Publications by authors named "Xianmin Zhang"

72 Publications

A robust edge-based template matching algorithm for displacement measurement of compliant mechanisms under scanning electron microscope.

Rev Sci Instrum 2021 Mar;92(3):033703

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, South China University of Technology, Guangzhou 510640, People's Republic of China.

This paper develops a robust edge-based template matching algorithm for displacement measurement of compliant mechanisms under a scanning electron microscope (SEM). The algorithm consists of three steps. First, the Sobel gradient operator and a self-adaptive segment strategy are used to establish the shape model in which the gradient directions of the object's edge points are calculated. Second, a similarity criterion based on image gradients that is robust to illumination change and image noise is utilized for template matching to obtain the coarse results. The third step is to refine the matching results by using an orientation-guided subpixel interpolation strategy. A series of simulations is conducted, and the results show that the proposed algorithm enjoys great robustness against strong image noise and gray-value fluctuation, as well as small rotations and background interferences, and thus is suitable for processing SEM images of compliant mechanisms. Finally, the application of the proposed algorithm in the measurement of the spring constant of the flexure hinges with a straight beam form under a SEM is demonstrated.
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http://dx.doi.org/10.1063/5.0023244DOI Listing
March 2021

Motion measurement system of compliant mechanisms using computer micro-vision.

Opt Express 2021 Feb;29(4):5006-5017

Position sensing is essential to testify the validity of the mechanical design and verify the performance in micromanipulation. A practical system for non-contact micro-motion measurement of compliant nanopositioning stages and micromanipulators is proposed using computer micro-vision. The micro-motion measurement method integrates optical microscopy and an optical flow-based technique, in which the motions of complaint mechanisms are precisely detected and measured. Simulations are carried out to validate the robustness of the proposed method, while the micro-vision system and a laser interferometer measurement system are also built up for a series of experiments. The experimental results demonstrate that the proposed measurement system possesses high stability, extensibility, and precision with 0.06 µm absolute accuracy and 0.05 µm standard deviation.
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http://dx.doi.org/10.1364/OE.415097DOI Listing
February 2021

Nonlinearity-aware optoelectronic terahertz discrete multitone signal transmission with a zero-bias diode.

Opt Lett 2020 Sep;45(18):5045-5048

The terahertz band has been recognized as a promising candidate to support future rate-greedy applications such as 6G communications. Optoelectronic terahertz communications are beneficial for the realization of high-speed transmission. In this Letter, we propose and experimentally demonstrate an optoelectronic terahertz transmission system with intensity modulation and direct detection, where a discrete multitone (DMT) waveform with high-order quadrature amplitude modulation (QAM) is used. A zero-bias diode (ZBD) is used in the system as a simple, cost-effective direct detection terahertz receiver. A nonlinearity-aware digital signal reception routine is proposed to mitigate the nonlinear impairments induced by subcarrier-to-subcarrier beating interference from the ZBD. In this experiment, up to a 60 Gbit/s line rate 16QAM-DMT signal is successfully transmitted over a 3 m wireless link in the 310 GHz band, and the mean signal-to-noise ratio is improved by 3 dB with nonlinearity-aware signal processing routine. The advantageous features of such a scheme make it a promising solution for terahertz wireless communications.
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http://dx.doi.org/10.1364/OL.401414DOI Listing
September 2020

Design and stiffness modeling of a four-degree-of-freedom nanopositioning stage based on six-branched-chain compliant parallel mechanisms.

Rev Sci Instrum 2020 Jun;91(6):065002

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacture Technology, South China University of Technology, 510641 Guangzhou, China.

