A MEMS Photosynthetic Electrochemical Cell Powered by Subcellular Plant Photosystems

A microelectromechanical systems (MEMS) photosynthetic electrochemical cell$(mu PEC)$was demonstrated that harnesses the subcellular thylakoid photosystems isolated from spinach cells to convert light energy into electricity. Subject to light intensity of 2000$mu mol$photons/$ m ^2$/s, it generated an open circuit voltage (OCV) of 470 mV and a current density of 1.1$mu A/cm^2$at 5.2$mu V$. In the dark, the$mu PEC$continued to yield power for a few minutes using reduced equivalents generated during illumination, generating 330 mV OCV and 0.1$mu A/cm^2$with a 1$ kOmega$load. The output level is comparable to other MEMS biological fuel cells previously reported. The biosolar cell was bulk-micromachined from silicon and Pyrex substrates and assembled like a fuel cell in an anode-PEM-cathode configuration. This biosolar cell could have potential to serve as a power source for micro-scale devices like remote sensors.1359     

Design and pressure analysis for bulk-micromachined electrothermal hydraulic microactuators using a PCM

Paraffin wax exhibits a volumetric expansion of ∼15%, at around its melting point. By exploiting this phenomenon, high performance bulk-machined electrothermal hydraulic microactuators have been demonstrated. The microactuators have been integrated into microfluidic valves, microgrippers and micropipettes. The paraffin wax is confined within a bulk-micromachined silicon container. This container is sealed using an elastic diaphragm of PDMS, while it is heated via gold microheaters located on an underlying glass substrate. All the layers used to make up the containers are bonded together using a unique combination of overglaze paste and PDMS. The hydraulic pressure of expanding paraffin wax was determined using the deflection theory of a circular plate. For the first time, the hydraulic pressure of expanding paraffin wax was calculated using the theory of large deflections for a circular plate and measured data from the type-A microgripper. This theory has been exploited for the deflection analysis of micromachined thin elastic diaphragms. In order to calculate the hydraulic pressure, the theory of large deflections of a circular plate is calculated using the measured actuation height, the PDMS diaphragm dimension of the microgripper (type-A) and mechanical properties of the PDMS. The hydraulic pressure was calculated to be approximately 0.12 MPa. All the devices were successfully demonstrated and operated at either 10 or 15 V.     

Thin-Film Piezoelectric Unimorph Actuator-Based Deformable Mirror With a Transferred Silicon Membrane

This paper describes a proof-of-concept deformable mirror (DM) technology, with a continuous single-crystal silicon membrane reflecting surface, based on$ PbZr _0.52 Ti_0.48 O _3$(PZT) unimorph membrane microactuators. A potential application for a terrestrial planet finder adaptive er is also discussed. The DM comprises a continuous, large-aperture, silicon membrane “transferred” onto a 20$,times,$20 piezoelectric unimorph actuator array. The actuator array was prepared on an electroded silicon substrate using chemical-solution-deposited 2-$mu m$-thick PZT films working in a$d _31$mode. The substrate was subsequently bulk-micromachined to create membrane structures with residual silicon acting as the passive layer in the actuator structure. A mathematical model simulated the membrane microactuator performance and aided in the optimization of membrane thicknesses and electrode geometries. Excellent agreement was obtained between the model and the experimental results. The resulting piezoelectric unimorph actuators with patterned PZT films produced large strokes at low voltages. A PZT unimorph actuator, 2.5 mm in diameter with optimized PZT/silicon thickness and design showed a deflection of 5.7$~mu m$at 20 V. A DM structure with a 20-$mu m$-thick silicon membrane mirror (50 mm$times,$50 mm area) supported by 400 PZT unimorph actuators was successfully fabricated and optically characterized. The measured maximum mirror deflection at 30 V was approximately 1$~mu m$. An assembled DM showed an operating frequency bandwidth of 30 kHz and an influence function of approximately 30%. 1738     

