WO2022018585A1

WO2022018585A1 - Millimeter wave antireflective structure

Info

Publication number: WO2022018585A1
Application number: PCT/IB2021/056401
Authority: WO
Inventors: Jeffrey M. Florczak; Min Ding; Shupeng WU; Weigang LIN; Jie Huang
Original assignee: 3M Innovative Properties Company
Priority date: 2020-07-23
Filing date: 2021-07-15
Publication date: 2022-01-27

Abstract

An antireflection structure includes a multilayer film having first and second antireflection layers. The first antireflection layer has a dielectric constant, ε₁, and a thickness, t₁. The second antireflection layer has a dielectric constant, ε₂, and a thickness, t₂. The thicknesses and the dielectric constants of the first and second antireflection layers are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

Description

MILLIMETER WAVE ANTIREFLECTIVE STRUCTURE

TECHNICAL FIELD

This disclosure relates generally to antireflective structures useful for millimeter wave applications such as mobile communication devices.

BACKGROUND

The 5th generation, or 5G, communication standard is an evolutionary change in wireless communication technologies with the goal of improving data transfer speeds, latency, reliability, and enabling denser wireless communication coverage. The 5G standard adds additional spectrum to achieve wider bandwidths, proposing spectrum allocations near 3.5 GHz and multiple bands in the 24-60 GHz range. The wavelengths in the 24-60 GHz range are often referred to as mm -wave or ultra- wide band (UWB) due to the large available bandwidths. Two frequency ranges, 24.25- 29.5 GHz and 37-40 GHz are often used in 5G mm-wave for mobile device communication.

BRIEF SUMMARY

Some embodiments discussed below include an antireflection structure comprising a multilayer film having first and second antireflection layers. The first antireflection layer has a dielectric constant, si, and a thickness, ti. The second antireflection layer has a dielectric constant, 82, and a thickness, Ϊ2. The thicknesses and the dielectric constants of the first and second antireflection layers are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

In accordance with some embodiments, an antireflection structure includes a substrate having a dielectric constant, e_s, and a thickness, t_s and a multilayer film comprising a first antireflection layer and a second antireflection layer. The first antireflection layer has a dielectric constant, si, and a thickness, ti_, and the second antireflection layer has a dielectric constant, 82, and thickness, Ϊ2. The thicknesses and dielectric constants of the first layer, the second layer, and the substrate are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm- wave band and a second peak near a lower frequency of the mm-wave band.

Some embodiments are directed to an electronic communication device. The device includes an enclosure and a mm-wave transceiver disposed within the enclosure. The mm-wave transceiver is configured to transmit and receive mm-wave communication signals. A multilayer film is disposed on an inner surface of at least a portion of the enclosure. The multilayer firm comprises first and second antireflection layers. The first antireflection layer has a dielectric constant, si, and a thickness, ti. The second antireflection layer has a dielectric constant, 82, and thickness, Ϊ2. The thicknesses and the dielectric constants of the first and second layers are configured such that the communication signals through the multilayer film and the enclosure in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and IB show graphs illustrating representative signal transmission losses of chemically strengthened aluminosilicate glass;

FIGS. 2A and 2B show graphs illustrating representative signal transmission losses of Zr02 ceramic;

FIG. 3 is a schematic cross-sectional diagram of an antireflective (AR) structure comprising a multilayer film disposed on a substrate in accordance with some embodiments;

FIG. 4 is a process flow diagram showing fabrication of a communications device that employs an antireflective structure in accordance with some embodiments;

FIGS. 5A and 5B show the far field transmission characteristic of an antireflective structure comprising a substrate with a multilayer film as shown schematically in FIG. 3;

FIG. 6 is a schematic cross-sectional diagram of a comparative two-layer structure in accordance with some embodiments;

FIGS. 7A and 7B show the far field transmission characteristic of an antireflective structure shown schematically in FIG. 6;

FIG. 7C shows a graph of realized gain obtained from near field simulation for the structure of FIG. 6;

FIG. 8 is a schematic cross-sectional diagram of an antireflective structure that includes a multilayer film comprising two antireflective layers disposed on a substrate in accordance with some embodiments;

FIGS. 9A and 9B show the far field transmission characteristic for mm-wave signals through the structure shown schematically in FIG. 8;

FIG. 9C shows the graph of realized gain obtained from near field simulation for the structure of FIG. 8;

FIG. 10 is a schematic cross-sectional diagram illustrating a comparative example of an antireflective structure in accordance with some embodiments;

FIGS. 11A and 1 IB show the transmission characteristic of the structure shown schematically in FIG. 10;

FIG. llC shows a graph of realized gain obtained from near field simulation of for the structure of FIG. 10; FIGS. 12A and 12B are diagrams illustrating an electronic communication device in accordance with some embodiments;

FIG. 13 provides overlaid graphs showing the transmission characteristics for glass plus an e = 27 material layer and glass plus an e = 27 material layer and an e = 7 material layer in accordance with some embodiments;

FIG. 14 shows comparative graphs of the transmission characteristics of an aluminosilicate glass substrate alone and the transmission characteristics of the substrate with the AR fdm disposed thereon in accordance with some embodiments; and

FIG. 15 shows comparative graphs of the transmission characteristics of a ZrCL substrate alone and the transmission characteristics of the substrate with an AR film disposed thereon in accordance with some embodiments.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Due to the short wavelengths at the mm-wave frequencies, the effects of materials on signal propagation can be profound. For example, a human hand, a glass window, or even tree leaves can interfere with the signal by way of reflection or absorption losses and thereby impair the signal integrity. In cellular telephones and other types of communication devices mm-wave transceivers are typically located within an enclosure. Reflection and absorption losses at the enclosure can significantly degrade the outgoing or incoming communication signal.

