MEMS Enabled Miniature Two-Photon Microscopy for Biomedical Imaging

The Deformable Mirror Demonstration Mission (DeMi) is a 6U CubeSat that will characterize the on-orbit performance of a Microelectromechanical Systems (MEMS) deformable mirror (DM) with both an image plane wavefront sensor and a Shack-Hartmann wavefront sensor (SHWFS). Coronagraphs on future space telescopes will require precise wavefront control to detect and characterize Earth-like exoplanets. High-actuator count MEMS deformable mirrors can provide wavefront control with low size, weight, and power. The DeMi payload will characterize the on-orbit performance of a 140 actuator MEMS Deformable Mirror (DM) with 5.5 μm maximum stroke, with a goal of measuring individual actuator wavefront displacement contributions to a precision of 12 nm. The payload will be able to measure low order aberrations to λ/10 accuracy and λ/50 precision, and will correct static and dynamic wavefront phase errors to less than 100 nm RMS. We present an overview of the payload design, the assembly, integration, and test process, and report on the development and validation of an optical diffraction model of the payload. Launch is planned for late 2019.

It is proposed in this paper to use phase only liquid crystal spatial light modulators to realize non-mechanical lateral and axial confocal microscopic laser scanning. With a phase only liquid crystal spatial light modulator used as a scanner to realize laser beam deflection, a confocal microscopic lateral beam scanning system is designed. A zoom illuminating lens is formed by incorporating a liquid crystal spatial light modulator along the confocal illumination light path, and thus the focus of the objective lens is axially shifted to realize the axial non-mechanical scanning. The theoretical analyses indicate that phase only liquid crystal spatial light modulators can be used to realize non-mechanical 3D confocal microscopic laser scanning.

Design and performance of an electrothermal MEMS microengine capable of bi-directional motion

We present a three-dimensional (3-D) endoscopic optical coherence tomography (OCT) system based on a dual axis microelectromechanical system (MEMS) mirror. The diameter of MEMS mirror was 1.2 mm and both axes were capable of scanning up to 20° (optical) at greater than 1 kHz with excellent linearity. The MEMS mirror was packaged in a machined acrylic endoscopic housing which provided mechanical protection and electrical interconnects as well as optical alignment of the MEMS device to a focusing GRIN lens. The endoscopic MEMS probe was integrated and tested with both a fiber-based time domain (TD) OCT system and Fourier domain (FD) OCT system. Combining the 2-axis lateral scanning of the MEMS device with an axial scan allowed 3-D volume images to be obtained at a rate of 3 frames/s for the TD system and 7 frames/s for the FD system. In the initial investigations, in vivo 3-D OCT images of a human finger as well as images of animal tissue such as healthy rabbit trachea, normal and cancerous regions of hamster cheek pouch tissue were obtained. These images allowed real-time diagnosis of diseased tissue and also clearly delineated important features and tissue structures.

Microelectromechanical systems (MEMS) resonators have been intensively investigated as an alternative for electronic filter components currently used in communication systems because of their small size and low operating voltages [1]. Electrothermal actuation, compared to other transduction techniques for electrical induction of mechanical vibrations, brings benefits in terms of simple fabrication, impedance matching and low actuation voltages. Electrothermally actuated resonators provide high resonant frequencies, high Q-factors and wide frequency tuning range [2, 3]. Recently, we have demonstrated the piezoelectric sensing of electrothermally actuated double-clamped beam MEMS resonators [3, 4]. Piezoelectric sensing technique, compared to the alternative electrostatic transduction, offers stronger electromechanical coupling, better impedance matching and simpler fabrication process. In addition, it allows active generation of electrical potential under applied mechanical stress, without need for external bias supply. In this work, we investigate on electrothermal actuator design solutions for optimizing frequency tuning range and Q-factor of the devices. Devices of two types were fabricated, with the only difference in the electrothermal actuator layout design, slab and u-shape layout, while other technological parameters and dimensions are the same (Fig. 1). Tested devices were taken from the same die and tested by performing two-port transmission frequency response measurements. The devices operate between 0.75 and 1.2MHz for tuning voltages of 1 to 7 V, and Q-factors up to ∼ 400 have been measured in atmospheric conditions. Experimental results have shown that the device actuated with u-shape electrode resonates at lower frequencies with higher Q-factor, and that wider frequency tuning has been obtained under the same actuating conditions. Design, fabrication and measurement setup details will be presented. Moreover, the influence of the electrothermal actuator design on the resonant behavior will be discussed.

