WO2008097440A2

WO2008097440A2 - Electro-wetting optical light steering

Info

Publication number: WO2008097440A2
Application number: PCT/US2008/001047
Authority: WO
Original assignee: Xtreme Energetics Inc.
Priority date: 2007-02-05
Filing date: 2008-01-24
Publication date: 2008-08-14
Also published as: WO2008097440A3

Abstract

A transmission-mode electro-optical system is presented for solar energy tracking and collection. The scale of the system may range from small portable systems to large-scale industrial power plants used for the production of environmentally benign energy. It maybe integrated directly into buildings and other platforms without the need for heliostats to hold photovoltaic cells or other energy conversion devices above the building or other host platform. The system makes separates solar energy harvesting systems into tracking, collection, concentration, aggregation, distribution, and energy conversion subsystems.

Description

Patent Application of

Leo D. DiDomenico

for

TITLE: ELECTRO-WETTING OPTICAL LIGHT STEERING

CROSS-REFERENCE TO RELATED APPLICATIONS: Not Applicable

FEDERALLY SPONSORED RESEARCH: Not Applicable

SEQUENCE LISTING OR PROGRAM: Not Applicable

BACKGROUND OF THE INVENTION— FIELD OF INVENTION:

The present invention relates to the field of variable-angle optical tracking collectors for nonimaging optical concentrator systems, more specifically to substantially flat profile fluid-fluid refractive index boundaries having a variable electronically controlled tilt to track an input source of light, especially for non-imaging applications, which do not have the point-to-point ordering constraint of rays found in imaging optical systems.

BACKGROUND OF THE INVENTION— PRIOR ART

There is a fundamental difference between imaging and non-imaging optical elements when they are used for the concentration of light. In the case of imaging optical systems, like lenses, there is a requirement that light which leaves the object must be reconstructed point-for-point at Patent Application of Leo D. DiDomenico for "Electro-Wetting Optical Light Steering" — Continued

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the image plane. This strict point-for-point constraint must be maintained so that the image is accurately reproduced at the image plane of the optical system.

In contradistinction, non-imaging optical systems do not have this constraint and therefore have a greater degree of freedom in the relative design of the intermediate optics. For example, a nonimaging concentrator may be required to transfer the maximum amount of energy from a source of energy to a receiver of the energy without regard to the point-to-point ordering of the light rays from the source to the receiver.

In the common case of non-imaging light concentrators that are based on the principles of ray optics the light must obey optical momentum-phase-space conservation limitations. These fundamental limitations physically link the acceptance and exit solid angles of the optical systems with the degree of obtainable light concentration. In particular, as a cone of light from a finite source of radiation becomes concentrated in an optical system its light-cone angle grows so that a narrow input beam of optical energy becomes spread out in solid angle as the area of the image becomes concentrated. This can be called the law of the conservation of optical momentum.

As a result of this principle optical devices that provide very high levels of concentration must have relatively small acceptance angles. This is seen in many prior art examples such as the example given by Roland Winston in U.S. Patent 6,676,263; and Juan C. Minano in U.S. Patent 6,639,733. Other examples include inhomogeneous medium devices as well as an assortment of other concentrator types as described by the author Roland Winston et. al. in the text "Nonimaging Optics", ISBN: 0-12-759751-4, published by Elsever in 2005.

In all the examples sited in these prior-art documents high levels of concentration are marked by small input acceptance angles, which typically have an acceptance half-angle of less than 1 degree for concentrations greater than about 3300. Even lower levels of concentration can have extremely small and restrictive input angles. For applications where the source moves, such as in solar energy applications, the small input angle of optical concentrators requires a tracking mechanism to stay fixed on the solar source. Examples of mechanical tracking for non-imaging concentrator systems are ubiquitous and many typical systems are listed in the text book mentioned above. These mechanical tracking systems are all of limited practical use because of the high cost and relatively Patent Application of Leo D. DiDomenico for "Electro-Wetting Optical Light Steering" — Continued

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low reliability associated with mechanical hardware compared to solid-state and wet-state devices.

The physical principles of electro-wetting have their origin in the fields of interfacial chemistry and electrostatics. The first theoretical description was made by Nobel Prize winner Gabriel Lipp- mann in his seminal paper in the year 1875 — Annals Of Chemical Physics 5, page-494. A more recent account can be found in "Equilibrium Behavior of Sessile Drops Under Surface Tension, Applied External Fields, and Material Variations", Journal of Applied Physics Volume 93, Number 9, 2003 May 1, by Benjamin Shapiro et. al..

