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[en] This paper reports measurement of random uncertainties in resonant characteristics (resonance frequency and quality factor) of micro electromechanical system (MEMS) resonators. We employ different methods to extract resonant characteristics of 4 different MEMS resonators which are either clamped-free or clamped-clamped beams. Each beam type operates either in air or in a partial vacuum, and therefore, different vacuum levels can be examined. Three different methods, including frequency sweep, impulse response, and thermal noise, are applied to each resonator type excited with electrostatic or piezo-crystal actuation. We make a thorough analysis and comparison for three different methods. Depending on device type and operating condition, there exists a better and recommended way to extract resonant characteristics of MEMS resonators. For example, the impulse response is best-suited for the quality factor measurement of a clamped-clamped beam operating in a vacuum. Our results show that the quality factor of MEMS resonators may be noticeably different and exhibit appreciable systematic and random uncertainties, and suggests a better way to extract the quality factor for a given situation.
[en] The authors earlier invented an electromechanical integrated electrostatic harmonic actuator consisting of a flexible ring and segmented stator. As the dimension of the actuator decreases, the effect of ring eccentricity on the dynamic behavior of the actuator becomes significant. In this paper, the equations for the displacements of the flexible ring and the electromechanical coupled dynamic equations under eccentricity are deduced. Using these equations, changes of the natural frequencies and vibrating modes as a function of the eccentric center distance are analyzed. For different eccentric center distances, changes of the forced response along with the system parameters are given. Results show that the ring eccentricity causes significant changes of the natural frequencies and vibrating amplitudes of the flexible ring, which could cause loss of the load-carrying ability for the actuator. The flexible ring radius, thickness, and clearance and voltage between the flexible ring and stator influence the relationship between the eccentricity and the dynamic behavior of the actuator.
[en] In this paper we present two different techniques for automated extraction of system models from FEA models. We discuss two different algorithms: for (i) automated N-DOF SME for electrostatically actuated MEMS and (ii) automated N-DOF SME for MEMS inertial sensors. We will present case studies for the two different algorithms presented
[en] A silicon (SiNW) nanowire device, made by the bottom-up method, has been assembled in a MEMS device for measuring stress in cantilevers. The process for assembling a SiNW on a cantilever has been introduced. The current as a function of the voltage applied to a SiNW have been measured, and the different resistances before and after cantilever releasing have been observed. A parameter, η, has been derived based on the resistances. For a fixed sample, a linear relationship between η and the stress in the cantilever has been observed; and, so, it has been demonstrated that the resistance of SiNW can reflect the variation of the cantilever stress.
[en] An insect can perform various flight maneuvers. However, the aerodynamic force generated by real insect wings during free flight has never been measured directly. In this study, we present the direct measurement of the four points of the differential pressures acting on the wing surface of a flying insect. A small-scale differential pressure sensor of 1.0 mm × 1.0 mm × 0.3 mm in size was developed using microelectromechanical systems (MEMS) and was attached to a butterfly wing. Total weight of the sensor chip and the flexible electrode on the wing was 4.5 mg, which was less than 10% of the wing weight. Four points on the wing were chosen as measurement points, and one sensor chip was attached in each flight experiment. During takeoff, the wing's flapping motion induced a periodic and symmetric differential pressure between upstroke and downstroke. The average absolute value of the local differential pressure differed significantly with the location: 7.4 Pa at the forewing tip, 5.5 Pa at the forewing center, 2.1 Pa at the forewing root and 2.1 Pa at the hindwing center. The instantaneous pressure at the forewing tip reached 10 Pa, which was ten times larger than wing loading of the butterfly. (paper)
[en] Transdermal drug delivery (TDD) has many advantages, the main one being the ability to maintain the prolonged release of drugs to attain optimal blood concentrations. Unfortunately, nature has provided a very effective protective barrier, the stratum corneum (sc), which limits TDD to certain types of drugs with specific properties. In order to enhance TDD, the idea of using microneedles to painlessly penetrate the sc barrier has previously been proposed. In this paper, we will review the different microneedles that are currently being developed as well as our own efforts in this area. Based on our experiences, we will offer our view on the key parameters for effective transdermal microneedle design as well as future directions in this area
[en] We are conducting a comprehensive experimental study of the electromechanical behavior of poled PZT 95/5 (lead zirconate titanate). As part of this study, eight plane-wave tests have been conducted on axially poled PZT 95/5 at stress levels ranging from 0.9 to 4.6 GPa, using VISAR and electrical diagnostics. Observed wave velocities were slightly decreased from ultrasonic velocity, by contrast' with unpoled samples. Compression waveforms show a step at 0.6 GPa more marked than for normally poled or unpoled samples; this may correspond to a poling effect on the ferroelectric/antiferroelectric transition. A similar step is observed on release. The released charge upon loading to 0.9 GPa is consistent with nearly complete depoling. Loading to higher stresses gave lower currents (factor of 10), suggesting shock-induced conductivity or electrical breakdown
[en] A mathematical model of the power plant with a pressurized water reactor has been prepared and tested. The model is intended for a schematic simulator based on a digital computer. The results of the simulation run for various normal transients are in good agreement with literature data. Equipment for computer control of the experimental reactor TRIGA has been completed. The equipment includes two microcomputers and associated interface circuits. Presently, only data logging is performed. The analyses of random signals on the TRIGA reactor have been continued. Measurements of neutron flux, fuel temperature and cooling water duct have been performed