For handheld mobile electronic devices such as cellular telephones, an added constraint is the industrial design. Consumers prefer mobile device designs with compact form factors that are aesthetically pleasing. For mobile devices this has resulted in device enclosures with relatively thin profiles that could easily be held in one hand. Materials for the device enclosure have evolved from primarily metallic or polymeric to a more diverse mix of glass, polymer, or ceramic based materials. The use of these materials needs to be considered in conjunction with the implementation of mm-wave technology, specifically reflection and transmission losses which degrade signal strength. It is this aspect of the design for mobile devices which can be problematic with many phone enclosure materials. For example, glass and ceramic materials in the back cover of mobile devices can cause noticeable signal loss in the mm-wave frequencies.

Equation 1 estimates the single interface reflection, R, of mm-waves at the cover of a mobile device at normal incidence at the air/back cover interface: where the index of refraction of the cover, h = (e₈m₈)¹^². the permittivity of the cover is ¾, and for non-magnetic materials the magnetic permeability, u = 1.0.

Examples of mobile device enclosures include polymers (¾ = 2-3.5, // = 1.4 - 1.9, and R ~ 9 %); glass (¾ ~ 7, h₅ ~ 2.65, and R ~ 20%); and ceramic (¾ ~ 20, h₅ ~ 4.47, and R ~ 40%). These interface reflections are not inconsequential and negatively impact signal strength.

The reflection loss of common dielectric materials used in mobile electronic enclosures indicates losses in the range of 3-10 dB for common enclosure thicknesses in use today.

Chemically strengthened aluminosilicate glass and ZrCE ceramic are commonly used enclosure materials for mobile communication devices. FIG. 1A is a graph illustrating the representative transmission losses of chemically strengthened aluminosilicate glass (e = 6.89, thickness = 0.55 mm) at normal incidence to the plane of the back cover. FIG. IB is a graph of the transmission losses of the aluminosilicate glass of FIG. 1 A in the 5G signal band from 24 GHz to 40 GHz. As will be appreciated from inspection of FIGS. 1A and IB, the mm-wave signal loss for GG5 is about -1.9 dB at 24.25 GHz, - 2.5 dB at 29.5 GHz, -3 at 37 GHz, and -3.22 dB at 40 GHz.

FIG. 2A shows a graph illustrating the representative transmission losses of ceramic, ZrC>2, (e = 36.0, thickness = 0.4 mm). FIG. 2B shows the representative transmission losses in the 5G signal band from 24 GHz to 40 GHz. As will be appreciated from inspection of FIGS. 2A and 2B, the mm-wave signal loss is about -9.29 dB at 24.25 GHz, -9.47 dB at 29.5 GHz, -9.4 at 37 GHz, and -9 dB at 40 GHz. Reducing these losses would enhance the overall transmission budget allowing for lower power levels from the mobile device amplifier to maintain good signal connection.

Embodiments discussed herein are generally directed to antireflection structures that reduce the reflection of electromagnetic signals in the mm-wave range. The disclosed approaches are particularly applicable to reduce reflection at the enclosure cover of mobile communication devices such as cellular telephones. These antireflection structures can use multiple antireflective layers that target different wavelengths of interest. Reducing reflection of multiple different wavelengths decreases the transmission losses over an extended bandwidth.

Example structures described herein can comprise several thin, e.g., less than 1 mm, layers, that reduce the reflection of mm-wave signals thereby increasing transmission of the signals through the structures. Signals through the structure have a transmission characteristic that is modified by the layers of the structure. At least some of the layers of the structure have a thickness and dielectric constant selected to produce a transmission peak in the transmission characteristic at a frequency within the mm-wave band of the communication signal. For example, in some embodiments a first one or more layers are selected to produce a transmission peak near a lower frequency of the mm-wave band of the communication signal and a second one or more layers are selected to produce a transmission peak near an upper frequency of the mm-wave band of the communication signal. In this disclosure the first one or more layers can be upper frequency antireflective layers and the second one or more layers can be lower frequency antireflective layers. The upper frequency antireflective layers are configured to produce a peak in the transmission characteristic at an upper frequency of the mm-wave band. The lower frequency antireflective layers are configured to produce a peak in the transmission characteristic at a lower frequency of the mm-wave band. For example, the upper frequency may be in a range of about 35 GHz to about 60 GHz and the lower frequency may be in a range of about 20 GHz to about 34 GHz.

FIG. 3 is a schematic cross-sectional diagram of an antireflective structure 300 comprising a multilayer film 320 disposed on a substrate 310. In a particular implementation, substrate 310 is the cover of a mobile communication device. Antireflective structure 300 can include three antireflective layers in some embodiments. In some embodiments, the cover 310 of the mobile device provides the first upper frequency antireflective layer of structure 300; the first layer 321 of the multilayer film 320 provides the second upper frequency antireflective layer of the structure 300; and the second layer 322 of the multilayer film 320 provides a lower frequency antireflective layer of the structure 300. In most implementations, the multilayer film 320 is positioned on the inside surface of the cover 310. There is a first air-dielectric interface 391 at the outside surface 310a of the cover 310 and a second air-dielectric interface 392 at the inside surface 321b of the first layer 321 of the multilayer film 320.

In some implementations, the substrate layer 310 has a thickness, t_s, and a dielectric constant, e_s, providing a peak in the transmission characteristic through the structure 300 at an upper frequency, li, of the mm-wave communication band.

The second layer of the 322 of the multilayer film 320 is disposed on the substrate 310 and can have a thickness, Ϊ2, and a dielectric constant, 82 _, that produces a peak in the transmission characteristic through the structure 300 at a lower frequency, , of the mm-wave communication band.

