GB2584466A

GB2584466A - Device for manipulating a substance

Info

Publication number: GB2584466A
Application number: GB1907987.0A
Authority: GB
Inventors: Frozanpoor Iman
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-06-05
Filing date: 2019-06-05
Publication date: 2020-12-09
Anticipated expiration: 2039-06-05
Also published as: GB201907987D0; GB2584466B

Abstract

A device 10 for manipulating a substance, e.g. a liquid droplet or ice, comprises: a plurality of interdigitated electrode pairs 12; and a dielectric layer 15 comprising one or more sub-layers disposed on the electrodes. The electrode pairs are selectively energisable and a first electrode of each pair is spaced from a second electrode of the pair by 100 µm or less. The dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 × 106 V/m when the plurality of electrode pairs are selectively energised by a voltage of 100V or less. The dielectric layer can comprise a sub-layer comprising photosensitive epoxy resin 14, e.g. SU8 photoresist, and/or a hydrophobic material 16 comprising a hydrophobic self-assembled monolayer including octadecyltrichlorosilane (OTS). A top sub-layer of the dielectric layer can include an oil-based lubricant. A liquid droplet may be caused to move across the top surface by selectively energising the electrodes. Alternatively, the electrodes may produce heat so that a frozen solid on the top surface is melted or sublimated. A vehicle, e.g. a windscreen of a vehicle, comprising one or more of the devices is also claimed.

Description

DEVICE FOR MANIPULATING A SUBSTANCE

TECHNICAL FIELD

The present disclosure relates to a device for manipulating a substance and particularly, but not exclusively, where the substance is a droplet or a solid. Aspects of the invention relate to a device for manipulating a substance, to a vehicle that includes the device, and to an assembly that includes the device.

BACKGROUND

The two conventional methods of electrically controlling a droplet on a surface are known as electrowetting and dielectrowetting. Although electrowetting has been predominantly studied for numerous applications, the technology is restricted by a range of practical constraints. Dielectrowetting, on the other hand, has been gaining considerable attention for overcoming the limitations of electrowetting. Dielectrowetting is based on liquid dielectrophoresis (L-DEP), which is a bulk force generated when a non-uniform electric field interacts with the electric dipoles within a liquid. It is known that dielectrowetting can overcome the contact angle saturation limitation associated with electrowetting in order to spread droplets into a thin liquid film. It is also known that there is a relationship between the change of contact angle at a solid-liquid interface (e.g. a droplet on a surface) and the voltage applied. The actuation of sessile droplets using L-DEP can be explained through asymmetric electrostatic forces changing the contact angle on one side of the droplet, thus causing motion.

However, there are certain drawbacks associated with existing prior art techniques.

Firstly, very high voltages (e.g. in excess of 360 V) are required to sufficiently change the contact angle, thus precluding the application of the technology to devices where such high voltages would not be possible or practical. Secondly, prior art studies demonstrating how droplets have been moved across a surface have been reliant on knowledge of the volume of the droplets (e.g. requiring feedback) in order to select the operating parameters required to move the droplets. Thus, such technology is not suitable for the manipulation of droplets of unknown volume.

It is an object of embodiments of the invention to at least mitigate one or more of the

problems of the prior art.

SUMMARY OF THE INVENTION

Aspects of the invention relate to a device for manipulating a substance, to a vehicle that includes the device, and to an assembly that includes the device, as defined in the appended claims.

In accordance with another aspect of the present invention, there is provided a device for manipulating a substance, the device comprising: a plurality of interdigitated electrode pairs; and a dielectric layer disposed on the plurality of interdigitated electrode pairs, the dielectric layer comprising one or more sub layers; wherein the plurality of interdigitated electrode pairs are selectively energisable and a first electrode of each interdigitated electrode pair is spaced from a second electrode of the interdigitated electrode pair by 100 lam or less; and wherein the dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100V or less; and wherein a substance on the top surface may be manipulated by the electric

field.

Such a device may facilitate manipulation of a substance, such as a droplet or a solid, using a low operating voltage when compared to prior art devices.

In certain embodiments, the dielectric layer may have a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 50 V or less, or 30 V or less.

In certain embodiments, the dielectric layer may have a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 1 x 107 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100 V or less, 50 V or less, or 30 V or less. Such an electric field is particularly effective at manipulating a substance on the top surface.

In certain embodiments, the dielectric layer may have a thickness less than 1 less than 500 nm, between 400 nm and 500 nm, or about 450 nm.

