Two-axis Scanning Research Articles

Microstructure and Solidification Crack Susceptibility of Al 6014 Molten Alloy Subjected to a Spatially Oscillated Laser Beam

Oscillating laser beam welding for Al 6014 alloy was performed using a single mode fiber laser and two-axis scanner system. Its effect on the microstructural evolution of the fusion zone was investigated. To evaluate the influence of oscillation parameters, self-restraint test specimens were fabricated with different beam patterns, widths, and frequencies. The behavior of hot cracking propagation was analyzed by high-speed camera and electron backscatter diffraction. The behavior of crack propagation was observed to be highly correlated with the microstructural evolution of the fusion zone. For most oscillation conditions, the microstructure resembled that of linear welds. A columnar structure was formed near the fusion line and an equiaxed structure was generated at its center. The wide equiaxed zone of oscillation welding increased solidification crack susceptibility. For an oscillation with an infinite-shaped scanning pattern at 100 Hz and 3.5 m/min welding speed, the bead width, solidification microstructure, and the width of the equiaxed zone at the center of fusion fluctuated. Furthermore, the equiaxed and columnar regions alternated periodically, which could reduce solidification cracking susceptibility.

Visualization of an acoustic stationary wave by optical feedback interferometry

This paper presents an experimental technique for two-dimensional imaging of dynamic acoustic pressure changes that is applied to visualize a stationary acoustic wave. This technique uses the optical feedback interferometry sensing scheme with a near-infrared laser diode and a two-axis scanning system. The stationary acoustic wave is generated by using a 40 kHz piezoelectric transducer pointing toward a concave acoustic reflector. The acoustic pressure dynamic changes are measured due to its impact on the propagating medium refractive index, which variation is integrated along the laser optical path from the laser diode to a distant mirror and back. The imaging system records a 100×50 pixels image of the acoustic pressure in 66 min.

Scanning system for angle-resolved low-coherence interferometry.

Angle-resolved low-coherence interferometry (a/LCI) detects precancer by enabling depth-resolved measurements of nuclear morphology in vivo. A significant limitation of a/LCI is the point-probe nature of the method, sampling <0.5 mm2 before probe relocation is necessary. In this work, we demonstrate a scanning method capable of assessing an area >100 mm2 without repositioning. By utilizing a reflection-only three-optic rotator prism and a two-axis scanning mirror, we demonstrate radial scans of a sample with a linear range of 12mm and a full rotational range of 180°. Use of this design will improve the diagnostic utility of a/LCI for wide-area screening of tissue health.

5 V Compatible Two-Axis PZT Driven MEMS Scanning Mirror with Mechanical Leverage Structure for Miniature LiDAR Application.

The MEMS (Micro-Electronical Mechanical System) scanning mirror is an optical MEMS device that can scan laser beams across one or two dimensions. MEMS scanning mirrors can be applied in a variety of applications, such as laser display, bio-medical imaging and Light Detection and Ranging (LiDAR). These commercial applications have recently created a great demand for low-driving-voltage and low-power MEMS mirrors. However, no reported two-axis MEMS scanning mirror is available for usage in a universal supplying voltage such as 5 V. In this paper, we present an ultra-low voltage driven two-axis MEMS scanning mirror which is 5 V compatible. In order to realize low voltage and low power, a two-axis MEMS scanning mirror with mechanical leverage driven by PZT (Lead zirconate titanate) ceramic is designed, modeled, fabricated and characterized. To further decrease the power of the MEMS scanning mirror, a new method of impedance matching for PZT ceramic driven by a two-frequency mixed signal is established. As experimental results show, this MEMS scanning mirror reaches a two-axis scanning angle of 41.9° × 40.3° at a total driving voltage of 4.2 Vpp and total power of 16 mW. The effective diameter of reflection of the mirror is 2 mm and the operating frequencies of two-axis scanning are 947.51 Hz and 1464.66 Hz, respectively.