A High-Performance MEMS Capacitive Strain Sensing System

This paper describes a high-performance strain sensing microsystem. The system consists of four parallel differential MEMS capacitive strain sensors with a nominal capacitance value of 440 fF, converting an input strain to a capacitance change with a sensitivity of 265 aF per microstrain$(mu varepsilon )$, and low-noise integrated sensing electronics, which employ a differential continuous-time synchronous detection architecture converting the capacitive signal to an output voltage for further signal processing. Based on system noise characterization, the prototype design shows a capability of measuring a strain resolution of 0.9$ nvarepsilon/sqrt Hz$, while demonstrating a maximum dc input stain range of 1000$mu varepsilon$. The overall system consumes 1.5 mA dc current from a 3-V supply.1392     

Radioisotope Thin-Film Fueled Microfabricated Reciprocating Electromechanical Power Generator

A radioisotope power generator with a potential lifetime of decades is demonstrated by employing a 100.3-year half-lifetime $^{63}hbox{Ni}$ radioisotope thin-film source to electrostatically actuate and cause reciprocation in a microfabricated piezoelectric unimorph cantilever. The radioisotope direct-charged electrostatic actuation of the piezoelectric unimorph cantilever results in the conversion of radiation energy into mechanical energy stored in the strained unimorph cantilever. The gradual accumulation of the actuation charges leads to the pull-in of the unimorph cantilever into the radioisotope thin-film, and the resulting discharge leads to vibrations in the unimorph cantilever. During the vibrations, the stored mechanical energy is converted into electrical energy by the piezoelectric thin-film. The generator was realized by using both microfabricated lead zirconate titanate oxide–silicon (PZT–Si) and aluminum nitride–silicon (AlN–Si) unimorph cantilevers. The radioisotope direct-charged electrostatic actuation of the AlN–Si unimorph cantilevers by a 2.9-mCi $^{63}hbox{Ni}$ thin-film radiating 0.3 $muhbox{W}$ led to charge–discharge–vibrate cycles that resulted in the generation of 0.25% duty cycle 12.95- $muhbox{W}$ power pulses (across an optimal load impedance of 521 $hbox{k}Omega$) at an overall energy conversion efficiency of 3.97%. These electrical power pulses can potentially be useful for periodically sampling sensor microsystems. $hfill$[2008-0009]      

Electrothermally Activated SU-8 Microgripper for Single Cell Manipulation in Solution

The development of a SU-8-based microgripper that can operate in physiological ionic solutions is presented. The electrothermally activated polymer gripper consists of two “hot-and-cold-arm” actuators that are fabricated in a two-mask surface micromachining process. The high thermal expansion coefficient of SU-8 (52$ ppm/^circ C$) compared to silicon and metals, allows the actuation of the microgripper with small average temperature elevations (10 – 32$^circ C$) at low voltages (1–2 V). The polymer microgripper can be used for the manipulation of single cells and other biological species in solution with minimal undesired interactions.hfillhbox[1330]     

Design, Simulation, Fabrication, and Characterization of a Digital Variable Optical Attenuator

In this paper, we present the design, simulation, fabrication, and some measurement and characterization of a novel 16-bit digital variable optical attenuator (VOA) that attenuates by switching individual mirror of an array as an attempt to achieve input voltage variation independence and output linearization. The design was aided by a simulation package that features coupled electrostatic and mechanical solver. The mirror array spans an area of 1500$,times,$1500$mu m^2$and contains 16 equal-length rectangular micromirrors. Each mirror is suspended by two torsion beams. Experiments on beam design and width variations are conducted. Assuming Gaussian distribution, the mirror widths computed by an iteration algorithm vary from about 40 to 250$mu m$. Based on silicon-on-insulator (SOI) technology, two fabrication schemes to open the backside optical entrance were investigated. A hydrofluoric (HF) acid vapor-phase-etching (VPE) setup built to release the microstructure anhydrously is the key to achieve high yield especially for fragile components. Surface flatness, resonance frequencies, and tilt angles of selected mirrors were characterized. Quartz chips patterned with aluminum electrodes and 10$mu m$-high SU8 spacer columns were fabricated and assembled to corresponding device chips. Optical performance adversely affected by mirror bending is believed to originate from the intrinsic stress of the SOI wafer. 1271     

${cal H}_{infty}$ Output-Feedback Control Based on an FIR-Type Quasi-Deadbeat Observer

This technical note proposes a novel output-feedback control law based on a finite impulse response (FIR)-type quasi-deadbeat observer for linear systems. For nominal systems without disturbances, this technical note first establishes the deadbeat condition that reduces the state estimation error to zero within a finite time and verifies that all the hidden poles of the closed-loop system under the quasi-deadbeat observer-based control law are zero and that the separation principle holds true. In order to enhance the disturbance rejection capability for systems with random-work disturbances, on the structural merit of the FIR-type observer, we have proposed the conditions for an ${cal H}_{infty}$ quasi-deadbeat observer and an ${cal H}_{infty}$ stabilizer based on the predetermined observer, respectively.      