The dielectric layer may include a sub layer comprising photosensitive epoxy resin. In certain embodiments, the photosensitive epoxy resin may comprise SU8 photoresist.

In certain embodiments, the dielectric layer may include a sub layer comprising a hydrophobic material. The hydrophobic material may comprise a hydrophobic self-assembled monolayer, which, in certain embodiments, may comprise octadecyltrichlorosilane (OTS).

Additionally or alternatively, the dielectric layer may include a top sub layer comprising a lubricant (e.g. an oil-based lubricant).

In certain embodiments, each of the first and second electrodes of each interdigitated electrode pair may comprise a root, a plurality of branches that extend from the root, and a plurality of sub-branches that extend from the branches. Such an arrangement may serve to enhance the local electric fields generated by the electrodes In certain embodiments, the plurality of branches of the first electrode of each interdigitated electrode pair may be interdigitated with the plurality of branches of the second electrode of the interdigitated electrode pair. The root of the first electrode of each interdigitated electrode pair may be substantially parallel to the root of the second electrode of the interdigitated electrode pair. The plurality of branches may extend substantially perpendicularly from the respective root. In certain embodiments, the plurality of sub-branches may extend substantially perpendicularly from the respective plurality of branches. Each of the plurality of sub-branches of the first electrode of each interdigitated electrode pair may have a longitudinal axis that is not coincident with a longitudinal axis of each of the plurality of sub-branches of the second electrode of the interdigitated electrode pair.

In certain embodiments, the plurality of sub-branches may extend from the respective plurality of branches at an inclined angle that is not 90°.

In certain embodiments, the plurality of sub-branches of each of the first and second electrodes of each interdigitated electrode pair may be substantially wedge-shaped.

In certain embodiments, the plurality of sub-branches of each of the first and second electrodes of each interdigitated electrode pair may comprise a first set of subbranches and a second set of sub-branches, where the first set of sub-branches is not identical to the second set of sub-branches. The first set of sub-branches may extend from the respective branch by a different amount relative to the second set of subbranches.

In certain embodiments, the device may comprise a substrate layer upon which the plurality of interdigitated electrode pairs are disposed. In certain embodiments, the substrate may be flexible.

In certain embodiments, the device may comprise a controller arranged to selectively energise the plurality of interdigitated electrode pairs.

In accordance with another aspect of the invention, there is provided a vehicle comprising one or more devices as described above.

In accordance with another aspect of the invention, there is provided an assembly comprising a substantially translucent material having one or more devices as described above embedded therein or affixed thereto. In certain embodiments, the substantially translucent material may comprise a vehicle windscreen or an optical component.

In accordance with an aspect of the invention, there is provided a controller for performing a method of manipulating a substance on a surface adjacent a plurality of electrode pairs, the controller being arranged to iteratively perform until a predetermined first condition is met: (a) a mth cycle comprising iteratively energising a nth subset of the plurality of electrode pairs in a nth step and a n=n+lth step until a predetermined second condition is met; wherein in the n=n+lth step (i) electrode pairs of the n=n+lth subset are adjacent to electrode pairs of the nth subset, and (h) the n=n+lth subset comprises the same number of electrode pairs as the nth subset; and (b) a m=m+lth cycle that is identical to the mth cycle except wherein in the m=m+lth cycle each subset comprises a different number of electrode pairs than each subset in the mth cycle; wherein the droplet is manipulated on the surface by an electric field created by energised subsets of the plurality of electrode pairs.

The method may facilitate manipulation of a substance on a surface adjacent a plurality of electrode pairs without requiring feedback in order to select the operating parameters required to manipulate the substance (e.g. move droplets).

In certain embodiments, in the n+1th step, none of the nth subset is energised.

In certain embodiments, each subset may comprise at least one pair of interdigitated electrodes. In an initial mth cycle, each subset may comprise a single pair of interdigitated electrodes. Each interdigitated electrode pair may intersect a common longitudinal axis.

In certain embodiments, in the m+1th cycle, each subset may comprise one more electrode pair than each subset in the mth cycle.

In certain embodiments, the mth cycle may terminate when a n+1th subset is energised and n+1 is equal to 3.

In certain embodiments, the method performed by the controller may terminate when a m+1th cycle is performed and m+1 is equal to 4.

In certain embodiments, manipulating a substance on a surface adjacent a plurality of electrode pairs may comprise moving a droplet across the surface.

In certain embodiments, energising electrode pairs may comprise energising electrode pairs using a voltage of 100 V or less, 50 V or less, or 20 V or less.

