Electrorheological (ER) fluids are suspensions of acutely accomplished non-conducting particles (up to 50 micrometres diameter) in an electrically careful fluid. The credible bendability of these fluids changes reversibly by an adjustment of up to 100,000 in acknowledgment to an electric field. For example, a archetypal ER aqueous can go from the bendability of a aqueous to that of a gel, and back, with acknowledgment times on the adjustment of milliseconds. The aftereffect is sometimes alleged the Winslow effect, afterwards its discoverer the American artist Willis Winslow, who acquired a US apparent on the aftereffect in 1947 1 and wrote an commodity
Wednesday, February 8, 2012
Applications
The accustomed appliance of ER fluids is in fast acting hydraulic valves 3 and clutches, with the break amid plates getting in the adjustment of 1 mm and the activated abeyant getting in the adjustment of 1 kV. In simple terms, if the electric acreage is applied, an ER hydraulic valve is shut or the plates of an ER clamp are bound together, if the electric acreage is removed the ER hydraulic valve is accessible or the clamp plates are disengaged. Other accepted applications are in ER brakes 4 (think of a anchor as a clamp with one ancillary fixed) and shock absorbers 5 (which can be anticipation of as bankrupt hydraulic systems area the shock is acclimated to try to pump aqueous through a valve).
There are abounding atypical uses for these fluids, including use in the US army's planned approaching force warrior project. They plan to actualize bulletproof vests appliance an ER aqueous because the adeptness to absorb the aqueous into bolt creates the abeyant for a actual ablaze belong that can change from a accustomed bolt into a harder accoutrement about instantaneously. Other abeyant uses are in authentic annoying cutting and as haptic controllers and concrete displays.6
ER aqueous has aswell been proposed to accept abeyant applications in adjustable electronics, with the aqueous congenital in elements such as rollable screens and keypads, in which the viscosity-changing qualities of the aqueous acceptance the rollable elements to become adamant for use, and adjustable to cycle and abjure for autumn if not in use. Motorola filed a apparent appliance for adaptable accessory applications in 2006.7
There are abounding atypical uses for these fluids, including use in the US army's planned approaching force warrior project. They plan to actualize bulletproof vests appliance an ER aqueous because the adeptness to absorb the aqueous into bolt creates the abeyant for a actual ablaze belong that can change from a accustomed bolt into a harder accoutrement about instantaneously. Other abeyant uses are in authentic annoying cutting and as haptic controllers and concrete displays.6
ER aqueous has aswell been proposed to accept abeyant applications in adjustable electronics, with the aqueous congenital in elements such as rollable screens and keypads, in which the viscosity-changing qualities of the aqueous acceptance the rollable elements to become adamant for use, and adjustable to cycle and abjure for autumn if not in use. Motorola filed a apparent appliance for adaptable accessory applications in 2006.7
The ER effect
The change in credible bendability is abased on the activated electric field, i.e. the abeyant disconnected by the ambit amid the plates. The change is not a simple change in viscosity, appropriately these fluids are now accepted as ER fluids, rather than by the earlier appellation Electro Viscous fluids. The aftereffect is bigger declared as an electric acreage abased microburst crop stress. When activated an ER aqueous behaves as a Bingham artificial (a blazon of viscoelastic material), with a crop point which is bent by the electric acreage strength. After the crop point is reached, the aqueous shears as a fluid, i.e. the incremental microburst accent is proportional to the amount of microburst (in a Newtonian aqueous there is no crop point and accent is anon proportional to shear). Appropriately the attrition to motion of the aqueous can be controlled by adjusting the activated electric field.
ER fluid composition and theory
ER fluids are a blazon of acute fluid. A simple ER aqueous can be fabricated by bond cornflour in a ablaze vegetable oil or (better) Silicone oil.
There are two capital theories to explain the effect: the interfacial astriction or 'water bridge' theory,8 and the electrostatic theory. The baptize arch approach assumes a three appearance system, the particles accommodate the third appearance which is addition aqueous (e.g. water) immiscible with the capital appearance aqueous (e.g. oil). With no activated electric acreage the third appearance is acerb admiring to and captivated aural the particles. This agency the ER aqueous is a abeyance of particles, which behaves as a liquid. When an electric acreage is activated the third appearance is apprenticed to one ancillary of the particles by electro assimilation and binds adjoining particles calm to anatomy chains. This alternation anatomy agency the ER aqueous has become a solid. The electrostatic approach assumes just a two appearance system, with dielectric particles basic chains accumbent with an electric acreage in an akin way to how magnetorheological aqueous (MR) fluids work. An ER aqueous has been complete with the solid appearance fabricated from a aqueduct coated in an insulator.9 This ER aqueous acutely cannot plan by the baptize arch model. However, although demonstrating that some ER fluids plan by the electrostatic effect, it does not prove that all ER fluids do so. The advantage of accepting an ER aqueous which operates on the electrostatic aftereffect is the abolishment of arising current, i.e. potentially there is no DC current. Of course, back ER accessories behave electrically as capacitors, and the capital advantage of the ER aftereffect is the acceleration of response, an AC accepted is to be expected.
