Yi-Chu Hsu

A Portable Micropump System Based on Piezoelectric Actuation

Despite significant efforts to develop micropumps, cumbersome driving equipment means that the design of portable micropumps remains a challenge. This study presents a stand-alone micropump system, which includes a peristaltic micropump based on piezoelectric actuation and a driving circuit. This battery-based driving circuit comprises a 12 V battery, an ATmega 8535 microprocessor, a 12 V-to-180 V DC to DC converter using transformerless technology, three differential amplifiers, an IC 7805, a phase controller, an A/D converter, a keyboard and an LCD module. The system can produce step-function signals with voltages of up to 228 V and frequencies ranging from 10 Hz to 100 kHz, as the inputs for the pump. It is portable and programmable with the package size of 22 cm times 12.8 cm times 9 cm. Additionally, this proposed system is used to design the driving signals of the pump which are 3-, 4, and 6- phase actuation sequences. This work performs the circuit testing and fluid pumping, and demonstrates the effects of actuation sequences on pump performance in terms of the dynamic behavior of the diaphragm, flow rates and back pressure of the system. The experimental results show that the pump excited by the 6-phase sequence results in better performance compared with the 3- and 4-phase sequences, and produces a maximum flow rate of 36.8 mul/min and a maximum back pressure of 520 Pa with deionized water at 100 Vpp and 700 Hz.

Constrained Layer Damping Treatments for Microstructures

This paper presents a bulk micromachining process to fabricate micro-constrained layer treatments (MCLT) on a microstructure to increase its damping, and demonstrates the damping improvement through calibrated experiments. MCLT consists of a silicon base structure (e.g., beams or plates), a viscoelastic photoresist layer, and an aluminum constraining layer. Silicon base beams and plates are fabricated from {100} wafer through Ethylene-Diamine-Pyrocatechol etch and buffered oxide etch. A 4.5-μm thick photoresist AZ4620 is spun on the silicon base beam as the viscoelastic layer. Finally, an aluminum layer is deposited through low-pressure vapor deposition as the constraining layer. To evaluate damping performance of MCLT, silicon beams with and without MCLT are subjected to swept-sine excitations by PZT from 0 to 100 kHz. In addition, a laser Doppler vibrometer and a spectrum analyzer measured frequency response functions (FRF) of the specimen. A finite element analysis identifies the resonance modes measured in FRF. Experimental results confirm that MCLT can increase damping of silicon beams by at least 40%. Significantly better damping performance is expected, if the loss factor of the viscoelastic layer is increased.

A Microfluidic Device for Capture of Single Cells and Impedance Measurement

A microfluidic device for capture of single cells and impedance measurement is presented. The device consists of a PDMS channel with three micro pillars and a glass substrate with electrodes. The experiments demonstrated that the HeLa cell (human cervical epithelioid carcinoma) was successfully captured by the micro pillars and its impedance was measured by impedance spectroscopy. The range of operation voltage is from 0.1 V to 1.5 V and the scan frequency is from 1 kHz to 100 kHz. According to experimental results, the HeLa cell is capacitive and its electrical model can be simplified to the parallel connection with one resistor and one capacitor. This developed technique for cell impedance analysis possesses advantages of physical capture, low cost, and easy of fabrication and measurement.

Fabrication and characterization of 3D aspheric microlenses with arbitrary surface profiles based on a novel excimer laser contour scanning method

This paper presents a new method for fabricating 3D microstructures with an excimer laser micromachining system. A novel mask contour scanning method is developed for obtaining precise 3D microstructures with pre-described continuous surface profile. Five different microlenses with spherical and parabolic surfaces profiles with dimension less than 500 /spl mu/m are fabricated on polycarbonate (PC) samples. The surface profiles are measured and compared with their theoretical counterparts. Excellent agreements both in profile shapes and dimensions are achieved. The surface roughness (Ra) of the machined surfaces is also measured and is less than 10 nm. The machining profile accuracy and surface smoothness of this proposed micromachining method show great potentials in fabricating micro-optic components such as aspheric microlenses or microlens arrays.