The controller may be arranged to selectively energise the electrode pairs at a frequency selected from a plurality of possible frequencies. In certain embodiments, the controller may be arranged to be additionally selectively operable in a heating mode in which the electrode pairs are selectively energisable at a frequency that causes a substance on the surface to be heated.

In accordance with another aspect of the present invention, there is provided an apparatus comprising a controller as described above and a device coupled to the controller, the device comprising: a plurality of interdigitated electrode pairs; a dielectric layer disposed on the plurality of interdigitated electrode pairs, the dielectric layer comprising one or more sub layers; wherein the plurality of interdigitated electrode pairs are selectively energisable by the controller and a first electrode of each interdigitated electrode pair is spaced from a second electrode of the interdigitated electrode pair by 100 pm or less; and wherein the dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100V or less; and wherein a droplet on the top surface may be manipulated by the electric

field

The dielectric layer may have a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 50 V or less, or 30 V or less.

The dielectric layer may have a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 1 x 107 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100 V or less, 50 V or less, or 30 V or less.

In certain embodiments, the dielectric layer may have a thickness less than 1 jtm, less 25 than 500 nm, between 400 nm and 500 nm, or about 450 nm.

In accordance with another aspect of the present invention, there is provided a vehicle comprising the controller described above or the apparatus of any of claims 13 to 16.

In accordance with another aspect of the present invention, there is provided a method of manipulating a substance on a surface adjacent a plurality of electrode pairs comprising iteratively performing: (a) a mth cycle comprising iteratively energising a nth subset of the plurality of electrode pairs in a nth step and a n=n+lth step until a predetermined second condition is met; wherein in the n=n+lth step (i) electrode pairs of the n=n+1th subset are adjacent to electrode pairs of the nth subset, and (ii) the n=n+lth subset comprises the same number of electrode pairs as the nth subset; and (b) a m=m+lth cycle that is identical to the mth cycle except wherein in the m=m+1th cycle each subset comprises a different number of electrode pairs than each subset in the mth cycle; wherein the substance is manipulated on the surface by an electric field created by energised subsets of the plurality of electrode pairs.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a partially cut-away perspective view of a device in accordance with an embodiment of the present invention; Figure 2A shows a top-down view of a device in accordance with an embodiment of the present invention; Figures 2B (i) to (iv) show chronologically progressive views of detail B of Figure 2A with a droplet present; Figure 3 shows a perspective view of a device according to an embodiment of the present invention with a droplet present on a top surface; Figure 4 shows a perspective view of a device according to an embodiment of the present invention during fabrication; Figure 5 shows a schematic overview of electrodes of a device according to an embodiment of the present invention; Figures 6A to 6D each show a schematic overview of alternative electrodes of a device according to an embodiment of the invention; Figure 7 shows a schematic representation of a method of controlling electrodes in accordance with an embodiment of the present invention; Figure 8 shows a schematic representation of how a specific method of controlling electrodes may be performed in accordance with an embodiment of the present invention; Figures 9a to 9h show chronologically progressive views of droplets on a device in accordance with an embodiment of the present invention; Figure 9i shows a schematic representation of the method performed to produce the effects shown in Figures 9a to 9h; and Figure 10 shows a vehicle according to an embodiment of the present invention.

DETAILED DESCRIPTION

Figure 1 shows a partially cut-away perspective view of a device 10 in accordance with an embodiment of the present invention. The device 10 is configured to be capable of manipulating a substance, such as a liquid droplet or a solid (e.g. ice), as is explained below.

The device 10 comprises a plurality of electrodes 12 disposed on a substrate 18. The electrodes 12 are energisable so that an electric field in the vicinity of the electrodes 12 may be created. The electrodes 12 are energisable by creating a potential difference between one of the plurality of electrodes 12 and another of the plurality of electrodes. For example, one electrode may act as a ground electrode relative to one or more of the other electrodes. The applied voltage may be constant or variable in time.

The plurality of electrodes 12 is overlaid by a dielectric layer 15. In the non-limiting embodiment shown in the Figures, the dielectric layer 15 comprises two sub layers, namely, a primary dielectric layer 14 and a hydrophobic layer 16 that is disposed on top of the primary dielectric layer 14. In certain embodiments, the dielectric layer 15 may include a superhydrophobic layer..

In certain embodiments, one of the sub layers of the dielectric layer 15 (e.g. the primary dielectric layer 14) may comprise a photosensitive epoxy resin, for example SU8 photoresist. A thinner dielectric layer 15 may be employed by using alternative insulating materials such as silicon dioxide or aluminium oxide.