The first layer 321 of the multilayer film 320 is disposed on the second layer 322 and can have a thickness, ti, and a dielectric constant, si _. that produces a peak in the transmission characteristic through the structure 300 at an upper frequency, li, of the mm-wave communication band. In some embodiments, the thickness, t_s, of the substrate 310 is about equal to ^ =: the d layer 322 is about equal to -7=: and the thickness t .

² ¾

In some embodiments li and l₂ are in a range from about 6 mm to 13 mm. The overall thickness of the antireflective structure 300 may be less than 3 mm, or less than 2.5 mm, or less than 2 mm, or even less than 1.5 mm. The thickness of each of the layers 310, 321, 322 can be less than 1 mm and/or less than any of the wavelengths of interest, for example.

In general, li and I can be any wavelengths in the mm-wave range, however, in most embodiments, li ¹ I . For example, li may be between 6 mm and 10 mm and l may be between about 10 mm and 13 mm in some embodiments. Additional antireflective layers may be included in the structure wherein the additional antireflection layers produce peaks in the transmission characteristic at additional wavelengths of interest within the mm-wave communication band.

In some configurations, the thickness of two (or more) of the layers can be selected to produce a peak in the transmission characteristic at a first wavelength li and the thickness of the remaining layer (or layers) can be selected to produce a peak in the transmission characteristic at the second wavelength h. In some implementations, the thickness, ti, of the first layer 321 and the thickness, t_s , of the substrate 310 can be selected to reduce reflection of the mm-wave signal near li = 7.69 mm (f = 39 GHz). The thickness, Ϊ₂, of the second layer 322 can be selected to reduce reflection of the mm-wave signal near = 12.49 mm (f = 24 GHz).

The substrate 310 and/or multilayer film 320 may be made of any materials that provide suitable mechanical and/or antireflective properties. In some implementations, the substrate 310 may comprise a polymer, a ceramic, or a glass. Suitable materials for the substrate 310 may comprise quartz, alumina and combinations thereof, glass-ceramics, metal oxide and/or metal carbide. For example, suitable glasses for the substrate 310 include alkali -aluminosilicate glass, quartz, borosilicate, aluminosilicate, aluminate, or borate glass. Suitable ceramics for the substrate 310 include ZrC>₂, aluminum oxide, aluminum/zirconium oxide mixtures and/or combinations thereof, glass-ceramics, metal oxide, and/or metal carbide materials including silicon carbide, boron carbide, silicon carbide/boron carbide mixtures, silicon nitride, rare earth oxides, rare earth aluminates, titanium oxide and/or, zinc oxide. Suitable polymers for the substrate 310 may include polycarbonate (PC), acrylonitrile butadiene styrene (ABS), PC-ABS, poly(methyl methacrylate) (PMMA), styrene ethylene butadiene styrene, glass fiber reinforced polyester.

The first layer 321 of the multilayer film 320 can comprise a polymer composite matrix with a filler. In some embodiments, the filler materials may comprise one or more of SrTi0₃, CaCuTiCb, BaTiCb, BaSrTiCb, PbLaZrTiCb, T1O2, A1₂0₃, Zr0₂, PbMgNb0₃+PbTi0₃, BaFei₂0i₉, SrFei₂0i₉, CaCTvTuOi . LaSrxNiCfi. for example. The polymer matrix may comprise rubber, polyurethane, acrylate, silicone, and/or polyolefin. The polymer matrix may comprise, consist essentially of, or consist of at least one thermoplastic polymer. Exemplary thermoplastic polymers include polyurethane, polyester (e.g., polyethylene terephthalate, polybutylene terephthalate, and polylactic acid), polyamide (e.g., nylon 6, nylon 6,6, nylon 12 and polypeptide), polyether (e.g., polyethylene oxide and polypropylene oxide), polycarbonate (e.g., bisphenol-A-polycarbonate), polyimide, polysulphone, polyethersulphone, polyphenylene oxide, polyacrylate (e.g., thermoplastic polymers formed from the addition polymerization of monomer(s) containing an acrylate functional group), polymethacrylate (e.g., thermoplastic polymers formed from the addition polymerization of monomer(s) containing a methacrylate functional group), polyolefin (e.g., polyethylene and polypropylene), styrene and styrene-based random and block copolymer, chlorinated polymer (e.g., polyvinyl chloride), fluorinated polymer (e.g., polyvinylidene fluoride; copolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; copolymers of ethylene, tetrafluoroethylene; hexafluoropropylene; and polytetrafluoroethylene), and copolymers of ethylene and chlorotrifluoroethylene.

In some embodiments, thermoplastic polymers include homopolymers or copolymers (e.g., block copolymers or random copolymers). In some embodiments, thermoplastic polymers include a mixture of at least two thermoplastic polymer types (e.g., a mixture of polyethylene and polypropylene or a mixture of polyethylene and polyacrylate). In some embodiments, the polymer may be at least one of polyethylene (e.g., ultra-high molecular weight polyethylene), polypropylene (e.g., ultra-high molecular weight polypropylene), polylactic acid, poly(ethylene- co-chlorotrifluoroethylene) and polyvinylidene fluoride. In some embodiments, the thermoplastic polymer is a single thermoplastic polymer (i.e., it is not a mixture of at least two thermoplastic polymer types). In some embodiments, the thermoplastic polymers consist essentially of, or consist of polyethylene (e.g., ultra-high molecular weight polyethylene), PMMA and/or silicone and the second layer 322 can comprise a composite comprising one or more of the materials previously discussed

According to some embodiments, an adhesive layer 330 disposed between the film 320 and the substrate 310 may be used to attach the film 320 to the substrate 310. When present, an adhesive layer may have a thickness range between about 1 pm and 100 pm. The 180° peel adhesion range for the adhesive layer may be between about 0.01 N/mm to about 2 N/mm.

Suitable materials for the adhesive layer include, but are not limited to, acrylic adhesive, rubber, polyolefin, and silicone.