Study of 4,4- Dithiodibutyric Acid as a Monolayer for Protein Chip

Despite considerable efforts, the fabrication of protein chips using a self-assembled monolayer (SAM) with a long chain length remains a challenge, due to its steric hindrance and disulfide deposited, which can generate multilayers and block the functional groups of the SAMs, and thus, significantly reduce the sensitivity of the chips. To improve their sensitivity, the feasibility of using a short-chain SAM, 4,4-dithiodibutyric acid (4,4-DTBA), as a monolayer for the protein chips based on a gold surface is studied. Experiments for characterizing 4,4-DTBA are performed by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and ellipsometry. Additionally, the fluorescent assay of 4,4-DTBA is characterized using protein A-FITC (fluorescein isothio cyanate) to investigate its binding capacity. The results of 4,4-DTBA are compared with those of 11-MUA (11-mercapto-undecanoic acid). The comparison results indicate that 4,4-DTBA can be adopted as a monolayer for the protein chips.

Active Vibration Control of Meso- And Microstructures via Piezoelectric Films

The purpose of this paper is to demonstrate the feasibility of active vibration control for meso- and microstrucutres through use of PZT (Lead-Zirconium-Titanium Oxide) thick films. This paper consists of two parts. The first part is to develop a sol-gel process to fabricate crack-free PZT thick films with thickness of 2 microns and area of 4 mm × 4 mm. The PZT thick film has a Pt/Ti bottom electrode and a gold top electrode. Moreover, the PZT thick film is fabricated on a silicon cantilever, whose dimensions are 20 mm × 15 mm × 0.4 mm. The second part is an experimental demonstration of active vibration control using the PZT thick film. In the experiment, a tiny bulk PZT patch is first glued to the silicon cantilever. A function generator drives the bulk PZT simulating a source of disturbance exciting the silicon cantilever. In the meantime, a laser Doppler vibrometer (LDV) measures velocity of the cantilever tip. With a phase shifter as the controller, the LDV measurement is fed back to the PZT thick-film actuator to actively control the cantilever vibration. To evaluate the effectiveness of the active vibration control, a spectrum analyzer measures the frequency response functions (FRF) from the bulk PZT voltage to the LDV response. Experimental results show that the simple active vibration control scheme can reduce resonance amplitude of the first bending mode by 66%.Copyright

Feasibility study of PZT thin-film sensors and actuators for smart microstructures and MEMS devices

This paper demonstrates the feasibility of using PZT thin films as sensors and actuators for smart structures and MEMS applications. The feasibility study includes specimen preparation and vibration testing. The specimen consists of a substrate, a PZT thin film, and a bulk PZT. The substrate is a doped conductive silicon wafer. The PZT thin film is fabricated through sol-gel dip-coating process with added PZT nano-particles to prevent homogeneous crystallization. The thickness of the PZT thin film is about 5 micrometers and the capacitance varies from 90 to 130 pF. The bulk PZT, which is commercially available, serves as a reference sensor and actuator for the specimen. The dimensions of the specimen are 2.7 cmx 1.4 cm . 0.4 mm. The vibration testing consists of sensor testing and actuator testing. In the sensor testing, the PZT thin film serves as a sensor, while the bulk PZT serves as an actuator. The specimen is cantilevered, and harmonic excitations are generated from 500 Hz to 500 kHz. A laser Doppler vibrometer also monitors the specimen vibration in addition to the PZT thin-film sensor. As a sensor, the PZT thin film produces legible harmonic output voltage ranging from 0.5 mV to 200 mV. In the actuator testing, the PZT thin film serves as an actuator, while the bulk PZT serves as a sensor. Similarly, harmonic excitations are generated from 100 Hz to 1 MHz. Depending on the excitation frequency, actuation voltage of the PZT thin film ranging from 0.1V to 100 V results in legible voltage response form the bulk PZT. Also, the PZT thin film experiences significant aging when it serves as an actuator. This might result from fatigue or accumulated defects of the PZT thin film. Finally, the PZT thin film can become nonlinear in sensing and actuation, when the excitation voltage is too high.