Multi-degree-of-freedom (multi-DOF) nanopositioning stages (NPSs) have rapidly growing applications in the spatial micro-/nano-machining and manipulation. Compliant parallel mechanisms (CPMs) demonstrate advantages to achieve a large output stiffness and high payload. A four-DOF NPS based on six-branched-chain CPMs is proposed in this paper. First, a mechanism design approach is introduced. One primary vertical DOF is generated using three parallel-kinematic lever amplifiers. A three-revolute-revolute-revolute mechanism acts as the kinematic configuration to produce three secondary planar DOFs. Three types of single-axis and one type of double-axis notch flexure hinges (NFHs) are employed to realize the nanoscale displacement/movement guiding, transferring, and decoupling. Second, a stiffness modeling approach is derived. Combined with exact compliance matrices of 54 NFHs and 95 flexible beams, a four-DOF high-efficiency stiffness model of the six-branched-chain CPM is built. The calculation procedure of the whole input/output stiffnesses and coupling ratios takes 12.06 ms. Simulation and prototype test results validate the calculation accuracy. For example, the maximum calculation deviation of input stiffnesses is verified to be 4.52% and 8.18%, respectively. The two proposed approaches contribute to the statics parameter optimization of spatial multi-DOF NPSs.
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http://dx.doi.org/10.1063/5.0008905DOI Listing
June 2020

Interface hybridization and spin filter effect in metal-free phthalocyanine spin valves.

Phys Chem Chem Phys 2020 May 14;22(20):11663-11670. Epub 2020 May 14.

School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.

Spin-orbit coupling (SOC) has long been regarded as the core interaction to determine the efficiency of spin conserved transport in semiconductor spintronics. In this report, a spin-valve device with a Co/metal-free phthalocyanine (HPc)/Co stacking structure is fabricated. The magnetoresistance effect was successfully obtained in the device. It is also found that the magnetoresistance response is relatively smaller than that of metallic phthalocyanines, clearly implying that SOC is not the key factor to affect the magnetoresistance in phthalocyanine spin-valves. The dominant mechanism that determines the spin transport efficiency in the present HPc devices was systemically explored by combining both experimental measurements and first-principles calculation analysis. It was noticed that both the crystalline structure and molecular orientation of the HPc layer could be modified by the contact under-layer materials, which changes the magnetization intensity of the ferromagnetic metallic electrode due to the strong interface hybridization of Co/HPc. Meanwhile, the theoretical calculations clearly demonstrated that the spin filter effect from the second HPc layer should be responsible for the decrease of the magnetoresistance response in the present spin-valves compared to those using metallic phthalocyanine layers. This investigation may trigger new insights into the role of SOC strength and interface hybridization in organic spintronics.
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http://dx.doi.org/10.1039/d0cp00651cDOI Listing
May 2020

Method of fiber transfer delay measurement based on phase quantization and delay synthesis.

Appl Opt 2020 Feb;59(4):918-922

A novel method, to the best of our knowledge, of fiber transfer delay (FTD) measurement based on phase quantization and delay synthesis is proposed and demonstrated. By detecting the differential phase shifts of a set of frequency-multiplied RF signals transmission through the fiber link with and without the FTD under the test, the ${2}\pi $2π phase ambiguity problem can be solved. To avoid the phase quantization error near the digital quantization boundary, a self-check and error-correction method is proposed so as to greatly improve the reliability of measurement. In the experiment, the measurement repeatability around 0.018 ps within a period of 80 s is achieved for a back-to-back fiber link, and a test resolution of 0.03 ps is proved with a motorized tunable delay line. The system is available for measurement of a large FTD range up to 100 µs with no dead zone.
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http://dx.doi.org/10.1364/AO.380136DOI Listing
February 2020

Sub-Nyquist computational ghost imaging with deep learning.

Opt Express 2020 Feb;28(3):3846-3853

We propose a deep learning computational ghost imaging (CGI) scheme to achieve sub-Nyquist and high-quality image reconstruction. Unlike the second-order-correlation CGI and compressive-sensing CGI, which use lots of illumination patterns and a one-dimensional (1-D) light intensity sequence (LIS) for image reconstruction, a deep neural network (DAttNet) is proposed to restore the target image only using the 1-D LIS. The DAttNet is trained with simulation data and retrieves the target image from experimental data. The experimental results indicate that the proposed scheme can provide high-quality images with a sub-Nyquist sampling ratio and performs better than the conventional and compressive-sensing CGI methods in sub-Nyquist sampling ratio conditions (e.g., 5.45%). The proposed scheme has potential practical applications in underwater, real-time and dynamic CGI.
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http://dx.doi.org/10.1364/OE.386976DOI Listing
February 2020

Design and Waveform Assessment of a Flexible-Structure-Based Inertia-Drive Motor.

