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May 2012

Volume 83, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 051101 (2012); http://dx.doi.org/10.1063/1.4709621 (18 pages)

Igor Lubomirsky and Oscar Stafsudd

The periodic pulsed heating technique for measuring pyroelectricity (the Chynoweth method) is one of several measurement techniques that have been significantly enhanced through advances in instrumentation such as fast digital averaging oscilloscopes and modulated light sources.

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back to top Sensors and Actuators/MEMS/NEMS

Remote vibration measurement: A wireless passive surface acoustic wave resonator fast probing strategy

J.-M. Friedt, C. Droit, S. Ballandras, S. Alzuaga, G. Martin, and P. Sandoz

Rev. Sci. Instrum. 83, 055001 (2012); http://dx.doi.org/10.1063/1.4705728 (6 pages)

Online Publication Date: 1 May 2012

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Surface acoustic wave (SAW) resonators can advantageously operate as passive sensors which can be interrogated through a wireless link. Amongst the practical applications of such devices, structural health monitoring through stress measurement and more generally vibration characteristics of mechanical structures benefit from the ability to bury such sensors within the considered structure (wireless and battery-less). However, measurement bandwidth becomes a significant challenge when measuring wideband vibration characteristics of mechanical structures. A fast SAW resonator measurement scheme is demonstrated here. The measurement bandwidth is limited by the physical settling time of the resonator (Q/π periods), requiring only two probe pulses through a monostatic RADAR-like electronic setup to identify the sensor resonance frequency and hence stress on a resonator acting as a strain gauge. A measurement update rate of 4800 Hz using a high quality factor SAW resonator operating in the 434 MHz Industrial, Scientific and Medical band is experimentally demonstrated.
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07.10.-h Mechanical instruments and equipment
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A novel driving principle by means of the parasitic motion of the microgripper and its preliminary application in the design of the linear actuator

Hu Huang, Hongwei Zhao, Zhaojun Yang, Jie Mi, Zunqiang Fan, Shunguang Wan, Chengli Shi, and Zhichao Ma

Rev. Sci. Instrum. 83, 055002 (2012); http://dx.doi.org/10.1063/1.4711869 (6 pages) | Cited 3 times

Online Publication Date: 4 May 2012

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This paper presents a novel driving principle by means of the parasitic motion of the microgripper. Actuators based on this principle can realize the large displacement range and high speed easily. Also the structure can be simple. A parasitic motion principle linear actuator mainly consisting of two piezoelectric stacks, two microgrippers and a mover was designed. Experimental results indicate that at a low driving frequency of 5 Hz, large velocity over 40 μm/s is obtained with the driving voltage of 100 V. Backward motion was observed and analyzed. Experimental results verify the feasibility of the new principle and it can be used to design new linear or rotary actuators.
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07.07.Tw Servo and control equipment; robots
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Tuning of nanogap size in high tensile stress silicon nitride thin films

Anıl Günay-Demirkol and İsmet İ. Kaya

Rev. Sci. Instrum. 83, 055003 (2012); http://dx.doi.org/10.1063/1.4712289 (5 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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High tensile stress suspended structures are demanded for high mechanical quality factor applications. However, high tensile stress causes distortion of the original shapes by contracting, buckling, and bending the suspended structures. We demonstrate a method to compensate for the shape deformation of suspended structures due to intrinsic tensile stress after they are released. With a new design, the distance between two suspended structures after wet etch can easily be tuned by a single fabrication beyond the lithographic resolution limits. The technique is simulated by finite element analysis and experimentally implemented to demonstrate a gap tuning capability with 2.4 nm standard error.
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68.60.Bs Mechanical and acoustical properties
62.20.mq Buckling
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Development of a micro cell compression stimulator for evaluating real-time cellular responses

Y. Nakashima, Y. Yang, and K. Minami

Rev. Sci. Instrum. 83, 055004 (2012); http://dx.doi.org/10.1063/1.4717683 (7 pages)

Online Publication Date: 11 May 2012

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This paper presents a micro cell compression stimulator for evaluating real-time cellular responses to compression stimuli. The device was produced by a micro three-dimensional structure fabrication process using multiple exposures to the photoresist. The device consists of a pressure inlet port, cell inlet ports, a gasket, microchannels, cell culture chambers, and a diaphragm on the culture chamber for applying compressive pressure to cells. Compression stimuli applied to the cells can be controlled by regulating the expansion of the diaphragm via a pressure control. The device permits the observation of cellular responses to compressive pressure in real time because it is made of transparent materials and stimulates the cells without deforming the cell culture surface, when observed by optical microscopy. We demonstrated the validity of the fabrication process, evaluated the performance of the fabricated device, and compared the experimental results with the FEM structural analysis results. We found through operational testing that the diaphragm was deformed quickly by applying negative/positive pressure and that the diaphragm displacement became larger with increasing applied pressure. These results indicate that this device can be used to control the intensity and the cell stimulus profile by regulating the applied pressure. In all cases, the cellular deformation during compression stimulus was successfully observed in real time using an optical microscope. The device is expected to facilitate the control of stem cell differentiation and the clarification of cellular mechanoreceptor mechanisms and signal transduction pathways.
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87.80.Ek Mechanical and micromechanical techniques
07.10.Cm Micromechanical devices and systems
87.17.-d Cell processes
47.60.Dx Flows in ducts and channels
87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction
87.64.M- Optical microscopy

