a complex sensing modality owing to large number of receptors (mechano, thermal, pain) nonuniformly embedded in the soft skin all over the body. These receptors can gather and encode the large tactile data, allowing us to feel and perceive the real world. This efficient somatosensation far outperforms the touch-sensing capability of most of the state-of-the-art robots today and suggests the need for neural-like hardware for electronic skin (e-skin). This could be attained through either innovative schemes for developing distributed electronics or repurposing the neuromorphic circuits developed for other sensory modalities such as vision and audio. This Review highlights the hardware implementations of various computational building blocks for e-skin and the ways they can be integrated to potentially realize human skin-like or peripheral nervous system-like functionalities. The neural-like sensing and data processing are discussed along with various algorithms and hardware architectures. The integration of ultrathin neuromorphic chips for local computation and the printed electronics on soft substrate used for the development of e-skin over large areas are expected to advance robotic interaction as well as open new avenues for research in medical instrumentation, wearables, electronics, and neuroprosthetics.

Printed synaptic transistor-based electronic skin for robots to feel and learn

An electronic skin (e-skin) for the next generation of robots is expected to have biological skin-like multimodal sensing, signal encoding, and preprocessing. To this end, it is imperative to have high-quality, uniformly responding electronic devices distributed over large areas and capable of delivering synaptic behavior with long- and short-term memory. Here, we present an approach to realize synaptic transistors (12-by-14 array) using ZnO nanowires printed on flexible substrate with 100% yield and high uniformity. The presented devices show synaptic behavior under pulse stimuli, exhibiting excitatory (inhibitory) post-synaptic current, spiking rate-dependent plasticity, and short-term to long-term memory transition. The as-realized transistors demonstrate excellent bio-like synaptic behavior and show great potential for in-hardware learning. This is demonstrated through a prototype computational e-skin, comprising event-driven sensors, synaptic transistors, and spiking neurons that bestow biological skin-like haptic sensations to a robotic hand. With associative learning, the presented computational e-skin could gradually acquire a human body-like pain reflex. The learnt behavior could be strengthened through practice. Such a peripheral nervous system-like localized learning could substantially reduce the data latency and decrease the cognitive load on the robotic platform.

Living wearables: Bacterial reactive glove

A reactive bacterial glove is a cotton glove colonised by Acetobacter aceti, an example of biofabrication of a living electronic sensing device. The bacterial colony, supported by a cellulose-based hydrogel, forms a several millimetres-thick living coating on the surface of the glove. This paper proposes a novel method for analysing the complex electrical activity of trains of spikes generated by a living colony. The proposed method, which primarily focuses on dynamic entropy analysis, shows that the bacterial glove responds to mechanical triaxial stimuli by producing travelling patterns of electrical activity. Kolmogorov complexity further supports our investigation into the evolution of dynamic patterns of such waves in the hydrogel and shows how stimuli initiate electrical activity waves across the glove. These waves are diffractive and ultimately are suppressed by depression. Our experiments demonstrate that living substrates could be used to enable reactive sensing wearable by means of living colonies of bacteria, once the paradigm of excitation wave propagation and reflection is implemented.

Fungal electronics

Fungal electronics is a family of living electronic devices made of mycelium bound composites or pure mycelium. Fungal electronic devices are capable of changing their impedance and generating spikes of electrical potential in response to external control parameters. Fungal electronics can be embedded into fungal materials and wearables or used as stand alone sensing and computing devices.

Recent Progress in Flexible Tactile Sensors for Human-Interactive Systems: From Sensors to Advanced Applications

Flexible tactile sensors capable of measuring mechanical stimuli via physical contact have attracted significant attention in the field of human-interactive systems. The utilization of tactile information can complement vision and/or sound interaction and provide new functionalities. Recent advancements in micro/nanotechnology, material science, and information technology have resulted in the development of high-performance tactile sensors that reach and even surpass the tactile sensing ability of human skin. Here, important advances in flexible tactile sensors over recent years are summarized, from sensor designs to system-level applications. This review focuses on the representative strategies based on design and material configurations for improving key performance parameters including sensitivity, detection range/linearity, response time/hysteresis, spatial resolution/crosstalk, multidirectional force detection, and insensitivity to other stimuli. System-level integration for practical applications beyond conceptual prototypes and promising applications, such as artificial electronic skin for robotics and prosthetics, wearable controllers for electronics, and bidirectional communication tools, are also discussed. Finally, perspectives on issues regarding further advances are provided.

