cMUT阵元的声学分析与环形扫描成像

电容式微机械超声换能器(cMUT)具有宽带宽、灵敏度高、机械阻抗低和与电子电路集成制造等优点.由于超声换能器声场设计的好坏决定了成像质量的优劣,为了明确阵元参数与辐射声场的关系,该文对不同的阵元参数进行了计算仿真.与压电陶瓷超声换能器的结构不同,cMUT阵元是由多个电容单元(cell)并联构成.因此分析了cell的半径...     

Membrane capacitive deionization

Membrane capacitive deionization (MCDI) is an ion-removal process based on applying an electrical potential difference across an aqueous solution which flows in between oppositely placed porous electrodes, in front of which ion-exchange membranes are positioned. Due to the applied potential, ions are adsorbed in the electrodes and a product stream with a reduced salt concentration is obtained. Including the membranes in the process has two advantages: first, they block co-ions from leaving the electrodes, thereby increasing the salt removal efficiency of the process, and second, when during ion release a reversed voltage is used, counterions can be more fully flushed from the electrode region, thereby increasing the driving force for ion removal in the next cycle. Here we present pilot-plant experimental data for salt removal in MCDI as function of inlet ionic strength and flow rate. In the subsequent stage of ion release the flow rate is temporarily reduced to zero and the voltage sign reversed. This “stop-flow” operation mode results in a small and concentrated product stream. We present a theoretical process model for MCDI which describes the time-dependent electric current and effluent ion concentration, both during the deionization stage and during the subsequent stage of ion release. The process model describes the MCDI cell as a number of stirred volumes placed in-series, and includes the transport resistance of the ion-exchange membrane and of the stagnant diffusion layer in front of the membrane. Ion storage in the electrodes is described according to the equilibrium Gouy–Chapman–Stern model for the electrostatic double layer.     

Enhanced electrical and mass transfer characteristics of acid-treated carbon nanotubes for capacitive deionization

Capacitive deionization (CDI) has attracted significant attention for the next generation water treatment due to its low energy consumption and environment friendly properties in comparison to widely established methods. For CDI technology to move forward, however, the development of carbon electrodes having superb electrosorption behavior is essential. In this study, we demonstrate the functionalization of carbon nanotubes (CNTs) via acid treatment shows enhanced electrochemical characteristics and effectively improves the wettability of the acid-treated CNTs (a-CNTs) via the addition of oxygen functional groups, leading to a higher electric double layer capacitance. Furthermore, defect formation in a-CNTs increases the conductivity and decreases the mass transfer resistance during CDI operation. CDI measurements confirmed a 270% increase in performance of a-CNTs in contrast to pristine CNTs (p-CNTs), attributable to the improved characteristics outlined above.     

Silicon Nitride Capacitive Chemical Sensor for Phosphate Ion Detection Based on Copper Phthalocyanine – Acrylate‐polymer

In this work, we report the development of a highly sensitive capacitance chemical sensor based on a copper C,C,C,C‐ tetra‐carboxylic phthalocyanine‐acrylate polymer adduct (Cu(II)TCPc‐PAA) for phosphate ions detection. A capacitance silicon nitride substrate based Al−Cu/Si‐p/SiO₂/Si₃N₄ structure was used as transducer. These materials have provided good stability of electrochemical measurements. The functionalized silicon‐based transducers with a Cu(II)Pc‐PAA membrane were characterized by using Mott‐Schottky technique measurements at different frequency ranges and for different phosphate concentrations. The morphological surface of the Cu(II)Pc‐PAA modified silicon‐nitride based transducer was characterized by contact angle measurements and atomic force microscopy. The pH effect was also investigated by the Mott‐Schottcky technique for different Tris‐HCl buffer solutions. The sensitivity of silicon nitride was studied at different pH of Tris‐HCl buffer solutions. This pH test has provided a sensitivity value of 51 mV/decade. The developed chemical sensor showed a good performance for phosphate ions detection within the range of 10⁻¹⁰ to 10⁻⁵ M with a Nernstian sensitivity of 27.7 mV/decade. The limit of detection of phosphate ions was determined at 1 nM. This chemical sensor was highly specific for phosphate ions when compared to other interfering ions as chloride, sulfate, carbonate and perchlorate. The present capacitive chemical sensor is thus very promising for sensitive and rapid detection of phosphate in environmental applications.     