Micromachines (Basel) 2019 Nov 12;10(11). Epub 2019 Nov 12.

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacture Technology, South China University of Technology, Guangzhou 510640, China.

This paper reports the mechanical design, waveform investigation and experimental validation of an flexible-structure-based inertia-drive linear motor. The flexible structure is designed and verified with finite element analysis to meet the bandwidth requirement for high-frequency actuation. In order to improve the output velocity, non-resonance low-harmonic driving waveform is implemented and evaluated. Experimental results show that the motor is capable of an output velocity of 2.41 mm/s with the waveform, compared to 0.73 mm/s with the classic saw-tooth waveform actuation. The improvement of the non-resonance low-harmonic waveform for the flexible-structure-based motor is confirmed.
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http://dx.doi.org/10.3390/mi10110771DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6915485PMC
November 2019

Calibration method for hand-eye system with rotation and translation couplings.

Appl Opt 2019 Jul;58(20):5375-5387

This paper develops a novel hand-eye calibration method for hand-eye systems with rotation and translation coupling terms. First, a nonlinear camera model with distortion terms and a model of a hand-eye system with rotation and translation coupling terms are established. Based on a non-linear optimization method and a reverse projection method, a decoupling calibration method for a lower-degree-of-freedom hand-eye system is proposed. Then the path planning for the calibration process is carried out. Based on the analysis of coupling constraints and hand-eye system motion constraints, three types of hand-eye calibration paths with high efficiency and easy operation are developed. In addition, the influence of key parameters on hand-eye calibration accuracy is analyzed. Finally, calibration experiments and parametric influence experiments are carried out. The results demonstrate that the proposed method is effective and practical for calibrating the hand-eye system.
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http://dx.doi.org/10.1364/AO.58.005375DOI Listing
July 2019

Integrated Design of Actuation and Mechanism of Dielectric Elastomers Using Topology Optimization Based on Fat Bezier Curves.

Soft Robot 2019 10 17;6(5):644-656. Epub 2019 Jun 17.

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, P.R. China.

Soft actuation technology has attracted considerable interest in recent decades, with the light weight, high response speed, and large deformation of dielectric elastomer actuators (DEAs) showing particular promise. DEAs composed of compliant frames and prestrained dielectric elastomers (DEs) can be considered as a soft actuation system, which is termed minimum-energy structure. Most existing DEAs come from a well-known design with a simple configuration but complex design process. In this article, we propose an integrated design method for the actuation and mechanism of DEs based on topology optimization using fat Bezier curves. In this method, the compliant frame is represented by fat Bezier curves, and the prestrained DE is distributed in the region bounded by the curves. This article first describes the theoretical modeling process, and then presents three design examples that validate the optimization algorithm. Finite element analysis (FEA) and experiments are conducted to assess the performance of the optimized configurations. The FEA simulations and experimental results show that the topology optimization algorithm results in DEAs that exhibit the desired motion.
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http://dx.doi.org/10.1089/soro.2018.0114DOI Listing
October 2019

A magnification-continuous calibration method for SEM-based nanorobotic manipulation systems.

Rev Sci Instrum 2019 May;90(5):053706

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, People's Republic of China.

Calibration for scanning electron microscope (SEM) based nanorobotic manipulation systems is important and difficult. Most current calibration methods are cumbersome because they require customized high precision calibration boards and repeated calibration procedures in different magnifications. This paper presents a convenient magnification-continuous calibration method with high precision for SEM-based nanorobotic manipulation systems. The projection matrix containing a continuous magnification factor is obtained by modifying the affine camera model. This facilitates the simplification of the parameter computing process. Movement features are used to align the moving axes of micropositioning stages and calibrate the system, which benefits for the realization of efficient automatic calibration. Three experiments are carried out, and the results demonstrate that the proposed method is effective and practical for calibrating SEM-based nanorobotic manipulation systems under a wide range of continuous magnifications. Experiments also confirm that high precision measurements can be conducted in different magnifications with only once calibration and the relative error is within 1%.
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http://dx.doi.org/10.1063/1.5086940DOI Listing
May 2019

Nonlinear Hysteresis Modeling of Piezoelectric Actuators Using a Generalized Bouc⁻Wen Model.