MnOx-Electrodeposited Fabric-Based Stretchable Supercapacitors with Intrinsic Strain Sensing

The increasing number of devices needed by wearable systems to bring radical advances in healthcare, robotics, and human-machine interfaces is a threat to their growth if the integration and energy-related challenges are not managed. A natural solution is to reduce the number of devices while retaining the functionality or simply using multifunctional devices, as demonstrated here through a stretchable supercapacitor (SSC) with intrinsic strain sensing. The presented SSC was obtained by electrodeposition of nanoflower MnO_x on fabric (as a pseudocapacitive electrode) and three-dimensional conductive wrapping of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to boost the performance. Among fabricated devices, the stretchable PEDOT:PSS/MnO_x/PEDOT:PSS supercapacitor (SPMP-SC) showed the best performance (specific capacitance of 580 mF·cm^-2 (108.1 F·g^-1); energy density of 51.4 μWh·cm^-2 at 0.5 mA). The stretchability (0-100%; 1000 cycles) analysis of SPMP-SC with Ecoflex encapsulation showed high capacitance retention (>90% for 40% stretch). The intrinsic strain sensing of the SSC was confirmed by the linear variation of capacitance (sensitivity -0.4%) during stretching. Finally, as a proof-of-concept, the application of SSC with intrinsic sensing was demonstrated for health monitoring through volumetric expansion of a manikin during ventilator operation and in robotics and by measuring the joint angle of a robotic hand.

Channel-Crack-Designed Suspended Sensing Membrane as a Fully Flexible Vibration Sensor with High Sensitivity and Dynamic Range

Vibration sensors are essential for signal acquisition, motion measuring, and structural health evaluations in civil and industrial applications. However, the mechanical brittleness and complicated installation process of micro-electromechanical system vibration sensors block their applications in wearable devices and human-machine interaction. The development of flexible vibration sensors satisfying the requirements of good flexibility, high sensitivity, and the ability to attach conformably on curved critical components is highly demanded but still remains a challenge. Here, we demonstrate a highly sensitive and fully flexible vibration sensor with a channel-crack-designed suspended sensing membrane for high dynamic vibration and acceleration monitoring. The flexible sensor is designed as a suspended vibration membrane structure by bonding a channel-crack-sensing membrane on a cavity substrate, of which the suspended sensing membrane can freely vibrate out of plane under external vibration. By inducing the cracks to be generated in the embedded multiwalled carbon nanotube channels and fully cracked across the conducting routes, the suspended vibration membrane shows high sensitivity, good reproducibility, and robust sensing stability. The resultant vibration sensor demonstrates an ultrawide frequency vibration response range from 0.1 to 20,000 Hz and exhibits the ability to respond to acceleration vibration with a broad response of 0.24-100 m/s². The high sensitivity, wide bandwidth, and fully flexible format of the vibration sensor enable it to be directly attached on human bodies and curvilinear surfaces to conduct in situ vibration sensing, which was demonstrated by motion detection, voice identification, and the vibration monitoring of mechanical equipment.

Towards fungal sensing skin

A fungal skin is a thin flexible sheet of a living homogeneous mycelium made by a filamentous fungus. The skin could be used in future living architectures of adaptive buildings and as a sensing living skin for soft self-growing/adaptive robots. In experimental laboratory studies we demonstrate that the fungal skin is capable for recognising mechanical and optical stimulation. The skin reacts differently to loading of a weight, removal of the weight, and switching illumination on and off. These are the first experimental evidences that fungal materials can be used not only as mechanical 'skeletons' in architecture and robotics but also as intelligent skins capable for recognition of external stimuli and sensorial fusion.

Artificial Skin Perception

Skin is the largest organ, with the functionalities of protection, regulation, and sensation. The emulation of human skin via flexible and stretchable electronics gives rise to electronic skin (e-skin), which has realized artificial sensation and other functions that cannot be achieved by conventional electronics. To date, tremendous progress has been made in data acquisition and transmission for e-skin systems, while the implementation of perception within systems, that is, sensory data processing, is still in its infancy. Integrating the perception functionality into a flexible and stretchable sensing system, namely artificial skin perception, is critical to endow current e-skin systems with higher intelligence. Here, recent progress in the design and fabrication of artificial skin perception devices and systems is summarized, and challenges and prospects are discussed. The strategies for implementing artificial skin perception utilize either conventional silicon-based circuits or novel flexible computing devices such as memristive devices and synaptic transistors, which enable artificial skin to surpass human skin, with a distributed, low-latency, and energy-efficient information-processing ability. In future, artificial skin perception would be a new enabling technology to construct next-generation intelligent electronic devices and systems for advanced applications, such as robotic surgery, rehabilitation, and prosthetics.

