Two-Dimensionally Deflecting Mirror Using Electromagnetic Actuation

This paper describes the structure and characteristics of a deflecting mirror using electromagnetic actuation. We used a moving magnet structure for mirror actuation and focused on designing a mirror structure with effective magnetic force (for low-power operation) and a simple fabrication process (to achieve low manufacturing cost). In this design, the magnetic forces of attraction and repulsion are simultaneously used for mirror deflection, allowing the mirror to be operated with low current. Moreover, the structures of the yoke core and magnet bar have been designed to further reduce the operating current. Such a mirror structure is simple and can be easily fabricated with a small number of components. This structure can be used not only for a one-dimensionally deflecting mirror but also for a two-dimensionally deflecting mirror by attaching a second yoke core.     

Design and fabrication of automated sedimentation-based separation and siphon-based extraction for detection of allergic reaction on a centrifugal microfluidic disc

We report the design and fabrication of a novel and fully integrated polymer-based centrifugal microfluidic disc for rapid automatic allergens detection. All essential steps for a single test including flow valving, sequencing, mixing, separation, extraction, and sedimentation for final detection are automatically conducted within 30 min on a centrifugal microfluidic disc. Our design features a siphon-based valving and analyte extraction structure where the released analyte is separated and subsequently extracted by a siphon valve into the detection chamber. Incorporating the siphon valve and a series of capillary valves, we realize automated detection of allergic reaction on a centrifugal microfluidic disc.     

Planar microcoil-based microfluidic NMR probes

Microfabricated small-volume NMR probes consisting of electroplated planar microcoils integrated on a glass substrate with etched microfluidic channels are fabricated and tested. 1H NMR spectra are acquired at 300 MHz with three different probes having observed sample volumes of respectively 30, 120, and 470 nL. The achieved sensitivity enables acquisition of an 1H spectrum of 160 microg sucrose in D2O, corresponding to a proof-of-concept for on-chip NMR spectroscopy. Increase of mass-sensitivity with coil diameter reduction is demonstrated experimentally for planar microcoils. Models that enable quantitative prediction of the signal-to-noise ratio and of the influence of microfluidic channel geometry on spectral resolution are presented and successfully compared to the experimental data. The main factor presently limiting sensitivity for high-resolution applications is identified as being probe-induced static magnetic field distortions. Finally, based on the presented model and measured data, future performance of planar microcoil-based microfluidic NMR probes is extrapolated and discussed.     

Fabrication of a 256-bits organic memory by soft x-ray lithography

This paper reports a procedure of soft x-ray lithography for the fabrication of organic crossbar structure. Electron beam lithography is employed to fabricate the mask for soft x-ray lithography, with direct writing technology to lithograph positive resist, polymethyl methacrylate on the polyimide film. Then Au is electroplated on the polyimide film. Hard contact mode exposure is used in x-ray lithography to transfer the graph from the mask to the wafer. The 256-bits organic memory is achieved with the critical dimension of 250~nm.     

Capture of DNA in microfluidic channel using magnetic beads: Increasing capture efficiency with integrated microfluidic mixer

We have studied the hybridization of target DNA in solution with probe DNA on magnetic beads immobilized on the channel sidewalls in a magnetic bead separator. The hybridization is carried out under a liquid flow and is diffusion limited. Two systems are compared: one with a straight microfluidic channel and one with an integrated staggered herringbone mixer. Fluorescence microscopy studies show that the hybridization is much more efficient in the system with the integrated mixer. The results, which are discussed in terms of a simple model, are relevant for any diffusion-limited reaction taking place on the surface in a microfluidic system.     

Three-dimensional microfluidic channel with arbitrary length and configuration fabricated inside glass by femtosecond laser direct writing

We demonstrate, for the first time to the best of our knowledge, fabrication of three-dimensional microfluidic channels with arbitrary lengths and configurations inside glass by femtosecond laser direct writing. The main fabrication process includes two steps: (1) direct formation of hollow microchannels in a porous glass substrate immersed in water by femtosecond laser ablation and (2) postannealing of the glass substrate at ～1150°C by which the porous glass can be consolidated. We show that a square-wavelike channel with a total length of ～1.4 cm and a diameter of ～64 μm can be easily produced ～250 μm beneath the glass surface.     

Pump-free transport of magnetic particles in microfluidic channels

The use of magnetic particles in microfluidic devices offers new possibilities and a new degree of freedom to sequential synthesis and preparative or analytical procedures in very small volumes. In contrast to most of the traditional approaches where the liquid phase is flushed or pumped along a solid phase, the transport of magnetic particles through a microfluidic channel has the advantage of reduced reagent consumption and simpler, smaller systems. By lining up different reservoirs along the transport direction, reactions with different agents can be accomplished. Here, we present a pump and valve-free microfluidic particle transport system. By creating a simple and very effective layout of soft magnetic structures, which concentrate an external homogeneous magnetic field, a passive, thus easy to operate structure was generated. Most importantly, this layout is based on a simple tube by which fluidic and magnetic parts are separated. The tube itself is disposable and can be replaced prior to vital reactions, thus helping reduce sample cross-contaminations without affecting the particle transport properties. The layout of the device was thoroughly examined by a computer simulation of the particle trajectories, and the results were confirmed by experiments on a micro-machined demonstrator, which revealed an effective transport speed of up to 5 mm/s in 30 mT magnetic fields. Thus, we present a microfluidic transport device that combines the advantages of magnetic particles in microfluidic systems with a simple single-use technology for, e.g., bioanalytical purposes.     