In certain embodiments, the hydrophobic layer 16 may comprise a hydrophobic self-assembled monolayer (e.g. octadecyltrichlorosilane (OTS)).

A top surface 15a of the dielectric layer 15 (which, in the embodiment shown in Figure 1, is a top layer of hydrophobic layer 16 and a top surface of the device 10 as a whole) defines a surface that may support a substance such as a liquid droplet or a solid such as ice, wherein the substance may be manipulated by an electric field generated by energised ones of the plurality of electrodes 12. For example, in accordance with methods according to embodiments of the present invention, a liquid droplet may be caused to move across the top surface 15a by selectively energising the plurality of electrodes 12. Additionally or alternatively, the energised electrodes 12 may produce heat so that a frozen solid disposed on the top surface 15a may be partially or fully melted (or sublimated). In alternative embodiments, the dielectric layer 15 may comprise one or more sub layers, and not necessarily the primary dielectric layer 14 and hydrophobic layer 16 described above.

In certain embodiments, the spacing between the plurality of electrodes 12 is 100 am or less. In other embodiments, the spacing between the plurality of electrodes 12 is 20 pm or less, or even as small as 5 pm or less.

In certain embodiments, the dielectric layer 15 has a thickness and composition such that an electric field at the top surface 15a of the dielectric layer 15 is at least 2 x 106 V/m when the plurality of electrodes are selectively energised by a voltage of 100 V or less.

The electric field at the top surface 15a causes a change in contact angle (at the solid-liquid interface) of a droplet disposed on the top surface. If the change in contact angle is sufficient, the droplet may be caused to move on the top surface.

Devices in accordance with certain embodiments of the present invention may be operable at lower voltages relative to prior art arrangements, thus facilitating their suitability to a wide variety of applications. Lower operating voltages are made possible by a reduction in the spacing between electrodes relative to prior art arrangements. However, this leads to a lower penetration depth of the electric field created by energised electrodes, so the dielectric layer (i.e. its thickness and composition) needs to be selected so that the electric field at the top surface 15a is at least 2 x 106 V/m. At such a magnitude, a droplet may have a contact angle at the solid-liquid interface such that it may be moved or otherwise manipulated by selective activation of the electrodes 12. In this context, the thickness of the dielectric layer 15 may be considered to be the dimension along a direction substantially perpendicular to the general plane that includes the plurality of electrodes 12. In particularly advantageous embodiments, the electric field at the top surface is at least 1 x 107 V/m despite using a voltage of 100 V or less. The electric field required to manipulate the droplet may be reduced by the presence of a lubricant (e.g. an oil-based lubricant) on the top surface 15a. In this sense a top sub layer of the dielectric layer 15 may be considered to be a lubricant layer.

In certain embodiments, the dielectric layer may have a thickness less than 1 rAm, less than 500 nm, between 400 nm and 500 nm, or about 450 nm.

Figure 2A shows a top-down view of a device 10 in accordance with an embodiment of the present invention. The device of Figure 2A comprises a plurality of electrodes 12 and may otherwise be in accordance with the device 10 described above in relation to Figure 1.

Figures 2B (i) to (iv) show chronologically progressive photographic views of detail B of Figure 2A with a droplet 20 present on the top surface. In Figure 2B electrodes in the shaded region 13 are energised while electrodes outside of shaded region 13 are not energised. As can be seen from the progression from (i) to (iv), as the shaded region 13 representing energised electrodes is moved across the device 10, the droplet 20 is also caused to move across the top surface 15a. In the example shown in Figure 2B, the droplet comprises deionised water and the electrodes were energised using 100 V at 50 kHz with 100 ms delay per step.

Figure 3 shows a perspective view of a device 10 according to an embodiment of the present invention. The device 10 extends along a longitudinal axis 24 that is intersected by each of the plurality of electrodes 12. In the non-limiting embodiment shown in Figure 3, one of the plurality of electrodes 12 serves as a common ground electrode, and others of the plurality of electrodes 12 are arranged to form pairs of electrodes between themselves and the common ground electrode. That is, a series of electrode pairs is provided, but the pairs share a common electrode so there are no unique pairs. The pairs of electrodes 12 are selectively energisable to create an electric field that is experienced by a droplet 20 on the top surface 15a and consequently manipulated. By sequentially energising the pairs of electrodes 12, the droplet 20 may be caused to move along the top surface 15a in the direction indicated by numeral 22 in Figure 3 (which is parallel to the longitudinal axis 24).

