On developing theory of reservoir computing for sensing applications: the state weaving environment echo tracker (SWEET) algorithm

As a paradigm of computation, reservoir computing has gained an enormous momentum. In principle, any sufficiently complex dynamical system equipped with a readout layer can be used for any computation. This can be achieved by only adjusting the readout layer. Owning to this inherent flexibility of implementation, new applications of reservoir computing are being reported at a constant rate. However, relatively few studies focus on sensing, and in the ones that do, the reservoir is often exploited in a somewhat passive manner. The reservoir is used to post-process the signal from sensing elements that are placed separately, and the reservoir could be replaced by other information processing system without loss of functionality of the sensor (‘reservoir computing and sensing’). An entirely different novel class of sensing approaches is being suggested, to be referred to as ‘reservoir computing for sensing’, where the reservoir plays a central role. In the State Weaving Environment Echo Tracker (SWEET) sensing approach, the reservoir functions as the sensing element if the dynamical states of the reservoir and the environment one wishes to analyze are strongly interwoven. Some distinct characteristics of reservoir computing (in particular the separability and the echo state properties) are carefully exploited to achieve sensing functionality. The SWEET approach is formulated both as a generic device setup, and as an abstract mathematical algorithm. This algorithmic template could be used to develop a theory (or a class of theories) of ‘reservoir computing for sensing’, which could provide guidelines for engineering novel sensing applications. It could also provide ideas for a creative recycling of the existing sensing solutions. For example, the Horizon 2020 project RECORD-IT (Reservoir Computing with Real-time Data for future IT) exploits the SWEET sensing algorithm for ion detection. Accordingly, the terms SWEET sensing algorithm and the RECORD-IT sensing algorithm can be used interchangeably.     

Use of a porous membrane for gas bubble removal in microfluidic channels: physical mechanisms and design criteria

We demonstrate and explain a simple and efficient way to remove gas bubbles from liquid-filled microchannels, by integrating a hydrophobic porous membrane on top of the microchannel. A prototype chip is manufactured in hard, transparent polymer with the ability to completely filter gas plugs out of a segmented flow at rates up to 7.4 μl/s/mm² of membrane area. The device involves a bubble generation section and a gas removal section. In the bubble generation section, a T-junction is used to generate a train of gas plugs into a water stream. These gas plugs are then transported toward the gas removal section, where they slide along a hydrophobic membrane until complete removal. The system has been successfully modeled, and four necessary operating criteria have been determined to achieve a complete separation of the gas from the liquid. The first criterion is that the bubble length needs to be larger than the channel diameter. The second criterion is that the gas plug should stay on the membrane for a time sufficient to transport all the gas through the membrane. The third criterion is that the gas plug travel speed should be lower than a critical value: otherwise a stable liquid film between the bubble and the membrane prevents mass transfer. The fourth criterion is that the pressure difference across the membrane should not be larger than the Laplace pressure to prevent water from leaking through the membrane.     

Simulation and experimental characterization of plug distortion in hybrid microchannels

The plug distortion for on-chip capillary zone electrophoresis systems with rectangular separation channels, manufactured in a hybrid layer system with different material properties of the vertical and the horizontal walls has been examined. Experimental data and simulation results indicate that plug widening caused by different values of the ζ-potential of the walls in contact with the fluid depends strongly on the aspect ratio of the channel cross section. If the height to width ratio is much greater or much smaller than 1, as is often the case for commonly used labchip architectures, plug widening may be negligible. The difference of the ζ-potentials between the vertical and the horizontal sidewalls has been determined from the shape of the plug edges. For an architecture using glass for the top and bottom walls, but SU-8 for the sidewalls, the difference of the ζ-potentials was measured to be on the order of only 2.4 mV for a pH of 9.2, suggesting that such device architectures may be used for on-chip electrophoresis analysis without uniform coating of the channel inside for less-demanding applications.     

