Thin polymer film based rapid surface acoustic wave humidity sensors

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) thin films, deposited on the surface of glass slides, were studied using transmission FTIR spectroscopy upon varying relative humidity (RH) from 2 to 70%. The obtained data revealed fast dynamics of water vapor adsorption-desorption with responses on the order of several seconds. Based on the fast FTIR signal intensity changes versus RH, it was proposed that a similar rapid response can be achieved for PVA and PVP coated SAW devices due to changes in mass-loading and film viscoelastic properties upon absorption of water vapor in the films. Sub-micron thickness films were spin-coated onto the surface of LiNbO₃ SAW substrates. Both PVA and PVP based humidity sensors revealed prompt reversible response to variations in humidity, although PVP-based device demonstrated better sensor parameters with total insertion loss variation of about 50 dB over the studied RH range and response time 1.5 s for the humidity step 5-95% (recovery time - 2.5 s), representing one of the fastest SAW-based humidity sensors reported to date.     

Embedding off-the-shelf filter in PDMS chip for microbe sampling

Filtration for microfluidic sample-collection devices is desirable for sample selection, concentration, preprocessing, and manipulation, but microfabricating the required sub-micrometer structures is an elaborate process. This article presents a simple method to integrate filters in polydimethylsiloxane (PDMS) devices to sample microorganisms in aqueous environments. An off-the-shelf membrane filter with 0.22-μm pores was embedded in a PDMS layer and sequentially bound with other PDMS channel layers. No leakage was observed during filtration. This device was validated by concentrating a large amount of biomass, from 15 × 10⁷ to 3 × 10⁸ cells/ml of cyanobacterium Synechocystis in simulated sample water with consistent performance across devices. The major advantages of this method are low cost, simple design, straightforward fabrication, and robust performance, enabling wide-utility of chip-based devices for field-deployable operations in environmental microbiology.     

Comparison of surface plasmon resonance spectroscopy and quartz crystal microbalance for human IgE quantification

Surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) have been known independently as surface sensitive analytical devices capable of label-free and in situ bioassays. In this study a SPR device and a 10 MHz QCM sensor are employed for the study of human IgE and anti-human IgE-binding reactions upon immobilizing the latter on the gold electrodes. The SPR and QCM response curves to the antibody immobilization and antigen binding are similar in shape but different in time scale, reflecting different resonation principles. Through optimization of the anti-human IgE coating, both the SPR and QCM sensors could detect IgE in a linear range from 5 to 300 IU/ml. Although the intrinsic sensitivity of the SPR device is five times of the 10 MHz QCM, the IgE detection sensitivity of the two methods is, however, different only in a factor of 2. The acceptable QCM sensitivity for the IgE detection is attributed to the fact that QCM measures the sum of molar mass of a protein layer and the entrapped water. Although both the devices use open, stand still liquid cell, and all the measurements are performed at room temperature, the SPR reproducibility and reliability are better than QCM, as the QCM frequency is more sensitive to temperature fluctuations, press changes and mechanical disturbances.     

Evaluating one- and two-source energy balance models in estimating surface evapotranspiration from Landsat-derived surface temperature and field measurements

This article compares one- and two-source energy balance (OSEB and TSEB) models in the estimates of surface energy components using Landsat imagery and surface measurements acquired from an experimental field at Yucheng Station in Northern China. Compared to surface measurements, similar performance between the TSEB and OSEB models has been observed for estimated surface net radiation and soil heat flux. The root mean square difference (RMSD) is within 14–39 W m^?2 in both the TSEB and OSEB models. The residual energy (E _R) correction method yields the best agreement in comparisons of the sensible (H) and latent (LE) heat fluxes estimated using both the TSEB and OSEB models to the eddy covariance (EC) system measurements. The TSEB model is shown to greatly outperform the OSEB model in reproducing surface H and LE measurements. Cirrus clouds are likely responsible for the surface temperature retrieved from the enhanced thematic mapper plus (ETM+) sensor being lower than air temperature on days of the year (DOYs) 178 and 218 of 2009. This atmospheric stability is contrary to the unstable atmosphere that the EC measurements observe. If data on these two days are excluded and the E _R correction method is applied, when comparing the estimated H and LE to the EC measurements, RMSD is within 55 W m^?2 in the TSEB model and is larger than 97 W m^?2 in the OSEB model.     

