Electromechanical biomonitoring is essential in human health evaluation, diseases prevention and life quality improvement. Nanogenerators (NGs) have demonstrated exceptional performances and ...versatility in self-powered flexible electronics including piezoelectric and electrostatic sensors. Combined with artificial intelligent (AI), five generation (5G) and internet-of-thing (IoT) technologies, the NGs-based flexible electronics are paving a new way for creating intelligent electromechanical biomonitoring systems which are also capable of analyzing, transmitting, and deciding. In this review, we cover the recent remarkable developments in monitoring electromechanical physiological signals using NGs-based flexible electronics. We begin by covering the fundamentals of NGs from the perspective of mechanisms, materials, device structures, and manufacturing methods. We then give an overview of NGs-based flexible electronics in various wearable and implantable sensing applications. Finally, the present limitations and future developing trends of this field are discussed and prospected.
•We review the fundamentals of nanogenerators-based flexible electronics.•We review the typical applications of nanogenerators-based flexible electronics in electromechanical biomonitoring.•We discuss the existing limitations and prospect the future developing trends of this research field.
Nowdays, the study of measurement of the biological field focuses on the research of improving surface plasmon resonance （SPR） in the fields of integration and detection sensitivity. We designed a ...kind of grating connected surface plasmon resonance sensor. Theoretically, we analyzed the wave vector and the. effective refractive index relations with the diffraction grating structure. Then we obtained the nanoparticles enhancement SPR structure with a resolution 10times higher than that of traditional SPR sensors. Also, we used the finite-difference time-domain （FDTD） analysis and simulation which showed that it was obvious with coupling effect by the nanoparticles enhancement SPR structure that the reflectance spectral bandwidth results validated the structure significantly which improved the sensitivity. Experimental results showed that the dynamic response of the designed sensor reached 10^-6 RIU （refractive index unit）. This study has the certain significance to long-distance and special sensing applications.
The trade‐off between sensitivity and linearity is critical for preserving the high pressure‐resolution over a broad range and simplifying the signal processing/conversion of flexible tactile ...sensors. Conventional dielectrics suffer from the difficulty of quantitatively controlling the interacted mechanical and dielectric properties, thus causing the restricted sensitivity and linearity of capacitive sensors. Herein, inspired by human skin, a novel hybrid dielectric composed of a low‐permittivity (low‐k) micro‐cilia array, a high‐permittivity (high‐k) rough surface, and micro‐dome array is developed. The pressure‐induced series‐parallel conversion between the low‐k and high‐k components of the hybrid dielectric enables the linear effective dielectric constant and controllable initial/resultant capacitance. The gradient compressibility of the hybrid dielectric enables the linear behavior of elastic modulus with pressures, which derives the capacitance variation determined by the effective dielectric constant. Therefore, an ultrawide linearity range up to 1000 kPa and a high sensitivity of 0.314 kPa–1 are simultaneously achieved by the optimized hybrid dielectric. The design is also applicable for triboelectric tactile sensors, which realizes the similar linear behavior of output voltage and enhanced sensitivity. With the high pressure‐resolution across a broad range, potential applications such as healthcare monitoring in diverse scenarios and control command conversion via a single sensor are demonstrated.
A skin‐inspired hybrid dielectric with gradient compressibility and dielectric property is presented based on a combined low‐permittivity (low‐k) micro‐cilia array and high‐permittivity (high‐k) rough surface and micro‐dome array. The derived linear elastic modulus and effective dielectric constant enable an ultrawide linear sensing range (0–1000 kPa) and enhanced sensitivity for capacitive/triboelectric tactile sensors.
Flexible and wearable devices with the capabilities of both detecting and generating mechanical stimulations are critical for applications in human–machine interfaces, such as augmented reality (AR) ...and virtual reality (VR). Herein, a flexible patch based on a sandwiched piezoelectret structure is demonstrated to have a high equivalent piezoelectric coefficient of d 33 at 4050 pC/N to selectively perform either the actuating or sensing function. As an actuator, mechanical vibrations with a peak output force of more than 20 mN have been produced, similar to those from the vibration mode of a modern cell phone, and can be easily sensed by human skin. As a sensor, both the pressure detection limit of 1.84 Pa for sensing resolution and excellent stability of less than 1% variations in 6000 cycles have been achieved. The design principle together with the sensing and driving characteristics can be further developed and extended to other soft matters and flexible devices.
This brief investigates the finite-time adaptive extended state observer (ESO) based dynamic sliding mode control (SMC) for the hybrid robot subject to uncertain problem, e.g., modeling error, joint ...friction, external disturbance and so on. A barrier function-based adaptive law is defined to adjust the switching gain of SMC system with unknown upper bound of the disturbance. Such an adaptive law-based control method ensures the finite-time convergence of the sliding variable to an adjustable vicinity of zero and realizes chattering reduction of SMC. Then, for estimating and compensating system uncertainties, the time-varying gain ESO (TESO) is designed without the condition of the disturbance change rate tending to zero. A system error-based adaptive law is designed to adjust the observer bandwidth gain, which can reduce the peaking value. Such a TESO reduces the burden of SMC and further weakens the chattering of SMC, so as to improve the control system robustness. The finite-time Lyapunov stability of the sliding variable and the boundness of the TESO error have been proved theoretically. The practical effectiveness is illustrated in simulations and experiments with the prototype of hybrid robot.
