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    • 专利摘要:
    FILTER FOR ELECTROMAGNETIC RADIATION FILTERING AND MANUFACTURING MANUFACTURING METHOD. The present invention relates to a filter (50) for filtering electromagnetic radiation, wherein said filter (50) is arranged to transmit electromagnetic radiation of a first predetermined wavelength and to block the transmission of electromagnetic radiation from a second, different predetermined wavelength; said filter (50) comprising a first metamaterial. Optionally, the metamaterial can be formed from a plurality of material elements in which each material element is at least one-dimensional and the size of the material element along each dimension is not greater than the size of the second predetermined wavelength. The filter (50) comprises a second metamaterial arranged to provide the second filtration of electromagnetic radiation.
    公开号:BR112014008611B1
    申请号:R112014008611-7
    申请日:2012-10-10
    公开日:2021-01-19
    发明作者:George Palikaras；Themos Kallos
    申请人:Lamda Guard Technologies Ltd.；
    IPC主号:
    专利说明:

    [001] The invention relates to the filter for the filtration of electromagnetic radiation (EM) and a method for planning and producing it. In particular, it refers to a barrier that can filter one or more specific narrow optical frequencies and can be optically transparent to other frequencies of electromagnetic radiation. Background
    [002] Filters for electromagnetic radiation are well known and have many practical uses. One such use is in laser light filtration in order to protect individuals from its effects. As is well known, when the eye is exposed to laser light, significant damage can occur. This is mainly due to the absorption of incoming photons and the heating of living eye tissue. The potential damage depends on the intensity of the laser, which is the energy per second from the laser impacting a given surface area, and the duration of the exposure. Two known types of lasers are continuous wave (CW) and pulsed lasers. The layers of CW are classified based on their intensity output whereas pulsed lasers are classified based on their total energy per pulse.
    [003] The protection of laser light has become increasingly important every day in practical situations due to the proliferation of cheaper and more powerful laser systems. Certain laser products have in recent years become cheap to produce and are thus commercially available. These products include so-called "laser pens" or "laser light indicators". In the UK there are adjustments in place so that it is only permissible for the production and sale of laser light indicators having a power of up to 5 milliWatts (mW). In any case, these adjustments are not consistent across the world and it is possible in some countries to buy cheaper on a 1 Watt laser light indicator that has an effective area of up to four times the effective area of the most powerful laser indicator. laser light available in the UK, and that can cause damage to the cornea of the human eye from as far as three miles away. Unfortunately there has been an increase in incidents of laser light indicators being deliberately aimed at vehicle drivers and also on aircraft while in flight. These incidents have potentially extremely serious security consequences. While laser light indicators are unable to damage or destroy most vehicles or planes, they can and often interfere with the ability of the driver, pilot or crew to maintain sufficient eye contact with the road, flight path or clue. The potential safety consequences are particularly serious when a laser light indicator is directed at an airplane during takeoff or landing.
    [004] The plane must be at a relatively low altitude in order to be affected by the use of laser indicators on the ground. For this reason, airplanes are most vulnerable during the approach of landing. During this phase an airplane should typically be flying at about 6,000 feet and be in line with the descending runway at a relatively stable rate of around 700 feet per minute. This makes the plane an easy object to aim at with a laser indicator. At the same time, the crew on board the plane must be increasingly focused on external stimuli outside the plane that allow the crew to control the plane's speed, rate of descent and destination towards a successful landing on the runway. This makes the crew more likely to be affected by a laser beam indicator and potentially even to receive serious eye damage. This is certainly the case when the crew is conducting a "visual landing" or an "unnecessary landing". During both such landing phases the flight crew navigates using mainly external stimuli to complete the approach and landing.
    [005] If a laser light is aimed at the crew at any stage of the approach phase, the crew may be injured, momentarily lose sight of the runway or decide that a safe interference-free landing is not possible. This can lead to "rushing" or "aborting" in order to avoid an event that could significantly endanger the plane and the safety of those on board. Dashing and its related procedures can lead to increased workload for flight crew and Air Traffic Control, which in turn can introduce other security threats. At busy airports, such as those found in Europe, a rush procedure can result in a high workload and a relatively dangerous situation.
    [006] The points of portable lasers on the plane can also have an impact on the efficiency and cost of air operations. A pitch involves wrapping the plane's tubing in the engines for an established takeoff boost at the same time as the climb and then is returned to the initial approach point to attempt another landing, all of which can at any time between 10 and 20 minutes. During such a maneuver, a 747-400 plane can burn up to 4 tons of additional fuel that at current prices can reach around 6,000 USD. Other factors, such as connections lost by the passenger and the use of the plane can produce an even more expensive dash.
    [007] There are many safety systems and adjustments already in place on the plane. Unfortunately, many systems and procedures introduced to improve safety can currently increase the gravity potential of laser indicators being aimed at the aircraft. For example, the use of Overhead Presentation (HUD) systems, an expensive technology since used only on military aircraft, is finding its way more and more into everyday commercial aircraft operations. The system is composed of glass in front of the pilot in which the flight parameters and the plane's position in relation to the runway are displayed. This system allows the flight crew to observe external stimuli as well as the plane's altitude and speed (among other parameters) without having to look down at the instrument panel. This results in the flight crew looking towards and out of the windshield throughout the approach and landing phase. In this way, any device with a laser point intended for the airplane's windshield must in all probability result in adverse effects to the crew.
    [008] There are numerous known solutions for laser light filtration to protect user safety. For example, Laser Protection Systems (LPS) are routinely used in laboratories around the world. They typically come in the form of goggles, visors or contact lenses that are used by the person susceptible to laser radiation. Also, they appear in the form of glazing, which is placed around the location of the laser to protect the environment. These filters are generally constructed using polymers for low-intensity lasers or glass for high heat densities.
    [009] There are several disadvantages associated with those currently available. They generally operate on a single band of light, providing protection from a single type of laser only. In addition, they are not narrow enough bandwidth, so they block more light than necessary and then distort the user's overall view. LPSs are also generally colored, artificially coloring the field of view. For this reason, they cannot always be employed - for example, it is not safe for an airline pilot to wear red goggles, while flying an airplane at night. And the glass-based filters are heavy and may not be comfortably used by people.