The first to successfully develop imaging lens devices with electro wetting is Bruno Berge of the Universite Joseph Fourier and patented as U.S. Patent 6,369,954 in April year 2002. This prior art discloses a variable focus lens that uses the Electro- Wetting (EW) phenomenon to vary the shape of a drop of transparent nonconducting fluid that is adjacent to a conducting fluid to achieve a variable focus lens. This prior art does not suggest the use of a flat — non-shape-deforming — tilting optical interface for non-imaging applications. Because this prior art is completely concerned with the creation of a variable-focus imaging lens there is a very important and explicit need to include in the patent a means to center the fluid lens — as was stated in the only independent claim of this prior art patent. The centering is through a symmetric change in the wettability around the lens and is caused by gradients of the electric field or gradients in the dielectric constant across the centering region, which in tern induce gradients in the electric field, for the purpose of causing a centering force on the lens-like drop. Without this centering capability an unintended translational shift of the curved lens surface (meniscus) of the device would introduce image abberations that destroyed the quality of the image at an image plane. Additionally, the prior art does not detail how to avoid the need for a centering mechanism. The present invention of this document does not need such a means for centering because it is related to non-imaging applications which have a different set of optical requirements — the most important of which is the relaxation of the point-to-point ordering restriction of the rays, which is found in imaging systems and assumed in U.S. patent 6,369,954. Finally, the deflection effects described in this prior art assume a bridging of multiple walls of the fluid confinement vessel, this is not necessary in the present invention as only one wall needs to be used when deflecting a light bundle — for example the one wall of a cylindrical Patent Application of Leo D. DiDomenico for "Electro- Wetting Optical Light Steering" — Continued

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embodiment.

In U.S. Patent Application 2005/0113912 entitled "Variable Focus Lens", and in International Patent application WO 99/18456, Phillips Electronics shows a variable focal length imaging lens that is extremely similar to U.S. Patent 6,369,954 — mentioned in the previous paragraph. Since the Phillips patent has all the same characteristics as the patent mentioned in the previous paragraph by Bruno Berge all the difficulties that existed in the former exist in the later as well and are not repeated here for the sake of brevity.

Yet another invention that uses EW technology is international patent WO 2004/102252 entitled "A variable Refractive Surface" by Philips Electronics. This patent uses an electrode that extends to the meniscus surface and which is internal to the volume of the optical device not on an inside wall of of the device. Hence, this is an obstruction to the light and is not needed or used in the present invention.

Note that all of the prior art items mentioned in the previous paragraphs have the stated objective of having a variable shape meniscus to affect the focal length of an EW imaging lens. The invention of this patent does not seek to change the shape of the meniscus ever, it is to remain substantially flat, however, it is the intention of this patent to have the angular orientation of this fixed-shape meniscus change in order to substantially change the optical momentum of the light so that high levels of non-imaging concentration can be achieved for large device input angles. This is a substantially different operation on the light than focusing for imaging.

In U.S. Patent 6,778,328, entitled "Tunable Field Of View Liquid Microlens", Lucent Technologies shows a tunable field of view liquid micro-lens capable of changing its field of view using EW technology. This patent uses an imaging lens that shifts laterally over a relatively large substrate area to achieve different viewing angles. Beside the fact that it is an imaging lens, which is not optimized for non-imaging applications, this device also has a large lateral size making it unsuitable for use in an array of closely packed tracking devices as might be needed in non-imaging applications like solar energy collection.

Thus the prior art described above is seen to have multiple deficiencies from the perspective of non-imaging applications, such as solar concentration and tracking. These deficiecies are ad- Patent Application of Leo D. DiDomenico for "Electro-Wetting Optical Light Steering" — Continued

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dressed and overcome in this patent.

BRIEF SUMMARY OF THE INVENTION

The prior art systems are inadequate for forming substantially flat interfaces that tilt to any orientation so that an extended source of light energy at an arbitrary direction is refracted into the narrow acceptance angle of a non-imaging concentrator and subsequently concentrated without violating optical momentum-phase-space conservation limits as denned below.

In particular, we observe that to optimally couple light energy from a source moving relative to a narrow-acceptance-angle optical concentrator it is necessary to utilize some form of tracking so that the narrow acceptance angle of the concentrator device is optimally matched the source solid- angle of radiation. Typically this has been achieved in the past by using rigid-body mechanical tracking systems. This is especially prevalent in solar energy applications. In this sequel, presented herein, the mechanical tracking is replaced by a hybrid solid-state and wet-state device which is actuated by one or more voltages to achieve tracking.

Accordingly several objectives and advantages of the present invention are:

(a) to provide an optical geometry that allows narrow acceptance angle concentrators to be used in applications where the radiation source moves relative to the receiver;

(b) to provide a hybrid solid-state and wet-state tracking device;

(c) to provide a substantially flat meniscus interface that tilts to any orientation based on the application of a suitable voltage;

(d) to provide a tracker that transforms an input light-cone into another light-cone directed towards a non-imaging concentrator;

(e) to provide a device that maintains or decreases the magnitude of the solid angle of the input light-cone to improve end-stage concentration. Patent Application of Leo D. DiDomenico for "Electro-Wetting Optical Light Steering" — Continued

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(f) to provide a physical geometry to combine a plurality of EW tracker-concentrator devices into an array with minimal shadowing loss;

(g) to provide a tilting refractive surface which is to control with voltages;

(h) to provide a means to auto track the source of light by the use of a feed-back control system;

Further objects and advantages will become apparent from a consideration of the ensuing description and drawing.

