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Types of actuators used in micro-fluidic applicationselectro-static and thermo-mechanical principles have
been applied to micro-actuation due to the fact that all fabrication processes for these micro-actuators were available from integrated circuit technology
magnetic micro-actuators offer considerable performance advantages, for example large actuation forces, large deflections, low driving voltages resulting from low input impedances, and robustness under harsh environments. However, the fabrication process is technologically challenging for many reasons. In order to achieve high forces, both the electric conductors of the micro-coils and the magnetic flux guide structures need to provide large cross sections to allow for sufficiently high current and magnetic flux, respectively. Problems also originate from the thickness of the dielectric layers serving as both insulation and planarization layers. These features demand high aspect ratio fabrication processes.
synchronous micro-motors In the center of the stator, an SU-8 guidance
structure is integrated for rotor assembling. The rotor composed of alternate polymer magnets inserted in an SU-8 mold. These magnets are alternately magnetized in axial direction. Therefore, the rotor follows the stator rotating field synchronously in operational mode. The driving speed depends on the frequency of the current. Maximum speeds of 7000 rpm were reached using operational currents between 20 mA and 300 mA
The excitation coils are made of Cu, insulation the epoxy based negative tone resist SU-8 has been used, which fills the gaps between the coil conductors
two synchronous motors are combined and enclosed by an SU-8 chamber wall.
One gear driven by the three-phase system actuates the other gear which rotates in the opposite direction. While rotating, the fluid is drawn from the inlet, split to both gears and transported in the space between the teeth and the chamber wall.
The system is closed by a structured glass cover which is fixed on the top of the chamber
The pump rate is approximated by: Vp=Q* Vn *Nwhere q is the number of spaces between two teeth, Vn is
the volume of one space and depends on the height, diameter, module and number of teeth and N is the rotational speed.
Micro Gear Pump
Piezoelectric Diaphragm Micro-pumptransport the tiniest amount of gases or liquids in a wide variety of applicationsThe functional principle is based on a piezoelectric diaphragm in combination with passive check valves. A piezo-ceramic mounted on a coated brass membrane is deformed when voltage is applied
In the majority of today’s micro-fluidic devices, silicone pneumatic valves are used to manipulate liquid samples. Pneumatic valves, however, require noisy compressors and complicated air channel systems, which are often too bulky for practical lab-on-a-chip applications. Piezoelectric actuators—inorganic crystals that change shape when electrically stimulated—are feasible alternatives, but while piezoelectric materials are less obtrusive than pressurized air technology, they are excessively large when compared to the size of the microchip itself.
Micro-fluidic valves
Micro fluidic valvesThermoplastics such as cyclic olefin copolymer (COC) and polymethylmethacrylate (PMMA) have been increasingly used in fabricating micro-fluidic devices. Bonding method for thermoplastics/PDMS has been developed for valving purposes because the ability of this material deform elastically.A basic micro-fluidic device is composed of two elastomeric layers. One layer contains channels for flowing liquids (flow layer), and the other layer contains channels that deflect the membrane valve into the flow channel and stop liquid flow when pressurized with air or liquid (control layer).
Micro-fluidic valvesSome scientists investigated the remarkable properties of electro-active polymers. These materials are rubber-like organic compounds that expand and contract when exposed to an electric current. It exhibits a large mechanical strain force at small scales which introduces a promising way to miniaturize micro-fluidic control valves. the polymer structure strongly resisted leaks because of its resilient structure.
By designing the micro-fluidic circuit, we should consider which type of valve is the most appropriate for our design. There are four available valve types: Push-down, Push-up, Sieve valve and Push-up and Push-down. The choosing for one of these valves is determined by the purpose as making a full or partial control over liquid
the researchers settled on a micrometer-sized, dome-shaped polymer diaphragm sandwiched between soft electrode sheets (as in Figure). They tested its ability to stop flow by fabricating it on top of a small hole drilled into a micro-fluidic channel. By monitoring fluorescent polystyrene tracking beads using high-speed video cameras
References
http://www.mdpi.com/2072-666X/5/3/442/htm
http://web.stanford.edu/group/foundry/Available%20Valve%20Types.html
http://www.nanowerk.com/news2/newsid=31292.php
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