Paul C.-P. Chao

Imaging brain hemodynamic changes during rat forepaw electrical stimulation using functional photoacoustic microscopy

The present study reported the development of a novel functional photoacoustic microscopy (fPAM) system for investigating hemodynamic changes in rat cortical vessels associated with electrical forepaw stimulation. Imaging of blood optical absorption by fPAM at multiple appropriately-selected and distinct wavelengths can be used to probe changes in total hemoglobin concentration (HbT, i.e., cerebral blood volume [CBV]) and hemoglobin oxygen saturation (SO(2)). Changes in CBV were measured by images acquired at a wavelength of 570nm (lambda(570)), an isosbestic point of the molar extinction spectra of oxy- and deoxy-hemoglobin, whereas SO(2) changes were sensed by pixel-wise normalization of images acquired at lambda(560) or lambda(600) to those at lambda(570). We demonstrated the capacity of the fPAM system to image and quantify significant contralateral changes in both SO(2) and CBV driven by electrical forepaw stimulation. The fPAM system complements existing imaging techniques, with the potential to serve as a favorable tool for explicitly studying brain hemodynamics in animal models.

A novel method to predict the pull-in voltage in a closed form for micro-plates actuated by a distributed electrostatic force

This study is devoted to finding the precise pull-in voltage/position of a micro-device formed by two parallel charged plates. Pull-in is a phenomenon where the electrostatic force induced by the applied voltage across two plates of the device exceeds the elastic, restoring force exerted by the deformed plates, leading to a contact between the two plates. To offer a precise prediction of the pull-in, a dynamic model in the form of a partial differential equation (PDE) is established based on the equilibrium among plate flexibility, residual stress and distributed electrostatic forces. The Galerkin method is employed to decompose the established PDE into discrete modal equations. By considering lower order modes and solving them, one arrives at a prediction of plate deflection in terms of the applied bias voltage. Approximating the solved deflection by a fifth-order series and full-order numerical integration, the pull-in position and voltage are successfully approximated. The pull-in position in terms of center deflection of the deformed plate is found to be 48% of the air gap between the plates, which presents a better estimation than the commonly used one-third of the gap derived by all past studies based on a less realistic one-dimensional lump model. A closed form of the pull-in voltage is derived to offer design guidelines for the device prior to production. The aforementioned theoretical findings are finally validated by finite element and experimental studies on a MEMS device of parallel charged micro-plates designed and fabricated in the laboratory.

Optimal Design of Magnetically Actuated Optical Image Stabilizer Mechanism for Cameras in Mobile Phones via Genetic Algorithm

This paper proposes an optimal electromagnetic actuator for the application of optical image stabilization in cameras of mobile phones. The image stabilization composes of vertical and horizontal moving platforms to compensate the shaking from hands. The platforms are actuated by the magnetic force from voice coil motors (VCMs). For the application of mobile devices, geometry size of the mechanism is extremely limited. However, the larger the size of yoke that covers the magnetic field is, the better uniformity it will perform. This study, therefore, is dedicated to conduct an optimal design with the coupled relationship between magnetic field and mechanical geometry. The magnetic field is converted to equivalent circuit in terms of mechanism geometry, and verified by ANSYS. The genetic algorithm (GA) is then applied for deriving optimal values of geometry dimensions of the system within satisfactory uniform magnetic field

DC dynamic pull-in predictions for a generalized clamped–clamped micro-beam based on a continuous model and bifurcation analysis

This study is devoted to providing precise predictions of the dc dynamic pull-in voltages of a clamped?clamped micro-beam based on a continuous model. A pull-in phenomenon occurs when the electrostatic force on the micro-beam exceeds the elastic restoring force exerted by beam deformation, leading to contact between the actuated beam and bottom electrode. DC dynamic pull-in means that an instantaneous application of the voltage (a step function such as voltage) is applied. To derive the pull-in voltage, a dynamic model in partial differential equations is established based on the equilibrium among beam flexibility, inertia, residual stress, squeeze film, distributed electrostatic forces and its electrical field fringing effects. The method of Galerkin decomposition is then employed to convert the established system equations into reduced discrete modal equations. Considering lower-order modes and approximating the beam deflection by a different order series, bifurcation based on phase portraits is conducted to derive static and dynamic pull-in voltages. It is found that the static pull-in phenomenon follows dynamic instabilities, and the dc dynamic pull-in voltage is around 91?92% of the static counterpart. However, the derived dynamic pull-in voltage is found to be dependent on the varied beam parameters, different from a fixed predicted value derived in past works, where only lumped models are assumed. Furthermore, accurate closed-form predictions are provided for non-narrow beams. The predictions are finally validated by finite element analysis and available experimental data.

Energy Harvesting Electronics for Vibratory Devices in Self-Powered Sensors

Recent advances in energy harvesting have been intensified due to urgent needs of portable, wireless electronics with extensive life span. The idea of energy harvesting is applicable to sensors that are placed and operated on some entities for a long time, or embedded into structures or human bodies, in which it is troublesome or detrimental to replace the sensor module batteries. Such sensors are commonly called “self-powered sensors.” The energy harvester devices are capable of capturing environmental energy and supplanting the battery in a standalone module, or working along with the battery to extend substantially its life. Vibration is considered one of the most high power and efficient among other ambient energy sources, such as solar energy and temperature difference. Piezoelectric and electromagnetic devices are mostly used to convert vibration to ac electric power. For vibratory harvesting, a delicately designed power conditioning circuit is required to store as much as possible of the device-output power into a battery. The design for this power conditioning needs to be consistent with the electric characteristics of the device and battery to achieve maximum power transfer and efficiency. This study offers an overview on various power conditioning electronic circuits designed for vibratory harvester devices and their applications to self-powered sensors. Comparative comments are provided in terms of circuit topology differences, conversion efficiencies and applicability to a sensor module.

