Scanning Scheme Research Articles

Full-field mode shape estimation of a rotating structure subject to random excitation using a tracking continuously scanning laser Doppler vibrometer via a two-dimensional scan scheme

A two-dimensional (2D) scan scheme is developed for a tracking continuously scanning laser Doppler vibrometer (CSLDV) system to scan the whole surface of a rotating structure subject to random excitation. A tracking CSLDV system is developed to track a rotating structure and sweep its laser spot on its surface. The measured response of the structure using the 2D scan scheme of the tracking CSLDV system is considered as the response of the whole surface of the structure subject to random excitation. The measured response can be processed by an operational modal analysis (OMA) method called the improved demodulation method based on a rigorous nonuniform rotating plate model to obtain modal parameters of the rotating structure, such as damped natural frequencies and undamped full-field mode shapes. Damped natural frequencies of the rotating structure are estimated from the fast Fourier transform of the measured response. Undamped full-field mode shapes are estimated by multiplying the measured response by sinusoids whose frequencies are estimated damped natural frequencies. Experimental investigation of the 2D scan scheme of the tracking CSLDV system and OMA method is conducted, and damped natural frequencies and undamped full-field mode shapes of a rotating fan blade with different constant speeds are estimated. It is theoretically and experimentally shown that damped natural frequencies of the rotating fan blade increases with its rotation speed.

Passive near-field optical scanning imaging based on semiconductor nanowire/tapered microfiber probe

<sec>In this paper, we propose a passive near-field scanning imaging system by using the structure of cadmium sulfide (CdS) nanowire/tapered microfiber probe, which combines the near-field scanning structure and the nanowire/microfiber coupling technology. In the passive near-field scanning imaging system, a passive nanoprobe is adopted to detect the intensity change of the reflected light field on the sample surface, which not only retains the advantage of the nanoprobe for the strong restriction of the reflected light on the sample surface, but also reduces the interference of strong excitation light during detection. Through the high efficiently evanescent field coupling between the CdS nanowire and the tapered microfiber, the collected light signal is transmitted to the photodetector in the far field, and finally the imaging of the target sample morphology can be realized.</sec><sec>At first, the light field model of the nanowire/tapered microfiber probe structure is verified by the finite element analysis method. The calculated collection efficiency from the sample to the probe is about 4.65‰ and the transmission efficiency from the nanowire to the tapered microfiber is about 74.47%. The collection efficiency is improved by an order of magnitude compared with traditional metal-coated near-field probe. In the experiments, a scanning step of 20 nm and a probe-sample distance of 230 nm are selected. The nanowire/tapered microfiber probe and traditional tapered fiber probe are both used to measure the widths of different CdSe nanoribbons samples, and the atomic force microscopy measurement is used as the benchmark to calculate their measurement error, which is increased about 3 times. By changing the angle <i>θ</i> between the probe and the sample, it is found that the resolution obtained using the designed nanowire/microfiber probe is always higher than only using the tapered microfiber probe. Comparing with the tapered microfiber probe scheme, the measurement error is reduced to a value less than 7.2%.</sec><sec>In addition, compared with the active luminescence probe scheme, this passive near-field scanning scheme reduces the preparation complexity of the optical probe and the detection structure complexity of the optical system. The large microscopic illumination area can avoid the influence of the small laser spot size on imaging, and the imaging range is determined only by the travel distance of the linear stage. Therefore, our work may provide an attractive approach for developing new near-field scanning microscopy systems in the future.</sec>

Dimensional quality assessment of cable-stayed bridge by combining terrestrial and drone laser scanner

