Active self-cleaning surface by electro-wetting

Abstract

An optical element having an outer surface is provided. The optical element includes a coating on the outer surface for forming any fluid into droplets thereon, a plurality of independently actuated electrodes positioned adjacent to the outer surface and extending across a region of the outer surface and having a plurality of comb-shaped fingers, and a drive circuit for selectively applying signals to the plurality of electrodes. The AC signals applied to the plurality of electrodes having adjacent fingers each have a phase shift such that the fluid droplets are continuously swept in a predetermined direction across the outer surface. The electrode fingers can be arranged with a uniform pitch, which can be the distance between the centers of the electrodes, and the pitch can be 750 μm or less. The plurality of electrode fingers can be arranged in a single plane with a gap therebetween.

Description

Technical Field

[0001] This embodiment relates generally to self-cleaning surfaces, and more particularly to self-cleaning surfaces for discharging fluids used in vehicles.

Summary of the Invention

[0002] In one aspect of the present invention, an optical element includes a substrate having an outer surface on which fluid droplets can be formed, N independently actuatable electrodes each distinguishable by an order criterion n (n = 1 to N), and a drive circuit for selectively applying a phase-modulated AC signal to the electrodes. Each electrode has a plurality of electrode fingers positioned adjacent to the outer surface and extending across a region of the outer surface. The plurality of electrode fingers are arranged in a repeating sequence of 1 to N. The drive circuit generates the phase-modulated AC signal by applying N phase-modulated signals to the AC signal. The number N of the phase-modulated signals is equal to the number N of the independently actuated electrodes. Each phase-modulated signal is also distinguishable by the order criterion n (n = 1 to N) corresponding to each of the electrodes. Each phase-modulated signal periodically imposes a phase shift on the AC signal back and forth between an in-phase state and an anti-phase state in a period of T. The phase shift of each phase-modulated signal n is delayed in time by a time step t from the phase shift of the continuously preceding phase-modulated signal n - 1 such that the droplet is continuously swept in a predetermined direction across the outer surface. w An optical element is provided, characterized in that. s it is delayed in time by only the time step t.

[0003] In another aspect of the present invention, there is provided an optical element comprising a substrate having an outer surface on which fluid droplets can be formed, a plurality of independently actuatable electrodes each having a plurality of fingers positioned adjacent to the outer surface and extending across a region of the outer surface, and a drive circuit for selectively applying signals to the plurality of electrodes, wherein the electrode fingers are arranged at a uniform pitch, the pitch being the distance between the centers of the electrodes, and the pitch is 750 μm or less.

[0004] In another aspect of the present invention, there is provided an optical element comprising a substrate having an outer surface on which fluid droplets can be formed, a plurality of independently actuatable electrodes each having a plurality of fingers positioned adjacent to the outer surface and extending across a region of the outer surface, and a drive circuit for selectively applying signals to the plurality of electrodes, wherein the plurality of electrode fingers are arranged in a single plane with a gap therebetween.

[0005] These and other features, advantages, and objects of the apparatus of the present invention will be further understood and appreciated by those skilled in the art upon examination of the following specification, claims, and appended drawings.

[0006] Embodiments will now be described with reference to the following drawings.

Brief Description of the Drawings

[0007]

Figure 1

[0008]

Figure 2

[0009]

Figure 3

[0010]

Figure 4

[0011]

Figure 5

[0012]

Figure 6

[0013]

Figure 7

[0014]

Figure 8

[0015]

Figure 9

[0016]

Figure 10

[0017]

Figure 11

[0018]

Figure 12

[0019]

Figure 13

[0020]

Figure 14

[0021]

Figure 15

[0022]

Figure 16

[0023]

Figure 17

[0024]

Figure 18

[0025]

Figure 19

[0026]

Figure 20

[0027]

Figure 21

[0028]

Figure 22

[0029]

Figure 23

[0030]

Figure 24

[0031]

Figure 25A

[0032]

Figure 25B

[0033]

Figure 26A

[0034]

Figure 26B

[0035]

Figure 27

[0036]

Figure 28

[0037]

Figure 29

[0038]

Figure 30

[0039]

Figure 31

[0040]

Figure 32

DETAILED DESCRIPTION OF THE INVENTION

[0041] For the purposes of the description in this specification, the terms "upper", "lower", "right", "left", "rear", "front", "vertical", "horizontal", and derivatives thereof shall relate to the disclosure oriented in Figure 2. Unless stated otherwise, the term "front" refers to the surface of an element that can be exposed to water, and the term "rear" refers to the surface of an element further away from the front surface. However, it should be understood that the invention can take various alternative orientations, unless specifically specified otherwise. It should also be understood that the specific devices and processes illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concept defined in the appended claims. Accordingly, specific dimensions and other physical characteristics relating to the embodiments disclosed herein should not be considered limiting, unless the claims explicitly state otherwise.

[0042] The terms "including", "comprises", "comprising", or any other variation thereof are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by "comprises a..." does not, without further limitation, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises that element.

[0043] As used herein, the term "and / or" when used in a listing of two or more items means that any one of the listed items can be used alone or any combination of two or more of the listed items can be used. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0044] In advanced driver assistance systems and autonomous vehicles, as optical and electromagnetic imaging devices and sensors become ubiquitous, a self-cleaning outer surface becomes important for the reliable operation of these sensors and imaging devices. Sensors and imaging devices operating in the field are affected by environmental factors, and contaminants or droplets adhere to the first surface of the sensing device. To avoid blocking the field of view, it is preferable that contaminants on the first surface be removed as quickly and efficiently as possible.

[0045] Mechanical wipers are a conventional method of removing fluid from the front windshield and the first surface of various sensors and imaging devices and cleaning the surface. As future technologies advance towards advanced driver assistance and unmanned systems, multiple sensors must be placed at several critical locations on the vehicle. Clear signals from these sensors require an unobstructed field of view through optical elements such as the first surface of an optical or sensor device. Wipers, while effective, can block the field of view of sensors during operation, and many of these mechanical wipers increase the weight of the vehicle, the likelihood of mechanical failure, and the power requirements. Adding wipers to self-cleaning surfaces, such as in bathrooms or on building surfaces, is obtrusive.