Continuous fabrication of Co-Cr perpendicular magnetic recording tape

To achieve high-throughput fabrication of Co-Cr/Ni-Fe double-layer perpendicular media, the optimum conditions for continuous preparation and construction of a new dc magnetron sputtering target have been investigated with respect to the aperture shield mask position and the magnetic circuit. The perpendicular magnetic tape media fabricated in a roll-coater equipped with the improved target showed high reproduced voltage at high densities.     

Laser-assisted magnetic recording light-delivery system with a coupling element and a laterally tapered vertically multistepped waveguide

In a light-delivery system for laser-assisted magnetic recording, which provides high-areal-density storage by heating the storage medium during the writing process, a laser diode light source and a near-field transducer must be efficiently coupled using inexpensive optical devices. We describe a light-delivery system using an element for end-fire coupling and a spot-size converter. To couple the light emitted from the end of an optical fiber to a spot-size converter inexpensively, a couple element requiring no other lens elements between the fiber and converter was developed. A vertically multistepped and laterally tapered waveguide suitable for fabrication by planar processing was also developed. These devices are well suited for practical use.     

Evanescent field-based optical fiber sensing device for measuring the refractive index of liquids in microfluidic channels

We report a simple optical sensing device capable of measuring the refractive index of liquids propagating in microfluidic channels. The sensor is based on a single-mode optical fiber that is tapered to submicrometer dimensions and immersed in a transparent curable soft polymer. A channel for liquid analyte is created in the immediate vicinity of the taper waist. Light propagating through the tapered section of the fiber extends into the channel, making the optical loss in the system sensitive to the refractive-index difference between the polymer and the liquid. The fabrication process and testing of the prototype sensing devices are described. The sensor can operate both as a highly responsive on-off device and in the continuous measurement mode, with an estimated accuracy of refractive-index measurement of approximately 5 x 10(-4).     

高温超导磁体指数损耗分析

本论文对高温超导磁体指数损耗(HTS index loss)的特点进行了分析.通过数值模拟,研究了由20个双饼组成的高温超导磁体在20k的温度下磁体的指数损耗,对每个双饼以及每匝线圈的指数损耗进行了计算,对整个磁体的指数损耗随电流变化情况进行了研究.在磁体的两端加上铁轭改变磁场的分布后,可以看出,铁轭可以有效地减少磁体上的指数损耗.     

Fabrication of planar gratings by direct ablation using an ultrashort pulse laser in a common optical path configuration

Planar gratings have wide applications and to date, many methods for the fabrication of gratings have been reported. Ultrashort pulse lasers have been used for the machining of gratings primarily because they allow direct ablation and the manufacturing of sub-wavelength structures. In this paper, we present a novel direct ablation technique for the fabrication of planar gratings which makes use of the interference of ultrashort pulses in a common optical path configuration. This technique of grating fabrication not only simplifies the optical setup, but also immunizes the system to extraneous and inherent vibrations, thus enabling the manufacturing of planar gratings of good edge acuity. We have successfully fabricated planar gratings on a copper substrate. Received: 6 November 2001 / Accepted: 4 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +65/77-904-674, E-mail: mvenkata@ntu.edu.sg     

Macromolecular nanoelectronics

We have explored new organic materials and fabrication methods to fabricate organic photodiodes and light emitting diodes. Grafting of a fullerene derivative to a polythiophene backbone yielded an integrated acceptor-donor polymer that we used as the active material in organic photodiodes. Using a method of soft lithography, soft embossing, we fabricated submicron structures to be used as organic light emitting diodes. Employing a silicone rubber replica (stamp) of an optical diffraction grating we transferred the grating pattern to an organic resist layer by placing the stamp in conformal contact with the resist. The transferred pattern was subsequently used as an etch mask for the processing of the device. The structures were successfully utilized as light emitting diodes and photodiodes, with device characteristics influenced by the imposed structure.     

A three-phase single sheet tester with digital control of flux loci based on the contraction mapping principle

Tight control of flux loci in 2D testing of soft magnetic laminations is realized by a method based on the principle of contraction mapping. It is implemented through digital control of the currents supplying a three-phase yoke magnetizer and the use of circular samples. Faithful realization of the prescribed loci and good measuring accuracy are demonstrated in grain-oriented and non-oriented Fe–Si laminations.     

