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Inspired by an electromagnetic generator containing multi-pole radial ring magnets, we designed a bipolar electret rotatory power generator (e-RPG) with a multi-phase core-shell structure to boost output performance and achieve high-precision self-sensing capabilities. A selectively localized rotary corona discharging method is invented to uniformly inject both positive and negative charges into a single electret’s curved surface. The experimental results show that the output power of the bipolar-charged e-RPG is increased to 384% compared with those of positive or negative charging alone, which is consistent with the results obtained from the theoretical model. By introducing the core-shell-structured multi-phase electrode design, both the rotation direction and speed can be precisely detected. The frequency sensitivity and linearity $\text{R}^{2}$ (coefficient of determination) are up to 3.0 rpm/Hz and 99.9%, respectively. The proposed e-RPG has potential applications in the Internet of Things, self-powered sensing and self-sensing of rotational motions. [ABSTRACT FROM AUTHOR]

Contact electrification (CE) at interfaces has been documented for over 2600 years, but its mechanism remains ambiguous and is not fully understood, especially for liquid-solid cases. For the first time, we proposed an electret micro-patterning charging method using flowing tap water. The selective oxygen plasma treatment restrained the involvement of the charge-transfer process in liquid-solid contact electrification and obtained an NPU-shaped 3D charge profile. The electret surface potential is up to −650V and able to maintain 82% of its initial potential after 45 days, demonstrating excellent charge stability. The water charging method can be further used for droplet-based electricity power generation and water-drop self-powered sensing applications. This work demonstrates the feasibility and effectiveness of the innovatively proposed electret water charging method and advances a novel application in the energy harvesting field. [2021-0263] [ABSTRACT FROM AUTHOR]

Micro-drop ejection technology has been widely employed in cell analysis, drug delivery, microreactors, and various other fields due to its high accuracy and resolution, which can accurately control and dispense liquid materials. However, the current development of this technology faces challenges due to nozzle diameter limitations. Smaller droplets require finer nozzles for ejection. Nevertheless, fine nozzles cause significant fluid resistance, hindering micro-droplet ejection. Overcoming the constraint posed by nozzle and achieving high-precision micro-droplets ejection has become a challenging task for the industry. Inspired by the phenomenon of cavity collapse in nature, we have developed a micro-droplet ejection technology based on actively controlling the cavity collapse within the confined interface. By analyzing the formation and collapse of the liquid cavity, we have identified three ejection modes: no droplet, single droplet, and satellite droplet, and further delineated the boundary conditions for minimizing droplet size and ejecting satellite-free droplets. Using this technology, we achieved precise control over droplet size within a defined range, with the minimum droplet diameter reaching 34 % of the nozzle diameter. Furthermore, the continuous ejection of single droplets demonstrated excellent stability and repeatability. This innovative technology could provide a novel approach to achieve high accuracy and controllability in micro-droplets ejection, liberating it from nozzle constraints, thus expected to play a significant role in the fields of biomedical research, chemical engineering, and printed electronics. [Display omitted] • Proposed an innovative droplet ejection technique combining precise piezoelectric control with cavity collapse principle. • Identified three ejection modes and defined conditions for minimizing droplet size and eliminating satellites. • The minimum droplet size for controlled ejection is only 34 % of nozzle diameter. • Continuous micro-droplet ejection has excellent stability and repeatability. [ABSTRACT FROM AUTHOR]

With the requirement for self-powering functionality in wearable electronics, a small power range flexible photovoltaic micro-power system is evidently needed. Furthermore, non-flexibility, large volume/weight, power consumption constraints, and cost considerations make it impractical to directly use the large power range complex maximum power point tracking (MPPT) algorithm and hardware in wearable electronics. This work aims to design a fully flexible photovoltaic micro-power system for reliable energy supply within the low power range for wearable electronics. In this study, a customized fractional open circuit voltage (FOCV) algorithm and a performance-matching DC-DC converter are designed, and then integrated with a flexible perovskite solar module to develop a fully flexible photovoltaic micro-power system. Indoor and outdoor experiments are conducted to evaluate its performance. The designed MPPT system achieves a high tracking accuracy of 99.25% at a power of 0.539 W with a fast tracking time of 0.20 s, which is an effective improvement over the traditional algorithms. These values are 97.8% and 0.21 s under shaded lighting conditions. The MPPT system is lightweight (4.6 g) with a size of <3 × 3 cm2. Tracking experiments with flexible solar modules after bending also demonstrate the flexibility of the system, which also shows the high utilization and fast response capability for small power range photovoltaic outputs. The fully flexible photovoltaic micro-power system demonstrates great potential for future wearable electronics and expands the way to efficiently harvest solar energy in highly adaptive and dynamic applications. • A customized MPPT algorithm and hardware is proposed. • The customized MPPT exhibits a high power tracking accuracy of 99.25% and a fast tracking time of 0.20 s. • A fully flexible photovoltaic micro-power system is developed by integrating a flexible MPPT and a flexible solar module. [ABSTRACT FROM AUTHOR]

Hot-film sensors measure wall-shear stress based on the forced convective heat transfer. Variations of ambient temperatures lead to significant measurement errors for such thermal sensors and must be corrected for sometimes. Although methods for correcting the temperature shifts of hot-film sensors driven in constant temperature or constant voltage mode have been suggested over the years, the temperature dependence and relevant correction schemes of constant current mode of operation are still open questions. In this study, temperature dependence characteristics of constant current hot-film sensors are investigated within relatively large temperature changes in air and water channel flows (28 °C and 16 °C, respectively). The specific property of constant overheat ratios under varying temperatures for constant current driving mode is found and a quite simple temperature correction function is derived on that basis to eliminate the temperature dependence without any assumed heat transfer correlation. With the correction function, the data at different ambient temperatures are collapsed to single curves with high R 2 factors over 0.99, typically. Furthermore, after correction, the relative errors of the measured wall-shear stress are reduced to within ±6 % of the true values. It will then enable the constant current hot-film sensors to calibrate at only one ambient temperature instead of a multiple range of temperatures as with many other schemes, which is more practical and convenient. • Experimental study of temperature dependence for constant current hot-film sensors. • New finding of temperature independent overheat ratios for constant current mode. • A new temperature correction function was established, based on the unique feature. • Achievement: reduction of temperature drift error for wall shear stress measurement. [ABSTRACT FROM AUTHOR]

