Biaxial piezoelectric MEMS mirrors with low absorption coating for 1550 nm long-range LIDAR

This paper presents the fabrication and characterization of a biaxial MEMS (MicroElectroMechanical System) scanner based on PZT (Lead Zirconate Titanate) which incorporates a low-absorption dielectric multilayer coating, i.e., a Bragg reflector. These 2 mm square MEMS mirrors, developed on 8-inch silicon wafers using VLSI (Very Large Scale Integration) technology are intended for long-range (>100 m) LIDAR (LIght Detection And Ranging) applications using a 2 W (average power) pulsed laser at 1550 nm. For this laser power, the use of a standard metal reflector leads to damaging overheating. To solve this problem, we have developed and optimised a physical sputtering (PVD) Bragg reflector deposition process compatible with our sol-gel piezoelectric motor. Experimental absorption measurements, performed at 1550 nm and show up to 24 times lower incident power absorption than the best metallic reflective coating (Au). Furthermore, we validated that the characteristics of the PZT, as well as the performance of the Bragg mirrors in terms of optical scanning angles, were identical to those of the Au reflector. These results open up the possibility of increasing the laser power beyond 2W for LIDAR applications or other applications requiring high optical power. Finally, a packaged 2D scanner was integrated into a LIDAR system and three-dimensional point cloud images were obtained, demonstrating the scanning stability and operability of these 2D MEMS mirrors.This research was funded by ECSEL Joint Undertaking (JU) grant number No. 826600 (project VIZTA).Peer ReviewedPostprint (published version

Electro-optic Beam Steering Using Domain Engineered Lithium Tantalate

The operation of a 14-channel five stage electro-optic beam steering device was studied. Beam deflection scanned from 0° to 10.1° was demonstrated. The maximum angle is within 0.3% of design. Many laser systems in operation today implement mechanical beam steering methods that are often expensive in terms of cost, weight and power. They are slow and subject to wear and vibration. A non-inertial beam scanning mechanism, such as one based on the device studied in this research could enhance the performance of these systems. The device studied here is fabricated in LiTaO3 using micro-patterned domain reversal. The 14 channels allow for steering large aperture beams while the five cascaded stages increase the total deflection angle. The steering mechanism is a series of prisms created through domain reversal with the index change across prism interfaces controlled electro-optically. The maximum coupling efficiency achieved was 61.6% for this device. Also, the far-field observations revealed a pattern consistent with a beam diffracted through a multi-slit aperture. Forbidden angles exist between modes caused by destructive interference regardless of the applied voltage. A discussion on a method to improve device design, which allows the forbidden angles, is presented

Optical MEMS

Optical microelectromechanical systems (MEMS), microoptoelectromechanical systems (MOEMS), or optical microsystems are devices or systems that interact with light through actuation or sensing at a micro- or millimeter scale. Optical MEMS have had enormous commercial success in projectors, displays, and fiberoptic communications. The best-known example is Texas Instruments’ digital micromirror devices (DMDs). The development of optical MEMS was impeded seriously by the Telecom Bubble in 2000. Fortunately, DMDs grew their market size even in that economy downturn. Meanwhile, in the last one and half decade, the optical MEMS market has been slowly but steadily recovering. During this time, the major technological change was the shift of thin-film polysilicon microstructures to single-crystal–silicon microsructures. Especially in the last few years, cloud data centers are demanding large-port optical cross connects (OXCs) and autonomous driving looks for miniature LiDAR, and virtual reality/augmented reality (VR/AR) demands tiny optical scanners. This is a new wave of opportunities for optical MEMS. Furthermore, several research institutes around the world have been developing MOEMS devices for extreme applications (very fine tailoring of light beam in terms of phase, intensity, or wavelength) and/or extreme environments (vacuum, cryogenic temperatures) for many years. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) novel design, fabrication, control, and modeling of optical MEMS devices based on all kinds of actuation/sensing mechanisms; and (2) new developments of applying optical MEMS devices of any kind in consumer electronics, optical communications, industry, biology, medicine, agriculture, physics, astronomy, space, or defense

Novel Techniques for Tissue Imaging and Characterization Using Biomedical Ultrasound

