Fast image-free autofocus method for passive FSPI microscopy.

Autofocus is crucial for capturing sharp images with imaging devices for information acquisition. Traditional autofocus strategies based on post-processing become less efficient for passive FSPI microscopy of yet low temporal resolution. In this Letter, a fast and image-free autofocus system is proposed for passive FSPI microscopy. Based on the complementary design of an optical path, the system can measure the focus degree at 5000 fps while maintaining a high light efficiency for imaging. The proposed system can be easily combined with existing trinocular microscopes, which provides a welcomed boost to the practicability of passive FSPI microscopy.

Research on the Sensing Characteristics of an Integrated Grid-like Sensor Based on a Triboelectric Nanogenerator.

With the development of the integration and miniaturization of sensing devices, the concept of self-sensing devices has been proposed. A motion state is self-sensed via the structure or integration of an actuator in the construction of a sensing unit. This device is then used to capture the perception and measurement of states such as position, displacement, and speed. A triboelectric nanogenerator converts mechanical energy into electrical energy through the coupling effect of contact generation and electrostatic induction, which represents one of the reliable ways through which to realize integrated sensing. In this world, the power generation technology of the TENG is applied to a sensing device. The sensing characteristics of a grid-like TENG are designed and analyzed in freestanding triboelectric mode. Firstly, a relation model of displacement, velocity, voltage, and charge is established. The charge-transfer increment and current amounts are linearly related to the velocity. The open-circuit voltage has a positive relationship with the displacement. The maximum open-circuit voltage and the maximum charge transfer are fixed values, and they are only related to the inherent parameters of a triboelectric nanogenerator. Next, the sensor model is constructed using COMSOL Multiphysics 6.0. The simulation results show that the relationships between output voltage and charge transfer, as well as those between the increments of charge transfer, velocity, and displacement, are consistent with the results derived from the formula. Finally, a performance test of the designed sensor is carried out, and the results are consistent with the theoretical deduction and simulation. After analysis and processing of the output electrical signal by the host computer, it can feedback the frequency and speed value of the measured object. In addition, the output signal is stable, and there is no large fluctuation or attenuation during the 521-s vibration test. Because the working unit of the sensor is thin filmed, it is small in size, easy to integrate, and has no external power supply; moreover, it can be integrated into a device to realize the self-sensing of a motion state.

Nanosphere Chain Model of Magnetic Fluid and Its Dynamic Performance.

The magnetorheological effect is a critically important mechanical property of magnetic fluids. Accurately capturing the macroscopic properties of magnetorheological fluids with elongated particle forms, such as nanosphere chains, remains a challenging task, particularly due to the complexities arising from particle asymmetry. Traditional particle dynamics primarily utilize spherical particles as computational units, but this approach can lead to significant inaccuracies, especially when analyzing nonspherical magnetorheological fluids, due to the neglect of particle asymmetry. In this work, an advanced particle dynamics model has been developed by integrating the rotation and collision of these asymmetric particles, specifically tailored for the configuration of nanosphere chains. This model exhibits a significant reduction in error by a factor of 3.883, compared to conventional particle models. The results demonstrate that alterations in the geometric characteristics of magnetic nanosphere chains can cause changes in mesoscopic structures and magnetic potential energy, thereby influencing the mechanical properties at the macroscopic level. This work has developed an accurate mesoscopic simulation method for calculating chain-type magnetorheological fluids, establishing a connection between mesoscopic structures and macroscopic properties, and unveiling the tremendous potential for accelerating the design of next-generation magnetic fluids using this approach.

Physics-informed and simulation-driven optimization for binary Fourier single-pixel imaging.

Binary patterns are used in fast Fourier single-pixel imaging (FSI) technology to increase the imaging speed at the expense of spatial resolution or image quality. In this Letter, we propose a method for optimizing the image quality-speed trade-off that is informed by physical principles and driven by data from simulations. To compensate for the quantization error induced by binary dithering, convolution kernels are proposed and optimized for both low and high spatial frequencies. The proposed method has been demonstrated to work in both simulation and experiments. Other single-pixel imaging (SPI) techniques may also benefit from this approach.