Acetobacter Biofilm: Electronic Characterization and Reactive Transduction of Pressure

The bacterial skin studied here is a several centimeter-wide colony of Acetobacter aceti living on a cellulose-based hydrogel. We demonstrate that the colony exhibits trains of spikes of extracellular electrical potential, with amplitudes of the spikes varying from 1 to 17 mV. The bacterial pad responds to mechanical stimulation with distinctive changes in its electrical activity. While studying the passive electrical properties of the bacterial pad, we found that the pad provides an open-circuit voltage drop (between 7 and 25 mV) and a small short-circuit current (1.5-4 nA). We also observed by pulsed tomography and spatially resolved impedance spectroscopy that the conduction occurs along preferential paths, with the peculiar side-effect of having a higher resistance between closer electrodes. We speculate that the Acetobacter biofilms could be utilized in the development of living skin for soft robots: such skin will act as an electrochemical battery and a reactive tactile sensor. It could even be used for wearable devices.

Flexible Artificial Sensory Systems Based on Neuromorphic Devices

Emerging flexible artificial sensory systems using neuromorphic electronics have been considered as a promising solution for processing massive data with low power consumption. The construction of artificial sensory systems with synaptic devices and sensing elements to mimic complicated sensing and processing in biological systems is a prerequisite for the realization. To realize high-efficiency neuromorphic sensory systems, the development of artificial flexible synapses with low power consumption and high-density integration is essential. Furthermore, the realization of efficient coupling between the sensing element and the synaptic device is crucial. This Review presents recent progress in the area of neuromorphic electronics for flexible artificial sensory systems. We focus on both the recent advances of artificial synapses, including device structures, mechanisms, and functions, and the design of intelligent, flexible perception systems based on synaptic devices. Additionally, key challenges and opportunities related to flexible artificial perception systems are examined, and potential solutions and suggestions are provided.

Fungal sensing skin

BACKGROUND

A fungal skin is a thin flexible sheet of a living homogeneous mycelium made by a filamentous fungus. The skin could be used in future living architectures of adaptive buildings and as a sensing living skin for soft self-growing/adaptive robots.

RESULTS

In experimental laboratory studies we demonstrate that the fungal skin is capable for recognising mechanical and optical stimulation. The skin reacts differently to loading of a weight, removal of the weight, and switching illumination on and off.

CONCLUSION

These are the first experimental evidences that fungal materials can be used not only as mechanical 'skeletons' in architecture and robotics but also as intelligent skins capable for recognition of external stimuli and sensorial fusion.

Tactile sensing biohybrid soft E-skin based on bioimpedance using aloe vera pulp tissues

Soft and flexible E-skin advances are a subset of soft robotics field where the soft morphology of human skin is mimicked. The number of prototypes that conformed the use of biological tissues within the structure of soft robots—to develop “Biohybrid Soft Robots”—has increased in the last decade. However, no research was conducted to realize Biohybrid E-skin. In this paper, a novel biohybrid E-skin that provides tactile sensing is developed. The biohybrid E-skin highly mimics the human skin softness and morphology and can sense forces as low as 0.01 newton . The tactile sensing feature is augmented through the use of Aloe Vera pulp, embedded in underlying channel, where the change in its bioimpedance is related to the amount of force exerted on the E-skin surface. The biohybrid E-skin employs high biomimicry as the sensorial output is an oscillating signal similar to signals sent from the human sensing neurons to the brain. After investigating different channel geometries, types of filling tissues, and usage of two silicone materials, their frequency-force behaviour is modelled mathematically. Finally, a functional multichannel prototype “ImpEdded Skin” is developed. This prototype could efficiently detect the position of a tactile touch. This work employs the development of discrete sensing system that exhibits morphological computation that consequently enhances performance.

Biodegradable Materials for Sustainable Health Monitoring Devices

The recent advent of biodegradable materials has offered huge opportunity to transform healthcare technologies by enabling sensors that degrade naturally after use. The implantable electronic systems made from such materials eliminate the need for extraction or reoperation, minimize chronic inflammatory responses, and hence offer attractive propositions for future biomedical technology. The eco-friendly sensor systems developed from degradable materials could also help mitigate some of the major environmental issues by reducing the volume of electronic or medical waste produced and, in turn, the carbon footprint. With this background, herein we present a comprehensive overview of the structural and functional biodegradable materials that have been used for various biodegradable or bioresorbable electronic devices. The discussion focuses on the dissolution rates and degradation mechanisms of materials such as natural and synthetic polymers, organic or inorganic semiconductors, and hydrolyzable metals. The recent trend and examples of biodegradable or bioresorbable materials-based sensors for body monitoring, diagnostic, and medical therapeutic applications are also presented. Lastly, key technological challenges are discussed for clinical application of biodegradable sensors, particularly for implantable devices with wireless data and power transfer. Promising perspectives for the advancement of future generation of biodegradable sensor systems are also presented.

