PATENT DOCUMENT

Publication Number: US-7973722-B1
Application Number: US-89709707-A
Country: US
Kind Code: B1

Title: Electronic device with conductive housing and near field antenna

Abstract:
An electronic device such as a computer monitor is provided that has an antenna that supports near field communications. The electronic device may have a housing with conductive housing surfaces. A display may be mounted in the housing. The conductive housing surfaces may contain a dielectric-filled hole. The antenna may have a substrate and one or more loops of conductive traces. The loops may exhibit mirror symmetry. The loops may overlap the display and the conductive housing surface. The loops may surround an inner loop-free portion of the antenna. The loop-free portion of the antenna may overlap the hole. Ferrite layers may be interposed between the loops of the antenna that overlap the display and the loops of the antenna that overlap the conductive housing.

Claims:
1. An electronic device, comprising:
 a housing having a conductive housing surface; 
 a dielectric-filled region in the conductive housing surface; and 
 a substantially planar antenna that at least partly overlaps the dielectric-filled region, wherein the conductive housing surface comprises a metal surface and a display having an exterior surface, wherein the metal surface surrounds the display, wherein the dielectric-filled region is formed in the metal surface, and wherein a portion of the planar antenna lies on the exterior surface of the display. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the substantially planar antenna comprises a near field communications antenna having at least one antenna loop. 
     
     
       3. The electronic device defined in  claim 1 , wherein the display comprises a computer monitor having a planar display, wherein the metal surface comprises a layer of metal, wherein the layer of metal surrounds the display, wherein the layer of metal comprises a lip, and wherein the dielectric-filled region is formed in the lip. 
     
     
       4. The electronic device defined in  claim 3 , wherein:
 the antenna comprises a substrate and a plurality of conductive loops formed on the substrate; 
 the plurality of conductive loops are bisected by a line; 
 the plurality of conductive loops exhibit mirror symmetry with respect to the bisecting line; 
 the plurality of conductive loops surround a loop-free region of the antenna; and 
 the antenna is attached to the electronic device so that at least some of the loop-free region overlaps the dielectric-filled region and so that a portion of the antenna lies on the exterior surface of the display. 
 
     
     
       5. The electronic device defined in  claim 3  further comprising at least one layer of ferrite interposed between the conductive housing surface and the antenna, wherein:
 the antenna comprises a substrate and a plurality of conductive loops formed on the substrate; 
 the plurality of conductive loops are bisected by a line; 
 the plurality of conductive loops exhibit mirror symmetry with respect to the bisecting line; 
 the plurality of conductive loops surround a loop-free region of the antenna; and 
 the antenna is attached to the electronic device so that at least some of the loop-free region overlaps the dielectric-filled region. 
 
     
     
       6. The electronic device defined in  claim 1  wherein the antenna comprises:
 a substrate; and 
 a plurality of conductive loops formed on the substrate, wherein the plurality of conductive loops surround a loop-free region of the antenna, and wherein the antenna is attached to the electronic device so that at least some of the loop-free region overlaps the dielectric-filled region. 
 
     
     
       7. The electronic device defined in  claim 1  wherein the antenna comprises:
 at least one conductive loop, wherein the conductive loop is bisected by a line and wherein the conductive loop exhibits mirror symmetry with respect to the bisecting line. 
 
     
     
       8. The electronic device defined in  claim 1  wherein the antenna comprises:
 a substrate; and 
 a plurality of conductive loops formed on the substrate, wherein the plurality of conductive loops are bisected by a line and wherein the plurality of conductive loops exhibit mirror symmetry with respect to the bisecting line. 
 
     
     
       9. The electronic device defined in  claim 1  wherein the antenna comprises:
 a substrate; 
 a plurality of conductive loops formed on the substrate, wherein the plurality of conductive loops are bisected by a line, wherein the plurality of conductive loops exhibit mirror symmetry with respect to the bisecting line, wherein the plurality of conductive loops surround a loop-free region of the antenna, and wherein the antenna is attached to the electronic device so that at least some of the loop-free region overlaps the dielectric-filled region. 
 