For achieving these objectives and advantages we note that a ray of light can be though of as either a wave or a stream of discrete photons. For the moment let us adopt the latter. The rays are then composed of massless particles, or quanta, of light each have an energy given by

E = hω , (1)

where E is the photon's energy, ω is the radian frequency, and h is the normalized Planck constant. Furthermore, the photon's vector momentum p is given by

P = fik , (2)

where and k is the vector wave number. If we assume that the amplitude of the light does not change significantly over the length scale of a wavelength then we can immediately write the wave vector in terms of the refractive index n and the speed of light in vacuum c_o as

k = hτ = nτ f-λ , (3)

where r is the unit vector that points along the photon's trajectory and is given by

T = — , (4) ds where r is the position vector of photon along its expected path and s is the arclength. Combining these results we obtain the photon's momentum p as

V = n τ - . (5)

(!) ^• Patent Application of Leo D. DiDomenico for "Electro- Wetting Optical Light Steering" — Continued

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For a photon of a given energy (color) we have that the physical momentum is proportional to the very special quantity (n r), which we shall call its generalized momentum. Furthermore, because the energy of a photon is a constant and the speed of light in vacuum is also a constant we shall adopt a system of units where the ratio E/c_o → 1 and write the optical momentum as

p = n τ . (6)

It can be shown that the optical vector momentum together with the coordinates of position, which are the components of r, define a six dimensional momentum-phase-space in which the laws of optical ray propagation follow essentially the same laws as particles of classical Newtonian physics. As a consequence of this all the results of the classical dynamics in momentum phase space have a corresponding optical analogy as long as we are mindful of the small wavelength approximation of ray optics — which is assumed to be valid throughout this patent.

Next we note that the problem of collecting a bundle of non-parallel rays is slightly more complicated than just finding the trajectory of a single ray through an optical system. We are actually interested in bundles of rays that have a range of input directions and that more-or-less simultaneously pass through the concentrator. For example, if a unit vector r can take on any direction inside a cone, which defines an input solid angle, at a particular point of the input aperture, then we must track all the rays in this sold angle to determine the output concentration. Fortunately, the momentum-phase-space formalism provides us a means to understand the requirements on the optical rays in order to achieve high levels of concentration.

We can represent a bundle of rays in physical space as a unique set of non-overlapping trajectories in momentum-phase-space that move according to the laws of optics. Those familiar with this field of Hamiltonian optics will recognize that the total momentum-phase-space volume of a collection of the points in the momentum-phase-space trajectories must remain constant. This is a form of Liouville's Theorem from theoretical physics. Additionally, it can be shown there are other sub-spaces, areas in the higher dimensional momentum-phase-space, that must be conserved — Poincare invariants. In particular, the etendue, a product of the physical area and the momentum area of at the input area must remain constant. Patent Application of Leo D. DiDomenico for "Electro-Wetting Optical Light Steering" — Continued

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We are thus allowed to trade physical area for momentum (angle of propagation). The smaller the physical area of the cross section of the light beam the greater the concentration and hence the larger the solid angle made by a cone of rays as they propagate through the optical system.

For an optical system where the physical orientation of the concentrator is fixed but where the source must be tracked, such as in the case of solar collectors that must track the sun, we can not simultaneously find a static optical configuration that will have both high concentration and large acceptance angle. This is a consequence of the conservation of etendue.

Therefore, we introduce the idea of using a narrow input acceptance angle of a non-imaging concentrator that has a hybrid solid-state and wet-state tracking system attached to it to precondition the input rays. In particular, a flat dielectric interface capable of variable orientations is formed by two liquid substances having substantially the same density, and substantially different refractive indices. One of the liquids is conducting and contains substantial built-in dipole moments (such as water with sodium ions to make it conductive). The other liquid having essentially no built-in dipole moments. The interface formed by these two liquids thus being made immiscible by the inability of the residual electrostatic attraction between molecules of the polar liquid to interact with the non-polar liquid. Therefore, the intermolecular van der Waals forces can not neutralize surface tension thus providing a optical boundary for refraction between media of substantially different refractive index. Note, under certain conditions, such as when the tracker is on a flat surface, it is possible for one of the fluids to have a higher density than the other. However, this is not the preferred embodiment.

The two liquids being held in a containment vessel with half hydrophobic and half hydrophilic boundaries, which are defined by a set of voltages along the boundary to maintain the flat profile of the interface. This flat interface is suitable for refracting a cone of light energy energy from a finite source (such as the sun) into the narrow acceptance angle of a high-performance non-imaging concentrator.

The basic invention provides a variable and tilted orientation of the relatively flat refractive index surface that separates the two fluids. The preferred embodiment having the refractive index of the input medium being less than the refractive index of the output medium to ensure that a Patent Application of Leo D. DiDomenico for

'Electro- Wetting Optical Light Steering" — Continued

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light-cone bundle has a smaller or unchanged solid angle after passing through the interface — instead of a larger solid angle. The liquids are immiscible and are contained inside a fixed volume containment vessel. The containment vessel being half filled with a polar conducting fluid and half filled with a nonconducting and non-polar fluid each having substantially the same mass density. The top and bottom ends of the containment vessel being optically transparent. The inner surface of the containment vessel walls being treated with a dielectric that is predominantly non-polar and thus hydrophobic to the conducting fluid.

