Papers by Keyword: Microvalve

Abstract: This paper presents the design structure of an electrorheological self-amplifying microvalve for electrorheological fluids. This self-amplifying valve can thereby be devided into two main parts, the steering valve and the self-amplifying unit. The first step - combining a conventional electrorheological valve with a self-amplifying unit is one very important aspect and already induced to a promising result in the past. In a next step the conventional electrorheological valve is replaced by an electrorheological microvalve. Smaller dimensions are the final result. The simulation results of the whole system based on measurement results of the electrorheological microvalve are presented in this paper.

Abstract: Over the last ten years, microfluidic technologies have gained considerable importance. However, realising highly integrated microsystems is a major challenge, which so far has only been solved insufficiently. Here, we present an innovative approach to fabricate low-cost, integrable mi- crofluidic platforms. As active elements, photopolymerised hydrogels based on Poly(N-isopropylacrylamide) (PNIPAAm) are introduced. PNIPAAm is temperature-sensitive. Heated in water above its lower crit- ical solution temperature (LCST), it reversibly changes from a swollen to a shrunken state (volume change in the order of 90%) and can, via an electrothermic interface, be employed as electrothermally switchable actuator. Varying specific parameters in the swelling agent, for example varying its alco- hol concentration, can shift the LCST. So not only micropumps or microvalves, but also valves with an appointed threshold value, so-called chemostats or chemical transistors, can be realised. Using the example of a microchip performing enzymatic endpoint analyses, we investigate characteristic be- haviour of active elements based on PNIPAAM and show the ability of integrating different fluidic operations like fluid transportation, metering, valving and mixing into one fully polymeric microchip.

Abstract: The lab-on-a-chip (LOC) technology was expected to influence our every day live in a similarly fundamental way as integrated circuits have. Unfortunately, this demand has not been met yet. The cause therefore lies in the complexity of microelectromechanical systems (MEMS), which form the base of the current LOC technology. We present a new concept of LOC which are based on fluidic microchemomechanical systems (μCMS). During the fabrication process, these μCMS are preprogrammed by monolithic integration of special active components. These active components are holding chemical energy that can be transformed at least once into mechanical energy and thus provide a timed and quantitative exactly defined fluidic function. With our simple and inexpensive fabrication method combined with the above mentioned advantages of the invented μCMS, new and better LOC technology can be developed.

Abstract: A novel ferrofluid-based microvalve adopting an electromagnetic actuation is presented. In the device, ferrofluid controlled by magnetic force is used as a microactuator. The deflection of the diaphragm caused by the ferrofluid-based actuator opens or closes the fluid flow in the microchannel. A detailed description of the design and working principle of the microvalve is presented. The driving force generated by the ferrofluid under applied magnetic field has been measured by a microforce sensor. And the deflection of the diaphragm has been simulated by ANSYS software.

Abstract: This paper reviews several suitable microvalves for polymerase chain reaction (PCR). First, three type micro-valves in PCR chips are discussed, including pneumatic, servomotor-controlled and passive plug microvalves. Then we present our servomotor-controlled microvalves, with the structure of long passive plug. This valve had many obvious advantages such as simple fabrication and operation, perfect sealing, the ability to withstand relatively high pressure. Furthermore, the microvalve can be operated in a self-actuated mode.

Abstract: Electrostatically actuated microvalves are appealing candidates to build fully integrated microfluidic circuits because of the direct transduction of electrical signals into mechanical responses at low power consumption levels. Practical solutions, however, are still lacking due to their multi-layered architecture and difficulties in incorporating heterogeneous materials. In this paper, we report the design and fabrication process of an electrostatically actuated gas microvalve amenable to large scale integration for gas flow control. The device we designed consists of an upper die, containing a flexible electrode sealed by a thin elastic membrane, and a lower die, containing gas channels of trapezoidal cross-section and fixed electrodes. Each microvalve is defined by one fixed electrode spanning the floor and sidewalls of the trapezoidal gas channel and one corresponding flexible electrode suspended above the channel. In contrast to the conventional parallel-plate arrangement of electrodes, the two electrodes are approximated starting from the edges of the trapezoidal gas channel during the actuation step, which is advantageous for lowering the required actuation voltage. The upper die was fabricated by replica molding in polymeric material, the lower die was fabricated in a glass substrate by conventional microfabrication techniques, and the two dies were subsequently aligned and bonded using an adhesive layer. This reported low cost fabrication process could be implemented in any basic microfabrication facility. When a net pressure up to 1 bar was applied to the gas channel, reasonable flow rate was achieved. We also observed displacement of the flexible membrane when a DC voltage of 200 V was applied to a pair of electrodes. These preliminary results show that this microvalve is a promising candidate for integrated on-chip valving and will allow for building large scale microfluidic circuits with reduced power consumption.

Abstract: A glucose sensitive actuator for drug delivery system (DDS) consists of silicon boss, micro channel and outlet of the microvalve.The microchannel is essential to carry liquid samples in the system. In this paper, two types of microchannel, rectangular and trapezoidal, were fabricated using anisotropic etching of Deep-RIE and wet chemical etching using KOH solution, respectively. Fabrication were done for micro channels with cross sectional width of 100 -120µm width and length of 2 mm.

Abstract: Stimuli-sensitive change their volume (equilibrium degree of swelling), mechanical properties (elasticity, stiffness) and molecular transport properties in response to a small change in the properties of the swelling agent, like temperature, solvent composition, pH value, ion concentration, etc. Widespread used smart gels take advantages of the volume phase transition induced by a change of temperature. The temperature of volume phase transition depends on the interaction between gel and solvent. For a gel with defined chemical structure it can be changed by the composition of the swelling agent, e.g. content of salt or organic components. For application, e.g. in MEMS, an easy and controlled stimulation of volume phase transition is required. The degree of swelling (Q) and therefore the dimension of gel structures are determined by temperature. It is possible to regulate Q to a predetermined value by heating/cooling. Thermal energy inside a gel-based device can be easily generated and regulated by incorporated heating resistors and temperature sensors. Different structures (micro-spheres, pads, patterned layers) of smart hydrogels are applied. The switching between two different states of swelling is induced by changes of temperature or by changing the environment. Using the example of gel-based microvalves, sensors, sensor arrays, pumps, and chemostats (concentration control of chemical substances) the sensor-actuator properties and advantages of this group of polymers are discussed.

Abstract: We propose a new PDMS microfluidic system including microvalves and a micropump that are easily integrated on the same substrate with the same process steps. The pumping rate of the fabricated microfluidic system was measured under various frequency and duty-ratio of applied power. The maximum pumping rate of about 26 nl/min is measured under the duty ratio of 1 % at 2 Hz of the applied pulse voltage. The dynamic response of the microvalve in the microfluidic system is measured under the on/off alternation with the applied power of 100 mW.