Thien Xuan Dinh

A MEMS-based silicon micropump with intersecting channels and integrated hotwires

This paper presents the development of a gas-jet micropump with different cross-junctions and integrated hotwire. The device is actuated by a piezoelectric lead zirconate titanate (PZT) diaphragm at its resonant frequency. The design focuses on a cross-junction formed by the intersection of the channels and neck of the pump chamber, which allows differences in fluidic resistance and fluidic momentum during each PZT diaphragm vibration cycle and thus enables rectification of the gas without valves. Three different designs were investigated by utilizing the ANSYS-FLUENT software. Simulations and experimental data revealed that the step nozzle structure with anti-choking space has much more advantages than the others. The device has been fabricated by the standard MEMS process, and the tiny hotwire has been realized together with the fluidic network. Experiments have been carried out. At a driven frequency of 7.9 kHz, a flow rate of 5.2 ml min−1 was obtained with an applied sinusoidal voltage of 50 Vp-p. The output voltage on the hotwire was measured to be 130 mV at a constant current of I = 0.1 mA.

Fabrication and Basic Characterization of a Piezoelectric Valveless Micro Jet Pump

A piezoelectric-driven valveless micro jet pump with a novel channel structure has been designed and fabricated. The simple structure micro jet pump consists of a lead zirconate titanate (PZT) diaphragm and flow channels. The design of the flow channels focuses on a cross junction formed by the neck of the pump chamber and one outlet and two opposite inlet channels. This structure allows differences in fluidic resistance and fluidic momentum inside the channels during each pump vibration cycle. To confirm the pump operation, a prototype was fabricated using polymethyl methacrylate as a base plate and a conventional machining technique. Two types of pump with nozzle depths of 0.5 and 0.2 mm were prepared, and the depth effect on the flow rate was investigated. The pump chamber has an 11.8 mm diameter, a 0.5 mm depth, and a volume of 0.055 cm3. The maximum flow rate of 17 ml/min at 400 Pa was obtained when the pump was driven at a resonant frequency of approximately 6 kHz by a sinusoidal voltage of 30 Vp–p.

Design and fabrication of convective inertial sensor consisting of 3DOF gyroscope and 2DOF accelerometer

This paper reports the design, simulation and fabrication of a MEMS fluidic inertial sensor, which integrates three-axis gyroscope and dual-axis accelerometer so that the device can independently detect three components of angular rate and two components of linear acceleration. The gyroscope utilizes jet flow directly created from an integrated micro pump. This simplifies packaging process while maintaining good characteristics of the device. The device was fabricated by standard bulk MEMS technology. Fundamental experiments have been done, the performance of the micro jet-pump was evaluated and the sensitivity of accelerometer was characterized.

A multi axis fluidic inertial sensor

This paper reports on the first time the design, simulation and fabrication of a novel MEMS fluidic inertial sensor, which integrates a new three-axis gyroscope and single-axis accelerometers. The device can independently detect three components of angular rate and two components of linear acceleration at high sensitivity and low power consumption. Compared with previous work, the proposed gyroscope was further optimized for simple packaging while maintaining good characteristics. The sensor was fabricated by standard bulk MEMS technology and the micro jet-pump developed for this device was evaluated by experiments. In inertial measurement applications, the multi axis inertial sensor is more advantageous than a multi single-axis sensors system in terms of directivity or cross-sensitivity because the alignment is now determined by photolithography, and further more, the sensor-to-sensor distance is also eliminated. The fluidic inertial sensor has high shock resistance and high durability in fatigue damage.

Design Study of Multidirectional Jet Flow for a Triple-Axis Fluidic Gyroscope

In this paper, we report the design study of a fluidic device that produces four microjet flows comprising two perpendicular pairs of flow and the application of these jets for an angular rate sensor. The jets were created in a closed fluidic network without a check valve and they can freely deflect in a confined sensing chamber. The formation of the continuous flow in a confined space has been confirmed by experiment. This allows the study to a triple-axis angular rate sensor whose working principle relies on the deflection of a jet in a rotating frame. In this paper, the formation of the jets is considered such that the jets have an axisymmetric property, which is key to overcoming the apparent decoupling and cross sensitivity. The triple-axis angular rate sensor can be designed with only four thermal sensing elements. The transient flow simulation under an applied angular velocity provides a design with small size and minimum number of hotwires, which is beneficial for single-chip development and also maintains compatibility with bulk microfabrication technology. While the sensing performances of the three axes are in the same order of magnitude, the cross sensitivity is two orders smaller than that in the published results. In addition to the inertial sensing application, this paper can be adapted to help researchers quickly develop a prototype or to integrate an inertial sensing component in their own microfluidic, microbio, or lab-on-a-chip systems.