Non-planar dynamic modeling for the optical disk drive spindles equipped with an automatic balancer

Abstract This study presents non-planar dynamic modeling and analysis of the spindle–disk system equipped with an Automatic Ball-type Balancer (ABB) system for optical disk drives. Recent studies have shown that the ABB system owns the capability for reducing radial vibrations of the rotating spindle–disk assembly by counter-acting the inherent imbalance. To extend the analysis to be practical, non-planar dynamic modeling and analysis are conducted in this study to re-affirm the pre-claimed capability of the ABB system. Euler angles are first utilized to formulate potential and kinetic energies. Lagrange’s equations are next applied to derive governing equations of motion. Numerical simulations of non-planar motions are finally carried out to calculate two performance indices, the level of residual radial vibration and the tilting angle of the rotating assembly. It is obtained that the levels of residual vibration as compared to those without the ABB, are significantly reduced. On the other hand, the tilting angle of the rotating assembly can be kept small if the ABB is installed below the inherent imbalance of the spindle–disk system.

A new low-voltage-driven GRIN liquid crystal lens with multiple ring electrodes in unequal widths

This work is dedicated to design a novel liquid crystal (LC) lens device with multiple ring electrodes in unequal widths, in order to offer tunability on focusing quality and to lower the level of applied voltage. The number and widths of the multiple ring electrodes are pre-designed and optimized to offer the on-line tunability on individual electrode voltages to render a better refraction index distribution for focusing, as compared to the past hole-type LC lenses. The resulted refractive index distribution is expected to offer similar focusing effects based on the theory of the gradient refraction index (GRIN) lens. The transparent electrodes of this new LC lens are placed at the inner surface of the LC cell to minimize the driving voltages, in results, less than 10 V, for the same level of focusing power and an easy practical operation. A new fabrication process in the wafer level to bury bus lines is developed for generating smooth electrical fields over the lens aperture. In addition, a dielectric layer is coated between electrodes and the LC layer.

11.1: An Auto‐Stereoscopic 3D Display Using Tunable Liquid Crystal Lens Array That Mimics Effects of GRIN Lenticular Lens Array

A tunable liquid crystal lenticular lens array is proposed to compose an auto-stereoscopic 3D display. The focusing can be achieved based on non-uniform phase retardation across the width of the LC lenticular lens, mimicking the effects of gradient index (GRIN) lens. The viewing distance and zones of this display can be adjusted in an on-line fashion to track the viewer position relative to the display. The proposed scheme can present the lenticular lens and the LC GRIN lens simultaneously, so that the simulation results can express the low value of crosstalk of 9% by the lenticular lens array and the LC GRIN lens array.

A Miniaturized Electromagnetic Generator With Planar Coils and Its Energy Harvest Circuit

This study presents design, analysis and experiment of a miniaturized rotary generator in size of 10 times 10 times 2 mm3 and its compact energy harvest circuit chip. The designed generator consists of patterned planar copper coils and a multipolar hard magnet ring made of NdFeB. To perform modeling, a harmonic-like magnetic field model along the circumferential path of each magnetic pole is assumed with the assistance from measured peak magnetic flux densities. This is followed by the application of Faradays law to predict generated electromotive forces (EMFs) in terms of the relative rotational speed between the magnet ring and coils. The genetic algorithm (GA) is next applied to optimize the critical dimensions of the miniaturized generator. The theoretical model of this power microgenerator is evaluated and compared with experimental results, and it is found that the analytical simulation shows a good agreement with the experimental results. The optimized generator offers 4.5 V and 7.23 mW in root mean square (rms) at 10 000 r/min. With microgenerator successfully fabricated, a novel energy harvest circuit employing Dickson charge pump is designed and fabricated via the 0.35-mum process offered by National Chip Implementation Center (CIC) of Taiwan. This charge pump circuit owns the merit of almost-zero thresholds of employed metal-oxide-semiconductor (MOS) transistors, enabling the conversion of low-power alternating current (ac) signals by the microgenerator to direct current (dc) ones.

Achieving high focusing power for a large-aperture liquid crystal lens with novel hole-and-ring electrodes

Aiming to equip commercial camera modules, such as the optical imaging systems with a CMOS sensor module in 3 Mega pixels, an ultra thin liquid crystal lens with designed hole-and-ring electrodes is proposed in this study to achieve high focusing power. The LC lens with proposed electrodes improves the central intensity of electric field which leads to better focusing quality. The overall thickness of the LC lens can be as thin as 1.2 mm and the shortest focal length of the 4 mm-aperture lens occurs at 20 cm under an applied voltage of 30 V at 1 KHz. The inner ring electrode requires only 40% of applied voltage of the external hole electrode. The applied voltages for this internal ring and external hole electrodes can simply be realized by a pre-designed parallel resistance pair and a single voltage source. Experiments are conducted for validation and it shows that the designed LC lens owns good image clearness and contrast at the focal plane. The proposed design reduces the thickness of LC lens and is capable of achieving relative higher focusing power than past studies with lower applied voltage.