Rapid advances in wearable electronics and mechno‐sensational human–machine interfaces impose great challenges in developing flexible and deformable tactile sensors with high efficiency, ultra‐sensitivity, environment‐tolerance, and self‐sustainability. Herein, a tactile hydrogel sensor (THS) based on micro‐pyramid‐patterned double‐network (DN) ionic organohydrogels to detect subtle pressure changes by measuring the variations of triboelectric output signal without an external power supply is reported. By the first time of pyramidal‐patterned hydrogel fabrication method and laminated polydimethylsiloxane (PDMS) encapsulation process, the self‐powered THS shows the advantages of remarkable flexibility, good transparency (≈85%), and excellent sensing performance, including extraordinary sensitivity (45.97 mV Pa−1), fast response (≈20 ms), very low limit of detection (50 Pa) as well as good stability (36 000 cycles). Moreover, with the LiBr immersion treatment method, the THS possesses excellent long‐term hyper anti‐freezing and anti‐dehydrating properties, broad environmental tolerance (−20 to 60 °C), and instantaneous peak power density of 20 µW cm−2, providing reliable contact outputs with different materials and detecting very slight human motions. By integrating the signal acquisition/process circuit, the THS with excellent self‐power sensing ability is utilized as a switching button to control electric appliances and robotic hands by simulating human finger gestures, offering its great potentials for wearable and multi‐functional electronic applications. [ABSTRACT FROM AUTHOR]

Anti-icing with low-energy consumption has important research value for unmanned aerial vehicles. In this study, a superhydrophobic electrothermal film for anti-icing applications was designed and prepared, and power consumption experiments were conducted at different temperatures and wind speeds in an icing wind tunnel. The anti-icing power consumption of the superhydrophobic electrothermal film was lower than that of a traditional electrothermal film. As the temperature decreased or the wind speed increased, the anti-icing power consumption of the two types of electrothermal films increased. A heat flux model was used to analyse the experimental results. It can be concluded that the water collection rate per unit area W and wetting coefficient ξ w are the main factors affecting the power consumption of the superhydrophobic electrothermal film. When the temperature decreased and the wind speed increased, the contact time and contact area between the droplet and the surface affected W and ξ w . Thus, this study is of considerable significance for the design of superhydrophobic electrothermal films for novel anti-icing applications in the future. [ABSTRACT FROM AUTHOR]

The limiting temperature of an In 2 O 3 thin film sensor is much lower than its melting point. Herein, the failure modes of In 2 O 3 thin films at high temperatures, including sublimation and changes in composition, have been studied. The edge and surface layer sublimation rates increased dramatically at 1350 °C, indicating that it is the limiting temperature of no-protection In 2 O 3 films. In addition, oxygen atoms will escape from In 2 O 3 thin films at high temperatures, forming oxygen vacancies. As the main current carrier type in In 2 O 3 , the increasing number of oxygen vacancies affects the resistance of In 2 O 3 thin film sensors. To solve these problems and promote the high temperature performance of In 2 O 3 thin films, protection methods based on Al 2 O 3 and ZrO 2 layers have been investigated. The ZrO 2 protective layer alleviated the serious considerable sublimation of In 2 O 3 thin films at high temperatures, and the Al 2 O 3 protective layer was beneficial for reduction the escape of oxygen atoms. Finally, different protection layers were evaluated by in-situ resistivity measurements of In 2 O 3 thin films at high temperatures. The resistance of the In 2 O 3 thin film resistor with a protective multilayer consisting of Al 2 O 3 and ZrO 2 remained stable at 1360 °C, verifying the protection method effectively increased the thermal stability of In 2 O 3 thin films. [ABSTRACT FROM AUTHOR]

Although blood flows are mostly laminar, transition to turbulence and flow separations are observed at curved vessels, bifurcations, or constrictions. It is known that wall-shear stress plays an important role in the development of atherosclerosis as well as in arteriovenous grafts. In order to help understand the behavior of flow separation and transition to turbulence in post-stenotic blood flows, an experimental study of transitional pulsatile flow with stenosis was carried out using time-resolved particle image velocimetry and a microelectromechanical systems wall-shear stress sensor at the mean Reynolds number of 1750 with the Womersley number of 6.15. At the start of the pulsatile cycle, a strong shear layer develops from the tip of the stenosis, increasing the flow separation region. The flow at the throat of the stenosis is always laminar due to acceleration, which quickly becomes turbulent through a shear-layer instability under a strong adverse pressure gradient. At the same time, a recirculation region appears over the wall opposite to the stenosis, moving downstream in sync with the movement of the reattachment point. These flow behaviors observed in a two-dimensional channel flow are very similar to the results obtained previously in a pipe flow. We also found that the behavior in a pulsating channel flow during the acceleration phase of both 25% and 50% stenosis cases is similar to that of the steady flow, including the location and size of post-stenotic flow separation regions. This is because the peak Reynolds number of the pulsatile flow is similar to that of the steady flow that is investigated. The transition to turbulence is more dominant for the 50% stenosis as compared to the 25% stenosis, as the wavelet spectra show a greater broadening of turbulence energy. With an increase in stenosis to 75%, the accelerating flow is directed toward the opposite wall, creating a wall jet. The shear layer from the stenosis bifurcates as a result of this, one moving with the flow separation region toward the upper wall and the other with the wall jet toward the bottom wall. Low wall-shear stress fluctuations are found at two post-stenotic locations in the channel flow – one immediately downstream of the stenosis over the top wall (stenosis side) inside the flow separation region, and the other in the recirculation region on the bottom wall (opposite side of the stenosis). [ABSTRACT FROM AUTHOR]