     
     
       10. The electronic device defined in  claim 1  wherein:
 the antenna comprises a substrate and has a plurality of conductive loops formed on the substrate; 
 the plurality of conductive loops are bisected by a line; 
 the plurality of conductive loops exhibit mirror symmetry with respect to the bisecting line; 
 the plurality of conductive loops surround a loop-free region of the antenna; and 
 the antenna is attached to the electronic device so that at least some of the loop-free region overlaps the dielectric-filled region. 
 
     
     
       11. The electronic device defined in  claim 1  further comprising a layer of ferrite interposed between the antenna and the conductive housing surface. 
     
     
       12. The electronic device defined in  claim 1  wherein the antenna comprises a plurality of loops and communicates using near field communications at a frequency of 13.56 MHz. 
     
     
       13. An electronic device, comprising:
 a housing having a conductive housing surface; 
 a dielectric-filled region in the conductive housing surface; 
 a substantially planar antenna that at least partly overlaps the dielectric-filled region; 
 a display mounted in the conductive housing surface, wherein the planar antenna comprises a loop antenna having a plurality of loops, wherein the loops overlap at least part of the display, and wherein the loops overlap at least part of the conductive housing surface; 
 first and second layers of ferrite, wherein the first layer of ferrite is interposed between the display and the loops that overlap the display and wherein the second layer of ferrite is interposed between the conductive housing surface and the loops that overlap the conductive housing surface. 
 
     
     
       14. A computer monitor, comprising:
 a display; 
 a conductive housing wall in which the display is mounted, wherein a dielectric-filled region is formed in the conductive housing wall; and 
 a near-field communications antenna mounted in the computer monitor that overlaps the dielectric-filled region, wherein the near-field communications antenna has at least one antenna loop. 
 
     
     
       15. The computer monitor defined in  claim 14 , wherein the antenna comprises:
 a flex circuit substrate; and 
 a plurality of conductive traces that form loops on the flex circuit substrate surrounding a loop-free region on the flex circuit substrate, wherein the antenna is mounted to the computer monitor so that some of the loops overlap the conductive housing surface, some of the loops overlap the display, and at least a portion of the loop-free region overlaps the dielectric-filled region. 
 
     
     
       16. The computer monitor defined in  claim 14 , wherein the antenna comprises:
 a flex circuit substrate; 
 a plurality of conductive traces that form loops on the flex circuit substrate surrounding a loop-free region on the flex circuit substrate, wherein the antenna is mounted to the computer monitor so that some of the loops overlap the conductive housing surface, some of the loops overlap the display, and at least a portion of the loop-free region overlaps the dielectric-filled region; and 
 a layer of ferrite interposed between the antenna and an interior surface of the conductive housing wall. 
 
     
     
       17. An electronic device, comprising:
 planar conductive structures having interior surfaces and exterior surfaces; and 
 a substantially planar near-field communications antenna, wherein a portion of the antenna lies on a given one of the interior surfaces of the planar conductive structures and wherein a portion of the antenna lies on a given one of the exterior surfaces of the planar conductive structures. 
 
     
     
       18. The electronic device defined in  claim 17  wherein the planar conductive structures have portions defining a hole, wherein the antenna comprises a plurality of conductive traces that exhibit mirror symmetry and comprises a central trace-free region, and wherein at least a portion of the trace-free region overlaps the hole, the electronic device further comprising:
 a first layer of ferrite interposed between the antenna and the given one of the exterior surfaces of the planar conductive structures; and 
 a second layer of ferrite interposed between the antenna and the given one of the interior surfaces of the planar conductive structures. 
 
     
     
       19. The electronic device defined in  claim 17 , wherein the planar conductive structures comprise a display and a metal housing wall, wherein the antenna lies on an interior surface of the metal housing wall, and wherein the antenna lies on an exterior surface of the display.