When in its rest state the EW device has its meniscus on the containment vessel wall, which does not include either the top and bottom surfaces of the containment vessel. In the rest state a unit normal vector to the flat meniscus is parallel to the optical axis of the EW device. For example, in a cylindrical containment vessel in the rest state, the meniscus spans the tubular wall of the cylinder and forms a circle on the wall. It does not form a perimeter on either the top or bottom surfaces of the containment vessel — which does occur in the prior art.

According to an embodiment of the invention no gradient induced forces, or other centering mechanism, is required to establish a meniscus on the top or bottom surfaces of the containment vessel. The planar meniscus interface spans all surfaces of the containment vessel except the top and bottom surfaces. For the special case of a cylindrical containment vessel the meniscus is, in general, an ellipse that never touches the top or bottom surfaces. The planar interface is a result of the constant volume of the polar liquid, the constant volume of the non-polar liquid, the constant volume of the containment vessel, the constant volume of each of the constituent liquids during the tilting process of the interfacial meniscus and a voltage distribution around the walls of the containment vessel that makes the boundary of a plane that cuts the containment vessel the demarcation between hydrophobic and hydrophillic surface properties with respect to the conducting and polar liquid.

The conducting fluid has a direct connection to a voltage source through an electrode. The conducting fluid also has an indirect connection to the influence of an opposing voltage at an alternate electrode by means of induced surface charges on the normally hydrophobic surface coating of the walls of the containment vessel. These voltage induced bound-surface-charges tend to organize Patent Application of Leo D. DiDomenico for

"Electro-Wetting Optical Light Steering" — Continued

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the dipole moments internal to the polar liquid so as to allow greater wetting at the internal surface having the induced charges. The induced surface charges in the solid dielectric mimic the internal charge separation of polar molecules in the adjacent polar liquid making it appear as if a polar liquid exists where it is absent and allowing to liquid to wet the solid material.

The light-cone entering the top of the containment vessel from a direction different form the optical axis of the EW device is refracted at the tilted meniscus surface and then sent directly parallel to the optical axis of the EW device. This axis is also parallel to any subsequent narrow acceptance angle optical concentrator. The amount of light being sent through the optical system providing an indication of how close to optimum the setting of the tilt angle is, and thus providing a means to update the meniscus surface tilt orientation through the intensity signal in a feedback control loop.

An array of EW tracking devices and optical concentrators thus providing a means to collect large amounts of radiant energy

BRIEF DESCRIPTION OF DRAWINGS

The foregoing discussion and other objects, features, aspects, and advantages of the present invention will become apparent from the following detailed description of embodiments and drawings of physical principles given by way of illustration. Unless otherwise stated the figures are drawn for improved clarity of the underlying physical principles and are not to scale.

FIG. 1 shows in cross section an embodiment of a tracking non-imaging electro-wetting sun tracker attached to a sunlight concentrator.

FlG. 2A to 21 shows in cross-section how the rays of a finite light source like the sun propagate through an electro-wetting optical boundary using refraction at different input angles for the light source.

FIG. 3 shows on coordinate axes of relative solid angle and incident input angle the amount of relative change of the output light-cone profile from normal incidence. Patent Application of Leo D. DiDomenico for

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FIG. 4 shows the momentum phase space manifold of a two dimensional etendue limited concentrator, teaching the need for a sun tracker.

FIG. 5 shows a detail of configuration space light-cones in a two dimensional etendue limited concentrator, teaching the need for a sun tracker.

FIG. 6 shows a ray trace of how a ray of light, which is not included in an acceptable momentum- phase-space manifold, is rejected from a simple flared optical concentrator, teaching the need for a sun tracker.

FIG. 7 shows schematically shows how the momentum-phase-space manifold changes configuration for a 2 -dimensional non-imaging electro-wetting concentrator system, teaching the need for a sun tracker.

FIG. 8 shows in cross section a second embodiment of a tracking non-imaging electro-wetting sun tracker.

FIG. 9A to 91 show the underlying physical process involved in electro-wetting.

FIG. 10 shows a side view of a third embodiment of a tracking non-imaging electro-wetting light sun tracker.

FIG. 11 shows in perspective a third embodiment of a tracking non-imaging electro-wetting sun tracker.

FIG. 12 A shows in perspective a limiting case wherein the number of electrodes is one per active face of a cube tracker.

FIG. 12B shows in perspective a limiting case wherein the number of electrodes is one per active face of a three dimensional triangular tracker.

Patent Application of Leo D. DiDomenico for

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DETAILED DESCRIPTION

Figure 1 shows one possible embodiment of a non-imaging light concentrator that has tracking ability. We shall call this an Electro Wetting Concentrator System (EWCS). The EWCS 100 is characterized by two main components: (1) the Electro Wetting Tracker (EWT) 150, which is defined by its input boundary 116, its output boundary 118, and its fluid-fluid boundary 128; and (2) an optical Non-Imaging Concentrator (NIC) 136. This patent is concerned primarily with an optically transparent EWT so long as one or more EWT components are followed by a NIC with appropriate properties as defined below. Therefore, the particular NIC 136 geometry shown in FIG. 1 is included for illustrative purposes only — other geometries are possible as will be recognized by those skilled in the field of non-imaging and Hamiltonian Optics.

