Flatness-based approach for the manipulation of a microscopic particle by optical tweezers

Based on the fact that optical tweezers (OT) constitute a flat system, with flat outputs given by the horizontal and vertical position coordinates of the geometric centre of the laser beam, a flatness-based control strategy for the manipulation of a microscopical particle is presented in this article. The control strategy is derived under the assumption that the particle is suspended in a frictionless medium, obtaining a simple controller with a relatively simple stability analysis. The control strategy is tested by tracking a straight line, an elliptic curve, and carrying out the rest-to-rest transfer manoeuvre task by using a smooth trajectory.     

Transient simulations of the electrophoretic motion of a cylindrical particle through a 90° corner

The trajectory of a cylindrical particle driven by electrophoresis was transiently simulated as the particle moves through a 90° corner. A variety of system parameters were tested to determine their impact on the particle motion. The zeta potential, channel width, and particle aspect ratio were shown to have a minimal effect on the particle motion. Conversely, the initial vertical position of the particle and initial angle with respect to the horizontal had a significant impact on the particle motion. The presence of the 90° corner acts to reduce the initial distribution of angles to the vertical of 90° to less than 30°, demonstrating the possibility of using a corner as a passive control element as part of a larger microfluidic system. However, the reduction in angle is limited to the area near the corner posing a limitation on this means of control.     

Electrical measurement of cross-sectional position of particles flowing through a microchannel

The first high-throughput system for the electrical detection of cross-sectional position and velocity of individual particles flowing through a rectangular microchannel is presented. Lateral position (along channel width) and vertical position (along channel height) are measured using two different sets of coplanar electrodes. In particular, the ratio of travel times measured with electrodes generating a current flow transverse or oblique with respect to particle trajectory yields lateral position. The relative prominence and transit time of a bipolar double-Gaussian signal obtained with a suited electrode configuration, respectively, supply vertical position and velocity. The operating principle is presented by means of finite element numerical simulations. The method is experimentally validated by comparing the electrical estimates of position and velocity of polystyrene beads with optical estimates obtained by processing high-speed images. The system is used to observe bead focusing at different particle Reynolds numbers. This system, providing a fully electrical characterization of single-particle motion, represents a powerful tool, e.g. to understand fluid motion at the microscale, in particle separation studies, or to assess the performance of particle focusing devices. Moreover, it can be simultaneously used to perform single-cell impedance spectroscopy, thus achieving an unprecedented multiparamteric characterization.     

New horizontal frustum optical waveguide fabrication using UV proximity printing

This paper presents a novel method for fabricating the horizontal frustum structure as a planar optical waveguide using the proximity printing technique. A horizontal frustum optical waveguide with both lateral and vertical taper structure was produced. The orthogonal and inclined masks with the diffraction effect were employed in the lithography process. This method can precisely control each horizontal frustum optical waveguide geometric profile in the fabrication process. The horizontal frustum optical waveguide and its array with the same inclined angle were generated. The beam propagation simulation software (BPM_CAD) was used to model the optical performance. The simulation results reveal that the mode profile matched into horizontal frustum optical waveguide and fiber from the laser diode. The optical loss of the horizontal hemi-frustum optical waveguide structure was less than 0.2 dB. The horizontal hemi-frustum waveguide will be used for fiber coupling on boards for future optical communication systems.     

Preliminary scanning fluorescence detection of a minute particle running along a waveguide implemented microfluidic channel using a light switching mechanism

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a “ubiquitous human healthcare system” in the near future. We have already proposed the fundamental structure for a light waveguide capable of illuminating a living cell or particle running along a microfluidic channel, as well as of detecting fluorescence even from the extremely weak power of such a minute particle. In order to develop novel functions to detect the internal structure of living cells quickly, an angular scanning method that sequentially changes the direction of illumination of the minute cell or particle may be crucial. In this paper, we investigate fluorescence detection from moving particles by switching the laser power delivery path of plural light waveguides as a preliminary experiment toward this novel method. To construct an experimental system able to incorporate a switching light source mechanism cost effectively, we utilized a conventional TAS chip with plural waveguide pairs arranged in parallel, and a forced vibration mechanism on an optical fiber tip by a piezoelectric actuator. With this system, we performed an experiment to detect extremely weak fluorescence using micro particles with a fluorescent substance attached and an optical TAS chip that incorporated a microfluidic channel and three pairs of laser-power-delivering light waveguide cores. We successfully obtained clear, quasi-triangular-shaped pulses in fluorescent signals from resin particles running across the intersection under three different conditions: (1) a particle with approximately the same velocity as that of a forced-vibrated optical fiber tip of approximately 700 mm/s, (2) a particle with velocity 1 digit smaller than that of an optical fiber tip, and (3) a particle with velocity approximately 1/20 that of an optical fiber tip.     