A portable sample concentrator on paper-based microfluidic devices

Microfluidic paper-based analytical devices (µPADs) provide a promising solution for low-cost point-of-care diagnostic applications. However, much work remains to be done in optimizing their design and performance. Accordingly, this study investigates the preconcentration performance of µPADs comprising one, two and three convergent channels, respectively. The performance of the three devices is evaluated experimentally using fluorescein and a fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) sample with an initial concentration of 10^?5 M. It is shown that the single-channel µPAD achieves a 20-fold improvement in the sample concentration in approximately 2 min. By contrast, the double- and triple-channel µPADs achieve preconcentration factors of 60- and 140-fold, respectively. Finally, a portable concentrator device is proposed. The experimental results show that a 100-fold improvement in the FITC-BSA sample concentration can be obtained in approximately 110 s given the use of four 16-V batteries, yielding a practical point-of-care diagnostic device.     

Carbon nanotube based sensors for the detection of viruses

Carbon nanotube biosensors were assembled using a layer-by-layer (LBL) technique exploiting the chemical functionalization on nanotubes to tailor their interactions with viruses and antiviral antibodies. Gold electrodes were patterned in the form of resistors onto a Si/SiO₂ substrate, followed by stepwise LBL assembly to change the resistivity of the channel. Polyelectrolyte multilayer films were prepared by the sequential electrostatic adsorption of poly(diallyldimethylammonium chloride), poly(styrene sulfonate), and functionalized single-walled carbon nanotubes. Viral antibodies were successfully immobilized between the electrodes and the binding of antibodies to the surface was enhanced by coating with poly(l-lysine). An antigen specific to the immobilized antibody was captured on these devices. The coupled antibody-antigen complex changed the conductance of the device and this change was related to the antigen concentration. The two factors affecting the performance of the device were the number of layers and the channel length between the electrodes. We were able to detect conductance change for a viral antigen with a titer of 10² TCID₅₀/ml (50% tissue culture infective dose).     

G2 quasi-developable Bezier surface interpolation of two space curves

Surface development is used in many manufacturing planning operations, e.g., for garments, ships and automobiles. However, most freeform surfaces used in design are not developable, and therefore the developed patterns are not isometric to the original design surface. In some domains, the CAD model is created by interpolating two given space curves. In this paper, we propose a method to obtain a G² quasi-developable Bezier surface interpolating two arbitrary space curves. The given curves are first split into a number of piecewise Bezier curves and elemental Bezier patches each of which passes through four splitting points are constructed. All neighboring elemental patches are G² connected and they are assembled optimally in terms of the degree of developability (the integral Gaussian curvature). Experiments show that the final composite Bezier surface is superior to a lofted one which is defined regardless of the final surface developability.     

一种高速贴片机在线贴装优化方法研究

贴装顺序是影响高速贴片机生产效率的关键因素,为了提高贴片机生产效率,研究多贴片头高速贴片机贴装顺序优化问题,通过吸嘴选择与分配和贴装顺序优化,提出一种在线贴装优化方法。实验以自主研发的高速贴片机为平台,验证优化方法的性能;实验结果表明该方法可以进一步提高高速贴片机的生产效率。     

Creation of single-particle environment by positive dielectrophoresis and liquid dielectrophoresis

Two electrical mechanisms for manipulating particles and fluids, dielectrophoresis (DEP) and liquid dielectrophoresis (LDEP), are integrated in a microfluidic chip for creating the single-particle environment. The fluid is activated by LDEP with a 100-kHz/240-V_pp signal. When the single polystyrene bead approaches the trapping area, positive DEP force is utilized to capture and immobilize the bead. After trapping the bead, the process of liquid cutting and droplet creation is employed to create a droplet containing a single bead by LDEP with a 100-kHz/320-V_pp signal.     