    [010] No known system can provide electromagnetic radiation filtering that is sufficiently accurate and focused for many practical purposes without distorting the propagation of electromagnetic radiation at other wavelengths that the user does not wish to filter. In addition, many existing filters are impractical and / or too expensive for widespread use.
    [011] Aspects of an invention are set out in the attached independent claims.
    [012] At this point, a filter is provided for selectively filtering electromagnetic radiation. The filter comprises a first metamaterial and a second metamaterial each metamaterial comprises a plurality of structural features having a size of less than a predetermined wavelength.
    [013] Electromagnetic radiation at the predetermined wavelength is blocked by the metamaterial because of carefully chosen structural features. The structural feature can be a thickness of a dielectric layer. The metamaterial can comprise a plurality of material elements and the structural feature can be the size of the material elements. Material elements can comprise any of: a metallic form, a photonic crystal, a polymeric material element or a liquid crystal. The metamaterials can comprise a nanostructured material, made of nanoscale material elements. The filter can provide optical transparency at all frequencies except for the frequencies or selected frequency that is configured to block. For this reason, it does not distort the user's view except for frequencies that have been deliberately blocked, for example, specific laser frequencies that may cause harm to the user. The filter can block the single narrow frequency band or it can block a plurality of distinct narrow frequency bands. Combining metamaterials. The filter can block a selected frequency or selected frequencies in a range of angles. Figures
    [014] The modalities and aspects must now be described with respect to the figures of which:
    [015] Figure 1 shows a filter including a metamaterial comprising a nanoscale unit cell arrangement, including an enlarged view of said arrangement and another enlarged view of a unit cell;
    [016] Figure 2a shows a unit cell for a metamaterial filter, which comprises a spherical plasmonic nanoparticle surrounded by a homogeneous dielectric host medium;
    [017] Figure 2b shows an alternative nanoparticle for the unit cell shown in Figure 2a, the nanoparticle having a cubic shape;
    [018] Figure 2c shows another alternative form of nanoparticle, comprising a helix or vortex;
    [019] Figure 2d shows another alternative form of nanoparticle, comprising a ring;
    [020] Figure 2e shows another form of alternative nanoparticle, comprising a sphere with the first and second conical projections at the top and bottom and four semi-rings around the sides;
    [021] Figure 2f shows another alternative nanoparticle form comprising a three-dimensional cross or X-shape;
    [022] Figure 2g shows another form of alternative nanoparticle having a triangular cross section;
    [023] Figure 3 shows a simulation of the distribution of the electric field over a surface of the nanoparticle in Figure 2;
    [024] Figure 4a shows the relationship between the imaginary part of the macroscopic permissiveness of the nanoparticle in Figure 2 and the antecedent permissiveness of the host environment;
    [025] Figure 4b shows the effect of the diameter (D) of the spherical nanoparticle on the absorption force of electromagnetic radiation at a specific frequency;
    [026] Figure 5a shows a metamaterial filter comprising the layers of spherical nanoparticles in which the two-dimensional period of the nanoparticles is 30 nm;
    [027] Figure 5b shows a filter as shown in Figure 5a, but with a two-dimensional period of 45 nm;
    [028] Figure 5c shows a side view of the filter of Figure 5a;
    [029] Figure 5d shows a side view of the filter of Figure 5b;
    [030] Figure 6 shows the geometry of the Bragg reflection for a Bragg mirror filter having the layers of the first and second materials with the first and second respective refractive indices;
    [031] Figure 7 shows the relationship between the refractive index n2 of the second material in the Bragg mirror of Figure 6 and the wavelength of electromagnetic radiation that is reflected by the Bragg mirror;
    [032] Figure 8 shows a plurality of cholesteric liquid crystals and the orientation of their area guide;
    [033] Figure 9a shows a cholesteric crystal to be rotated 180 degrees along a propagation axis;
    [034] Figure 9b shows the crystal of Figure 9a with incident light comprising three different electromagnetic frequencies incident on the crystal in the direction of propagation; and
    [035] Figure 10 shows the levels of reflectivity obtained by a filter having the first and second layers of cholesteric liquid crystals that retain the first and second respective frequencies of electromagnetic radiation. Overview
    [036] In the overview a filter is provided for filtering out of electromagnetic radiation over a specific desired wavelength range or wavelength.
    [037] A filter is provided that can be, for example, optically transparent to all light received in the visible electromagnetic spectrum with the exception of one or more predetermined narrow bands of wavelengths. For example, the optical filter can be non-transparent only for red light, or for green light, or for red and green light, and so on. The wavelength or wavelengths for which the filter is optically non-transparent can be simultaneously smoothed inside the filter using one of the carefully designed metamaterials, such as a nanostructured metamaterial. Alternatively, filtration can be implemented using a Bragg mirror or helices formed from liquid crystals.
    [038] The optical filter is preferably supplied in the form of a thin film. The thin film can be adhesive to be applied to any optically transparent surface, such as windshield, glass, glass panel or optical lens. A unique combination of structural features is comprised within the thin film structure, thereby protecting a person or persons located behind the filter from sources of concentrated light, such as a laser operating at predetermined wavelengths. In this way, the filter can protect users from laser radiation at the predetermined wavelengths chosen in a passive way. Detailed Description
    [039] Laser safety zones have been defined for an airplane by the Federal Aviation Authority (FAA) in the United States, which imposes the maximum permitted laser intensity requirements at different distances from an airport. For about 7 NM of the tracks and up to 2000 feet in height, the zone must be laser-free, that is, having a maximum intensity of 50 nW / cmA2. The critical flight zone is understood to be up to 8000 ', with an allowable intensity of 5 μW / cmA2. In addition to this zone there is a sensitive flight zone, with a maximum intensity of 100 μW / cmA2. In any case, these guidelines are only voluntarily followed by laser users when the FAA is notified of upcoming laser operations. These guidelines are not always adhered to and, as discussed in the previous section above, more and more of these guidelines are deliberately ignored. The filter described here can be used to protect individuals from damage incurred due to lasers when such guidelines are ignored.