Xinglinpu Bridge was built on the S3801 freeway in 2019 in preparation for the winter Olympics in Beijing, China. It is a cable-stayed steel bridge with pylons in the shape of flower baskets. Using Xinglinpu Bridge as a case study, a systematic approach to the dimensional quality assessment of complex bridges using a combination of three-dimensional (3D) point clouds obtained by terrestrial laser scanning (TLS) and unmanned aerial vehicle (UAV) surveys is proposed in this paper. The currently available methods for dimensional quality assessment of complex bridges rely largely on manual inspection and contact-type measurement devices, which are time consuming and costly. To overcome these limitations, this paper presents a framework for dimensional quality assessment composed of three parts: scanning schemes for TLS and UAV, scanning implementation and measurement of geometric dimensions. The results of configuration detection verified the high-quality construction of Xinglinpu Bridge, although millimetre-scale differences were obtained between the point clouds and the design value. The potential and limitations of 3D laser scanning for assessing the quality of complex bridges are discussed.

Lung ultrasound B-lines in systemic sclerosis: cut-off values and methodological indications for interstitial lung disease screening.

Lung ultrasound (LUS), through assessment of B-lines and pleural line alterations, is able to evaluate interstitial lung disease (ILD), a frequent complication of SSc. Different scanning schemes and counting methods have been proposed but no clear cut-off values have been indicated for screening. We aimed to evaluate the accuracy of different LUS methodological approaches to detect ILD compared with high-resolution CT (HRCT) as the gold standard. Sixty-nine SSc patients underwent LUS and chest HRCT on the same day. Both exams were scored by expert readers. The accuracy of different scanning schemes and counting methods was assessed and clinical and functional data were compared with imaging findings. B-lines were more numerous in patients with the diffuse skin subset and Scl70 autoantibody positivity. The number of B-lines correlated with the Scleroderma Lung Study (SLS) I HRCT score (R = 0.754, P < 0.0001). A total of >10 B-lines on the whole chest or >1 B-line on the postero-basal chest showed 97% sensitivity for detecting even very early ILD signs (corresponding to an SLS I score of 1). Sensitivity increased to 100% when pleural line alterations were included in the analysis. LUS has a very high sensitivity in detecting SSc-related ILD. A cut-off value of >10 B-lines on the whole chest or >1 B-line on the postero-basal chest can be used for the screening of SSc-ILD. Assessing only the postero-basal chest seems to be mostly effective, combining high sensitivity with a less time-consuming approach.

An adaptive microscope for the imaging of biological surfaces

Scanning fluorescence microscopes are now able to image large biological samples at high spatial and temporal resolution. This comes at the expense of an increased light dose which is detrimental to fluorophore stability and cell physiology. To highly reduce the light dose, we designed an adaptive scanning fluorescence microscope with a scanning scheme optimized for the unsupervised imaging of cell sheets, which underly the shape of many embryos and organs. The surface of the tissue is first delineated from the acquisition of a very small subset (~0.1%) of sample space, using a robust estimation strategy. Two alternative scanning strategies are then proposed to image the tissue with an improved photon budget, without loss in resolution. The first strategy consists in scanning only a thin shell around the estimated surface of interest, allowing high reduction of light dose when the tissue is curved. The second strategy applies when structures of interest lie at the cell periphery (e.g. adherens junctions). An iterative approach is then used to propagate scanning along cell contours. We demonstrate the benefit of our approach imaging live epithelia from Drosophila melanogaster. On the examples shown, both approaches yield more than a 20-fold reduction in light dose -and up to more than 80-fold- compared to a full scan of the volume. These smart-scanning strategies can be easily implemented on most scanning fluorescent imaging modality. The dramatic reduction in light exposure of the sample should allow prolonged imaging of the live processes under investigation.

High‐resolution passive imaging by electromagnetic vortex beams

AbstractA new scheme to achieve high resolution in passive millimeter wave imaging (PMMWI) using electromagnetic (EM) vortex beams is proposed in this article. The spatial resolution of the traditional PMMWI system based on the mechanically or electronically controlled scanning scheme is mainly limited by the beam width of the receiver. However, it is not practical to fabricate an antenna that is too large, another possible way to improve the resolution is to increase the sampling points but will increase the imaging time. In this article, the multimode EM vortex beam is applied to achieve high resolution with less sampling points. The imaging scene is first discretized into small grid cells, and then multimode measurements are conducted during the scanning process to construct equations to solve the unknown brightness distribution. The compress sensing method is applied to reduce the number of orbital angular momentum mode. Simulation results demonstrate that high resolution can be achieved by the proposed method.