Aerogels are a novel type of open‐cell porous material. They are particularly suitable for passive sound‐absorption due to their high porosity and high‐surface areas of the internal structures, but with the drawbacks of limited absorption rate of low‐frequency sound and poor mechanical performance. Here, it is first demonstrated that the M13 phage aerogel(M13AG) with hierarchically porous and ribbing structures is beneficial to sound‐absorption and the local piezoelectric effect attributed to M13 phages can further improve the sound‐absorption ability in the low‐frequency. The sound‐absorption coefficient of the M13AG with thickness of 20 mm attains peak value of 0.992 at 1600 Hz. In addition, the M13AG is assembled on a metallic foam framework to enhance its mechanical performance. The resulting M13AG/nickel foam exhibits enhanced compressive yield strength up to 0.14 MPa. This study opens up a new opportunity for passive sound‐absorption. [ABSTRACT FROM AUTHOR]

The effect of annealing on the thermoelectricity of indium tin oxide (ITO) thin film thermocouples (TFTCs) was studied. A microstructure characterisation indicate the influence of two different annealing mechanisms on the thermoelectric properties, namely, recrystallisation and carrier concentration. The ITO thin films recrystallised when the annealing temperature reached 1100 ∘ C in air, which improved the thermoelectric reproducibility, linearity, and stability of the TFTCs. More oxygen vacancies were produced in the ITO thin films after annealing at 400 ∘ C in vacuum, but were reduced after annealing at 1100 ∘ C in air. The Sn2+ ions transformed into Sn4+ ions in the ITO 90/10 thin films after annealing, providing additional free electrons in the films. These microstructural transformations are related to changes in the thermoelectric properties of the ITO TFTCs, as described by the thermoelectric theory of degenerated semiconductors. A decrease in the Seebeck coefficient after annealing was attributed to increases in the carrier concentrations and recrystallisation. Additionally, after annealing at 1100 ∘ C in air, the Seebeck coefficient of the ITO TFTCs agreed with the theoretical value. These results can be used to control thin film thermoelectric properties by different annealing processes. [ABSTRACT FROM AUTHOR]

This paper proposes a flexible double-sided attached microwave sensor film for real-time measurement of the liquid dielectric constant, and proposes a nested-complementary split ring resonator（NCSRR）structure with high sensitivity and quality factor values that is based on the structure evolution of a complementary split ring resonator（CSRR）. The sensor films are composed of a ground film with an NCSRR structure and a U-shaped microstrip line film. By taking a borosilicate glass beaker and a polypropylene beaker as examples, two types of microwave sensors are formed by attaching films to both sides of the beakers. Lubricating oil with 0%− 25% water content is added to the beakers separately, and the dielectric constants of the mixture are characterized nondestructively by the transmission coefficient (S21) of the device. According to the mathematical model established from the measurement results, the resonant frequencies of both sensors are linearly and negatively correlated with the dielectric constant of the liquid to be measured, which proves that the sensor film can be attached to a substrate with arbitrary curvature to form a microwave resonant sensor. [Display omitted] • The sensor films are flexible and can be attached to a curved substrate to form a microwave sensor. • The sensor is loaded with an NCSRR-based resonant ring that can be used to detect the dielectric constant of lubricant-water mixtures. • The sensor films are attached to both sides of the beaker to form the sensor, eliminating the need to prepare a chamber to carry the liquids. • The designed sensor offers a high sensitivity in comparison with the state-of-art designs in the literature. [ABSTRACT FROM AUTHOR]

Ice accumulation and adhesion on solid surfaces can cause various problems in aircrafts, power lines, roads, ships, wind turbines, oil platforms, and telecommunication systems. A feasible strategy to combat icing is to cover the surface by using a flexible hydrophobic film. In this study, ice accumulation and adhesion were reduced by using a flexible PDMS micro-rod film. A simulative closed-loop ice wind tunnel and an ice adhesion measurement apparatus were custom built to investigate the relationship between PMDS micro-rod geometry and ice accumulation and adhesion. Our experiments show that decreasing the micro-rod space on the flexible PDMS film will increase the contact angle and decrease the contact angle hysteresis of the surface, thus reducing ice accumulation and adhesion. Wettability change is interpreted by a speculative and qualitative model of intruding depth variation. The reduction in ice accumulation is attributed to ice nucleation delay because of the increased energy barrier in the heterogeneous nucleation. The reduction in ice adhesion is explained by the reduced ice–solid contact area and mechanical interlock. Results indicate that the flexible micro-rod film has great potential in future anti-icing applications. [ABSTRACT FROM AUTHOR]

This paper presents the design, fabrication and characterization of a low-noise Z-axis micromachined gyroscope. A triple-mass scheme is adopted to obtain a decoupled mode and matched vibration structure. The gyroscope was fabricated based on a 30-μm silicon on insulator wafer. A DRIE, lag-effect-based, dicing-free process was used to easily and rapidly create the gyroscope devices without requiring normal dicing. The fabricated gyroscopes were vacuum packaged (pressure of approximately 2,000 Pa) and tested. The measured power spectral density of the noises is as low as 17.5 μV/√Hz, and the resolution of the fabricated gyroscope is 7.1 × 10-4°/s/√Hz (2.52°/h/√Hz). [ABSTRACT FROM AUTHOR]

Highlights: [•] The surface with hierarchical micro-nano-pillars had the least ice adhesion, which was far less than the surface with micro-pillars and smooth surface without any structure (MN