Description:
BACKGROUND 
     This invention relates generally to wireless communications, and more particularly, to near field communications. 
     Short range wireless communications schemes are of growing interest for applications such as mobile commerce and electronic keys. Such communications schemes are characterized by working distances of about 4-8 inches or less. Devices may communicate using magnetic field induction in a frequency band such as the unlicensed radio-frequency communications band of 13.56 MHz. This type of radio-frequency communications is often referred to as near field communications. 
     In a typical scenario, a smart card, mobile telephone, key fob, or other handheld device wirelessly interacts with a host device such as a smart card reader when a user places the handheld device within range of the host (e.g., within a few inches). 
     Because of the potentially diverse set of applications for near field communications, it would be desirable to be able to incorporate near field communications antennas into a range of electronic devices. 
     SUMMARY 
     In accordance with an embodiment of the present invention, an electronic device is provided that has an antenna. The electronic device may be a computer monitor or other device with a display. The electronic device may include a housing in which the display is mounted. The housing may have conductive surfaces. For example, the housing may have substantially planar front, rear, and side surfaces. 
     The conductive surfaces of the housing may be provided with a hole. The hole may be filled with air or other dielectric. The antenna may be mounted in the housing overlapping the hole. 
     The antenna may be substantially planar and may have a substrate such as a flex circuit substrate. Conductive antenna traces may be formed on the flex circuit substrate. The conductive antenna traces may be formed in a spiral shape or as one or more loops. The loops of the antenna traces may be bisected by a line. The loops of antenna traces may exhibit mirror symmetry with respect to the bisecting line. 
     One or more conducting loops in the antenna may surround a loop-free region of the antenna. The antenna loops may overlap the display. The antenna loops may also overlap the conductive housing surface. The inner loop-free region of the antenna may overlap the hole in the conductive housing surface. 
     One or more layers of ferrite may be interposed between the antenna and conductive structures in the electronic device. For example, a layer of ferrite may be interposed between antenna loops that overlap the display and the display. A layer of ferrite may also be interposed between antenna loops that overlap the conductive housing surface and the conductive housing surface. 
     The antenna may support near field communications in a suitable frequency band such as the 13.56 MHz band. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative system that includes an electronic device such as a computer monitor with a near field communications antenna and a mobile electronic device such as a smart card with a near field communications antenna in accordance with an embodiment of the present invention. 
         FIG. 2  is a top view of an illustrative antenna having a spiral conductor layout and a substantially square footprint in accordance with an embodiment of the present invention. 
         FIG. 3  is a top view of an illustrative antenna having a spiral conductor layout and a substantially rectangular footprint in accordance with an embodiment of the present invention. 
         FIG. 4  is a top view of an illustrative antenna having a symmetric conductor layout with four loops of conductive traces in accordance with an embodiment of the present invention. 
         FIG. 5  is a top view of an illustrative antenna having a symmetric conductor layout with eight loops of conductive traces in accordance with an embodiment of the present invention. 
         FIG. 6  is a front view of an illustrative computer monitor having a conductive housing surface with a dielectric-filled region that accommodates a near field communications antenna in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of an illustrative portion of a conductive housing showing how a housing wall may have portions defining a lip in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of an illustrative portion of a conductive housing with a housing wall, portions defining a lip, and a hole in the lip in accordance with an embodiment of the present invention. 
         FIG. 9  is a front view of a portion of a conductive electronic device housing and an adjacent conductive electronic component such as a liquid crystal diode display that form a hole for an antenna in accordance with an embodiment of the present invention. 
         FIG. 10  is a front view of a portion of a conductive electronic device housing having a near field antenna that overlaps a hole in the device housing and an adjacent liquid crystal diode display in accordance with an embodiment of the present invention. 