The Value of Ultrashort Echo Time MR in Depiction of the Eustachian Tube at 3 Tesla.

To investigate the feasibility of ultrashort echo time (UTE) imaging in the visualization of Eustachian tubes (ETs). The local institutional review board approved the study protocol. Twenty volunteers were involved in this study. The scanning scheme consisted of T2-sampling perfection with application-optimized contrasts by using different flip angle evolutions (T2-SPACE) MR imaging with water excitation, a UTE scan with a prototype sequence and a CT scan. The UTE images were compared with both the T2-SPACE and CT images. The quality of the images was rated by two radiologists blindly. Interobserver agreement was assessed using the kappa statistic. Statistical analysis was performed using SPSS software (version 17, SPSS Inc.). A value of p < 0.05 was considered statistically significant. For all subjects, the T2-SPACE images successfully displayed the cartilaginous part of the ET (Fig. 1). The CT images fully showed the bony part of the ET for all the subjects (Fig. 2). The UTE images successfully displayed both the cartilaginous and bony parts of the ET (Fig. 3). However, the UTE images showed the cartilaginous and bony portions of the ET as a whole. By analyzing the depiction of the ET from UTE images and comparing it with that from MR and CT images, we found that UTE images could display not only the cartilaginous structure of the ET that cannot be seen by conventional MR sequences, but also the bony structure that previously could only be seen on CT images. This imaging modality could help provide a convenient and new method to display the overall shape of the ET.

Multi-segment spectral reconstruction via zero-value set prior

Most scanning schemes of multi-energy computed tomography (MECT) require multiple sets of full-scan measurements under different x-ray spectra, which limits the application of MECT with incomplete scan. To handle this problem, a flexible MECT scanning strategy is proposed in this paper, which divides one half scan into three curves. Also, a novel MECT reconstruction algorithm is developed to relax the requirement of data acquisition of MECT. For MECT, gradient images of CT images at different energies ideally share the same position of zero-value set (Pos-OS) for the same object. Based on this observation, the characteristics of limited-angle artifacts is first explored, and it is found that the limited-angle artifacts in the image domain are closely related to the angle trajectory of the scan. Inspired by this discovery, the Pos-OS of the gradient image from the fusion CT image is extracted, and it is incorporated as prior knowledge into the TV minimization model in the form of equality constraints. The alternating direction method is exploited to solve the improved optimization model iteratively. Based on this, the proposed algorithm is derived to eliminate the limited angle artifacts in the image domain.The experimental results show that the proposed method achieves higher reconstruction quality under the designed scanning configuration than other methods in the literature.

Adhesive-free bonding of PI/PDMS interface by site-selective photothermal reactions

Effective bonding between polyimide (PI) and polydimethylsiloxane (PDMS) is important for the development of both implanted and externally mounted biomedical devices; however, achieving an adhesive-free bonding between the two materials without using surface chemical treatments has been largely unsuccessful to date. We discovered that, within a narrow range of laser parameters, laser-induced photothermal reactions at a specific site on the PI/PDMS interface led to an unexpected reinforcement of the adhesion strength between the two materials. This result was verified by microscopic in situ observations in which PDMS residues were observed to remain on the PI surface after forced delamination. The effect of heat pulses on the PI/PDMS interface was evaluated on the atomic scale through molecular dynamics simulations, and the results showed that as the heat pulses were added, the roughness values of both the PI and PDMS surfaces increased, accompanied by an improvement in the elastic properties at the interface, thus increasing the effective adhesion energy per unit area. The incorporation of a scanning scheme enabled the continuous bonding of the two materials, demonstrating that the proposed process can be easily scaled up for practical applications.