Suppression of pull-in in a microstructure actuated by mechanical shocks and electrostatic forces

This work investigates the effect of a high-frequency voltage (HFV) on the pull-in instability in a microstructure actuated by mechanical shocks and electrostatic forces. The microstructure is modelled as a single-degree-of-freedom mass-spring-damper system. The method of direct partition of motion is used to split the fast and slow dynamics. Analysis of steady-state solutions of the slow dynamic allows the investigation of the influence of the HFV on the pull-in. The results show that adding HFV rigidifies the system, creates new stable equilibria and suppresses the pull-in instability for adequate high-frequency voltages. To illustrate the applicability of the result, a specific capacitive microelectromechanical system consisting of a clamped-clamped microbeam is considered.     

Effect of Mass and Charge of Ionic Species on Spatio‐Temporal Evolution of Transient Electric Field in CCP Discharges

The formation of capacitive sheath and existence of the transition electric field between sheath edge and bulk plasma in RF‐CCP discharge is predicted (PRL 89, 265006 2002); such structures are sensitive to the plasma composition. On the basis of semi‐infinite particle‐in‐cell (PIC) simulation the effect of charge and mass of ionic species on the spatio‐temporal evolution of the transient electric field and phase mixing phenomena in linear and weakly nonlinear regime has been explored. As an important feature, the simulation results predict that the maximum amplitude of the transient electric field decreases with increasing ionic mass and charge; further the sheath width increases with increasing ionic mass while follow opposite trend with increasing ionic charge. The excitation of wave like structures in the transition region and efficient energy transport to the bulk region of CCP discharges in a nonlinear regime has also been predicted. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fullerene derived molecularly imprinted polymer for chemosensing of adenosine-5′-triphosphate (ATP)

For molecular imprinting of oxidatively electroactive analytes by electropolymerization, we used herein reductively electroactive functional monomers. As a proof of concept, we applied C₆₀ fullerene adducts as such for the first time. For that, we derivatized C₆₀ to bear either an uracil or an amide, or a carboxy addend for recognition of the adenosine-5′-triphosphate (ATP) oxidizable analyte with the ATP-templated molecularly imprinted polymer (MIP-ATP). Accordingly, the ATP complex with all of the functional monomers formed in solution was potentiodynamically electropolymerized to deposit an MIP-ATP film either on an Au electrode of the quartz crystal resonator or on a Pt disk electrode for the piezoelectric microgravimetry (PM) or capacitive impedimetry (CI) determination of ATP, respectively, under the flow-injection analysis (FIA) conditions. The apparent imprinting factor for ATP was ∼4.0. After extraction of the ATP template, analytical performance of the resulting chemosensors, including detectability, sensitivity, and selectivity, was characterized. The limit of detection was 0.3 and 0.03 mM ATP for the PM and CI chemosensor, respectively. The MIP-ATP film discriminated structural analogues of ATP quite well. The Langmuir, Freundlich, and Langmuir–Freundlich isotherms were fitted to the experimental data of the ATP sorption and sorption stability constants appeared to be nearly independent of the adopted sorption model.     

Phase Sensitive Alternating Current Polarography: A Chemometric Approach for the Selection of Phase Angles

A method based on the combined use of multivariate curve resolution by alternating least squares (MCR‐ALS) with phase sensitive alternating current polarography (ACP) is proposed to evaluate the phase angle where capacitive current is minimized in a much more accurate way than the visual inspection of ACP signals. The method allows, through the analysis of series of AC polarograms measured at different phase angles out the potential, to distinguish between faradaic and capacitive contributions. Then the angle at which the capacitive current is negligible can be shown and, in some cases, the influence of adsorption on measured currents minimized.     

Optimized design for an efficient 3-dB single-mode Y-junction

A design for a 3-dB single-mode Y-junction has been developed and investigated by the beam propagation method with a purpose of decreasing radiation loss in the case of power dividers. The design has two aspects. The first introduces a general design of the boundaries of the 3-dB Y-junction. The second aspect is the replacement of a strip of the guiding material with a lower refractive index near the branching vertex. The design is optimized for low radiation loss, so the output power is increased by 42% over a conventional design.     

CFD simulation of methane dispersion and innovative methane management in underground mining faces

This study addresses methane dispersion in a mine tunnel with discrete methane sources and various methods to handle it. Air flow behavior and methane dispersion in the tunnel are simulated utilizing the computational fluid dynamics (CFD) approach. Various possible conditions which may occur in a mine tunnel are investigated. Simulation results indicate that methane dispersion inside the mine tunnel is influenced significantly by the number as well as location of the sources and quantity of methane released from each source. Furthermore, application of an innovative flow divider which comprises volumetric flow control and flow director, is investigated. It is found that by properly directing the ventilation flow to the location where methane is accumulating can reduce methane concentration below the safe level. In addition, it is noted that focusing the ventilation flow at a point is more effective as compared to dispersing it at several points. This study provides some new ideas for designing an “intelligent” underground mine ventilation system which can cost-effectively maintain methane concentration below the critical value.