A device 10 according to an alternative embodiment is shown in Figure 4. The device of Figure 4 is not fabricated on a substrate per se (that is distinct from the dielectric layer). Rather, the dielectric layer 15 acts as a substrate for supporting the electrodes 12. Moreover, the dielectric layer 15 comprises a flexible material so that the device 10, as a whole, is flexible. The flexible device 10 may be affixed (indicated by arrow 28 in Figure 4) to a surface 26 that may be curved and/or be flexible itself. In some embodiments, the device 10 may be provided with an adhesive protecting layer for affixing the device 10 to a surface.

Figure 5 shows a schematic overview of a plurality of electrodes 12 of a device 10 according to an embodiment of the present invention. Each electrode 12 comprises a root 12a, a plurality of branches 12b that each extend from the root 12a, and a plurality of sub-branches 12c that each extend from each of the plurality of branches 12b. Each electrode 12 additionally includes an electrode pad 12d that is greater in area relative to adjacent areas of the respective electrode 12. The electrode pad 12d may be used to electrically connect the electrode to a source of electrical energy so as to apply a potential difference. In the non-limiting embodiment shown in Figure 5, some electrodes 12 (every alternate one) share a common electrode pad 12d. In alternative embodiments, each electrode 12 may comprise an individual electrode pad 12d. Also in the non-limiting embodiment shown in Figure 5, certain ones of the electrodes 12 include branches 12b that extend from opposite sides of the respective root 12a. In the particular embodiment shown, the branches 12b extending from one side of the respective root 12a are of a different length to the branches 12b extending from the other side of the root 12a. In alternative embodiments, branches 12b extending from both sides of a root 12a may be of substantially equal length.

The electrodes 12 are arranged in pairs so that the plurality of branches 12b of a first electrode 12 are interdigitated with the plurality of branches 12b of a second, adjacent electrode 12 of the pair. Thus, the two adjacent electrodes 12 may be described as an interdigitated electrode pair. As noted above, in some embodiments, a single electrode 12 may serve as a common electrode to two or more of the other electrodes 12 so that not all pairs comprise unique electrodes 12.

In the specific embodiment shown in Figure 5, the interdigitated electrode pairs are unique as no one electrode features in more than one pair.

The non-limiting embodiment of Figure 5 additionally shows an arrangement in which the root 12a of the first electrode 12 of each interdigitated electrode pair is substantially parallel to the root 12a of the second electrode 12 of the interdigitated electrode pair. Furthermore, each of the plurality of branches 12b extends substantially perpendicularly from the respective root 12a. Each of the plurality of sub-branches 12c extends from the respective plurality of branches 12b at an inclined angle (i.e. an angle that is not 90°). In the embodiment of Figure 5, the sub-branches 12c all extend from their respective branch 12b in the same direction relative to the longitudinal axis 24 irrespective of which of the electrodes of the pair they belong.

Figures 6A to 6D each show a partial view of alternative electrodes of a device according to an embodiment of the invention. In particular, Figure 6A shows an arrangement that is similar to the embodiment of Figure 5, but wherein the spacing between adjacent sub-branches 12c is smaller relative to the respective spacings shown in Figure 5.

In certain embodiments, the plurality of sub-branches 12c of each of the first and second electrodes 12 of each interdigitated electrode pair comprise a first set of subbranches and a second set of sub-branches, where the first set of sub-branches is not identical to the second set of sub-branches. For example, in the embodiment shown in Figure 6B, a first set of sub-branches 12c comprise longer sub-branches 12c than a second set of sub-branches and individual ones of the first set are alternately arranged with individual ones of the second set. For the avoidance of doubt, a "longer" subbranch 12c extends further from the respective branch 12b relative to a "shorter subbranch 12c.

Figure 6C shows an embodiment in which the sub-branches 12c are substantially wedge-shaped (i.e. generally triangular) and extend from the respective branches 12b to form a saw-tooth profile.

In the embodiment of Figure 6D, the plurality of sub-branches 12c extend substantially perpendicularly from the respective plurality of branches 12b. Moreover, each of the plurality of sub-branches 12c of the first electrode of each interdigitated electrode pair has a longitudinal axis that is not coincident with a longitudinal axis of each of the plurality of sub-branches 12c of the second electrode of the interdigitated electrode pair. To state this another way, the plurality of sub-branches 12c of the first electrode of each interdigitated electrode pair are not aligned with the plurality of sub-branches 12c of the second electrode of the interdigitated electrode pair along an axis that is perpendicular to the axes along which the branches 12b extend.

The geometrical "irregularities" provided by the arrangements shown in Figures 5 and 6A to 6D serve to enhance the local electric fields generated by the electrodes 12.