A prior image constraint robust principal component analysis reconstruction method for sparse segmental multi-energy computed tomography.

Multi-energy computed tomography (MECT) is a promising technique in medical imaging, especially for quantitative imaging. However, high technical requirements and system costs barrier its step into clinical practice. We propose a novel sparse segmental MECT (SSMECT) scheme and corresponding reconstruction method, which is a cost-efficient way to realize MECT on a conventional single-source CT. For the data acquisition, the X-ray source is controlled to maintain an energy within a segmental arc, and then switch alternately to another energy level. This scan only needs to switch tube voltage a few times to acquire multi-energy data, but leads to sparse-view and limited-angle issues in image reconstruction. To solve this problem, we propose a prior image constraint robust principal component analysis (PIC-RPCA) reconstruction method, which introduces structural similarity and spectral correlation into the reconstruction. A numerical simulation and a real phantom experiment were conducted to demonstrate the efficacy and robustness of the scan scheme and reconstruction method. The results showed that our proposed reconstruction method could have achieved better multi-energy images than other competing methods both quantitatively and qualitatively. Our proposed SSMECT scan with PIC-RPCA reconstruction method could lower kVp switching frequency while achieving satisfactory reconstruction accuracy and image quality.

Трехмерная рентгеновская томография промышленных объектов при ограниченных размерах регистрирующего экрана

The article investigates the possibilities of using a 3D tomograph with a limited-sizes registering screen for detecting arbitrarily oriented crack-like defects in large industrial objects. Circular and spiral scanning schemes are considered, the principal possibility of detecting defects in the case of two-pass spiral scanning and a registering screen covering half of the view field of the test object cross-section is shown. The performance of the 3D reconstruction algorithm for the selected scanning method has been demonstrated.

Study on application of laser in maskless localized electrodeposition and surface quality enhancement

To obtain electrodeposited layers with different patterns, the additional auxiliary measures such as mask prepared by photoresist are usually required for traditional electrodeposition (ECD) technology, which may reduce the flexibility and convenience of this method. Meanwhile, the ultrashort pulsed laser can be introduced into ECD process and increase current density in the selected area on cathode, and has potential in helping achieve maskless localized ECD. In this paper, the picosecond (ps) laser-assisted ECD (LECD) method is studied, in which a cyclic laser scanning scheme is used to produce different electrodeposited layers on the cathode substrate. In addition, the realizing mechanism of localized ECD is discussed, and the surface quality of Ni-P coating prepared by LECD is evaluated. The results show that the electrodeposited layers with different sizes (1 × 1 mm, 2 × 2 mm and 3 × 3 mm) can be obtained by laser selective irradiation on the copper substrate (10 × 10 mm), demonstrating that the critical current can be increased to reach the reaction conditions in the irradiated zone by the laser-caused thermal effects. Analysis also shows that the theoretical diameter of zigzag edge can be calculated, which is consistent with that of actual electrodeposited layer, indicating that the precision and localization of electrodeposited layer is controllable by adjusting laser processing parameters. Furthermore, measurement shows that a surface roughness of 0.012 μm and better surface flatness can be obtained by LECD under a pulse energy of 16 μJ, and the amorphous degree Ni-P can be increased by the thermal and photoelectric effects of ps laser irradiation. Besides, the corrosion potential and current density are −0.19 V and 3.83 × 10−6 A/cm2, respectively, and the AC impedance spectrum also indicates a higher electron transfer resistance, illustrating better corrosion resistance can be achieved by LECD (16 μJ).

Realization of noncontact confocal optical microsphere imaging microscope.

