MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

MEMS devices for the control of trapped atomic particles

This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 μm and 400 μm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners.This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 μm and 400 μm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners

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

Dynamical control of one- and two-dimensional optical fibre scanning

This thesis investigates the dynamical control of one- and two-dimensional optical fibre scanning. One dimensional scanning is performed with a mechanically biaxial polarisation-preserving fibre mounted on a piezoelectric transducer with one of its principal mechanical axes aligned parallel to the excitation direction. The addition of an apertured reflector in front of the imaging lens allows a position sensing mechanism based on intermittent optical feedback to be integrated into the scanner. Over-scanning the lens generates timing pulses interlaced with back-scattered signals from the target. The timing information can be used for closed loop control of the phase and amplitude of vibration. Suitable control algorithms are developed and their convergence and stability is studied. This thesis also investigates the construction of fibres with enhanced mechanically asymmetry and their dynamical properties during two-dimensional imaging based on Lissajous scan patterns. Dip-coating is proposed as a method of forming two-cored waveguide cantilevers from two separate, parallel fibres that are encapsulated in a plastic coating. The frequency ratio between the two orthogonal bending mode resonances can be controlled with number of coatings. An exact image reconstruction algorithm based on Lissajous scanning is proposed. Latency, transient response and steady-state phase errors are all shown to cause dramatic deterioration of the reconstructed image. Solutions are provided by ensuring the correct starting time for data acquisition and introducing a drive phase correction to one of the axes. Two methods of resolution enhancement are demonstrated. The first is based on combining data sets obtained during separate scans carried out with deliberately applied phase offsets. The second operates by combining data sets from separate imaging operations carried out using the two different fibre cores. Finally, this thesis demonstrates potential applications in optogenetics by combining the two operations of imaging and writing, using different light sources that may also have different wavelengths.Open Acces

MEMS based catheter for endoscopic optical coherence tomography

Ph.DDOCTOR OF PHILOSOPH

Low Voltage Electrostatic Actuation and Displacement Measurement through Resonant Drive Circuit

An electrostatic actuator driven by conventional voltage control and charge control requires high actuation voltage and suffers from the pull-in phenomenon that limits its operation range, much less than its entire gap. To provide effective solutions to these problems, we present complete analytical and numerical models of various electrostatic actuators coupled with resonant drive circuits that are able to drive electrostatic actuators at much lower input voltage than that of conventional actuation methods and to extend their operation range beyond their conventional pull-in points in the presence of high parasitic capacitance. Moreover, in order to validate the analytical and numerical models of various electrostatic actuators coupled with the resonant drive circuits, we perform the experiment on the microplate and the micromirror coupled with the resonant drive circuit. For instance, using a high voltage amplifier, we manage to rotate the micromirror with sidewall electrodes by 6 ° at 180 V. However, using the resonant drive circuit, we are able to rotate the same micromirror by 6 ° at much lower input voltage, 8.5 V. In addition, the presented work also facilitates the stability analysis of electrostatic actuators coupled with the resonant drive circuits and provides how the effect of the parasitic capacitance can be minimized. For example, the resonant drive circuit placed within a positive feedback loop of a variable gain amplifier is able to extend the operation range much further even in the presence of very high parasitic capacitance. The resonant drive circuit with the proposed feedback controllers is also able to minimize the detrimental effects of the parasitic capacitance and to displace a parallel-plate actuator over its entire gap without the saddle-node bifurcation. Finally, we present a new displacement measurement method of electrostatic actuators coupled with the resonant drive circuits by sensing the phase delay of an actuation voltage with respect to an input voltage. This new measurement method allows us to easily implement feedback control into existent systems employing an electrostatic actuator without any modification or alteration to the electrostatic actuator itself. Hence, this research work presents the feasibility of electrostatic actuators coupled with the resonant drive circuit in various industrial and medical applications, in which the advantages of miniaturization, low supply voltage, and low power consumption are greatly appreciated

Design and simulation of a direct and indirect drive electrostatically actuated resonant micro-mirrors for scanner applications

Laser scanners have been an integral part of MEMS research for more than three decades. The demand for electrostatically actuated scanning micro-mirrors have been growing in the last decade, mainly for pico-projection and medical applications. These type of actuation wins over others, because it provides long-term stability, size advantages and fabrication schemes which are easier to render CMOS compatibility. The growing field in softwares capable of design and simulate MEMS devices, have been a crucial help for engineers, which are limited to a few of them and still cost huge amount of time. MEMS+® is a software platform that provides simulation results up to 100 times faster than conventional finite element analysis tools and allows to integrate designs in MathWorks®. In this work two types of electrostatically actuated scanning micro-mirrors were designed and simulated using both MEMS+® and MathWorks®, one is a direct drive micro-mirror and the other an indirect drive micro-mirror. In the first the torque is imparted directly from the actuation mechanism to the frame containing the mirror, and in the second the resonance mode amplifies a small motion in a larger mass to a considerably larger motion in the smaller mirror. Regarding the direct-drive micro-mirror, the presented work mainly shows the reliability of MEMS+® compared to other softwares. The indirect drive one, is a state-of-art solution for high frequency electrostatically actuated micro-mirrors, and all the simulations taken on it were aimed to verify it´s behaviour, and then proceed with the microfabrication step. The target microfabrication technology is SOIMUMPs