Two-axis water-immersible microscanning mirror for scanning optics and acoustic microscopy

Fast multiaxis scanning is useful for not only optical but also acoustic microscopic imaging. Although they have been used for optical scanning, the application of (MEMS) scanning mirrors in acoustic microscopy is still very limited due to their small mirror plate size, and more importantly, inability to operate in liquids (as ultrasound coupling media). A microfabricated two-axis water-immersible scanning mirror for optical and acoustic microscopy is reported. It has an optical and acoustically reflective mirror plate (6 mm×4 mm) to provide numerical aperture for ultrasound beam steering. Electromagnetic and mechanical analysis and simulation were conducted to estimate the mechanical tilting angle and resonance frequency of both fast and slow axes, which matches well with the measurement results. The fast axis has a resonant frequency of 320 Hz in air and 220 Hz in water, which is more than 10 times higher than that of the slow axis (24 Hz in air and 14 Hz in water). Under a 100-mA driving current, the scanning angles of the fast axis reached ±9.5 deg in both air and water at the resonance frequency, respectively. The scanning angles of the slow axis reached ±15 deg in air and ±12.5 deg in water at resonant frequencies, respectively. Raster scanning of a collimated laser beam was achieved by driving both axes simultaneously close to their own resonance frequencies. The feasibility of using the two-axis water-immersible scanning mirror in scanning acoustic microscopy was also demonstrated.

Coherent artifact suppression in line-field reflection confocal microscopy using a low spatial coherence light source.

Line-field reflection confocal microscopy (LF-RCM) has the potential to add a dimension of parallelization to traditional confocal microscopy while reducing the need for two-axis beam scanning. LF-RCM systems often employ light sources with a high degree of spatial coherence. This high degree of spatial coherence potentially leads to unwanted coherent artifact in the setting of nontrivial sample scattering. Here, we (a) confirm that a coherent artifact is a nontrivial problem in LF-RCM when using spatially coherent light, and (b) demonstrate that such a coherent artifact can be mitigated through the use of reduced spatial coherence line-field sources. We demonstrate coherent noise suppression in a full-pupil line-field confocal microscope using a large number of mutually incoherent emitters from a vertical-cavity surface-emitting lasers (VCSEL) array. The coherent noise from a highly scattering sample is significantly suppressed by the use of this synthesized reduced spatial coherence light source compared to a fully coherent light source. Lastly, with scattering samples, the axial confocality of line-field confocal microscopy is compromised independent of the source spatial coherence, as demonstrated by our experimental result. Our results highlight the importance of spatial coherence engineering in parallelized reflection confocal microscopy.

A Self-Aligned 45°-Tilted Two-Axis Scanning Micromirror for Side-View Imaging

This paper presents a two-axis electrothermal single-crystal-silicon micromirror that is tilted 45° out of plane on a silicon optical bench (SiOB). The SiOB provides mechanical support and electrical wiring to the tilted two-axis scanning mirror, as well as aligned trenches for assembling other optical components, such as optical fibers and GRIN lens. The pre-set tilting of the mirror plate is achieved via the bending of a set of stressed bimorph cantilevers. A stopper connected on the bending bimorphs reaches and is stopped by the adjacent silicon sidewall. The tilt angle can be precisely controlled by properly choosing the distance from the stopper to the silicon sidewall and the flexure bimorph length. The fabricated mirror plate is 0.72 mm $\times $ 0.72 mm and the footprint of the entire MEMS device is 2.22 mm $\times$ 1.25 mm. The measured maximum total optical scan angle of the mirror is approximately 40° in both $x$ -axis and $y$ -axis at only $5.5~V_{\mathrm{ dc}}$ . This technology will enable a new class of more compact microendoscopic optical imaging probes for in vivo early cancer detection. [2015-0315]

Electromagnetically actuated biaxial scanning micromirror fabricated with silicon on glass wafer

In this paper, we present an electromagnetically actuated two-axis scanning micromirror with large aperture and tilting angle for laser pointing applications. The two-axis micromirror with the plate size of 3 mm in diameter was realized using gimbaled single crystal silicon with a single-turn electroplated copper coil, and it was assembled with permanent magnets forming radial magnetic field. The micromirror was fabricated on SiOG (Silicon on Glass) wafer using 4 photolithography masks. The permanent magnet assembly composed of a cylindrical and a ring-type magnet was designed to optimize the radial magnetic field, and thus maximize the torque on the coil. Three different magnet assemblies were applied to the fabricated micromirror in order to verify the design. Horizontal resonance frequency of the fabricated micromirror was measured 1.421 kHz and vertical resonant frequency was 396 Hz. The vertical scan angle was 16.87°, 26.32° and 22.61° with the cylindrical magnet diameter of 2.6, 4.0 and 4.8 mm, respectively, at 60 Hz sinusoidal input of 640 mApp. For horizontal scan, maximum scan angle of 24.45° was obtained at 48 mApp input signal in resonance mode. In addition, the temperature distribution on the micromirror surface was measured with the applied current to the coil.

