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Introduction To Electrodynamics

Cardiovascular diseases remain the leading cause of death worldwide. The rapid development of flexible sensing technologies and wearable pressure sensors have attracted keen research interest and have been widely used for long‐term and real‐time cardiovascular status monitoring. Owing to compelling characteristics, including light weight, wearing comfort, and high sensitivity to pulse pressures, physiological pulse waveforms can be precisely and continuously monitored by flexible pressure sensors for wearable health monitoring. Herein, an overview of wearable pressure sensors for human pulse wave monitoring is presented, with a focus on the transduction mechanism, microengineering structures, and related applications in pulse wave monitoring and cardiovascular condition assessment. The conceptualizations and methods for the acquisition of physiological and pathological information related to the cardiovascular system are outlined. The biomechanics of arterial pulse waves and the working mechanism of various wearable pressure sensors, including triboelectric, piezoelectric, magnetoelastic, piezoresistive, capacitive, and optical sensors, are also subject to systematic debate. Exemple applications of pulse wave measurement based on microengineering structured devices are then summarized. Finally, a discussion of the opportunities and challenges that wearable pressure sensors face, as well as their potential as a wearable intelligent system for personalized healthcare is given in conclusion.

Wearable Pressure Sensors for Pulse Wave Monitoring

More than 75% of the Earth surface is covered by water in the form of oceans. The oceans are unexplored and very far-fetched to investigate due to distinct phenomenal activities in the underwater environment. Underwater wireless communication (UWC) plays a significant role in observation of marine life, water pollution, oil and gas rig exploration, surveillance of natural disasters, naval tactical operations for coastal securities and to observe the changes in the underwater environment. In this regard, the widespread adoption of UWC has become a vital field of study to envisage various military and commercial applications that have been growing interest to explore the underwater environment for numerous applications. Acoustic, Optical and RF wireless carriers have been chosen to be used for data transmission in an underwater environment. The internet of underwater things (IoUT) and next-generation (5G) networks have a great impact on UWC as they support the improvement of the data rate, connectivity, and energy efficiency. In addition to the potential emerging UWC techniques, assisted by 5G network and improve existing work is also focusing in this study. This survey presents a comprehensive overview of existing UWC techniques, with possible future directions and recommendations to enable the next generation wireless networking systems in the underwater environment. The current project schemes, applications and deployment of latest amended UWC techniques are also discussed. The main initiatives and contributions of current wireless communication schemes in underwater for improving quality of service and quality of energy of the system over long distances are also mentioned.

Recent Advances and Future Directions on Underwater Wireless Communications

The seamless integration of emerging triboelectric nanogenerator (TENG) technology with traditional wearable textile materials has given birth to the next‐generation smart textiles, i.e., textile TENGs, which will play a vital role in the era of Internet of Things and artificial intelligences. However, low output power and inferior sensing ability have largely limited the development of textile TENGs. Among various approaches to improve the output and sensing performance, such as material modification, structural design, and environmental management, a 3D fabric structural scheme is a facile, efficient, controllable, and scalable strategy to increase the effective contact area for contact electrification of textile TENGs without cumbersome material processing and service area restrictions. Herein, the recent advances of the current reported textile TENGs with 3D fabric structures are comprehensively summarized and systematically analyzed in order to clarify their superiorities over 1D fiber and 2D fabric structures in terms of power output and pressure sensing. The forward‐looking integration abilities of the 3D fabrics are also discussed at the end. It is believed that the overview and analysis of textile TENGs with distinctive 3D fabric structures will contribute to the development and realization of high‐power output micro/nanowearable power sources and high‐quality self‐powered wearable sensors.

Advances in High‐Performance Autonomous Energy and Self‐Powered Sensing Textiles with Novel 3D Fabric Structures

Implantable sensors can be used to monitor biomechanical strain continuously. However, three key challenges need to be addressed before they can be of use in clinical practice: the structural mismatch between the sensors and tissue or organs should be eliminated; a practical suturing attachment process should be developed; and the sensors should be equipped with wireless readout. Here, we report a wireless and suturable fibre strain-sensing system created by combining a capacitive fibre strain sensor with an inductive coil for wireless readout. The sensor is composed of two stretchable conductive fibres organized in a double helical structure with an empty core, and has a sensitivity of around 12. Mathematical analysis and simulation of the sensor can effectively predict its capacitive response and can be used to modulate performance according to the intended application. To illustrate the capabilities of the system, we use it to perform strain measurements on the Achilles tendon and knee ligament in an ex vivo and in vivo porcine leg. A capacitive, fibre-like stretchable strain sensor, formed of two conductors in a double helical structure, can be combined with an inductive coil to create a wireless strain-sensing system for biomedical applications.

