The permittivity of the medium in a vacuum is 8.85 x 10^-12 C^2/N-m^2 or 8.85 pF/m.
An effective way to pump fluid through capillary tubes. The tube wall is flexible and the outside wall is coated with piezoelectric crystal film. Radio-frequency voltage is applied to the interdigital transducers (IDTs), resulting in mechanical squeezing in sections of the tube, similar to squeezing toothpaste. This results in a smooth flow with a uniform velocity profile across the tube cross section. An example includes ZnO with aluminum IDTs.
At macroscale, actuation is typically achieved by hydraulic, pneumatic, and motor-based systems.
The driving power for actuators varies for different applications.
The output action is usually a prescribed motion.
The advantages of microfluidic actuators include the ability to work with small samples and better performance with reduced power consumption.
The driving forces for micro motors are primarily the parallel electrostatic forces between pairs of misaligned electrically charged plates (electrodes).
A microactuator is a device used to achieve actuation at microscale.
The four principal means are thermal forces, shape memory alloys, piezoelectric crystals, and electrostatic forces.
A micro valve is actuated by thermal force generated by heating rings.
Pressure can go up to 500 hPa, down to -350 hPa (vacuum), and flow rate can be up to 3.5 ml/min.
The relative permittivity range for mica is 3 to 7.
The conformational change in viral proteins used in VPL Motors is caused by the pH change associated with the vicinity of the host cell.
Actuators can be as simple as an electrical relay switch or as complex as an electric motor.
The primary driving force for micro motors is the parallel electrostatic forces between pairs of misaligned electrically charged plates (electrodes).
Piezo Plate expands and contracts due to the applied potential difference, pumping water in and out by its motion. Membrane foils regulate the flow at the inlet and outlet valves.
The relative permittivity range for paper is 2.0 to 3.5.
Viral Protein Linear (VPL) Motors are based on the principle of change in the shape of a macromolecule observed in a family of viral envelope proteins when subjected to a changing pH environment.
Shape Memory Alloys are extensively used in micro rotary actuators, micro joints and robots, and microsprings.
A microfluidic system consists of nozzles, pumps, channels, reservoirs, mixers, oscillators, and valves in micro scales.
The induced capacitance, C, is given by the formula: C = ε_r * ε_0 * (A / d) = ε_r * ε_0 * (W * L / d), where ε_r is the relative permittivity of the dielectric material, ε_0 is the permittivity of free space, A is the area of the plates, W is the width, L is the length, and d is the gap between the plates.
The capacitance of a parallel-plate capacitor with air as the dielectric medium, given L = W = 1000 μm and d = 2 μm, is 4.43 pF.
Bimetallic Strips are actuators based on thermal forces, made by bonding two materials with distinct thermal expansion coefficients. The strip bends when heated or cooled from the initial reference temperature due to incompatible thermal expansions of the bonded materials and returns to its initial reference shape once the applied thermal force is removed.
Actuation is the action of causing something (a machine or device) to move.
The transduction unit converts the power into the desired form of actions of the actuating element.
The piezoelectric effect is the property of piezoelectric crystals to deform with the application of electric voltage and vice-versa.
Maximal pressure is up to 2,000 hPa and maximal flow rate is up to 0.4 ml/min.
The relative permittivity range for porcelain is 6 to 7.
The two types of micro motors mentioned are linear stepping motors and rotary stepping motors.
Actuators are important parts of microsystems that involve motion.
An actuating element is a material or component that moves.
Rotary stepping motors involve two sets of electrodes - one set for the rotor and the other for the stator. The dielectric material between the rotor and stator is air, and there is a preset mismatch of pitches of the electrodes in the two sets.
Electrostatic force is used as the driving force, based on the repulsive or attractive forces generated by charged particles.
The relative permittivity of transformer oil is 4.5.
Linear stepping motors generate movement by energizing misaligned electrode pairs sequentially. Energizing set A-A' generates a force pulling A' over A due to initial misalignment. Once aligned, the next pair B-B' becomes misaligned and is energized, generating electrostatic force pulling B' over B. This process is repeated, causing continuous movement of the moving set over the stationary set. The step size of the motion is w/3, or the size of the pitch between the two electrode sets.
The power supply provides electric current or voltage to the microactuator.
An SMA strip has an original shape that is bent at a preset temperature T. It is set straight at room temperature, and when heated to T, it returns to its bent shape, causing actuation.
Normal plate electrodes are not practical because they require more space.
A pair or combs (pairs) of charged plates are used in microactuation based on electrostatic forces.
The relative permittivity of Pyrex is 4.7.
A 'Comb Drive' actuator is a type of microactuator that uses arrangements of electrodes to achieve actuation, where an increase in the number of electrode pairs drastically reduces the required actuation voltage.
An acidic environment with a pH of approximately 5.0 causes the expansion of viral protein residue B in VPL Motors.
Other novel approaches are also emerging.
Microfluidic actuators are used in biomedical precision manufacturing processes and pharmaceutical industries. Applications include chemical analysis, biological and chemical sensing, drug delivery, and molecular separation such as DNA analysis.
Coulomb’s Law explains the relationship of electrostatic force between two charged particles with respect to the charge and distance between them.
The relative permittivity of water is 80.
When heated or cooled, materials with distinct thermal expansion coefficients will expand or contract differently and will return to their initial reference shape once the applied thermal force is removed.
An actuator is a mechanical device for moving or controlling something.
Actuators are designed to deliver motion when driven by a power source.
Magnetic shape memory alloys (MSMAs), also called ferromagnetic shape memory alloys (FSMA), are particular shape memory alloys that produce forces and deformations in response to a magnetic field.
Microfluidic actuators can be built with a variety of materials such as quartz and glasses, plastics, polymers, ceramics, and semiconductors.
The induced normal force, F_d, is given by the formula: F_d = (1/2) * ε_r * ε_0 * (W * L / d^2) * V^2, where ε_r is the relative permittivity of the dielectric material, ε_0 is the permittivity of free space, W is the width, L is the length, d is the gap between the plates, and V is the voltage applied.
Linear stepping motors consist of two sets of electrodes in the form of plates separated by dielectric materials, such as quartz film. One electrode set is fixed, while the other can slide over it with little friction. The two sets have slightly different pitches between electrodes.
Titin fibers, which are 36 amino-acid residues, can be used as passive spring elements to join two platforms and form a single degree of freedom parallel platform actuated by a viral protein linear (VPL) actuator.
Shape memory alloys (SMA) tend to return to their original shape at a preset temperature. Examples include Nitinol and TiNi alloys.
A micro pump is an effective way to pump fluid through capillary tubes.
The formula is F = (1 / (4πε)) * (q * q') / r^2, where ε is the permittivity of the medium between the particles, q and q' are point charges, and r is the distance between the particles.
The relative permittivity of silicon is 12.
Heat pipes, also known as heat pumps, are closed systems that transport heat from high temperature sources to low temperature sinks. Major applications are in micro and molecular electronics. A triangular or trapezoidal micro pipe containing a liquid (such as ethanol) is in contact with a heat source (like an IC) and a sink (like a fan). The liquid vaporizes at the heat source end and condenses at the heat sink end. The condensed liquid, due to capillary effect, moves to the corners and returns to the source end, repeating the cycle.
A micro gripper is an essential component in micro robots, micro assemblies, and surgery.
The sliding plate electrodes method is popular and can have many sets to make 'Comb Drive' actuators.
The relative permittivity of air is 1.0.