Spin coating of hydrophilic polymeric films for enhanced centrifugal flow control by serial siphoning

In this paper, we implement rotational flow control on a polymeric microfluidic “lab-on-a-disc” platform by combining serial siphoning and capillary valving for sequential release of a set of on-board stored liquid reagents into a common (assay) channel. The functionality of this integrated, multi-step, multi-reagent centrifugal assay platform critically depends on the capability to establish very reproducible, capillary-driven priming of the innately only weakly hydrophilic siphon microchannels made from common poly(methyl methacrylate) (PMMA) substrates. Due to the relatively high contact angle of the native PMMA substrate, it was practically impossible to ensure sequential release of on-board stored reagents using the capillary-driven serial siphon valves. In this work, we demonstrate that spin-coated hydrophilic films of poly(vinyl alcohol) (PVA) and (hydroxypropyl)methyl cellulose (HPMC) provide stable contact angles on PMMA substrates for more than 60 days. The deposited films were characterized using contact angle measurements, surface energy calculations and X-ray photoelectron spectroscopy spectra. The PVA and HPMC films reduced the water contact angle of the PMMA substrate from 68° to 22° and 27° while increasing their surface energies from 47 to 62 and 57 mN m^?1, respectively. On the centrifugal microfluidic platform, the films were validated to enable the effective and reproducible priming of the serial siphon microchannels at low rotational frequencies while ensuring that the in-line capillary valves are not opened until their respective burst frequencies are passed. Furthermore, the biocompatibility of the proposed surface modification method was examined, and the platform was used to run a sandwich immunoassay for the detection of human immunoglobulin G, and its performance was proven to be comparable to dynamic coating using surfactants.     

Estimating net surface longwave radiation from net surface shortwave radiation for cloudy skies

This work addresses the estimation of net surface longwave radiation (NSLR) from net surface shortwave radiation (NSSR) by analysing the Surface Radiation Budget Network (SURFRAD) radiation data under cloudy conditions. A general model is developed to estimate NSLR from the NSSR for cloudy skies with a root mean square error (RMSE) of 23.16 W m^?2 compared with in situ data. The model is applied to AmeriFlux data. The results show that the mean error and RMSE are –2.31 W m^?2 and 29.25 W m^?2, respectively, compared with the measurement of AmeriFlux. To examine the significance of the influence of seasons on the estimated NSLR, the model is proposed as a function of seasonal variation. The results show a slight improvement for winter and spring, whereas a larger error is found for autumn compared with the results obtained by the general model. The influences of land cover and elevation on the model are also investigated. The results show that the model is slightly sensitive to the normalized difference vegetation index (NDVI) and the elevation. The RMSE of the model decreases from 23.16 W m^?2 to 21.04 W m^?2 when the NDVI and the elevation are considered in the model.     

Ink‐jet‐printable phosphorescent organic light‐emitting‐diode devices

Abstract— A novel method for the fabrication of ink‐jet‐printed organic light‐emitting‐diode devices is discussed. Unlike previously reported solution‐processed OLED devices, the emissive layer of OLED devices reported here does not contain polymeric materials. The emission of the ink‐jet‐printed P²OLED (IJ‐P²OLED) device is demonstrated for the first time. It shows good color and uniform emission although it uses small‐molecule solution. Ink‐jet‐printed green P²OLED devices possess a high luminous efficiency of 22 cd/A at 2000 cd/m² and is based on phosphorescent emission. The latest solution‐processed phosphorescent OLED performance by spin‐coating is disclosed. The red P²OLED exhibits a projected LT50 of >53,000 hours with a luminous efficiency of 9 cd/A at 500 cd/m². The green P²OLED shows a projected LT50 of >52,000 hours with a luminous efficiency of 35 cd/A at 1000 cd/m². Also discussed is a newly developed sky‐blue P²OLED with a projected LT50 of >3000 hour and a luminous efficiency of 18 cd/A at 500 cd/m².     

