Xiongying Ye

Passive valves based on hydrophobic microfluidics

Fluid-surface interactions can become dominant in microfluidics, which is a central technology in a number of miniaturized systems for chemical, biological and medical applications. In this paper, two kinds of hydrophobic valves in microfluidic applications were presented. One is based on special geometrical designs and chemical modification for silicon dioxide and glass microchannels. Silicon dioxide and Pyrex glass surfaces, which are hydrophilic originally, are modified with octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) to be hydrophobic, with the contact angles up to ∼102 and 103°, respectively, for water. The formation of OTS SAMs takes <5 min. The OTS SAMs based stop valve can function well to enable stopping the flow of a liquid inside a microchannel in both directions. Tested for deionized water, the hydrophobic valve blocked successfully the liquid for many consecutive times and yielded pressure barrier up to ∼490 Pa, which is near to the theoretical prediction. The OTS SAMs, therefore the hydrophobic valve function, can be retained in a suitable environment for a long time and can rebirth conveniently when destroyed. The other kind of hydrophobic valve is based on hydrophobic pattern, which is formed by plasma depositing CHF 3 patterns on the surfaces of silicon dioxide. The hydrophobic CHF 3 patterns (measured for contact angle for water to be 102°) can block the liquid to flow forward. The theoretical analysis and the process design were presented.

A colloid micro-thruster system

Abstract A PCB (print circuit board)-based micro-thruster and a silicon micro-pump are fabricated and integrated into a novel colloid micro-thruster system. The system works on an electrical colloid propulsion principle. A silicon micro-pump is designed and fabricated as the propellant supplying unit of the micro-thruster system, which obtains the maximal volume–flow rate up to 300 μl/min and the minimum down to 10 μl/min, with the flow control precision better than 1 μl/min. The micro-thruster is fabricated with PCB processing technology, which is simpler and cost-cheaper, compared with other micromachining technologies. For the measurement of micro-thrust, an experiment set-up based on vibration test is developed and applied for the thruster system. The primary test results show that the PCB-based colloid micro-thruster can produce controllable thrust up to the order of μN.

Towards micro air vehicle flight autonomy research on the method of horizon extraction

Recently, more and more research has been done on the Micro Air Vehicles (MAVs). Due to the limitation of the size, weight and energy of MAVs, the technologies with sensors on larger aircrafts are not currently available for MAVs. Video-based method is a feasible technique to extract the flight parameter. Pitch angle and roll angle of the MAVs can be extracted based on the horizon in the video images. In this paper, a new robust method to extracting horizon is put forward. The algorithm makes full use of the orientation information of the images. The position and orientation of horizon are obtained in the end. The method cannot only extract the horizon from the fine video images, but also applicable to those unclear images. Compared with the other horizon detection method, the algorithm has less amount of calculations and more robust to the practical situations. The experiment testified that this algorithm is feasible and effective. Our horizon extraction algorithm can correctly identify the horizon in over 99.9% of cases.

A PZT-driven micropump

The design, fabrication and characterization of a PZT-driven micropump is presented in this paper. It consists of a chamber, a membrane, two microvalves and a driving mechanism. The thickness of the micropump membrane is 11 /spl mu/m. The micropump chamber is round with diameter of 5 mm and depth of 0.4 mm. The microvalves made of single crystallite silicon are used on this micropump as flow direction control elements. The dimension of the valve cover is 1.5 mm/spl times/1.0 mm/spl times/7.4 /spl mu/m and dimension of the valve opening is 200 /spl mu/m/spl times/200 /spl mu/m. Its capability of flow is more than 10 ml/min at a pressure level of about 10 kPa. The open pressure in the obverse direction is less than 200 Pa while the leakage of reverse direction is almost zero. The features of the microvalve fit the requirement of the micropump well. When the micropump chamber chip and two valve chips are assembled together as a micropump, this micropump is mounted on a metal base and then the PZT bimorph cantilever is mounted above the micropump membrane. The maximum flow rate of the micropump is 365 /spl mu/l/min under 100 V, 20 Hz square wave power supply and zero pressure fall. The back pressure is 2.38 kPa and the flow control precision is better than 1 /spl mu/l.

A magnetic levitation actuator for micro-assembly

The magnetic levitation actuator, which is composed of three layers of silicon structures and a permanent magnet, has been fabricated using micromachining technology and assembled. The top layer consists of a groove and many pairs of small square coils which are used to generate driving forces. The middle layer consists of a groove which composes the moving guide of the permanent magnet with that of top layer. A long rectangle coil is built on the bottom layer, which is used to generate a levitating force. Simulation results show that the magnetic levitation actuator works effectively.