The use of ultrasound technology in the biomedical field has been widely increased in recent decades. Ultrasound modalities are considered more safe and cost effective than others that use ionizing radiation. Moreover, the use of high-frequency ultrasound provides means of high-resolution and precise tissue assessment. Consequently, ultrasound elastic waves have been widely used to develop non-invasive techniques for tissue assessment. In this work, ultrasound waves have been used to develop non-invasive techniques for tissue imaging and characterization in three different applications.;Currently, there is a lack of imaging modalities to accurately predict minute structures and defects in the jawbone. In particular, the inability of 2D radiographic images to detect bony periodontal defects resulted from infection of the periodontium. They also may carry known risks of cancer generation or may be limited in accurate diagnosis scope. Ultrasonic guided waves are sensitive to changes in microstructural properties, while high-frequency ultrasound has been used to reconstruct high-resolution images for tissue. The use of these ultrasound techniques may provide means for early diagnosis of marrow ischemic disorders via detecting focal osteoporotic marrow defect, chronic nonsuppurative osteomyelitis, and cavitations in the mandible (jawbone). The first part of this work investigates the feasibility of using guided waves and high frequency ultrasound for non-invasive human jawbone assessment. The experimental design and the signal/image processing procedures for each technique are developed, and multiple in vitro studies are carried out using dentate and non-dentate mandibles. Results from both the ultrasonic guided waves analysis and the high frequency 3D echodentographic imaging suggest that these techniques show great potential in providing non-invasive methods to characterize the jawbone and detect periodontal diseases at earlier stages.;The second part of this work describes indirect technique for characterization via reconstructing high-resolution microscopic images. The availability of well-defined genetic strains and the ability to create transgenic and knockout mice makes mouse models extremely significant tools in different kinds of research. For example, noninvasive measurement of cardiovascular function in mouse hearts has become a valuable need when studying the development or treatment of various diseases. This work describes the development and testing of a single-element ultrasound imaging system that can reconstruct high-resolution brightness mode (B-mode) images for mouse hearts and blood vessels that can be used for quantitative measurements in vitro. Signal processing algorithms are applied on the received ultrasound signals including filtering, focusing, and envelope detection prior to image reconstruction. Additionally, image enhancement techniques and speckle reduction are adopted to improve the image resolution and quality. The system performance is evaluated using both phantom and in vitro studies using isolated mouse hearts and blood vessels from APOE-KO and its wild type control. This imaging system shall provide a basis for early and accurate detection of different kinds of diseases such as atherosclerosis in mouse model.;The last part of this work is initialized by the increasing need for a non-invasive method to assess vascular wall mechanics. Endothelial dysfunction is considered a key factor in the development of atherosclerosis. Flow-mediated vasodilatation (FMD) measurement in brachial and other conduit arteries has become a common method to assess the endothelial function in vivo. In spite of the direct relationship that could be between the arterial wall multi-component strains and the FMD response, direct measurement of wall strain tensor due to FMD has not yet been reported in the literature. In this work, a noninvasive direct ultrasound-based strain tensor measuring (STM) technique is presented to assess changes in the mechanical parameters of the vascular wall during post-occlusion reactive hyperemia and/or FMD, including local velocities and displacements, diameter change, local strain tensor and strain rates. The STM technique utilizes sequences of B-mode ultrasound images as its input with no extra hardware requirement. The accuracy of the STM algorithm is assessed using phantom, and in vivo studies using human subjects during pre- and post-occlusion. Good correlations are found between the post-occlusion responses of diameter change and local wall strains. Results indicate the validity and versatility of the STM algorithm, and describe how parameters other than the diameter change are sensitive to reactive hyperemia following occlusion. This work suggests that parameters such as local strains and strain rates within the arterial wall are promising metrics for the assessment of endothelial function, which can then be used for accurate assessment of atherosclerosis

Near-Field Scanning Microwave Microscopy in the Single Photon Regime

The microwave properties of nano-scale structures are important in a wide variety of applications in quantum technology. Here we describe a low-power cryogenic near-field scanning microwave microscope (NSMM) which maintains nano-scale dielectric contrast down to the single microwave photon regime, up to $10^{9}$ times lower power than in typical NSMMs. We discuss the remaining challenges towards developing nano-scale NSMM for quantum coherent interaction with two-level systems as an enabling tool for the development of quantum technologies in the microwave regime