Hexapod locomotive Micro-Electro Mechanical Systems (MEMS) microrobot with Pulse-type Hardware Neural Networks (P-HNN) locomotion controlling system is presented in this chapter. MEMS microrobot is less than 5 mm width, length, and height in size. MEMS microrobot is made from a silicon wafer fabricated by micro fabrication technology to realize the small size mechanical components. The mechanical components of MEMS microrobot consists of body frames, legs, link mechanisms, and small size actuators. In addition, MEMS microrobot has a biologically inspired locomotion controlling system, which is the small size electrical components realized by P-HNN. P-HNN generates the driving pulses for actuators of the MEMS microrobot using pulse waveform such as biological neural networks. The MEMS microrobot emulates the locomotion method and the neural networks of an insect with small size actuator, link mechanisms, and P-HNN. As a result, MEMS microrobot performs hexapod locomotion using the driving pulses generated by P-HNN.

A variable focus microscope without moving parts for axial focusing within the sample in two-photon microscopy can provide a faster, more robust, and cost-effective solution to 3D imaging at high resolution. A custom dynamic focusing objective was recently developed that incorporates a liquid lens within the optical design of a custom microscope. In this paper, we investigate the use of a liquid lens embedded in an aberration-corrected custom microscope for z-dimension scanning in 3D resolved two-photon microscopy. Results show that we can achieve imaging speed of 50 frames per sec for an arbitrary plane in 3D space, a leap forward in scan speed for two-photon microscopy.

In this thesis, two inversion-based feedforward control approaches have been developed and implemented to high-speed large-range atomic force microscope (AFM) imaging and nanofabrication, respectively. High-speed large-range AFM imaging and nanofabrication are needed in many areas and have attracted great interests. Challenges, however, must be overcome because in high-speed largerange AFM operation, large positioning error of the AFM probe relative to the sample can be generated due to the adverse effects of the hardware. The nonlinear hysteresis and the vibrational dynamics effects of the piezotube actuator must be addressed during the high-speed lateral scanning of the AFM imaging over large imaging size. In addition, precision positioning of the AFM probe in the vertical direction is even more challenging (than the lateral scanning) because the desired trajectory (i.e., the sample topography profile) is unknown in general, and the probe positioning is also effected by and sensitive to the probe-sample interaction. Finally, in AFM multi-axis nanofabrication, additional positioning errors are induced by the large cross-axis dynamics coupling effect. The large positioning errors generated during high-speed, large-range fabrication will lead to large defects in the fabricated structures or devices. In the thesis, firstly, to compensate for the adverse effects generated during high-speed large-range AFM imaging, an integrated approach is proposed, which combines the enhanced inversion-based iterative control technique (EIIC) for lateral x-y axis scanning with a dual-stage piezoactuator for the vertical z-axis positioning. The main contribution of this integrated approach is the combination of an advanced control algorithm with an advanced hardware platform. This approach is demonstrated in experiments by imaging a large-size (50 μm) calibration sample at high speed (50 Hz scan rate). Then secondly, to achieve high-speed large-range multi-axis AFM nanofabrication, a recently developed model-less inversion-based iterative control technique (MIIC) is utilized to overcome the adverse effects involved in high-speed large-range multi-axis AFM nanofabrication. By using this advanced control technique,