A radiant source, such as the sun 102, radiates into a light-cone 104 of finite solid angle. In the case of the sun this solid angle is defined by a half angle of approximately 0.275 degrees. This energy from the radiant source 102 is incident on the input boundary 116 of the NIC. The NIC has an optical axis 148 that defines an average input incidence angle with 104. The input surface 116 may have a anti-reflection coating on it to reduce optical losses. The energy from the radiant source 102 is then refracted at boundary 116 into light-cone 106. The medium outside of the NIC is typically air with a refractive index of about unity. The first internal medium 112 of the NIC is a relatively low refractive index fluid that is conductive. An example of this might be water, made conductive by the addition of ions of sodium — with a combined refractive index of about 1.33. The light-cone 106 is again refracted at a fluid-fluid boundary 128 into a second non-conducting fluid 114, which typically has a greater refractive index than the first conducting fluid 112. This fluid might be a oil with refractive index as high as 2.0 or more. The two fluids in the NIC being substantially of the same mass density (to negate the effects of gravity) and of different refractive indices. The First fluid 112 is typically conductive and polar — possessing and intrinsic dipole moment. The second fluid being non-conductive and typically not containing a dipole moment. Note that it it is possible for the first refractive index to be higher than the second refractive index medium. When this occurs the fluids must reverse the sense of rotation for the Patent Application of Leo D. DiDomenico for

"Electro-Wetting Optical Light Steering" — Continued

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sunlight to be refracted to a subsequent concentrator.

A voltage source 144 exists external to the EWSC 100. This voltage source has a voltage across its terminals 140 and 142. The conductive fluid has a direct connection to voltage source 144 by way of electrode 132. The conductive and non-conductive fluids also feel the influence of the voltage source through the electrodes 124 and 126, which are in each case a plurality of electrodes around the containment vessel 120 that have a high or low potentials relative to a reference potential at 140. Additionally, the voltages may be strategically applied at different positions on the containment vessel 120 through electrodes 124 and 126.

Furthermore, the electrodes outside the inner surface of the containment wall are separated from the internal fluids by a non conducting dielectric or coating 122 that is substantially hydrophobic to the conductive liquid 112. The electric field across the dielectric 122, which is due to electrodes 124 and the conductive fluid 112 electrode 146, causes a bound surface charge 132 to be induced on the normally hydrophobic dielectric material 122. This has the effect of inducing the hydrophobic material to now behave as a hydrophilic material — thus wetting the dielectric material 122 and inducing a orientational change 130 in the fluid-fluid interface 128. In this patent we are substantially interested in choosing those voltages that will maintain the fluid-fluid boundary 128 as a flat surface for the purpose of optimal non-imaging concentration in a NIC 136.

Note that the Exact orientation of the molecules 134 and the polarity of the surface charges 132, and the polarity of the voltages 124 and 126 depend on the species of molecules used in the conductive liquid and may be different then that shown in FIG. 1. Also, other physical phenomena other than the bound state surface charges may induce a change in the wettability. The important point being, however, is that the effect of a voltage is a change in the wettability of the inside surface of the containment vessel in such a way so as to orientate a flat fluid-fluid meniscus in a predetermined direction so as to force the input light-cone 104 to be transformed into an out-put light-cone 108 that is symmetrically orientated about the optical axis 148. Additionally, other input light-cones at the surface 116 are mapped into offset output light-cones 110, which have a symmetry axis this is parallel to the optical axis 148. The the output light-cones being predominantly along a direction parallel to the optical axis without regard to the input light-cone direction 104 — Patent Application of Leo D. DiDomenico for

"Electro-Wetting Optical Light Steering"— Continued

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as shown in the series FIG. 2A to FIG. 21. The correct choice of voltages 124 and 126 will force this geometry to be enforced. Note, if the input light-cone 104 has a circular symmetry then, in general, the output light-cones 108 or 110 will be more elliptical in shape in cross section due to the series of refractions.

Figure 3 shows the relative change in the output angle, in the incidence plane, for a specific choice of refractive index contrast. The important feature is that the largest that the output angle θ can achieve is the value at normal incidence. Thus when a design of the NIC is implemented the edge-ray theorem, as described by Winston and Minano, may be applied conservatively along the normal incidence rays.

In FIG. 4 the underlying physical geometry of a simple 2-dimensional etendue limited NIC is shown. The momentum-phase-space pipe-like manifold 1 represents all the possible ray trajectories of a light concentrator. The incident light rays in the light-cone 402 strike the concentrator along the x-axis 403 and propagates in the general y-axis direction 404. The input light-cone 402 may be incident at any point along the x-axis 403. The input aperture in the phase-space is at 405. Furthermore, the angular extent of the input light-cone 402is represented by the generalized momentum p-axis 406. The greater the input angle then the greater the value of the momentum p. An edge ray of the input light cone 402 traverses the outside surface of the manifold along a spiraling phase-space trajectory 407 and works its way to the exit aperture 408. At the exit aperture 408 the manifold of light trajectories 407 has become compressed along the x-axis 403 but has expanded along the p-axis 406 so that the total momentum-phase-space volume is maintained constant along the pipe. This results in light being compresses along the x-axis 403 and the angle of exit 409 being expanded relative to 402. A projection 410 from the momentum-phase-space 401 down to the configuration space 411 shows the trajectories 407 as trajectories 412 and the generalized coordinates 413 as coordinates 414 respectively.