[0046] Self-cleaning devices that apply (impart) strong mechanical vibrations to the surface have been proposed for cleaning vehicles. An example of such a device is disclosed in U.S. Patent No. 8,899,761 by the same applicant. The vibrations can eject fluid and debris perpendicularly from the surface, but in a moving vehicle, debris is likely to be propelled back onto the surface by the airflow unless it is blown onto the side. Droplets are swept along the surface, as conventional wipers do. When designed and oriented to sweep in the same direction, external forces such as gravity and airflow will assist and improve the efficiency of surface cleaning.

[0047] Another approach is to use a surface dehumidification device that uses an electrical signal on a surface having a patterned electrode. The surface is hereinafter referred to as an electro-wetting actuated self-cleaning hydrophobic (eWASH) surface. An example of an eWash surface is disclosed in U.S. Patent No. 8,172,159. This uses a DC voltage applied to the patterned electrode.

[0048] The present disclosure relates to an improved eWASH surface. The improved eWASH surface in the present disclosure is a non-shielding, robust, non-mechanical solution for cleaning surfaces. These improved eWASH surfaces can be made of a transparent material that is not visible to the naked eye.

[0049] The improved eWash surface enables the movement of multiple droplets of fluids of various droplet sizes on the order of tens of microns to millimeters for any application and can be extended over a large area. The improved eWash surface not only generally makes the surface transparent or clean, but more generally moves droplets. This can be useful for other purposes such as active water collection in coastal deserts where fog occurs constantly during part of the day but there is no rainfall. In water collection applications, water can be actively swept (flushed) into a water collection tank before the water evaporates or before the dew and accumulated water reach a volume threshold where gravity overcomes static friction and affects the movement of the droplets. The droplet size required for gravity to move the droplets may not be achievable depending on the weather conditions. However, according to this technique, the droplets can be moved without having to wait for the droplet size to become large enough for the action of gravity.

[0050] A new feature of this eWASH surface cleaning device, not seen in conventional self-cleaning surfaces, is the induced movement of droplets by electro-wetting, gravity, or other mechanisms to effectively sweep fluid from the surface. The eWASH system can aggregate small droplets of water, common solvents, and cleaning fluids into larger droplets and discharge (drop off) the droplets by an external force such as gravity. In various regions of the surface, simultaneously and / or at various times, the self-cleaning device can actively and continuously sweep the fluid droplets along one or more directions appropriate for the application.

[0051] As shown in FIGS. 1 and 2, the embodiments described below relate to an optical element 10 having an outer surface 15, the optical element 10 including a selective hydrophobic (or omniphobic) coating 20 on the outer surface 15 for forming any fluid thereon into fluid droplets 5, a dielectric layer 25 on which the hydrophobic coating 20 is disposed, a plurality of comb-shaped electrodes 30, 40, 60, 70 positioned on the dielectric layer 25 adjacent to the outer surface 15 and extending across regions of the outer surface 15, and a drive circuit 50 for selectively applying an AC signal to the plurality of electrodes 30, 40, 60, 70, wherein the AC signals applied to adjacent electrodes have a phase shift relative to each other in a manner that continuously sweeps the fluid droplets 5 in a predetermined direction across the outer surface 15.

[0052] According to one embodiment, the plurality of electrodes may include a first electrode 30 positioned adjacent to the outer surface 15 and a second electrode 40 positioned adjacent to the outer surface 15, the first electrode 30 having a plurality of first fingers 32 extending across regions of the outer surface 15, and the second electrode 40 having a plurality of second fingers 42 that are comb-shaped with and spaced from the plurality of first fingers 32 and extend across regions of the outer surface 15.

[0053] The plurality of electrodes may further include a selective third electrode 60 having a plurality of first fingers 32, a plurality of second fingers 42, and a plurality of third fingers 62 that extend across and are spaced apart in the region of the outer surface 15 and are comb-shaped, and a selective fourth electrode 70 having a plurality of first fingers 32, a plurality of second fingers 42, a plurality of third fingers 62, and a plurality of fourth fingers 72 that extend across and are spaced apart in the region of the outer surface 15 and are comb-shaped. As will be described below with respect to additional embodiments, a greater number of electrodes may be provided.

[0054] The drive circuit 50 may be further configured to selectively apply a voltage potential between the first electrode 30 and the second electrode 40 (and optionally between the third electrode 60 and the fourth electrode 70) in a manner that causes the fluid droplets to coalesce into larger fluid droplets and / or sweeps the fluid droplets across the surface.

[0055] The optical element 10 can be used in several applications. One example is a transparent cover for a vehicle camera or imaging device where the transparent cover includes the optical element 10. Other non-limiting examples include lens cover slips, the first surface of a lens, a windshield, a vehicle window, a building window, a solar cell, a mirror, any self-cleaning surface (automotive, household), a cover lens for Lidar or Radar, and a camera cover.

[0056] FIG. 2 shows the basic structure of the eWASH system on the surface 15 or substrate 12 according to the first embodiment. The electrode array layer (32, 42, and optionally 62, 72), the dielectric layer 25, and the hydrophobic, omniphobic, and / or oleophobic layer 20 can each be made from a plurality of layers of the same or different materials. The hydrophobicity and / or oleophobicity of the top layer 20 that contacts the fluid is the contact angle (θ of the fluid on the surface 15 C) It is characterized by. The dielectric layer 25 and the hydrophobic layer 20 can be made of different material layers or can be made of one and the same layer. The substrate 12 itself can be the same as the dielectric layer 25 or can be a separate layer from the dielectric layer 25. Further, the substrate 12 itself or the dielectric layer 25 itself can have hydrophobic properties, thereby eliminating the need for a separate coating 20. The conductive electrodes 30, 40, 60, 70 and / or their fingers 32, 42, 62, 72 can be arranged on the bottom surface of the dielectric layer 25. On the active region, the individual electrodes 30, 40, 60, 70 are not necessarily in electrical contact with each other, but the fingers 32, 42, 62, 72 can be grouped into a plurality of sets via contacts outside the active region. The overall pattern of the electrodes 30, 40, 60, 70 varies according to the embodiment or application. One or more of the electrodes 30, 40, 60, 70 can be directly exposed to the environment or can be arranged on the first surface 15. The gaps between the electrodes 30, 40, 60, 70 do not have to be uniform. The electrodes 30, 40, 60, 70 can be opaque or transparent. The outer surface 15 is preferably hydrophobic, but the embodiments described below can act on surfaces that are not considered hydrophobic (i.e., when the contact angle is less than 90 degrees).