Size-dependent magnetomechanically enhanced photothermal antibacterial effect of Fe3O4@Au/PDA nanodurian.

The global health crisis of bacterial resistance to antibiotics requires innovative antibacterial strategies. One promising solution is the exploitation of multifunctional nanoplatforms based on non-resistant antibacterial mechanisms. This work reports a novel Fe3O4@Au/polydopamine (PDA) nanodurian with excellent photothermal-magnetomechanic synergistic antibacterial effects. The one-step formed Au/PDA hybrid shell provides good photothermal properties and spiky surfaces for enhanced magnetomechanic effects. Upon near-infrared (NIR) irradiation, the Fe3O4@Au/PDA nanodurian (200 µg mL-1) achieved nearly 100% antibacterial effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The efficiency of photothermal antimicrobial activity was further enhanced by the application of a rotating magnetic field (RMF), with the sterilization efficiency being increased by up to more than a half compared to the action alone. Interestingly, the size of the nanodurian has a significant impact on the synergistic sterilization effect, with larger particles showing a superior performance due to stronger chain-like structures in the magnetic field. Finally, the Fe3O4@Au/PDA nanodurian also demonstrates effective biofilm removal, with larger particles exhibiting the best eradication effect under the photothermal-magnetomechanic treatment. Overall, this magnetic field enhanced photothermal antibacterial strategy provides a promising broad-spectrum antimicrobial solution to combat bacterial infections. Thus, it possesses great potential in future nanomedicine and pollution treatment.

Dynamic 3D Measurement without Motion Artifacts Based on Feature Compensation.

Phase-shift profilometry (PSP) holds great promise for high-precision 3D shape measurements. However, in the case of measuring moving objects, as PSP requires multiple images to calculate the phase, the movement of the object causes artifacts in the measurement, which in turn has a significant impact on the accuracy of the 3D surface measurement. Therefore, we propose a method to reduce motion artifacts using feature information in the image and simulate it using the six-step term shift method as a case study. The simulation results show that the phase of the object is greatly affected when the object is in motion and that the phase shift due to motion can be effectively reduced using this method. Finally, artifact optimization was carried out by way of specific copper tube vibration experiments at a measurement frequency of 320 Hz. The experimental results prove that the method is well implemented.

Polar coordinate Fourier single-pixel imaging.

Traditional single-pixel imaging uses Fourier patterns to modulate objects in the Cartesian coordinate system. The Cartesian Fourier pattern of single-pixel imaging is inappropriate to display in a circular field of view. However, a circular field of view is a widespread form of display in computed optical imaging. Here, circular patterns are adopted to adapt to the circular visual area. The circular patterns are displayed in polar coordinates and derived from two-dimensional Fourier transform in polar coordinates. The proposed circular patterns have improved imaging efficiency significantly from 63.66% to 100%. The proposed polar coordinate Fourier single-pixel imaging is expected to be applied in circular field-of-view imaging and foveated imaging.

Flexible and Stretchable Elastomer Composites Based on Lightweight Liquid Metal Foam Spheres with Pod-like Contacts.

Liquid metal (LM) is increasingly employed as a conductive filler in soft and flexible elastomer composites owing to its favorable conductivity and liquid fluidity. However, the high density of LM inevitably increases the weight of composites, which brings limitations in large-area and weight-sensitive applications. This work reports a flexible and stretchable elastomer composite composed of pod-like contacting lightweight LM foam spheres and polydimethylsiloxane matrix (LMS/PDMS). The lightweight LMS reduces the amount of LM used in the preparation process while imparting good electrical conductivity and deformability to the composite. The different contact modes of LMS endow the final composites with diverse strain sensitivity. The mechanism of interfacial contact conduction between the LMS with different melting points has been systematically studied, and the result shows that the liquid-solid contact mode of LMS further improves the strain sensitivity of the composite. Moreover, the composite also has satisfactory electrothermal properties and the temperature can quickly reach 70 °C within 30 s, showing good applicability in electric heating. Finally, the composites containing LMS with different contact modes can be developed as multifunctional sensors to detect human activities, temperature variation, and even underwater vibration, demonstrating the great potential in next-generation sensors and electronics.

