Accurate temperature field measurement provides critical information in many scientific problems. Herein, a new paradigm for highly sensitive, flexible, negative temperature coefficient (NTC) thermistor‐based artificial skin is reported, with the highest temperature sensing ability reported to date among previously reported NTC thermistors. This artificial skin is achieved through the development of a novel monolithic laser‐induced reductive sintering scheme and unique monolithic structures. The unique seamless monolithic structure simultaneously integrates two different components (a metal electrode and metal oxide sensing channel) from the same material at ambient pressure, which cannot be achieved by conventional heterogeneous integration through multiple, complex steps of photolithography or vacuum deposition. In addition to superior performance, electronic skin with high temperature sensitivity can be fabricated on heat‐sensitive polymer substrates due to the low‐temperature requirements of the process. As a proof of concept, temperature‐sensitive artificial skin is tested with conformally attachable physiological temperature sensor arrays in the measurement of the temperatures of exhaled breath for the early detection of pathogenic progression in the respiratory system. The proposed highly sensitive flexible temperature sensor and monolithic selective laser reductive sintering are expected to greatly contribute to the development of essential components in various emerging research fields, including soft robotics and healthcare systems.
Future electronics are expected to develop into wearable forms, and an adequate stretchability is required for the forthcoming wearable electronics considering various motions occurring in human body. Along with stretchability, transparency can increase both the functionality and esthetic features in future wearable electronics. In this study, we demonstrate, for the first time, a highly stretchable and transparent electromagnetic interference shielding layer for wearable electronic applications with silver nanowire percolation network on elastic poly(dimethylsiloxane) substrate. The proposed stretchable and transparent electromagnetic interference shielding layer shows a high electromagnetic wave shielding effectiveness even under a high tensile strain condition. It is expected for the silver nanowire percolation network-based electromagnetic interference shielding layer to be beyond the conventional electromagnetic interference shielding materials and to broaden its application range to various fields that require optical transparency or nonplanar surface environment, such as biological system, human skin, and wearable electronics.
Near-infrared spectroscopy (NIRS) can be employed to investigate brain activities associated with regional changes of the oxy- and deoxyhemoglobin concentration by measuring the absorption of near-infrared light through the intact skull. NIRS is regarded as a promising neuroimaging modality thanks to its excellent temporal resolution and flexibility for routine monitoring. Recently, the general linear model (GLM), which is a standard method for functional MRI (fMRI) analysis, has been employed for quantitative analysis of NIRS data. However, the GLM often fails in NIRS when there exists an unknown global trend due to breathing, cardiac, vasomotion, or other experimental errors. We propose a wavelet minimum description length (Wavelet-MDL) detrending algorithm to overcome this problem. Specifically, the wavelet transform is applied to decompose NIRS measurements into global trends, hemodynamic signals, and uncorrelated noise components at distinct scales. The minimum description length (MDL) principle plays an important role in preventing over- or underfitting and facilitates optimal model order selection for the global trend estimate. Experimental results demonstrate that the new detrending algorithm outperforms the conventional approaches.
To add more functionalities and overcome the limitation in conventional soft robots, highly anisotropic soft actuators with color shifting function during actuation is demonstrated for the first time. The electrothermally operating soft actuators with installed transparent metal nanowire percolation network heater allow easy programming of their actuation direction and instantaneous visualization of temperature changes through color change. Due to the unique direction dependent coefficient of thermal expansion mismatch, the suggested actuator demonstrates a highly anisotropic and reversible behavior with very large bending curvature (2.5 cm −1 ) at considerably low temperature (≈40 °C) compared to the previously reported electrothermal soft actuators. The mild operating heat condition required for the maximum curvature enables the superior long-term stability during more than 10 000 operating cycles. Also, the optical transparency of the polymer bilayer and metal nanowire percolation network heater allow the incorporation of the thermochromic pigments to fabricate color-shifting actuators. As a proof-of-concept, various color-shifting biomimetic soft robots such as color-shifting blooming flower, fluttering butterfly, and color-shifting twining tendril are demonstrated. The developed color-shifting anisotropic soft actuator is expected to open new application fields and functionalities overcoming the limitation of current soft robots.Unlike the conventional rigid actuators, the soft actuators are composed of elastic and lightweight materials with simple operating systems. [1] Due to their unique soft features, the soft actuators have been utilized in bioapplications such as artificial muscles, [2,3] soft manipulators, [4,5] biomimicking robots, [6][7][8][9] prosthesis, [10] and so on. The soft actuators operates by various physical, chemical, and optical stimulus such as electricity, [11][12][13][14][15] heat, [16][17][18] light, [7,8,19] magnetism, [20] pressure, [21] and humidity. [9,18,[22][23][24] Among them, considering the practical uses, the electrical signal has been the most popular input signal due to its easy and intuitive control of actuators. Typically the approaches to establish electrically operated soft actuators can be divided into two categories which are using electroactive polymeric (EAP) materials [4,5,12,15,25,26] and thermal expansive materials. [16][17][18]24,[27][28][29] However, since the EAP-based actuators need high operating voltage [4,5] and electrolyte environment, [12,25,26] their application in various fields is limited. On the other hand, the electrothermal actuator (ETA) which basically operates by different thermal expansive volume changes between the polymers composing a bilayer requires much lower operating voltage and Color-Changing Soft ActuatorsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.