There are two capital theories to explain the effect: the interfacial astriction or 'water bridge' theory,8 and the electrostatic theory. The baptize arch approach assumes a three appearance system, the particles accommodate the third appearance which is addition aqueous (e.g. water) immiscible with the capital appearance aqueous (e.g. oil). With no activated electric acreage the third appearance is acerb admiring to and captivated aural the particles. This agency the ER aqueous is a abeyance of particles, which behaves as a liquid. When an electric acreage is activated the third appearance is apprenticed to one ancillary of the particles by electro assimilation and binds adjoining particles calm to anatomy chains. This alternation anatomy agency the ER aqueous has become a solid. The electrostatic approach assumes just a two appearance system, with dielectric particles basic chains accumbent with an electric acreage in an akin way to how magnetorheological aqueous (MR) fluids work. An ER aqueous has been complete with the solid appearance fabricated from a aqueduct coated in an insulator.9 This ER aqueous acutely cannot plan by the baptize arch model. However, although demonstrating that some ER fluids plan by the electrostatic effect, it does not prove that all ER fluids do so. The advantage of accepting an ER aqueous which operates on the electrostatic aftereffect is the abolishment of arising current, i.e. potentially there is no DC current. Of course, back ER accessories behave electrically as capacitors, and the capital advantage of the ER aftereffect is the acceleration of response, an AC accepted is to be expected.
DC current
The particles are electrically active. They can be ferroelectric or, as mentioned above, fabricated from a administering actual coated with an insulator, or electro-osmotically alive particles. In the case of ferroelectric or administering material, the particles would accept a top dielectric constant. There may be some abashing actuality as to the dielectric connected of a conductor, but "if a actual with a top dielectric connected is placed in an electric field, the consequence of that acreage will be measurably bargain aural the aggregate of the dielectric" (see capital page: Dielectric constant), and back the electric acreage is aught in an ideal conductor, again in this ambience the dielectric connected of a aqueduct is infinite.
Another agency that influences the ER aftereffect is the geometry of the electrodes. The addition of alongside acclimatized electrodes showed slight access in the ER aftereffect but perpendicularclarification needed acclimatized electrodes angled the ER effect.10 A abundant beyond access in ER aftereffect can be acquired by blanket the electrodes with electrically polarisable materials. This turns the accepted disadvantage of dielectrophoresis into a advantageous effect. It aswell has the aftereffect of abbreviation arising currents in the ER fluid.11
The behemothic electrorheological (GER) aqueous was apparent in 2003,12 and is able to sustain college crop strengths than abounding added ER fluids. The GER aqueous consists of Urea coated nanoparticles of Barium Titanium Oxalate abeyant in silicone oil. The top crop backbone is due to the top dielectric connected of the particles, the baby admeasurement of the particles and the Urea coating. Another advantage of the GER is that the accord amid the electrical acreage backbone and the crop backbone is beeline afterwards the electric acreage alcove 1 kV/mm. The GER is a top crop strength, but low electrical acreage backbone and low accepted body aqueous compared to abounding added ER fluids. The action for alertness of the abeyance is accustomed in.12 The above affair is the use of oxalic acerbic for the alertness of the particles as it is a able amoebic acid.
Another agency that influences the ER aftereffect is the geometry of the electrodes. The addition of alongside acclimatized electrodes showed slight access in the ER aftereffect but perpendicularclarification needed acclimatized electrodes angled the ER effect.10 A abundant beyond access in ER aftereffect can be acquired by blanket the electrodes with electrically polarisable materials. This turns the accepted disadvantage of dielectrophoresis into a advantageous effect. It aswell has the aftereffect of abbreviation arising currents in the ER fluid.11
The behemothic electrorheological (GER) aqueous was apparent in 2003,12 and is able to sustain college crop strengths than abounding added ER fluids. The GER aqueous consists of Urea coated nanoparticles of Barium Titanium Oxalate abeyant in silicone oil. The top crop backbone is due to the top dielectric connected of the particles, the baby admeasurement of the particles and the Urea coating. Another advantage of the GER is that the accord amid the electrical acreage backbone and the crop backbone is beeline afterwards the electric acreage alcove 1 kV/mm. The GER is a top crop strength, but low electrical acreage backbone and low accepted body aqueous compared to abounding added ER fluids. The action for alertness of the abeyance is accustomed in.12 The above affair is the use of oxalic acerbic for the alertness of the particles as it is a able amoebic acid.
Problems and advantages
A above botheration is that ER fluids are suspensions, appropriately in time they tend to achieve out, so avant-garde ER fluids accouterment this botheration by agency such as analogous the densities of the solid and aqueous components, or by application nanoparticles, which brings ER fluids into band with the development of magnetorheological fluids. Another botheration is that the breakdown voltage of air is ~ 3 kV/mm, which is abreast the electric acreage bare for ER accessories to operate.
An advantage is that an ER accessory can ascendancy appreciably added automated ability than the electrical ability acclimated to ascendancy the effect, i.e. it can act as a ability amplifier. But the capital advantage is the acceleration of response, there are few added furnishings able to ascendancy such ample amounts of automated or hydraulic ability so rapidly.
Unfortunately, the access in credible bendability accomplished by a lot of Electrorheological fluids acclimated in microburst or breeze modes is about limited. The ER aqueous changes from a Newtonian aqueous to a partially apparent "semi-hard slush". However, an about complete aqueous to solid appearance change can be acquired if the electrorheological aqueous additionally adventures compressive stress.13 This aftereffect has been acclimated to accommodate electrorheological Braille displays 14 and actual able clutches.15
An advantage is that an ER accessory can ascendancy appreciably added automated ability than the electrical ability acclimated to ascendancy the effect, i.e. it can act as a ability amplifier. But the capital advantage is the acceleration of response, there are few added furnishings able to ascendancy such ample amounts of automated or hydraulic ability so rapidly.
Unfortunately, the access in credible bendability accomplished by a lot of Electrorheological fluids acclimated in microburst or breeze modes is about limited. The ER aqueous changes from a Newtonian aqueous to a partially apparent "semi-hard slush". However, an about complete aqueous to solid appearance change can be acquired if the electrorheological aqueous additionally adventures compressive stress.13 This aftereffect has been acclimated to accommodate electrorheological Braille displays 14 and actual able clutches.15
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