Enhancing Bioinspired Aramid Nanofiber Networks by Interfacial Hydrogen Bonds for Multiprotection under an Extreme Environment.

In nature, many insects have evolved sclerotic cuticles to shelter their soft bodies, which are considered as "body armor". For beetles, the epidermis is composed of cross-linked intertwined fiber structures; such a fiber network structure could provide an anti-impact function for composites. Aramid nanofibers (ANFs) are of great interest in various applications due to their 1D nanoscale, high aspect ratio, excellent strength and modulus, and impressive chemical and thermal stability. In this paper, a kind of ANF network is prepared by a layer-by-layer assembly method. The enhancing ANF networks are developed by introducing carboxylated chitosan acting as a hydrogen-bondin donors as well as a soft interlocking agent (C-ANFs). As a result of the formation of a nanostructure and the hydrogen-bond interactions, the assembled C-ANF networks presented a high tensile strength (551.4 MPa) and toughness (4.0 MJ/m2), which is 2.41 times and 32.69 times those of neat ANF networks, respectively. The excellent mechanical properties endow C-ANF networks with distinguished anti-impact performance. The specific dissipated energy after mass normalization reaches 7.34 MJ/kg, which is significantly superior to traditional protective materials such as steel and Kevlar composites. A nonlinear spring model is also used to explain the mechanical behavior of C-ANF networks. In addition to anti-impact protection, C-ANF networks can realize more than 99% of UV irradiation absorption and have excellent thermal stability. The chemical stability of C-ANF networks make them survive in acid and alkali environments. The above characteristics show that C-ANF networks have great application value in multiscale protection scenarios under an extreme environment.

High-Performance Liquid Metal/Polyborosiloxane Elastomer toward Thermally Conductive Applications.

With the combination of high flexibility and thermal property, thermally conductive elastomers have played an important role in daily life. However, traditional thermally conductive elastomers display limited stretchability and toughness, seriously restricting their further development in practical applications. Herein, a high-performance composite is fabricated by dispersing room-temperature liquid metal microdroplets (LM) into a polyborosiloxane elastomer (PBSE). Due to the unique solid-liquid coupling mechanism, the LM can deform with the PBSE matrix, achieving higher fracture strain (401%) and fracture toughness (2164 J/m2). Meanwhile, the existence of LM microdroplets improves the thermal conductivity of the composite. Interestingly, the LM/PBSE also exhibits remarkable anti-impact, adhesion capacities under complex loading environments. As a novel stretchable elastomer with enhanced mechanical and thermal behavior, the LM/PBSE shows good application prospects in the fields of thermal camouflages, stretchable heat-dissipation matrixes, and multifunctional shells for electronic devices.

Bio-Inspired Bianisotropic Magneto-Sensitive Elastomers with Excellent Multimodal Transformation.

Magneto-sensitive soft materials that can accomplish fast, remote, and reversible shape morphing are highly desirable for practical applications including biomedical devices, soft robotics, and flexible electronics. In conventional magneto-sensitive elastomers (MSEs), there is a tradeoff between employing hard magnetic particles with costly magnetic programming and utilizing soft magnetic particle chains causing tedious and small deformation. Here, inspired by the shape and movement of mimosa, a novel soft magnetic particle doped shape material bianisotropic magneto-sensitive elastomer (SM bianisotropic MSE) with multimodal transformation and superior deformability is developed. The high-aspect-ratio shape anisotropy and the material anisotropy in which the magnetic particles are arranged in a chainlike structure together impart magnetic anisotropy to the SM bianisotropic MSE. A magneto-elastic analysis model is proposed, and it is elucidated that magnetic anisotropy leads to peculiar field-direction-dependent multimodal transformation. More importantly, a quadrilateral assembly and a regular hexagon assembly based on this SM bianisotropic MSE are designed, and they exhibit 2.4 and 1.7 times the deformation capacity of shape anisotropic samples, respectively. By exploiting the multidegree of freedom and excellent deformability of the SM bianisotropic MSE, flexible logic switches and ultrasoft magnetic manipulators are further demonstrated, which prove its potential applications in future intelligent flexible electronics and autonomous soft robotics.