Some embodiments may include an optional protective film 340 positioned over the substrate 310. In many applications, the protective film 330 is removable. The thickness range for the protective film may be between about 1 pm and about 200 pm. Suitable materials for the protective film include, but are not limited to, paper or PET (polyethylene terephthalate) film.

In some embodiments the substrate is the back cover of the device and a decorative film is disposed over the back cover to enhance aesthetics of the device.

In general, ei ¹ 82 ¹ e_s. In some embodiments, two or more of the dielectric constants, si_,

82_, 8_s may be equal. For example, in some configurations, the dielectric constant, ei, of the first layer 321 can be in a range from 60 to 2 or in a range from 30 to 2 of in a range from 30 to 1.3 or in a range from 20 to 1.3. The dielectric constant, 82, of the second layer 322 can be in a range from 400 to 20 or in a range from 450 to 1.5, for example. In some configurations, the dielectric constant, e_s, of the substrate 310 can be in a range from 40 to 2 or in a range from 20 to 2. In some embodiments it is useful for the material of the center layer 322 to have a dielectric constant that is the square of the dielectric constant of the materials of the outer two antireflection layers 310, 321.

In some scenarios, shown in FIG. 4, the multilayer film 320 can be formed by a roll-to-roll manufacturing process that winds the multilayer film 320 onto a roll 450. The multilayer film 320 is then singulated into individual pieces 320-1, e.g., by cutting the multilayer film 320. The enclosure cover of a mobile device is used as the substrate 310. The pieces 320-1 of multilayer film 320 are placed inside the cover 310 of the mobile device during manufacture of the device 400.

FIGS. 5A and 5B show the far field transmission characteristic of an antireflective structure comprising a substrate with a multilayer film disposed thereon as discussed above and as shown schematically in FIG. 3. Structure 300 was designed to reduce signal transmission losses within the 5G communication band from 24GHz to 40GHz. In this example, the cover 310 comprises aluminosilicate glass having a nominal thickness of 0.55 mm. The center (second) layer 322 is configured to have thickness tuned to produce a peak in the transmission characteristic at one edge of the 24GHz to 40GHz band. The outer two layers (substrate 310 and first layer 321) are tuned to produces a peak in the transmission characteristic at the other edge of the 24GHz to 40GHz band. This construction achieves a relatively thin profile with a wide pass band through the structure 300.

In this example, the substrate 310 has a dielectric constant s_s= 6.89 and thickness t_s = 0.55 mm; the first layer 321 of the multilayer film 320 has a dielectric constant si = 7 and thickness ti = 0.8 mm; and the second layer 322 of the multilayer film 320 has a dielectric constant 82 = 49 and thickness Ϊ2 = 0.62 mm

FIG. 5 A shows a graph of the far field transmission characteristic of the structure 300 at normal incidence between 0 and 40 GHz. FIG. 5B shows a graph of the transmission characteristic of the structure 300 between 24 and 40 GHz. As will be appreciated from inspection of FIGS. 5A and 5B, the signal loss when the antireflection structure is used is about -0.78 dB at 24.25 GHz, - 1.35 dB at 29.5 GHz, -0.9 dB at 37 GHz, and -0.33 dB at 40 GHz. The decrease in signal loss through the structure when the multilayer film is applied to aluminosilicate glass is evident from comparison of FIGS. 1A and IB to FIGS. 5A and 5B. When the multilayer film 320 is used in conjunction with the substrate 310 to provide multiple antireflection portions targeted to different wavelengths of interest, the transmission characteristic through the antireflection structure exhibits a peak at or near each wavelength of interest. FIG. 5B indicates the transmission peaks which in this example occur near the lower band edge, 24 GHz, and the upper band edge, 39 GHz.

A comparative example of an antireflective structure 600 is illustrated in the schematic cross-sectional diagram of FIG. 6. Structure 600 is designed to reduce transmission loss of the mm-wave signal at a single wavelength of interest. In this example, the transmission characteristic of structure 300 shown in FIGS. 5 A and 5B exhibits overall higher transmission magnitude across the mm-wave band when compared to the transmission characteristic of structure 600

Antireflection structure 600 comprises two layers, the cover 610 and layer 620 disposed on the cover. When structure 600 is an enclosure for a mobile device, the structure 600 includes a first air-dielectric interface 691 at the outer enclosure surface 610a and a second air dielectric interface within the enclosure at the inner surface of layer 620. The two layers 610, 620 combined are designed as an antireflection structure having a total thickness, t, that produces a peak in the transmission characteristic near l, a wavelength within the mm-wave band.

In one example, the substrate 610 comprises alkali-aluminosilicate glass having a dielectric constant, e_s = 7 and a thickness 0.55 mm. The thickness and dielectric constant of layer 620 is selected so that the total thickness of the structure 600 provides a peak in the transmission characteristic at 28 GHz (l = 10.7 mm). Layer 620 comprises a composite material, e.g.,

BaSrTiCL powder loaded into a silicone polymer matrix and mixed to yield a dielectric constant of

7. For example, the optimal total thickness, t, of the structure according to the equation t = is

2.02 mm at 28 GHz. With a total thickness of 2.02 mm, 0.55 mm is allocated to the glass back cover 610 and the remaining component of the thickness is provided by layer 620 which has a eia_yer=7.0 and thickness 1.47 mm.

FIGS. 7A and 7B show the far field transmission characteristic of the antireflective structure 600 comprising substrate 610 with a film 620 disposed thereon as shown schematically in FIG. 6. FIG. 7A shows a graph of the transmission characteristic of the structure 600 for an angles of incidence 0 degrees between 0 and 40 GHz. FIG. 7B shows a graph of the transmission characteristic of the structure between 24 and 40 GHz. As will be appreciated from inspection of FIGS. 7A and 7B, the signal loss when the antireflection structure 600 is used is about-24.25GHz - 0.86dB, 29.5GHz -O.ldB, 37GHz -2.8dB, 40 GHz -3.38dB. FIG. 7B indicates the single peak in the transmission characteristic provided by the antireflection structure 600 which in this example occurs at about 28 GHz.

