GB2474430A

GB2474430A - Display or e-paper pixels using ferrofluids and an immiscible fluid

Info

Publication number: GB2474430A
Application number: GB0917881A
Authority: GB
Inventors: Anthony Miles; Robert Glyn Miles
Original assignee: Mr A & R Miles
Current assignee: Mr A & R Miles
Priority date: 2009-10-13
Filing date: 2009-10-13
Publication date: 2011-04-20
Also published as: GB0917881D0

Abstract

A picture element or pixel consists of a Ferro fluid in a cell and a fluid which will not mix with the ferrofluid. This fluid can be coloured or transparent. A magnetic effector can be used to obscure a coloured fluid when the ferrofluid is energised and to allow the colour element to be visible when the effector is not energised. The pixels can be part of a display, such as a white board, or can be used as electronic paper. A magnetic pen can be used to write on the paper or display and also to erase images.

Description

Problem to be solved To make a low energy printable picture element for the manufacturer of display screens, moving display graphics and the like.

Background to the invention

A standard picture element (pixel) as used in display screens is normally designed to emit light. E-paper uses an electrophoretic process designed to reflect light by re-arranging electrically charged particles using an applied electrical field.

In a standard form, an electrophoretic pixel consists of electrically charged particles placed between two conductive plates one conductive plate is made from, or coated with, clear material. When an appropriate electrical charge is placed onto the plates, the electrophoretic particle will migrate toward the clear plate with the opposite charge to that of the particle, and the particle will then become visible.

One of the problems with this method is that the process is relatively slow compared to LCD and other pixels. This makes the electrophoretic pixel unsuitable for moving displays due to the low refresh rates of the pixel. One reason why the reaction speed of the electrophoretic display is so poor, is that the particles have to travel enough distance in a forward direction to be visible and enough distance in a reverse direction to be invisible. If this distance were to be reduced, the reaction time would be greatly improved. The other main problem with this technology is that it is difficult to obtain coloured displays.

This invention allows the obfuscation or revelation of coloured cells using the displacement ofpigments or dyes using the unique properties of Ferro fluid, driven by a conductive matrix as the motive force. And a method of construction, enabling fast deployment.

Statement of the invention

Ferro fluids are colloidal mixtures composed of nano scale Ferro magnetic or Fern magnetic particles suspended in a carrier fluid. Agglomeration is prevented by the addition of a surfactant. Ferro magnetic materials do not retain magnetism in the absence of a magnetic field and exhibit a large amount of magnetic suscepabillity.

Nano sized (generally below 100 Angstroins) Ferro magnetic particles will generally remain in suspension due to Brownian motion and the properties of the surfactant which stops the particles clumping together.

Ferro fluid is colloidal and therefore has two states of matter one liquid and one solid, the phase change between these two states is obtained by the application of an externally applied magnetic field. When a magnetic field is applied to a Ferro fluid the random magnetic moments of the particles immediately orient themselves to the magnetic field lines of the applied field and the material presents a change of state.

When the magnetic field is removed the particles in the fluid rapidly return to their previous random moments and the first state is reinstated.

This property may be used to provide mechanical force as the shape of the liquid changes to follow the magnetic field lines of the externally applied magnetic field.

This force may be used to displace another fluid as in this application.

A Ferro fluid manufactured using a carrier of one viscosity is mixed proportionally with a coloured fluid manufactured with a carrier of another viscosity, These materials will separate into two layers, one a passive coloured layer and one an active Ferro fluid layer.

When an external magnetic field is applied to this material, the Ferro fluid layer will try to align itself with the field lines of the applied magnetic field, and if this magnetic field is oriented in a specific direction, the Ferro fluid can be forced to displace the coloured fluid. If the Ferro fluid itself is coloured, it may be used alone and there will be no need to displace a coloured fluid.

Using this general methodology a picture element may be constructed using the properties of Ferro fluid, which will obfuscate or reveal a coloured element to produce a sub pixel. Or used by itself, be the coloured element. A group of these sub pixels will be used together to construct a pixel and then a viewing screen.

Statement of the invention

A first sheet of material is prepared as in Fig 1(1) with cavities to hold the Ferro fluid and the coloured material. Separators Fig 1(2) are added to outline and define the pixel. Also included are the matrix circuitry (active or passive) and magnetic coils or effectors.

The cavities are shaped to allow the rapid displacement or deployment of the coloured fluid by the Ferro magnetic material when an external magnetic field is applied to it, and a phase change is exhibited. The cavities are coated with a surfactant or repellent to stop the materials adhering to it when de-energised.