    [040] The specific filter modalities are described in detail below. In general terms, the solution provided here comprises a filter that can be supplied in the form of a relatively thin film with a typical thickness ranging from a few nanometers to a few millimeters, which can be applied inside or outside an optically transparent surface, such as , a windshield in front of an airplane. The film can be applied to the windshield using an adhesive. The film itself may comprise an adhesive layer in order to be self-adhesive or any suitable separate adhesive may be employed. The film is designed to be durable and easy to clean and maintain. In addition, it is able to maintain its mechanical and optical properties under different environmental conditions, such as changes in temperature and changes in heat levels and solar radiation.
    [041] Although very thin, the film can comprise layers of different materials or periodic repetitions of two or more materials. For this reason, it can be designed for multiple band performance. The layers and / or components within the film can be selected to provide protection to the user of laser light in one or more narrow wavelength bands. It can protect the user from lasers having a power of anything from about 5 milliwatts up to 2 Watts (class IV lasers) and has the ability to protect from the highest power lasers once they are developed. For all other visible wavelengths of light, except those that have been selected for filtering by the film, the film is optically transparent in all polarizations and angles of incidence. For this reason, it should not distort the user's view of "normal" light when it is being used to filter specific wavelengths of laser light.
    [042] The filter is a passive system that does not require an external power source or an active control system in order to operate. Once the filter has been installed, for example, to be attached to a windshield, it can continue to operate for a long period of time without any maintenance being required or operating costs being incurred.
    [043] A variety of different materials can be used to produce the filter, as discussed in more detail below. The filter can be produced using the same or all of: liquid crystal materials, polymers, nanocomposites or nanostructured metamaterials or photonic crystal components. It can be produced from 100% recyclable materials and for this reason it is a beneficial solution to the environment.
    [044] According to one embodiment, the filter provided in the form of a film. The film can comprise metamaterial elements, such as metallic metamaterial nanoparticles.
    [045] Metamaterials are artificially created materials that can be obtained by electromagnetic properties that do not occur naturally, such as negative refractive index or electromagnetic concealment. At the same time, the theoretical properties of meta materials were first described in the 1960s, in the past 10-15 years there have been significant developments in the design, engineering and manufacture of such materials.
    [046] An example of a metamaterial comprises a large number of unit cells, that is, multiple individual elements (sometimes referred to as "meta-atoms") in each one having a size much smaller than the operating wavelength . These unit cells are microscopically constructed from conventional materials, such as metals and dielectrics. In any case, its exact shape, geometry, size, orientation and combination can macroscopically affect light in an unconventional way, such as the creation of resonances or unusual values for macroscopic permeability and permissiveness. These individual elements or meta-atoms can be considered as "structural elements" or "material elements" having a size no larger than a predetermined wavelength.
    [047] Some examples of available metamaterials are negative index metamaterials, chiral metamaterials, plasmatic metamaterials, photonic metamaterials, etc. Due to their sub-wavelength characteristics, metamaterials operating at microwave frequencies have a typical unit cell size of a few millimeters, while metamaterials operating in the visible part of the spectrum have a typical cell size. a few nanometers. Metamaterials are also inherently resonant, that is, they can vigorously absorb light over a narrow range of frequencies.
    [048] For conventional materials, electromagnetic parameters, such as magnetic permeability and electrical permissiveness, originate from the response of the atoms or molecules that make up the material to an electromagnetic wave to be passed through them. In the case of Metamaterials, these electromagnetic properties are not determined at an atomic or molecular level. Instead, these properties are determined by the selection and configuration of one of the structural elements of sub-wavelength, such as a collection of smaller objects that make up the Metamaterial. Although such a collection of structural elements and their structure does not "indicate" at an atomic level like a conventional material, a Metamaterial can nevertheless be designed as soon as an electromagnetic wave will pass through it as if it were passed on a conventional material. Furthermore, because the properties of Metamaterial can be determined from the composition and structure of such small objects (nanoscale), the electromagnetic properties of Metamaterial, such as permissiveness and permeability can be precisely adapted on a very small scale.
    [049] Another form of a metamaterial comprises multiple dielectric layers in which the thickness of the layers is not greater than one wavelength of interest. The layers can be formed of different materials having different refractive indices, for example. In this type of metamaterial, the thickness of the layers is sub-wavelength. That is, the structural characteristic of the sub-wavelength determining the electromagnetic properties of the multilayer structure is the thickness of the layers. An example of this type of metamaterial is a Bragg structure, such as a Bragg reflector or Bragg mirror. At the same time that each layer is formed from a conventional material, the exact values of the refractive index and their thickness can be adapted to obtain the filtration of light in the same way as a metamaterial structure comprising the meta-atoms or meta-elements of sub-wavelength, that is, a phenomenon that is obtained through the design of the multilayer structure and not through the individual material properties.
    [050] At this point, metamaterials comprising a plurality of structural features having sub-wavelength dimensions are provided. In the modalities, the structural characteristics of the sub-wavelength are the meta-atoms (for example, nanoparticles with a diameter of the sub-wavelength) and, in other modalities, the structural characteristics are the respective thicknesses of the dielectric layers in a Bragg reflector.
    [051] According to one embodiment, in which the filter comprises a film comprising metamaterial elements (or nanoparticles), the metamaterial elements (or nanoparticles) in the filter are arranged in unit cells, where each unit cell includes a nanoparticle and a surrounding host medium.
    [052] The metamaterials nanoparticles within the unit cells - the structural elements - are made of silver, gold and / or alumina, or any other material that supports plasmon resonances at optical frequencies. They can have spherical, cubic, cylindrical, ellipsoidal, or rod-like shapes and nanoscale sizes, for example, between 1-50 nm. The host medium is a conventional low-loss dielectric with relative permittivity up to 5. This serves as a support structure for nanoparticles, as well as being an adjustable parameter for the strength and frequency of resonances. This means that by choosing the appropriate host material, with the appropriately selected physical properties, such as density, thickness, geometry, and so on, the optical properties of the entire filter can be controlled in this way.