Experimental Measurement System for 3-6 GHz Microwave Breast Tomography

This paper presents an experimental measurement system for 3?6 GHz microwave tomography (MT) of the breast. The measurement system is constructed as a minimal test bed to verify key components such as the sensing antennas, radio frequency (RF) transceiver, sensing mechanism, and image reconstruction method for our advanced MT system detecting breast cancer at an early stage. The test bed has eight RF channels operating at 3 to 6 GHz for high spatial resolution and a two-axis scanning mechanism for three-dimensional measurement. The measurement results from the test bed are shown and discussed.

Relative continuous-time SLAM

Appearance-based techniques for simultaneous localization and mapping (SLAM) have been highly successful in assisting robot-motion estimation; however, these vision-based technologies have long assumed the use of imaging sensors with a global shutter, which are well suited to the traditional, discrete-time formulation of visual problems. In order to adapt these technologies to use scanning sensors, we propose novel methods for both outlier rejection and batch nonlinear estimation. Traditionally, the SLAM problem has been formulated in a single-privileged coordinate frame, which can become computationally expensive over long distances, particularly when a loop closure requires the adjustment of many pose variables. Recent discrete-time estimators have shown that a completely relative coordinate framework can be used to incrementally find a close approximation of the full maximum-likelihood solution in constant time. In order to use scanning sensors, we propose moving the relative coordinate formulation of SLAM into continuous time by estimating the velocity profile of the robot. We derive the relative formulation of the continuous-time robot trajectory and formulate an estimator using temporal basis functions. A motion-compensated outlier rejection scheme is proposed by using a constant-velocity model for the random sample consensus algorithm. Our experimental results use intensity imagery from a two-axis scanning lidar; due to the sensors’ scanning nature, it behaves similarly to a slow rolling-shutter camera. Both algorithms are validated using a sequence of 6880 lidar frames acquired over a 1.1 km traversal.

Tailored fibre waveguides for precise two-axis Lissajous scanning.

A two-axis optical imaging system using a Lissajous scan pattern with non-integer frequency ratio is presented. A waveguide with precisely tuned mechanical resonant frequencies is constructed by dip coating two fibres with a transparent polymer. Motion is achieved by mounting a waveguide cantilever at 45° on a single piezoelectric actuator with a dual-frequency drive. Confocal signal collection is achieved using a mode-stripping detector, and feedback signals needed for frequency and phase locking are derived from intermittent reflection from an apertured mirror. The first scan axis is locked to the resonance of one of the modes, while the second scan axis is locked to the correct phase at the desired frequency ratio. Accurate acquisition of two-dimensional images is demonstrated.

Non-resonant 2-D piezoelectric MEMS optical scanner actuated by Nb doped PZT thin film

This paper reports a non-resonant 2-D piezoelectric MEMS scanner actuated by a Nb doped PZT (PNZT) thin film for endoscopic optical coherence tomography (E-OCT) application. The unimorph actuator with the PNZT film shows more than twice as large displacement as that with a non-doped PZT films, and is suitable for large angle non-resonance scan, which was difficult for conventional non-resonant piezoelectric scanners. We designed a gimbal-less scanner with folded L-shape actuators enabling two-axis scan motion of a 1mm×1mm mirror within a compact device size of 2.2mm×2.7mm. The fabricated MEMS scanner with PNZT actuators showed an optical scan angle of 18.6° for both scan axes at a drive voltage of 40Vpp in non-resonance mode. This scan angle is more than 1.7 times larger than that of the scanner with PZT actuators, and is high enough to achieve a clinically useful scan area of 1mm×0.7mm at 3mm working distance in a side-imaging probe. The resonance frequency of the scanner was greater than 1.37kHz, which was sufficiently high for non-sinusoidal actuation up to 50Hz in OCT imaging. The scanner was driven by 25Hz triangle waves and 50Hz sawtooth waves through a low pass filter for linear OCT imaging at 50 lines per second.