Figure 7 shows a schematic representation of a method 100 of controlling a plurality of electrodes 12 in accordance with an embodiment of the present invention.

The method 100 starts at block 102 and a cycle number m is set to 1 at block 104 (since a first cycle of controlling the electrodes 12 must take place prior to any subsequent cycle) and a counter n is set to 1 at block 106. The counter n is used to define a step number.

The method 100 includes an outer iterative loop 124 in which m is increased by 1 each time until a maximum value of m, mmax, is reached. The method 100 additionally includes an inner iterative loop 122 which is nested in the outer iterative loop 124 and in which n is increased by 1 each time until a maximum value of n, nmax, is reached. Considering the inner iterative loop 122, at block 108 a check is made to verify that n has not yet reached nmax. If it has not, an nth subset of the plurality of electrode pairs 12 is energised in a nth step at block 110. Next, n is increased by 1 at block 112 and the verification at block 108 is repeated. If n=n+1 remains below nmax, then the inner iterative loop 124 continues and a nth subset (for n=n+i) of the plurality of electrode pairs 12 is energised at block 110 in a n=n+lth step. In the n=n+lth step, electrode pairs of the n=n+lth subset are adjacent to electrode pairs of the nth (i.e. previously energies) subset. Additionally, in the n=n+lth step the n=n+lth subset comprises the same number of electrode pairs as the nth subset. That is, for a given cycle (i.e. a given value of m) the number of electrode pairs energised in each subset does not change.

The value of n is increased at block 112 once more and the inner iterative loop 122 is repeated until the updated value of n equals nmax.

If block 108 determines that n=nmax then a check is made at block 114 as to whether the cycle number m has reached mmax. If it has not, then a notional change is made to the number of pairs of electrodes that are to be energised in the forthcoming cycle (relative to the number of energised electrode pairs in each subset in the previous cycle). The change made at block 116 could be an increase or a decrease which may be according to a fixed increment or a changeable increment. In certain embodiments, the change made at block 116 is an increase where the increment of the change is according to a sequence or a part of a sequence. For example, the change made at block 116 may be an increase according to a part of the Fibonacci sequence, e.g. 1, 2, 3, 5. Once the change has been made at block 116, the cycle number m is increased at block 118 and the inner iterative loop 122 cycles from n=1 to n=nmax, where the number of electrode pairs energised at block 110 is according to the number set previously at block 116.

The inner iterative loop 122 and the outer iterative loop 124 continue until n=n max as determined at block 108 and m=mmax as determined at block 114. When these two conditions are met, the method 100 ends at block 120.

In alterative embodiments, other suitable predetermined conditions (i.e. other than n=nmax and/or m=mmax) may be used to terminate the outer iterative loop 124 and/or the inner iterative loop 122.

In certain embodiments, the inner iterative loop 122 may be performed and repeated with the same number of energised electrode pairs before the outer iterative loop 124 causes the number of energised electrode pairs to be changed.

In certain embodiments the method 100 may be performed simultaneously over several regions of an array of electrodes. That is, the area over which the method is performed may be easily varied so that the present invention may be suitably scaled to a wide variety of applications.

Figure 8 shows a schematic representation of how a specific method 100' of controlling electrodes 12 (labelled IDEs for interdigitated electrodes) may be performed in accordance with an embodiment of the present invention. In particular, Figure 8 schematically represents electrode pairs 12 by a 0 or a 1, where a 0 denotes a non-energised electrode pair 12 and a 1 denotes an energised electrode pair 12. In Figure 8, the step numbers 1 to 3 correspond to n=1, 2, 3 (where nmax = 3) with respect to the inner iterative loop 122 described above. Similarly, the cycle numbers 1 to 4 correspond to m=1, 2, 3, 4 (wherein mmax=4) with respect to the outer iterative loop 124 described above.

In a -151 cycle (i.e. m=1), 1" to ad steps (i.e. n=1, 2, 3) are performed. In a 1st step (n=1), a single electrode pair is energised. That is, the subsets of the 1st cycle comprise a single electrode pair. In a second step (n=2), a single electrode pair that is adjacent to the previously energised electrode pair is energised (i.e. relative to the 1st step). In a third step (n=3) a single electrode pair that is adjacent to the previously energised electrode pair is energised (i.e. relative to the 2"d step).