The separators define the pixel and help contain the fluids. When the magnetic field is removed the Ferro liquid will revert to its original phase state and will allow the replacement of the coloured fluid to its original position.The Ferro fluids ability to return to its original position is assisted by the meniscus formed by its carrier and or the application of a further magnetic field applied in the assistive direction.

A second clear sheet is then applied to the first sheet thereby creating a sealed screen.

Additional layers may be added depending on the required embodiment.

A video matrix driver circuit is used to energise or de-energise the individual pixel cells and thereby reveal or obscure the coloured material to the required patterns.

The amount of material displaced will depend on the magnitude of the external magnetic field applied. This will allow control of the amount of coloured particle to be exposed and therefore allow control of the contrast ratio of the pixel. A further matrix of particles capable of permanent magnetisation may be applied to the clear sheet.

This matrix will be permanently magnetised by the same magnetic field used to activate the pixel and will maintain the state of the pixel until the permanently magnetised particles are reset by the application of a further alternating magnetic field. This will enable the retention of the screen image in the absence of applied power.

Possible Embodiments Low power rewritable signage display screen A plurality of Ferro fluid pixels (Fig) 2 are arranged in groups of four, one of each required colour, constructing a display screen of the size designed. These pixels are addressed by a standard method, well known in the art, and are switched on or off by a controlling computer and program to obtain the required graphic display.

The graphic may be selected and displayed and the power may then be removed from the display. The selected pixels will retain their on or of state due the particles now permanently magnetised, or not magnetised, by the magnetic effector, maintaining their state due to the energised pixel requiring less magnetic field to maintain the on state than to initially create the on state. When a new graphic is required, the screen is degaussed by a signal from the controlling computer before a new graphic is written to the screen.

Moving display screen A plurality of Ferro fluid pixels (Fig) 2 are constructed without the permanently magnetisable material (Fig 2.1) are arranged in groups of four, one of each required colour, constructing a display screen of the size designed. These pixels are addressed by a standard method, well known in the art, and are switched on or off by a controlling computer and program to obtain the required graphic display.

Meeting display board (white board) A plurality of Ferro fluid pixels of the required colours are arranged to form a display board, The user then draws' on the board with a magnetic pen device.

The pixels are operated by the proximity of the magnetic pen, and an image is drawn on the screen. This image is retained by the permanently magnetisable particles (fig 2.1). When the image is no longer required, the display board is then degaussed, either electromagnetically or by a non powered magnetic wiper.

Alternative Embodiments The embodiments described above are illustrative of rather than limiting to the present invention. Alternative embodiments apparent on reading the above description may nevertheless fall within the scope of the invention.

Claims

Claims 1. A display screen pixel activated by the application of an external magnetic field to a Ferro fluid material, by using material displacement to reveal a coloured fluid.
2. A display screen pixel activated by the application of an external magnetic field to a Ferro fluid material, allowing the Ferro fluid colour to be observed.
3. A display screen where the energised pixel state is maintained by the permanent magnetisation of a matrix of magnetic particles aligned to the Ferro fluid/coloured particle pixel.
4. A display screen pixel with a cavity designed to accelerate the displacement of a coloured fluid.
5. A display screen pixel with a cavity designed to accelerate the replacement of a coloured fluid.
6. A display screen as in claim 1 and 2 where the substrate is flexible.
7. A display screen as in claims land 2 where the magnetic field and pixel state is retained as in claim 2
8. A display screen as in claims 1 and 2 where the retained pixel state, as in claim 7, is reset by the application of a further demagnetising magnetic field.
9. A display screen as in claims 1 and 2 with a touch screen matrix for tactile operation
10. A display screen as in claims 1 and 2 where the magnetic elements are printed to the substrate.
11. A pixel where the Ferro fluid is transparent colloidal fluid
12. A pixel where the Ferro fluid is coloured colloidal fluid
13. A display screen as in claim 1 where the image may be written with a magnetic pen device
14. A display screen as in claim 1 where the image may be erased with a magnetic pen device
15. A presentation board (white board) using the Ferro fluid pixel, where the write is performed with a magnetic pen device and erasure with a magnetic pen device.
16. A product label manufactured using the Ferro fluid pixel
17. A product manufactured with the Ferro fluid pixel on its surface to enable a colour change to its surface in the presence of a magnetic field
18. A product manufactured, with the Ferro fluid pixel, to be "paper like" in its tactile and visual properties that may be written and erased at will.