Liquid lens with adjustable focus for ultrasonic imaging

Novel DC-40 GHz MEMS series-shunt switch for high isolation and high power applications

In the last decade, there has been a tremendous development in the field of miniaturization of chemical and biochemical sensor devices. Microelectromechanical systems (MEMS) refer to microscopic devices that have a characteristic length of less than 1 mm but more than 100 nm and combine electrical and mechanical components. Nanoelectromechanical systems (NEMS) refer to nanoscopic devices that have a characteristic length of less than 100 nm and combine electrical and mechanical components. In mesoscale devices, if the functional com‐ ponents are on microor nanoscale, they may be referred to as MEMS or NEMS, respective‐ ly. These are referred to as an intelligent miniaturized system comprising sensing, processing, and/or actuating functions and combine electrical and mechanical components. The acronym MEMS originated in the USA. The term commonly used in Europe is micro system technology (MST) and in Japan, the term is micromachines. Another term generally used is micro/nanodevices.

Biological studies, drug discovery, and medical diagnostics benefit greatly from automated microscope platforms that can outperform even the most skilled human operators in certain tasks. However, the small field-of-view of a traditional microscope operating at high resolution poses a significant challenge in practice. The common approach of using a moving stage suffers from relatively low dynamic bandwidth and agitation to the specimen. This paper describes an automated microscope station based on the novel adaptive scanning optical microscope (ASOM), which combines a high-speed post-objective scanning mirror, a custom design scanner lens, and a microelectromechanical systems (MEMS) deformable mirror to achieve a greatly expanded field-of-view. After describing the layout and operating principle of the ASOM imaging subsystem, we present a system architecture for an automated microscope system suitable for the ASOM's unique wide field and high-speed imaging capabilities. We then describe a low-cost experimental prototype of the ASOM that demonstrates all critical optical characteristics of the instrument, including the calibration of the MEMS deformable mirror. Finally, we present initial biological (living nematode worms) imaging results obtained with the experimental apparatus and discuss the impact of the ASOM on biomedical imaging activities.

Electrothermal actuators are preferred in Microelectromechanical Systems (MEMS) devices when large force and stroke at comparatively lower driving voltages are desired. A generic electrothermal microactuator moves only in one direction that depends on its geometry and is independent of the polarity of voltage applied across its terminals, unlike electric motors and actuators. There are a few applications where electrothermal actuators are required to actuate in both directions. Towards fulfilling this need, a novel actuator that initially retracts and then moves forward upon application of a rising voltage is presented. It consists of an integrated pair of V-beam or inclined beam electro-thermal actuators, which actuate in opposite directions operating as an antagonistic pair. When the voltage is applied, the actuator moves backward for some time and then moves forward to attain a steady state position, hence the name “initially-retracting actuator”. Desired degree of antagonism can be achieved by varying the geometric parameters such as length, number of inclined beams, and offset for the integrated pair of V-beam actuators. In this paper, we describe the analytical model to design the actuator for desired behavior. Results pertaining to thermal imaging and dynamic response of the actuator are presented for experimental validation of the model.

It is now common practice to measure isodose curves with an ionization chamber driven by two Magslip motors which are themselves controlled by a similar pair of motors situated outside the X-ray room. Kemp (1946) and Mauchel and Johns (1954) have described apparatus by which the chamber is automatically made to trace out each isodose in turn, but where such facilities are not available it is still very convenient to be able to plot the curves directly rather than to construct them from a number of axial and lateral scans.

We have developed a novel confocal microscopy system, which can perform both axial and lateral scanning at an ultra high speed. A rotary mirror array (RMA) consists of 36 small mirrors deployed on the surface of a round plate with a small tilting angle and a discrete rotational symmetry. When the RMA rotates at a constant speed, the focal point is scanned inside a sample periodically and linearly. We have demonstrated a scanning rate of 2400 lines per second, which can be readily improved to more than 20000 lines per second. Our scheme can also be used in a fast scanning multi-photon microscope.