Tunable blazed gratings

In this paper, we report on the design, fabrication, and characterization of blazed gratings made tunable by electrostatic actuation. We combine KOH etching and deep-reactive ion etching (DRIE) to fabricate tunable blazed gratings (TBGs) on silicon-on-insulator wafers with optical-quality mirror surfaces on {111} crystalline planes. The actuators that are used to position the individual grating elements are designed to reduce rotation to levels acceptable for spectroscopic applications. We characterize the fabricated devices mechanically, verify the rotation-reduction design, and demonstrate the functionality of TBGs as tunable filters.     

Pull-In Analysis of Torsional Scanners Actuated by Electrostatic Vertical Combdrives

This paper presents pull-in analysis of torsional MEMS scanners actuated by electrostatic vertical combdrives with general comb gap arrangements and cross sections. The analysis is based on a 2-DOF actuator with a single voltage control. Three failure modes of the scanners are identified as in-plane twist, transversal motion, and out-of-plane twist. For each failure mode, analytical expressions of pull-in deflection are obtained by applying 2D analytical capacitance models to the derived pull-in equations. From these, the dominant pull-in mechanism is shown to be in-plane twist for scanners with high-aspect-ratio torsional springs. The analytical calculations for both symmetric and asymmetric capacitances are shown to be in good agreement with simulation results. The optimum scanner design is achieved when the pull-in deflection matches the capacitance maximum angle. The condition can be expressed in terms of the ratio of the comb thickness to the comb gap, which is smaller than the typical aspect ratio of deep reactive ion etching. The optimum tradeoff between the maximum deflection angle and the number of movable combs is achieved by adjusting the overlap of the movable and fixed combs and the distance of the comb sets from the axis of the rotation.     

Microoptical characterization of piezoelectric vibratory microinjections in drosophila embryos for genome-wide RNAi screen

In this paper, we study the effect of acoustic agitation on the penetration force for microinjections in Drosophila embryos for genome-wide RNA interference (RNAi) screens, using an integrated optical MEMS force encoder for in vivo characterization of the dynamic penetration forces. Two modes of operation are investigated. In the first mode of operation, the injector is brought into contact and acts on the embryo with a fixed force, and the vibration amplitude of the microinjector is increased till penetration occur. We observed a linear decrease in the penetration force of 1.6 /spl mu/N with every 0.1 m/s tip velocity increase. In the second mode of operation, the vibration amplitude is kept constant and the injector is pushed into the embryo until penetration. We simulate the optical force encoder eigenmodes and measure the injection force over the frequency range from 0 to 16 kHz with actuation voltages up to 150V. Among the eight encoder eigenmodes with resonant frequency up to 16 kHz, the longitudinal vibration along the injector is shown to dominate the force reduction at 14 kHz. Two other modes, both involving significant out-of-plane injector motion, reduce the penetration force by 52% around 3.1 kHz. The average penetration force is calculated based on injections into multiple embryos for each experimental condition. For each microinjection, the peak (or average) penetration force can be derived from the peak (or average) relative displacement of the two gratings upon penetration. The achieved minimum peak penetration force was 15.6 /spl mu/N (/spl sim/29.7% of the static penetration force), while the minimum average penetration force was 2.7 /spl mu/N (5.1% of the static penetration force).     

High fill-factor two-axis gimbaled tip-tilt-piston micromirror array actuated by self-Aligned vertical electrostatic combdrives

In this paper, we present a high fill-factor micromirror array actuated by self-aligned vertical electrostatic combdrives. To meet the requirements of applications in free-space communication and imaging, each micromirror has three degrees of freedom of motion: rotation around two axes in the mirror plane and linear translation perpendicular to the mirror plane. Our approach is to integrate the high fill-factor reflectors into the fabrication process of the actuators on the wafer-scale. Multilevel silicon-on-insulator (SOI) bonding is utilized to form the high optical quality reflectors and high aspect-ratio vertical combdrive actuators. The wiring for electrical access to the multielectrode per pixel array is fabricated on separate wafers by thin film processing, and flip-chip bonded to the reflector/actuator chip. This architecture overcomes the fill-factor limitation of top-side accessed electrical addressing of mirrors made on SOI. Our 360/spl mu/m pixel size mirror array achieves a 99% fill-factor with optically flat reflectors.     

Microoptical phased arrays for spatial and spectral switching

This article describes two optical devices based on linear arrays of micromirrors. The first is a phased array of micromirrors that can be rotated as well as translated vertically to maintain coherence across the array. We demonstrate experimentally that such micromirrors are capable of high-diffraction-efficiency phased-array scanning of laser beams. The second device is a Gires-Tournois (1969) interferometer with a micromirror array that provides tunable phase modulation for the multitude of partially reflected beams within the interferometer. We demonstrate experimentally that the MEMS-GT interferometer can operate as a tunable deinterleaver for dense wavelength-division multiplexed fiber optic communication.     