A novel noncontact confocal optical microsphere imaging microscope (COMIM) is proposed to achieve high contrast optical nano-imaging at a high scanning speed. The developed setup obtains images with significantly higher contrast when compared with conventional bright-field microsphere nano-imaging, as well as with a commercial confocal laser scanning microscope (CLSM). With the image-by-image scanning scheme, COMIM takes only 11% time to complete a three-dimensional (3D) scanning image than using a commercial CLSM, while still offers an outstanding resolving power for the nano-features on the sample.

Pixel dislocation correction method for a laser confocal scanning microscope through the nonlinear triangular wave driving mode and square wave index reconstruction.

The reciprocate scanning scheme of two-dimensional galvanometers is widely used in laser confocal scanning microscopes with high speed. However, the equal interval acquisition of an analog digital acquisition card (AD) and the unequal change of the galvanometer's scanning speed will cause the dislocation of pixels and distortion of the reconstructed image. Meanwhile, the movement properties of the galvanometers in the edge of the scanning area are complex, which will increase the difficulty of segmenting the collected one-dimensional data stream the AD collected into row data of a two-dimensional reconstructed image. Therefore, how to timely and accurately segment the one-dimensional data stream the AD collected into the row data of two-dimensional reconstructed image is not only the key to solve image distortion of a laser confocal scanning microscope with high speed but also the prerequisite to improve the accuracy of row data dislocation correction. A driving mode based on the nonlinear triangular wave and a dislocation-correcting method using a square wave index are proposed. Namely, on the basis of the galvanometer's scanning analysis, the equation of a nonlinear triangular wave driving voltage is established, and the switching frequency of the Y-galvanometer's driving voltage is obtained by calculating the collected switching frequency of the X-galvanometer; thus, the uniformity of the galvanometer's scanning trajectories is secured. Finally, the row segmentation flag pulse is first introduced into the one-dimensional data stream the AD collected, and the square wave index is used to segment the collected data, which means the one-dimensional data stream can be segmented timely and accurately via hardware method. Meanwhile, the pixel dislocation can be corrected. The experimental result shows that, compared with the Nikon A1R+ confocal microscope, the proposed method can effectively correct the pixel dislocation, and the position coincidence error is less than 0.7%. The proposed method will be helpful to improve the image quality of a laser confocal scanning microscope with high speed.

Influence of spot overlapping in laser paint stripping with moving repetitive pulses

Spot overlapping acts as one of the main concerns in getting ideal results in the laser paint stripping operations. In order to describe the process of paint removal with repetitively pulsed lasers in a scanning scheme, a simplified three-dimensional numerical model is developed and demonstrated to be able to present paint stripping results obtained with movable laser pulses. The influences of spatial overlapping between neighboring pulsed laser spots on the thermal distribution and on the corresponding paint removal are discussed. A series of experiments is designed, and the results agree well with the numerical simulation. It is found that a spot overlapping ratio higher than 50% is able to give uniformly heated zones and hence leads to no paint residues within the stripped region. An experimental linear dependence of laser paint stripping depth on the incident laser energy density is also obtained and may provide a guide for the parameter selection in the laser paint removal operations.

Scan Planning Optimization for 2-D Beam Scanning Using a Future Geostationary Microwave Radiometer

A 2-D beam scanning subsystem provides an effective means for a real-aperture microwave radiometer (MWR) to observe atmospheric events from a geostationary Earth orbit (GEO). However, it is practically difficult to achieve a high-quality and high-efficiency beam coverage in the specified regional target scene under different working modes of the MWR and their corresponding observation constraints. In this study, a scan planning model used by China's future GEO MWR is derived. This model is useful for achieving the optimal balance between the scan quality and time. Additionally, we establish a framework to compute the solution of our model. In the framework, we first present nominal-grid-based algorithms to numerically calculate the model constraints and objective function, and then introduce a multilevel neighbor search strategy to find the optimized solution. The significance of the framework lies in its capability to balance the tradeoffs between time consumption and global optimality. Preliminary test results demonstrate the validity and feasibility of the proposed model. The methods and results presented in this study are expected to provide constructive insights into the scanning scheme design of China's future GEO MWR and benefit the development of other similar 2-D beam scanning systems.