[0057] This eWASH surface effectively dehumidifies. Other fluids and solvents such as water-alcohol mixtures and salt water can also be cleaned. The degree of effectiveness for various fluids depends on the fluid interaction with the hydrophobic coating 20 and the polarity of the fluid. The power or voltage level applied to the electrodes 30, 40, 60, 70 by the drive circuit can be adjusted to be more efficient with fluids or solvents other than water.

[0058] Fluids that are either non-polar, polar, or electrolytic can be polarized to varying degrees in the presence of an electric field. For example, applying an electric field to a non-polar molecule, such as isopropyl alcohol, causes the electron cloud to move and induces a dipole moment. On the other hand, water is polar and is composed of molecules with a net permanent dipole due to its molecular charge distribution. These water molecule dipoles align along the electric field whenever it is present (Figure 3).

[0059] The dielectrophoresis phenomenon is a principle often mentioned when explaining the dynamics of the system by the force on this polarized dielectric or droplet 5. A simple explanation of the phenomenon is provided below. Due to the polarization of permanent or induced dipoles in the fluid, these neutral fluid droplets are subjected to electric forces. For example, the energy minimization of the induced droplet dipoles in the presence of an electric field gradient induces a driving force of

Number

[0060] An equivalent way to view the electro-wetting phenomenon is from the perspective of the dynamic change in the induced contact angle of the fluid 5 on the surface. When there is a non-uniform electric field in the region with a gap or differential voltage, the droplet is attracted to the electrode gap or wetting on the region while showing a decrease in the contact angle. When the voltage difference is removed, the contact angle increases.

[0061] As described above, the droplet can be removed by agglomeration or sweeping. In addition, a combination of agglomeration and sweeping can be used. These three cleaning modes are described below.

[0062] First, the aggregation mode is described with reference to FIGS. 4A through 4C. FIGS. 4A through 4C show electrodes (IDEs) 30, 40, 60, 70 that are parallel or comb-shaped, and an alternating voltage can be applied to them all at once, or any voltage can be applied to individual fingers at various times and in various sequences. An electric field is generated when a differential voltage is applied between electrode fingers 32, 42, 62, 72. The profile and intensity of the electric field result in the flattening of droplet 5. The flattened droplet 5 reaches other flattened droplets 5 and fuses to form a larger droplet 5. The large droplet 5 slides and is discharged more efficiently via external forces such as gravity and air flow.

[0063] Passive aggregation can also be achieved by precisely patterning a surface having hydrophobic and hydrophilic regions. This is further explained below.

[0064] Another novel idea is a process of actively removing fluid droplet 5 from the eWASH surface 15 by continuously sweeping the presence of an electric field across surface 15. The sweeping mode is illustrated in FIG. 5. As described above, droplet 5 is attracted toward a region having pairs of electrode fingers 32, 42, 62, 72 having a differential voltage with a non-uniform electric field present. Thus, when pairs or groups of electrode fingers 32, 42, 62, 72 are continuously powered as shown in FIGS. 5A through 5C, droplet 5 of fluid that can span to the next electrode is moved in the direction of the electrical sweep. The electrical sweep, sweep direction, and profile of the geometry are described below.

[0065] Exemplary results using a glass substrate, indium tin oxide (ITO) electrodes 30, 40, 60, 70, SU8 photoresist as dielectric 25, and Teflon (registered trademark) AF as hydrophobic layer 20 are shown in FIGS. 6A through 6C and FIGS. 7A through 7C. FIGS. 6A through 6C show examples of aggregation (vertical orientation) and shedding (gravity along the fingers). FIGS. 7A through 7C show examples of sweeps without assistance from gravity (horizontal orientation).

[0066] Efficient dehumidification and surface cleaning can involve both aggregating droplets and sweeping droplets during the cleaning procedure. The power supply profile, aggregation, or sweeping can be performed in any order or simultaneously in different regions of the sample.

[0067] There are various ways to sweep the electrodes by sequentially supplying power to the group of electrodes 30, 40, 60, 70. One novel idea is that it is possible to supply power continuously and sequentially to the electrodes 30, 40, 60, 70 without the need to supply power to each electrode independently. FIG. 8 is helpful for explaining the implementation of this idea. It starts with a manageable number of electrodes 30, 40, 60, 70 that can be independently powered, for example, four electrode fingers 32, 42, 62, 72, which are sequentially numbered from 1 to 4. These sets of four electrode fingers can be repeatedly increased to the desired number of electrode fingers. In this example, as shown in FIG. 8, there are three sets (or tiles) of fingers 32, 42, 62, 72, each tagged with R, G, B respectively, for a total of 12 electrode fingers. The electrode fingers 32R, 32G, and 32B numbered 1 for all three sets are physically connected (the connection method is described below), and the electrode fingers 42R, 42G, and 42B numbered 2, the electrode fingers 62R, 62G, and 62B numbered 3, and the electrode fingers 72R, 72G, and 72B numbered 4 are also connected in the same way. Therefore, when electrode number 1 (30) is powered, all other sets of fingers numbered 1, 32R, 32G, and 32B are also powered. In other words, the fingers 32R, 32G, and 32B receive the same signal with the same phase from the drive circuit 50. Therefore, these electrode fingers are considered to be interconnected in a comb-like manner and arranged within the tile. In other words, a plurality of comb-like interconnected fingers 32, 42, 62, 72 are arranged within a plurality of tiles R, G, and B, and each tile R, G, and B includes one finger 32, 42, 62, 72 of each of the plurality of electrodes 30, 40, 60, 70 provided in a continuous order. The continuous order is repeated for each tile R, G, and B.

[0068] To create an effectively continuous sweep across all electrodes, drive circuit 50 may be constructed such that the signal period, i.e., the power supply cycle, on fingers 32, 42, 62, 72 is made equal to the period of the sweep across the set. When this protocol is applied continuously to all sets, droplets of fluid positioned on the first set are swept as if continuously as they move along all sets of electrodes 30, 40, 60, 70. This continuous sweep effect is shown in the exemplary timing charts of FIGS. 9 and 10.

[0069] With respect to the geometry or direction of the sweep, electrodes 30, 40, 60, 70 may be oriented such that, for example, their fingers 32, 42, 62, 72 extend horizontally perpendicular to the direction of gravity, such that the sweep direction may be parallel or antiparallel to the direction of gravitational attraction. The ability to orient electrode fingers 32, 42, 62, 72 and direct the sweep with appropriate electrode power supply sequencing and aggregation opens up an unlimited number of directions in which fluid droplets may be swept (the novel electrode geometries are described below).

