This invention relates to a fibre or filament, especially one that is suitable for inclusion in a fabric or garment having one or more indicator displays incorporated therein.
Various types of fibres and filaments formed from electro-optical materials which are capable of undergoing colour change are known. For example it is known to form a fibre or filament from an electro-optically active material such as an electro-luminescent material or a polymer LED material. It is also possible to use liquid crystals, electrophoretic particles or electrochrome materials as the electro-optic material forming the fibre or filament.
In general, all known fibres and filaments of this type have the same basic structure and comprise:
1. A conducting core or electrode generally running axially through the fibre or filament at or towards the centre of the fibre or filament;
2. An electro-optic layer coating the core electrode; and
3. A transparent conducting outer electrode.
By applying a voltage difference between the core electrode and the outer electrode, an electric field is generated in the electro-optic layer, over the entire length of the fibre. The electric field produced is homogeneous, in a direction along the fibre, and induces a change in the optical state of the electro-optical layer. The change in the optical state is dependent on the material forming the electro-optic layer, and the field applied across the electrodes.
It is an object of the present invention to provide a fibre or filament in which the length of the optically active part of the fibre or filament can be controlled by tuning the voltage difference applied across the electro-optically active layer.
According to a first aspect of the present invention there is provided a fibre or filament comprising an electro-optically active layer;
By means of the present invention it is possible to control the optical state of a predetermined region of the fibre or filament in such a way that the length of the predetermined region may be controlled.
The optical state at a position within a fibre or filament is characterised by the light that is emitted, reflected or absorbed by the electro-optically active layer. It is to be understood that the present invention as claimed relates to fibres or filaments having electro-optically active layers that reflect or absorb light from both internal or external light sources.
In use, the optical state of the predetermined region may be such that it emits light when no other parts of the fibre emits light.
This is in sharp contrast to known colour change fibres or filaments in which it is only possible to change the optical state of the electro-optically active layer homogeneously over the entire length of the electrodes. In practice this means that the optical state in a known colour change fibre is the same along the entire length of the fibre.
This means that for example when the electro-optically active layer is formed from a material having a threshold voltage above which it is in an on state, and below which it is in an off state, in a known colour change fibre, the entire fibre will either be in the off state emitting no light or the on state emitting light.
By means of the present invention, it is possible to vary the optical state of the electro-optically active material along the length of the fibre or filament so that a variable length of the fibre or filament may be in the on state and therefore emitting light at any given time.
The predetermined region of the fibre or filament may comprise a portion only of the fibre or filament or may comprise the entire fibre or filament.
The present invention is particularly suited for use as an indicator, or as an indicator incorporated into a garment.
Advantageously, the fibre or filament comprises voltage means for applying a voltage difference across the electro-optically active layer.
Preferably, the control means controllably varies the voltage difference applied across the electro-optically active layer, along the length of the fibre.
The voltage difference may be a direct voltage difference, or an AC voltage difference.
Preferably, the fibre or filament is substantially cylindrical.
Advantageously, the first electrode is positioned at or close to a central portion of the fibre or filament, and the second electrode is positioned at or close to an outer surface of the fibre or filament.
Advantageously the first electrode extends substantially along the axis of the fibre or filament.
Conveniently, the second electrode comprises a first conducting coating which, in a preferred embodiment is transparent.
Preferably, the electro-optically active layer comprises an electroluminescent material, although other types of electro-optically active material could also be used.
Alternatively, the electro-optically active layer could comprise a light emitting polymer (poly LED), liquid crystal material, electrophoretic particle suspensions or electrochrome material.
The optical state of an electroluminescent material may be altered by varying an electric field applied across the electroluminescent material. The material has a threshold voltage typically of about 200 volts. When electric fields of below the threshold voltage are applied to the material, the material remains in an off state, and does not emit light. When electric fields above the threshold level are applied across the material, the material switches into an on state in which it emits light.
Preferably, the control means comprises a conductor extending between the first and second electrodes.
The conductor may take any convenient form and may for example be in the shape of a disc extending through the electro-optically active material from the first electrode to the second electrode.
The conductor thus serves to create a short circuit between the first electrode and the second electrode. This in turn means that if a voltage difference is applied across the first and second electrodes, the strength of the field created in the electro-optically active layer will decrease towards the conductor.
This in turn means that, since the optical state of the electro-optically active material is governed by the strength of the field existing in the material, the optical state of the electro-optically active material will vary with the voltage difference applied along the length of the first and second electrodes.
One of the first and second electrodes may be formed from a material with a higher resistance.