         FIG. 11  is a front view of the portion of the conductive electronic device housing and display of  FIG. 10  showing illustrative locations for ferrite materials that improve antenna performance in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional side view taken along the cross-sectional line of  FIG. 11  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to wireless communications, and more particularly, to wireless communications using near field wireless communications schemes. 
     Near field communications schemes are of interest for applications where long range communications such as traditional cellular telephone communications are inappropriate. Near field communications schemes rely on short-range electromagnetic coupling and typically operate at distances of 4-8 inches or less. 
     Because communications are generally not possible at distances larger than about 8 inches, near field communications schemes are useful in scenarios in which a user of the scheme must be physically present. As an example, near field communications schemes may be advantageous when implementing an electronic lock for a door. When a near field communications scheme is used to control access to a building in this way, only people who physically present their smart cards or other near field communications devices will be allowed to gain access to the building. As another example, an electronic payment scheme may benefit from requiring the physical proximity between a purchaser&#39;s mobile device and a point of sale terminal. 
     Because near field communications schemes rely on electromagnetic communications, conventional host devices such as smart card readers generally avoid the use of conductive enclosures for their antennas. This prevents signal loss due to the presence of conductive housing walls near the near field antennas that might otherwise prevent effective transmission and reception of wireless signals. 
     In accordance with an embodiment of the present invention, near field communications antennas and electromagnetic device housing arrangements for near field communications antennas are provided that allow use of near field antennas in a variety of contexts. 
     As an example, an electronic device such as a computer monitor may be provided that has an antenna located within a conductive exterior. The conductive exterior surfaces of the computer monitor may include, for example, conductive housing walls and a conductive display screen. The near field antenna may be located within the computer monitor in the vicinity of a dielectric-filled region (a hole) in the conductive housing surface. 
     Ferrite elements such as adhesive-backed ferrite tape (e.g., ferrite tape of about 0.8 mm thickness) may be used to reduce signal losses due to electromagnetic field interactions between the near field antenna&#39;s electromagnetic fields and conductive materials such as the conductive exterior surface of the computer monitor. With one suitable arrangement, a strip of ferrite tape may be placed immediately in front of an antenna to shield the antenna from a conductive housing wall. Another strip of ferrite material may be placed directly behind the antenna to prevent the antenna from being degraded due to the presence of a conductive liquid crystal diode (LCD) display screen. 
     A near field antenna may be formed in a planar arrangement using a thin substrate such as a flex circuit substrate. A flex circuit substrate may be, for example, 0.01 to 1 mm thick. The use of a thin planar substrate such as a flex circuit substrate allows the near field antenna to be incorporated into a computer monitor or other electronic device without taking up too much room. A typical antenna thickness may be about 0.08 mm. 
     The circuit traces on the flex circuit substrate may use a spiral antenna architecture, a loop architecture with conductive traces that exhibit mirror symmetry, or any other suitable arrangement. An advantage of forming a near field antenna whose conductive traces exhibit mirror symmetry is that this type of antenna layout tends to exhibit coherent electromagnetic field patterns and therefore interacts well with near field antennas in corresponding portable electronic devices (e.g., smart cards). 
     With one suitable arrangement, which is described herein as an example, the near field antenna is formed from eight concentric loops of conductive traces on a flex circuit substrate. Crossover connections may be made between adjacent loops of traces to ensure that the antenna has mirror symmetry. Because multiple antenna loops are used, antenna effectiveness is improved. 
     An illustrative system that includes an electronic device with a near field communications antenna is shown in  FIG. 1 . In the example of  FIG. 1 , electronic device  10  is a computer monitor. This is merely illustrative. Electronic device  10  may be any suitable equipment. 