3D Printing Ultraflexible Magnetic Actuators via Screw Extrusion Method.

Soft magnetic actuators with programmable structure design and controllable deformation ability based on 3D printing technology have attracted extensive attention. In this paper, a novel 3D printing strategy is developed to manufacture the ultraflexible magnetic actuator, in which the printed material is composed of magnetic particles and thermoplastic rubber materials. Different from the traditional fused deposition printing, this printing strategy introduces screw extrusion technology to the heating components of the printer to overcome the problem of filament buckling in the flexible material. Thus, the tensile modulus of the printed products can be reduced to as low as ≈2 MPa. Based on the above method, biomimetic magnetic actuators of the sucker and the pump are constructed for adhering and releasing object and pumping liquid. The contraction performance of the magnetic actuator is studied via a series of experiments and the magnetic field-induced deformation is analyzed by the multiphysics-based finite element model. This work proves that ultraflexible magnetic actuators fabricated by this 3D printing strategy show broad prospects in the fields of soft robotics and bionics.

Reflection removal detection enabled by single-pixel imaging through the semi-reflective medium.

Due to the substantial reflection information of the surrounding environment, it is difficult for a conventional camera to directly capture the distinct image behind without interference from the reflected virtual image through semi-reflective media such as an acrylic plate, glass, or water. Traditional reflective artifact removal methods either demand a major commitment of calculations or constrained photography conditions such as the use of a polarizer, which often degrades the performance of the reflection removal process and imposes a limitation on the application area. A different reflection removal method is investigated, where the interfering light rays can be attenuated effectively based on a differential calculation with a Fourier single-pixel imaging method. Experiments show that this method eliminates the interference caused by reflection from interfering objects and obtains clear images through an acrylic plate (with thicknesses of 1 mm, 2 mm, and 3 mm), glass (5 mm), and even transparent water (100 mm). Another experiment has been carried out to effectively image the target by removing the reflection through the glasses, which have the same thickness (1.1 mm) but different reflectivity (20%, 30%, 40%, and 50%).

Single-pixel imaging of high-temperature objects.

For visual measurement at high temperature, one challenge is how to reduce the radiation emitted by the high-temperature components themselves and the influence of hot gas flow on the image quality, which has a significant impact in fields such as aerospace or automotive manufacturing. Owing to the complicated optical imaging environment at high temperature, a new, to the best of our knowledge, image acquisition method of high-temperature components is proposed in combination with single-pixel imaging in this paper. A series of illumination patterns is emitted to the object, and the light waves measured by the single-pixel detector are used to reconstruct the image of the object. Single-pixel imaging of high-temperature objects at different temperatures and different spectral segments has been studied in this paper. The experiment proves that the method presented in this paper can decrease the strong light interference of the high-temperature object's own radiation light and reduce the halo caused by the high temperature. This study provides a good impetus for the development of single-pixel imaging in the industrial field of high-temperature components by reducing the radiation light.

Transmissive Single-Pixel Microscopic Imaging through Scattering Media.

Microscopic imaging is of great significance for medical diagnosis. However, due to the strong scattering and absorption of tissue, the implementation of non-invasive microscopic imaging is very difficult. Traditional single-pixel microscopes, based on reflective optical systems, provide an alternative solution for scattering media imaging. Here, the single-pixel microscope with transmissive liquid crystal modulation is proposed. The microscopic ability of the proposed microscope is calibrated. The multi-spectral microscopic imaging of the object is demonstrated. The transmissive imaging of the object behind the scattering media is analyzed. The proposed prototype of the transmissive single-pixel microscope is expected to be applied in microscopic imaging through scattering media and medical imaging.

Target orientation detection based on a neural network with a bionic bee-like compound eye.