加权方位特征的纹理图像FCM聚类分割

针对自然纹理的弱规则性特点,提出一种结合图像灰度分布、纹理能量统计的加权FCM纹理分割方法,并在该方法中尝试引入水平位置、垂直位置、中心径向距离等三种方位特征参数。实验证明,该加权FCM聚类算法简单高效、可控性强,纹理分割效果明显,其中样本的三种加权方位特征参数能增强区域分割的聚敛度,有效地提高纹理尤其是非均质粗糙纹理的分割精度。     

一种空间运动体与固定平面位置关系的激光测量方法

在激光测距实际应用中,空间运动物体与固定平面位置关系的测量必须满足传感器安装于运动物体,且其光轴垂直于被测平面的条件.对于传感器光轴无法垂直对准被测面的情况,传统的方法无法实现测量.结合实际应用,创新性地提出了一种空间运动物体上传感器光轴无需垂直对准被测平面的激光测距方法.通过实验室的验证,证明该方法可以实现空间运动体与固定平面之间高度与角度关系的精确测量.     

Design, fabrication, and test of an on-chip micro flow cytometer with integrated out-of-plane microlenses

A micro flow cytometer with an integrated three-dimensional hydro-focusing unit and out-of-plane microlenses was successfully fabricated and tested. The entire system was fabricated with SU-8 ultra-violet lithography process. In the hydro-focusing unit, sheath flows pass through a trapezoid-shaped chamber with three 30° slopes to focus the sample flow in both horizontal and vertical directions. As an essential component in the on-chip optical detection system, integrated out-of-plane microlens was embedded in the sidewall of the fluid outlet channel in the detection area. A pre-aligned optical fiber holder was fabricated on chip to fix the output optical fiber in a position aligned to the microlens. Optical simulation and analysis were also conducted using commercial software Zemax. Numerical simulation results confirmed that the use of microlens substantially improved the detection efficiency by focusing the fluorescent light from the sample cells into the output optical fiber. Preliminary cell counting experiment was performed using the fabricated micro flow cytometer system and the experimental results proved the feasibility of the integrated micro flow cytometer design.     

Standing centre of pressure alters the vibration transmissibility response of the foot

Abstract

Vibration-white foot as an occupational disease has underscored the need to better understand the vibration response of the foot. While vibration transmissibility data exist for a natural standing position, it is anticipated that weight distribution will affect the response. The purpose of this study was to determine the effects of changes in centre of pressure (COP) on the foot’s biomechanical response. Twenty-one participants were exposed to vertical vibration of 30?mm/s, with a sine sweep from 10–200?Hz. Z-axis (vertical) vibration was measured at 24 locations on the right foot, with the COP shifted forward or toward the heel. A mixed model analysis at each location revealed significant differences (p?<?.001) in the transmissibility response when the COP was altered to the forefoot and rearfoot. In general, the peak frequency of the average vibration response increased for a region of the foot when the COP was shifted toward that region.

Practitioner Summary: Altering the centre of pressure location resulted in changes in the transmission of vibration through the foot. The forward lean position was associated with the greatest amplitude of vibration transmissibility at the toes. This information is relevant for clinicians studying vibration-induced white-foot and engineers designing protective equipment.     

