The cognition of spatiotemporal tactile stimuli, including fine spatial stimuli and static/dynamic temporal stimuli, is paramount for intelligent robots to feel their surroundings and complete manipulation tasks. However, current tactile sensors have restrictions on simultaneously demonstrating high sensitivity and performing selective responses to static/dynamic stimuli, making it a challenge to effectively cognize spatiotemporal tactile stimuli. Here, we report a high-sensitive and self-selective humanoid mechanoreceptor (HMR) that can precisely respond to spatiotemporal tactile stimuli. The HMR with PDMS/chitosan@CNTs (PDMS: polydimethylsiloxane; CNT: carbon nanotube) graded microstructures and polyurethane hierarchical porous spacer exhibits high sensitivity of 3790.8 kPa⁻¹. The HMR demonstrates self-selective responses to static and dynamic stimuli with mono signal through the hybrid of piezoresistive and triboelectric mechanisms. Consequently, it can respond to spatiotemporal tactile stimuli and generate distinguishable and multi-type characteristic signals. With the assistance of the convolutional neural network, multiple target objects can be easily identified with a high accuracy of 99.1%. This work shows great potential in object precise identification and dexterous manipulation, which is the basis of intelligent robots and natural human-machine interactions.

The triboelectric nanogenerators (TENGs), suppling power for freely mobile and distributed electronic equipment from Internet of Things, have been considered as “the energy for the new era”. Research on the service behavior has become increasingly important for achieving the reliability evaluation and life prediction of TENGs, as TENGs advance from prototypes to practical applications. Due to the wide selection of materials, the diversity of device structures, and the complexity of working environment, TENGs show unique characteristics in the service behavior. These dilemmas lead to the fact that systematical summary of service behavior for TENGs is still in its infancy. Here, the progresses of the service behavior for TENGs are comprehensively reviewed from the influence of environmental factors on the service performance of TENGs to the impact of TENGs during the service on their surroundings. We summed up the performance evolution of TENGs in the real environment and the reproducibility of TENGs of which the electrical output will be restored after failure. Then, the service adaptability of TENG is systematically discussed, including the biological and environmental compatibility. Finally, the challenges and opportunities that the related research faced are proposed to promote the emerging technology from laboratory to factory.

Since the invention of the triboelectric nanogenerator (TENG) in 2012, it has become one of the most vital innovations in energy harvesting technologies. The TENG has seen enormous progress to date, particularly in applications for energy harvesting and self-powered sensing. It starts with the simple working principles of the triboelectric effect and electrostatic induction, but can scavenge almost any kind of ambient mechanical energy in our daily life into electricity. Extraordinary output performance optimization of the TENG has been achieved, with high area power density and energy conversion efficiency. Moreover, TENGs can also be utilized as self-powered active sensors to monitor many environmental parameters. This review describes the recent progress in mainstream energy harvesting and self-powered sensing research based on TENG technology. The birth and development of the TENG are introduced, following which structural designs and performance optimizations for output performance enhancement of the TENG are discussed. The major applications of the TENG as a sustainable power source or a self-powered sensor are presented. The TENG, with rationally designed structures, can convert irregular and mostly low-frequency mechanical energies from the environment, such as human motion, mechanical vibration, moving automobiles, wind, raindrops, and ocean waves. In addition, the development of self-powered active sensors for a variety of environmental simulations based on the TENG is presented. The TENG plays a great role in promoting the development of emerging Internet of Things, which can make everyday objects connect more smartly and energy-efficiently in the coming years. Finally, the future directions and perspectives of the TENG are outlined. The TENG is not only a sustainable micro-power source for small devices, but also serves as a potential macro-scale generator of power from water waves in the future.

Magnetic metals (Fe, Co, Ni) and alloys thereof are easily synthesized as nanoparticles, but obtaining highly dispersed graphene-based magnetic nanomaterials remains challenging. Here, three CoNi/graphene nanocomposites (CoNi/GN) are successfully assembled for the first time via a one-pot strategy without templating by manipulating the reaction time and solvents used for the same precursors. Moreover, the reduction of graphene oxide utilizing this method is more effective than that by conventional methods and the alloy particles are firmly embedded on the GN substrate. Compared to n- and p-CoNi/GN nanocomposites, o-CoNi/GN nanocomposites show the best electromagnetic wave absorption properties with the maximum reflection loss of-31.0 dB at 4.9 GHz for a thickness of 4 mm; the effective absorption bandwidth (< 10.0 dB) is 7.3 GHz (9.5–16.8 GHz) for a thickness of 2 mm. The structures and electromagnetic wave absorption mechanisms of the three composites were also investigated. This research provides a new platform for the development of magnetic alloy nanoparticles in the field of microwave-absorbing devices.

A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite (CoNSs@RGO) was successfully prepared as a light-weight broadband electromagnetic wave absorber. The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated. Due to the nanosheet-like structure of Co₃O₄, the surface-to-volume ratio of the wave absorption material was very high, resulting in a large enhancement in the absorption properties. The maximum refection loss of the CoNSs@RGO composite was–45.15 dB for a thickness of 3.6 mm, and the best absorption bandwidth with a reflection loss below–10 dB was 7.14 GHz with a thickness of 2.9 mm. In addition, the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings. The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO. Compared to previously reported absorbing materials, CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band.

We report the preparation of nanocomposites of reduced graphene oxide with embedded Fe₃O₄/Fe nanorings (FeNR@rGO) by chemical hydrothermal growth. We illustrate the use of these nanocomposites as novel electromagnetic wave absorbing materials. The electromagnetic wave absorption properties of the nanocomposites with different compositions were investigated. The preparation procedure and nanocomposite composition were optimized to achieve the best electromagnetic wave absorption properties. Nanocomposites with a GO: α-Fe₂O₃ mass ratio of 1:1 prepared by annealing in H₂/Ar for 3 h exhibited the best properties. This nanocomposite sample (thickness = 4.0 mm) showed a minimum reflectivity of–23.09 dB at 9.16 GHz. The band range was 7.4–11.3 GHz when the reflectivity was less than–10 dB and the spectrum width was up to 3.9 GHz. These figures of merit are typically of the same order of magnitude when compared to the values shown by traditional ferric oxide materials. However, FeNR@rGO can be readily applied as a microwave absorbing material because the production method we propose is highly compatible with mass production standards.