    [053] Optionally, the filter can also comprise the dielectric layers of the thickness of the sub-wavelength and the layers of meta-atoms. That is, in another modality, the filter comprises the dispositions of the multiple layers of nanoparticles, with each arrangement / layer consisting of a different combination of nanoparticles. For example, each layer can have a different host medium, or nanoparticles differently classified by size, or nanoparticles spaced apart at different distances from each other. In addition, some of the layers between the nanoparticle layouts can be Bragg-like structures, that is, alternating the dielectric layers without any nanoparticles present. This is a fusion structure that offers the performance of opening the band of the Bragg reflectors with the response of the isotropic filtration of the absorption of the nanoparticle.
    [054] In order to build a metamaterial structure comprising metaelements, the unit cells of the metaelements are layered in a periodic form in at least 2 dimensions, preferably in 3 dimensions (x, y, z). Each layer of metamaterial can be much shorter in the third dimension (z) than in the first two dimensions (x, y). The layers with different respective electromagnetic properties can be superimposed on top of each other in the third dimension to obtain the performance of the multiple filter bands. Non-metamaterial layers can also be added on top and / or bottom of the overlapping layers of Metamaterial to provide the system with adhesive properties, structural strength of scratch resistance and / or temperature insulation.
    [055] As mentioned above, the filter can be designed and produced to filter one or more selected narrow bands of laser wavelength. The physical properties of the structural elements of the metamaterial, such as the size and shape of the nanoparticles and their surrounding environment or the relative thicknesses and refractive indexes of the layers, can be selected according to the desired filtering wavelengths for a film specific. In particular, metamaterial nanoparticles, or Bragg-like layers, can be selected and adapted to provide specific desired values of electrical permittivity and magnetic permeability, which are the electromagnetic properties that must determine how the film treats electromagnetic radiation passing through from them.
    [056] Figure 1 shows a possible implementation of a thin-film filter 10, comprising the meta-elements, in an airplane cabin. The filter 10 comprises a protective layer 12, a layer of metamaterial 14, and an adhesive layer 16 which is applied directly inside the glass of the cabin 18.
    [057] In this example, nanoparticles 22 are provided in an array 20 of nanospheres 24 made of silver.
    [058] As can be seen in Figure 1, the layout 20 of nanoparticles 22 makes up layer 14 within the filter 10. Layer 14 can be a single metamaterial, with nanoparticles 22 within layout 20 arranged to block a single narrow band of electromagnetic frequencies, or alternatively the layer 14 may comprise several metamaterials superimposed together, where each metamaterial blocks a different respective band of electromagnetic frequencies.
    [059] The protective layer 12 is formed on top of the layer, to act as a barrier when the filter 10 is applied inside a window pane of the cabin, or on another surface. The protective layer 12 can be added to the structural strength of the filter 10 and / or it can have anti-scratch properties to minimize damage to the filter 10 during use.
    [060] Adhesive layer 16 is provided on the other side of layer 14, to allow it to be applied to a cabin glazing or other surface. The adhesive layer 16 and the protective layer 12 must both be optically transparent, in order not to distort the transmission of electromagnetic radiation through the filter.
    [061] Figure 2a shows a unit cell comprising a nanoparticle 22 within the metamaterial layer 14 at a higher level of magnification. The nanoparticle 22 comprises a metallic sphere 24 in its center surrounded by a dielectric medium 26. Figures 2b to 2g show alternative shapes for the metamaterial element in the center of the unit cell. The form chosen may depend on the use required for the filter, or on any appropriate criteria as it should be known to the skilled reader.
    [062] Figure 3 shows a simulation of the distribution of the electric field on the surface of the silver sphere 24, which is part of a periodic arrangement 20 in two dimensions shown in Figure 1, for an electromagnetic wave that enters with a frequency equal to the resonant frequency of sphere 24, after the steady state is reached. The wave propagates in the plane, that is, along the surface of the periodicity. For a single spherical metallic particle, such as the one shown in Figure 2a, the amplitude of field A is verified by:

    [063] where α is the radius of the sphere and em is the relative permissiveness of the host environment that can be assumed with frequency and have a higher value than, that is, a permissiveness of conventional material.
    [064] The permissiveness of a sphere 24 is indicated as e (w) and is generally negative at optical frequencies. It vigorously depends on the frequency of the w wave, typically having a Drude-like dependency. For a given material, e (w) is fixed and the location of the resonance in the frequency can be adjusted by adjusting the antecedent permissiveness. In this example, the point at which resonance, and consequently maximum absorption, occurs is the frequency Oc for which:

    [065] (2) Figure 4a shows how the imaginary part of the macroscopic permissiveness of the arrangement 20 of the silver nanoparticles in Figure 1 is altered based on the antecedent permissiveness of the host medium 26.
    [066] Figure 4b shows that the force of absorption of an electromagnetic wave by arrangement 20 can be controlled by employing nanospheres of a slightly different size. In this example, doubling the diameter of ball 24 (D) increases absorption by approximately 40%.
    [067] The permissiveness and permeability of a layer of metamaterial or layers can be extracted from the reflection and the coefficients of light transmission incident on the metamaterial. These can be evaluated either experimentally or through simulations of the layers of metamaterials. Assuming a metamaterial of thickness d, and that the incident light has a k wave vector, the function of permittivity and permeability is found in the equations:

    [068] Here is the effective index of refraction, Z the impedance of the metamaterial, m an integer that depends on the thickness of the metamaterial, the reflection coefficient, and

    [069] the normalized reflex coefficient. "Re" indicates the real part of the effective index and "Im" indicates the imaginary part.
    [070] Figures 5a to 5d show examples of a filter based on metamaterial 50 consisting of spherical nanoparticles. The nanoparticles are periodically arranged in a two-dimensional plane in a rectangular or square lattice. Different layers of nanoparticles are then superimposed together along the direction of the laser propagation (that is, the 'z' direction). Each layer 52 can include a different antecedent host medium that has a different respective permittivity. Each layer here shows around 200 particles, and this is potentially just a small section of the total surface of the filter 50 which should normally extend much longer in each direction. In addition, nanoparticles may have a different shape than the spherical one. Some examples of possible nanoparticle shapes are shown in Figures 2a to 2g.
    [071] According to another modality, an optical filter is provided in the form of a film comprising the overlapping layers of photonic crystals.