A spiking and adapting tactile sensor for neuromorphic applications

The ongoing research on and development of increasingly intelligent artificial systems propels the need for bio inspired pressure sensitive spiking circuits. Here we present an adapting and spiking tactile sensor, based on a neuronal model and a piezoelectric field-effect transistor (PiezoFET). The piezoelectric sensor device consists of a metal-oxide semiconductor field-effect transistor comprising a piezoelectric aluminium-scandium-nitride (AlxSc1-xN) layer inside of the gate stack. The so augmented device is sensitive to mechanical stress. In combination with an analogue circuit, this sensor unit is capable of encoding the mechanical quantity into a series of spikes with an ongoing adaptation of the output frequency. This allows for a broad application in the context of robotic and neuromorphic systems, since it enables said systems to receive information from the surrounding environment and provide encoded spike trains for neuromorphic hardware. We present numerical and experimental results on this spiking and adapting tactile sensor.

High-performance printed electronics based on inorganic semiconducting nano to chip scale structures

The Printed Electronics (PE) is expected to revolutionise the way electronics will be manufactured in the future. Building on the achievements of the traditional printing industry, and the recent advances in flexible electronics and digital technologies, PE may even substitute the conventional silicon-based electronics if the performance of printed devices and circuits can be at par with silicon-based devices. In this regard, the inorganic semiconducting materials-based approaches have opened new avenues as printed nano (e.g. nanowires (NWs), nanoribbons (NRs) etc.), micro (e.g. microwires (MWs)) and chip (e.g. ultra-thin chips (UTCs)) scale structures from these materials have been shown to have performances at par with silicon-based electronics. This paper reviews the developments related to inorganic semiconducting materials based high-performance large area PE, particularly using the two routes i.e. Contact Printing (CP) and Transfer Printing (TP). The detailed survey of these technologies for large area PE onto various unconventional substrates (e.g. plastic, paper etc.) is presented along with some examples of electronic devices and circuit developed with printed NWs, NRs and UTCs. Finally, we discuss the opportunities offered by PE, and the technical challenges and viable solutions for the integration of inorganic functional materials into large areas, 3D layouts for high throughput, and industrial-scale manufacturing using printing technologies.

Tacsac: A Wearable Haptic Device with Capacitive Touch-Sensing Capability for Tactile Display

This paper presents a dual-function wearable device (Tacsac) with capacitive tactile sensing and integrated tactile feedback capability to enable communication among deafblind people. Tacsac has a skin contactor which enhances localized vibrotactile stimulation of the skin as a means of feedback to the user. It comprises two main modules—the touch-sensing module and the vibrotactile module; both stacked and integrated as a single device. The vibrotactile module is an electromagnetic actuator that employs a flexible coil and a permanent magnet assembled in soft poly (dimethylsiloxane) (PDMS), while the touch-sensing module is a planar capacitive metal-insulator-metal (MIM) structure. The flexible coil was fabricated on a 50 µm polyimide (PI) sheet using Lithographie Galvanoformung Abformung (LIGA) micromoulding technique. The Tacsac device has been tested for independent sensing and actuation as well as dual sensing-actuation mode. The measured vibration profiles of the actuator showed a synchronous response to external stimulus for a wide range of frequencies (10 Hz to 200 Hz) within the perceivable tactile frequency thresholds of the human hand. The resonance vibration frequency of the actuator is in the range of 60–70 Hz with an observed maximum off-plane displacement of 0.377 mm at coil current of 180 mA. The capacitive touch-sensitive layer was able to respond to touch with minimal noise both when actuator vibration is ON and OFF. A mobile application was also developed to demonstrate the application of Tacsac for communication between deafblind person wearing the device and a mobile phone user who is not deafblind. This advances existing tactile displays by providing efficient two-way communication through the use of a single device for both localized haptic feedback and touch-sensing.

Complex electrical spiking activity in resistive switching nanostructured Au two-terminal devices

Networks of nanoscale objects are the subject of increasing interest as resistive switching systems for the fabrication of neuromorphic computing architectures. Nanostructured films of bare gold clusters produced in gas phase with thickness well beyond the electrical percolation threshold, show a non-ohmic electrical behavior and resistive switching, resulting in groups of current spikes with irregular temporal organization. Here we report the systematic characterization of the temporal correlations between single spikes and spiking rate power spectrum of nanostructured Au two-terminal devices consisting of a cluster-assembled film deposited between two planar electrodes. By varying the nanostructured film thickness we fabricated two different classes of devices with high and low initial resistance respectively. We show that the switching dynamics can be described by a power law distribution in low resistance devices whereas a bi-exponential behavior is observed in the high resistance ones. The measured resistance of cluster-assembled films shows a [Formula: see text] scaling behavior in the range of analyzed frequencies. Our results suggest the possibility of using cluster-assembled Au films as components for neuromorphic systems where a certain degree of stochasticity is required.