Papers by Author: Chiang Ho Cheng

Abstract: This paper aims to present the design, fabrication and test of a novel piezoelectrically actuated, check valve embedded micropump having the advantages of miniature size, light weight and low power consumption. The micropump consists of a piezoelectric actuator, a stainless steel chamber layer with membrane, two stainless steel channel layers with two valve seats, and a nickel check valve layer with two bridge-type check valves. The check valve layer was fabricated by nickel electroforming process on a stainless steel substrate. The chamber and the channel layer were made of the stainless steel manufactured using the lithography and etching process based on MEMS fabrication technology. The effects of check valve thickness, operating frequency and back pressure on the flow rate of the micropump are investigated. The micropump with check valve 20 μm in thickness obtained higher output values under the sinusoidal waveform of 120 Vpp and 160 Hz. The maximum flow rate and backpressure are 1.82 ml/min and 32 kPa, respectively.

Abstract: The present research applies the microelectronmechanical system (MEMS) technology to design and fabricate a novel micro-bubble generator by using a piezoelectric actuator. The main structure of the proposed generator adopts an annular piezoelectric ceramic which is coupled with a nickel nozzle plate. In the experiment, a flow visualization setup employs a high magnification microscope and a high speed charge coupled device (CCD) camera to photograph the time evolution of meniscus shape of gaseous bubbles dispensed from the micro-bubble generator. The bubble formation process including the effects of inlet gas pressure as well as driving voltage and resonance frequency on generated bubble size is also discussed in the study.

Abstract: The current paper endeavors to present the design, fabrication, and test of a novel valveless piezoelectrically actuated micropump. The proposed micropump mainly comprises a stainless-steel structured chamber with a piezoelectric (PZT) diaphragm as a driving source to propel liquid stream under actuation. During tests, the micropump, operating at the frequency of 250 Hz and the voltage of 160 Vpp, engendered a mean water flowrate up to 0.779 ml/min. In the analysis, the computational fluid dynamics (CFD) software ACE+® was utilized to examine the time-varying flow phenomenon in a full-scale PZT micropump throughout an actuation cycle. The computational approach adopted the transient three-dimensional conservation equations of mass and momentum with the moving boundary specified to represent the movement of the diaphragm. At the frequency ranging from 150 to 250 Hz, the vortex pairs were evidently formed and thereby caused a relatively high pressure drop near the diffuser outlet inside the micropump chamber. Numerical experiments were also carried out by varying the opening angle of the diffuser/nozzle module within the range of 8°－12°, the angle setting of 8° can provide the best performance in term of the maximum pumping flowrate achieved.

Abstract: A micropump with the function of ejecting droplet is designed and fabricated. It consists of the three components including the PZT actuator, pump body and nozzle plate. The pump body is made of the silicon while the nozzle plate is formed by nickel electroforming. The nozzle plate with single orifice is assembled to the pump body. The micropump is designed with the rectangular pressure chamber and the diffuser as the dynamic passive valve. It is driven by the PZT actuator which deflects the rectangular diaphragm through a bulge on diaphragm. The design of diaphragm with a bulge makes the assembly of the actuator easier and generates sufficient volume displacement. The volume displacement is not only predicted by ANSYS simulation but also verified by 2-dimensional laser scanning vibrometer. And, the prediction and measurement agree to some extent. The ejected droplets are observed by a visualization setup.

Abstract: The droplet formation process of a novel piezo-actuated micro-injector is studied using a computational approach. In simulations, the theoretical model is based on the time-dependent threedimensional conservation equations of mass and momentum. The surface tension effect at the gasliquid boundary is treated using the continuous surface force (CSF) scheme. The volume-of-fluid (VOF) method in conjunction with the piecewise linear interface construction (PLIC) technique is exploited to describe interfacial movements. The time evolution of the droplet meniscus shape is predicted throughout the formation process and compared with Shield's micro-photographed images for the computer package validation. To explore the feasibility of proposed new micro-injector in practical applications, the droplet deformation characteristics are determined in terms of droplet topology, breakup length and time, and flight velocity for dispensing different liquids such as water, anisol, Pedot, PLED, and blood.

Abstract: This paper presents the fabrication and preliminary experimental studies of flow performance on a valveless micro impedance pump actuated by the shear mode PZT actuator, a novel method of pumping fluid on the microscale. The micro impedance pump was constructed of three nickel electroforming components, two glass tubes, a PZT actuator and a glass substrate. The three electroforming components include a bottom structure plate, a channel plate and a top structure plate. The AZ-type positive photoresist was used as the electroforming mould, which was patterned by UV lithography. The top and bottom structure plates were aligned and assembled with the channel plate by epoxy adhesive such that a micro channel with a compressible section coupled at both ends to rigid sections of different impedance was formed. A pressure head can be built up to drive flow through the accumulative effects of wave propagation and reflection originating from the periodic PZT excitation, located asymmetrically along the length of the compressible section of the channel. Experimental results showed that the flow was reversible and pressure heads had a highly non-linear dependence on the frequency and amplitude of the excitation. Maximum flow rates of 13 μl min-1 have been achieved with the channel size of 15μm high and 4 mm wide.