     Electronic device  10  may contain control electronics, electrical components such as a display, fans, power supplies, input-output jacks, printed circuit boards, etc. Electronic device  10  may be, for example, a desktop or laptop computer, a router, a kiosk, a point of sale terminal, industrial equipment (e.g., on a factory floor), medical equipment, a printer, a camera, a mobile telephone, a media player, a handheld computer or other handheld device, a hard disk drive enclosure, or any other suitable electronic equipment. For clarity, the present invention will sometimes be described in connection with electronic devices such as computer monitors. This is, however, merely illustrative. 
     Device  10  may contain control circuitry such as control circuitry  20  and electrical components such as display  16  and wireless communications circuitry  22 . The electrical components associated with device  10  may be mounted in a housing  12 . Housing  12  may be formed of metals, conductive plastics, and other conductive materials, dielectrics such as plastics and glass, combinations of conductors and dielectrics, or any other suitable materials. A stand such as stand  30  or other suitable support structure may be used to help support housing  12 . Stand  30  may be formed of plastic, metal, other suitable materials, or a combination of such materials. 
     Control circuitry  20  may be based on one or more integrated circuits, one or more printed circuit boards or other mounting structures on which integrated circuits are mounted, discrete electrical components, combinations of such circuitry, or any other suitable control circuitry. Integrated circuits that may be included in control circuitry  20  include microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, field programmable gate arrays, video and audio chips, memory, etc. 
     Display  16  may be any suitable type of display, such as a plasma display, a liquid crystal diode (LCD) display, an organic light emitting diode (OLED) display, or any other display. The outermost surface of display  16  may be formed from one or more plastic or glass layers. If desired, touch screen functionality may be integrated into display  16 . Although covered with insulating materials such as plastic or glass, most displays such as LCD display  16  contain a sufficient quantity of conductive components that they are conductive for electromagnetic purposes. If, for example, a conventional antenna were to be placed directly behind an LCD display, the conductive nature of the internal components of the LCD display would serve as radio-frequency shielding and would block electromagnetic fields emanating from the antenna. 
     As shown in  FIG. 1 , control circuitry  20  may communicate with display  16  using a communications path such as path  26 . Control circuitry  20  may communicate with wireless communications circuitry  22  using a path such as path  28 . The communications paths associated with device  10  may be formed using any suitable arrangement. For example, communications paths  26  and  28  may be formed using one or more electrical buses, traces on one or more printed circuit boards, optical paths, etc. 
     Wireless communications circuitry  22  may include transceiver circuitry  24  and antenna circuitry  14 . Antenna circuitry  14  may include one or more antennas. The use of arrangements involving a single antenna are sometimes described herein as an example. 
     Transceiver circuitry  24  may include transceiver integrated circuits. For example, transceiver circuitry  24  may include a printed circuit board with multiple transceiver integrated circuits that share a single antenna  14  using time-division multiplexing, radio-frequency couplers, radio-frequency switches, etc. In a typical configuration, circuitry  24  may contain a single transceiver that supports radio-frequency communications over a near field communications band (e.g., 13.56 MHz). 
     Device  10  may communicate wirelessly with one or more external devices. As shown in  FIG. 1 , for example, device  10  may communicate with one or more portable electronic devices such as device  34  using wireless communications links such as wireless path  32 . 
     Portable device  34  may be a handheld electronic device such as a cellular telephone, a media player, a handheld computer, a hybrid device that combines the functions of a cellular telephone, media player, and handheld computer, or any other suitable electronic device. Portable device  34  may be a security device such as a smart card, a key fob device, or other suitable compact wireless device. Some devices may contain wireless circuitry for communicating with local area networks (e.g., IEEE 802.11 networks), wireless circuitry for communicating with cellular base stations (e.g., using cellular telephone voice and data communications frequencies), etc. 