Micromachines (Basel) 2019 Mar 12;10(3). Epub 2019 Mar 12.

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China.

Hysteresis behaviors exist in piezoelectric ceramics actuators (PCAs), which degrade the positioning accuracy badly. The classical Bouc⁻Wen (CB⁻W) model is mainly used for describing rate-independent hysteresis behaviors. However, it cannot characterize the rate-dependent hysteresis precisely. In this paper, a generalized Bouc⁻Wen (GB⁻W) model with relaxation functions is developed for both rate-independent and rate-dependent hysteresis behaviors of piezoelectric actuators. Meanwhile, the nonlinear least squares method through MATLAB/Simulink is adopted to identify the parameters of hysteresis models. To demonstrate the validity of the developed model, a number of experiments based on a 1-DOF compliant mechanism were conducted to characterize hysteresis behaviors. Comparisons of experiments and simulations show that the developed model can describe rate-dependent and rate-independent hysteresis more accurately than the classical Bouc⁻Wen model. The results demonstrate that the developed model is effective and useful.
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http://dx.doi.org/10.3390/mi10030183DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470998PMC
March 2019

Erratum: "An enhanced Bouc-Wen model for characterizing rate-dependent hysteresis of piezoelectric actuators" [Rev. Sci. Instrum. 89(11), 115002 (2018)].

Rev Sci Instrum 2019 01;90(1):019902

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China.

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http://dx.doi.org/10.1063/1.5087005DOI Listing
January 2019

Unusual interfacial magnetic interactions for τ-MnAl with Fe(Co) atomic layers.

Phys Chem Chem Phys 2019 Jan;21(5):2443-2452

Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.

The interfacial magnetic interaction and coupling mechanism for τ-MnAl with Fe(Co) atomic layers have been studied using first principles calculations. The stable surface and interface were firstly determined by the surface energy of τ-MnAl and interface energy of τ-MnAl/Fe(Co) films, respectively. Their magnetic coupling interactions were investigated by varying the Fe(Co) atomic layer numbers. It is noted that both Fe and Co exhibited ferromagnetic coupling with τ-MnAl. Interestingly, an unusual oscillation phenomenon of magnetic coupling for τ-MnAl with Fe(Co) atomic layers was observed depending on the layer thickness of Fe(Co). Moreover, Fe and Co showed different oscillation modes. The energy difference between antiferromagnetic and ferromagnetic states is larger for τ-MnAl/Fe and τ-MnAl/Co when the Fe(Co) layer numbers are even and odd, respectively. Their mechanisms were analyzed based on the band structures and the confinement of electrons in quantum wells. It is found that the magnetic coupling oscillation in τ-MnAl/Fe originated from both the spin up Δ1 band and spin down Δ5 band at the [capital Gamma, Greek, macron] points. Comparatively, the oscillation of τ-MnAl/Co is due to the spin up band at the X[combining macron] point. The present results could provide insight to further understand interfacial exchange interactions among magnetic layers.
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http://dx.doi.org/10.1039/c8cp06599cDOI Listing
January 2019

A three-step displacement measurement method for a 3-DOF macro-micro positioning stage.

Rev Sci Instrum 2018 Nov;89(11):113701

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China.

A high-performance displacement measurement method for the displacement measurement of a three degree of freedom (3-DOF) macro-micro positioning stage based on the micro-vision measurement system is proposed. The method is built up by three steps. In the first step, a fast search algorithm combined with triangular relations and a ring projection with illumination and noise correction is adopted to achieve the selection of candidate pixels. Subsequently, an orientation code based algorithm is adopted to determine the integer-pixel displacement and rotation angle estimation. The third step is to obtain the sub-pixel displacement through a similarity function based algorithm. Simulations are carried out, and the results show that the proposed method has the characteristics of translation and rotation invariance, and the matching accuracy can reach 0.01-pixel theoretically. Moreover, the proposed method consumes less time than that of the orientation code and pseudo-Zernike moment based algorithm. Finally, a capacitance sensor measurement system is established to compare the accuracy of the proposed method. The experiment results demonstrate that it has a high accuracy.
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http://dx.doi.org/10.1063/1.5046700DOI Listing
November 2018

An enhanced Bouc-Wen model for characterizing rate-dependent hysteresis of piezoelectric actuators.