The compound eye of insects has many excellent characteristics. Directional navigation is one of the important features of compound eye, which is able to quickly and accurately determine the orientation of an objects. Therefore, bionic curved compound eye have great potential in detecting the orientation of the target. However, there is a serious non-linear relationship between the orientation of the target and the image obtained by the curved compound eye in wide field of view (FOV), and an effective model has not been established to detect the orientation of target. In this paper, a method for detecting the orientation of the target is proposed, which combines a virtual cylinder target with a neural network. To verify the feasibility of the method, a fiber-optic compound eye that is inspired by the structure of the bee's compound eye and that fully utilizes the transmission characteristics and flexibility of optical fibers is developed. A verification experiment shows that the proposed method is able to realize quantitative detection of orientations using a prototype of the fiber-optic compound eye. The average errors between the ground truth and the predicted values of the horizontal and elevation angles of a target are 0.5951 ° and 0.6748°, respectively. This approach has great potential for target tracking, obstacle avoidance by unmanned aerial vehicles, and directional navigation control.

Multi-camera calibration method based on a multi-plane stereo target.

Machine vision techniques, including camera calibration methods, are of great importance for the development of vision-based measurements. However, in multi-camera calibration methods, rapidly constructing accurate geometric relationships among different coordinates is very difficult. Herein, we present a multi-camera calibration method capable of calibrating the intrinsic and extrinsic parameters of four cameras using only a single captured image per camera. Unlike Zhang's method, which relies on multiple captured images to calibrate the cameras, the method uses a multi-plane stereo target containing multiple fixed planes to which coded patterns are attached. This target greatly reduces the time required for calibration and improves calibration robustness. The proposed method was experimentally compared with traditional camera calibration. The problem affecting the calibration accuracy in single calibration of multiple cameras is that the feature points on the captured images produce occlusion or different degrees of blurring; in the calibration of multiple cameras multiple times, the error accumulation caused by the calibration of two adjacent cameras is solved. This demonstration of a multi-camera calibration method improves camera calibration and provides a new design philosophy, to the best of our knowledge, for machine vision and vision-based measurement.

Modal learning displacement-strain transformation.

The displacement-strain transformation is essential for revealing the internal mechanics of structures and developing strain measurement methods. This transformation typically depends on the environment of the structure. In contrast to the traditional invariant transformation, this paper proposes a method to obtain a variable displacement-strain transformation by self-learning of the modal parameters of the structure in operation. The beam experimental results demonstrate that the transformation is able to take account of different forms of excitation and to obtain strain measurements under sinusoidal and random excitation with up to 99.82% and 99.70% accuracy, respectively. Moreover, these results indicate that the proposed displacement-strain transformation is able to take account of the environmental conditions encountered in practical situations more consistently than conventional approaches. The introduction of a modal-learning displacement-strain transformation in the proposed approach provides a welcome boost to the development of strain measurement methods.

Interface modeling of magnetorheological elastomers subjected to variable working strain.

A magnetorheological elastomer (MRE) is a type of particle-matrix composite material, whose properties depend on the strain to which it is subjected in different applications. This paper proposes an interface model in which the magnetorheological characteristics of an MRE are described in terms of the effect of variable strain on the strength of interfacial bonding between the particles and the matrix. The model can describe the whole process of interface change from a strong interface to a strong-weak mixed interface and then to a weak interface under variable strain. The results indicate that the combined effects of the magnetic flux density, particle content, and strain amplitude are responsible for the magnetorheological performance of the MRE. The maximum value of the shear modulus under large strain is decreased by 0.75 × 105 Pa compared to the value under small strain. This model opens new opportunities for the development of high-performance MREs and MRE-based devices under variable strain conditions.

Dynamic Visual Measurement of Driver Eye Movements.

Vibrations often cause visual fatigue for drivers, and measuring the relative motion between the driver and the display is important for evaluating this visual fatigue. This paper proposes a non-contact videometric measurement method for studying the three-dimensional trajectories of the driver's eyes based on stereo vision. The feasibility of this method is demonstrated by dynamic calibration. A high-speed dual-camera image acquisition system is used to obtain high-definition images of the face, and the relative trajectories between the eyes and the display are obtained by a set of robust algorithms. The trajectories of the eyes in three-dimensional space are then reconstructed during the vehicle driving process. This new approach provides three-dimensional information and is effective for assessing how vibration affects human visual performance.