Resistive electrodes can be made from Titanium (ρ=5.6·10−7 Ωm) or Nickel-Chrome alloys, such as Inconel (ρ=9.8·10−7 Ωm) or Nichrome (ρ=11·10−7 Ωm).
Alternatively, the fibre may be manufactured as such that it has appropriate dimensions to provide a sufficiently high resistance. For instance, a very thin wire made from copper (ρ=0.17·10−7 Ωm) that has a diameter of 20 μm (corresponding to the American Wire Gauge standard 52) has a resistance that is 100 times larger than a copper wire with a more conventional diameter of 200 μm (corresponding to the American Wire Gauge standard 32). A 20 μm thin copper wire has a comparable resistance to a 200 μm thick wire made out of Nichrome.
In such embodiments of the invention, the electric field across the first and second electrodes, and therefore across the electro-optically active layer will decrease gradually along the length of the fibre or filament.
Advantageously, the first or second electrode is divided in a plurality of length segments comprising at least a first length segment and a last length segment which first and last length segments are positioned at or towards opposite ends of the first electrode.
In one embodiment of the invention, the control means may comprise a first resistor positioned between a pair of adjacent length segments. Preferably the control means comprises a plurality of first resistors, each of which first resistors is positioned between respective pairs of adjacent length segments. Advantageously the control means further comprises a second resistor associated with the last length segment.
In such an embodiment, the conductor is preferably positioned at or close to the last length segment.
Each length segment of the electro-optical layer may be modelled by a parallel connection between the first and second electrodes via the resistance (Rfibre) and the capacitance (Cfibre) of the electro-optical layer. Each length segment of the first or second electrode together with each resistor forms a resistive element having a resistance Rwire. When the resistance of a resistive element (Rwire) is chosen such that it is lower than Rfibre, then a DC voltage applied to the first electrode will linearly divide over the length of the first electrode.
In another embodiment, an AC voltage is used to drive the electro-optically active layer. When an AC voltage is used, the impedance of the resistive elements (length segment and resistor) should be lower than the total impedance of the electro-optically active layer. In other words the impedance of each resistive element, Rwire, should be lower than both Rfibre and 1/(2πfCfibre).
Due to the presence of the resistive elements, when a voltage difference is applied across the first and second electrodes, power is not uniformly distributed over the entire fibre. The first segment receives more power than the second segment and the second more than the third and so on, to the last segment. This means that up to a certain voltage difference, only the first segment will be in the on state. As the voltage difference increases, the second segment will also emit light, and so on to the last segment, assuming that sufficient power is applied to the fibre.
The second resistor can be used to tune the division of power along the length of the fibre. The higher the resistance of the second resistor, the less power will be required to cause successive length segments to switch into the on state.
In a preferred embodiment of the invention, the control means comprises a first capacitor positioned between a pair of adjacent segments.
Preferably, the control means comprises a plurality of first capacitors each of which first capacitors is positioned between respective pairs of adjacent length segments.
Advantageously, the fibre or filament further comprises a second capacitor associated with the last length segment.
An advantage of using capacitors rather than resistors is that capacitors do not in themselves dissipate power. A fibre or filament incorporating capacitors will therefore have a lower power requirement than a fibre or filament incorporating resistors.
When an AC voltage is supplied across the first and second electrodes, the capacitors will divide the voltage but they will not dissipate any power. The impedance of each capacitor (1/(2πfCwire)) should be lower than the equivalent impedance of the electro-optically active layer (and lower than both Rfibre and (1/(2πfCfibre))).
Alternatively, the first or second electrode comprises a plurality of spaced apart insulators.
The plurality of insulators form capacitive connections to the length segments.
In such a fibre or filament it is not necessary to use discrete capacitors since the material used to form the first electrode contains within it, a “capacitative” material. The material forming the first electrode may comprise a light sensitive conducting material comprising an insulating porous host material filled with gold particles, for example.
The light sensitive conducting material could then be exposed to a laser causing the gold to evaporate and establish a non-conducting spacer that acts as a capacitive connection between adjacent length segments.
Advantageously, the fibre or filament comprises a plurality of first conductors positioned at spaced apart intervals along the first electrode, and a diode associated with each conductor.
Preferably, the control means comprises at least one diode associated with each of one or more length segments.
Advantageously, the fibre or filament further comprises a third electrode, and the control means further comprises at least one third capacitor associated with each of the one or more length segments, and connected to the third electrode.
The third electrode may be grounded in some embodiments.