[0070] A non-exhaustive list of sweep geometries and directions includes up-down sweeps, left-right sweeps, center-out sweeps, center-in sweeps, sweeps towards one or more aggregation points, radial sweeps (inward or outward), as well as diagonal and arbitrary angle sweeps.

[0071] A droplet staging / initialization region may be created for a snowball effect. The idea here is to give an aggregation and / or sweep head start outside of the active region such that the droplet grows to a size that more efficiently sweeps the active region or reaches a volume that is more susceptible to dehumidification and external forces before reaching the active region.

[0072] The difference in the electric field between the electrodes / fingers can be achieved by applying an AC voltage signal in various waveforms (such as square, sine wave, etc.). The frequency, waveform, phase, and voltage can be optimized according to the geometric shape (finger width, gap width, layer thickness) and electrical properties of the materials (substrate, dielectric, hydrophobic coating).

[0073] Each of the electrodes 30, 40, 60, 70 can be switched between an operating state, a grounded state, and a floating state, or can be flip-flopped continuously among a plurality of states during operation. Intermittently grounding all of the electrodes 30, 40, 60, 70 leaves time when the droplets are not electrically attracted to the surface, which can help to efficiently sweep the droplets and contaminants by external forces such as gravity and / or wind. An example of such an approach is shown in FIG. 11.

[0074] The signal applied to the electrodes can be phase-modulated. A uniform waveform can be applied to all of the electrodes 30, 40, 60, 70. The differential voltage is achieved by applying a phase difference of the waveform between the electrodes 30, 40, 60, 70. Next, the region with the phase shift can be continuously swept through the fingers to achieve the sweeping of the fluid droplets. An example is shown in FIG. 12.

[0075] The modulation of the amplitude and phase can be applied at various times, or the modulation of both the amplitude and phase can be applied simultaneously in separate regions of the active area. The phase difference of one gap with respect to another gap can be fixed, or the phases of a series of gaps can change continuously or arbitrarily. The amplitude of the voltage difference can also be adjusted by adjusting the phase difference between the electrodes 30, 40, 60, 70. The drive circuit 50 can supply a two-phase or multi-phase output signal to the individual electrodes. Next, a multi-pole or multi-throw switch between the available plurality of signals and the individual fingers 32, 42, 62, 72 can toggle between different signals or select waves to create an appropriate voltage sweep profile.

[0076] Various novel geometric shapes can be adopted for the electrodes 30, 40, 60, and 70. Parallel or comb-shaped electrodes (IDEs) are the simplest patterns that can be realized for the active self-cleaning feature by electro-wetting, but many other electrode pattern variations are possible. An example of this is the floating finger 82. Depending on the self-cleaning operation mode (aggregation and / or sweeping), the direction of the IDE can be oriented parallel or perpendicular to the drop / swelling direction. For example, when the fingers 32, 42, 62, 72 have alternating high and low voltages (see FIGS. 13A and 13B), the droplet 5 has difficulty crossing the next gap due to the orientation of the electric field on the next gap. In this case, the self-cleaning on the surface is more efficient when the IDEs are aligned along the direction of gravity or other external forces. This avoids the dead end (stack) of the droplets that have to cross the gap with the opposing electric field or opposing force.

[0077] A useful trick for the droplet to spread and cross the gap is to place an electrically insulated, i.e., floating, conductive electrode finger 82 between two electrode fingers 32, 42 with a voltage difference. If the droplet 5 is large enough, the droplet 5 can extend across the entire gap between the two operating electrode fingers 32, 42 (see FIG. 13B). Also, there is no opposing electric field between the operating electrode fingers 32, 42. The electric field around the gap of the floating electrode finger 82 is always in the same direction. This has the additional advantage that the droplets in the active electrode fingers 32, 42 are attracted to each other.

[0078] The floating electrode finger 82 also avoids the droplet 5 being statically attracted to the electrode fingers 32, 42, as shown in FIGS. 14 and 14B. When the dielectric 25 is very thin (dielectric thickness << gap width), the probability of leaving residual charges on the electrode fingers 32, 42 and the static polarization of the droplet 5 increase (see FIGS. 15A and 15B).

[0079] The floating finger 82 is neutral and insulated. Therefore, the net charge does not change or is always balanced. All the charge separation that would occur when the device is powered is lost on the floating finger when the device's power supply ends.

[0080] Having the exposed electrode finger 92 can be useful because the exposed electrode finger 92 can transfer charge by ionization of the droplets it contacts. FIGS. 16A and 16B show the comb-shaped exposed electrodes 92 on the surface 15 of interest. Additional insulating electrodes 90a, 90b are disposed around above the dehumidifying surface 15, and the insulated comb-shaped fingers 32, 42, 62 are below the surface 15. The first step of the process is to apply a voltage difference between the exposed electrode finger 92 and the peripheral electrodes 90a, 90b. Charge transfer occurs between the exposed electrode finger 92 and the droplets. The second step includes sweeping the droplet 5 by a suitable series of power supplies and potentials on the insulated comb-shaped electrode fingers 32, 42, 62. The electrophoresis phenomenon is the principle that appropriately describes the force generated on the charged droplet 5.

[0081] The electrode fingers can also be serrated as shown in FIG. 17. Fingerless fingers without pins (smooth) increase the density of the gap lines, the number of gaps, the effective length of the gap lines, or the area to which the droplet is attracted. The spikes on the electrode fingers are also useful for generating a non-uniform electric field that creates an unbalanced force that can propel the droplet 5. The droplet 5 stops moving at the boundary, and if the boundary is spiky, the droplet is continuously drawn to the end of the spike. This can, in some serrated designs, draw the droplet 5 to the start of the next electrode and thus prevent the droplet 5 from stacking.

[0082] The sizes of fingers 32, 42, 62, 72 and the gap width can also change gradually. This can increase the droplet sweeping efficiency. For example, the sweep can start from a narrower finger / gap to a larger finger / gap, and as droplet 5 starts small and grows as it moves across the fingers and gaps, it can be swept more efficiently.

[0083] Also, it is possible to combine / group the individual fingers 32, 42, 62, 72 to effectively create larger fingers. As gradually more individual fingers are powered together simultaneously / identically, the droplet can be efficiently moved as the droplet grows or "snowballs" across the electrode fingers.

[0084] Thin film transistors (TFTs) are an option for generating the active electrode pattern on the surface of a support substrate 12 such as glass or transparent polyimide. The electrode pattern can be pixelated, and a differential voltage can be applied between pairs or groups of pixels to move the droplet in any direction. TFTs enable integrated circuits on the substrate, thereby enabling applications that require a large area or a high number of channels. Using TFTs can also reduce the number of contacts required.