Design and vibration analysis of a piezoelectric-actuated MEMS scanning mirror and its application to laser projection

This study presents the design and analysis of a two-axis scanner driven by lead-zirconate-titanate (PZT) ceramic. The proposed device consists of a silicon-based MEMS scanning mirror and a bulk-type piezoelectric actuator. The MEMS process involves three masks. The experimental results showed that the fast and slow frequencies at resonance are 29.6 kHz and 4.8 kHz, respectively. For the fast scan, the scanning angle is 46.9 degrees at a driving voltage of 10 V. For the slow scan, the scanning angle is 22.6 degrees at a driving voltage of 20 V. A multi-DOF vibration model was developed to analyze the scanning characteristics of the device. The numerical simulations, including the resonance frequency, scanning angle and the mode coupling phenomenon, were validated with the experimental observations. This study also develops a laser projection module integrated with the scanning device. The module can receive a video content with a resolution of 720 p and project a 16:9 image that is 19 inches in diagonal at a projection distance of 600 mm.

Development of an electrostatic method of nondestructive testing with high noise immunity

New electrostatic method of nondestructive testing with high noise immunity for a wide range of materials and structures, dielectrics and conductive materials without using contact liquid is proposed in the paper. A block diagram of the device to use this method in the field of nondestructive testing is provided.The method includes generating electrostatic field by supplying a reference signal with a given frequency to one pair of electrodes, registering induced charge using another measuring electrodes, and multiplying reference and measuring signals with further processing and visualization of results on the screen. The method involves two-axis scanning of the control object. Moreover, the measuring signal is defined as the difference of output signals of two pairs of measuring electrodes.Using the proposed nondestructive testing allows to test products under normal laboratory conditions without using special facilities and special screening means. The results of experiments confirm that under normal laboratory conditions, the level of noise from power supply networks exceeds the level of the useful signal by more than 40 dB, which prevents the realization of the known testing under such conditions. Testing can be conducted with one-way access to the control object.

One-axis on-the-fly laser system development for wide-area fabrication using cell decomposition

We have developed a one-axis on-the-fly system that can continuously process a large area by using a laser scanner. Existing laser processing using scanner systems can be used for precision processing, but have a limitation in the area of processing. To supplement this shortcoming, a step and scanning technique using a stage has been developed. This technique can process a large area in such a way that, after laser processing, the stage moves repetitively; however, this method has a demerit in that processing quality in the part between the scan areas is not even. To solve this problem, there is a method of synchronizing the scanner and the stage. This study developed an on-the-fly system that synchronizes the one-axis stage and the two-axis scanner. Also, in synchronized processing, the velocity of the stage due to the velocity of fabrication is very important. If the velocity of the stage is not proper, the laser processing deviates from the scanner work area. We proposed an algorithm in which, using a cell decomposition method, the velocity of the stage is automatically calculated by compensating for the acceleration/deceleration time occurring in the stage rotation and the reverse rotation due to the velocity of the fabrication. We compared the step and scanning method to the on-the-fly method through a low-frequency experiment and proved that the latter has better precision for the boundary of the scan area; we further analyzed the precision by using a large area marking and an overlapping experiment. In addition, by measuring encoder output signals, a compensation algorithm for the stage acceleration/deceleration time was verified.