    [072] Photonic crystals can be considered as a special case of metamaterials. They are periodic combinations of optical nanostructures, typically consisting of dielectric or metallo-dielectric materials, for example, in the form of sticks, and a surrounding environment. The photonic crystal unit cells are usually the same size or slightly less than the wavelength of electromagnetic radiation that operate them. While some photonic crystals have been found in nature, they have been studied extensively since the 1980s that it became possible to manufacture them experimentally.
    [073] The photonic crystal filter operates by controlling the band openings that originate from the periodicity of the lattice that is formed when the unit cell is periodically repeated. The exact absorption frequencies are adapted by adjusting the truss period and the size of the cross section of the rods. The absorption bandwidth of the frequencies of interest is adapted by the contrast index, that is, the relationship between the refractive index of the rods and the refractive index of the surrounding environment. The absorption force is controlled by increasing the thickness of the photonic crystal lattice, in the third (z) dimension.
    [074] The unit cell for each layer of photonic crystals in the filter is square or hexagonal (alveolus) and consists of a central dielectric rod surrounded by air. The stick can have a square, cylindrical, or other cross-section. The rod has a typical relative permittivity of approximately 10 (for example, obtained using the GaAs material) and a typical radius of about 0.2 * α, where α is the layer period. The unit cell is thus repeated periodically in 2 dimensions (perpendicular to the axis of the rods) with the period α. In the third dimension, multiple identical layers can be superimposed or different layers can be superimposed to obtain absorption for multiple frequencies and for multiple polarizations.
    [075] As mentioned above, according to another embodiment, a filter comprising a film is provided. The film comprises a stratified medium which can be manufactured, for example, by centrifuging the polymer materials, to assemble a Bragg structure, such as Bragg reflector or Bragg mirror. It consists of periodically alternating layers of two or more materials with the thickness of a sub-wavelength, such as a nanometer-scale thickness for the optical wavelengths. Each layer of the film causes a partial reflection of an electromagnetic wave that enters at a certain frequency. When the optical thickness of the mirror is at least five times longer than the wavelength of an incoming electromagnetic wave of a specific frequency, constructive interference occurs and a narrow range of wavelengths around the incoming frequency is reflected.
    [076] Figure 6 shows the light path of the incident light in a Bragg 60 mirror.
    [077] The Bragg 60 mirror made of a multilayer system composed of layers with the respective refractive indexes n1 and n2. The refractive indices are alternated in the layers in the z dimension of the three-dimensional film. The structure is periodic along the axis with a period "p" as shown in Figure 6. This period is also known as the "pitch" of the film. The film structure acts as a reflector at a single frequency with a limited bandwidth. The values of the refractive indices n1 and n2 are around 1.5. Its contrast (or ratio) controls the bandwidth of the reflection provided by the film. The typical contrast ratio is 1.7 / 1.5 which produces a bandwidth of ~ 2 - 5%. The magnitude of the reflectivity is controlled by the total length of the structure, in the direction of the laser radiation propagation, at the same time that the pitch and the absolute values of the indexes control the exact frequencies of interest. By stacking the multiple sets of Bragg mirrors, the operation of multiple bands can be achieved.
    [078] The R reflectivity of the Bragg 60 mirror is given approximately by the equation

    [079] Here n1 and n2 are the refractive indices of two alternating materials within the Bragg 60 mirror, while no and ns are the refractive indices of the source medium and the terminating medium respectively. If the film is applied inside a transparent glass surface as shown in Figure 6, the source medium must be glass and the termination medium must be air. N is the number of periodic layers comprising mirror 60.
    [080] The ΔA bandwidth of the Bragg 60 mirror is given by

    [081] Here Ao is the central wavelength of the reflected radiation and n1 and n2 are the alternating refractive indices of the Bragg layers as before. In order to increase the reflectivity of the Bragg 60 mirror, the number of layers can be increased, while the operating bandwidth can be made narrower by decreasing the contrast index.
    [082] An example of the reflectivity of the Bragg 60 mirror as a function of the wavelength for various refractive index contrasts is shown in Figure 7. Here the index of the first layer of each pair is constant at 1.50, and the index of the second layer of each successive pair is varied.
    [083] In an advantageous mode, a filter is provided to filter the light unidirectionally, that is, over a wide range of angles. This is a serious limitation of conventional Bragg mirrors that operate over a very narrow range of angles. In modalities, this is achieved by combining two or more metamaterials. For example: a first metamaterial may reflect a first wavelength of the radiation received at a first angle; a second metamaterial can reflect the first wavelength received at a second angle; and a third metamaterial can reflect the first wavelength received at a third angle. By combining three such metamaterials, a pseudo-wide-angle filter is provided for the incident radiation at the first wavelength.
    [084] In another modality, the metamaterial is designed to be omnidirectional and / or block multiple wavelengths of light. In one example, green (532 nm), blue (445 nm), and red (635 nm) target wavelengths require a 5-10 nm bandwidth around each wavelength in order to preserve the full transparency of the filters. Either way, the filters can be adapted to operate on another wavelength as well, adjusting the thickness and refractive indexes of the layers. The operation of multiple wavelengths and / or multiple angles of the structure is achieved by specifically planning the structure, such as a photonic crystal mirror structure, to consist of multiple sub-mirrors, each mirror operating for a specific range of length waveform and a specific range of angles (typically +/- 30 degrees). That is, in one example, at that point three sub-mirrors are provided for each wavelength in order to cover all the angles of incidence, in which they must be superimposed together for omni-directional performance. In the modalities, high-index materials, such as MoO3 and TiO2 are used since the omnidirectional performance is enhanced with the increased index. In yet other embodiments, other layers are added after these multiple overlapping layers in order to enhance the transmission of light outside the multiple strip openings. For example, one of the three (or more) layers of anti-reflective coating can be added to optimize transmission.
    [085] Thus, at this point a filter is provided comprising a first metamaterial arranged to provide the first and a second metamaterial arranged to provide the second filtration. The first / second filtration can be angle and / or filtration depending on the incidence-dependent filtration wavelength. By overlapping the performance of metamaterials, pseudo omnidirectional filtration can be provided. Also, filtration of the multiple bands can be provided.