In the example of Figure 8, the method is performed multiple times simultaneously across the array of electrode pairs (10 times in the lst cycle in the specific example shown in Figure 8). In this example, the simultaneously energised electrode pairs are spaced from one another so that the final subset (i.e. in the n th step) of energised electrode pairs in the cycle is adjacent to the first subset (i.e. e in the 1st step) of rna.x_ energised electrode pairs in that same cycle.

In the 2" cycle (i.e. m=2), 1' to ad steps (i.e. n=1, 2, 3) are performed once more, but with a different number of electrode pairs in each energised subset (relative to the previous cycle, m=1). In particular, two electrode pairs are energised in each step (n=1, 2, 3) of the 2"d cycle.

In the 3rd cycle (i.e. m=3), 1st to ad steps (i.e. n=1, 2, 3) are performed once more, but with a different number of electrode pairs in each energised subset (relative to the previous cycle, m=2). In particular, three electrode pairs are energised in each step (n=1, 2, 3) of the 3rd cycle.

In the 4th cycle (i.e. m=3), 1st to as steps (i.e. n=1, 2, 3) are performed once more, but with a different number of electrode pairs in each energised subset (relative to the previous cycle, m=3). In particular, five electrode pairs are energised in each step (n=1, 2, 3) of the 4th cycle. n,

The number of electrode pairs energised in the 1st Znd 3rd and 4th cycles are 1, 2, 3, 5 respectively which is in accordance with a part of the Fibonacci sequence.

Figures 9a to 9e demonstrate an example of the effectiveness of a method of the type described above in relation to Figures 7 and 8. A schematic representation of the method performed to produce the effects shown in Figures 9a to 9h is shown in Figure 9i.

Figures 9a to 9h show chronologically progressive views of droplets 20 on a top surface 15a of a device in accordance with an embodiment of the present invention. In Figure 9a, three droplets 20 are present and are of different volumes, namely 2.5 4 pl, and 9 al. The droplets comprise droplets of deoinised water.

The top surface 15a is a top surface of a lubricant layer (i.e. the dielectric layer includes a lubricant layer as its uppermost layer). The electrode pairs (not visible in Figures 9a to 9h) are selectively energised in accordance with a method 100" that is schematically represented in Figure 9i in order to produce the effects shown in Figures 9a to 9h. The electrode pairs are energised at a voltage of 85 V with a frequency of 50 kHz, with a 100 ms delay per step (an additional delay time was also employed to enable a precise monitoring of the droplets in this example). The method 100" causes the movement of the droplets across the top surface 15a. The cycles were each repeated three times and this ensured a complete transition of the droplets to the left side of the top surface 15a. In the specific method 100", the code repeats itself every three electrode pairs. The method 100" may be applied to any number of electrode pairs, but a minimum of nine electrode pairs are needed for the three iteration cycles depicted in Figure 9i.

Considering the effect of the method 100" on the droplets 10, the smaller droplets 20 are initially caused to move (by the activation of single electrode pairs) and the 4 pl droplet merges with the 9 pl droplet. However, after 1.5 seconds, the newly formed larger droplet covers an area of the top surface 15a that overlays more than three electrode pairs and, as a consequence, the actuation towards the left side of the device is delayed until the full set of iterations is repeated multiple times. The actuation process of a droplet moving from one electrode pair to another is only possible when the droplet moves to an area over an electrode pair which is due to be active (i.e. energised), otherwise it will move back to the previous electrode for the next set of iterations. Furthermore, depending on the application, the back-and-forth motion of the droplets on the top surface 15a may be desirable as it can be used to remove impurities from the top surface 15a. Alternatively, a direct linear actuation, which avoids the backand-forth motion, can be realised using a longer activation of the electrode pairs, or a device with a higher electrode resolution.

The results shown in Figures 9a to 9h verify that the actuation of droplets with varying volume is possible using low operating voltages, without the need of any active feedback control system. Furthermore, the generated electric fields can penetrate mild ionic solutions (such as salty water) when they are applied with a sufficient high frequency.

Figure 10 shows a vehicle 200 according to an embodiment of the present invention. The vehicle 200 may incorporate any of the devices described above and/or any component that is controlled according to the methods described above. For example, a windscreen 202 of the vehicle 200 may include any of the devices described above such that liquid droplets may be caused to move to a specified region of the windscreen (e.g. an edge). In alternative embodiments, other components such as substantially translucent materials of the vehicle may incorporate the above-described devices and/or be controlled according to the above-described methods.