[0085] The layered geometry of the electrode fingers 32, 42, 62, 72 can also be used. An example of the layered geometry is an in-plane geometry IDE with an insulating ground plane 95 below, as shown in FIG. 18. Additional electrode fingers 32, 42, 62, 72 or the conductive plane 95 can also be arranged in separate layers on a surface separated by an insulating material or dielectric 25. For example, FIG. 18 shows an in-plane geometry. The conductive plane 95 is arranged below the comb-like electrodes. The non-uniform electric field to which the droplet is attracted is generated by powering the individual electrodes with a polarity opposite to that of the conductive plane 95 and leaving its adjacent electrodes floating.

[0086] Another example of a layered geometry is a layered parallel geometry. When power is applied, the electrode fingers 32 can have regions of zero or uniform electric field, such as at the center of the electrode fingers or at the center of the gaps. Thus, droplets located in those regions may not experience cohesive or sweeping forces. A way to minimize regions with little electric field non-uniformity is to add another lower layer of electrode fingers 42 offset from the first pattern, as shown in FIG. 19.

[0087] Yet another example of a layered geometry is a layered hash. The additional underlying electrode fingers 62, 72 need not be parallel to the first layer pattern of electrode fingers 32 and 42. As shown in FIG. 20, the comb-shaped layers may be orthogonal to each other. This hash pattern allows for multi-directional sweeping of the droplets.

[0088] Another geometry that can be used is an inverted-coated geometry. The last layer is covered with an electrode, inverted, and then bonded to the substrate with the electrode sandwiched between the last layer and the substrate. Electrodes, such as ITO, PDOT, graphene, can be coated on the back surface of the first layer (e.g., glass, parylene).

[0089] Other geometries include stacked IDEs (IDE|Dielectric|IDE), stacked IDEs with a slight angular shift, and tiled agglomerations (Tiled IDE) to avoid larger capacitances.

[0090] While various geometries of electrodes have been described, various connection configurations of the electrodes will be described. One such connection is an overlapping link mechanism or a bypassed cross electrode. The electrode fingers can be grouped together by shortening the overlap and thereby providing an overlapping link mechanism. An electrically insulated cross, bypassed cross between electrodes can be achieved by placing a layer of high dielectric strength material between the overlapping electrodes. These are useful ways to group or route electrode fingers 32, 42, 62, 72 having a spiral or overlapping geometry as shown in FIG. 21. Other connections can be made by vias or anisotropic conductive films (ACF).

[0091] The heater can be used in combination with electro-wetting. This can be useful when the surface 15 is exposed to snow and ice, the heater melts the snow and ice into water, and the water can then be removed using the methods described above.

[0092] Also, it may be desirable to utilize capacitance sensing to trigger (operate) the capabilities of the device. The IDE is basically a capacitor. Contaminants and droplets on the surface of the electro-wetting device change the effective capacitance measured within the device via capacitive coupling and change the effective dielectric constant due to additional layers of water and contaminants. An example is shown in FIG. 22. This inherent capacitance sensing ability of eWASH can be used to trigger voltage sweeps or water sprays, air blowing, and other complementary or supplementary cleaning procedures of the device. The capacitance sensing ability can be used to trigger internal and external processes inside and outside the eWASH surface. In other words, a plurality of comb-shaped fingers provide capacitance sensing of droplets on the outer surface, and the drive circuit is configured to apply a plurality of signals to the plurality of electrodes in response to capacitance sensing of droplets on the outer surface.

[0093] In the following embodiments, a plurality of electrodes are provided in a single plane, and there are a plurality of gaps between the plurality of electrodes. In such an arrangement, the following metrics enable active and efficient sweeping of various droplet sizes. [Figure 2] Pitch < droplet diameter < N * pitch Where N is the number of independently actuated electrode fingers per tile, and pitch is the distance between the centers of adjacent electrode fingers that are uniformly sized and spaced. FIGS. 23A and 23B show the effect of pitch on small droplets 5. In FIG. 23A, the pitch between adjacent electrodes is greater than the diameter of droplet 5. At such a large pitch, it may be difficult to move droplet 5. In FIG. 23B, the pitch is smaller, thereby facilitating the sweeping of small droplet 5. FIG. 24A shows a larger droplet 5, with the pitch the same as in FIG. 23B but smaller than the diameter of the droplet. The example of FIG. 24A has two independently actuated electrodes 30, 40 (N = 2), each having fingers 32, 42. Thus, there are two electrode fingers 32, 42 per tile. Since the tile size is relatively small compared to droplet 5, it may be difficult to move the larger droplet 5. In FIG. 24B, the number of independently actuated electrodes is N = 8 for eight electrode fingers 32, 42, 62, 72, 82, 92 per tile with a phase change for every four electrode fingers. A larger tile size is more effective in moving the larger droplet 5. However, for moving smaller droplets, it is beneficial to perform sweeping, as further explained below.

[0094] The inventors have found that a smaller pitch is better because it allows smaller droplets to be moved more effectively and larger droplets to still be moved, especially when the tiling concept is used to group sets of electrode fingers together. Thus, the pitch can be 750 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less.

[0095] The replication of a limited number (N) of active independent electrodes by tiling or generation is a new technique used to construct a larger active area from a small number of independent electrodes. By tiling, this technique can be extended to large areas. Tiling is performed by connecting a set of electrode fingers (see sets A - G in FIG. 27) to the bus wire / conductive connector 18. By tiling, when a voltage is set on any one individual electrode finger, for example, electrode finger 1 of set A, it is replicated within the remaining electrode fingers 1 of electrode sets B - G. In tiling, the sweeping of the active region 17 of the outer surface 15 occurs simultaneously on multiple sweeping fronts. FIGS. 25A, 25B, 26A, and 26B illustrate the sweeping motion of the negatively charged sections and the non - negatively charged sections (or tiles). The droplet is attracted to the boundary between the shadowed section where the electric field exists and the non - shadowed section.