     With one suitable arrangement, which is described herein as an example, portable electronic device  34  communicates at least partly with antenna  14  using near field communications. In this type of situation, path  32  may be about 4-8 inches or less, 2-10 inches or less, 15 inches or less, or any other suitable near field communications range. As an example, path  32  may be less than about 5 inches. 
     Near field communications arrangements such as these may be particularly advantageous in situations in which it is desired to ensure that a particular user or device is in close physical proximity to electronic device  10 . For example, if it is desired to offer a service to a particular person, it may be advantageous to ensure that the person (or at least their portable device  34 ) is at the same physical location as electronic device  10 . Services that may be provided include financial services such as electronic payment services, building access, computer network access, etc. 
     As an example, consider the situation in which credentials stored on a security device such as a smart card or key fob are being used to verify a user&#39;s identity. In this type of arrangement, the use of near field communications is advantageous, because it requires that the security device be located within several inches of the electronic device  10 . 
     Device  10  may be placed in a particular location such as within the confines of a building with restricted access, near a point of sale terminal for a merchant, at a reception desk of a building, or other location which benefits from the short-range nature of near field communications. For example, device  10  may be placed within the secure confines of a building, so that only those users who are able to gain entry to the building will be able to bring portable device  34  into near field communications with electronic device  10 . As another example, electronic device  10  may be located at a merchant&#39;s point of sale terminal, so that an employee of the merchant (e.g., a cashier) will be present when a user makes an electronic payment or conducts other financial transactions. If device  10  is located at a reception desk of an organization, a receptionist may be able to visually monitor visitors to an organization as they bring portable device  34  into communication with electronic device  10 . 
     Portable device  34  may have control circuitry  36 . Control circuitry  36  may be based on one or more integrated circuits and discrete electronic components. Integrated circuits that may be included in control circuitry  20  include microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, field programmable gate arrays, video and audio chips, memory, etc. 
     Control circuitry  36  may communicate with wireless communications circuitry  38  over a communications path such as path  44 . Path  44  may include any suitable communications paths such as electrical buses, optical paths, etc. 
     Wireless communications circuitry  38  may include one or more antennas such as antenna  42  and transceiver circuitry  46 . Transceiver circuitry  46  may include a printed circuit board with one or more transceiver integrated circuits. If portable device  34  is a handheld electronic device that communicates over cellular telephone bands, antenna circuitry  42  may include a cellular telephone antenna in addition to a near field communications antenna for communicating with antenna  14  over path  32 . Such a device may also include one or more additional antennas (e.g., for local area network access, etc.). As another example, device  34  may be a smart card or key fob device that contains a single near field communications antenna  42 . 
     Near field communications over path  32  may be supported using any suitable frequency band or bands. One suitable near field communications band that may be used for path  32  is the 13.56 MHz band. The communications protocol used for path  32  may be, for example, a protocol that is compliant with the ISO 18092 Standard promulgated by the International Organization for Standardization. 
     Any suitable antenna arrangement may be used for antennas  14  and  42 . An illustrative near field communications antenna that may be used for one or both of these antennas is shown in  FIG. 2 . As shown in  FIG. 2 , antenna  48  may be constructed from a conductive line  56  that is formed in a generally spiral shape. Conductive line  56  may be formed on a substrate  54 . Substrate  54  may be formed from a dielectric such as a rigid or flexible printed circuit board. With one suitable arrangement, line  56  may be a conductive trace such as a copper trace. Line  56  may be formed by screen printing, blanket deposition and etching, or any other suitable technique. 