Observations on the electrical resistivity of steel fibre reinforced concrete

Steel fibre reinforced concrete (SFRC) is in many ways a well-known construction material, and its use has gradually increased over the last decades. The mechanical properties of SFRC are well described based on the theories of fracture mechanics. However, knowledge on other material properties, including the electrical resistivity, is sparse. Among others, the electrical resistivity of concrete has an effect on the corrosion process of possible embedded bar reinforcement and transfer of stray current. The present paper provides experimental results concerning the influence of the fibre volume fraction and the moisture content of the SFRC on its electrical resistivity. The electrical resistivity was measured by alternating current (AC) at 126 Hz. Moreover, an analytical model for the prediction of the electrical resistivity of SFRC is presented. The analytical model is capable of predicting the observed correlation between the fibre volume fraction and the electrical resistivity of the composite (the SFRC) for conductive fibres and moisture saturated concrete. This indicates that the steel fibres were conducting when measuring the electrical resistivity by AC at 126 Hz. For partly saturated concrete the model underestimated the influence of the addition of fibres. The results indicate that the addition of steel fibres reduce the electrical resistivity of concrete if the fibres are conductive. This represents a hypothetical case where all fibres are depassivated (corroding) which was created to obtain a conservative estimate on the influence of fibres on the electrical resistivity of concrete. It was observed that within typical ranges of variation the influence of the moisture content on the electrical resistivity was larger than the effect of addition of conductive steel fibres, but also that the relative impact on the electrical resistivity due to conductive steel fibres increased when the moisture content of the concrete was reduced.     

Continuous intrathecal infusion of baclofen. A new therapeutic method for spasticity

Intrathecal administration of baclofen is now generally accepted as a powerful treatment of spasticity caused by spinal lesions. 35 patients with severe spasticity, 29 of spinal origin and six of supraspinal origin resistant to conservative treatment, had a programmable pump (Synchromed, Medtronic) for continuous intrathecal baclofen infusion implanted. The patients were followed-up for an average of 29 months (0-68). The initial effect of the treatment was positive for all patients; spasms were less frequent, there was remission of pain caused by cramps, and in some cases improved ambulation. In five patients, however, the pump was later removed: in two patients the pump ceased to be effective, two patients became infected, and one experienced multiple catheter problems. Problems with the catheter was the most common complication experienced, and this was seen in nine patients. Three patients died of the underlying disease. The majority of patients became accommodated to intrathecal baclofen and it was necessary to administer increasingly larger doses to maintain the clinical effect. Long-term control of spinal spasticity by intrathecal baclofen can be achieved in most patients, but close follow-up is necessary for assessing efficacy and refilling the pump.     

Non-cemented acetabular cup in hip arthroplasty. Prosthesis survival and clinical results after 1-8 years

This is a retrospective clinical evaluation of 1028 primary hip arthroplasties performed with the non-cemented Harris-Galante I acetabulaer cup. Hospital records regarding all hips operated from July 1985 through March 1992 were evaluated after a median of 48 (12-93) months. Furthermore, questionnaires were sent out to all patients still alive in order to establish the actual function of the hips. At time of evaluation, 43 of the 1028 primary acetabular cups (4.2%) had been or were due to be revised. (20 because of one or more episodes of dislocation or displacement of the cup, 10 due to deep infection, eight following aseptic loosening of the cup, two because of implant failure and three due to other reasons). Four hundred and twenty-six hips were without pain, 274 had only mild or slight pain, whereas 84 experienced moderate or worse pain. We conclude, that the results after non-cemented hemispheric acetabular arthroplasties in this study are satisfying with a low rate of aseptic loosening.     

Linear microvibromotor for positioning optical components

We report an electrostatically driven linear microvibromotor fabricated using surface-micromachining technology. This device is developed for use in actuated micro-optical systems on silicon. Its submicron positioning resolution and a travel range of over 350 μm are excellent properties for this application. Vibromotor precision and velocity are characterized, and various drive methods are discussed. A simulation of the vibromotor dynamics is presented to explore optimization and control issues for this device     

Optical raster-scanning displays based on surface-micromachinedpolysilicon mirrors

We demonstrate high-resolution, raster-scanning display systems based on pairs of orthogonally scanning, surface-micromachined mirrors. The first mirror of the raster-scanning pair determines the line-scan rate of the display and is driven at its resonant frequency which is on the order of 4.7 kHz. The second mirror, driven at a frequency below its resonance and scanning orthogonally to the first mirror, determines the image refresh rate. Both mirrors have a maximum optical scanning angle of 15°. Single-chip and two-chip scanners are demonstrated. The resolution of the single-chip display, based on average pixel size, is 102×119 pixels. The curvature of the mirror surfaces are characterized and optically compensated to achieve this resolution