In FIG. 5 a schematic representation of the internal workings of a simple two parameter έtendue limited concentrator 501 in configuration space. The internal optical components may include such devices as mirrors, lenses, and variable refractive index materials. An input aperture 502 receives light energy in solid angles 503, 504, and 505 at different points along its aperture. Each solid angle Patent Application of Leo D. DiDomenico for

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has extreme rays called edge rays such as 506 and 507 as well as normal rays such as 508. Each solid angle of rays constitutes a ray bundle in momentum-phase-space and a light-cone such as 509 in the configuration space shown above. This configuration space has coordinate curves q^a such as the coordinate curve q¹ at 510 and the coordinate curve q² at 511, which represent the solutions to Hamilton's canonical equations with H = O. The momentum coordinates p_a are not available in this schematic of configuration space because we have projected down to the configuration space from the momentum-phase-space. However, FIG. 4 does show the corresponding edge ray manifold in momentum-phase-space. As the light-cone at the input 509 evolves in time its phase- space volume must remain a constant of the dynamics for maximum light throughput. The light- cone 509 must therefore increase in solid angle along the q² coordinate contour at 512 as the light becomes more and more concentrated in area. This increase in solid angle is shown at the intermediate light-cone 513 and the exit aperture light-cone 514. The exit light-cone 514 has edge rays 515 and 516 as well as a normal ray 517. The normal ray 517 at the exit aperture is the same as the normal ray 508 at the input aperture. However, the exit aperture edge rays 515 and 516 may come from different input positions, such as 506 and 507. Therefore, we can see that although the light-cone 509 follows a coordinate contour 512 most of the rays in the exit light-cone 514 must have taken complicated paths to reach the output 514. The important point to observe is that the output light-cone 514 contains rays that fill a very large solid angle and therefore the output is rich in modal content.

Note that an etendue limited NIC may not always be desirable, especially in cases when coupling to subsequent stages is necessary. This sub-etendue limit is achieved for manifolds that are slightly shorter than this shown. These sub-etendue NICs are still ideal and capture all of the input light.

In FIG. 6 we see a slightly flared and mirrored horn NIC 601. The profile and length 602 of the NIC is chosen to require more phase-space volume than is available and thus violates the needed condition of momentum-phase- space conservation for maximum throughput. Light at the input 603 does not reach the output 604. Instead it is actually rejected 605 by the collector 601 before reaching the output 604. Note, the path of the photon shown is typical of classical concentrators in Patent Application of Leo D. DiDomenico for

"Electro-Wetting Optical Light Steering" — Continued

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that it becomes more and more directed perpendicular to the desired direction of propagation 606.

In FIG. 7 it is observed that the input light cones 702, 704,and 706 corresponds to a bending pipe-like manifold in momentum-phase-space 701, 703, and 705. As the EWT moves the manifold changes shape an the fluid of points inside the manifold is forces into a concentrated state. It is important to recognize that the 3-dimensional Manifolds with 2-dimensional surfaces, as has been shown in the figures in this patent are representative of what happens in systems with more degrees of freedom, which may have 6-Dimensional momentum-phase-space manifolds-which can not be easily visualized.

An alternative embodiment 800 of the EWT is shown in FIG. 8. As before a first solid refractive index boundary 806 acts as the input surface. A final solid refractive index boundary 808 is the output surface. A substantially flat fluid-fluid meniscus 822 defines a variable orientation fluid- fluid boundary that can reorientation according to a set of predetermined voltages on electrodes 824 and 826 for the purpose of providing refraction of light. The input conductive fluid 802 and the output non-conductive fluid 804 are are of substantially the same mass density, of different refractive index, and optically clear. The internal surface of the containment vessel 810 and 812 is a non-conductive dielectric that is substantially hydrophobic to the conductive liquid 802 when no voltages is applied at the electrodes. The electrodes 824 and 826 are a mirror image of each other physically although the voltages on them are not mirror images. For example the electrodes 824 contain a direct connection the conductive fluid 820 through the electrode insert 818 and a plurality of capacitive electrodes, such as 828, which are internal to the non-conductive dielectric 814. Each electrode has a section that protrudes past the previous electrode whereby the previous metallic electrode acts as a shield to the electric field of the subsequent electrode if it is held at a different potential. In this way a controlled portion of the normally hydroscopic dielectric 810 can be induced into a hydrophillic state and being wetted by the conductive and polar input liquid 802 and thus reorientation the meniscus 822. The number of electrodes is chosen to correspond to the angular resolution of the tilted meniscus 822 that is required for a particular application. The electrodes protrude out the bottom of the EWT for connection to external circuitry.

Additionally, the cross sectional views of the EWT in this patent so far correspond to 3 dimen- Patent Application of Leo D. DiDomenico for

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sional geometries such as cylindrical and trough-like shapes and nothing should be construed to limit the geometric form of the invention so long as the non-imaging functions described herein are maintained.