FIG. 7C shows a graph 703 of realized gain obtained from near field simulation of an antenna array positioned 1 mm from aluminosilicate type glass back cover 610 of the structure 600. The maximum realized gain for anti -reflection structure 600 occurs at a single peak located approximately at 27 GHz. For comparison, FIG. 7C also shows a graph of the near field simulation of the realized gain of the substrate 610 without the film 620 (graph 704) and of free space (graph 705).

Comparing the transmission characteristic for structure 600 shown in FIGS. 7A - 7C to the transmission characteristic for structure 300 shown in FIGS. 5A and 5B indicates that the multiple layers of structure 300 are more effective at reducing transmission losses. The transmission losses for structure 300 are decreased within a wider band when antireflective layers are employed to provide multiple peaks in the transmission characteristic, e.g., at upper and lower frequencies within the mm-wave band, when compared to a narrower bandwidth of transmission losses when only one layer is used as in structure 600.

FIG. 8 is a schematic cross-sectional diagram of an antireflective structure 800 that includes a multilayer film 820 comprising two antireflective layers 821, 822 disposed on a substrate 810 in accordance with some embodiments. In a particular implementation, substrate 810 is the cover of a mobile communication device made of a material having a dielectric constant that precludes using the cover 810 as an antireflection layer of the structure. For example, for a cellphone enclosure made of ceramic Zr(¾, the dielectric constant is relatively high, e.g., about 36, which is not suitable for an antireflective layer as previously discussed in connection with the structure 300 of FIG. 3. A typical thickness for cover 810 is about 0.4 mm in some implementations. In structure 800, the multilayer film 820 comprising first layer 821 and second layer 822 provides the upper and lower frequency layers that are configured to provide dual peaks in the transmission characteristic within the mm-wave communication signal band.

As shown in FIG. 8, the second layer of the 822 of the multilayer film 820 is disposed on the substrate 810 which can form the cover of a communications device. The first layer 821 is disposed on the second layer 822. There is a first air-dielectric interface 891 at the outer surface 810a of the cover 810 and a second air-dielectric interface 892 at the inner surface 821b of the first layer 821.

The second layer 822 has a thickness, Ϊ₂, and a dielectric constant, 8₂ that produces a second peak in the transmission characteristic at a second wavelength, l , within the mm-wave band of the communication signal. The first layer 821 is disposed on the second layer 822 and can have a thickness, ti, and a dielectric constant, si, that produces a first peak at a first wavelength, li, within the mm-wave band of communication signal. In some embodiments li and l₂ may be in a range from about 6 mm to 13 mm. The overall thickness of the structure 800 may be less than 3 mm, or less than 2.5 mm, or less than 2 mm, or even less than 1.5 mm. The thickness of each of the layers 810, 821, 822 may be less than 1 mm and/or less than any of the wavelengths of interest, for example.

In general, li and l₂ can be any wavelengths in the mm-wave range, however, in most embodiments, li ¹ l₂. For example, li may be between 6 mm and 10 mm and l_2h^ be between about 10 mm and 13 mm in some embodiments. The first and second layers may comprise a polymer composite loaded with high dielectric powder to a loading ratio that gives the correct dielectric constant as discussed above.

In some implementations the thickness, ti, of the first layer 821 can be selected to reduce reflection of the mm-wave signal near li = 7.69 mm (f = 34 GHz). The thickness, t₂. of the second layer 822 can be selected to reduce reflection of the mm-wave signal near l₂ = 12.49 mm (f = 24 GHz).

FIGS. 9A and 9B show the far field transmission characteristic for mm-wave signals through the structure 800 shown schematically in FIG. 8. FIG. 9A shows a graph of the transmission characteristic for an angle of incidence 0 degrees between 0 and 40 GHz. FIG. 9B shows a graph of the transmission characteristic between 24 and 40 GHz. As will be appreciated from inspection of FIGS. 9A and 9B, the signal transmission loss when the antireflection layer 800 is used is about -1.42 dB at 24.25 GHz, - 2.97 dB at 29.5 GHz, -2.99 dB at 37 GHz, and -1.34 dB at 40 GHz. FIG. 9B indicates the dual transmission peaks due to the multilayer 820. In this example, the peaks occur near about 25 GHz and about 40 GHz in this example.

FIG. 9C shows the graph 903 of realized gain obtained from near field simulation of an antenna array positioned 1 mm from the structure 800. The maximum realized gain for anti reflection structure 800 occurs at peaks located approximately at 27GHz and 37GHz. For comparison, FIG. 9C also shows a graph of the near field simulation of the realized gain of the cover 810 without the multilayer film 820 (graph 904) and of free space (graph 905).

A comparative example of an antireflective structure 1000 having a ceramic Zr0₂ substrate is illustrated in the schematic cross-sectional diagram of FIG. 10. Structure 1000 is designed to decrease transmission losses of the mm-wave signal at a single wavelength of interest. As discussed below, comparison of the transmission characteristic of structure 1000 to the transmission characteristic of structure 800, which also includes a Zr0₂ substrate, shows that structure 1000 provides decreased transmission losses within a narrower bandwidth when compared to structure 800.

Structure 1000 includes a Zr0₂ ceramic substrate 1010, e.g., a ceramic mobile device cover, with a layer 1020 disposed thereon. Layer 1020 may comprise a polymer composite loaded with high dielectric powder to a loading ratio that gives the correct dielectric constant as discussed above.