Cooperation-Assisted Spectrum Handover Mechanism in Vehicular Ad Hoc Networks

This paper proposes a cooperation-assisted spectrum handover (CASH) scheme in vehicular ad hoc networks (VANETs). In CASH, each vehicle uses cognitive radio technology to collect the surrounding spectrum information, computes the stability of the spectrum, exchanges neighbor information by vehicle-to-vehicle collaboration technology, and then executes a partial prescan mechanism to reduce the handover delay. The proposed method can improve the spectrum utilization, shorten the delay time of the spectrum handover, and reduce the total number of handovers. Finally, the simulation results show that the proposed method outperforms other existing schemes. In spectrum utilization, CASH is about 20% better than that of the traditional full scan method. In average scan time, the time of CASH is about 5 times less than the time of the traditional full scan method. In total number of handovers, CASH improves the performance of the full scan scheme by 33%.

High-Contrast and -Resolution 3-D Ultrasonography with a Clinical Linear Transducer Array Scanned in a Rotate-Translate Geometry

We proposed a novel solution for volumetric ultrasound imaging using single-side access 3-D synthetic aperture scanning of a clinical linear array. This solution is based on an advanced scanning geometry and a software-based ultrasound platform. The rotate-translate scanning scheme increases the elevation angular aperture by pivoting the array (−45° to 45°) around its array axis (axis along the row of its elements) and then scans the imaged object for each pivoted angle by translating the array perpendicularly to the rotation axis. A theoretical basis is presented so that the angular and translational scan sampling periods can be best adjusted for any linear transducer array. We experimentally implemented scanning with a 5-MHz array. In vitro characterization was performed with phantoms designed to test resolution and contrast. Spatial resolution assessed based on the full-width half-maximum of images from isolated microspheres was increased by a factor of 3 along the translational direction from a simple translation scan of the array. Moreover, the resolution was uniform over a cross-sectional area of 4.5 cm2. Angular sampling periods were optimized and tapered to decrease the scan duration while maintaining image contrast (contrast at the center of a 5-mm cyst on the order of −26 dB for 4° angular period and a scan duration of 10 s for a 9-cm3 volume). We demonstrated that superior 3-D ultrasound imaging can be obtained with a clinical array using our scanning strategy. This technique offers a promising and flexible alternative to development of costly matrix arrays toward the development of sensitive volumetric ultrasonography.

A Compact MEMS-Based Optical Scanning System with Large Field of View for Lidars

In this work, a design of a compact optical MEMS-based lidar scanning system with a large field of view (FOV) and small distortion is presented. The scanning system applies an off-axis structure and the length of the system can be reduced to about 10 cm in an optimized way. Simulation results show that a large FOV is achieved under a uniform scanning scheme. In addition, the spot size less than 20 cm at distance of 100 m is also realized. The optical scanning system can be used for the vehicle-mounted Lidar.

Design and Implementation of 5.8 GHz RF Wireless Power Transfer System

In this paper, we present a 5.8 GHz radio-frequency (RF) wireless power transfer (WPT) system that consists of 64 transmit antennas and 16 receive antennas. Unlike the inductive or resonant coupling-based near-field WPT, RF WPT has a great advantage in powering low-power internet of things (IoT) devices with its capability of long-range wireless power transfer. We also propose a beam scanning algorithm that can effectively transfer the power no matter whether the receiver is located in the radiative near-field zone or far-field zone. The proposed beam scanning algorithm is verified with a real-life WPT testbed implemented by ourselves. By experiments, we confirm that the implemented 5.8 GHz RF WPT system is able to transfer 3.67 mW at a distance of 25 meters with the proposed beam scanning algorithm. Moreover, the results show that the proposed algorithm can effectively cover radiative near-field region differently from the conventional scanning schemes which are designed under the assumption of the far-field WPT.