This paper reports a novel design for electrostatic microgrippers. The new structure utilizes rotary comb actuators to solve the pull-in problem of microgrippers during large displacement manipulation and therefore avoids the widely used conversion systems which necessitate a high driving voltage. The gripper is fabricated using a SOI process with a 60 μm structural layer. Test results show the gripper obtained a displacement of 94 μm with an applied voltage of 100 V. An animal hair is gripped to demonstrate the applicability of the gripper for micro object manipulations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Increasing the height and decreasing the space of the micro-rod may result in Cassie wetting state. [•] Decreasing the height and increasing the space of the micro-rod may result in Wenzel wetting state. [•] A suspended wetting state model due to wall scallops was proposed. [•] The wetting state transition was interpreted by intruding height, de-pinning and sag mechanism. [ABSTRACT FROM AUTHOR]

A new type of flexible balloon actuator for active flow control is developed. Compared with the existing balloon actuator with a rigid substrate, it possesses total structural flexibility and perfect air-tightness even with internal high pressure gas. Finite element method is used to analyze the mechanical properties of elastic membrane. The maximum deflection of the balloon membrane is calculated to be 1.5 mm. To investigate the control ability of the actuators, numerical simulation is carried out. The results show that the actuators can dramatically alter the flow field within the boundary layer. Flight test shows that the inflated balloon actuators lead to local flow separation. The imbalance of localized pressure on the airfoils induces an extra rolling moment and the rolling angle of the UAV is changed about 30°. [ABSTRACT FROM AUTHOR]

Abstract: An effective fabrication method combining deep reactive ion etching and galvanic etching for silicon micro–nano hierarchical structures is presented in this paper. The method can partially control the morphology of the nanostructures and enables us to investigate the effects of geometry changes on the properties of the surfaces. The forming mechanism of silicon nanostructures based on silver nanoparticle galvanic etching was illustrated and the effects of process parameters on the surface morphology were thoroughly discussed. It is found that process parameters have more impact on the height of silicon nanostructure than its diameter. Contact angle measurement and tilting/dropping test results show that as-prepared silicon surfaces with hierarchical structures were superhydrophobic. What’s more, two-scale model composed of micropillar arrays and nanopillar arrays was proposed to study the wettability of the surface with hierarchical structures. Wettability analysis results indicate that the superhydrophobic surface may demonstrate a hybrid state at which water sits on nanoscale pillars and immerses into microscale grooves partially. [Copyright &y& Elsevier]

Abstract: Wettability tailoring of patterned silicon surface has great potential in fields producing integrated circuits, solar cells, sensors, detectors, and micro/nano electromechanical systems. The present paper presents a convenient yet effective method of combining reactive ion etching and catalyzed etching to prepare silicon surface with micro–nano dual-scale pillars. The experimental results indicate that the hydrophilic surface transformed to a superhydrophobic surface when micro–nano dual-scale pillars were formed. The surface preserved superhydrophobicity even when the geometric parameters of the micropillars were changed. Overhangs of water drops on steep micro–nano dual-scale pillars result in superhydrophobicity. This method offers a new way for tailoring the wettability of patterned silicon surfaces. [Copyright &y& Elsevier]

Multimode Nd:YAG pulse laser was applied to remove micron and submicron particles by vaporizing a thin paint film pre-coated on super-smooth optical substrate surface. By analyzing the poor absorption of the optical glass substrate to the irradiative Nd:YAG pulse laser, the removal mechanism of contaminated colloidal particles from the super-smooth surface through vaporization of a volatile solid film is described. A limit analysis was proposed to determine the lower and the upper threshold of laser fluence for cleaning the SiO2 contaminants from super-smooth K8 optical substrate. Relevant experiments on laser cleaning of micron-polishing particles from super-smooth K8 optical substrate confirmed the usefulness of this method in assisting the selection of effective cleaning fluence for accomplishing high cleanliness, which was in a range of 80–90% of the predicted upper threshold. [Copyright &y& Elsevier]

Micron and submicron SiO2 polishing particle and remaining polishing powder contaminations on super-smooth glass surface adversely influences: (i) the performance and quality of glass and (ii) the productivity of optical product. To remove these particles, multimode Nd:YAG pulse laser was used to vaporize an applied thin film of black paint on the substrate surface. Experiments to examine the removal efficiency of polishing particles from poor laser absorptive super-smooth K8 optical glass (K8 OG) substrate were performed, and they showed good workability of the cleaning method. Based on the experimental and theoretical results, some mechanisms related to the laser removal of the contaminating colloidal particles from the surface were described. [Copyright &y& Elsevier]

Nonlinearity is a common problem for many types of microgrippers and can make it difficult to achieve high precision control over the entire input variation range. This paper presents a linear electrostatic driving scheme consisting of a bidirectional rotary actuator and a divider circuit for microgrippers. Different from the conventional approach, the rotary actuator in the linear electrostatic driving scheme is driven by two differential driving voltages provided by the divider circuit. Using the linear electrostatic driving scheme, the displacement of the microgripper's jaw is proportional to the resistance of potentiometer of the divider circuit. The experiment shows that the jaw gap of the microgripper varies from 0 to 220 μm when the potentiometer rotates from 300° to 3240°. The nonlinear error of the rotatory microgripper is 0.14%, which is an improvement of over 100 times compared with the conventional driving scheme. In addition, a pick–release grasping experiment on glass spheres is performed to prove the capability of the rotatory microgripper in handling micro objects. [Display omitted] • A new linear electrostatic driving (LED) scheme is presented for microgrippers to solve nonlinear problems. • The linear motion of the rotatory microgripper is proved theoretically and experimentally. • A grasping experiment is performed to prove the capability of the microgripper in handling micro objects. • The LED scheme promotes control accuracy and provides higher driving efficiency. [ABSTRACT FROM AUTHOR]