[0096] The tiling that creates the section of the active region 17 generates a new continuous voltage operation on the electrodes such that, even though the tiling is a mirror of the other sections and what occurs in each section is the same as the other sections, the droplet 5 is acted upon by a continuous pull across the entire region of the active region 17. One key to effectively creating a continuous sweep across all the electrodes is to make an integer multiple of the voltage signal period or power supply cycle on the electrode fingers equal to the time that the entire sweep signal / pattern spatially traverses the set of electrode fingers. When this protocol is applied to all sets, the droplet 5 of fluid positioned on the first set corresponding to a certain section is swept as it moves along all sets of the electrode fingers as if it were continuous. The continuous sweep effect is illustrated by the timing chart shown in FIG. 28, which shows the phase modulation signals used for each electrode to adjust the phase of the AC signal. Thereby, the phase modulation AC signal is applied to each electrode. In FIG. 28, the modulation signal is either “low” or “high”, representing “in-phase” and “anti-phase” respectively. For the purpose of explanation, each electrode can be identified by an order criterion n (where n = 1 to N, and N is the total number of electrodes independently activated). Each electrode has a plurality of electrode fingers that inherit the reference number of the said electrode. The electrode fingers are arranged in a continuous order of repetition from 1 to N for each tile A, B, C,.... Each electrode 1 to N is driven by a corresponding phase modulation AC signal. Each phase modulation AC signal is generated from a single AC signal. For example, using the corresponding number N of the phase modulation signals shown in FIG. 28, it is phase-modulated separately for each electrode. Thus, each phase modulation signal can also be identifiable by an order criterion n corresponding to each electrode (where n = 1 to N). Each phase modulation signal imposes a phase shift on the AC signal periodically back and forth between an in-phase state (e.g., 0°) and an anti-phase state (e.g., 180°) during a period of T w such that the phase shift of each phase modulation signal n is delayed in time by a time step t s from the phase shift of the preceding phase modulation signal n - 1 sequentially so that the droplet is continuously swept in a predetermined direction across the outer surface.

[0097] In the example shown in FIG. 27, electrode fingers of 12 independently controlled electrodes (N = 12) are provided for each set of electrodes (or tiles) A to G, and the phase-modulated AC signals applied to each finger are the same, but each electrode is in the in-phase or antiphase state determined by the phase-modulated signal shown in FIG. 28. To provide a continuous sweep, for any number of independently actuated electrodes, the time step t s is t s = T w / N. The values of t s and T w can change over time. Thus, the droplet continues to be swept from the Nth finger of tile A to the first finger of tile B. If the timing reference (t s = T w / N) is not met, this “hand-off” between tiles will result in a discontinuity in the sweep. As an example, the AC signal can have a frequency of 500 Hz, the number N of independently actuated electrodes is 12, and the phase-modulated signal can have a period T w of 24 milliseconds. In this case, the time step t s is 2 milliseconds. For a square-wave phase-modulated signal that imposes a phase of either 0° or 180° on the AC signal at any instant, the progression of the 0° / 180° phase offset moves from one pair of fingers to the next pair every t s (e.g., 2 ms). A further advantage of the in-phase / antiphase (0° / 180° phase) selection is that it allows for a two-fold effective voltage while minimizing the voltage supplied by the driver. The higher the voltage of the driver, the more complex and costly it becomes. Using the example of N = 12 and a phase shift of 0° or 180°, the following table shows the phase shifts applied to the AC signal for each of 36 electrode fingers (3 fingers per electrode) over a time interval w during one period T ts .

Table 1-1

Table 1-2

[0098] The combination of the aggregation and sweep cycles is a novel idea. Sweeping may be more effective by aggregating smaller droplets into larger droplets.

[0099] The aggregation cycle is the application of a voltage such that the overall voltage pattern does not move in a particular direction on average. The sweep cycle is a voltage pattern that spatially shifts in a certain direction over time. In the sweep cycle, an instantaneous or average velocity can be defined for the overall voltage pattern. In the aggregation cycle, there may be movement in individual parts of the pattern, but the overall pattern of the voltage within the active region does not shift in space.

[0100] In this application for removing and cleaning fluid droplets, both the aggregation cycle and the sweep cycle can be used. The sweep cycle has been previously described and is illustrated in FIGS. 27 and 28. The aggregation cycle applies an AC or DC electric field by applying a voltage difference across two electrodes or across a group of electrodes. Recall that the droplets are attracted to the region where the differential voltage is generated. The aggregation cycle enables multiple droplets to be attracted to the region having the differential voltage, and the droplets can grow by aggregating or combining with each other. For aggregation, all other electrode fingers can be of opposite phase, and thus only two channels may be required. For sweeping, more independent channels are better, and such an arrangement can still perform the aggregation.

[0101] AC sweeping is different from a DC voltage that is swept across an electrode or voltage channel. AC sweeping means that the polarity of each electrode is reversed one or more times before the sweep pattern spatially moves to the next electrode. Note that the next electrode does not necessarily mean an adjacent electrode. AC sweeping is more effective in (1) avoiding charge accumulation on electrodes that can cause pinning (stacking), (2) removing droplets from pinning points due to droplet vibration during AC sweeping, and (3) pushing and attracting droplets. Also note that simply shorting an electrode driven by a DC voltage may not be sufficient to remove accumulated charge from the outer surface. However, when using an AC voltage, the voltage changes from positive to negative and since there is no net charge on the surface, the average voltage is zero.

[0102] It is possible to push droplets by AC sweeping. Pushing / repelling droplets rather than attracting them is a novel idea. When the electric field or voltage is DC, a droplet with a fixed dipole orientation reorients with the nearby DC so that the dipole moment is anti-parallel or angled with respect to the electric field. With an AC voltage or AC electric field sweep, a portion of the droplet can reorient its dipole, but each reorientation causes an instant of increased overall potential energy within the droplet. This increase is associated with a repulsive force on the induced dipole on the droplet. Here, as shown in FIGS. 29 and 30, ground (GND) is the voltage level between a low voltage and a high voltage. By using an intermediate ground voltage to push droplet 5, the electric field generated from the ground electrode is not as strong as the electric field generated by the voltage difference across the high-low voltage electrodes. This means that the electric field from the ground electrode provides pushing but is not sufficient to reverse the dipole orientation, while the electric field of the high-low voltage is strong enough to maintain the dipole orientation fixed.

[0103] There is a distinct advantage in expanding the regions of the first and last electrodes 16, 19 so that the droplets are not repelled on the first or last (depending on the direction of sweeping) electrodes. FIG. 31 shows an example of the repulsion of a droplet on the end of the last electrode or the repulsion from outside the active region.