    [086] According to another modality, an optical filter comprises a film that uses cholesteric liquid crystals. Liquid crystals are of a state of matter between a liquid and a crystal. The molecules in liquid crystals can flow slowly, as in a liquid, but at the same time, they maintain a preferable orientation, as in a crystal. Liquid crystals are routinely used on screens and monitors, when they can be electrically controlled to block or transmit a certain polarization of light.
    [087] Liquid crystals are inherently anisotropic and can be described by the orientation of their area guide, that is, the preferred axis along which the elongated molecules 80 of a liquid crystal are oriented on average, as shown in Figure 8. The orientation of the axis is usually defined using the "guide" n, a smaller unit vector.
    [088] Of particular interest here are cholesteric liquid crystals, that is, liquid crystals for which the area guide (its orientation of the molecule's axis) rotates as a function of space in one dimension.
    [089] If this dimension is along the z axis, the guide n is a function of z, that is, n = n (z). For this reason, the form of liquid crystals of a helical structure. The pitch of the helical structure for each liquid crystal is determined by the distance between the beginning and the ends of the crystal along that dimension when it rotates 360 degrees.
    [090] Figures 9a and 9b show an example of a cholesteric liquid crystal that has a 180 degree rotation. For this reason the difference between the beginning and the end positions of the crystal in Figures 9a and 9b is the means of bearing the crystal. For an optical filter that filters one or more narrow bands of laser light, the typical pitch (p) of the helical structure must be between 100 and 1000 nanometers (nm).
    [091] The exact orientation of the guide for a crystal with respect to the structure of the laboratory can be determined by rotating the guide from an angle

    [092] which varies depending on the propagation distance z of the electromagnetic wave. If the permissiveness tensor at the origin of the liquid crystal has the shape

    [093] And then the permissiveness after the wave has propagated a distance z across the crystal is

    [094] In Figures 9a and 9b the guide is rotated inside the x-y plane at the same time as the crystal evolves (and then has a heaving) in the z direction.
    [095] Figure 9a shows a cholesteric liquid crystal structure. The liquid crystals (represented as dark colored ellipsoidal elements) revolve around the axis (z) of propagation that coincides with the axis of the helix. In Figure 9b, white light illumination of the multiple wavelengths is shown incident on the structure along its axis of rotation (represented by the z axis). In this example, green light is filtered although other wavelengths of light are taken into account through the crystal structure.
    [096] In order to form an optical filter of cholesteric liquid crystals, the helical structure is repeated several times (~ 5-10 or more) along the axis of the helix, which also coincides with the main direction of laser propagation, in the Figure 9b. The polarized fields of electromagnetic radiation collide in the structure must be reflected at a specific frequency depending on the pitching value. The force of the reflex is controlled by the number of times the pitch is repeated (the total length of the propeller). When stacking the multiple layers of liquid crystals with different pitches together, the multiple frequencies and multiple polarizations can be reflected, as shown in Figure 10, in which two different layers, each with a reflexively (R) of about 1, are shown to reflect electromagnetic radiation at two different respective frequencies.
    [097] For that reason in each of the modalities described above a film is provided which can comprise the multiple overlapping layers of material elements, such as unit cells or crystals, in which the shape, composition or combination of these elements materials can be deliberately designed to alter the behavior of the film in order to filter out certain wavelengths of electromagnetic radiation, such as laser light, but allow other wavelengths through the film without any distortion. The filter may comprise nanoparticles, a Bragg reflector, and / or liquid crystals. The multiple layers of metamaterials having different respective filtration capacities can be superimposed together to form a film, therefore allowing more than one wavelength band to be filtered by the film or omnidirectional filtration to be obtained. Alternatively, the filter must contain multiple metamaterials, each of which has the same electromagnetic properties so that the film is designed only to filter a band of wavelengths.
    [098] In each modality described above the filter is provided as a result of the engineering materials at the nanoscale. As the knowledgeable reader must know, the visible light wavelength is about 500 nm. In order to provide a light handling material that can filter out certain frequencies chosen from laser or other light or electromagnetic radiation, structural elements such as material elements, less than (or at most the same size) the length of radiation wave must be provided. In the solution provided here, these material elements are preferably in the range of 1 to 100 nm in size.
    [099] The multiple metamaterials formed from the structural elements described above can be overlapped or otherwise combined together in a number of different ways. For example, physical vapor deposition, vapor phase deposition, polymer implantation, chemical vapor phase deposition or centrifugation coating of the layers can be employed. The centrifugal coating method, as an example, consists of four different stages. First, the material (for example, the polymer) is poured onto a flat surface or substrate through a nozzle. Second, the surface begins to rotate quickly, accelerating to a final speed. Third, at the same time that the surface is rotating, the material is evenly distributed across the surface area, dominated by the centrifugal and viscous forces. Finally, a solvent is applied to the top of the rotating material, in order to adjust the thickness to the required value. The process is repeated for each layer of the filter.
    [0100] In one modality, a metamaterial is manufactured using a sol-gel process. That is, another method for making a Bragg-based metamaterial is sol-gel. Sol-gel is a distinct, low-cost, and powerful approach that offers innovative strategies for adapting nanostructured films with controllable properties including size distribution, morphology, porosity, shape, and surface area. It is a chemical method that also provides an alternative route for the synthesis of multiple components of oxide materials with different compositions and in which the distribution of heterometalline bonds is highly homogeneous. Sol-gel is a unique technology that allows you to choose the thickness and refractive index of the thin film layer by simply changing the synthetic conditions including the chemical composition of the precursors, the addition of the additives, the concentrations, the speed and the angle of dip coating, etc. Sol-gel technology allows the manufacture of thin film coatings on various substrates with different sizes and shapes. To create new devices, which typically consists of alternating layers of two different materials (with different refractive indices), two mixtures are prepared that have the corresponding refractive indices necessary for blocking the light based on the Bragg design. Then, a layer of one of the two mixtures is deposited on a substrate (which can be a transparent flexible substrate), and then it is dried or baked until it solidifies. Subsequently, the second layer is deposited and then dried until it solidifies. The procedure is repeated until the required number of layers is reached, which can be more than 100. At the end of the process other layers (using new mixtures with different refractive indexes from the original two) can be added in order to provide the scratch protection and / or anti-reflective coatings to optimize transmission.