A gimbal-less two-axis electrostatic scanner with tilted stationary vertical combs and serially connected springs via a microassembly process

We propose a gimbal-less two-axis electrostatic microelectromechanical system (MEMS) scanner with tilted stationary vertical combs (TSVCs) fabricated via a microassembly process. The gimbal-less two-axis scanner has the advantage of being of a compact size and also does not need any additional fabrication sequence for electrical isolation. The TSVCs and coupled springs (T-shaped springs and folded springs) allow the mirror scanner to rotate around two axes with a large scanning angle. The fabrication steps for the proposed scanner can be remarkably reduced by employing a microassembly process, as there is no need to conduct a multistep etching process for height offset between two vertical combs. It was found that the width of the folded spring and the T-shaped spring dominated the resonant frequency of the fast axis and the slow axis, respectively. By modeling the capacitance change of TSVCs with respect to the rotational angle (θ), the effective tilted angle (ETA), as a new design criterion, was introduced to determine an adequate operation range. The optical scanning angle of the fabricated scanner was up to 7.8° at 90 V for the slow axis in quasistatic mode and up to 17.3° at 100 V for the fast axis in resonant mode at 2.84 kHz. The fabricated scanner can be used for various endoscopic optical applications.

J2220102 薄膜金属ガラスCu-Zr-Tiを用いた二軸駆動マイクロミラーデバイスの製作と駆動([J222-01]マイクロ・ナノ材料創成とそのデバイス応用(1))

In Micro Electro Mechanical Systems (MEMS) technology, structure of amorphous alloy thin film is manufactured by sputter deposition and lift-off process. But its thickness is not uniform because lift-off masking material block off. The structure thickness of amorphous alloy thin film is low in the vicinity of lift-off masking material, and its cross-sectional shape is not rectangular. For these problems, we proposed new fabrication method of thick film structure of metallic glass with the sputtering jig, which combines projection surfaces and spacers. As this application, we have successfully fabricated two-axis scanning micro mirror device with thin film metallic glass Cu-Zr-Ti, which have uniform film thickness, rectangular cross-sectional shape and electrical factors. However, the sample was not able to be driven in driving test, because the torsion bar of sample had been broken for Cu-Zr-Ti crystallization. In this paper, we proposed low temperature production process which is not to crystallize Cu-Zr-Ti. And we have succeeded in fabricating and driving the two-axis scanning micro mirror device.

Correction of image distortions in endoscopic optical coherence tomography based on two-axis scanning MEMS mirrors

A two-axis scanning microelectromechanical (MEMS) mirror enables an optical coherence tomography (OCT) system to perform three-dimensional endoscopic imaging due to its fast scan speed and small size. However, the radial scan from the MEMS mirror causes various distortions in OCT images, namely spherical, fan-shaped and keystone distortions. In this paper, a new method is proposed to correct all of three distortions presented in OCT systems based on two-axis MEMS scanning mirrors. The spherical distortion is corrected first by directly manipulating the original spectral interferograms in the phase domain, followed by Fourier transform and three-dimensional geometrical transformation for correcting the other two types of distortions. OCT imaging experiments on a paper with square ink printed arrays and a glass tube filled with milk have been used to validate the proposed method. Distortions in OCT images of flat or curved surfaces can all be effectively removed.

Endoscopic swept-source optical coherence tomography based on a two-axis microelectromechanical system mirror

A microelectromechanical system (MEMS) mirror based endoscopic swept-source optical coherence tomography (SS-OCT) system that can perform three-dimensional (3-D) imaging at high speed is reported. The key component enabling 3-D endoscopic imaging is a two-axis MEMS scanning mirror which has a 0.8×0.8 mm2 mirror plate and a 1.6×1.4 mm2 device footprint. The diameter of the endoscopic probe is only 3.5 mm. The imaging rate of the SS-OCT system is 50 frames/s. OCT images of both human suspicious oral leukoplakia tissue and normal buccal mucosa were taken in vivo and compared. The OCT imaging result agrees well with the histopathological analysis.

3-D Confocal Laser Scanning Microscopy Based on a Full-MEMS Scanning System

We have developed a confocal microscope using MEMS devices for laser scanning in all three axes. This full-MEMS laser scanning system is equipped with a MEMS lens scanner for deep scanning and a MEMS mirror for two-axis lateral scan. The MEMS lens scanner can move an objective lens axially by 515 μm at only 3.2 V. The two-dimensional MEMS mirror can achieve ± 20° optical scan angle at 4.5 V. Two-dimensional and three-dimensional confocal reflectance images of microparticles embedded in PDMS and acute rat brain tissue are obtained. The axial and lateral resolutions are measured as 9.0 and 1.2 μm, respectively.