Micromachined Acoustic Resonant Mass Sensor

This paper describes a highly sensitive, film bulk acoustic resonator (FBAR) mass sensor (built on a micromachined silicon-nitride diaphragm with a piezoelectric thin film and Al electrodes) that can operate in vapor and liquid. The sensitivity of the device to mass change on its surface has been investigated by having various thicknesses of silicon-nitride support layer and also of Al layer. The sensor is measured to have a mass sensitivity of 726 cm$^2$/g, which is about 50 times that of a typical quartz crystal microbalance (QCM). In vapor, the sensor (operating at around 1 GHz and having a relatively high quality (Q) factor of 200–300) shows a minimum detectable frequency shift of about 400 Hz, which corresponds to a mass change of$10^-9$g/cm$^2$on the sensor surface, comparable with that detectable by a QCM. In liquid, though the Q usually drops more than an order of magnitude, we obtain a Q of 40 at 2 GHz by using a second harmonic resonance of the resonator. And with the Q, a minimum 5 ppm resonant frequency shift can be detected, which corresponds to$10^- 8$g/cm$^2$change on the sensor surface.hfillhbox[1374]     

Large-Deflection Spiral-Shaped Micromirror Actuator

We present a new two-axis spiral-shaped micromirror manipulator developed for free-space optical switching. The actuator is an electrostatic actuator, which is composed of two different parts that are fabricated using conventional surface-micromachining processes and are then assembled. Instead of conventional monolithic self-assembling design approaches, these two parts are fabricated on two different chips and assembled using a spatial–mechanical approach. The design utilizes the increased flexibility of the spiral-shaped electrode and the zipping-effect technique in order to increase the maximum rotation angle. The footprint of the assembled device is $600 muhbox{m} times 600 muhbox{m}$, and the height of the micropyramid is 200 $muhbox{m}$. The switch is simulated using an energy method and a coupled electromechanical model. Its performance is measured statically using a reflection measurement approach. A continuous rotational actuation of 17$^{ circ}$ has been achieved with an actuation voltage of 235 V.$ hfill$[2008-0319]      

FOS: A Funnel-Based Approach for Optimal Online Traffic Smoothing of Live Video

Traffic smoothing is an efficient means to reduce the bandwidth requirement for transmitting a variable-bit-rate video stream. Several traffic-smoothing algorithms have been presented to offline compute the transmission schedule for a prerecorded video. For live video applications, Sen present a sliding-window algorithm, referred to as$SLWIN(k)$, to online compute the transmission schedule on the fly.$SLWIN(k)$looks ahead$W$video frames to compute the transmission schedule for the next$k$frametimes, where$kleq w$. Note that$W$is upper bounded by the initial delay of the transmission. The time complexity of$SLWIN(k)$is$O(Wast N/k)$for an$N$frame live video. In this paper, we present an$O(N)$online traffic-smoothing algorithm and two variants, denoted as$FOS$,$FOS1$and$FOS2$, respectively. Note that$O(N)$is a trivial lower bound of the time complexity of the traffic-smoothing problem. Thus, the proposed algorithm is optimal. We compare the performance of our algorithms with$SLWIN(k)$based on several benchmark video clips. Experiment results show that$FOS2$, which adopts the aggressive workahead heuristic, further reduces the bandwidth requirement and better utilizes the client buffer for real-time interactive applications in which the initial delays are small.     