For mobile electronic devices with ceramic back covers, a typical thickness of the back

cover is on the order of 0.4 mm. Calculating the t = antireflection condition at 27 GHz

(wavelength = 11.1 mm) yields an optimal thickness value for the design of 0.92 mm. To attain this total thickness, the layer 1020 with e =36 having a thickness of 0.52 mm is disposed onto the ceramic ZrC>₂ enclosure 1010 which has a thickness of 0.4 mm. Graphs of the far field transmission characteristics for the structure 1000 are provided in FIGS. 11A and 11B.

FIGS. 11A and 1 IB show the transmission characteristic of the structure 1000 comprising a ceramic ZrC>₂ substrate 1010 with a layer 1020 disposed thereon as shown schematically in FIG. 10. FIG. 11A shows a graph 1101 of the transmission characteristic between 0 and 40 GHz. FIG.

1 IB shows a graph of the transmission characteristic between 24 and 40 GHz. As will be appreciated from inspection of FIGS. 11A and 1 IB, the signal loss when the antireflection structure 1000 is used is about -2.73 dB at 24.25 GHz, - 2.2 dB at 29.5 GHz, -9 dB at 37 GHz, and -9.69 dB at 40 GHz. FIG. 1 IB indicates the single transmission peak due to the antireflection structure 1000 which in this example occurs at about 27 GHz.

FIG. llC shows the graph of realized gain obtained from near field simulation of an antenna array positioned 1 mm from the ZrC>₂ ceramic substrate 1010 and anti-reflection structure 1020. The maximum realized gain for anti-reflection structure 1000 occurs at approximately 26.5 GHz. For comparison, FIG. 11C also shows a graph of the near field simulation of the realized gain of the ceramic substrate 1010 without the layer 1020 (graph 1104) and of free space (graph 1105).

By comparing the transmission characteristics shown in FIGS. 11A - 11C to those shown in FIGS. 9A - 9C it can be seen that enhancement in the transmission bandwidth with using multiple layers that provide multiple peaks in the transmission characteristic (as in structure 800 of FIG. 8) is superior to using only one layer that provides a single transmission characteristic peak (as in structure 1000).

FIG. 12A is a plan view and FIG. 12B is a side cross sectional view of an electronic communication device 1200 that includes an antireflective structure as previously discussed. The device 1200 comprises an enclosure 1210 having a mm-wave transceiver 1250 disposed within the enclosure 1210. The mm-wave transceiver 1250 is configured to transmit and receive mm-wave signals 1291, 1292. A multilayer film 1220 is disposed on an inner surface 1210a of at least a portion of the enclosure 1210. The multilayer film includes a first antireflection layer 1221 having a dielectric constant, si, and a thickness, ti and a second antireflection layer 1222 having a dielectric constant, 8₂, and thickness, Ϊ₂. The thicknesses and the dielectric constants of the first and second layers 1221, 1222 are configured such that the communication signals 1291, 1292 through the multilayer film 1220 and the enclosure 1210 in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band. According to some aspects, the dielectric constant and a thickness of the portion of the enclosure 1210 are configured to provide the transmission characteristic that includes the first peak.

Various embodiments are described in this disclosure. Embodiment 1 is directed to an antireflection structure comprising: a multilayer film comprising: a first antireflection layer having a dielectric constant, si , and a thickness, ti_; and a second antireflection layer having a dielectric constant, 8₂, and thickness, Ϊ₂, thicknesses and the dielectric constants of the first and second antireflection layers are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band. Embodiment 2 is directed to the structure of embodiment 1, wherein the mm-wave band includes frequencies between 20 GHz and 100 GHz. Embodiment 3 is directed to the structure of embodiment 1, wherein: the upper frequency is in a range of about 35 GHz to about 60 GHz; and the lower frequency is in a range of about 20 GHz to about 34 GHz. Embodiment 4 is directed to the structure of embodiment 1, wherein: the dielectric constant of the first layer is in a range from 30 to 1.3; and the dielectric constant of the second layer is in a range from 450 to 1.5. Embodiment 5 is directed to the structure of embodiment 1, wherein: the dielectric constant of the first layer is in a range from 20 to 1.3; and the dielectric constant of the second layer is in a range from 400 to 20. Embodiment 6 is directed to the structure of any of embodiments 1 through 5, wherein 8₂ is about equal to 8i². Embodiment 7 is directed to the structure of any of embodiments 1 through 6, wherein the first and second layers comprise one or more inorganic fillers in a polymer matrix. Embodiment 8 is directed to the structure of embodiment 7, wherein the polymer matrix comprises one or more of rubber, polyurethane, acrylate, silicone, polyolefin. Embodiment 9 is directed to the structure of embodiment 7, wherein the inorganic fillers comprises one or more of BaTiCE, SrTiCE, CaCmTriOn, LaSrsNiCfi, T1O₂, ZrCE, BaFei₂0i9, SrFei₂0i9. Embodiment 10 is directed to the structure of embodiment 1, wherein the polymer matrix comprises one or more of rubber, polyurethane, acrylate, silicone, polyolefin. Embodiment 11 is directed to the structure of embodiment 1, further comprising an additional layer, wherein the second layer is arranged between the additional layer and the first layer. Embodiment 12 is directed to the structure of embodiment 11 wherein a dielectric constant and a thickness of the additional layer are configured such that the transmission characteristic includes the first peak. Embodiment 13 is directed to the structure of embodiment 1, wherein a thickness of the film is less than about 2 mm. Embodiment 14 is directed to the structure of embodiment , wherein a thickness of the fdm is less than about 1.5 mm.