High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes

金沢大学理工研究域数物科学系The atomic force microscope (AFM) has a unique capability of allowing the high-resolution imaging of biological samples on substratum surfaces in physiological solutions. Recent technological progress of AFM in biological research has resulted in remarkable improvements in both the imaging rate and the tip force acting on the sample. These improvements have enabled the direct visualization of dynamic structural changes and dynamic interactions occurring in individual biological macromolecules, which is currently not possible with other techniques. Therefore, high-speed AFM is expected to have a revolutionary impact on biological sciences. In addition, the recently achieved atomic-resolution in liquids will further expand the usefulness of AFM in biological research. In this article, we first describe the various capabilities required of AFM in biological sciences, which is followed by a detailed description of various devices and techniques developed for high-speed AFM and atomic-resolution in-liquid AFM. We then describe various imaging studies performed using our cutting-edge microscopes and their current capabilities as well as their limitations, and conclude by discussing the future prospects of AFM as an imaging tool in biological research. © 2008 Elsevier Ltd. All rights reserved

Structural Health Monitoring for Composite Materials

Computer networking & communication

Mechanical compression of coiled carbon nanotubes

Carbon nanotubes are molecular-scale tubes of graphitic carbon that possess many unique properties. They have high tensile strength and elastic modulus, are thermally and electrically conductive, and can be structurally modified using well established carbon chemistries. There is global interest in taking advantage of their unique combination of properties and using these interesting materials as components in nanoscale devices and composite materials. The goal of this research was the correlation of the mechanical properties of coiled carbon nanotubes with their chemical structure. Individual nanocoils, grown by chemical vapor deposition, were attached to scanning probe tip using the arc discharge method. Using a scanning probe microscope the nanocoils are repeatedly brought into and out of contact with a chemically-modified substrate. Precise control over the length (or area) of contact with the substrate is achievable through simultaneous monitoring the cantilever deflection resonance, and correlating these with scanner movement. The mechanical response of nanocoils depended upon the extent of their compression. Nonlinear response of the nanocoil was observed consistent with compression, buckling, and slip-stick motion of the nanocoil. The chemical structure of the nanocoil and its orientation on the tip was determined using scanning and transmission electron microscopy. The mechanical stiffness of eighteen different nanocoils was determined in three ways. In the first, the spring constant of each nanocoil was computed from the slope of the linear response region of the force-distance curve. The assumptions upon which this calculation is based are: 1) under compression, the cantilever-nanocoil system can be modeled as two-springs in series, and 2) the nanocoil behaves as an ideal spring as the load from the cantilever is applied. Nanocoil spring constants determined in this fashion ranged from 6.5x10-3 to 5.16 TPa for the CCNTs understudy. In the second, the spring constant of the nanocoil was computed from measuring the critical force required to buckle the nanocoil. The critical force method measured the force at the point where the nanocoil-cantilever system diverges from a linear region in the force curve. Nanocoil spring constants determined in this fashion ranged from 1.3x10-5 to 10.4 TPa for the CCNTs understudy. In the third, the spring constant of each nanocoil was computed from the thermal resonance of the cantilever-nanocoil system. Prior to contact of the nanocoil with the substrate, the effective spring constant of the system is essentially that of the cantilever. At the point of contact and prior to buckling or slip-stick motion, the effective spring constant of the system is modeled as two springs in parallel. Nanocoil spring constants determined in this fashion ranged from 2.7x10-3 to 0.03 TPa for the CCNTs understudy. Using the thermal resonance of the cantilever system a trend was observed relating nanocoil structure to the calculated modulus. Hollow, tube-like nanostructures had a higher measured modulus than solid or fibrous structures by several orders of magnitude. One can conclude that the structure of carbon nanocoils can be determined from using their mechanical properties. This correlation should significantly contribute to the knowledge of the scientific and engineering community. It will enable the integration of carbon nanocoils in microelectromechanical (MEMS) or nanoelectromechanical systems (NEMS) as resonators, vibration dampers, or any other application in which springs are used within complex devices.Ph.D.Committee Chair: Lawrence Bottomley; Committee Member: Aldo Ferri; Committee Member: E. Kent Barefield; Committee Member: Levent Degertekin; Committee Member: Robert Whetten; Committee Member: Satish Kumar; Committee Member: Zhong Lin Wan