A portable,hand-powered microfluidic device for sorting of biological particles

Manually hand-powered portable microfluidic devices are cheap alternatives for point-of-care diagnostics. Currently, on-field tests are limited by the use of bulky syringe pumps, pressure controller and equipment. In this work, we present a manually operated microfluidic device incorporated with a groove-based channel. We show that the device is capable to effectively sort particles/cells by manual hand powering. First, the grooved-based channel with differently sized polystyrene particles was characterized using syringe pumps to study their distributions under various flow rate conditions. Afterward, the particle mixtures were sorted manually using hand power to verify the capability of this device. Finally, the manually operated device was used to sort platelets from peripheral blood mononuclear cells (PBMCs). The platelets were collected with a purity of ~ 100%. The purity of PBMCs was enhanced from 0.8 to 10.4% after multiple processes which results in an enrichment ratio of 13.8. During the process of manual hand pumping, the flow fluctuation caused by unstable injection will not influence the sorting performance. Due to its simplicity, this manually operated microfluidic chip is suitable for outfield settings.     

A two-stage electrophoretic microfluidic device for nucleic acid collection and enrichment

Sample purification and enrichment is an important and usually time-consuming step for on-chip nucleic acid detection and analysis. This paper presents an electrophoretic DNA focusing method in microfluidic devices to enrich nucleic acid concentration by around 2700-fold. The electrical waveforms applied to five individual electrodes are such designed that DNAs move successively to the collection electrodes at high speed, while the interferences from bubbles due to electrohydrolysis are minimized. In a spiral channel with a total length of 48 cm, 1 ml DNA sample is purified and enriched by 57 times at a flow rate of 30 μl/min at first. The captured DNAs are then released and transported to the second microfluidic chamber where DNAs are collected and concentrated by 49 times. Thus, in about 40 min, the two-stage device can extract DNAs from 1 ml sample volume and enrich its concentration by 2790-fold. A trade-off exists between the process throughput and the DNA collection efficiency. A DNA capture efficiency of 99.7 % is reached when the flow rate is 1 μl/min, and the maximum DNA capture throughput is achieved at a flow rate of 30 μl/min. As a platform technology, the device can be integrated into bio-sensing and genetic analysis assays for DNA extraction and pre-concentration.     

Experimental and computational study of gas bubble removal in a microfluidic system using nanofibrous membranes

This paper presents a simple and efficient method for removing gas bubbles from a microfluidic system. This bubble removal system uses a T-junction configuration to generate gas bubbles within a water-filled microchannel. The generated bubbles are then transported to a bubble removal region and vented through a hydrophobic nanofibrous membrane. Four different hydrophobic Polytetrafluorethylene membranes with different pore sizes ranging from 0.45 to 3 μm are tested to study the effect of membrane structure on the system performance. The fluidic channel width is 500 μm and channel height ranges from 100 to 300 μm. Additionally, a 3D computational fluid dynamics model is developed to simulate the bubble generation and its removal from a microfluidic system. Computational results are found to be in a good agreement with the experimental data. The effects of various geometrical and flow parameters on bubble removal capability of the system are studied. Furthermore, gas–liquid two-phase flow behaviors for both the complete and partial bubble removal cases are thoroughly investigated. The results indicate that the gas bubble removal rate increases with increasing the pore size and channel height but decreases with increasing the liquid flow rate.

     

A disposable electrochemical immunofiltration test strip for rapid detection of α-fetoprotein

A disposable electrochemical immunofiltration test strip for the rapid detection of α-fetoprotein (AFP) was developed. The test strip was constructed by assembly of screen-printed carbon electrodes, absorption-water pad, nitrocellulose membrane modified by anti-AFP antibody and glass fiber membrane conjugated with ferrocene monocarboxylic acid (FC) labeling AFP. The analytical system utilizes flow-through immunofiltration and competitive immunoassay techniques in combination with an amperometric sensor. The parameters affecting the immunoassay such as selection of filter membrane, membrane pore-size, and antibody binding capacity were investigated and optimized. The immunofiltration system allows us to specifically and directly detect AFP in serum with a low detection limit of 6 ng/mL. The working range is from 6 to 500 ng/mL with an overall analysis time of 5 min for one sample. This electrochemical immunoassay system enabled us to construct a novel point-of-care testing device for the monitoring of biomarker including AFP.     