A pressure gauge based on gas density measurement from analysis of the thermal noise of an atomic force microscope cantilever

Dongjin Seo, Mark R. Paul, and William A. Ducker

Rev. Sci. Instrum. 83, 055005 (2012); http://dx.doi.org/10.1063/1.4717678 (5 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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We describe a gas-density gauge based on the analysis of the thermally-driven fluctuations of an atomic force microscope (AFM) cantilever. The fluctuations are modeled as a ring-down of a simple harmonic oscillator, which allows fitting of the resonance frequency and damping of the cantilever, which in turn yields the gas density. The pressure is obtained from the density using the known equation of state. In the range 10–220 kPa, the pressure readings from the cantilever gauge deviate by an average of only about 5% from pressure readings on a commercial gauge. The theoretical description we use to determine the pressure from the cantilever motion is based upon the continuum hypothesis, which sets a minimum pressure for our analysis. It is anticipated that the cantilever gauge could be extended to measure lower pressures given a molecular theoretical description. Alternatively, the gauge could be calibrated for use in the non-continuum range. Our measurement technique is similar to previous AFM cantilever measurements, but the analysis produces improved accuracy.
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06.30.Dr Mass and density
07.07.Mp Transducers
07.79.Lh Atomic force microscopes

Fiber-optic liquid level sensor based on coupling optical path length variation

Pabitra Nath, Hidam Kumarjit Singh, Dhananjay Tiwari, and Tenisen Basumatry

Rev. Sci. Instrum. 83, 055006 (2012); http://dx.doi.org/10.1063/1.4717725 (4 pages)

Online Publication Date: 16 May 2012

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The concept for a new and simple fiber-optic liquid level sensor is presented and experimental results are shown to demonstrate the principle. The sensing principle is based on light intensity modulation when rising and falling mode of liquid level causes coupling optical path distance variation between two optical fibers. Near continuous mode of liquid level variation could be monitored with resolution as low as 1 mm can be measured in the length scale of 25 cm.
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42.81.Pa Sensors, gyros
47.80.-v Instrumentation and measurement methods in fluid dynamics
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A new concept in underwater high fidelity low frequency sound generation

Paulo J. Fonseca and J. Maia Alves

Rev. Sci. Instrum. 83, 055007 (2012); http://dx.doi.org/10.1063/1.4717680 (4 pages)

Online Publication Date: 18 May 2012

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This article reports on a new type of system for high fidelity underwater sound generation (patent pending PT105474). The system includes an underwater sound actuator and the corresponding electronic driver. The sound is generated by a rigid plate that is actuated (both for positioning/dumping and excitation) using purely electromagnetic forces, thus, avoiding the use of any elastic membrane. Since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure. Characterization of the frequency response, the radiation characteristics, and the dynamic range of this new device for underwater sound generation is presented.
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43.30.-k Underwater sound
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound
07.64.+z Acoustic instruments and equipment
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Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms

C. Malhaire

Rev. Sci. Instrum. 83, 055008 (2012); http://dx.doi.org/10.1063/1.4719964 (10 pages)

Online Publication Date: 23 May 2012

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The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ0 = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ0 = (172 ± 5) MPa.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
62.20.de Elastic moduli
07.10.-h Mechanical instruments and equipment
07.10.Cm Micromechanical devices and systems

Magnetostatic detection using magnetoresistive sensors with vertical motion flux modulation

Jiafei Hu, Mengchun Pan, Wugang Tian, Dixiang Chen, and Jianqiang Zhao

Rev. Sci. Instrum. 83, 055009 (2012); http://dx.doi.org/10.1063/1.4723823 (4 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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Recently, the flux modulation has been presented to deal with the 1/f noise of magnetoresistive (MR) sensors. However, the efficiency of most flux modulation schemes with simple micro- electromechanical-system (MEMS) actuators is not satisfying yet. In this paper, the vertical motion flux modulation (VMFM) is proposed to improve the modulation efficiency. In VMFM, the soft magnetic film driven by a MEMS actuator vibrates vertically above the MR sensors with a pair of flux concentrators. Consequently, the detected magnetostatic field is modulated to the higher frequency where the 1/f noise is much lower. A VMFM prototype based on AA002 (multi-layered giant magnetoresistive sensors) was fabricated and its flux modulation efficiency can reach 18.7%, which exceeds most achieved efficiency with other schemes. Also, the magnetostatic detection ability is improved to 530 pT/√Hz.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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