• Polarization-sensitive subtractive structural color generated by the elliptical metal-insulator-metal (MIM) nanostructure arrays as the building block for information encoding and dynamic display. • Wide color gamut, strong polarization sensitivity. • Increasing the concealment of information and improving the information encoding capacity by the combination of polarization dependent and independent nanostructures. • Generating the animation effect by polarization controllable dynamic display with the well-designed pixels of different polarizations. Structural color with polarization sensitivity has been widely studied due to its benefits for improving information storage and dynamic color display capacity. However, large amount and good concealment of information encoding are the major issues to be addressed. Here, we propose the elliptical Al/ a -Si/Al (metal-insulator-metal, MIM) nanostructure arrays as the basic building blocks to realize polarization-sensitive subtractive structural colors for information encoding, and dynamic polarization-resolved displays. The experimentally realized structural color exhibits a wide color gamut covering the whole cyan, magenta, and yellow (CMY) color system, and presents a strong dependence on the incident polarization state due to its shape anisotropy. A new approach to improve the information encoding capacity is demonstrated using this structure combined with the polarization-independent nanostructures, increasing the concealment of information. Additionally, the polarization controllable dynamic display is engineered by the well-designed pixels with respect to different polarizations, generating the animation effect. These intrinsic properties and functionalities of the proposed structural color significantly extend its potential to the fields of information encoding, security encryption, and dynamic displays, not limited to color printing and filtering devices. [ABSTRACT FROM AUTHOR]

Thermal films based on carbon nanotube (CNT) composite film have attracted focus in practical applications. This paper develops a highly flexible and multi-role CNT/Polyimide (PI) composite film by employing the dielectrophoresis technique to incorporate bundles of SWCNT into patterned PI substrates. The CNT composite film with a nickel conductive layer exhibits a tunable temperature coefficient of resistivity (TCR) while vacuum thermally treated at diverse temperature. The evolution of the TCR could be controlled from the negative correlation (reached −15000 ppm/°C) to the positive (up to nearly 10000 ppm/°C), which is mainly determined by the reform of the tube connection and covalent bonds in composites due to accumulated thermal energy of annealing, resulting in the change of charge transport. Moreover, the transient response of film devices annealed at different temperature could remain on the order of microseconds proving the robustness of the technology. Demonstrations in human body temperature sensing and micro wind tunnel flow measuring represent excellent sensitivity and reproducibility. The proposed thermal film based on CNT/PI composite with a tunable resistance-temperature characteristic gives a great application potential in intelligent protection electronics, sensing elements and other related thermal applications. Image 1 [ABSTRACT FROM AUTHOR]

3D bioprinting is recognized as a promising biomanufacturing technology that enables the reproducible and high-throughput production of tissues and organs through the deposition of different bioinks. Especially, bioinks based on loaded cells allow for immediate cellularity upon printing, providing opportunities for enhanced cell differentiation for organ manufacturing and regeneration. Thus, extensive applications have been found in the field of tissue engineering. The performance of the bioinks determines the functionality of the entire printed construct throughout the bioprinting process. It is generally expected that bioinks should support the encapsulated cells to achieve their respective cellular functions and withstand normal physiological pressure exerted on the printed constructs. The bioinks should also exhibit a suitable printability for precise deposition of the constructs. These characteristics are essential for the functional development of tissues and organs in bioprinting and are often achieved through the combination of different biomaterials. In this review, we have discussed the cutting-edge outstanding performance of different bioinks for printing various human tissues and organs in recent years. We have also examined the current status of 3D bioprinting and discussed its future prospects in relieving or curing human health problems.

A VCF-based mode-matching micromachine-optimized tuning fork gyroscope is proposed to not only maximize the scale factor of the device, but also avoid use of an additional quadrature-nulling loop to prevent structure complexity, pick-up electrode occupation, and coupling with a mode-matching loop. In detail, a mode-matching, closed-loop system without a quadrature-nulling loop is established, and the corresponding convergence and matching error are quantitatively analyzed. The optimal straight beam of the gyro structure is then modeled to significantly reduce the quadrature coupling. The test results show that the frequency split is narrowed from 20 Hz to 0.014 Hz. The scale factor is improved 20.6 times and the bias instability (BI) is suppressed 3.28 times. The observed matching accuracy demonstrates that a mode matching system without a quadrature suppression loop is feasible and that the proposed device represents a competitive design for a mode-matching gyroscope.

There is huge demand for recreating human skin with the functions of epidermis and dermis for interactions with the physical world. Herein, a biomimetic, ultrasensitive, and multifunctional hydrogel-based electronic skin (BHES) was proposed. Its epidermis function was mimicked using poly(ethylene terephthalate) with nanoscale wrinkles, enabling accurate identification of materials through the capabilities to gain/lose electrons during contact electrification. Internal mechanoreceptor was mimicked by interdigital silver electrodes with stick-slip sensing capabilities to identify textures/roughness. The dermis function was mimicked by patterned microcone hydrogel, achieving pressure sensors with high sensitivity (17.32 mV/Pa), large pressure range (20-5000 Pa), low detection limit, and fast response (10 ms)/recovery time (17 ms). Assisted by deep learning, this BHES achieved high accuracy and minimized interference in identifying materials (95.00% for 10 materials) and textures (97.20% for four roughness cases). By integrating signal acquisition/processing circuits, a wearable drone control system was demonstrated with three-degree-of-freedom movement and enormous potentials for soft robots, self-powered human-machine interaction interfaces of digital twins.