Optimum design and investigation on diffuser polymethylmethacrylate (PMMA) peristaltic micropumps

Utilizing micro-electro-mechanical-systems (MEMS) techniques and a solvent-assisted bonding process, a new generation of diffuser peristaltic polymethylmethacrylate (PMMA) micropumps was optimized and fabricated. The main purpose of this study is to compare the performance of optimized and un-optimized micopump which have the same diffuser throat/inlet area (i.e. 16000 µm2). Furthermore, an additional optimized design which has smaller diffuser inlet area was considered to validate and analyze the effect of diffuser inlet area to the micropump performance. The experimental results were validated by comparing with previous generation which had not been optimized the diffuser element. Specifically, the experimental results showed that, with similar diffuser element inlet area (i.e. 160000 µm2), with and without optimized micropumps yield maximum flow rates of 246.4 µL/min and 194.8 µL/min, respectively. Furthermore, it is shown that the back pressure in the optimized micropump is 6.9 kPa, while that in the un-optimized pump is 5.69 kPa. The effect of diffuser element throat/inlet area to pump flow rate and back pressure was investigated by comparing the experimental results of two optimized designs, one with 80 µm × 80 µm and the other with 127 µm × 127 µm cross-sectional area. The results indicated that, the design with larger inlet area gave higher flow rate. However, the rate of reduction in the maximum flow rate with increasing back-pressure increases at the higher inlet area design, which is due to the greater pressure dissipation/loss associated with a larger channel cross-sectional area.

Inertance Effects to Diffuser Micropumps Flow Rate Spectrum

This study presents a diffuser micropump and characterizes its output flow rates, like the parabola shape on the frequency domain and the effecting factors. First, equivalent circuit using fluid-electric analogy was built up; then, the flow rate analysis results were compared to experiment results to verify the applicability of the circuit simulation. The operation frequency was 800 Hz for both cases and the maximum flow rates were 0.078 and 0.075 μl/s for simulation and experiment result, respectively. The maximum flow rate difference was 3.7%. The circuit then was used to analyze the inertial effects of transferred fluid as well as system components to the output flow rates. This work also explains why the flow rate spectrum has the shape of parabola. The analysis results showed that without inertial effects, the micropump flow rates are linearly proportional to the operation frequency; otherwise it has parabola shape. The natural frequency of the actuator-membrane structure was recognized using finite element method to verify if this parameter affects the characteristics of the flow rates. The experiment and simulation results demonstrated 800 Hz and 91.4 kHz for the frequency of the maximum pumping flow rate and the first mode natural frequency of actuator-membrane structure, respectively. It indicates that the structure natural frequencies of the actuator-membrane structure do not play any role to operate the micropumps.Copyright

Development of protein chips based on self-assembled monolayer and protein A

In order to improve the steric hindrances and less ordered structures in the long-chain SAMs, the SAM of 4,4-Dithiodibutyric acid (4,4- DTBA) was investigated to be a thin monolayer for the protein chip. This work presents the feasibility study of 4,4- DTBA as a monolayer of the protein chip based on gold surface. Characterizations of surface topography using atomic force microscopy (AFM), contact angle and fluorescence using protein A-FITC were performed to investigate the binding efficiency for the SAMs of 4,4- DTBA and 11- mercaptoundecanoic acid (11- MUA). The results show that the binding efficiency of 4,4- DTBA is higher than that of 11-MUA. The SAM of 4,4-DTBA can be used as a monolayer for the protein chip and may have a comparable binding efficiency