[0104] The explanation for this is something like a droplet pressing effect. Instead, the regions outside the electrodes are grounded so that the electric field from outside the active region to the end electrodes opposes the dipoles induced in the droplet. To avoid repulsion at the end of the sweep, as shown in FIG. 32, the area of the last electrode (or the first electrode depending on the sweep direction) can be expanded. This generates an equipotential surface outside the active region, and as a result, the force due to the electric field does not stop the droplet from sliding beyond the active region during operation.

[0105] In addition to or as an alternative to the expanded first and second electrodes 16, 19, those regions can be coated with a hydrophilic material so as to draw the droplet 5 out of the active region 17. In other words, the hydrophilic coating can be positioned close to the edge of the outer surface where the droplet is swept.

[0106] Note that the outer surface layer does not need to be hydrophobic. It can be omniphobic. Oils and other droplets, such as ice water droplets or snow removal flakes, can also be moved. In various patterns of droplet repellency or droplet affinity, the droplets can be collected as a reservoir or can sink to positions inside and outside the active region.

[0107] The drive circuit 50 can be configured to variably adapt the frequency of the AC signal to change the speed at which the droplet is swept across the outer surface. For example, the sweep speed can be adjusted between about 20 - 40 mm / second by changing the frequency between about 400 Hz and 1 KHz. The period of the AC signal can be selected such that each period moves the droplet by the distance of one electrode finger. The speed of droplet sweeping can be adapted to be the terminal speed of the droplet.

[0108] Another means of controlling the droplets on the surface is through the use of patterned hydrophobicity. When a droplet lands on the boundary between a more hydrophobic region and a less hydrophobic region, the droplet will typically move towards the less hydrophobic region. This can be utilized to passively direct the droplets into smaller regions (or to induce them to coalesce), which helps to fuse the droplets and form larger droplets in addition to aggregation or sweeping. For example, it can have alternating stripes of a more hydrophobic layer and a less hydrophobic layer. If the less hydrophobic region is too hydrophilic, the water will be too wet and will not protrude, fall, or be extruded from the glass, which is not ideal or may interfere with the sweeping. Another embodiment is a checkerboard pattern of more hydrophobic regions and less hydrophobic regions, or less hydrophobic spots on a more hydrophobic background. In either case, the goal is an alternative way to increase the coalescing droplets. Hydrophobic patterning can be used independently of or in combination with electrowetting.

[0109] A hydrophobic gradient (true gradient) is a continuous version of hydrophobic patterning that can be considered as adjacent regions of more finely varying hydrophobicity. The idea is that droplets tend to move more easily in the direction of lower hydrophobicity, and this can be utilized to help drive the droplets in the desired direction. The gradient can also be generated by two binary combinations of hydrophobicity, but can be patterned on a scale much smaller than the droplets, so the effective hydrophobicity is the gradient. The different hydrophobicities can be two spatially patterned coatings of different materials, the removal of a single coated material, or the surface patterning of a single substrate or coating material.

[0110] The hydrophobic layer 20 can be sprayed or coated on the surface, or can be fabricated by microstructuring and / or nanostructuring the surface. Possible hydrophobic materials include Teflon® AF, Optool UD120, parylene AF4, Optool DSX, CYTOP, PDMS, polyisobutylene (PIB), rare earth ceramic oxides, and Aquapel.

[0111] The substrate 12 can be made of any type of glass or plastic and can be rigid or flexible.

[0112] The electrodes can be made of indium tin oxide, a transparent ceramic conductor, or PEDOT, a transparent polymer conductor.

[0113] The dielectric 25 can be made of SU-8 (a photoresist polymer), a polymer-ceramic composite, ultrathin glass, a ceramic oxide or nitride (Al2O3, SiO2, Si3N4), or parylene.

[0114] Although 2 to 12 electrodes have been described above, of course, any number of electrodes can be used.

[0115] The above material list is not exhaustive as far as what can be used. It is preferred that the electrodes be sufficiently conductive (we do not have a specific value for this property that we know of), that the dielectric not allow surface water to reach the electrodes (and be electrically insulating), and that the hydrophobic layer be sufficiently hydrophobic. By definition, hydrophobic means a water contact angle > 90 degrees. In some cases, both the hydrophobic function and the dielectric function can be achieved by a single layer of material.

[0116] Those skilled in the art will understand that the described disclosure and the construction of other components are not limited to any particular materials. Other exemplary embodiments of the invention disclosed herein can be formed from a wide range of materials, unless otherwise described herein.

[0117] As used herein, the term "coupled" (in all of its forms, such as couple, coupling, coupled, etc.) generally means that two components (electrical or mechanical) are joined to each other, either directly or indirectly. Such a joining can be essentially stationary or essentially movable. Such a joining can be achieved with two components (electrical or mechanical), as well as with additional intermediate members integrally formed with each other or with the two components and a single unit. Such a joining can be essentially permanent, or, unless otherwise stated, can be essentially removable, i.e., detachable.

[0118] It is also important to note that the construction and arrangement of the elements of the present disclosure as shown in the exemplary embodiments are merely illustrative. Although only a few embodiments of the present invention are described in detail in this disclosure, those skilled in the art who consider this disclosure will readily recognize that many modifications are possible (e.g., the sizes, dimensions, structures, shapes and ratios of various elements, parameter values, attachment methods, use of materials, colors, orientations, etc.) without departing from the novel teachings and advantages of the recited subject matter. For example, an element shown as integrally formed can be composed of a plurality of parts or elements shown such that the plurality of parts can be integrally formed, the operation of the interface can be changed inversely or in other ways, the structure of the system and / or the length or width of the members or connectors or other elements can be changed, and the nature or number of adjustment positions provided between the elements can be changed. The elements and / or assemblies of the system can be composed of any wide range of materials that provide sufficient strength or durability in any wide range of colors, textures, and combinations. As a result, all such modifications are intended to be included within the scope of the present invention. Other substitutions, modifications, changes, and omissions can be made in the design, operating conditions, and arrangement of other desired exemplary embodiments without departing from the spirit of the present invention.

[0119] It should be understood that any described process or steps within a described process may be combined with other disclosed processes or steps to form a structure within the scope of the present device. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting.

[0120] Also, without departing from the concept of the present device, modifications and changes can be made to the aforementioned structures and methods, and furthermore, it should be understood that such concepts are intended to be covered by the following claims, unless otherwise explicitly stated in the claims in words.

[0121] The foregoing description is considered to be only of the illustrated embodiments. Those skilled in the art, as well as manufacturers or users of the present device, will envision variations of the device. Therefore, the embodiments shown in the drawings and the foregoing description are for illustrative purposes only and are not intended to limit the scope of the present device, which is defined by the following claims interpreted in accordance with the principles of patent law, including the doctrine of equivalents.