When a low driving voltage of less than the breakdown voltage of the diodes is applied across the first and third electrodes, the diode in the first length segment behaves like a highly resistive connection. This means that all current will flow through the first fibre segment and then towards ground. This is because the impedance of the third capacitor to ground is selected to be lower than the total impedance of the electro-optically active layer. This in turn means that at low driving voltages, all power will be directed to the first length segment.
When the amplitude of the driving voltage increases beyond the threshold breakdown voltage, then the at least one diode associated with the first length segment will “break down” and start to conduct with low impedance. The excess voltage over the threshold breakdown voltage will be absorbed by the third capacitor. This raises the voltage over the third capacitor. At the same time the voltage over the second length segment will start to increase. This sequence is repeated along the entire length of the electrode.
In an alternative embodiment, the fibre or filament comprises a third resistor rather than a third capacitor connected to the third electrode. In other embodiments, the fibre or filament may comprise a combination of one or more capacitors and resistors.
Preferably, the control means comprises a plurality of conductors positioned at spaced apart intervals along the first electrode, and a diode associated with each conductor.
Advantageously, each conductor comprises an insulator. Preferably, the fibre or filament further comprises an outer insulating coating. Conveniently, the fibre or filament comprises a second conducting coating.
According to a second aspect of the present invention there is provided a method of manufacturing a fibre or filament comprising:
Preferred and advantageous features of the second aspect of the invention are set in appended claims 25 to 38.
According to a third aspect of the present invention there is provided a fabric or textile formed from a plurality of fibres or filaments.
The invention will now be further described by way of example only with reference to the accompanying drawings in which:
a and 1b are schematic representations showing the off and on states of a conventional colour change fibre;
a to 2d are schematic representations showing how the optical state of a predetermined portion of a fibre or filament according to the present invention may be varied according to the present invention;
Referring to
Referring to
In
Thus, by means of the present invention it is possible to vary the length of the light emitting portion of the fibre 4.
Fibres according to the present invention may be used to form garments and other wearable electronics.
Turning now to
Referring now to
In an alternative embodiment of the invention, the conducting core 12 is formed from a material having a lower resistance for example, copper which has a resistivity of ρ=0.17·10−7 Ωm. The first electrode 12 is divided into a plurality of length segments (not shown), including at least a first length segment positioned towards the first end 20, and a last length segment associated with the conducting disc 18 and positioned at the second end 22 of the fibre 10. Resistors are positioned between adjacent length segments of the first electrode 12. Each length segment, together with an adjacent resistor, forms a resistive element.
Each length segment of the electro-optically active layer 16 can be modelled by a parallel connection between the fibre electrodes via the resistance (Rfibre) and the capacitance (Cfibre) of the electro-optically active layer 16.
The resistance of a resistive element (Rwire), is chosen so that it is lower than Rfibre. This means that when a DC voltage is applied to the first electrode 12 the voltage will linearly divide over the length of the core electrode.
A first resistor 24 is positioned between adjacent length segments 500, and a second resistor 26 is associated with the conducting disc 18.
The voltage applied to the first electrode 12 may also be an AC voltage. In embodiments of the invention in which an AC voltage is applied to the first electrode 12, the impedance of each resistive element is less than the total impedance of the electro-optically active layer 16 of the corresponding length segment. In other words the impedance of each resistive element is lower than both Rfibre and 1/(2πfCfibre).
The first electrode 12 may be formed into any convenient number of length segments 500.
Turning now to
In this embodiment of the invention, there is a power threshold of 0.2 Watts which must be overcome in order to change the optical state in any length segment such that the electro-optically active layer emits light.
The results shown in the graph of
The power for each of five segments is indicated by the lines labelled 28, 30, 32, 34 and 36 respectively. It can be seen that at a drive voltage of 200 volts, the power in the first segment represented by line 28 reaches the power threshold. At this point the first length segment will emit light but no other segments will emit light.
Sequentially the optical state of the other segments will be changed so that in this example at a drive voltage of just under 300 volts, the second segment will emit light as represented by line 30, and at a drive voltage of approximately 450 volts, the third segment will emit light as indicated by line 32. At a drive voltage of approximately 700 volts, the fourth segment will also emit light as indicated by line 34. In this example shown, the drive voltage is never sufficient to allow the fifth segment to emit light.
In other words, for an increasing drive voltage, initially the first segment will switch to a light emitting state, followed by the second segment and so on. This makes use of the properties of the electroluminescent material forming the electro-optically active layer 16. Such material has a threshold power of 200 mW (per segment) below which no significant light is emitted.
