Shih-Fu Ling

A silicon-on-insulator based micro check valve

In this paper we present a bulk micromachined check valve with very high frequency and extremely low leak rates. The valve is designed to have a hexagonal orifice, a hexagonal membrane flap and three flexible tethers. The three elbow-shaped flexible tethers are used to secure the membrane flap to the valve seat and to obtain large flap displacement in the forward flow direction. A silicon-on-insulator wafer and deep reactive ion etching technology are used to implement this microvalve. A very simple fabrication process has been developed, and only two photolithographic masks are required. Preliminary fluidics testing on a 1.44 mm size check valve was performed. A maximum flow rate (deionized water) of 35.6 ml min−1 was obtained at a forward pressure of 65.5 kPa, and only negligible leakage rate was observed at a reverse pressure of up to 600 kPa. The frequency response of the valve in air was also measured and its first resonance frequency was found at 17.7 kHz.

A digital miniature pump for medical applications

This paper describes the principle, design, control and performance of a novel miniature linear peristaltic pump. Exhibiting dual and bi-directional feed capabilities that allow the simultaneous pumping of two distinct fluids at measured and precise flow rate, the pump consists of two resilient tubes and two directly actuated pumping units. Both of the two flexible tubes are placed in the pumping units in such a way that when a pumping element reciprocates in any direction to collapse one adjacent segment of the tubing, it will release the other adjacent segment of the same tubing at the same time. The two pumping elements reciprocate in a sequence so that fluid in the flexible tubing is continuously pumped in preset direction. For each pumping element, two reflective optical sensors are used to detect its position. Based on the output of the four position sensors, a digital logical control circuit is built for the pump. Experimental results show that this kind of miniature pump has potential applications in portable infusion/suction systems.

A piezoelectric spherical motor with two degree-of-freedom

A novel ultrasonic spherical motor is presented in this paper. With only a single moving part (rotor), the spherical motor is capable of providing two-DOF (degree-of-freedom) motions required for micro-satellite and space robot actuation. The operating principle of the motor is elaborated and an initial prototype was fabricated and tested. The elliptical trajectories of the rotor tip were demonstrated by making use of two MTI Fotonic 2000 displacement probes. The feasibility of the operating principle was verified using a normal ball bearing held on to the top of the rotor, and a fast spinning of the ball-bearing occurs at resonance frequencies of 10.67, 18.9 and 28.9 kHz, respectively. Finally, further improvement issues of the motor are briefly discussed.

Motion control of an electrostrictive actuator

Electrostrictive actuators are a relatively new development in the field of smart material actuators. However, a major deficiency of electrostrictive actuators is their limitation of motion accuracy due to inherent non-linearity and hysteresis. This paper presents a new iterative learning control approach to improve the positioning/tracking accuracy of electrostrictive actuators. In this scheme, the iterative gain is not fixed but variable according to previous trial result and the nominal input/output relationship of the electrostrictive actuator. The convergence to the desired position/trajectory is theoretically proved. The effectiveness ofthis control scheme is experimentally demonstrated through actual positioning and tracking control ofa stacked electrostrictive actuator. The results show that using this variable gain iterative learning control scheme, not only can the stability of precision positioning be obviously improved, but also precise and non-delay tracking can be achieved.

Design of a novel ultrasonic spherical motor

This paper presents a novel ultrasonic spherical motor. With only a single moving part, this spherical motor is capable of providing 2-DOF motions required for micro satellite and space robot actuation. The operating principle of the motor is explicated and an initial prototype was fabricated and tested. The elliptical trajectories of the rotor tip were observed via two MTI Fotonic 2000 displacement probes. The feasibility of the working principle was verified using a normal ball bearing held on to the top of the rotor, and a fast spinning of the ball-bearing occurs at resonant frequencies of 10.67, 18.9 and 28.9KHz respectively. Finally, further improvement issues of the motor are briefly discussed.

