Jyh-Jong Sheen

Interlacing Properties for Mass-Dashpot-Spring Systems With Proportional Damping

A mass-dashpot-spring system with proportional damping is considered in this paper. On the basis of an appropriate nonlinear mapping and the root-locus technique, the interlacing property of transmission zeros and poles is investigated if the columns of the input matrix are in the column space generated by the transpose of the output matrix. It is verified that transmission zeros interlace with poles on a specific circle and the nonpositive real axis segments for a proportional damping system. Finally, three examples are given to illustrate the property.

Development and Application of an Alternating-Color Micro-PIV System

In this study, light emitted from red, green, and blue LEDs is adopted as the light source of an alternating-color micro-PIV system for micro flows measurement. The strobe frequency of the LED can easily reach 20,000Hz, which is high enough to provide the time resolution required for most micro flows measurement. A cardioid annular condenser is adopted in the micro-PIV system so that the incident light from the LED is redirected and only the light emitted from fluorescent particles reaches the object lens of the microscope. The image quality is significantly improved. Clear dark background particle images of micro flows are recorded from the proposed LED micro-PIV system. In addition, the diffraction limit of the microscope is improved from half of the wavelength to one-fifth of the wavelength. For alternating-color multiple-exposure image application, a triple-exposure alternating-color image — sequentially illuminated by red, green, and blue LED light — is recorded on a single frame by a color CCD camera. Three unique color images — a blue, a green, and a red image respectively — are obtained from separating the triple-exposure image. With three sequential images available, the velocity, acceleration distributions of micro flow, and different phases of the multiphase flow can be measured from these unique color sequential images. The alternating-color micro-PIV system is then applied to measure micro flow past a cylinder, circulation in a micro-droplet, hydrodynamic focusing sheath flow, and two-phase flow in micro channels. Satisfactory results are obtained for all the flows measured.Copyright

Micro-flows measurement from a LED micro-PIV system

In this study, light emitted from LED is adopted as the light source of a micro Particle Image Velocimetry system for micro-flows measurement. The strobe frequency of LED can easily reach 20,000Hz, which is high enough to provide the time resolution required for most micro-flows measurement. The problem of relative low power of LED is resolved by adopting a cardioid annular condenser in the microscope, so LED light is focused on the micro-flows and image quality is significantly improved; in addition, image resolution is improved from half of wavelength to one-fifth of wavelength. Clear, dark background particle images of micro-flows are recorded from the proposed LED micro-PIV system. The LED micro-PIV system developed is then applied to measure flow past circular cylinder and hydrodynamic focusing flow in micro channels. Satisfactory results are obtained for all the flows measured.

Three-Dimensional Hydrodynamic Focusing With a Circular Microchannel

We propose a simple method to implement three-dimensional (3D) hydrodynamic focusing with a circular micro-channel for the sample flow. We utilized soft lithography technique and a cylindrical object such as an optical fiber to construct a 3D hydrodynamic focusing master mold made of photoresist and the fiber. The 3D microfluidic focusing device can be duplicated by polydimethylsiloxance (PDMS) casting. When peeling the PDMS cast from the master, there is a crack along the circular channel. However, this crack can be recovered from the thermal bonding of the PDMS cast and a PDMS substrate. We applied this technique to fabricate 3D flow-focusing devices for a microfluidic fluorescence detection chip and a micro-emulsion chip. In the case of microfluidic fluorescence detection, the sample flow can form a small and stable cylindrical flow by controlling the flow rates of sheath flow and sample flow. This allows fluorescent particles to be focused at the center of the channel and to be excited uniformly by laser. Experimental results show that the coefficients of variation for 3D hydrodynamic focusing is 4 to 10 times lower than those of 2D hydrodynamic focusing. As a consequence, the 3D focusing chip provides advantages of stable sample flow and highly uniform detection signals. The micro emulsion chip with 3D hydrodynamic focusing can avoid the wetting problem of two immiscible fluids and successfully produce emulsion droplets.Copyright

A Pneumatic Micro Peristaltic Pump With Slanted Membranes

We designed and fabricated a bi-directional micro pneumatic peristaltic pump driven by slanted membranes. Unlike most micro peristaltic pumps with discrete polydimethylsiloxane (PDMS) flat membranes, ours has two opposite slanted PDMS membranes tandem along the fluid channel. Since the thickness of the slanted membrane is not uniform, it will produce continuous and asymmetric deflections under increasing pneumatic pressure. The pumping action is achieved by using one membrane as the driving membrane and the other as a stop valve. The flow direction can be controlled by changing phase difference of two driving square waves. Experimental results show that our peristaltic pump achieves much higher maximum flow rate than that of a micro peristaltic pump with three flat membranes of similar size.Copyright