Fei Tang

Separation of Ions from Volatile Organic Compounds Using High-Field Asymmetric Waveform Ion Mobility Spectrometry-Mass Spectrometer

A combination of high-field asymmetric waveform ion mobility spectrometry (FAIMS) with mass spectrometer (MS) was analyzed. FAIMS separates ions from the volatile organic compounds in the gas-phase as an ion-filter for MS. The sample ions were created at ambient pressure by ion source, which was equipped with a 10.6 eV UV discharge lamp (A = 116.5 nm). The drift tube of FAIMS is composed of two parallel planar electrodes and the dimension is 10 mm × 8 mm × 0.5 mm. FAIMS was investigated when driven by the high-filed rectangular asymmetric waveform with the peak-to-peak voltage of 1.36 kV at the frequency of 1 MHz and the duty cycle of 30%. The acetone, the butanone, and their mixture were adopted to characterize the FAIMS-MS. The mass spectra obtained from MS illustrate that there are ion-molecular reactions between the ions and the sample neutral molecular. And the proton transfer behavior in the mixture of the acetone and the butanone is also observed. With the compensation voltage tuned from −30 V to 10 V with a step size of 0.1 V, the ion pre-separation before MS is realized.

Simulation Research on Micro-Cavity Flow Field Characteristics of Liquid Floating Rotor Gyro

The liquid floating rotor gyro is a gyroscope using electrostatic or electromagnetic forces to levitate rotor, and filling rotor-stator cavities with liquid in order to improve stability of motion. Under influence of the relative surface roughness, rotor velocity, dimension of flow field and fluid nature, flow characteristics of cavity flow field vary under different boundary conditions and geometrical conditions. This paper adopts three-dimensional model and periodic boundary conditions to conduct numerical modeling on cavity flow field. Its results show that, with velocity rising, distribution of flow field speed and pressure manifests partial fluctuations in turbulent-flow-intensive area; resistance torque amid rotor rotation is nonlinearly correlated with velocity, whose rules can be obtained through high-order curve fitting.

Negative Corona Discharge Ion Source Under Ambient Conditions with Mini Line-cylinder Electrodes

A novel ambient negative corona discharge ion source with mini line-cylinder electrodes is designed. The diameters of inner and outer electrode are 0.16 and 4 mm respectively. With a special assembly method, a perfect coaxiality of the two electrodes is obtained. An injection system utilizing a temperature control technique, achieves a constant and stable concentration of the sample, which is critical to the experiment. The formulas of the corona onset voltage of line-cylinder electrodes are also introduced. The experiment results show that negative substances such as formic acid and acetic acid can be ionized under ambient conditions. When combined with micro electrical mechanical system fabrication process, the volume of the ion source can be reduced dramatically, but there is an undesirable surface discharge. To solve the surface discharge problem, an improved structure was designed and tested. The simplicity of the interface of the ion source makes it suitable for mass spectrometer, micro mass spectrometer, ion mobility spectrometer, and high-field asymmetric waveform ion mobility spectrometer applications.

A study on the deep etching and ohmic contact process of 6H-SiC high-temperature pressure sensor

In all the process steps of manufacturing high-temperature pressure silicon carbide sensors, deep etching and ohmic contact are two crucial processes. Reactive ion etching is used for the deep etching of silicon carbide in our experiment, and the surface has a high quality after etching. Using nickel as the mask material on the C layer by electroplating, the depth of deep etching reaches about 81u2009µm and the thickness uniformity is fairly good, fluctuating within 200u2009nm or less. The Ti–TiN–Pt system is proposed for metallization, in which Ti, TiN and Pt are used as the contact layer, the diffusion impervious layer and the lead interaction layer, respectively. The Kelvin test shows that stable ohmic contact is achieved and a specific contact resistivity of 8.42 × 10−4Ωu2009cm2 is detected. The etching depth of 81u2009µm meets the requirement of forming a sensitive circular membrane, and the metal system of Ti–TiN–Pt ensures reliable connection and stable ohmic contact between the metal and semiconductor at high temperatures.

Design of 6H-SiC High Temperature Pressure Sensor Chip

Over the last decade, a relatively in-depth research on the different structures and types of the full SiC pressure sensors including the piezoresistive, the capacitive and the optical SiC pressure sensors etc. has been conducted with a view to realizing the pressure measurement in high temperature circumstances. The piezoresistive SiC pressure sensor has gradually become the focus of research due to its simple structure and convenience application. In our research, the piezoresistance strip is designed on the deep-etching sensitive circular diaphragm formed via deep etching. Firstly, the 6H-SiC strain coefficient GF value is compared on the radial direction and the transverse direction by analyzing the circular diaphragm deformation theory. It’s concluded that both in the radial direction, four resistance strips are assigned in the center of circular diaphragm and along the edge respectively, with equal number on these two locations. Better consistency and sensitivity are achieved by this solution. Secondly, the design size of the sensitive circular diaphragm and the pressure resistance strips are determined with the expected work temperature and the target measuring range being taken into consideration. The final layout scheme design of four pressure resistance strips is determined through simulation on the consideration of the thermal stress caused by the AlN packaging.

Experimental Research on Lift up and Drag Reduction Effect of Streamwise Travelling Wave Wall

Travelling wave wall used for Micro Air Vehicle flow control is studied to find out its drag reduction effect. Aerodynamic characteristics of the airfoil with and without a streamwise travelling wave on its surface are calculated. The interrelationship is also analyzed among lift, drag and ratio of motion phase speed to the external flow velocity. The flexible airfoil that can generate streamwise travelling waves is realized via electromagnetic coil actuation. Thirty-six coils are placed streamwisely under heat shrink film and magnets producing magnetic field are placed under coils. Every single coil is controlled by current to move vertically in harmonic motion with 30 degrees phase difference between adjacent ones. So heat shrink film is actuated, and streamwise travelling wave is generated. Meanwhile, a prototype is designed and tested in wind tunnel. The experimental aerodynamic data proves that streamwise traveling wave airfoil can increase lift and reduce air drag.

Generation and Application of the Atmospheric Pressure DC Glow Discharge Using Minor Electrodes under N2 Flow

A new discharge system which can generate stable atmospheric pressure DC glow discharge is reported in this paper. The system is made up of an inner line electrode and an outer cylinder-like electrode. The radii of the inner and outer electrodes are only 0.08 and 2 mm, respectively. The transition from corona discharge to glow discharge is observed. The experiments show that the discharge has typical features of normal glow discharge and can produce nonthermal plasma. It has been used as an ambient ion source, and chemicals such as formic acid, acetic acid, phenol, and benzoic acid can be ionized well.