Planar super-oscillatory lens (SOL), a far-field subwavelength-focusing diffractive device, holds great potential for achieving sub-diffraction-limit imaging at multiple wavelengths. However, conventional SOL devices suffer from a numerical-aperture-related intrinsic tradeoff among the depth of focus (DoF), chromatic dispersion and focusing spot size. Here, we apply a multi-objective genetic algorithm (GA) optimization approach to design an apochromatic binary-phase SOL having a prolonged DoF, customized working distance (WD), minimized main-lobe size, and suppressed side-lobe intensity. Experimental implementation demonstrates simultaneous focusing of blue, green and red light beams into an optical needle of ~0.5λ in diameter and DOF > 10λ at WD = 428 μm. By integrating this SOL device with a commercial fluorescence microscope, we perform, for the first time, three-dimensional super-resolution multicolor fluorescence imaging of the "unseen" fine structures of neurons. The present study provides not only a practical route to far-field multicolor super-resolution imaging but also a viable approach for constructing imaging systems avoiding complex sample positioning and unfavorable photobleaching., (© 2023. Springer Nature Limited.)

Moisture condensation, fogging, and frost or ice formation on structural surfaces cause severe hazards in many industrial components such as aircraft wings, electric power lines, and wind-turbine blades. Surface-acoustic-wave (SAW) technology, which is based on generating and monitoring acoustic waves propagating along structural surfaces, is one of the most promising techniques for monitoring, predicting, and also eliminating these hazards occurring on these surfaces in a cold environment. Monitoring condensation and frost/ice formation using SAW devices is challenging in practical scenarios including sleet, snow, cold rain, strong wind, and low pressure, and such a detection in various ambient conditions can be complex and requires consideration of various key influencing factors. Herein, the influences of various individual factors such as temperature, humidity, and water vapor pressure, as well as combined or multienvironmental dynamic factors, are investigated, all of which lead to either adsorption of water molecules, condensation, and/or frost/ice in a cold environment on the SAW devices. The influences of these parameters on the frequency shifts of the resonant SAW devices are systematically analyzed. Complemented with experimental studies and data from the literature, relationships among the frequency shifts and changes of temperature and other key factors influencing the dynamic phase transitions of water vapor on SAW devices are investigated to provide important guidance for icing detection and monitoring.

Sub-diffraction-limit quasi-non-diffracting light sheets (SQLSs) are crucial for a resolution-enhanced and field of view (FOV)-enlarged light sheet microscope. However, it has aways been plagued by sidelobes inducing severe background noise. Here, a self-trade-off optimized method is proposed to generate sidelobe-suppressed SQLSs based on super-oscillatory lenses (SOLs). An SQLS thus obtained shows sidelobes of only 15.4%, first realizing the sub-diffraction-limit thickness, quasi-non-diffracting characteristic, and suppressed sidelobes simultaneously for static light sheets. Moreover, a window-like energy allocation is realized by the self-trade-off optimized method, successfully further suppressing the sidelobes. In particular, an SQLS with theoretical sidelobes of 7.6% is achieved within the window, which provides a new strategy to deal with sidelobes for light sheets and shows great potential in high signal-to-noise ratio light sheet microscopy (LSM).

Biomimetic riblet surfaces, such as blade, wavy, sinusoidal, and herringbone riblet surfaces, have widespread applications for drag reduction in the energy, transportation, and biomedicine industries. The drag reduction ability of a blade riblet surface is sensitive to the yaw angle, which is the angle between the design direction of the riblet surface and the average flow direction. In practical applications, the average flow direction is often misaligned with the design direction of riblet surfaces with different morphologies and arrangements. However, previous studies have not reported on the drag reduction characteristics and regularities related to the yaw angle for surfaces with complex riblet microstructures. For the first time, we systematically investigated the aerodynamic drag reduction characteristics of blade, wavy, sinusoidal, and herringbone riblet surfaces affected by different yaw angles. A precisely adjustable yaw angle measurement method was proposed based on a closed air channel. Our results revealed the aerodynamic behavior regularities of various riblet surfaces as affected by yaw angles and Reynolds numbers. Riblet surfaces with optimal air drag reduction were obtained in yaw angles ranging from 0 to 60° and Reynolds numbers ranging from 4000 to 7000. To evaluate the effects of the yaw angle, we proposed a criterion based on the actual spanwise spacing ( d + ) of microstructure surfaces with the same phase in a near-wall airflow field. Finally, we established conceptual models of aerodynamic behaviors for different riblet surfaces in response to changes in the airflow direction. Our research lays a foundation for practical various riblet surface applications influenced by yaw angles to reduce air drag.

We propose a non-paraxial diffraction model of the digital micromirror device (DMD) by combining the conventional Fraunhofer diffraction and a simple method of coordinative mapping. It is equivalent to adding aberrations of diffracted wave fields to the aberration-free Fraunhofer diffraction instead of complex integral calculations, allowing the simulated diffraction patterns to be consistent with the actual experimental counterparts. Moreover, it is verified by the experiments and literature that the diffraction angles, orders, and efficiency can all be well predicted for arbitrary incident angles and wavelengths. Especially for diffracted zenith angles within 50°, the predicted values reveal ∼1% error, and in a broader range, the predicted errors of diffracted azimuth angles are less than 4%. To the best of our knowledge, it is the first model capable of describing the non-paraxial diffraction behavior of the DMD. The proposed model with universality and effectiveness will help users to optimally construct DMD-based optical systems by guiding optical layouts, selection of light sources, and utilization and suppression of diffraction effects.