ICSSSS: An intelligent channel selection scheme for cognitive radio ad hoc networks using a self organized map followed by simple segregation

In Cognitive Radio Ad Hoc Networks (CRAHNS), several spectrum bands with different channel characteristics may be available over a large frequency range. It is essential to identify the most appropriate spectrum band correctly which allow the Secondary Users (SUs) to exploit the band without disturbing the Primary Users (PUs). Many channel selection solutions, based on cooperative spectrum sensing, have been employed for this purpose depending on their prediction models for primary users’ activities. In practice, cooperative spectrum sensing cannot completely solve the sensing problems which are false alarm and miss detection, especially in heavily shadowed or fading environment. This paper presents, ICSSSS, as an Intelligent Channel Selection Scheme for cognitive radio ad hoc network using Self organized map followed by simple Segregation. The contribution of the proposed scheme is twofold: using an unsupervised learnable Self Organizing Map (SOM) method to efficiently minimize the probability of the sensing errors (false alarm and miss detection), in addition to segregated channel selection strategy to speed up the search for the available best channel. Simulation results based on NS2 simulations show that the proposed scheme can be used with the advantage of better performance than other existing channel selection strategies.     

A fast microfluidic mixer based on acoustically driven sidewall-trapped microbubbles

Due to the low Reynolds number associated with microscale fluid flow, it is difficult to rapidly and homogenously mix two fluids. In this letter, we report a fast and homogenized mixing device through the use of a bubble-based microfluidic structure. This micromixing device worked by trapping air bubbles within the pre-designed grooves on the sidewalls of the channel. When acoustically driven, the membranes (liquid/air interfaces) of these trapped bubbles started to oscillate. The bubble oscillation resulted in a microstreaming phenomenon—strong pressure and velocity fluctuations in the bulk liquid, thus giving rise to fast and homogenized mixing of two side-by-side flowing fluids. The performance of the mixer was characterized by mixing deionized water and ink at different flow rates. The mixing time was measured to be as small as 120 ms.     

Fabrication of the cyclical fluid channel using the surface acoustic wave actuator and continuous fluid pumping in the cyclical fluid channel

A surface acoustic wave (SAW) device has been reported as a micro fluid device such as a pump of a water droplet so far (Renaudin et al. in μTAS, pp 599–601, 2004, 1:551–553, 2005; Sritharan et al. in Appl Phys Lett 88:054102, 2006; Wixforth in Anal Bioanal Chem 379:982–991, 2004; Yamamoto et al. in μTAS, pp 1072–1074, 2005). The SAW device is an interdigital transducer (IDT) fabricated on the piezoelectric substrate only. IDTs are advantageous in terms of integration, miniaturization, free position setting on the substrate and simple fabrication process because of their simple structure. Therefore, the SAW device is easy to apply to integrated chemical system such as lab-on-a-chip. The SAW drives the liquid homogenously by the transmission of surface vibrations of the substrate. Thus, both ends of the channel for pressure loading are not necessary to pump the liquid by using the SAW. The SAW can pump the liquid in both of a closed channel and an opened channel, although continuous flow pumping using an external pump is difficult for no loading pressure in the closed fluid channel. In this paper, we proposed and fabricated the micro fluid devices combined cyclical fluid channel and SAW actuator for liquid pumping. This device is fabricated on a piezoelectric substrate (LiNbO₃) with UV photolithography and wet etching. Structure material of cyclical fluid channel is epoxy photoresist SU-8 100. Then, it is demonstrated to continuous flow pumping and reciprocal flow pumping in the channel. As a result of optimization of a SAW pump’s structural parameter, 32.5, 71.3 and 108.0 mm/s are achieved in the 500, 1,000 and 2,000 μm channel width as a maximum flow velocity.     

Gas�Cliquid flow stability and bubble formation in non-Newtonian fluids in microfluidic flow-focusing devices

This communication describes the gas–liquid two-phase flow patterns and the formation of bubbles in non-Newtonian fluids in microfluidic flow-focusing devices. Experiments were conducted in two different polymethyl methacrylate (PMMA) square microchannels of, respectively, 600 × 600 and 400 × 400 μm. N₂ bubbles were generated in non-Newtonian polyacrylamide (PAAm) solutions of different concentrations. Slug bubble, missile bubble, annular and intermittent flow patterns were observed at the cross-junction by varying gas and liquid flow rates. Gas and liquid flow rates, concentration of PAAm solutions, and channel size were varied to investigate their effect on the mechanism of bubble formation. The bubble size was proportional to the ratio of gas/liquid flow rate for slug bubbles and could be scaled with the ratio of gas/liquid flow rate as a power–law relationship for missile bubbles under wide experimental conditions.     