     If desired, substrate  54  may be a flexible integrated circuit substrate formed from a polymer such as polyimide. Flexible circuit substrates such as these, which are sometimes referred to as flex circuits, may be relatively inexpensive to manufacture and relatively straightforward to handle during assembly operations. In the example of  FIG. 2 , substrate  54  has been formed in a generally square shape to match the generally square outline of the spiral trace  56 . This is merely illustrative. Antenna substrate  54  may have any suitable shape (e.g., rectangular with sides of unequal length, oval, polygonal with no curved sides, polygonal with curved portions, circular, etc. 
     Antenna  48  may have a positive terminal  52  and a negative terminal  50 . Terminal  52  may sometimes be referred to as a positive feed or positive antenna feed terminal. Terminal  50  may sometimes be referred to as a negative or ground feed. 
     Antennas that are spiral in shape such as the antenna of  FIG. 2  may spiral inwards toward a central point such as point  60 . A conductive line  58  may be used to connect the trace  56  at point  60  to ground terminal  50 . Line  58  may be formed from a wire or a trace of conductor (e.g., copper). To prevent trace  58  from shorting adjacent coils of spiral trace  56 , the spiral traces  56  and trace  58  may be insulated from one another by depositing a layer of polymer (e.g., polyimide) or other insulator between trace  56  and trace  58 . If desired, trace  58  may be formed on the underside of a two-sided flex circuit. Wires or other suitable conductors may be electrically connected to antenna  54  and ground feed  50  and positive feed  52 . 
     Another illustrative antenna  62  that may be used to support communications over path  32  (e.g., near field communications) is shown in  FIG. 3 . As shown in  FIG. 3 , antenna  62  may be formed from a rectangular spiral of conductive lines  74  (e.g., a non-square spiral). Conductive line  70  may be used to connect the inner point  72  of conductive spiral  74  to an antenna feed terminal such as positive feed  66  or ground feed  68 . In the example of  FIG. 3 , line  70  is used to connect point  72  to positive feed terminal  66 , whereas ground feed terminal  68  is connected directly to spiral conductive line  74 . Lines such as lines  74  and  70  may be formed from conductive traces such as copper traces on a substrate  64 . Substrate  64  may be a rigid or flexible dielectric substrate such as a flex circuit. 
     In the arrangement of  FIG. 2 , antenna  48  has a conductive line  56  that spirals inwardly to a point  60 . With the arrangement of  FIG. 3 , line  74  also spirals inwardly. However, with the arrangement of  FIG. 3 , a central area  76  remains uncovered by conductive lines. This central area may be, for example, 10%-50% or more of the total antenna area. The use of an antenna arrangement that has a conductor-free central area helps to ensure that the electromagnetic fields that emanate from the antenna are coherent and thereby improves the ability of the antenna to interact with a corresponding antenna over path  32 . 
     Antenna arrangements of the types shown in  FIGS. 2 and 3  are asymmetrical, because their antenna traces do not exhibit mirror symmetry. Symmetrical antenna arrangements may be advantageous, because they may exhibit superior electromagnetic field coherence and may therefore perform better than asymmetrical antennas. 
     An illustrative symmetrical antenna  78  is shown in  FIG. 4 . Antenna  78  exhibits mirror symmetry, because one half of the antenna (i.e., the conductive antenna lines to the left of dotted bisecting line  120 ) is identical to the other half of the antenna (i.e., the antenna conductive lines to the right of dotted bisecting line  120 ). 
     Antenna  78  may be formed on a substrate  80 . Substrate  80  may be a rigid or flexible dielectric such as a rigid printed circuit board or a polymer substrate such as a polyimide flex circuit substrate. The conductive lines of antenna  78  may be formed from wires or conductive traces. For example, copper traces or other conductive traces may be formed on substrate  80  by screen printing or by blanket conductive film deposition followed by wet or dry etching. 
     Antenna  78  may have positive terminal  82  (i.e., a positive antenna feed) and negative terminal  84  (i.e., an antenna ground feed). Resistors  86  and  88  (e.g., 3-4 ohm resistors) or other electrical components (e.g., a network of one or more resistors, capacitors, and inductors) may be provided to ensure that the impedance of antenna  78  is sufficiently matched to the impedance of transceiver circuitry  46  to prevent excessive radio-frequency signal reflections. 
     As shown in  FIG. 4 , each conductive line on the left side of dotted line  120  has a mating conductive line on the right of dotted line  120 . As an example, consider conductive line  94  in antenna  78 , which connects point  98  to point  96 . Line  94  has an identical matching conductive line  100 , which electrically connects points  102  and  104  on the right side of dotted line  120 . 