Embodiment 15 is directed to an antireflection structure comprising: a substrate having a dielectric constant, e_s , and a thickness, t_s; a multilayer fdm comprising: a first antireflection layer having a dielectric constant, si , and a thickness, ti_; and a second antireflection layer having a dielectric constant, , and thickness, Ϊ , thicknesses and dielectric constants of the first layer, the second layer, and the substrate are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm- wave band. Embodiment 16 is directed to the structure of embodiment 15, wherein: the substrate forms at least a portion of an enclosure of an electronic communication device; and the multilayer film is disposed on an inner surface of the enclosure. Embodiment 17 is directed to the structure of embodiment 15, wherein the substrate comprises at least one of a glass, a ceramic, and a polymer. Embodiment 18 is directed to the structure of embodiment 15, further comprising an adhesive layer disposed between the substrate and the multilayer film.

Embodiment 19 is directed to an electronic communication device comprising: an enclosure; a mm-wave transceiver disposed within the enclosure, the mm-wave transceiver configured to transmit and receive mm-wave communication signals; a multilayer film disposed on an inner surface of at least a portion of the enclosure, the multilayer firm comprising: a first antireflection layer having a dielectric constant, si , and a thickness, ti_; and a second antireflection layer having a dielectric constant, , and thickness, Ϊ , thicknesses and the dielectric constants of the first and second layers configured such that the communication signals through the multilayer film and the enclosure in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band. Embodiment 20 is directed to the device of embodiment 19, wherein a dielectric constant and a thickness of the portion of the enclosure are configured to adjust the transmission characteristic that includes at least one of the first peak and the second peak.

EXAMPLES

Samples of several of the multilayers were prepared and tested. Different composite materials were prepared to achieve the desired dielectric constants. The dielectric film construction can be achieved by loading high dielectric constant filler into a polymer matrix to provide a composite material with the appropriate dielectric constant. Below are examples of the preparation of several films with different dielectric constants. Preparatory Example A Fabrication of e = 7 material:

Vinyl silicon polymer (low molecular weight) 5000 (10 g) available from AB Specialty Silicones, Waukegan, IL was mixed with Pt catalyst (0.25 g) available from Heraeus, Hanau, Germany with strong stirring (1000-3000 rpm) for 1 minute then 1-Ethynyl-l-cyclohexanol (0.08 g) available from Sinopharm Chemical Reagent Co. Ltd, Shanghai, China was added. After strong stirring for 1 min, Hydrogen polysiloxane XL 1341 (0.5 g) available from AB Specialty Silicones was added and the mixture was stirred for 2 min.

After stirring for 2 min, FeAlSi (10.5 g) available from Guang Zhou Jin Nan Material Co. Ltd, Guangdong Province, China was added, the mixture was strongly mixed for 2 min.

The mixture was hand spread coated on a liner at the appropriate thickness of 0.1 mm - 2 mm and heated at 120 degrees C for 1.5 hr. The film was then peeled off the liner for use. The film coating was checked for appropriate thickness and dielectric constant.

Preparatory Example B Fabrication of e = 5.5 material:

VS 5000 (10 g) was mixed with Pt catalyst (0.25 g) with strong stirring for 1 min, then 1- Ethynyl-l-cyclohexanol (0.08 g) was added, after strong stirring for 1 min, XL 1341 (0.5 g) was added and the mixture was stirred for 2 min.

After stirring for 2 min, FeSi (5.5 g) was added, and the mixture was strongly mixed for 2 min.

The mixture was coated by a hand spreading technique onto a liner to the appropriate thickness and heated at 1200 C for 1.5 h, then the film was peeled off from liner for use.

Example 1

Design and construction for high transmission at 23GHz and 25GHz:

Two- and three-layer constructions using alkali-aluminosilicate glass 0.55 mm thick as a substrate were made to reduce overall thickness of the constructions and have higher bandwidth for decreased transmission loss.

Two-layer constructions were fabricated comprising a substrate comprising alkali- aluminosilicate glass 0.55 mm thick and a layer of e = 27 material 0.9 mm thick. Three-layer constructions were fabricated comprising a substrate of glass 0.55 mm thick, a layer of e = 27 material 0.9 mm thick, and a layer of e = 7 material 0.33 mm thick.

Individual layers were prepared by a process similar to above process steps. Transmission loss for these constructions is provided in graphs of FIG. 13. Graph 1301 shows the transmission characteristic for glass; graph 1302 shows the transmission characteristic for glass plus the e = 27 material layer, and graph 1303 shows the transmission characteristic for glass plus the e = 27 material layer and the e = 7 material layer. The graphs 1301, 1302, 1303 indicate a decrease in transmission loss for the glass + e = 27 material layer and an increase in the bandwidth of the signal transmission loss for the glass + e = 27 material layer + e = 7 material layer.

Example 2

A four layer example construction was prepared comprising a substrate of 0.55 mm thick alkali-aluminosilicate glass having e = 6.89, a two layer AR fdm that included a first layer 1.1 mm thick with of e = 10 material disposed on the deco film, and a second layer 1.2 mm thick with e = 4. The measured properties of the first and second AR film, referred to as AR1 and AR2 are provided in TABLE 1, wherein Dk is the dielectric constant, e, and Df is the dielectric loss of the layer. Table 1 indicates the filler and the polymer material used in the composite AR layer and the ratio of the filler material in the composite. The polymer material used a thermoplastic elastomer, Styrene-ethylene-butylene-styrene (SEBS) sold as Monprene® CP -22140, available from Teknor Apex Company, Pawtucket RI.

TABLE 1

The thermoplastic elastomeric composite films were compounded with a Banbury mixer. The mixer was preheated to 200°C. Enough material of SBS and dielectric powder(s) to form the appropriate film size was first mixed dry. These materials were then added to the air sealed chamber of the mixer and compounded at a speed of 50 rpm. The mixing torque was monitored and when the torque reached a constant value, after approximately 20 min, the processing was complete. The compounded material was processed to form the appropriate film thickness using a hot press. The hot press platen temperature was set to 200°C and spacers of appropriate dimension were placed on the lower platen to achieve the required thickness. The composite material was pressed at a pressure of lOMPa for lminute. If a two-layer sample was required, this process was repeated for the second layer thickness and composition and the AR film was formed by combining the two layers.