Flexible superomniphobic doubly re-entrant (Dual-T) microstructures inspired by springtails have attracted growing attention due to their excellent liquid-repellent properties. However, the simple and practical manufacturing processes of the flexible Dual-T microstructures are urgently needed. Here, we proposed a one-step molding process coupled with the lithography technique to fabricate the elastomeric polydimethylsiloxane (PDMS) Dual-T microstructure surfaces with high uniformity. The angle between the downward overhang and the horizontal direction could reach 90° (vertical overhang). The flexible superomniphobic Dual-T microstructure surfaces, without fluorination treatment and physical treatments, could repel liquids with a surface tension lower than 20 mN m -1 in the Cassie-Baxter state. Owing to the excellent robustness of the one-step molding downward overhanging, the max breakthrough pressure of this surface could reach up to 164.3 Pa for ethanol droplets. Furthermore, the flexible superomniphobic Dual-T surface allowed impinging ethanol droplets to completely rebound at the Weber number up to 7.1 with an impact velocity of ∼0.32 m s -1 . The Dual-T microstructure surface maintained excellent superomniphobicity even after surface oxygen plasma treatment and exhibited excellent structural robustness and recoverability to various large mechanical deformations.

Static light sheets are widely used in various super-resolution three-dimensional (3D) imaging applications. Here, a multifocal diffraction-free optimized design method is proposed for super-oscillatory lenses (SOLs) owning an enlarged field of view (FOV) to generate sub-diffraction-limit light sheets with reduced divergence. Various propagation lengths of sub-diffraction-limit thickness for light sheets can be obtained by adopting corresponding numbers of discrete foci and spacing between them. In particular, the propagation lengths of 150.4λ and 118.9λ are obtained by SOLs with an enlarged FOV of 150λ and 820λ, respectively, which show the longest depth of focus (DOF), as far as we know, and are the first to realize the combination of enlarged DOF and FOV for SOLs. We show a way of using binary-amplitude modulation to generate static light sheets with sub-diffraction-limit thickness and reduced divergence, which is simple, easy to integrate, and sidelobe-suppressed.

Lower stiffness can improve the performance of capacitive-based microelectromechanical systems sensors. In this paper, softened beams, achieved by the electrostatic assembly approach, are proposed to lower the stiffness of a capacitive MEMS accelerometer. The experiments show that the stiffness of the accelerometer is reduced by 43% with softened beams and the sensitivity is increased by 72.6%. As a result, the noise of the accelerometer is reduced to 26.2 μg/√Hz with an improvement of 44.5%, and bias instability is reduced to 5.05 μg with an enhancement of 38.7%. The electrostatic assembly-based stiffness softening technique is proven to be effective and can be used in many types of MEMS devices.

One of the critical issues for electret/triboelectric devices is the poor charge viability and stability in humid environments. Herein, we propose a new origami-inspired "W-tube"-shaped triboelectric nanogenerator (W-TENG) with two thin-film electrets folded based on Miura-origami. The Miura-origami fold is capable of transforming flat materials with large surface areas into reduced and compressed complex 3D structures with parallelogram tessellations. The triboelectric power generation components can thus be hermetically sealed inside the "W-tube" to avoid contact with the external humid environment. Furthermore, the elastic nature of the Miura-origami fold endows the proposed W-TENG device with excellent deformability, flexibility, and stretchability. Therefore, it is capable of harvesting kinetic energy from various directions and forms of movement, including horizontal pressing, vertical tapping, and lateral bending. The compact, light weight, and self-rebounding properties of the origami structure also make it convenient for integration into wearable devices. Various parameters of the W-TENG are intensively investigated, including the number of power generation units, original height of the device, acceleration magnitude, excitation direction, and water-proof capability. Triggered by hand tapping impulse excitation in the horizontal and vertical directions, the instantaneous open-circuit voltages can reach 791 V and 116 V with remarkable optimum powers of 691 μW at 50 MΩ and 220 μW at 35 MΩ, respectively. The outcomes of this work demonstrate the fusion of the ancient art of origami, material science, and energy conversion techniques to realize flexible, multifunctional, and water-proof TENG devices., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© The Author(s) 2020.)

Super-oscillatory lens (SOL) optical microscopy, behaving as a non-invasive and universal imaging technique, as well as being a simple post-processing procedure, may provide a potential application for sub-diffraction-limit fluorescence imaging. However, the low energy concentration, high-intensity sidelobes and micrometer-scale working distance of the reported planar SOLs impose unavoidable restrictions on the ground-state applications. Here, we demonstrate step-shaped SOLs based on the multiple-phase-modulated (MPM) method to improve the focusing efficiency. Two pivotal advantages are thus generated: (i) the fabrication complexity can be effectively reduced based on several conventional optical lithography steps; (ii) the focusing efficiency is much higher than that of the random MPM ones due to the efficient manipulation of the wavefronts, bringing about a stronger light concentration to the focal spot. Additionally, the ratio of the sidelobe intensity is flexibly tuned to meet the customized requirements, and a 2 mm-working-distance MPM SOL with the sidelobe intensity highly suppressed is finally exploited. For the first time, as far as we know, a SOL-based fluorescence microscopy without the pinhole filter to map the horizontal morphology of the dispersive fluorescent particles is established. Compared with the results achieved by the conventional wide-field microscopy, the sample details beating the diffraction limit can be reconstructed by simple imaging fusion. This research demonstrates the promising applications of SOLs for low-cost, simplified and highly customized sub-diffraction-limit fluorescence imaging systems free from photobleaching and an extremely short working distance.

Conventional optics suffer from the diffraction limit. Our recent work has predicted a nanoslit-based two-dimensional (2D) lens with transverse-electric (TE) polarized design that is capable of realizing the super-resolution focusing of light beyond the diffraction limit in the quasi-far field. Furthermore, the super-resolution capability can be kept in a high-refractive-index dielectric over a wide wavelength range from ultraviolet to visible light. Here, we systematically investigate the influence of various factors on the super-resolution focusing performance of the lens. Factors such as lens aperture, focal length and nanoslit length are considered. In particular, the influence of nanoslit length on lens focusing was ignored in the previous reports about nanoslit-based 2D lenses, since nanoslit length was assumed to be infinite. The numerical results using the finite-difference time-domain (FDTD) method demonstrate that the super-resolution focusing capability of a nanoslit-based 2D lens increases with the lens aperture and reduces with the increase of the lens focal length. On the other hand, it is notable that the length of the lens focus is not equal to but smaller than that of the nanoslits. Therefore, in order to achieve a desired focus length, a lens should be designed with longer nanoslits., Competing Interests: The authors declare no conflict of interest.