On the NP-Hardness of Checking Matrix Polytope Stability and Continuous-Time Switching Stability

Motivated by questions in robust control and switched linear dynamical systems, we consider the problem checking whether all convex combinations of $k$ matrices in $R^{n times n}$ are stable. In particular, we are interested whether there exist algorithms which can solve this problem in time polynomial in $n$ and $k$. We show that if $k= lceil n^{d} rceil $ for any fixed real $d>0$, then the problem is NP-hard, meaning that no polynomial-time algorithm in $n$ exists provided that $P ne NP$, a widely believed conjecture in computer science. On the other hand, when $k$ is a constant independent of $n$ , then it is known that the problem may be solved in polynomial time in $n$. Using these results and the method of measurable switching rules, we prove our main statement: verifying the absolute asymptotic stability of a continuous-time switched linear system with more than $n^{d}$ matrices $A_{i} in R^{n times n}$ satisfying $0 succeq A_{i} + A_{i}^{T}$ is NP-hard.      

$ {cal L}_{2}$ Gain of Periodic Linear Switched Systems: Fast Switching Behavior

We investigate the $ {cal L}_{2}$ gain of periodic linear switched systems under fast switching. For systems that possess a suitable notion of a time-average system, we characterize the relationship between the ${cal L}_{2}$ gain of the switched system and the ${cal L}_{2}$ gain of its induced time-average system when the switching rate is sufficiently fast. We show that the switched system ${cal L}_{2}$ gain is in general different from the average system ${cal L}_{2}$ gain if the input or output coefficient matrix switches. If only the state coefficient matrix switches, the input-output energy gain for a fixed ${cal L}_{2}$ input signal is bounded by the ${cal L}_{2}$ gain of the average system as the switching rate grows large. Additionally, for a fixed ${cal L}_{2}$ input, the maximum pointwise in time difference between the switched and average system outputs approaches zero as the switching rate grows.      

A Latchable Phase-Change Microvalve With Integrated Heaters

This paper presents a latchable phase-change microvalve with integrated microheaters, which is suitable for lab-on-a-chip systems where minimal energy consumption is desired. The microvalve exploits low-melting-point paraffin wax, whose solid–liquid phase changes allow switching of fluid flow through deformable microchannel ceiling. Switching is initiated by melting of paraffin through an integrated microheater, with an additional pneumatic pressure used for the open-to-close switching. The valve consumes energy only during initiation of valve switching. When paraffin solidifies, the switched state is maintained passively. The microvalve was fabricated from polydimethylsiloxane through multilayer soft lithography techniques. Experiments show that the valve can switch flow within 4–8 s due to the small thermal mass and localized melting of paraffin wax; when closed, the valve can passively withstand an inlet pressure over 50 kPa without leakage. Time response of the valve can be further improved with improved heater and wax chamber designs, while the latching ability can be improved by optimizing the wax chamber/membrane design. Compared to existing latchable phase-change valves, the microvalve has no risk of cross-contamination. In addition, the improved sealing offered by the compliant membrane makes the valve robust and flexible in operation, allowing large ranges of initiation pressure from various actuation schemes. $hfill$[2008-0303]      

Microassembly Fabrication of Tissue Engineering Scaffolds With Customized Design

This paper presents a novel technique to fabricate scaffold/cell constructs for tissue engineering by robotic assembly of microscopic building blocks (of volume 0.5$,times,$0.5$,times,$0.2 ${hbox{mm}}^{3}$ and 60 $mu {hbox{m}}$ thickness). In this way, it becomes possible to build scaffolds with freedom in the design of architecture, surface morphology, and chemistry. Biocompatible microparts with complex 3-D shapes were first designed and mass produced using MEMS techniques. Semi-automatic assembly was then realized using a robotic workstation with four degrees of freedom integrating a dedicated microgripper and two optical microscopes. Coarse movement of the gripper is determined by pattern matching in the microscopes images, while the operator controls fine positioning and accurate insertion of the microparts. Successful microassembly was demonstrated using SU-8 and acrylic resin microparts. Taking advantage of parts distortion and adhesion forces, which dominate at micro-level, the parts cleave together after assembly. In contrast to many current scaffold fabrication techniques, no heat, pressure, electrical effect, or toxic chemical reaction is involved, a critical condition for creating scaffolds with biological agents.      