FIG. 14 shows graphs of the transmission characteristics of the substrate alone (graph 1401) and the transmission characteristics of the substrate with the AR film disposed thereon (graph 1402). As will be appreciated, the transmission through the structure increases when the AR film is used. Graph 1502 shows transmission peaks at about 24 GHz and about 35 GHz. Example 3

Design and construction of an anti-reflective structure with a ZrCE ceramic-based back cover:

A three layer construction was fabricated comprising a 0.4 mm thick back cover substrate of ZrCE having a thickness of 0.4 mm and e = 36 at 24 GHz. A multilayer AR fdm was disposed on the substrate. The AR fdm included a layer 0.33 mm thick of e = 36 material and a layer 0.82 mm thick of e = 8 material. Since the dielectric constant of the ZrCE is relatively high, it is not used as one of the AR layers in this design. In this example, the 0.33 mm thick layer was tuned to approximately 24 GHz and the 0.82 mm thick layer was tuned to about 34 GHz.

FIG. 15 shows a graph 1503 of realized gain obtained from near field simulation of an antenna array positioned 1 mm from ZrCE glass back cover. The maximum realized gain for the anti-reflection structure occurs at peaks located approximately at 23 GHz and 36 GHz. For comparison, FIG. 15 also shows a graph of the near field simulation of the realized gain of the cover without the multilayer film (graph 1504) and of free space (graph 1505).

Various modifications and alterations of the embodiments discussed above will be apparent to those skilled in the art, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein. The reader should assume that features of one disclosed embodiment can also be applied to all other disclosed embodiments unless otherwise indicated. It should also be understood that all U.S. patents, patent applications, patent application publications, and other patent and non-patent documents referred to herein are incorporated by reference, to the extent they do not contradict the foregoing disclosure.

Claims

1. An antireflection structure comprising: a multilayer film comprising: a first antireflection layer having a dielectric constant, si , and a thickness, ti_; and a second antireflection layer having a dielectric constant, 8₂, and thickness, Ϊ₂, thicknesses and the dielectric constants of the first and second antireflection layers are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

2. The structure of claim 1, wherein the mm-wave band includes frequencies between 20 GHz and 100 GHz.

3. The structure of claim 1, wherein: the upper frequency is in a range of about 35 GHz to about 60 GHz; and the lower frequency is in a range of about 20 GHz to about 34 GHz.

4. The structure of claim 1, wherein: the dielectric constant of the first layer is in a range from 30 to 1.3; and the dielectric constant of the second layer is in a range from 450 to 1.5.

5. The structure of claim 1, wherein: the dielectric constant of the first layer is in a range from 20 to 1.3; and the dielectric constant of the second layer is in a range from 400 to 20.

6. The structure of claim 1, wherein 8₂ is about equal to 8i².

7. The structure of claim 1, wherein the first and second layers comprise one or more inorganic fillers in a polymer matrix.

8. The structure of claim 7, wherein the polymer matrix comprises one or more of rubber, polyurethane, acrylate, silicone, and polyolefin.

9. The structure of claim 7, wherein the inorganic fillers comprises one or more of BaTiCL, SrTiCL, CaCmTriOn, LaSrsNiCfi, T1O2, ZrOi, BaFei20i9, and SrFei20i9.

10. The structure of claim 1, wherein the polymer matrix comprises one or more of rubber, polyurethane, acrylate, silicone, and polyolefin.

11. The structure of claim 1, further comprising an additional layer, wherein the second layer is arranged between the additional layer and the first layer.

12. The structure of claim 11, wherein a dielectric constant and a thickness of the additional layer are configured such that the transmission characteristic includes the first peak.

13. The structure of claim 1, wherein a thickness of the film is less than about 2 mm.

14. The structure of claim 1, wherein a thickness of the film is less than about 1.5 mm.

15. An antireflection structure comprising: a substrate having a dielectric constant, e_s, and a thickness, t_s; a multilayer film comprising: a first antireflection layer having a dielectric constant, si, and a thickness, ti_; and a second antireflection layer having a dielectric constant, , and thickness, Ϊ , thicknesses and dielectric constants of the first layer, the second layer, and the substrate are configured such that a transmission characteristic of a communication signal through the multilayer film in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

16. The structure of claim 15, wherein: the substrate forms at least a portion of an enclosure of an electronic communication device; and the multilayer film is disposed on an inner surface of the enclosure.

17. The structure of claim 15, wherein the substrate comprises at least one of a glass, a ceramic, and a polymer.

18. The structure of claim 15, further comprising an adhesive layer disposed between the substrate and the multilayer film.

19. An electronic communication device comprising: an enclosure; a mm-wave transceiver disposed within the enclosure, the mm-wave transceiver configured to transmit and receive mm-wave communication signals; a multilayer film disposed on an inner surface of at least a portion of the enclosure, the multilayer firm comprising: a first antireflection layer having a dielectric constant, si, and a thickness, ti_; and a second antireflection layer having a dielectric constant, 82, and thickness, Ϊ2, thicknesses and the dielectric constants of the first and second layers configured such that the communication signals through the multilayer film and the enclosure in a mm-wave band comprises a first peak near an upper frequency of the mm-wave band and a second peak near a lower frequency of the mm-wave band.

20. The device of claim 19, wherein a dielectric constant and a thickness of the portion of the enclosure are configured to adjust the transmission characteristic that includes at least one of the first peak and the second peak.