Rev Sci Instrum 2018 Nov;89(11):115002

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China.

A classical Bouc-Wen model is widely applied in hysteresis modeling and compensation for piezoelectric ceramic actuators. However, the classical Bouc-Wen model cannot characterize rate-dependent hysteresis under excitations at high frequencies precisely. In this paper, an enhanced Bouc-Wen model is developed by introducing the frequency of input voltage based on the classical Bouc-Wen model. A number of experiments were conducted to characterize the rate-dependent hysteresis of piezoelectric ceramic actuators under sinusoidal excitations at a range of 1-150 Hz. The measured data were used to demonstrate the validity of the developed model. A method of parameter estimation based on the Matlab/Simulink parameter estimation tool is adopted to identify the parameters of models. The comparisons of experiments and simulations show that the developed model can describe rate-dependent hysteresis more accurately than the classical Bouc-Wen model. The modeling errors of the developed model were decreased by nearly 75% compared with that of the classical Bouc-Wen model. The root-mean-square error of the developed model is controlled in 0.1719 m.
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http://dx.doi.org/10.1063/1.5038591DOI Listing
November 2018

Study on Residual Vibration Suppress of a 3-DOF Flexible Parallel Robot Mechanism.

Sensors (Basel) 2018 Nov 26;18(12). Epub 2018 Nov 26.

Department of Mechatronics, Foshan University, Foshan 528000, China.

Residual vibration suppression of a 3-DOF flexible parallel robot mechanism is implemented in this paper. Considering the direct and inverse piezoelectric effect of PZT (lead zirconium titanate) material, a general motion equation is established which includes an input equation of PZT actuators and an output equation of PZT sensors. A strain and strain rate feedback (SSRF) controller is designed based on the established general motion equation. A numerical simulation is implemented to verify the effectiveness of the SSRF controller in driving the proposed robotic mechanism. The simulation results reveal that the SSRF controller can decrease the elastic vibration displacement of the flexible links rapidly and improve the position accuracy of the moving platform. In the experimental study, one scheme with three passive flexible links is controlled by the SSRF controller at the same time as the performance of the introduced solutions. The experimental results show that the strain and strain rate feedback controller is able to effectively suppress the residual vibration of the 3-DOF flexible parallel robot mechanism. The results of the numerical simulation and experiment are completely consistent.
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http://dx.doi.org/10.3390/s18124145DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6308442PMC
November 2018

3D Visible-Light Invisibility Cloak.

Adv Sci (Weinh) 2018 Jun 14;5(6):1800056. Epub 2018 Apr 14.

State Key Laboratory of Modern Optical Instrumentation Zhejiang University Hangzhou 310027 China.

The concept of an invisibility cloak is a fixture of science fiction, fantasy, and the collective imagination. However, a real device that can hide an object from sight in visible light from absolutely any viewpoint would be extremely challenging to build. The main obstacle to creating such a cloak is the coupling of the electromagnetic components of light, which would necessitate the use of complex materials with specific permittivity and permeability tensors. Previous cloaking solutions have involved circumventing this obstacle by functioning either in static (or quasistatic) fields where these electromagnetic components are uncoupled or in diffusive light scattering media where complex materials are not required. In this paper, concealing a large-scale spherical object from human sight from three orthogonal directions is reported. This result is achieved by developing a 3D homogeneous polyhedral transformation and a spatially invariant refractive index discretization that considerably reduce the coupling of the electromagnetic components of visible light. This approach allows for a major simplification in the design of 3D invisibility cloaks, which can now be created at a large scale using homogeneous and isotropic materials.
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http://dx.doi.org/10.1002/advs.201800056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6010732PMC
June 2018

Mechanical Structural Design of a Piezoresistive Pressure Sensor for Low-Pressure Measurement: A Computational Analysis by Increases in the Sensor Sensitivity.

