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Ferro Liquid Display or Ferro-electric Liquid Display (FLD) or Ferro Fluid Display (FFD) is based on Ferro electric properties of
certain liquids. Not all such fluids are crystal but they are generically referred to as Ferro Liquid Crystal Display (FLCD) also.

Description

These fluids have bistable properties that can be switched with a magnetic field. The switching time is much shorter than that of a typical LCD that twist/untwist due to electric rather than magnetic interactions.

Also see Ferrofluid for how some liquids behave in presence of a magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

. Practically the switching time is just the same as the time it takes for the electric signal to switch (the magnetic field). The ferro liquid reacts almost instantly when used in µg quantities (thin layer) as in a typical LCD's crystal layer.

The dot pitch

Dot pitch

Dot pitch is a specification for a computer display, computer printer, image scanner, or other pixel-based device that describes the distance, for example, between dots of the same color on the inside of a display screen...

 of such displays can be as low as 10 µm giving a very dense high resolution

Display resolution

The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...

 display on a small area. These might find applications in 3D displays and head mounted displays (HMD

HMD

HMD can mean:* Heavy Metal Detox * Head-mounted display* Haughton Mad Dogs - Darlington* Helmet mounted display* the ISO 3166-1 three-letter country code and an abbreviation for Heard Island and McDonald Islands...

) where typical LCDs have failed to provide anything better than a 640x480 (RGB pixel) resolution on a sq.cm display area.

Displays based on these are still experimental or of less commercial value only due to the costs. Gradual adoption in consumer electronics is expected to bring the costs down.

A major drawback is that the angle of twist is not easily controlled by intensity of magnetic field. To produce color scales, time multiplexing might be used exploiting the quick switching time. The materials found so far are sensitive to vibration and shock.

Working of Ferro Electric Crystals

Those based on crystals can retain polarisation permanently. FLCDs are smectic liquid crystals that have a natural layered order. Most FLCDs are

• of the smectic C phase (SmC^*)
  • i.e., they are tilted away from the layer normal (90°) and
• possess a chiral
  Chirality (chemistry)
  A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
  
   behaviour
  • i.e., they have a layered structure with the molecules at some angle (the "cone angle") away from the layer normal, and there is some inherent twist in the structure.

So, an unconstrained system, the azimuthal direction in which the molecules tilt away from the layer normal will differ slightly from one layer to the next.

Typically, the FLCDs are built with cell gaps less than 2 µm for stable molecular alignment. Alignment layer causes perpendicular stacked alignment. The cell's polarisation is determined by the magnetic field applied. That in turn results in opaque or transparent layer when used in combination with polarised layers as in LCD.

Properties and uses

• Very thin layer (less than 2 µm thick) can help produce a 90° polarisation twist.
  • High density displays with small display areas can be produced.
  • DisplayTECH claims that a stamp sized FLCD can drive resolutions needed for 50 inch screens.
• Switching time is less than 100 µs
  • High frame rate video displays are possible.
• Magnetic polarisation effect is bistable.
  • Can be used for low frame rate displays that can run on very low power
  • This property can help build display with non-volatile memory with the advantage that the memory can be changed easily.
• Viewing angle is greater than 120°
  • This makes it suitable for commercial TV applications.

Some commercial products do seem to utilize FLCD.

High switching allows building optical switch

Optical switch

In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....

es and shutters in printer

Computer printer

In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

heads.