Performances of a broad range of dielectric stacks for liquid dielectrophoresis transduction

Among digital microfluidic techniques, liquid dielectrophoresis (LDEP) is well adapted to displace insulating liquids. One of the current challenges for LDEP concerns the robustness of both the dielectric and hydrophobic coatings (deposited atop the driving electrodes). Indeed, such layers may be exposed to high electric field, during operation. There is a need to optimize this stack of insulating layers to first prevent from their dielectric breakdown, secondly reduce the actuation voltage, and lastly ensure a reproducible and well-controlled droplet-generation process. For the first time, an extensive study is presented in that paper, comparing the performances of more than twenty different dielectric stacks (including SiN, High-K materials, hydrophobic coatings) from micro–nanoelectronics know-how and implemented onto a given LDEP design. This generic design features lateral bumps regularly spaced across coplanar electrodes to generate an array of 30 pL DI water droplets in a single open-plate architecture. The experiments have been carefully analyzed to identify which are the best stacks in terms of efficiency and quality for the LDEP transduction. As a result to that study, we propose a guideline to adjust the dielectric coating properties (thickness, material) depending on the liquids to displace and targeted applications.     

Enhancement of Johnson figure of merit in III‐V HEMT combined with discrete field plate and AlGaN blocking layer

The performance of AlGaN/GaN HEMT is enhanced by using discrete field plate (DFP) and AlGaN blocking layer. The AlGaN blocking layer provides an excellent confinement of electrons toward the GaN channel, resulting very low subthreshold drain current of 10^?8 A/mm. It reveals very high off state breakdown voltage (BV) of 342 V for 250 nm gate technology HEMT. The breakdown voltage achieved for the proposed HEMT is 23% higher when compared to the breakdown voltage of conventional field plate HEMT device. In addition, the DFP reduces the gate capacitance (C_G) from 12.04 × 10^?13 to 10.48 × 10^?13 F/mm. Furthermore, the drain current and transconductance (g_m) reported for the proposed HEMT device are 0.82 A/mm and 314 mS/mm, respectively. Besides, the cut‐off frequency (f_T) exhibited for the proposed HEMT is 28 GHz. Moreover, the proposed HEMT records the highest Johnson figure of merit (JFOM) of 9.57 THz‐V for 250 nm gate technology without incorporating T‐gate.     

Evaluation of feature values of surface electromyograms for user authentication on mobile devices

At the present time, mobile devices, such as tablet-type PCs and smart phones, have widely penetrated into our daily lives. Therefore, an authentication method that prevents shoulder surfing is needed. We are investigating a new user authentication method for mobile devices that use surface electromyogram (s-EMG) signals, not screen touching. The s-EMG signals, which are generated by the electrical activity of muscle fibers during contraction, are detected over the skin surface. Muscle movement can be differentiated by analyzing the s-EMG. In this paper, a method that uses a list of gestures as a password is proposed. And also, results of experiments are presented that was carried out to investigate the performance of the method extracting feature values from s-EMG signals (using the Fourier transform) adopted in this research. \(Myo^{TM}\), which is the candidate of s-EMG measurement device used in a prototype system for future substantiative experiments, was used in the experiment together with the s-EMG measuring device used in the previous research to investigate its performance.     

One-step rapid fabrication of paper-based microfluidic devices using fluorocarbon plasma polymerization

In this work, we demonstrated an all-dry, top-down, and one-step rapid process to fabricate paper-based microfluidic devices using fluorocarbon plasma polymerization. This process is able to create fluorocarbon-coated hydrophobic patterns on filter paper substrates while maintaining the trench and detection regions intact and free of contamination after the fabrication process, as confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. We have shown that the processing time is one critical factor that influences the device performance. For the device fabricated with a sufficiently long processing time (180 s), the sample fluid flow can be well confined in the patterned trenches. By testing the device with an 800 μm channel width, a sample solution amount as small as 4.5 μL is sufficient to perform the test. NO₂ ^? assay is also performed and shows that such a device is capable for biochemical analysis.     