Stretchable and suturable fibre sensors for wireless monitoring of connective tissue strain

Passive and wireless, implantable glucose sensing with phenylboronic acid hydrogel-interlayer RF resonators.

Wearable and implantable sensors can be linked together to create multi-node wireless networks that could be of use in the development of advanced healthcare monitoring technologies. Such body area networks require secure, seamless and versatile communication links that can operate across the complex human body, but they typically suffer from short ranges, low power or the need for direct-connection terminals. Here we show that textile-integrated metamaterials can be used to drive long-distance near-field communication (NFC)-based magneto-inductive waves along and between multiple objects. The metamaterials are built from arrays of discrete, anisotropic magneto-inductive elements, creating a mechanically flexible system capable of battery-free communication among NFC-enabled devices that are placed anywhere close to the network. Our approach offers a secure and on-demand body area network that has the potential for straightforward expansion and can span across different pieces of clothing, objects and people. Textile-integrated metamaterials can be used to drive long-distance near-field-communication-based magneto-inductive waves along and between multiple objects, creating a secure and on-demand body area network.

Textile-integrated metamaterials for near-field multibody area networks

Multi‐Functional Hydrogel‐Interlayer RF/NFC Resonators as a Versatile Platform for Passive and Wireless Biosensing

Eating activity recognition (EAR) plays an important role in ensuring healthy eating habits. Recent advancements of the Internet of Things (IoT) have bolstered automated EAR through various wearable edge devices. State-of-the-art work uses some offline trained classifiers at the fog device to recognize eating activities. However, the eating habits of a person change quite frequently and vary from person to person. Therefore, the classifiers should be updated continuously with new data to adapt to these changes and be personalized over time through online learning. To the best of our knowledge, no state-of-the-art work has addressed this issue so far. In this article, we propose an online learning methodology called human eating activity recognition (HEAR) by introducing an online update phase. We also design an algorithm to be used in the online update phase that provides approximate true labels for the new data. Moreover, we also design a wearable neckband as the edge device to capture eating activity data ( Chewing, Swallowing, Talking, and Idle ) in a lab environment. Through a detailed experimental evaluation on 12 users, we show that an online learned neural network (OLNN) classifier using our HEAR methodology performs better than any state-of-the-art offline trained classifier. We also demonstrate that our OLNN classifier is energy efficient compared to the competitive offline trained classifiers.

HEAR: Fog-Enabled Energy-Aware Online Human Eating Activity Recognition

Some unavoidable shortcomings of acoustic wave based communications leads to the use of low frequency electromagnetic (EM) waves for underwater vehicle communication. Electric conductivity, causing frequency dependent attenuation, limits communication distance and data transfer rate in sea environment. An enhancement in range and bandwidth can be achieved by: 1) allowing EM signals to cross seawater-to-air boundary and achieve long-range horizontal communication using air path, followed by air to water signal transmission, if needed, and 2) exploring guided waves phenomenon at the water side of the seawater-air interface. A computational investigation to compare the EM wave propagation characteristics in seawater, in both sides of the seawater-air interface within a thin layer, and in air after crossing interface, in order to determine the optimum operating frequencies, ranges of communication, antenna orientation, and vertical offset of submerged antenna is presented in this paper. It is shown that with approximately 70 dB loss of signal strength, guided electric fields through air-water interface can be transmitted to a distance of 1 km at 10 KHz when the transmitter is 5 m below the interface.

Manik Dautta

Papers

Passive and wireless, implantable glucose sensing with phenylboronic acid hydrogel-interlayer RF resonators.

Textile-integrated metamaterials for near-field multibody area networks

Multi‐Functional Hydrogel‐Interlayer RF/NFC Resonators as a Versatile Platform for Passive and Wireless Biosensing

HEAR: Fog-Enabled Energy-Aware Online Human Eating Activity Recognition

Underwater vehicle communication using electromagnetic fields in shallow seas