Claims

1. An optical element comprising: a substrate having an outer surface on which fluid droplets can be formed; N independently activatable electrodes, each identifiable by an order criterion n (n = 1 to N); a drive circuit for selectively applying a phase-modulated AC signal to the electrodes; wherein each electrode has a plurality of electrode fingers positioned adjacent to the outer surface and extending across a region of the outer surface, the plurality of electrode fingers are arranged in a repeating sequence of 1 to N, the drive circuit generates the phase-modulated AC signal by applying N phase-modulated signals to the AC signal, the number N of the phase-modulated signals is equal to the number N of the independently activated electrodes, each phase-modulated signal is also identifiable by the order criterion n (n = 1 to N) so as to correspond to each of the electrodes, Each phase modulation signal periodically applies a phase shift to the AC signal forward and backward between an in-phase state and an anti-phase state at the period of T w and The phase shift of each phase modulation signal n is continuously delayed by a time step t from the phase shift of the immediately preceding phase modulation signal n-1 so that the droplet is continuously swept in a predetermined direction across the outer surface. s only temporally characterized in that it is an optical element.

2. The plurality of electrode fingers are arranged in a single plane with a gap therebetween, characterized in that it is the optical element according to claim 1.

3. The plurality of electrode fingers are arranged with a uniform pitch, the pitch is the distance between the centers of the electrodes, the pitch is 750 μm or less, characterized in that it is the optical element according to claim 1 or 2.

4. The drive circuit is further configured to selectively apply a voltage potential between adjacent fingers so as to agglomerate the fluid droplets into larger fluid drops, characterized in that it is the optical element according to any one of claims 1 to 3.

5. the time step t s is equal to w T / N characterized in that it is the optical element according to any one of claims 1 to 4.

6. The drive circuit is configured to variably adapt the frequency of the AC signal to change the speed at which the droplets are swept across the outer surface, characterized in that it is the optical element according to any one of claims 1 to 5.

7. The last electrode finger of the plurality of electrode fingers is positioned close to the edge of the outer surface across which the droplets are swept, the last electrode finger of the plurality of electrode fingers is larger than the other electrode fingers, characterized in that it is the optical element according to any one of claims 1 to 6.

8. a hydrophilic coating positioned close to the edge of the outer surface across which the droplets are swept, characterized in that it further comprises the optical element according to any one of claims 1 to 7.

9. The plurality of electrode fingers provides capacitance sensing of droplets on the outer surface, and the drive circuit is configured to apply the phase-modulated AC signal to the electrodes in response to the capacitance sensing of the droplets on the outer surface. The optical element according to any one of claims 1 to 8, characterized in that.

10. The plurality of electrode fingers are arranged in a plurality of tiles, each tile including one finger of each of the number of electrodes provided in a continuous order, and the continuous order is repeated for each tile. The optical element according to any one of claims 1 to 9, characterized in that.

11. An optical element, comprising: a substrate having an outer surface on which droplets of a fluid can be formed; a plurality of independently actuated electrodes each having a plurality of fingers positioned adjacent to the outer surface and extending across a region of the outer surface; a drive circuit for selectively applying signals to the plurality of electrodes; wherein: the electrode fingers are arranged with a uniform pitch, the pitch being the distance between the centers of the electrodes, and the pitch is 750 μm or less. The optical element, characterized in that.

12. The pitch is 200 μm or less. The optical element according to claim 11, characterized in that.

13. The pitch is 100 μm or less. The optical element according to claim 12, characterized in that.

14. The drive circuit is configured to selectively apply a phase-modulated AC signal to the plurality of electrodes. The optical element according to any one of claims 11 to 13, characterized in that.

15. The phase-modulated AC signals applied to the plurality of electrodes having adjacent fingers are each the same, but in a manner that continuously sweeps the droplets of the fluid in a predetermined direction across the outer surface, with a time delay in the phase shift relative to each other at time step t s having a time delay of The optical element according to claim 14, characterized in that.

16. The plurality of electrode fingers are arranged in a single plane with a gap therebetween. The optical element according to any one of claims 11 to 16, characterized in that.

17. The drive circuit is further configured to selectively apply a voltage potential between adjacent fingers so as to aggregate the droplets of the fluid into larger fluid drops. The optical element according to any one of claims 11 to 16, characterized in that.

18. The plurality of comb-shaped electrode fingers provides capacitance sensing of droplets on the outer surface, and the drive circuit is configured to apply the signal to the plurality of electrodes in response to the capacitance sensing of the droplets on the outer surface. The optical element according to any one of claims 11 to 17, characterized in that.

19. The plurality of comb-shaped electrode fingers are arranged in a plurality of tiles, each tile including one finger of each of the plurality of electrodes provided in a sequential order, the sequential order being repeated for each tile The optical element according to any one of claims 11 to 18, characterized in that.

20. An optical element, a substrate having an outer surface on which droplets of a fluid can be formed, a plurality of independently actuated electrodes each having a plurality of fingers positioned proximate to and extending across a region of the outer surface, a drive circuit for selectively applying signals to the plurality of electrodes, comprising the plurality of electrode fingers are arranged in a single plane with gaps therebetween The optical element according to claim 20, characterized in that.

21. The drive circuit is configured to selectively apply a phase-modulated AC signal to the plurality of electrodes The optical element according to claim 20, characterized in that.

22. The phase-modulated AC signals applied to the plurality of electrodes having adjacent fingers are each the same, but in a manner such that a droplet of fluid is continuously swept in a predetermined direction across the outer surface, with a time delay in the phase shift relative to each other at time step t s having a time delay of The optical element according to claim 21, characterized in that.

23. the plurality of electrode fingers are arranged with a uniform pitch, the pitch being the distance between the centers of the electrodes, the pitch being 750 μm or less The optical element according to any one of claims 20 to 22, characterized in that.

24. the plurality of comb-shaped electrode fingers provide capacitance sensing of droplets on the outer surface, the drive circuit being configured to apply the signal to the plurality of electrodes in response to the capacitance sensing of droplets on the outer surface The optical element according to any one of claims 20 to 23, characterized in that.

25. the plurality of comb-shaped electrode fingers are arranged in a plurality of tiles, each tile including one finger of each of the plurality of electrodes provided in a sequential order, the sequential order being repeated for each tile The optical element according to any one of claims 20 to 24, characterized in that.

Images