Sensors (Basel) 2018 Jun 24;18(7). Epub 2018 Jun 24.

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China.

This paper proposes a novel micro-electromechanical system (MEMS) piezoresistive pressure sensor with a four-petal membrane combined with narrow beams and a center boss (PMNBCB) for low-pressure measurements. The stresses induced in the piezoresistors and deflection of the membrane were calculated using the finite element method (FEM). The functions of the relationship between the dimension variables and mechanical performance were determined based on the curve fitting method, which can provide an approach for geometry optimization of the sensor. In addition, the values in the equations were varied to determine the optimal dimensions for the proposed membrane. Then, to further improve the sensitivity of the sensor, a series of rectangular grooves was created at the position of the piezoresistors. The proposed diaphragm was compared to existing diaphragms, and a considerable increase in the sensitivity and a considerable decrease in nonlinearity error could be achieved by using the proposed sensor. The simulation results suggest that the sensor with the PMNBCB structure obtained a high sensitivity of 34.67 mV/kPa and a low nonlinearity error of 0.23% full-scale span (FSS) for the pressure range of 0⁻5 kPa. The proposed sensor structure is a suitable selection for MEMS piezoresistive pressure sensors.
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http://dx.doi.org/10.3390/s18072023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6069098PMC
June 2018

Multifocus image fusion method for image acquisition of 3D objects.

Appl Opt 2018 Jun;57(16):4514-4523

We propose a multifocus image fusion method for achieving all-in-focus images of three-dimensional objects based on the combination of transform domain and spatial domain techniques. First, the source images are decomposed into low-frequency and high-frequency components by the discrete wavelet transform technique. Next, a correlation coefficient is employed to obtain the maximum similarity among low-frequency components. Then, in order not to interrupt the correlations among decomposition layers, the comparison among high-frequency components is executed by transforming them to spatial domain. In addition, a sliding window is used to evaluate the local saliency of the pixels more accurately. Finally, the fused image is synthesized from source images and the saliency map. The variance, entropy, spatial frequency, mutual information, edge intensity, and similarity measure (Q) are used as metrics to evaluate the sharpness of the fused image. Experimental results demonstrate that the fusion performance of the proposed method is enhanced compared with that of the other widely used techniques. In the application of three-dimensional surface optical detection, the proposed method is suitable for obtaining the complete image at varying distances in the same scene, so as to prepare for subsequent defect identification.
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http://dx.doi.org/10.1364/AO.57.004514DOI Listing
June 2018

Magnetoresistance Effect and the Applications for Organic Spin Valves Using Molecular Spacers.

Materials (Basel) 2018 May 3;11(5). Epub 2018 May 3.

Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.

Organic spin devices utilizing the properties of both spin and charge inherent in electrons have attracted extensive research interest in the field of future electronic device development. In the last decade, magnetoresistance effects, including giant magetoresistance and tunneling magnetoresistance, have been observed in organic spintronics. Significant progress has been made in understanding spin-dependent transport phenomena, such as spin injection or tunneling, manipulation, and detection in organic spintronics. However, to date, materials that are effective for preparing organic spin devices for commercial applications are still lacking. In this report, we introduce basic knowledge of the fabrication and evaluation of organic spin devices, and review some remarkable applications for organic spin valves using molecular spacers. The current bottlenecks that hinder further enhancement for the performance of organic spin devices is also discussed. This report presents some research ideas for designing organic spin devices operated at room temperature.
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http://dx.doi.org/10.3390/ma11050721DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5978098PMC
May 2018

Topology optimization of fusiform muscles with a maximum contraction.

Int J Numer Method Biomed Eng 2018 May 9:e3096. Epub 2018 May 9.

Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, 510640, People's Republic of China.

Understanding the optimal designs in nature is critical in bionics. This paper presents a method for designing the configuration of fusiform muscle with a maximum contractile displacement based on topology optimization methods. A nearly incompressible continuum constitutive model of skeletal muscle is utilized. The contractile displacement from the relaxed state to the contracted state is regarded as the objective function. To handle the numerical difficulties that result from the existence of element density, an energy interpolation equation is employed, and a modification of the constitutive model of skeletal muscle is proposed. Several numerical examples are given to demonstrate the reasonability of the proposed method.
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http://dx.doi.org/10.1002/cnm.3096DOI Listing
May 2018

Estimation of Handgrip Force from SEMG Based on Wavelet Scale Selection.