Designing, fabrication, and test of a MEMS colloid thruster

A MEMS based micro colloid thruster (including an source emitter array and an extractor) is designed, fabricated and tested. Source emitter array of the thruster is silicon column etched by ICP. The negative electrode on the extractor can be controlled separately. After bonding together, a single emitter and extractor works on an electrical colloid propulsion principle, and produce µN order thrust. Such a small and controllable thrust is the urgent requirement for a micro-satellite. Thrust test for the micro colloid thruster is made in high vacuum box. Thrust is acted on a cantilever beam, and the displacement of cantilever beam is detected by a current vortex sensor. Analysis to the recording data shows that the maxim thrust produced by a single emitter is about 2 µN, which is agreement with theory estimate.

Design and modeling of a novel micro-displacement sensor based optical frequency comb

Pumping a single-mode, tunable, external-cavity laser to excite the whispering gallery modes (WGM) of micro ring resonators (MRRs), a series of equidistant, wide free spectrum range (FSR) can be observed. Frequency shift of FSR can be used to feedback external changes, making MRR very promising in high-sensitivity sensing. In this paper, a novel displacement sensor composed of a micro ring resonator and a waveguide is presented and a designing route for this sensor is discussed. Based on mathematical analysis and the beam propagation methods (BPM), the major parameters including the geometry of MRR and micro cantilever are investigated in detail. Materials selection and fabrication method under current processing technic are also presented. For the typical structure in this paper, the final Q factor is estimated approximately 103 in theory at the wavelength of 1.5μm.Displacement alteration of cantilever is 0.296x10-6m - 0.535x10-5m approximately corresponding 10-8-10-6N force loading. The shift of transmission spectrum is about 3.9nm versus perimeter of MRR changing 1μm.

A precise measurement of quality factor for Planar Microtoroid Resonators

The quality factor(Q) parameter is the most important parameter for optical micro cavities. In this paper, we present the Planar Microtoroid Resonators fabricated in our laboratory. Then, measuring methods common used are introduced. After that, a precise measurement of quality factor is demonstrated in which the photon lifetime was directly measured by cavity ringdown. This is done by repeatedly scanning the laser into resonance with a mode that was critically coupled to the taper. As the laser scanned into resonance, the power transferred into the cavity increased until the maximal power of the resonant mode was attained. At this moment, an external modulator is used to cut-off the pumping laser. As the resonant power outpouring, a cavity ringdown spectrum is observed and recorded. The cavity lifetime can be obtained through analyzing the spectrum. Finally, the quality factor is estimated from the cavity lifetime which is consistent with the widely used measurement of the frequency line shape.

Design of the miniature optical fiber voltage sensor

Based on the typical microcavity quantum property and integration of the planar microtoroid with ultra-high Q value(about 108), this paper theoretically proposes the design of the micro-optical voltage sensor. The voltage sensor belongs to the field of MOEMS, the entire device is composed of one microtoroid (diameter from 60µm to 120µm) with the ohmic contact in the middle and a fiber taper waveguide. Through contact dot the outside detected voltage is connected with the ohmic contact, as a result of the ohmic contact heat effect, the external voltage signal through the device transforms into a strong frequency shift which is coupled out through the fiber taper waveguide. After that it will be showed on the photoelectric detector and then the voltage value under test could be calculated.

Water vapor detecting using high-Q microcavity

The target of this paper is to design a novel water-vapor sensor used in humidity transducer system based on high-quality factor (Q) spherical microcavities, which at present obtained the highest Q value induced by surface tension. Sensitive mechanics and its high sensitivity are discussed according to optical loss sensitization to coupling system composed of a microsphere cavity and a tapered fiber. After that, fabrication methods of master parts of the sensor in our lab are introduced. Additionally, a sensing structure composed of a gas-chamber and a vacuum-chamber is also designed. According to water absorption band, telecom band around 1550nm is used to pump the microsphere optical mode. In a vacuum environment, a transmitted spectrum is obtained through output end, revealing some information about the core system including the size of the microcavity and the optical loss of the regime. However, when the core system is placed in a water vapor environment, the transmitted spectrum will change due to extra optical loss induced by water molecules absorption, behaving as spectral shift, free spectrum range (FSR) or line width broadening. Contrasting and analyzing two different spectrums in the two situations, the gas concentration can be deduced. Indispensable experiments were also carried out, showing that, the two spectrums are different from resonance hump, formant strength and formant line width. Even an ultra low water vapor concentration induced a measurable output signal, ensuring a high detecting sensitivity. Certainly, the analyted vapor should not only be water vapor. This kind of sensitive mechanics is versatile. Changing the pumping light corresponding to the analyted absorption band, we are able to detect a series of vapor.