Frequency characterization of thin soft magnetic material layers used in spiral inductors

The paper details the characterization of thin magnetic materials layers, particularly soft materials, with respect to their behaviour in frequency (from 10 MHz to 1 GHz). The proposed method is suitable for any soft but insulating magnetic material; Yttrium Iron Garnet (YIG) is used as an example. The principle is based on a comparison between simulations for different values of the permeability and measurement values versus frequency of planar inductor structures; an experimental validation is proposed as well. Thin magnetic material is first deposited on an alumina substrate using RF sputtering technique; a planar spiral winding of copper is then deposited on the magnetic material by the same technique. The effective permeability versus frequency is obtained by comparing two samples of spiral windings with and without magnetic material. Network analyser measurements on samples of various geometrical dimensions and of different thicknesses are necessary to determine the effective magnetic permeability; we have obtained a relative effective permeability of about 30 for seven turns spiral inductor of a 17 μm YIG film.     

Sol–gel concave micro-lens arrays fabricated by combining the replicated PDMS soft mold with UV-cured imprint process

Photosensitive TiO₂/organically modified silane organic–inorganic hybrid thin films were synthesized by combining a low-temperature sol–gel process with a spin-coating method. Optical transmittance properties and the photochemical activities of the planar hybrid films were characterized by UV–Visible spectroscopy and Fourier transform infrared spectroscopy. Advantages for fabrication of the concave micro-lens arrays (MLAs) based on the photosensitive hybrid films were demonstrated by using the replicated polydimethylsiloxane (PDMS) soft mold as the imprint mold and a UV soft imprint technique. Morphological and surface profile properties of the master, the PDMS soft molds and the as-fabricated sol–gel concave MLAs were observed by scanning electron microscopy and laser confocal scanning microscopy. Contact angles of water on the PDMS soft molds baked at different temperatures were studied. Optical imaging properties of the as-fabricated concave MLAs were confirmed by a self-made optical test system. Results indicate that the as-prepared photo-patternable hybrid materials have great applicability for the fabrication of photonic components, thus providing an effective method to fabricate concave MLAs based on the as-synthesized hybrid films by combining the UV-cured imprint technique with the replicated PDMS soft mold, which has advantages of simplicity, cost-effective and mass production and potential application in industry production.     

Microfabricated polydimethylsiloxane microfluidic system including micropump and microvalve for integrated biosensor

We present a microfluidic system with paraffin-actuated microvalves and a thermopneumatic-actuated micropump that are easily integrated on the same substrate using the same fabrication process. The fabrication process of this microfluidic system using polydimethylsiloxane (PDMS), indium tin oxide (ITO) and glass is relatively simple, and its performance is good for the application of the disposable lab-on-a-chip. A maximum pumping rate of about 2.0 μl/min was measured at a duty ratio of 5% and a frequency of 1 Hz. The flow cut-off powers for the microvalves with the channel depth of 220 μm, were 300 and 350 mW for valve seat diameters of 1.5 and 2.0 mm, respectively. The power for flow cut-off depends on the channel depth and the diameter of the valve seat in the microvalves.     

Towards a programmable magnetic bead microarray in a microfluidic channel

A new hybrid magnetic bead separator that combines an external magnetic field with 175 μm thick current lines buried in the back side of a silicon wafer is presented. A microfluidic channel was etched into the front side of the wafer. The large cross-section of the current lines makes it possible to use larger currents and obtain forces of longer range than from thin current lines at a given power limit. Guiding of magnetic beads in the hybrid magnetic separator and the construction of a programmable microarray of magnetic beads in the microfluidic channel by hydrodynamic focusing is presented.     

THE FINITE ELEMENT ANALYSIS OF EDDY-CURRENT FIELDS OF A C-TYPE SOLID YOKE BENDING MAGNET

The finite element method developed recent years and used for solving two-dimensional timedependent magnetic fields is introduced.Using this method,we have calculated the eddycurrent fields of a C-type solid yoke bending magnet which is a model magnet of the 800MeV electron storage ring in Hefei.The calculation results are in agreement with measurements.The possibility of applying a solid yoke bending magnet in the case of slow acceleration is discussed.     

Application of nanocrystalline FeHfN soft magnetic films to power inductors

In the communications industry, miniaturization is a requirement for inductor devices. To miniaturize power inductors, high inductance is necessary. To this end, high-permeability FeHfN magnetic films are used to enhance the inductance of power inductors. These nanocrystalline FeHfN soft magnetic films, each roughly 700 nm thick, were deposited onto Si substrates using nitrogen reactive sputtering. In this study, planar sandwiched power inductors containing FeHfN films have a higher inductance than air-core power inductors. Inductance (L) of high-permeability FeHfN films is enhanced significantly by roughly 13% compared with that of air-core inductors at 5 MHz. Integrating power inductors with FeHfN films may increase extra parasitic capacitance. Moreover, the increased eddy current loss is created by the low resistivity of FeHfN films. Therefore, the quality factor (Q) of sandwiched power inductors decreases at 5 MHz. Conversely, saturation current (I_sat) of these planar sandwiched power inductors exceeds 2 A. Such planar power inductors with the high-permeability FeHfN films are a promising candidate for applications in DC-DC converters.