Electric potential produced in deformed piezoelectric nanostructures is of significance for both fundamental study and practical applications. To reveal the piezoelectric property of ZnO nanohelices, the piezoelectric potential in single-crystal nanohelices was simulated by finite element method calculations. For a nanohelix with a length of 1200 nm, a mean coil radius of 150 nm, five active coils, and a hexagonal coiled wire with a side length 100 nm, a compressing force of 100 nN results in a potential of 1.85 V. This potential is significantly higher than the potential produced in a straight nanowire with the same length and applied force. Maintaining the length and increasing the number of coils or mean coil radius leads to higher piezoelectric potential in the nanohelix. Appling a force along the axial direction produces higher piezoelectric potential than in other directions. Adding lateral forces to an existing axial force can change the piezoelectric potential distribution in the nanohelix, while the maximum piezoelectric potential remains largely unchanged in some cases. This research demonstrates the promising potential of ZnO nanohelices for applications in sensors, micro-electromechanical systems (MEMS) devices, nanorobotics, and energy sciences.

Artificial photosynthesis is the imitation of natural photosynthesis, which promises an efficient way to use solar energy to synthesize organic matters, in which the key step is the coenzyme regeneration (NADH/NADPH). To achieve an efficient regeneration rate, various photocatalysts have been developed, such as g-C₃N₄ and mesoporous carbon nitride (mpg-C₃N₄). Generally, efficiency determination of different photocatalysts requires laborious experiments, high consumption of reagents, and a considerable amount of time. Here, based on the one-step artificial photosystem I method, we processed the analytical experiment in a very simple PDMS well (20 μL, a drop) to achieve a rapid screening of photocatalysts. For comparison, we used two types of graphitic carbon nitrides, few-layer g-C₃N₄ and mpg-C₃N₄. Compared with the slurry systems, firstly, the regeneration rate of mpg-C₃N₄ drop-reactor system is 4.3 times and 7.1 times those of the few-layer g-C₃N₄-slurry system and mpg-C₃N₄-slurry system, respectively. Secondly, this one-drop method reduces the typical verification time from 90 min to 5 min and lowers the liquid volume from 20 mL to 20 μL. Thirdly, this operation is a pump-free and soft lithography technique-free process. The miniaturization of the photocatalytic reaction in the PDMS well improves the regeneration rates, saves samples, and achieves high-throughput screening of multiple photocatalysts.

Based on the previously developed fixed-displacement asymmetric axial piston pump, a variable displacement asymmetric axial piston pump (VDAAPP) with three independent suction/delivery ports is proposed. A basic linear model of VDAAPP is established to get open-loop bode diagram. Based on open-loop Bode diagram features and design requirements, P-controller is determined for VDAAPP. Then VDAAPP's performance is investigated by advanced modeling environment for performing simulations of engineering systems (AMESim) and automatic dynamic analysis of mechanical systems (ADAMS) joint simulation, and some key design parameters are obtained. Next, a VDAAPP prototype with a maximum displacement of 40 cc/rev is designed and manufactured, ratio of flow rates at ports A, B and T is 1:0.6:0.4. Due to hard limitations of the test bench, the performance only under the conditions of the opposite passive loads is tested. Preliminary test results indicate that VDAAPP prototype works normally and meets the design requirements for flow ratio, and the maximum rise time of the test pressure is about 0.32 s. However, due to special design of VDAAPP valve plate, the swash plate torque severely limits system dynamic response. Therefore, an improved swashplate control system based on asymmetric-valve-controlled asymmetric-piston scheme is presented as well, it is found to be an effective way to suppress the negative impact of swash plate torque on system dynamic performance. This provides a direction for the optimization of the swashplate control system for asymmetric axial piston pumps in the future.

Flexibility piezoelectric sensors play an extraordinary significant role in force detection in many fields, such as biomedical, mechanical engineering, environmental monitor & measurement, and others. However, the limitations of the performance of sensing materials and and sensor functionality restrict their applications. Herein, a high-sensitivity arrayed stretchable piezoelectric force sensor based on PVDF-TrFE/nano-Fe₃O₄ was proposed. The flexible sensor consists of a double-layer PDMS substrate with different ratios of main agent and curing agent, serpentine stretchable silver electrodes, and a nanofiber-sensitive layer. The composite nanofiber was fabricated by doping Fe₃O₄ nanoparticles (NPs) into polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and utilizing high-voltage electrospinning technology. X-ray diffraction (XRD) and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy results indicate that the addition of Fe₃O₄ NPs promotes the formation of the β-phase in the PVDF-TrFE polymer. Comparative experiments demonstrate that when the Fe₃O₄ NPs content is 5 wt%, the sensor exhibits better frequency (higher than 16 V at 3 Hz) and faster response time (45 ms). More importantly, the arrayed stretchable piezoelectric force sensor demonstrates exceptional sensitivity in detecting pressure, stretching, and bending deformations, with values of 740 mV/kPa, 380 mV/N, and 21.16 mV per 10% deformation, respectively. It also exhibits high reliability, as its output maintains durability and stability after undergoing 10000 stability cycles at 7 Hz. Application experiments with the arrayed sensor reveal its capability to detect distributed forces applied by weights and fingers, presenting novel applications in identifying object weight and hardness. Looking ahead, this research offers an unprecedented multimodal detection strategy for next-generation stretchable sensors, demonstrating exceptional practicality.

Two-dimensional (2D) piezoelectric semiconductor materials are garnering significant attention in applications such as intelligent sensing and energy harvesting due to their exceptional physical and chemical properties. Among these, molybdenum disulfide (MoS₂), a 2D wide-bandgap semiconductor, exhibits piezoelectricity in odd-layered structures due to the absence of an inversion symmetry center. In this study, we present a straightforward chemical vapor deposition (CVD) technique to synthesize monolayer MoS₂ on a Si/SiO₂ substrate, achieving a lateral size of approximately 50 µm. Second-harmonic generation (SHG) characterization confirms the non-centrosymmetric crystal structure of the wide-bandgap MoS₂, indicative of its piezoelectric properties. We successfully transferred the triangular MoS₂ to a polyethylene terephthalate (PET) flexible substrate using a wet-transfer method and developed a wide-bandgap MoS₂-based micro-displacement sensor employing maskless lithography and hot evaporation techniques. Our testing revealed a piezoelectric response current of 5.12 nA in the sensor under a strain of 0.003% along the armchair direction of the monolayer MoS₂. Furthermore, the sensor exhibited a near-linear relationship between the piezoelectric response current and the strain within a displacement range of 40–100 µm, with a calculated response sensitivity of 1.154 µA/%. This research introduces a novel micro-displacement sensor, offering potential for advanced surface texture sensing in various applications.