MEMS micromirrors for imaging applications

Strathclyde theses - ask staff. Thesis no. : T13478Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz.Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz

Polymer NdFeB Hard Magnetic Scanner for Biomedical Scanning Applications

Micromirror scanners are the most significant of the micro-optical actuator elements with applications in portable digital displays, automotive head-up displays, barcode scanners, optical switches and scanning optical devices in the health care arena for external scanning diagnostics and in vivo scanning diagnostics. Recent development in microscanning technology has seen a shift from conventional electrostatic actuation to electromagnetic actuation mechanisms with major advantages in the ability to produce large scan angles with low voltages, remote actuation, the absence of the pull-in failure mode and the acceptable electrical safety compared to their electrostatic counterparts. Although attempts have been made to employ silicon substrate based MEMS deposition techniques for magnetic materials, the quality and performance of the magnets are poor compared to commercial magnets. In this project, we have developed novel low-cost single and dual-axis polymer hard magnetic micromirror scanners with large scan angles and low power consumption by employing the hybrid fabrication technique of squeegee coating to combine the flexibility of polydimethylsiloxane (PDMS) and the superior magnetic performance of fine particle isotropic NdFeB micropowders. PCB coils produce the Lorentz force required to actuate the mirror for scanning applications. The problem of high surface roughness, low radius of curvature and the magnetic field interaction between the gimbal frame and the mirror have been solved by a part PDMS-part composite fabrication process. Optimum magnetic, electrical and time dependent parameters have been characterized for the high performance operating conditions of the micromirror scanner. The experimental results have been demonstrated to verify the large scan angle actuation of the micromirror scanners at low power consumption

Thin-Film PZT Scanning Micro-actuators for Vertical Cross-sectional Imaging in Endomicroscopy

The advancement of optics and the development of microelectromechanical systems (MEMS) based scanners has enabled powerful optical imaging techniques that can perform optical sectioning with high resolution and contrast, large field of view, and long working distance to be realized in endoscope-compatible form factors. Optical endomicroscopes based on these imaging techniques can be used to obtain in vivo vertical cross-sectional images of dysplastic tissues in the hollow organs before they progress to mucosal diseases such as colorectal cancer. However, existing endomicroscopic systems that use imaging modalities compatible with the use of fluorescent biomarkers are not capable of deep vertical sectioning in real time. This work proposes a unique MEMS-based scanning mechanism to be incorporated into endoscopic microscopes for real-time in vivo deep into-tissue scanning for early cancer detection. For this task, a class of novel multi-axis micro-scanners based on thin-film lead-zirconate-titanate (PZT) has been developed. Leveraging the large piezoelectric strain coefficient of PZT, the prototypes have demonstrated more than 400 μm of out-of-plane displacement with bandwidths on the order of 100-200 Hz in only a 3.2 mm-by-3.2 mm footprint, which meets the requirements for this application. The scanners have a central rectangular-shaped reflector, whose corners are supported by four symmetric PZT bending legs that generate vertical translation. This design gives the reflector a three-axis motion. The challenges to fabricate high performance piezoelectric actuators are discussed with device failure mechanisms observed during the fabrication of the 1st generation scanners. Improved fabrication steps are presented that solve the issues with the 1st generation devices and enhance the robustness of the scanners for instrument integration. Remaining non-ideal fabrication outcomes cause MEMS devices to produce unwanted motions, which can degrade imaging quality. To overcome this problem, a method to drive MEMS actuators having multiple vibration modes with close frequencies to produce a desired motion pattern with a single input is presented, and was used to generate a pure vertical motion for imaging. Two-photon based vertical cross-sectional images of mouse colon was obtained in real time for the first time using a thin-film piezoelectric microscanner. To understand the effects of fabrication non-idealities on the device behavior and produce more robust scanner performance, analytical models that describes large vertical and rotational motions including multi-axis coupling were developed. A static model that was initially developed for design optimization was calibrated, along with a transient model, using experimental data to incorporate the effects of dimensional variations and residual stress. This models can be used with future integrated sensors and feedback controllers for more precise and robust motion of the scanner. This calibration technique can be useful in developing analytic models for MEMS devices subject to fabrication uncertainty. In addition, nonlinear dynamic behavior due to large vertical stroke in the presence of fabrication non-idealities is captured by linearizing an expanded dynamic model about different static positions obtained by numerically solving the expanded nonlinear model.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137124/1/jongs_1.pd