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This paper presents a particle flow velocity profiler that employs in-channel electrodes with unevenly divided inter-electrode gaps. The proposed electrical method measures both the particle position and velocity from the voltage signals generated by particles passing across three sensing electrodes, thus obtaining the flow velocity profile of the particles in a microfluidic channel. In this paper, we use polystyrene microparticles to characterize the performance of the present particle flow velocity profiler. At flow rates of 1.85, 2.68, and 3.60 [micro]L/min, a flow velocity profile of 6.59-[micro]m-diameter particles is measured with an uncertainty of 5.44%, which is comparable to the uncertainty (5%) in a previous microparticle image velocimetry. From the voltage signals for 6.59- and 5.47-[micro]m particles, we also verify that the present device detects the particle position showing less sensitivity to particle size variation than an existing particle impedance spectroscopy. In addition, in-channel clogging detection using the present electrical method is demonstrated. The present particle flow velocity profiler offers advantages of simpler structure, cheaper cost, and higher measurement stability that is insensitive to particle size for use in integrated microbiofluidic systems. [2007-0181] Index Terms--Fluid flow measurements, microsensors, particle measurements.

We present a novel cell-deformability-monitoring chip based on the digitally measured cell-lysis rate which is dependent on the areal strain of the cell membrane. This method offers simple and automated cell-deformability monitoring based on the mechanical property of the cell membrane. We suggest a filter design that considers the areal strain imposed on the cell membrane passing through the filter array with a gradually increased orifice length. In the experiment using erythrocytes, we characterized the cell deformability in terms of the average fracture areal strains that were 0.24 [+ or -] 0.014 and 0.21 [+ or -] 0.002 for normal and chemically treated erythrocytes, respectively. We also verified that the areal strain of 0.15 effectively discriminates the deformability difference of the normal and chemically treated erythrocytes. We compared the lysis rates and their difference for the samples from different donors and found that the patient-specific difference is negligible. However, the additional work on clinical demonstration is required to apply the present chips to the diagnostics. The experimental results demonstrate the simple structure and high performance of the present cell-deformability-monitoring chips, which are applicable to simple and cost-effective cell-aging-process monitoring. [2006-0238] Index Terms--Areal strain, cell deformability, cell lysis, erythrocyte deformability.

We present a novel method of measuring cell concentration using two electrical cell counters across a fixed control volume. Our device counts cells at the inlet and outlet of a fixed control volume and then measures the cell concentration by calculating the number of cells in the fixed control volume. Previous methods of measuring cell concentration (such as a Coulter counter and a flow cytometer) have attempted to count cells in a given fluid volume or at a known flow rate. Thus, in spite of the miniature nature of previous devices, the accuracy of their results depends on the performance of external mechanisms such as delicate pumps and flow sensors. Our prototype, however, does not depend on accurate fluid measurement or precise control of the flow rate because it measures the number of cells in a fixed control volume. In the experimental study, we measured cell concentrations ranging from 5.8 x [10.sup.5] to 11.5 x [10.sup.5] cells/mL without measuring or controlling the flow rate. For measuring the cell concentration, our prototype shows a maximum cell concentration measurement error of 10.3%, which is within the error range of a hemacytometer. [2006-0127] Index Terms--Biomedical equipment, biomedical impedance imaging, biomedical laboratories.

We present a new class of the protein concentration detector based on the mechanical stiffness measurement of protein-receptor layers in a squeezed nanogap. Compared to the previous protein size detector, the present device reduces the distortion and uncertainty in the displacement measurement by adding an actuated nanogap and reference electrodes. Compared to the conventional protein detectors based on electrochemical, optical, optomechanical, and mechanical principles, the present device also offers simple, inexpensive, and high-precision protein detection. We design and fabricate the protein concentration detector using an electrothermal actuator and two nanogaps with reference electrodes. In an experimental study, we verify that the present protein detector measures the size of the proteins streptavidin and m-antibiotin as 12.1 [+ or -] 2.3 and 13.2 [+ or -] 3.3 nm at the measurement uncertainty of [+ or -] 1.9 nm, respectively, while showing the concentration detection sensitivity of 2.88 N/m/nM in the m-antibiotin concentration range of 5-10 nM. [2006-0262] Index Terms--Biomedical measurements, biomedical transducer, mechanical engineering, proteins.

We present a high-accuracy digital-to-analog (DA) actuator using a linear load spring capable of compensating the output displacement errors caused by fabrication errors. The load spring is designed to modify the modulation line slope in the presence of fabrication errors, thus reducing the output displacement errors. We compare three prototypes including the uncompensated design, the compensated design at the fabrication error of [delta] = 0, and the compensated design in the fabrication error range of -0.3 [micro]m < [delta] < 0, respectively. The two different compensated linear DA actuators generate the output displacement errors of -0.20 [+ or -] 0.23 [micro]m and -0.13 [+ or -] 0.18 [micro]m, respectively, thus reducing their output errors by 64.3% and 76.8% of the errors, i.e., 0.56 [+ or -] 0.20 [micro]m, produced by the conventional uncompensated linear DA actuator. The dynamic characteristics of the compensated linear DA actuators show the response time below 1.5 ms, the resonant frequency of 3.7 kHz, and the lifetime of [10.sup.7] cycles. Consequently, we experimentally verify the fabrication error compensation function of the compensated linear DA actuators for applications to high-accuracy actuators insensitive to fabrication errors. [2006-0156] Index Terms--Digital-to-analog (DA) actuators, fabrication errors, high-accuracy actuation, microactuators.