instruments, and wearable assistive devices, but which mostly are restricted to discrete motions. However, soft robotics with entirely soft bodied system often solve difficulties in conventional rigid robots by overcoming their constraints, exceeding the performances and creating new applications. [1][2][3] Therefore, these soft machines have already taken many roles in industrial processing, automation, marine engineering, etc. [4][5][6] Technological advances in robots and wearable devices are closely connected to optical and mechanical compliance depending on their use. By taking advantages of recent advancements in transparent actuators and sensors, combining their soft and stretchy mechanical compliance with optically transparent property affords to create a new class of soft robotics, which can be referred to as an imperceptible soft robotics (ISR). As shown in Figure 1, systematic diagram of imperceptible soft robotics describes that ISR will mainly consist of transparent systems and camouflage skin. Transparent systems embrace optically transparent soft actuators and sensors in order to build mechanically interactive robotics that are rarely seen by others. As a supportive component, camouflage skin aims to provide for transparent systems to adapt in natural environment or humans for undercover operation and safe user-friendly interactions. This new conception of imperceptible soft robotic system that exhibits optically transparent interface or visually imperceptions through camouflage skin provides new functionalities over ones without such properties. Imperceptions of an assistive wearable device can be crucially important in wearer's daily life. Mechanically compliant and visually imperceptive human assistive device can serve the user's rehabilitation process or support disabled parts in the body without discomfort, altering biomechanics, and obstructive to others. [7] In a similar fashion, robotic prosthetics that requires soft sensing capability of motherly touch for caring babies demand integrated sensors and actuators to be imperceptible. [8] Tactile sensation with an implementation of ISR delivering information to user in private also possesses a wide range of possibility in virtual/augmented reality for human-machine interface and smart-living environment. [9][10][11][12] Undercover mission enabled by disguising into nature through optical transparency or environmentally skin will also be achieved by imperceptibleThe advent of soft robotics has led to great advancements in robots, wear ables, and even manufacturing processes by employing entirely soft-bodied systems that interact safely with any random surfaces while providing great mechanical compliance. Moreover, recent developments in soft robotics involve advances in transparent soft actuators and sensors that have made it possible to construct robots that can function in a visually and mechanically unobstructed manner, assisting the operations of robots and creating more applications in various fields. In this aspect, imperceptible soft robo...
Along with visual and tactile sensations, thermal sensation by temperature feeling on the skin can provide rich physical information on the environment and objects. With a simple touch of objects, relative temperature can be sensed and even objects can be differentiated with different thermal properties without any visual cue. Thus, artificially reproducing accurate/controllable thermal sensation haptic signals on human epidermis will certainly be a major research area to reconstruct a more realistic virtual reality (VR) environment. In this study, for the first time, a skin‐like, highly soft and stretchable and bi‐functional (both cold and hot sensation) thermo‐haptic device is reported for wearable VR applications with a single device structure (not separate heater and cooler). The skin‐like thermo‐haptic (STH) device can actively cool down and heat up deformable skin surfaces with instantaneous and accurate adjustment of temperature based upon a feedback control algorithm to mimic desirable thermal sensation with 230% stretchability. As a proof‐of‐concept, the STH device is integrated with a finger‐motion tracking glove to provide artificial thermal sensation information to the skin in various situations such as touching cold beer bottles and hot coffee cups in virtual space. This new type of STH device can offer potential implications for next‐generation haptic devices to provide unique thermal information for a more realistic virtual‐world field and medical thermal treatment.
This review focuses on the silver nanowires (Ag NWs) based stretchable and flexible energy devices for self-sustainable devices.
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