On Compensating Long Actuator Delays in Nonlinear Control

We are interested in finite-escape open-loop unstable plants that are globally stabilizable in the absence of actuator delay but require controller redesign in the presence of delay. The simplest such plant is $ {mathdot Z} (t)= Z(t)^{2} + U(t-D)$, where $D$ is actuator delay of arbitrary length. For this system we present a control law that compensates the delay and achieves feedback linearization (of the entire ODE+delay infinite-dimensional cascade). However, even though exponential stability is achieved, the result is not global because the plant can have a finite escape with an initial condition $Z(0)geq 1/D$ before the feedback control “reaches” it at $t=D$ . We prove a stability result whose region of attraction is essentially $Z(0)≪ 1/D$ and for which we derive an asymptotic stability bound in terms of the system norm $Z(t)^{2} + int _{t-D}^{t} U(theta )^{2} dtheta $.      

Binaural Sound Source Distance Learning in Rooms

A method for learning the distance of a sound source in a room is presented. The proposed method is based on short-time magnitude-squared coherence between the two channels of a binaural signal. Based on white noise as the training data, a coherence profile is obtained at each desired position in the room. These profiles can then be used to identify the most likely distance of a speech signal in the same room. The proposed approach is compared to a previous method for learning the position of a sound source. The results indicate that the both methods are able to identify the distance of a speech sound source correctly in a grid with 0.5-m spacing in most cases, when the orientation of the listener is 0$^{circ}$ , 30$^{circ}$ , 60$^{circ}$ , 90$^{circ}$ , or 180$^{circ}$ on the horizontal plane.      

11-Megapixel CMOS-Integrated SiGe Micromirror Arrays for High-End Applications

In this paper, we report on the design, fabrication, packaging, and testing of very reliable CMOS-integrated 10-$hbox{cm}^{2}$ 11-megapixel SiGe-based micromirror arrays on top of planarized six-level metal 0.18-${rm mu}hbox{m}$ CMOS wafers. The array, which is to be used as a spatial light modulator (SLM) for optical maskless lithography, consists of $8 {rm mu}hbox{m} times 8 {rm mu}hbox{m}$ pixels, which can be individually addressed by an analog voltage to enable accurate tilt angle modulation. Due to very stringent requirements on mounted-die flatness ($< hbox{0.01}$ mrad), the first level packaging of SLM die is done using specially designed SiC holders. To avoid trapped particles between the die and holder, which would jeopardize the flatness spec, special backside cleaning of the dies (less than or equal to one 0.8-${rm mu}hbox{m particle/cm}^{2}$ ) is needed before mounting the SLM die on the holder. To enable this backside cleaning and to avoid front-side particles during dicing, handling, and wire bonding, a temporary wafer- or zero-level packaging cap, which can be placed and removed at room temperature, was developed. The dynamic white light interferometer measurements of packaged dies showed that 99.5% of the 123 648 mirrors tested are within the spec. In addition, a stable average cupping of below 7 nm, an rms roughness of below 1 nm, and a stable actuation of over 2.5 teracycles are demonstrated.$hfill$[2009-0169]      

Impairment-Based 3-D Robotic Intervention Improves Upper Extremity Work Area in Chronic Stroke: Targeting Abnormal Joint Torque Coupling With Progressive Shoulder Abduction Loading

The implementation of a robotic system ( $hbox{ACT}^{rm 3D}$ ) that allowed for a quantitative measurement of abnormal joint torque coupling in chronic stroke survivors and, most importantly, a quantitative means of initiating and progressing an impairment-based intervention, is described. Individuals with chronic moderate to severe stroke (n $=$ 8) participated in this single-group pretest-posttest design study. Subjects were trained over eight weeks by progressively increasing the level of shoulder abduction loading experienced by the participant during reaching repetitions as performance improved. Reaching work area was evaluated pre- and postintervention for ten different shoulder abduction loading levels along with isometric single-joint strength and a qualitative clinical assessment of impairment. There was a significant effect of session (pre versus post) with an increase in reaching work area, despite no change in single-joint strength. This data suggests that specifically targeting the abnormal joint torque coupling impairment through progressive shoulder abduction loading is an effective strategy for improving reaching work area following hemiparetic stroke. Application of robotics, namely, the $hbox{ACT}^{rm 3D}$ , allowed for quantitative control of the exercise parameters needed to directly target the synergistic coupling impairment. The targeted reduction of abnormal joint torque coupling is likely the key factor explaining the improvements in reaching range of motion achieved with this intervention.