Sensors (Basel) 2018 Feb 24;18(2). Epub 2018 Feb 24.

Guangdong Provincial Key Laboratory of Precision Equipment and Manufacturing Technology, South China University of Technology, Guangzhou 510640, China.

This paper proposes a nonlinear correlation-based wavelet scale selection technology to select the effective wavelet scales for the estimation of handgrip force from surface electromyograms (SEMG). The SEMG signal corresponding to gripping force was collected from extensor and flexor forearm muscles during the force-varying analysis task. We performed a computational sensitivity analysis on the initial nonlinear SEMG-handgrip force model. To explore the nonlinear correlation between ten wavelet scales and handgrip force, a large-scale iteration based on the Monte Carlo simulation was conducted. To choose a suitable combination of scales, we proposed a rule to combine wavelet scales based on the sensitivity of each scale and selected the appropriate combination of wavelet scales based on sequence combination analysis (SCA). The results of SCA indicated that the scale combination VI is suitable for estimating force from the extensors and the combination V is suitable for the flexors. The proposed method was compared to two former methods through prolonged static and force-varying contraction tasks. The experiment results showed that the root mean square errors derived by the proposed method for both static and force-varying contraction tasks were less than 20%. The accuracy and robustness of the handgrip force derived by the proposed method is better than that obtained by the former methods.
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http://dx.doi.org/10.3390/s18020663DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5855185PMC
February 2018

Properties and Applications of the β Phase Poly(vinylidene fluoride).

Polymers (Basel) 2018 Feb 26;10(3). Epub 2018 Feb 26.

Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.

Poly(vinylidene fluoride), PVDF, as one of important polymeric materials with extensively scientific interests and technological applications, shows five crystalline polymorphs with α, β, γ, δ and ε phases obtained by different processing methods. Among them, β phase PVDF presents outstanding electrical characteristics including piezo-, pyro-and ferroelectric properties. These electroactive properties are increasingly important in applications such as energy storage, spin valve devices, biomedicine, sensors and smart scaffolds. This article discusses the basic knowledge and character methods for PVDF fabrication and provides an overview of recent advances on the phase modification and recent applications of the β phase PVDF are reported. This study may provide an insight for the development and utilization for β phase PVDF nanofilms in future electronics.
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http://dx.doi.org/10.3390/polym10030228DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6415445PMC
February 2018

Photonics-enabled compressive sensing with spectral encoding using an incoherent broadband source.

Opt Lett 2018 Jan;43(2):330-333

In this Letter, we propose an approach to achieving photonics-enabled compressive sensing of sparse wideband radio frequency signals in which an incoherent broadband source is applied, and the mixing and integration functions are realized in the optical domain. A spectrum shaper is employed to slice and encode the spectrum of the broadband light according to a predetermined random sequence. Because of the dispersion-induced group delay, the mixing between the incoming signal and the random bit sequence is achieved. At the output of the spectrum shaper, an array of photodetectors is employed to realize down-sampling, and the input sparse signal can be captured in a single-shot mode. Since no pulsed laser is employed, our scheme obviates the need for time-domain synchronization between the repetitive ultra-fast pulses and the random sequence. Experimental demonstrations and numerical results are presented to verify the feasibility and potential of the approach.
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http://dx.doi.org/10.1364/OL.43.000330DOI Listing
January 2018

Experimental generation of linearly chirped 350  GHz band pulses with a bandwidth beyond 60  GHz.

Opt Lett 2017 Dec;42(24):5242-5245

We present in this Letter the experimental generation of linear frequency modulated (LFM) terahertz pulses with large bandwidths by using an optical interferometer-based photonic scheme and cutting-edge terahertz transceiver technology. The LFM pulses exhibiting a bandwidth in excess of 60 GHz centered at 350 GHz are successfully generated in the experiment, which represents the first demonstration of large time-bandwidth products (TBWPs) in the terahertz region above 300 GHz, to the best of our knowledge. The achieved TBWP of up to 527 has great potential in many prospective applications such as high-resolution radar sensing and imaging.
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http://dx.doi.org/10.1364/OL.42.005242DOI Listing
December 2017

Micro-motion detection of the 3-DOF precision positioning stage based on iterative optimized template matching.