In alternative embodiments, the methods and/or apparatus described above may be used to manipulate substance in a manner other than that depicted in Figures 9a to 9h (i.e. other than transporting liquid droplets along the top surface). For example the substance that is to be manipulated may be a solid (e.g. ice). Devices and/or methods according to embodiments of the present invention may be used to cause melting or sublimation of the solid substance. Such an operation may be achieved by selecting the frequency at which the voltage is applied to the electrode pairs to be one that causes heating of the substance. Alternatively, devices and/or methods according to embodiments of the present invention may be used to spread a liquid substance (that may initially, for example, be in droplet form) over the top surface.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims

CLAIMS1. A device for manipulating a substance, the device comprising: a plurality of interdigitated electrode pairs; and a dielectric layer disposed on the plurality of interdigitated electrode pairs, the dielectric layer comprising one or more sub layers; wherein the plurality of interdigitated electrode pairs are selectively energisable and a first electrode of each interdigitated electrode pair is spaced from a second electrode of the interdigitated electrode pair by 100 ttm or less; and wherein the dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100V or less; and wherein a substance on the top surface may be manipulated by theelectric field.
2. A device according to claim 1, wherein the dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 2 x 106 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 50 V or less, or 30 V or less.
3. A device according to claim 1, wherein the dielectric layer has a thickness and composition such that an electric field at a top surface of the dielectric layer is at least 1 x 107 V/m when the plurality of interdigitated electrode pairs are selectively energized by a voltage of 100 V or less, 50 V or less, or 30 V or less.
4. A device according to any preceding claim, wherein the dielectric layer has a thickness less than 1 pm, less than 500 nm, between 400 nm and 500 nm, or about 450 nm.
5. A device according to any preceding claim, wherein the dielectric layer includes a sub layer comprising photosensitive epoxy resin.
6. A device according to claim 5, wherein the photosensitive epoxy resin comprises SU8 photoresist.
A device according to any preceding claim, wherein the dielectric layer includes a sub layer comprising a hydrophobic material.
8. A device according to claim 7, wherein the hydrophobic material comprises a hydrophobic self-assembled monolayer.
9. A device according to claim 8, wherein the hydrophobic self-assembled monolayer comprises octadecyltrichlorosilane (OTS).
10. A device according to any preceding claim, wherein the dielectric layer includes a top sub layer comprising a lubricant.
11. A device according to claim 9, wherein the lubricant is an oil-based lubricant.
12. A device according to any preceding claim, wherein each of the first and second electrodes of each interdigitated electrode pair comprises a root, a plurality of branches that extend from the root, and a plurality of sub-branches that extend from the branches.
13. A device according to claim 12, wherein the plurality of branches of the first electrode of each interdigitated electrode pair are interdigitated with the plurality of branches of the second electrode of the interdigitated electrode pair.
14. A device according to claim 12 or 13, wherein the root of the first electrode of each interdigitated electrode pair is substantially parallel to the root of the second electrode of the interdigitated electrode pair.
15. A device according to any of claims 12 to 14, wherein the plurality of branches extend substantially perpendicularly from the respective root.
16. A device according to any of claims 12 to 15, wherein the plurality of sub-branches extend substantially perpendicularly from the respective plurality of branches.
17. A device according to claim 16, wherein each of the plurality of sub-branches of the first electrode of each interdigitated electrode pair has a longitudinal axis that is not coincident with a longitudinal axis of each of the plurality of subbranches of the second electrode of the interdigitated electrode pair.
18. A device according to any of claims 12 to 17, wherein the plurality of sub-branches extend from the respective plurality of branches at an inclined angle that is not 90°.
19. A device according to any of claims 12 to 17, wherein the plurality of subbranches of each of the first and second electrodes of each interdigitated electrode pair are substantially wedge-shaped.
20. A device according to any of claims 12 to 19, wherein the plurality of subbranches of each of the first and second electrodes of each interdigitated electrode pair comprise a first set of sub-branches and a second set of sub-branches, where the first set of sub-branches is not identical to the second set of sub-branches.
21. A device according to claim 20, wherein the first set of sub-branches extends from the respective branch by a different amount relative to the second set of sub-branches.
22. A device according to any preceding claim, comprising a substrate layer upon which the plurality of interdigitated electrode pairs are disposed.
23. A device according to claim 22, wherein the substrate is flexible.
24. A device according to any preceding claim, comprising a controller arranged to selectively energise the plurality of interdigitated electrode pairs.
25. A vehicle comprising one or more devices according to any preceding claim.
26. An assembly comprising a substantially translucent material having one or more devices according to any of claims 1 to 24 embedded therein or affixed thereto.
27. An assembly according to claim 26, wherein the substantially translucent material comprises a vehicle windscreen or an optical component.