    [0101] Another method for manufacturing the filter is a self-assembling nanoparticle. Self-assembly is a "bottom" approach in which nanoparticles are simply placed on a specially prepared surface and automatically organizes based on the electrochemical interactions between the particles and the surface. This method has the advantage that it can be much simpler and faster than placing the nanoparticles on the film by manipulating them individually. Surface preparation for self-assembly can be achieved using a variety of techniques, such as the fountain pen, laser lithography, electron beam lithography, and chemical lithography.
    [0102] Through the combination of multiple thin metamaterials differently adapted together, the protection of lasers in multiple different wavelengths of light can be achieved simultaneously using the same filter. In addition, filtration can be extended to other laser frequencies in addition to the visible spectrum, such as ultraviolet lasers. As mentioned above, the filter operates passively and there is no user intervention required in order to select which frequency or frequencies of radiation are to be filtered at any given time. Instead, the filter reacts immediately to incoming electromagnetic radiation by filtering out any components of that radiation that are within one or more of the wavelength bands in which the filter has been pre-engineered to attenuate. This allows any other components within the radiation, which are not within these wavelength bands, to pass through the film without being distorted in frequency, wavelength, angle or any other property.
    [0103] In any case, the inventors have found that the simple combination, such as stacking, of independently designed metamaterials, such as Bragg reflectors, does not give rise to multiple ideal bands or performance from multiple angles. That is, the performance of a combined metamaterial device does not simply reach the sum of its parts. More specifically, the inventors have found that the overall efficiency of filtration is reduced by combining metamaterials because the layers of one metamaterial affect the electromagnetic behavior of the other metamaterial or metamaterials in the combination. Thus, in the modalities, at that point a method for forming an improved filter comprising a plurality of metamaterials is provided, the method comprising changing the sub-wavelength properties of the respective metamaterials to provide the improved performance of the multiple bands. Likewise, in the embodiments, at that point a method of forming an improved filter comprising a plurality of metamaterials is provided, the method comprising altering the sub-wavelength properties of the respective metamaterials to provide improved performance from multiple angles. At this point, an improved invariant angle, or filter, is provided for this reason. The method can result in the deterioration of the single band performance or the unique angle of each metamaterial when used alone. Such optimization of the multiple bands / multiple angles can be obtained experimentally or theoretically by monitoring the optical properties of the combined device at, for example, multiple wavelengths and / or multiple incidence angles although adjusting the parameters of the sub-length of wave of metamaterials. For example, optimization can be achieved using an optimization algorithm. Thus, a first metamaterial can predominantly provide the first filtration characteristics, and a second metamaterial can predominantly provide the second filtration characteristics, and the method comprises changing the sub-wavelength properties of the first metamaterial in view of the first and of the second filtration characteristics, not just the first filtration characteristics. The inventors have found that employing this approach, yet another improved multi-band and / or multiple-angle filter can be provided.
    [0104] The filter can provide laser radiation filtering up to and including Class 3B lasers, which have rated power of up to 500 milliWatts. It also provides protection for many Class 4 lasers with rated wattages of up to 2 Watts and can be used to protect against the strongest lasers in the future. As indicated in the preceding section above, a one Watt laser is the highest laser power generally available today, however it could change over time and the filter as described here is equipped to accommodate such changes.
    [0105] The filter can attenuate laser light or other electromagnetic radiation that is placed directly on the filter and can also filter out specular reflections. This is important when even specular reflections can cause serious immediate damage to the eye from one or more parts of the eye including the cornea, iris, lens or even the retina. Lasers can also cause distraction, intense glare or temporary flash blindness, all of which are uncomfortable and are potentially very dangerous if the affected person is driving a vehicle, plane or piece of machinery at the time, even if the damage in the eye is not permanent. The filter described here acts to eliminate the security risk posed by lasers and their potential damage to the eyes and skin of individuals.
    [0106] As an example, a 5 mW green laser indicator seen from 3,000 feet away corresponds to an intensity of 0.5 μW / cmA2 causing significant distraction. The same intensity is obtained from a 300 mW laser as seen from 16,000 feet away. An intensity level of 50 μW / cmA2 can temporarily blind a person, while laser intensities of 1 mW / cmA2 or more have serious physical effects. These effects occur even when the laser beam travels through thin air, which refracts less light, so that the laser beam cannot be seen by the human eye. The sizes of the laser beam may differ, and shaking hands holding a laser can turn a laser beam indicator into a camera with a flash when viewed from a distance.
    [0107] The wavelengths for which such phenomena are strongest are ultraviolet (from 200 to 390 nm), visible (from 390 to 750 nm) and infrared (from 750 nm to 1 mm). Lasers exist for all sections of the electromagnetic spectrum, such as He-Ne (Helium-Neon) at 632.8 nm, Nd: Yag (Yttrium and aluminum grenade doped with neodymium) at 946 nm, or the third harmonic titanium-sapphire between 235 to 330 nm. Of specific relevance to the filter described here are the lasers that emit radiation in the visible part of the spectrum because it means the spectrum in which human eyes are most sensitive, and in which inexpensive lasers are more readily available to operate on the market. For example, one of the most commonly used lasers is the doubled frequency Nd: YAG at 532 nm (green laser), which is closest to the peak of human photopic sensitivity.
    [0108] The filter described here can be specifically adapted to filter the wavelengths at which the most commonly used laser products are known to operate. Due to the sensitivity of the nanoparticle structure, and the precision to which the particles can be adapted, the filter can comprise extremely narrow band elements that selectively block specific wavelengths of light without affecting other frequencies, resulting in almost complete transparency to the user behind the filter. However, the physical form in which the filter is provided, does not have to be colored or dyed and therefore its presence leads to minimal distortion of the user's vision (<10%).
    [0109] Although a film has been described here above, the filter can be provided in a plurality of different physical forms while still being composed of one or more layers of nanoparticle structure as described in detail here. The filter can be applied to flat or curved glass in buildings or equipment equipped with a laser, or to any of: transparent acrylic boxes used for the protection of laser light, goggles, visors, contact lenses, protective gloves, vehicle panes, windshields and airplane cabins. As well as or instead of being a safety device, the filter can be used for aesthetic or entertainment purposes to deliberately filter the specific components of light from the walls, screens or frames. Such filtering can be controlled by a user for the results immediately visible.
