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Metamaterials with honeycomb structures have garnered significant attention in energy-harvesting applications. In this study, we present three conventional cantilever resonators with honeycomb substrates featuring positive, zero, and negative Poisson's ratios (PPR, ZPR, and NPR). Polyvinylidene fluoride consisting electrode layers is attached to the substrate surfaces. A process parameter optimization method of honeycomb structure design was proposed, in which finite element simulation for data generation, backpropagation neural network for data prediction, and nondominated sorting genetic algorithm II (NSGA-II) for data optimization. This method aims to determine the optimum geometric parameters of the honeycomb structures, which addresses general cantilever resonators, where the first structural vibration modes are typically of interest and have to match specific target eigenfrequencies for engineering applications. Finite element simulations show that the peak voltage of PPR, ZPR, and NPR resonators at 75 Hz is increased by 12 %, 22 %, and 32 %, respectively, due to optimization. The optimized structures are fabricated and measured to validate the numerical model. The performance of the resonators with cellular materials featuring a full characteristic range of Poisson's ratios is then compared systematically to explore their energy-harvesting potential. The results revealed that the NPR structure exhibits superior performance for energy-harvesting. Moreover, stress distribution and displacement have also been highlighted in this paper. [Display omitted] • A backpropagation neural network is trained to predicting the performance of piezoelectric energy harvester. • An optimization method combining backpropagation neural network and evolutionary algorithm is developed. • The performance of piezoelectric energy harvesters with different cellular substrates are systematically compared. • The optimization results are validated by finite element analysis and experiments. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric sensors have received widespread attention in wearable electronics for their ability to convert mechanical energy into electrical energy, while the insufficient output power and complex preparation process have limited their application. In this work, several honeycomb structures based on graphene macro-film (GAMF) were created via laser engraving, which can utilize negative Poisson's ratio (NPR) properties to improve the output electric performance of flexible piezoelectric sensors. The effect of different electrode materials on the piezoelectric output was investigated in the experiments and compared with the theoretical equations, indicating that the output power of the sensor could be enhanced up to 142 % by improving the materials auxetic mechanical properties. The stability tests have proven that the sensors can operate effectively for a long time under different operating conditions. Moreover, the optimized sensor shows powerful potential for monitoring human movements such as finger tapping, joint bending, and foot stepping. This work opens up a new development path for the preparation of convenient and high-performance wearable electronic devices. The negative Poisson's ratio characteristic of the honeycomb graphene macro-film is used to increase the deformation of PVDF film to increase the electrical output performance of the flexible piezoelectric sensor. The optimized sensor can be used to detect human movements. [Display omitted] • Honeycomb graphene macro-films with different mechanical properties were prepared by laser engraving. • Flexible piezoelectric sensors based on honeycomb graphene macro-films are prepared. • The output performance of piezoelectric sensors can be improved by adjusting mechanical properties of electrode materials. • The flexible piezoelectric sensors can be used to detect human movements. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel absorber metamaterial with the perspective of honeycomb geometry is designed. • Optical characterization and experimental realization are presented. • Multiple band biochemical detection on a footprint range in mid-infrared regime. Abstract Nowadays, accessing to new electromagnetic properties can be realized by fabricating metamaterials consist of artificial functional and subwavelength-scaled structures. Promoting artificial and functional metamaterial designs with large electromagnetic near-field enhancement especially over throughout multiband spectral range can provide critical contributions for infrared spectroscopy applications. In this context, the design and experimental realization of a photonic metamaterial are presented which can be utilized as an infrared biosensor. We utilize a honeycomb-shaped plasmonic nanoantenna for the design of the proposed novel absorber metamaterial. The fabrication and optical characterization of the structures are carried out and the sensor potential of the metamaterial is demonstrated through the detection of a polymer nanofilm. [ABSTRACT FROM AUTHOR]