Appl Opt 2017 Dec;56(34):9435-9443

This study presents a method for micro-motion detection of the three-degrees-of-freedom (3-DOF; x, y, θ) precision positioning stage (PPS) based on iterative optimized template matching (IOTM). In this method, a micro-vision system (MVS) is constructed and employed to capture magnified images of the measured PPS's surface with high quality. In addition, an efficient and accurate IOTM algorithm, which includes a pyramid hierarchical matching step for generating the initial guess and an iterative searching step for 3-DOF fine matching, is proposed to detect the micro-motion of the 3-DOF PPS. The simulation results show that the locating accuracy of the translation component (TC) and rotation component of this algorithm can respectively reach 0.01 pixels and 0.01 deg when the image quality is high and the initial guess is close to the real location. Measurement tests of a nano-PPS verify that the proposed method is practical and effective for 3-DOF micro-motion detection and the absolute accuracy of the TC of the MVS can easily reach the nanometer level.
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http://dx.doi.org/10.1364/AO.56.009435DOI Listing
December 2017

Frequency-dependent noise figure analysis of continuous photonic time-stretch system.

Appl Opt 2017 Oct;56(29):8246-8251

In this paper, the frequency-dependent noise figure of a continuous photonic time-stretch system is theoretically analyzed and experimentally demonstrated. Mathematic analysis discloses that the frequency-dependent noise figure in the continuous photonic time-stretch system is mainly owing to the dispersion-induced phase shift in the link. In the experiment, a completely continuous signal is reconstructed with time-interleaved joining of four sections of time-stretched signals from optical wavelength-division de-multiplexing channels. The result of the frequency-dependent noise figure property agrees well with that of theoretical analysis.
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http://dx.doi.org/10.1364/AO.56.008246DOI Listing
October 2017

Highly sensitive demodulation of a vibration-induced phase shift based on a low-noise OEO.

Opt Lett 2017 Oct;42(20):4052-4054

A highly sensitive demodulation approach of a vibration-induced phase shift based on a low-noise optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The vibration-induced optical phase variation is directly converted to the electrical oscillating signal of the OEO with carrier phase-shifted double-sideband (CPS-DSB) modulation, which is realized by cascading a dual-output Mach-Zehnder modulator (DOMZM) and a fiber interferometer. Theoretically, within a CPS-DSB modulated OEO, the minimum detectable optical phase shift is determined by the phase noise achievable, and the sensitivity of the optical phase shift demodulation no longer depends on its frequency. A proof-of-concept OEO oscillating at 100 MHz with ultralow phase noise is built for demonstration. The achieved minimum detectable optical phase shift is 0.58  μrad/√Hz at 1 kHz and 0.21  μrad/√Hz at 10 kHz, which are the best results ever reported, to the best of our knowledge.
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http://dx.doi.org/10.1364/OL.42.004052DOI Listing
October 2017

All-positive-coefficient microwave photonic filter with rectangular response.

Opt Lett 2017 Aug;42(15):3012-3015

In conventional approaches to realizing microwave photonic filters (MPFs) with rectangular response, both positive and negative coefficients should be included in the systems, which is a difficulty in incoherent MPFs. Electrical or optical ways to realize the MPFs with bipolar taps, such as those using balanced detectors or based on two opposite modulation slopes of dual-input Mach-Zehnder modulators, usually involve more components compared with the MPFs with unipolar taps. In this Letter, a design of MPFs with rectangular response using all positive coefficients is proposed. There is only one optical link as well as one photodetector utilized in the approach, which largely simplifies the filter structure. Experimental demonstrations of 55-positive-tap MPFs with different passbands are presented to verify the feasibility and potential of the approach.
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http://dx.doi.org/10.1364/OL.42.003012DOI Listing
August 2017