Ion Wind Generator Utilizing Bipolar Discharge in Parallel Pin Geometry

We present a simple and efficient airflow generator utilizing the effect of ion wind by generating simultaneously both the positive and negative ions from two sharp electrodes mounted parallel to each other. The unique bipolar geometrical setup eliminates the effect of space charge by the high recombination rate of oppositely charged ions. The two-electrode arrangement is symmetrical, where the electrode creating charged ions of one polarity also serves as the reference electrode to establish the electric field required for ion creation by the opposite electrode, and vice versa. Unlike the conventional setup, with a single electrode generating ion wind with movement toward the reference electrode, in this configuration the air movement is parallel to the electrodes, and is directed away from the device. The airflow behavior is studied by both experiments and numerical simulation. The ion wind speed has a linear relationship with the square root of the discharge current, U ∝ √I, and its measured values agree well with simulation. The characterization of the discharge current-voltage relationship was derived from mathematical processing in the general form I = b(V - Vo)n. The ion wind speed and the current-voltage characteristics depend on the interspace between the electrodes and the electrode geometry. An ion wind speed on the order of ms-1 is created with a microampere discharge current, resulting in a total net charge of only several femtoampere. The proposed configuration is beneficial in minimizing the power consumption of the system, and in enabling air recirculation for airflow control applications, cooling applications, propulsion technology, and micropump design, especially for the applications where neutralized ion wind flow is required.

A Fully Integrated MEMS-Based Convective 3-DOF Gyroscope

This paper presents the concept, design and simulation of the first 3-DOF convective gyroscope, which can detect three components of applied angular rate independently. The working principle of this gas gyroscope is based on forced convection heat transfer and thermoresistive effect. The design, flow simulation, and sensitivity analyses have been done. Optimization in terms of sensitivity and stability was taken into account. The simulated sensitivities of the sensor for the X-axis, F-axis and Z-axis are SFx = 1.9 muV/degs, SFy= 1.1muV/degs, SFZ= 0.4 muV/degs, respectively, with power consumption of 5.4mW. The proposed fabrication process and some preliminary results will be introduced.

A micromirror with CNTs hinge fabricated by the integration of CNTs film into a MEMS actuator

This paper reports a robust fabrication process to integrate carbon nanotubes (CNTs) film into a micro electromechanical systems actuator by the design and fabrication of a silicon micromirror supported by CNTs hinges. Vertically aligned single wall carbon nanotubes forest film was synthesized by water-assisted chemical vapor deposition. CNTs film was then condensed, manually maneuvered and patterned by EB lithography to form a flexible hinge of a mirror. The mirror is actuated by a electrostatic angular vertical comb actuator and the performance had been characterized. The mirror could be driven by a low voltage with a rotate angle of 1.5° and a response frequency of 500 Hz.

A Principle to Generate Flow for Thermal Convective Base Sensors

This paper presents a thin millimeter-scaled device that can generate a closed flow within itself with a velocity of the order of a few m/s. The device comprises a piezoelectric pump with a PZT membrane, housing chamber, and a closed network channel connected to the housing chamber through a specific throat. We investigate the device by computational fluid dynamics. This device is used to produce several free jet flows depending on the structure of the network channel. In this study, four jet flows comprising two perpendicular pairs of flows are demonstrated. If the PZT membrane vibrates within a suitable range, the self-similarity of the axial velocity (along the jet direction) to the cross distances scaled by the half-widths of the jet is observed for a certain range of axial distance. Each jet flow can bend almost freely in three dimensions. The two remaining flow components are small as compared to the axial component. The device potentially has wide applications in flow-based sensors.

Piezo-resistive and thermo-resistance effects of highly-aligned CNT based macrostructures

Recent advances in assembling Carbon NanoTubes (CNTs) into macrostructures with outstanding properties, such as high tensile strength, high conductivity and porosity, and strong corrosive resistance, have underpinned potentially novel applications. For example, in advanced electronics, bioengineering and nanomechanics. This paper focuses on the development of (i) the piezoresistive polydimethylsiloxane–CNT (PDMS–CNT) composite membrane, and (ii) the thermo-resistive CNT hotwire using a technique of producing highly aligned CNT yarns and films. Our experimental results show that while PDMS–CNT films possess an outperformed gauge factor (10.7) compared with ones of CNT films in recent publications and several metals, a clear linear relationship of the resistance versus the temperature for a hotwire using CNT yarn is observed. Hence, the work supplies valuable evidence in the use of CNT films and yarns in several potential applications as thermal sensing elements and anemometric hotwires, respectively.