Finally, the voltages on the electrodes are chose to maximize the optical through put of the EWCS. This may be done by a number of hardware, software, and firmware systems that monitor the light flow. An array of such EWCS devices can provide large area coverage.

FIGS. 9A-I show the underlying physics of Electro Wetting and why the voltages on the electrodes are needed to control the fluid-fluid boundary. In particular, FIG. 9A shows a Lewis structure of a water molecule H2O showing covalent bonds and residual fractional charges of magnitude δ due to a more electronegative oxygen atom than hydrogen atom. FIG. 9B shows the three dimensional geometry of a water molecule having a bent molecular structure with the angle of about 104.5 degrees. This geometry is a result of Columbic repulsion of electrons in the covalent bonds and the electrons in the loan-pair p-orbitals. FIG. 9C shows a 2-dimensional representation of four water molecules sticking together due entirely to dipole-dipole Columbic attraction called Van der Waals forces. Even through the polar molecules are electrically neutral overall, the attraction that occurs between molecules of water is due entirely to Columbic hydrogen bonding between the water molecules and this gives rise to a large molecular enthalpy of vaporization. FIG. 9D shows the inside a continuous volume of water (a highly polar medium) the hydrogen bonding averages out to have zero net force on any given water molecule due to thermal agitation. FIG. 9E shows a boundary with vacuum (or air) the lack of sufficient hydrogen bonding, due to missing water molecules, provides the mechanism for a net inward force called surface tension. FIG. 9F shows a boundary with a non-polar dielectric and having a similar surface tension at the dielectric instead of with vacuum or air. FIG. 9G shows a boundary having bound surface charges, which are induced by a voltage on electrodes, the water is effectively allowed to have a hydrogen bond with the bound surface charges of the dielectric, thereby maximizing the wetting of the dielectric with the water. FIG. 9H shows a drop of water on a non-polar dielectric over an electrode with no applied voltage. Finally, FIG. 91 shows that if a voltage induces bound surface charges the surface wetting is increased and the drop spreads out. This is effectively a force on the water drop. This principe Patent Application of Leo D. DiDomenico for

"Electro-Wetting Optical Light Steering" — Continued

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of electronic control of the wetting properties is used in the devices described in this invention.

FIGS. 10 and 11 shows a side view and perspective of a sun tracker, EWT, respectively. The sun 0110 is shown sending light 0120 into an EWT. The EWT is comprised of a transparent containment vessel 0160 having a top cover 0130 and a bottom cover 0170, both of which are also transparent. Sunlight 0120 is refracted at the top cover 0130 and propagates to an optical boundary 0140 between two fluids of a fluid system located above and below said optical boundary. The first member of the fluid system 0190 having a preferred refractive index that is greater than the refractive index of a second member 0150 said fluid system. Although, it is not always needed, in the preferred embodiment of the EWT the first fluid and the second fluid have substantially the same mass density so that the effects of gravity are nullified. The first and second fluids are immiscible and the first fluid is a non-polar insulating fluid, while the second fluid is a polar and conducting fluid. As we explained in FIGS. 9 the voltages at electrodes 0185 are used to change the wettability of the containment vessel 0160 inner surface.

In particular, the polar fluid 0150 is allowed to wet the containment vessel 0160 up from an electrode 0185 up to the optical boundary 0140 by patterning said electrodes with a voltage up to said desired boundary. This is exemplified by the electrodes shown in black, which are assumed to all to have a constant voltage on them, which is not allowed to directly short to the polar fluid, with perhaps one exception such as electrode 0180. That is, most electrodes 0185 form a capacitor with one place of the electrode being the metal of said electrodes, the other place being the polar fluid, which is energized from one or more electrodes 0180, and the dielectric between the capacitor plates being that part of the containment vessel between the electrodes and the polar fluid.

In all cases, as the pattern of voltages on the electrodes changes so does the pattern of bound charges on the inner surface of the containment vessel. These bound surface charges effectively create hydrogen bonds with the polar liquid, such as but not limited to water, thereby allowing the wetting properties of the containment vessel to steer the optical boundary where Snell law refraction occurs.

FIGS. 12A and 12B show two embodiments of a trackers that use less electrodes instead of more electrodes to create the boundary. In particular, FIGS. 12A and 12B show one electrode per Patent Application of Leo D. DiDomenico for

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side of the containment vessel. The cube based containment vessel of FIG. 12A having voltages Vl, V2, V3, and V4. The triangular based containment vessel of FIG. 12B having voltages V5, V6, and V7. A ground is placed on one of the remaining sides — the top or bottom — as shown in Gl and G2. The advantage of these embodiments is simplicity where the fields create the optical boundaries 1210 or 1220. The disadvantage is that a meniscus is formed near the glass at the optical boundary, thereby causing the edges of the optical boundary to refract light in a way that is not based on a perfect flat optical boundary. In some applications this abberation may be tolerable and the essentially flat optical boundary sufficient to cause the majority of the input light to be steered to the desired output.

Finally, there are many possible fluids that can potentially be used for the polar and non-polar members of the fluid system. Examples are Polydimethyl Siloxane as a non-polar fluid and Saline Solution for the polar solution. These fluids have a usable temperature range of -20C to 60 C and have a mass density match of about 1 : 1. Alternatively, the fluids Poly methylphenyl Siloxane and Trifluoropropy lsilicon can also be utilized, although they have a mass density match of about 1 :1.2.