This paper presents digital microflow controllers (DMFC), where a fluidic digital-to-analog converter (DAC) is used to achieve high-linearity and fine-levels in flow-rate control for applications to precise biomedical dosing systems. The fluidic DAC, composed of binary-weighted flow resistance, is designed to control the flow-rate based on the ratio of the flow resistance to achieve finer flow-rate levels. The binary-weighted flow resistance has been specified by a serial or a parallel connection of an identical flow resistor to improve the linearity of the flow-rate control by making the flow-resistance ratio insensitive to the size errors of flow resistors in micromachining process. We have designed and fabricated three types of 4-digit DMFC: Prototype S and P with serial and the parallel combinations of an identical flow resistor and Prototype V with width-varied flow resistors. In the experimental study, we perform static DMFC tests at forward and backward flow conditions as well as dynamic DMFC tests at pulsating flow conditions. The present DMFC shows the nonlinearity of 5.0 % and finer flow-rate levels of 16 ([2.sup.N]) for 4(N) digital valves. From the measured flow-rate deviation due to micromachining errors, Prototype S and P show 27.2% and 27.6% of the deviation measured from Prototype V, respectively; thus, verifying that Prototype S and P are less sensitive to the micromachining errors than Prototype V. [1365] Index Terms--Digital microflow controller (DMFC), flow resistor, fluidic digital-to-analog converter (DAC), micromachining errors.

In this paper, we present the design, fabrication, and experimental results of 4-bit digital microinjectors, whose ejected droplet volumes are adjusted by the digital operation of a 4-bit microheater array. We design the reference microinjectors as well as its comparative test structures. In the fabrication process, we use a five-mask micromachining process and the total chip size of the fabricated microinjector is 7640 [micro]m x 5260 [micro]m. We observe the microbubble generation and collapse on the microheater array. The microbubbles initiate and grow individually on top of each operating microheater, however the microbubbles merge together before collapse. We measure the ejected droplet volumes and velocities, which are adjusted from 12.1 ~ 55.6 p1 and 2.3 15.7 m/s, respectively, depending on the 15 possible combinations of 4-bit microheater array. We also experimentally characterize the effect of geometric variation including the microheater size, intermicroheater gap, microchannel width and sequential operation of microheater array on the ejected droplet volume and velocity. Thus, the present microinjector has a potential for application to the high-resolution inkjet printers with multiple gray levels or high-precision fluid injectors with variable volume control. [1348] Index Terms--Droplet volume adjusting, inkjet printer, microheater array, microinjector.

This paper presents a navigation-grade capacitive microaccelerometer, whose low-noise high-resolution detection Capability is achieved by a new electrode design based on a high-amplitude anti-phase sense voltage. We reduce the mechanical noise of the microaccelerometer to the level of 5.5 [micro]g [square root of Hz] by increasing the proof-mass based on deep RIE process of an SOI wafer. We reduce the electrical noise as low as [micro]g/ [square root of Hz] by using an anti-phase high-amplitude square-wave sense voltage of 19 V. The nonlinearity problem caused by the high-amplitude sense voltage is solved by a new electrode design of branched finger type. Combined use of the branched finger electrode and high-amplitude sense voltage generates self force-balancing effects, resulting in an 140% increase of the bandwidth from 726 Hz to 1734 Hz. For a fixed sense voltage of 10 V, the total noise is measured as 2.6 [micro]g/ [square root of Hz] at the air pressure of 3.9 torr, which is the 51% of the total noise of 5.1 [micro]g/ [square root of Hz] at the atmospheric pressure. From the excitation test using 1 g, 10 Hz sinnsoidal acceleration, the signal-to-noise ratio of the fabricated microaccelerometer is measured as 105 dB, which is equivalent to the noise level of 5.7 [micro]g/[square root of Hz]. The sensitivity and linearity of the branched finger capacitive microaccelerometer are measured as 0.638 V/g and 0.044%, respectively. [803] Index Terms--Branched finger electrode, electrical noise, highamplitude sense voltage, mechanical noise, navigation-grade microaccelerometer, self force-balancing.

Viscous energy loss in oscillating fluid-film dampers that provide frictional shear for laterally-driven planar microstructures is investigated. It is found that Stokes-type fluid motion models viscous damping more accurately than Couette-type flow field. This paper characterizes the damping property of a fluid layer in terms of viscous energy dissipation, then derives analytic damping formulae for practical Q estimation. Theoretical Q-factors are compared to the experimental values, measured from surface-micromachined polysilicon resonators. Data reported by previous investigators are also analyzed and compared. The experimental results indicate that the Stokes-type damping model presents a more general damping treatment with better Q estimation, although discrepancies of 10 to 20% still remain between the estimated and measured Q.

We present a new electrostatic actuation method using a lateral repulsive-force induced by an asymmetric distribution of planar electrostatic field. The lateral repulsive-force has been characterized by a simple analytical equation, derived from a finite element simulation. Quality-factors are estimated from the computer simulation based on creep flow model. A set of repulsive-force polycrystalline silicon microactuators has been designed and fabricated by a four-mask surface-micromachining process. Static and dynamic response of the fabricated microactuators has been measured at the atmospheric pressure for the driving voltage range of 0-140 V. The static displacement of 1.27 [micro]m is obtained at the dc voltage of 140 V. The resonant frequency of the repulsive-force microactuator increases from 11.7 kHz to 12.7 kHz when the dc induction voltage increases from 60 V to 140 V. The measured quality-factors are increased from 12 to 13 in the voltage range of 60-140 V. Fundamental characteristics of the force, frequency and quality-factor of the electrostatic repulsive-force microactuator have been discussed and compared with those of the conventional electrostatic attractive-force microactuator. [576] Index Terms--Creeping flow, electrostatic force, frequency-tuning, microresonator, quality-factor, repulsive-force.