Inspired by natural biological systems, soft robots have recently been developed, showing tremendous potential in real‐world applications because of their intrinsic softness and deformability. The ...confluence of electronic skins and machine learning is extensively studied to create effective biomimetic robotic systems. Based on a differential piezoelectric matrix, this study presents a shape‐sensing electronic skin (SSES) that can recognize surface conformations with minimal interference from pressing, stretching, or other surrounding stimuli. It is then integrated with soft robots to reconstruct their shape during movement, serving as a proprioceptive sense. Additionally, the robot can utilize machine learning to identify various terrains, demonstrating exteroception and pointing toward more advanced autonomous robots capable of performing real‐world tasks in challenging environments.
Self‐sensing of their body shape is significant for soft robots planning trajectories and actions, which can also be a feedback to interactions with the environment. We present a shape‐sensing electronic skin, confluence with machine learning technique, endows soft robots with proprioception of their own status and exteroception of environment awareness, exhibiting advanced artificial intelligence.
The rapid development of electrical skin and wearable electronics raises the requirement of stretchable strain sensors. In this study, an active fiber‐based strain sensor (AFSS) is fabricated by ...coiling a fiber‐based generator around a stretchable silicone fiber. The AFSS shows the sensitive and stable performance and has the ability to detect the strain up to 25%, which is also demonstrated to detect finger motion states. It may play an essential role in future self‐powered sensor system.
A fiber‐based electret generator is coiled around a stretchable silicone fiber to form an active fiber‐based strain sensor (AFSS). The AFSS shows the sensitive and stable performance and has the ability to detect the strain up to 25%, which is also demonstrated to detect finger motion states. It may play an essential role in future self‐powered sensor system.
•A human–machine interactive interface for in-plane force detection was developed.•The interface can provide non-overlapping signals according to the force direction.•Intensified signal was observed ...owing to the fast recovery of deformed micropillar.•Signal interference was avoided by optimizing the decay of micropillar oscillation.•Diverse commands can be produced based on one device and one communication channel.
The merging of flexible technologies with human machine interaction (HMI) is now optimizing the way people communicates with electrical terminals. Compared with “press” and “strain”, “sliding” is a directional operation which requires the interface to identify the directions of the applied force for accurate interaction. Previous efforts that explore the “directional force” in HMI system are mainly based on sensor array, which brings concern of complex electrode design and multiple communication channels to prevent cross-talk. In view of this, we developed a self-powered and wearable HMI interface that can distinguish the axial directions of in-plane force based on Faraday’s law of induction. The interface consists of well-orientated magnetized micropillars, and a conductive coil that collects and transmits the electrical signals during the interaction process. When in-plane sliding force was applied, distinguishable signals were generated to reflect the different axial directions (+X/−X/+Y/−Y) according to the polarity and number of voltage peaks. With this unique behavior, the HMI process can be completed with two electrodes and one communication channel in an interference-free manner. Through the systematic optimization, the intrinsic oscillation from the micropillars results in obviously enhanced signals for a high accuracy and reliability towards real application. The MMPs-based interface was successfully established for HMI platforms such as intelligent robot control, and Morse code communication, etc. Owing to the robustness, humid resistance, accuracy and reliability, we expect that the interface design can inspire the development of flexible and wearable devices in HMI especially for scenarios that require a high command capacity.
Wearable triboelectric devices have been widely used for sensing and energy harvesting applications, and further improving the compactness will enhance the convenience and comfortability. In this ...work, an easy-fabricated and compact untethered triboelectric patch is proposed with Polytetrafluoroethylene (PTFE) as triboelectric layer and human body as conductor. We find that the conductive characteristic of human body has negligible influence on the outputs, and the untethered triboelectric patch has good output ability and robustness. The proposed untethered triboelectric patches can work as sensor patches and energy harvester patches. Three typical applications are demonstrated, which are machine learning assisted objects distinguishing with accuracy up to 93.09–94.91 %, wireless communication for sending typical words to a cellphone, and human motions energy harvesting for directly powering electronics or charging an energy storage device.
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•The untethered patches with human body as conductor are proposed for enhancing the convenience and comfortability.•Conductive characteristic of human body has negligible influence on the output performances of the untethered patches.•The untethered patches exhibit good smart sensing and energy harvesting performances.
Paper-based pressure/strain sensors could have potential wide applications with wearable features in disposable products. In this study, molybdenum carbide-graphene (MCG) composites with porous and ...stacking micro-structures are fabricated on top of the paper substrate to act as piezo-resistivity strain/pressure sensors. As a strain sensor, this paper-based device can detect not only the amplitude and frequency of applied strain but also the direction as tensile or compressive deformation. The gauge factors are 73 and 43 for tensile and compressive strain, respectively, with demonstration example in detecting and recognizing human body motions. As a pressure sensor, this MCG-based paper device has high sensitivity to weak pressure signals such as sounds by distinguishing the seven piano notes. Our study provides a simple strategy for developing paper-based electronics with unique properties toward practical applications.
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