CONCLUSION, RAMIFICATION, AND SCOPE

Accordingly, the reader will see that this method and device for controlling a flat meniscus between different refractive index has the following advantages:

1. it permits a substantially flat meniscus interface between liquids of different refractive index;

2. it permits a voltage induced change in the orientation of said interface;

3. it permits tracking (or scanning) of a source of radiation;

4. it permits a bundle of input rays to be transformed into an output bundle of rays while maintaining or decreasing the solid angle of said rays for subsequent processing in a non- imaging concentrator; Patent Application of Leo D. DiDomenico for

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5. it permits a hybrid solid-state and wet-state array of energy collectors to track the sun and substantially concentrate the energy of the sun without regard to the sun's position.

6. it permits reversing the direction of propagation of the ray so that a light collection system becomes a light distribution system,

7. it permits many prior art non-imaging concentrators to become tracking concentrators without the need for additional design;

8. it permits less than etendu limited operation of the concentrator while still maintaining the ideal ideal nature of passing all the input energy to the tracker to the output of of the concentrator;

9. it permits the use of other physical phenomena to cause wetting other than that described in this document.

While the above description contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.

Claims

Patent Application of Leo D. DiDomenico for"Electro- Wetting Optical Light Steering" — ContinuedPage 21CLAIMS

1. An optical system for tracking a light source, comprising:

a. a polar transparent fluid having a first refractive index, b. a non-polar transparent fluid having a second refractive index, c. a transparent, or partially transparent, dielectric containment vessel containing said polar transparent fluid and said non-polar transparent fluid, said dielectric containment vessel having a an electronically controllable hydrophobic or hydrophillic coating on its inner surface, d. a relatively flat optical boundary, formed by the immiscible and the physically contiguous contact of said polar transparent fluid and said non-polar transparent fluid, e. a system of electrodes imbedded in, or attached to, said transparent containment vessel, f. a means to induce a voltage on a desired subset of said electrodes, which are embedded in said containment vessel,

whereby said induced voltage on said electrodes causes a electric polarization of the inside surface of said containment vessel so that an electric polarization induced wettability of said inner surface of said containment vessel, relative to said transparent polar fluid, is controlled and patterned and thereby induces a substantially flat optical boundary between said transparent polar fluid having said first refractive index and said transparent non-polar fluid having said second refractive index, whereby said voltages on said electrodes are varied to cause said optical boundary to track said light source by means of a process of light redirection at said optical boundary, thereby causing said light to be steered in a desired output direction for concentration, distribution, or energy conversion.

2. The system for light redirection in Claim 1 wherein said containment vessel is cylindrical.

3. The system for light redirection in Claim 1 wherein said containment vessel is hexagonal. Patent Application of Leo D. DiDomenico for

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4. The system for light redirection in Claim 1 wherein said containment vessel is an elongated trough-like structure.

5. The system for light redirection in Claim 1 wherein said electrodes are discrete and electrical pads.

6. The system for light redirection in Claim 1 wherein said electrodes are discrete and electrical pads with a predetermined shape and orientation.

7. The system for light redirection in Claim 1 wherein said refractive index materials are reversed in order to make the tracker a non-imaging scanner.

8. The system for light redirection in Claim 1 wherein electrodes are transparent and made of materials like indium tin oxide or other highly conductive and transparent materials.

9. The system for redirecting light in Claim 1 wherein said optical system for tracking light is arrayed into an array having one degree of angle-tracking freedom.

10. The system for redirecting light in Claim 1 wherein said optical system for tracking light is arrayed into an array having two degrees of angle-tracking freedom.

11. The system for light redirection in Claim 1 wherein said redirected light is used to produce power.

12. The system for light redirection in Claim 1 wherein said redirected light is used to produce light at a user defined level of concentration.

13. The system for light redirection in Claim 1 wherein said redirected light is used to produce electricity, the magnitude of which can also provide a feedback control to direct the tracking of a light source.

14. The system for light redirection in Claim 1 wherein said redirected light is used to produce stored electrical energy. Patent Application of Leo D. DiDomenico for

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15. The system for light redirection in Claim 1 wherein said redirected light is used to produce stored chemical energy such as a liquid, solid, or gas fuel.

16. The system for light redirection in Claim 1 wherein said redirected light is used to produce desalinated water.

17. The system for light redirection in Claim 1 wherein said redirected light is used to process materials, such as, but not limited to, hydrogen, methane hydrates, bio fuels, and raw materials processing.

18. The system for light redirection in Claim 1 wherein said redirected and light is used to power any land, sea, air, or Space vehicle, or component thereof such as, but not limited to, an automobile, ship, an Unmanned Autonomous Vehicle, or satellite in real time, or at a later time, by storing the energy in real time and then consuming said stored energy at a later time.

19. The system for light redirection in Claim 1 wherein said light redirection is based on refraction from said optical boundary.

20. The system for light redirection in Claim 1 wherein said light redirection is based on reflection from said optical boundary.