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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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back to top Sensors and Actuators/MEMS/NEMS

A micro gas chromatography column with a micro thermal conductivity detector for volatile organic compound analysis

J. H. Sun, D. F. Cui, X. Chen, L. L. Zhang, H. Y. Cai, and H. Li

Rev. Sci. Instrum. 84, 025001 (2013); http://dx.doi.org/10.1063/1.4789526 (5 pages)

Online Publication Date: 4 February 2013

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In this paper, a micro gas chromatography (μGC) system contained a μGC column and a micro thermal conductivity detector (μTCD) was proposed. In order to reduce the volume of the system, some micro heaters were integrated on the surface and backside of the GC column, which could provide a robust temperature programming capability and rapidly increase the temperature of the μGC column. In addition, a silicon-glass μTCD with four-thermistor thermal conductivity cells that can offer significant advantages over previously reported designs including low dead volume, good thermal isolation, and elimination of the thermal noise was proposed in this paper. Experimental results have indicated that the μGC system with a detection limit of several ppm concentration levels separated and detected the benzene, toluene, and styrene in less than 3 min, and the μGC system also exhibited a good linear response in the test range.
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82.80.Bg Chromatography
51.20.+d Viscosity, diffusion, and thermal conductivity

Design and performance evaluation of polyvinyl alcohol/polyimide coated optical fibre grating-based humidity sensors

L. Alwis, T. Sun, and K. T. V. Grattan

Rev. Sci. Instrum. 84, 025002 (2013); http://dx.doi.org/10.1063/1.4789768 (6 pages)

Online Publication Date: 5 February 2013

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Optical fibre grating based sensors make a significant contribution to relative humidity measurement for various applications and a number of different designs and sensor configurations have been produced and discussed in the literature. Recent developments have included using sensitive polymers and indeed other materials that experience a variation of their physical and optical properties as a result of the absorption of moisture and which thus creates a modification of the characteristic spectral features of the gratings used. The strain and the effective refractive index of the gratings are affected by the change induced by the polymer and these effects were calibrated against the relative humidity variations that initially induce variations in the polymer layer. In this work, an evaluation is made of the performance characteristics of two different moisture sensitive polymers, i.e., polyimide and polyvinyl alcohol, as the basis of such sensors, while at the same time using different types of fibre gratings i.e., fibre Bragg gratings and long period gratings. Their performance is discussed in light of the operation of similar types of polymer-coated and other grating based sensors reported in the literature.
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42.81.Pa Sensors, gyros
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.07.Vx Hygrometers; hygrometry

Comb-drive micro-electro-mechanical systems oscillators for low temperature experiments

M. González, P. Zheng, E. Garcell, Y. Lee, and H. B. Chan

Rev. Sci. Instrum. 84, 025003 (2013); http://dx.doi.org/10.1063/1.4790196 (10 pages)

Online Publication Date: 11 February 2013

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We have designed and characterized micro-electro-mechanical systems (MEMS) for applications at low temperatures. The mechanical resonators were fabricated using a surface micromachining process. The devices consist of a pair of parallel plates with a well defined gap. The top plate can be actuated for shear motion relative to the bottom fixed plate through a set of comb-drive electrodes. Details on the operation and fabrication of the devices are discussed. The geometry was chosen to study the transport properties of the fluid entrained in the gap. An atomic force microscopy study was performed in order to characterize the surface. A full characterization of their resonance properties in air and at room temperature was conducted as a function of pressure, from 10 mTorr to 760 Torr, ranging from a highly rarefied gas to a hydrodynamic regime. We demonstrate the operation of our resonator at low temperatures immersed in superfluid 4He and in the normal and superfluid states of 3He down to 0.3 mK. These MEMS oscillators show potential for use in a wide range of low temperature experiments, in particular, to probe novel phenomena in quantum fluids.
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81.16.-c Methods of micro- and nanofabrication and processing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Some aspects of achieving an ultimate accuracy during insertion device magnetic measurements by a Hall probe

I. B. Vasserman, N. O. Strelnikov, and J. Z. Xu

Rev. Sci. Instrum. 84, 025004 (2013); http://dx.doi.org/10.1063/1.4790422 (7 pages)

Online Publication Date: 11 February 2013

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An extensive test of a new Senis 2-axis Hall probe was done at the Advanced Photon Source using the Undulator A device and calibration system. This new probe has clear advantages compared with previously used Bell and Sentron Hall probes: very stable zero offset (less than the noise of 0.026 G) and compensated planar Hall effect. It can be used with proper calibration even for first and second field integral measurements. A comparison with reference measurements by long stretched coil shows that the difference in the first field integral measurement results for a 2.4-m-long Undulator A device is between 17 G cm for the best of four Hall probes used for the test and 51 G cm for the worst of them for all gap ranges from 10.5 mm to 150 mm.
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07.55.-w Magnetic instruments and components
85.75.Nn Hybrid Hall devices
06.20.fb Standards and calibration

An energy-efficient readout circuit for resonant sensors based on ring-down measurement

Z. Zeng, M. A. P. Pertijs, and D. M. Karabacak

Rev. Sci. Instrum. 84, 025005 (2013); http://dx.doi.org/10.1063/1.4792396 (8 pages)

Online Publication Date: 25 February 2013

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This paper presents an energy-efficient readout circuit for resonant sensors that operates based on a transient measurement method. The resonant sensor is driven at a frequency close to its resonance frequency by an excitation source that can be intermittently disconnected, causing the sensor to oscillate at its resonance frequency with exponentially decaying amplitude. By counting the zero crossings of this ring-down response, the interface circuit can detect the resonance frequency. In contrast with oscillator-based readout, the presented readout circuit is readily able to detect quality factor (Q) of the resonator from the envelope of the ring-down response, and can be used even in the presence of large parasitic capacitors. A prototype of the readout circuit has been integrated in 0.35 μm CMOS technology, and consumes only 36 μA from a 3.3 V supply during a measurement time of 2 ms. The resonance frequency and quality factor of a micro-machined SiN resonator obtained using this prototype are in good agreement with results obtained using impedance analysis. Furthermore, a clear transient response is observed to ethanol flow using the presented readout, demonstrating the use of this technique in sensing applications.
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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
07.10.Cm Micromechanical devices and systems
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