Mobile Camera Localization Using Apollonius Circles and Virtual Landmarks

We investigate the localization of a camera subject to a planar motion with horizontal optical axis in the presence of known vertical landmarks. Under these assumptions, a calibrated camera can measure the distance to the viewed landmarks. We propose to replace the trilateration method by intersecting a pair of Chasles-Apollonius circles. In the case of square pixels but unknown focal length we introduce a new method to recover the camera position from one image with three vertical landmarks. To this end we consider virtual landmarks and Apollonius-like circles. We extend this method in order to deal with an unknown principal point by using four landmarks.     

3D visualization of convection patterns in lab-on-chip with open microfluidic outlet

Open-outlet microfluidics is getting more and more attention, thanks to the generation of capillarity-driven flows which simplify the connection with the macro-world. It is known that convection flows are generated at the interface with air, i.e., the meniscus. Several works have investigated evaporation-induced convection, but its effect on particle position control in open-outlet biodevices is still not characterized. In this paper, we present the results of 3D measurement of particle traces near the meniscus in an open-outlet vertical 400 μm micro-channel filled with a water-based saline solution. Using a standard optical microscope and a system of mirrors, we observe the 3D position of individual micro-beads floating in the solution, in a way akin to particle image velocimetry technique. A single vortex is generated at the meniscus and occupies the whole region under observation at a distance of 1.5–2.7 mm from the meniscus. The generation of the convection pattern and the vortex rotational speed are described. The convection patterns disappear when evaporation is inhibited, while both the vortex generation and the rotational speed are faster for highly saline solutions. These results are relevant to the design of biochips which require control of the particle position in a fluid since they emphasize that in open-outlet microfluidic systems not only the gravitational fall but also the convection drag must be counteracted.     

Micro-optofluidic switch realized by 3D printing technology

This paper presents a PDMS micro-optofluidic chip that allows a laser beam to be driven directly toward a two-phase flow stream in a micro-channel while at the same time automatically, detecting the slug’s passage and stirring the laser light, without the use of any external optical devices. When the laser beam interacts with the microfluidic flow, depending on the fluid in the channel and the laser angle of incidence, a different signal level is detected. So a continuous air–water segmented flow will generate a signal that switches between two values. The device consists of a T-junction, which generates the two-phase flow, and three optical fiber insertions, which drive the input laser beam toward a selected area of the micro-channel and detects the flow stream. Three micro-channel sections of different widths were considered: 130, 250, 420 μm and the performance of the models was obtained by comparing ray-tracing simulations. The master of the device has been realized by 3D printing technology and a protocol which realizes the PDMS chip is presented. The static and dynamic characterizations, considering both single flows and two-phase flows, were carried out, and in spite of the device’s design simplicity, the sensitivity of the system to capture changes in the segmented flows and to stir the laser light in different directions was fully confirmed. The experimental tests show the possibility of obtaining satisfactory results with channel diameters in the order of 200 μm.     

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45deg to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2 Omega. A two-dimensional scanner with mirror size of 1.5 mm in diameter was fabricated. Maximum optical scan angle of 8.8deg in horizontal direction and 8.3deg in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7 kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.     

Motion of a rigid cylinder between parallel plates in stokes flow : Part 1: Motion in a quiescent fluid and sedimentation

A general numerical scheme for solution of two-dimensional Stokes equations in a multiconnected domain of arbitrary shape [1, 2] is applied to the motion of a rigid circular cylinder between plane parallel boundaries. Numerically generated boundary-conforming coordinates are used to transform the flow domain into a domain with rectilinear boundaries. The transformed Stokes equations in vorticity-stream function form are then solved on a uniform grid using an iterative algorithm. In Part I coefficients of the resistance matrix representing the forces and torque on the cylinder due to its translational motion parallel or perpendicular to the boundaries or due to rotation about its axis are calculated. The solutions are obtained for a wide range of particle radii and positions across the channel. It is found that the force on a particle translating parallel to the boundaries without rotation exhibits a minimum at a position between the channel centerline and the wall and a local maximum on the centerline.