If the resistance of the end resistor 26 is increased, the division of power over the segments may be tuned. The higher the resistance of resistor 26 (compared to resistor 24), the more closely spaced will become the turn on voltages of the fibre segments as shown in
In the examples shown in
Referring now to
The fibre 80 is again divided into five length segments 500, and between adjacent length segments are positioned first capacitors 38. The fibre 80 further comprises a second capacitor 40 positioned towards the second end 22 of the fibre and associated with the conducting disc 18.
Referring to
An advantage of using capacitors rather than resistors is that capacitors do not dissipate any power and therefore the power requirements of the fibre 10 using capacitors rather than resistors will be lower.
Referring to
The insulating spacers 54 could for example be made by locally exposing a light sensitive conducting material to a laser, such that the conductance of the exposed areas significantly reduces at the illuminated positions. A light sensitive material could for example comprise an insulating porous host material, filled with gold particles. The exposure by a laser beam will evaporate the gold and thus establish a non-conducting spacer 54.
Referring to
The fibre 58 comprises parts similar to those shown in
The fibre 58 comprises a pair of diodes 60 parallel to each length segment. The diodes are substantially identical and have a (combined) breakdown voltage of about 200V.
The pair of diodes 60 have a defined break down voltage, and connected in series with opposite forward directions. When using discrete components conventional rectifier diodes can be used (for example the Philips Semiconductor BYV27 series).
In addition, associated with each diode 60, is a short connecting the first and second electrodes 12, 14, and a third capacitor 62 that is connected to the third electrode 64.
The first electrode 12 comprises a plurality of spaced apart conducting discs 80 each of which is insulated on one side by an insulating ring 82. On the other side of the conducting disc to the insulating ring 82 the first electrode 12 comprises a pair of diodes 60. The diodes could be formed for example by using a semi-conducting base material for the conducting core, which is highly doped (either P or N type doping) except in small areas where opposite doping simultaneously creates two matched junction diodes.
The transparent conducting coating 14 contacts the non-insulated side of the discs 80. The insulating transparent coating 76 positioned between first and second transparent conducting coatings 14, 64 forms a capacitive coupling.
An alternating voltage difference is applied initially to the first length segment between the first 12 and third 64 electrodes. Due to the short between the first and second electrodes 12, 14, the alternating current potential is directed to the second electrode 14. However, the diode 60 blocks the alternating current voltage if the magnitude of the voltage is below its breakdown voltage, while the third capacitor 62 conducts the zero potential of the third electrode 64 to the first electrode 12. This means that in the first length segment of the first electrode 12, on the right side of the diode 60 the potential will be zero. This in turn means that that electro-optical material between the first 12 and second 14 electrodes will experience substantially all of the alternating current voltage applied between the first 12 and third 64 electrodes. However, in all other length segments, the potentials on the first 12 and second 14 electrodes will both be equal to a zero voltage, and therefore the electro-optical layers in those segments will not experience a voltage.
This changes when the alternating current voltage exceeds the breakdown voltage of the first diode 60. At this point the diode will transfer the part of the AC voltage level that is above its breakdown level (the over voltage) to the right side of the diode 60 in the first segment of the first electrode 12. This in turn means that the voltage over the first electro-optical layer will become equal, and limited to, the breakdown voltage of the diode. The over voltage is transferred by the short to the second electrode 14 of the second length segment. The diode of the second length segment, however, will block the over voltage as long as it is below its breakdown level, that is, when the AC voltage applied to the fibre is below a level equal to twice the breakdown level of the diodes 60.
This means that in the second length segment the first electrode 12 on the right side of the diode 60 will remain at zero potential. This in turn means that the electro-optical layer 16 in the second length segment will experience the over voltage, and therefore its optical properties will change. This will continue until the AC voltage is more than twice the breakdown level of the diodes 60 and then the third length segment forming the fibre will begin to be activated and so on along the length of the fibre.
Although
In embodiment depicted in
Turning now to
As can be seen from
In the example depicted in
Referring now to
Fabric 88 is formed from a plurality of fibres according to the first aspect of the present invention having length segments 100. Each of the length segments 100 comprises a first electrode 102 comprising a resistive material. The core electrodes 102 are connected to one another at both ends of the fibres. First and second electrodes of each length segment are shorted at end 104 of the fabric. By applying a voltage V to the first electrodes at an opposite end 106 of the fabric, the optically-active length of each of the length segments can be controlled at the same time.
Number | Date | Country | Kind |
---|---|---|---|
0420705.6 | Sep 2004 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/IB2005/053027 | 9/15/2005 | WO | 00 | 3/13/2007 |