It is worthwhile to efficiently and cost-effectively capture the vibration energy in the operation of rotating machinery and convert it from mechanical energy to electrical power for a specific application. Currently, triboelectric nanogenerators as vibration energy harvesters are mainly studied for the start and stop of mechanical equipment but less for its resonance. In this paper, a self-powered circular-honeycomb triboelectric nanogenerator (CH-TENG) is proposed as a vibration energy harvester. Firstly, tests are carried out on a Vibration Platform to obtain the output performance of CH-TENG at different excitation amplitudes, frequencies, and accelerations. The factors affecting the output of CH-TENG are then summarized. Stability experiments are also carried out to verify the stability of CH-TENG. Secondly, the CH-TENG is applied on a 7.5 kW convex pole synchronous machine to verify its practicality. Finally, the homemade CH-TENG is improved with springs installed at the bottom to amplify the vibration energy amplitude. The experimental results show that the synchronous machine will have apparent voltage and current output pulses when it reaches the resonance frequency. It indicates that the CH-TENG can be used not only as a vibration energy harvester but also for detecting the resonance state of a synchronous machine, which has significant potential for monitoring resonance faults of the machine when it is at service. [Display omitted] • The TENG body is designed as a circular honeycomb structure, which can save space. • The TENG can be used as a vibration energy harvester and its output performance has been tested. • The introduction of springs increases the output of the TENG. • The TENG is applied in a 7.5 kW synchronous generator to monitor its resonance and start-stop status. [ABSTRACT FROM AUTHOR]

• Defromation of the auxetic structure can be transformed into a change in voltage. • Displacement measuring system based on auxetic structure has a non-contact scheme. • Non-contact scheme can effectively avoid the interference and noise transmission. • Displacement measuring system based on auxetic shows good linearity and sensitivity. [Display omitted] It is essential to measure the amount of displacement in mechanical systems and architectural structures. Researchers have developed displacement sensors using various materials and fabrication methods. However, the components of displacement sensors are in contact with each other, which would cause the interference and noise transmission between the sensing device and conversion element, and also bring much inconvenience to the design and preparation of the sensor. In this study, a non-contact displacement measurement method based on the auxetic structure was developed. The scheme of this method consists of a light source, an auxetic structure and a solar cell. These three parts are not in contact with each other. By this method, the change in transmittance of the auxetic structure due to elastic deformation is transformed into a change in the output current of the solar cell. The proposed method has potential applicability for measuring and monitoring structural parts. The effectiveness of this method is investigated by geometrical analysis and experiments. The results show that the input and output of the proposed methods have good sensitivity. This study provides a new structural view for the displacement sensor and puts forward the future research. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrothermal scanners have limited bandwidth due to a large thermal time constant. • Scanner's thermal and inertial mass is reduced using the honeycomb support structure. • As a result, an increase in both bandwidth and efficiency of a scanner is demonstrated. • A sample two-photon 3D images of pollen grain are taken on benchtop system. Design and testing of a low-mass electrothermal vertical scanning mirror for fast axial scanning during multi-photon microscopy is presented. The mirror makes use of a novel honeycomb mechanical support structure to substantially reduce both thermal and inertial mass relative to mirror size. At the same time, undesirable mirror curvature due to residual thermal stress is controlled without adversely affecting the image quality. In addition, the support structure makes the complete mirror area usable which otherwise is not possible in devices that rely on isotropic silicon etching. A high actuator efficiency with static displacement per unit power of 2.08 μm/mW was achieved due to the reduced thermal capacitance at the actuator legs, when using a 700 nm thin structural layer of SiO 2. The resulting scanning mirror achieves open loop time constant as small as 3.42 ms with both thermal and mechanical bandwidths exceeding 100 Hz. Mirror surface non-idealities related to the mirror structure and their influence on image quality are discussed. Sample 3D multi-photon images captured by performing remote scanning in both lateral and axial direction on a benchtop testbed are presented. The efficacy of remote axial scan is ascertained by comparisons with images obtained by moving specimens relative to the objective. [ABSTRACT FROM AUTHOR]

• First employment of the GaN honeycomb nanonetwork for NH 3 sensors. • First employment of Pt nanonetwork as the catalyst for NH 3 gas dissociation. • Investigation of the absorption activation energy E a of NH 3 sensors. • Fast response of 23 s and small LOD of 0.31 ppm. In this work, we have demonstrated a FET-like ammonia (NH 3) gas sensor fabricated on a unique structure namely GaN honeycomb nanonetwork (GaN-HN) which is in-plane electrically conductive together with large surface-to-volume ratio. Utilizing ohmic contact Ti/Al/Ti/Au multilayers as the source and the drain terminals and Pt nanonetwork layer as the gate terminal, the FET-like NH 3 gas sensors were fabricated by a two-mask photolithography process. The fabricated NH 3 gas sensors have high selectivity, fast response/recovery, and a wide detection range up to 5000 ppm. The response and recovery time for 5 ppm NH 3 gas are 23 s and 101 s at a moderate operating temperature of 120 °C. Interestingly, this sensor is capable to detect trace NH 3 gas and the low limit of detection (LOD) is as small as 0.31 ppm. Its absorption activation energy E a is also investigated by the transient-state study. [ABSTRACT FROM AUTHOR]