A broadband optical absorber based on the nanostructured germanium (Ge) film composed of single-sized circular nanodisk-nanohole arrays is proposed, which demonstrates high efficiency, strong polarization independence, and large viewing angle. Due to the electric and magnetic resonance absorption modes excited by the nanostructure arrays in highly lossy Ge film, the absorber obtains a high absorptivity, reaching above 90% over the full visible wavelength, and it can be maintained well at a large viewing angle over ±50°. Based on the geometrical symmetry, the absorber is proved to be polarization independent. Moreover, the simple single-sized nanostructure within a certain size tolerance decreases the design and fabrication complexity. The structural configuration with a slight Ge sidewall formed in the nanofabrication process could enhance the overall light absorption. These results indicate that the proposed broadband absorber has great potential in various applications such as anti-reflective coating and perfect cloaking.

Planar super-oscillatory lenses (SOLs) can exert far-field foci beyond the diffraction limit free from the contribution of evanescent waves. However, the reported design methods of SOLs are always complicated and divergent, leading to a poor control over the desired focusing patterns. Furthermore, the existing device sizes of SOLs are mainly within hundreds of micrometers accompanied by a subwavelength-scale feature size. Here, we propose a general optimization design model for realizing flexible focusing patterns, e.g. multifocal and achromatic contours. Additionally, a novel design called the chromatic-customized SOL fighting against the dispersion rule of traditional diffractive optical elements (DOEs) is also demonstrated based on the proposed flexible algorithm. The diameters for all the SOLs reach 12 mm with 30 μm minimum feature size, which can be easily fabricated by employing the conventional optical lithography technique. Such centimeter-scale, light weight and low-cost lenses reveal new capacities of arbitrarily customized optical patterns in various interdisciplinary fields including parallel particle trapping, full-color high-resolution imaging, and compact spectral imaging.

Slit arrays based on noble metals have been widely proposed as planar transverse-magnetic (TM)-lenses, illuminated by a linearly polarized light with the polarization perpendicular to slits and implementing the focusing capability beyond the diffraction limit. However, due to intrinsic plasmonic losses, these TM-lenses cannot work efficiently in the ultraviolet wavelengths. In this Letter, taking advantage of the unique transmission through metallic slits not involving plasmonic losses, a metallic slit array with transverse-electric (TE)-polarized design is proposed, showing for the first time, to the best of our knowledge, the realization of sub-diffraction-limit focusing for ultraviolet light. Additionally, in contrast to the situations of TM-lenses, a wider slit leads to a greater phase delay and much larger slits can be arranged to construct the TE-lenses, which is quite beneficial for practical fabrication. Furthermore, deep-subwavelength focusing can be achieved by utilizing the immersing technology.

Obtaining a correlation factor is a prerequisite for fusing multiple outputs of a mircoelectromechanical system (MEMS) gyroscope array and evaluating accuracy improvement. In this paper, a mathematical statistics method is established to analyze and obtain the practical correlation factor of a MEMS gyroscope array, which solves the problem of determining the Kalman filter (KF) covariance matrix Q and fusing the multiple gyroscope signals. The working principle and mathematical model of the sensor array fusion is briefly described, and then an optimal estimate of input rate signal is achieved by using of a steady-state KF gain in an off-line estimation approach. Both theoretical analysis and simulation show that the negative correlation factor has a favorable influence on accuracy improvement. Additionally, a four-gyro array system composed of four discrete individual gyroscopes was developed to test the correlation factor and its influence on KF accuracy improvement. The result showed that correlation factors have both positive and negative values; in particular, there exist differences for correlation factor between the different units in the array. The test results also indicated that the Angular Random Walk (ARW) of 1.57°/h 0.5 and bias drift of 224.2°/h for a single gyroscope were reduced to 0.33°/h 0.5 and 47.8°/h with some negative correlation factors existing in the gyroscope array, making a noise reduction factor of about 4.7, which is higher than that of a uncorrelated four-gyro array. The overall accuracy of the combined angular rate signal can be further improved if the negative correlation factors in the gyroscope array become larger., Competing Interests: The authors declare no conflict of interest.

A novel low-cost, batch-fabrication method combining the spin-coating nanosphere lithography (NSL) with the conventional photolithographic technique is demonstrated to efficiently produce the metallic planar microlenses and their arrays. The developed microlenses are composed of subwavelength nanoholes and can focus light effectively in the entire visible spectrum, with the foci sizes close to the Rayleigh diffraction limit. By changing the spacing and diameter of nanoholes, the focusing efficiency can be tuned. Although the random defects commonly exist during the self-assembly of nanospheres, the main focusing performance, e.g., focal length, depth of focus (DOF), and full-width at half-maximum (FWHM), keeps almost invariable. This research provides a cheap way to realize the integrated nanophotonic devices on the wafer level.

A new variant of MEMS surface fence is proposed for shear-stress estimation under high-speed, high-temperature flow conditions. Investigation of high-temperature resistance including heat-resistant mechanism and process, in conjunction with high-temperature packaging design, enable the sensor to be used in environment up to 400 °C. The packaged sensor is calibrated over a range of ~65 Pa and then used to examine the development of the transient flow of the scramjet ignition process (Mach 2 airflow, stagnation pressure, and a temperature of 0.8 MPa and 950 K, respectively). The results show that the sensor is able to detect the transient flow conditions of the scramjet ignition process including shock impact, flow correction, steady state, and hydrogen off., Competing Interests: The authors declare no conflict of interest.