Droplet creation using liquid dielectrophoresis

Dielectrophoresis (DEP) is defined as polarizable particles moving into regions of higher electric field intensity. In liquid DEP (LDEP), a dielectric liquid tends to flow toward regions of high electric field intensity under a non-uniform electric field. This work presents a theoretical model of LDEP based on parallel electrodes. The LDEP force is derived using the lump parameter electromechanical method. The relationship between the minimum actuation voltage and the electrode width is investigated experimentally and theoretically. We also propose a method for creating a 20 nl droplet of deionized water using LDEP. The creation of a water droplet containing 15 μm polystyrene beads is placed at the desired location from a continuous flow driven by LDEP using the developed method.     

Droplets coalescence and mixing with identical and distinct surface tension on a wettability gradient surface

The influence of identical and distinct surface tensions on the coalescence and mixing of droplets after a direct collision on a wettability gradient surface (made from a self-assembled monolayer, SAM technique) was investigated. The results indicate that their mixing is driven sequentially by interior convection and diffusion; the convection endures less than 100 ms but dominates more than 60 % of the mixing. If the stationary droplet has a large surface tension (73.28 mN × m^?1), whether the moving droplet has a large surface tension (73.28 mN × m^?1) or a small surface tension (38.63 mN × m^?1), the mushroom-shaped mixing pattern is generated within the coalesced droplet that enhances the convective mixing and also significantly enlarges the interface for mass diffusion. The mixing index of these two cases was greater than 0.8 at 120 s after the collision. For the cases in which the stationary droplet with a small surface tension collided by the moving droplet with a large surface tension, a mixing pattern with a round-head shape developed, which was insufficient to benefit the mixing. When the stationary and moving droplets both had small surface tension, the moving droplet was unable to merge with stationary droplet and had poor mixing quality due to the small surface Gibbs energy of both stationary and moving droplets. For the collision of droplets of identical surface tension, the surface tension affects the coalescence behavior; for the collision of droplets with distinct surface tension, the coalescence behavior and mixing quality depend on the colliding arrangement of stationary and moving droplets.     

Estimating clear-sky land surface longwave upwelling radiation from MODIS data using a hybrid method

Surface longwave upwelling radiation (LWUP) is one of the four components for calculating the earth’s surface radiation budget. Under the general framework of the hybrid method, we developed linear models for estimating the global 1-km instantaneous clear-sky LWUP from the top-of-atmosphere (TOA) radiance of the Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared channels 29, 31, and 32. Extensive radiative transfer simulations were conducted to produce a large number of representative samples, from which the linear model was derived. The derived hybrid model was first evaluated using ground measurements collected at 15 sites from two networks (SURFRAD and ASRCOP). According to the validation results, the average bias and root mean square error (RMSE) of ?0.55 and 15.76 W m^?2, respectively, were obtained by averaging the mean bias and RMSE for the two networks. Compared to a hybrid method developed by a previous study and the temperature-emissivity method, our linear model had a superior performance.     

Anisotropic thin films formation rate on PEDOT : PSS layer with high azimuthal anchoring

Oriented organic layers have great potential for organic electronics devices because of the unique modification of material properties without extensive chemical synthesis. Such layers can be prepared by wet coating of anisotropic organic molecules on top of specific surface of alignment layer. One of the most important parameter that indicates alignment properties of the surface is the anchoring energy. In this paper, we investigate azimuthal anchoring energy of pure and glycerol‐doped PEDOT : PSS layers and study the influence of the alignment layer preparation on the order parameter of the top wet‐coated oriented organic emitter. We confirm that the azimuthal anchoring energy increase leads to improvement of both dichroic ratio and contrast ratio of polarized emitter layer rod‐coated on top of the PEDOT : PSS. Suggested mechanism of anisotropic emitter formation at wet deposition grounds possibility of linear deposition rate of 2 m/s on top of PEDOT : PSS layer with obtained azimuthal anchoring above >10^?4 J/m².