The resistance matrix is utilized to calculate translational and angular velocities of a free particle settling under gravity in a vertical channel. It is found that the translational velocity has a maximum at some lateral position and a minimum on the centerline; the particle angular velocity is opposite in sign to that of a particle rolling along the nearer channel wall except when the gap between the particle and the wall is very small. These results are compared with existing analytical solutions for a small cylindrical particle situated on the channel centerline, and with solutions of related 3-D problems for a spherical particle in a circular tube and in a place channel. It is shown that the behavior of cylindrical and spherical particles in a channel in many cases is qualitatively different. This is attributed to different flow patterns in these two cases. The motion of a spherical particle in a circular tube has qualitative and quantitative features similar to those for a cylindrical particle in a plane channel.     

空气质量流量传感器的内部流道建模与设计

对于空气质量传感器中的热电阻表面流场分布,需要设计一种合适的内部小流道,能使得热电阻表面的流场分布合理.选择流场湍流模型,仿真分析了直线形壁面和几种圆弧形壁面的内部小流道的流场分布,研究了它们的流场分布特性,确定了热电阻的安装位置.仿真结果表明:与直线形流道相比,圆弧形流道具有较好的同一水平方向的速度一致性和较小的垂直...     

反射式大面积光幕测速装置研究

介绍了一种基于反射式的大面积光幕测速装置,靶面的横向距离可达6000mm,避免了现有弹丸测速区截装置测试区域小、安全距离近、容易损坏测速装置等缺点。该装置由激光光学系统、回归式反光材料（反光膜）及其固定支架、反射镜、光电探测器与处理电路组成。将激光光源投射到另一端的反光膜上,形成光幕探测区,当弹丸或破片穿过光幕时,引起光通量变化,通过测时仪或数据采集系统即可获得过靶速度。用7．62mm枪弹经与高精度的框架式800mm×800mm的光幕靶进行了比对试验,结果满足测量精度要求。试验证明：该装置具有靶面大、精度高、使用维护方便,成本低等显著优点,不仅能进行常规的弹丸速度测试,同时,也适用于破片、弹幕武器等的速度测量。     

Deposition of suspensions in the entrance of a parallel-plate channel with gravity effect

The deposition of aerosols near the inlet region of a horizontal parallel channel (for a distance of 7 channel widths) was investigated by solving numerically the governing equations for both the fluid and particulate phases with boundary layer assumptions. Surface adhesion between the channel walls and the aerosol particles along with the gravitational influence was varied.This analysis took into consideration the simultaneous development of both the fluid and particle phases. The deposition for the present analysis for high surface adhesion was found to be greater for $\text{X ≥ 2}$ than the deposition obtained by Ingham for Plug flow who used only the diffusion equation with zero particulate density at the wall.     

Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and - 16° downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.     

Eccentric electrophoretic motion of a sphere in circular cylindrical microchannels

The eccentric electrophoretic motion of a spherical particle in an aqueous electrolyte solution in circular cylindrical microchannels is studied in this paper. The objective is to investigate the influences of separation distance and channel size on particle motion. A theoretical model is developed to describe the electric field, the flow field and the particle motion. A finite element based direct numerical simulation method is employed to solve the model. Numerical results show that, when the particle is eccentrically positioned in the channel, the electric field and the flow field are not symmetric, and the strongest electric field and the highest flow velocity occur in the small gap region. It is shown that the rotational velocity of the particle increases with the decrease of the separation distance. With the decrease of the separation distance, the translational velocity increases in a smaller channel; while it decreases first and then increases in a relatively large channel. When a particle moves eccentrically at a smaller separation distance from the channel wall, both the translational velocity and the rotational velocity increase with the decrease of the channel size.     

Analysis of the reflected image by the cylindrical concave surface of the mobile display

Reflection from the display surface affects the user's viewing experience. Cylindrical concave displays had been reported to be used for TV and mobile smart phone. The position and magnification of reflection at the curved mobile display were determined by the user's position and the focal distance of the cylindrical concave surface of the curved display. If the focal position of the curved surface was smaller or nearer to the user position, the enlarged reflection of the user would block the lights from the surrounding, and the curved display would be effective to reduce the inconvenience due to reflection. As the curvature of the cylindrical surface was different for the vertical and horizontal directions, the reflected image was not located at one distance. Hence, the refractive power of the eye of the user would be difficult to adjust to the position of the reflected image, and the reflected image would look defocused or hazed even for the display surface of the specular reflection.