煤矿井下主排水自动控制系统的应用

针对目前煤矿井下主排水系统人工控制方式存在的工序繁琐、耗能大等问题,提出采用主排水自动控制系统实现对井下水泵的自动控制;介绍了主排水自动控制系统的结构功能及其在花山煤矿的应用情况,详细介绍了系统的器件选型及水泵自动控制流程。该系统采用PLC作为控制核心,采用各种传感器采集排水管道及水泵电动机的参数,实现了对水泵运行状态、运行过程的自动检测和自动控制,减轻了工作人员劳动强度,降低了水泵运行成本。     

基于大数据分析的低频电磁信号光纤传感检测装置设计

为了提高低频电磁信号光纤传感检测能力,提出一种基于大数据分析的低频电磁信号光纤传感检测装置,采用光纤传感器进行低频电磁信号采集,构建低频电磁信号的时频特征分析模型,提取光纤传感检测的低频电磁信号谱特征量,采用大数据融合方法进行光纤传感检测的低频电磁信号谱特征融合,构建光纤传感检测的低频电磁信号时频分解模型,采用快速分数阶傅里叶变换实现低频电磁信号光纤传感检测和噪声分离,结合盲源检测结果,提高对低频电磁信号的光纤传感检测能力。仿真结果表明,采用该方法进行低频电磁信号光纤传感检测的准确性较高,联合感知能力较强,信号的主瓣展宽较高,说明检测的抗干扰性较好。     

A biocompatible Parylene thermal flow sensing array

A microelectromechanical systems (MEMS) thermal flow sensing array constructed of biocompatible materials has been designed, fabricated, and tested. In addition to the construction, the electronic biasing conditions were selected such that sensor operation was compatible with biological fluids. The device comprises several thin film platinum sensing elements sandwiched in a Parylene C membrane. The membrane is suspended over a bulk-micromachined silicon channel for improved thermal isolation. This sensing array layout permits, for the first time, operation in multiple flow sensing modes using a single device. Multi-mode testing was performed in hot-film, calorimetric, and time-of-flight modes at low overheat ratios. Furthermore, constant current (CC) and constant temperature (CT) biasing methods were explored in hot-film mode. The results of the various testing modes were compared and flow sensing down to 0.5 μL/min has been demonstrated.     

Comprehensive study of hydrogen sensing characteristics of Pd metal–oxide–semiconductor (MOS) transistors with Al0.24Ga0.76As and In0.49Ga0.51P Schottky contact layers

The interesting hydrogen sensing characteristics of two transistors with an Al_0.24Ga_0.76As (device A) and In_0.49Ga_0.51P (device B) Schottky layer are demonstrated and studied. Experimentally, device A shows a lower hydrogen detection limit of 4.3 ppm H₂/air, a higher current variation of 7.79 mA and a shorter adsorption time of 10.95 s in a 9970 ppm H₂/air at room temperature. On the other hand, device B exhibits more stable hydrogen-sensing characteristics at high temperatures. Even at a low concentration of 14 ppm H₂/air the hydrogen sensing properties of device B can be obtained as the temperature increases from 30 to 160 °C. Because the Al_0.24Ga_0.76As and In_0.49Ga_0.51P materials are lattice-matched to the GaAs substrate, the studied devices can be integrated as sensor arrays to obtain superior hydrogen sensing characteristics including higher sensing signals, lower detection limit, shorter response time, and widespread detection and temperature regimes.     

Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly

Recently, a novel SPR sensor with on-chip referencing has been realized. In this sensor, one-half of the gold sensing surface is covered with a high refractive index overlayer of tantalum pentoxide (Ta₂O₅). When polychromatic beam illuminates the sensing surface, surface plasmon resonance in the areas with and without the overlayer occur at different wavelengths. Therefore, the reflected light exhibits two dips associated with SPRs in those two areas. When functionalized properly, one of the areas can be used as a specific sensing channel for detection of specific bio-interactions and the other can act as a reference channel for compensation for background refractive index fluctuations. In this paper we present a new functionalization approach for these mixed architecture chips. The gold side of the chip is functionalized with a mixed self-assembled monolayer of polyethylene oxide (PEO) and biotin terminated (BAT) thiols whereas the Ta₂O₅ side is coated with PEO terminated silanes. The PEO terminated thiols and silanes serve as a protein resistant background, while the biotin terminated thiols are used to bind streptavidin, which in turn immobilizes biotinylated antibodies. Hence, the gold side of the chip is used for the binding and detection of target analytes and the Ta₂O₅ side functions as a reference channel that monitors bulk refractive index changes and temperature drift. We have studied human chorionic gonadotropin (hCG) as a model system, currently detecting down to 5 ng/ml. In addition, we demonstrate the power of the on-chip reference channel for compensating for refractive index changes and eliminating false alarms.     

A high-shear, low Reynolds number microfluidic rheometer

We present a microfluidic rheometer that uses in situ pressure sensors to measure the viscosity of liquids at low Reynolds number. Viscosity is measured in a long, straight channel using a PDMS-based microfluidic device that consists of a channel layer and a sensing membrane integrated with an array of piezoresistive pressure sensors via plasma surface treatment. The micro-pressure sensor is fabricated using conductive particles/PDMS composites. The sensing membrane maps pressure differences at various locations within the channel in order to measure the fluid shear stress in situ at a prescribed shear rate to estimate the fluid viscosity. We find that the device is capable to measure the viscosity of both Newtonian and non-Newtonian fluids for shear rates up to 10⁴ s^?1 while keeping the Reynolds number well below 1.     

基于开关矩阵的多通道信号切换设备研制

为提高多通道信号系统的硬件资源利用率和信道切换效率,使用AD75019型宽信号范围模拟开关矩阵为核心设计了一款信号切换设备;设备支持外接电源和内置电池的双电源供电模式,并可通过触摸式液晶屏完成通道间连接状态的配置,确保了设备使用的便利性和灵活性;同时接口采用了高密度接插件进一步减小了设备的体积和重量,提高了产品的便携性;测试试验证明,信号切换设备实现了 32输入至32输出通道之间任意组合的连接和切换,且配置完成后的通道切换响应时间小于100 ms,使用该设备避免了多通道信号系统中整理线缆和插拔接口的工作,能够显著的提高系统的信道切换效率和配对可靠性,可广泛应用于大型测量、控制和试验系统中.     

Potentiometric characterisation of a dual-stream electrochemical microfluidic device

A microfluidic device is presented with off-chip electrodes residing in a reservoir and connected via micro-capillaries to the Y-shaped microfluidic channel. The device is tested by potentiometric measurements involving dual-stream laminar flow of two aqueous solutions carrying different electrolytes at various concentrations. Open circuit potentials are measured for a series of solutions of alkali metal chlorides and tetraalkylammonium chlorides as well as for dilute hydrochloric acid. The open circuit potential for the microfluidic chip was calculated by taking into account the diffusion potential at finite ionic strength as well as the potential difference introduced by the reference electrode system. The liquid junction potential developed at the boundary of the co-flowing aqueous solutions may be manipulated to have greater or lesser relative contributions to the measured open circuit potential based on use of electrolyte salts having cation and anion pairs of similar or dissimilar mobilities in solution. A reasonable agreement between theoretical and experimental values of the open circuit potential is observed for these situations. The results show that simple microfluidic structures possess a rich environment for exploration and application of the solution chemistry of ions.     

新型双并联电渗微泵的制备与测试

设计了一个双并联电渗驱动泵,它由三条并联的主通道和叉指型电极两部分组成,其中每条主通道由若干个与电渗流形成方向成45°角的沟槽并联构成。通过选用ITO载玻片作为芯片基底并获得其最佳工艺参数,制作了带电极的PDMS-玻璃微流控芯片。最后对制作的电渗微泵进行测试,通过记录一段时间内单个主通道泵输送液体的体积,得出单个主通道的流速与微泵总流速。实验发现在5V内,微泵泵送液体的能力随着电压的增加而增大,微泵流速可以达到正常人体眼球房水生成速度,该结构在未来房水引流器件制作方面具有潜在的应用价值。