    [0110] Although the filter has been described here above only being passive, if it was small enough in size it can be electronically controlled although still having only low energy consumption requirements. By imposing low static electric fields, nanoparticles can have different properties and the filtration action can be adapted and adapted to demand. A field can be applied using transparent conductive films (made from organic or inorganic materials, such as silver oxide, carbon nanotubes or graphene) and an external battery source. This is useful in situations where it may be desired not to block any moon at all, during certain periods of time. In addition, the system can be adapted ahead of time to operate on different wavelengths of light other than visible, such as infrared and ultraviolet. The functioning of multiple bands must also be obtained over these spectral regions.
    [0111] Although the specific modalities and aspects have been described above, variations can be made without departing from the inventive concepts described here. The filter can block any one or more wavelengths or narrow bands of the wavelengths in the EM spectrum. The filter can comprise any appropriate number of layers. The filter and / or an individual layer within the filter can comprise a combination of the different types of material elements. It may comprise an adhesive or other means for bonding to a surface. Material elements or unit cells within the filter layers may be solid or include a cavity or perforation, which may include an air bubble.
    [0112] The filter is completely adaptable so it can be produced to fit any size and shape of surface. It can be applied to examples or to all of a surface. It can be replaced over time with a different filter if the filtering required for a surface change. And it can be adapted prior to use by selecting and combining the appropriate material elements in one or more layers to provide filtration at any desired wavelength or wavelength.
    [0113] For this reason, a highly useful and efficient solution is provided. It can be produced with relatively cost effective and can be used in many different practical situations. They enhance user safety by protecting against laser damage, and can also provide electromagnetic filtering and masking for a wide range of applications.
    [0114] At this point, a filter is provided for filtering electromagnetic radiation, in which said filter is arranged to transmit electromagnetic radiation of a first predetermined wavelength and to block the transmission of electromagnetic radiation from a second, different wavelength predetermined; said filter comprising a first layer formed of a plurality of material elements, wherein each material element is at least one-dimensional and the size of the material element along each dimension is not greater than the size of the second predetermined wavelength.
    [0115] The second predetermined wavelength can be in the visible part of the electromagnetic spectrum. The filter may further comprise an adhesive layer. A size of the material element along each dimension can be less than the size of the second predetermined wavelength. The material elements can be the nanoscale elements. Each material element can have a size along each dimension of between 1 nanometer (nm) and 100 nanometers (nm).
    [0116] The filter can be arranged to be optically transparent to electromagnetic radiation at all wavelengths except at the wavelength or wavelengths that are specifically arranged to block the transmission. The filter can be substantially transparent to the human eye.
    权利要求:
    Claims (6)
    [0001]
    1. Method of manufacturing a filter to filter ultraviolet to infrared electromagnetic radiation, characterized by the fact that said filter combines: a first metamaterial having sub-wavelength properties and willing to provide the first filtering of electromagnetic radiation incident on a first angle in a first range of angles; and a second metamaterial having sub-wavelength properties and arranged to provide a second filtering of electromagnetic radiation at a second angle in a second range of angles, where the first and second angles are different and the first and second ranges of angles partially overlap and in which the first metamaterial and the second metamaterial are configured as stacked filter layers, where the first filtering comprises blocking electromagnetic radiation in a first frequency bandwidth around a first wavelength and the second filter comprises blocking electromagnetic radiation at a second frequency bandwidth around the first wavelength, where the second frequency bandwidth is substantially similar to the first frequency bandwidth and where the first and the second frequency bandwidth are within the ultraviolet spectrum for infrared, while each of the first and second metamaterials transmit ultraviolet to infrared electromagnetic radiation that is not in the first or second frequency bandwidth over the first wavelength; wherein the filter is comprised of a film; and where the first metamaterial is a Bragg reflector or a photonic crystal and the second metamaterial is a Bragg reflector or a photonic crystal, the method comprising: selecting the size, shape, material or configuration of the structural characteristics of the first and / or the second metamaterial to provide the correct material properties to obtain said block within the ultraviolet ultraviolet spectrum to the infrared, where the selection comprises optimizing the filter, to improve the performance of various angles, monitoring the optical properties of the combined filter in multiple incidence angles, while adjusting the sub-wavelength properties of the first and second metamaterials.
    [0002]
    2. Method according to claim 1, characterized by the fact that the filter is comprised within or on a windshield.
    [0003]
    3. Method, according to claim 1 or 2, characterized by the fact that the filter is comprised inside or over an aircraft cabin.
    [0004]
    4. Method according to any one of the preceding claims, characterized by the fact that the filter is passive.
    [0005]
    5. Method according to any one of the preceding claims, characterized in that the filter appears substantially transparent to the human eye.
    [0006]
    6. Method according to any one of the preceding claims, characterized by the fact that the first bandwidth and the second bandwidth are from 5 to 10 nm.
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    同族专利:
    公开号 | 公开日
    US20140293467A1|2014-10-02|
    US10698143B2|2020-06-30|
    CA2851347C|2016-09-13|
    JP6334403B2|2018-05-30|
    EP2748655A1|2014-07-02|
    GB201117480D0|2011-11-23|
    CA2851347A1|2013-04-18|
    JP2014534459A|2014-12-18|
    US20190146133A1|2019-05-16|
    CN104067149A|2014-09-24|
    IL231830A|2019-09-26|
    US10996385B2|2021-05-04|
    CN104067149B|2016-11-16|
    EP2748655B1|2019-01-02|
    IL231830D0|2014-05-28|
    DK2748655T3|2019-03-18|
    BR112014008611A2|2017-05-23|
    WO2013054115A1|2013-04-18|
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    法律状态:
    2018-12-11| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2020-03-31| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-12-01| B09A| Decision: intention to grant|
    2021-01-19| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 10/10/2012, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    GB1117480.2|2011-10-10|
    GBGB1117480.2A|GB201117480D0|2011-10-10|2011-10-10|Filter|
    PCT/GB2012/052518|WO2013054115A1|2011-10-10|2012-10-10|Filter made of metamaterials|
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