Fabrication of PZT microdevices using a high-yield sol-gel process

Piezoelectric micro devices based on lead zirconate titanate (PZT) thin film have received considerable attention because of their wide potential in nanotechnology, biosensors and microelectromechanical systems. Thin film cracking, device short-circuiting and substrate surface degrading are commonly encountered problems for PZT micro device fabrication using chemical solution deposition (or CSD) process. These problems often lead to an extreme low yield (<10%) of fabrication and hinder the integration of piezoelectric components into micro-electromechanical systems. In this work, a new manufacturing method for PZT micro devices is developed for the first time to avoid all these problems. Unlike other modified PZT sol-gel processes, in our process pyrolysised PZT thin film is patterned by wet etching before (rather than after) the high temperature sintering treatment. This new process can tremendously reduce the cracking of thin film and eradicate the diffusion of PZT to those substrate surfaces without Pt buffer layer. The effectiveness of the process is proved by 1) the 100% fabrication yield of a number of PZT micro cantilevers, bridges and platforms, 2) the complete elimination of contaminated surfaces by PZT diffusion.

A ROTARY MICROMIRROR FOR FIBER-OPTIC SWITCHING

We demonstrate a novel rotary micromirror for fiber-optic switching. A very simple fabrication process which uses SOI wafer and DRIE technology has been employed to micromachine this electrotastically actuated vertical mirror. Based on this one-mask process, 2N-switch-architecture crossconnects with all the components, inlcuding optic fiber couplers electrostatic comb drives and reflective vertical mirrors, has been integrally fabricated on a monolithic silicon substrate.

A New Transducer for Rotational and Translational Impedance Measurement

Measurement of rotational frequency response functions (FRFs) is important for a complete description of a dynamic system, as a full description requires consideration of both translational and rotational excitations. However, so far rotational FRFs have usually been neglected from analysis due to the absence of reliable and accurate measurement transducers and methods. This study presents a novel bimorph impedance transducer (BIT), which can accurately and easily measure rotational FRFs as well as translational ones. Through careful design, this transducer is only sensitive to one translational and one rotational degree of freedom (DOF) at a structural point, which are further decoupled from each other through controlling the phase of the electrical excitation supplied to the transducer. To investigate the effectiveness of the transducer, experiments using a one-dimensional beam as a test structure are carried out. The results show that the BIT is accurate in measuring both rotational and translational impedance of elastic structures. The measurement is performed simply by measuring the input electrical parameters of the BIT; consequently the direct measurement of moment/force and linear velocity/angular velocity, which are usually difficult to conduct in experiments, is avoided. As this transducer functions actuating and sensing simultaneously during measurement, the measurement system is also greatly simplified and the accurate driving-point measurement is achieved.

Dynamic testing of micro devices using PZT base excitation

Dynamic testing of micro devices by lead zirconate titanate (PZT) base excitation is presented in this work. Followed with a brief discussion of base excitation principle, the suitability of piezoelectric plate for high bandwidth vibration excitation is revealed. To compare the dynamic testing results based on this method, a 1.21mm (L) by 0.52mm (W) PZT micro cantilever with self-exciting capability is designed and fabricated by a sol-gel process. The fabricated PZT micro cantilever beam is then attached to a 10mm by 10mm by 1 mm piezoelectric plate (PI piezoceramic). A Polytech scanning laser Doppler vibrometer (SLDV) system is used to measure the resonance frequencies and corresponding modal shapes of the micro cantilever beam under the piezoelectric plate base excitation and the PZT micro cantilever self-excitation, respectively. It is found that piezoelectric plate base excitation would be more powerful than self excitation to stimulate the mode shapes of a micro device under testing.

DEVELOPMENT OF AN SOI-BASED MICRO CHECK VALVE

This paper presents a bulk micromachined check valve with very high frequency and extremely low leak rates. The valve is designed to have a hexagonal orifice, a hexagonal membrane flap and three flexible tethers. The three elbow-shaped flexible tethers are used both to secure the membrane flap to the valve seat and to abtain a large flap displacement in the forward flow direction. SOI wafer and DRIE technology are used to implement this micro valve. A very simple farbication process has been developed, and only two photolithographic masks are employed. Preliminary testing on a 1.5 milimeters size check valve shows that a maximum flow rate (DI water) of 35.6ml/min was obtained at pressure drop of 65.5kPa and negligible leakage rate in the reverse flow direction observed at pressure up to 600kPa.