     Moreover, identical crossovers are used to ensure that the conductive antenna lines in the inner portions of antenna  78  also exhibit mirror symmetry with respect to bisecting line  120 . For example, line  94  is connected to crossover line  106  at point  96 . Crossover line  106  connects point  96  and line  94  to point  108  and line  110 . Line  110  connects crossover point  108  to point  112 . In an identical fashion, line  100  is connected to crossover line  122  at point  102 . Crossover line  122 , which is a symmetric version of crossover line  106 , connects point  102  and line  100  to point  114  and line  116 . Line  116 , which is identical to line  110 , connects crossover point  114  to point  118 . Just as line  110  exhibits mirror symmetry about bisection line  120  with respect to line  116 , the other conductive traces of antenna  78  each exhibit mirror symmetry with respect to a corresponding conductive trace. 
     As a result of these relationships, all of conductive lines  90  in antenna  78  exhibit mirror symmetry with respect to bisecting dotted line  120 . The symmetric layout of antenna  78  avoids the need for conductive traces such as traces  58  and  70  that run perpendicular to the loops of the antenna. The mirror symmetry of the loops and the avoidance of perpendicular traces helps to produce coherent electromagnetic fields during operation of antenna  78  and thereby helps ensure that antenna  78  will perform well when communicating over path  32 . 
     Performance may also be enhanced by ensuring that there is an area  92  in the center of antenna  78  that is not covered by antenna traces. Area  92  may be any suitable shape (e.g., rectangular, square, etc.) and may have any suitable size. For example, area  92  may consume about 10-90% of the total area of antenna  78  (e.g., 10-90% of the total area of the antenna that lies within the outermost antenna loop). 
     To prevent short circuits, a layer of insulator may be formed between the conductive lines that cross over each other. For example, insulator may be placed between crossover line  122  and crossover line  106  to ensure that there is no electrical connection between lines  106  and  122  at point  124 . The insulating layer may be a layer of polymer such as polyimide or any other suitable dielectric. The insulating layer may be deposited over the underlying conductive line during the process of fabricating antenna  78 . 
     If desired, a two-sided flex circuit arrangement may be used for antenna  78 . With this type of arrangement, one of the crossover lines (e.g., crossover line  122 ) may be formed on the top surface of flex circuit substrate  80 , whereas the other of the crossover lines (e.g., line  106 ) may be formed on the lower (opposing) surface of flex circuit substrate  80 . An advantage of using a symmetrical antenna arrangement for antenna  78  is that the backside crossover lines need not be overly large, thereby helping to minimize the thickness of the antenna. 
     The illustrative antenna of  FIG. 4  has four conductive loops of lines  90  surrounding area  92 . The use of multiple loops may help to improve antenna performance. If desired, fewer loops may be used (e.g., 1-3 loops) or more loops may be used, e.g., 4-12 or more than 12. Particularly good performance may be obtained when using antenna arrangements with about 8 loops. An illustrative antenna  78  that has been formed with eight loops of conductive traces  90  is shown in  FIG. 5 . The length L 1  of antenna  78  in dimension  126  may be about 50 mm (as an example). The length L 2  of antenna  78  in dimension  128  may be about 30 mm (as an example). The width W of the conductive loops  90  of antenna  78  may be about 8 mm (as an example). The width of the traces and the spaces between adjacent traces in loops  90  may be about 0.5 mm (as an example). 
     Antennas of the types described in connection with  FIGS. 2-4  are merely illustrative. Other suitable antenna configurations may be used for antennas  42  and  44  if desired. For example, antennas  42  and  44  may have spiral loops formed in a circle, an oval spiral of loops, loops formed in a polygonal shape with no curved sides, loops formed in a polygon with at least one curved side, etc. These antenna shapes may use either asymmetrical layouts of the types described in connection with  FIGS. 2 and 3  or symmetrical layouts of the type described in connection with  FIGS. 4 and 5 . 
     The antenna layouts used for antennas  42  and  14  may be the same (e.g., both using a  FIG. 5  layout) or may be different. For example, a symmetrical layout of the type shown in  FIGS. 4 and 5  may be used for antenna  14 , while an asymmetrical layout may be used for antenna  42 . 
     Antenna  14  may be mounted in housing  12  of device  10 , even when housing  12  contains conductive portions. With one suitable arrangement, housing  12  is formed entirely (or almost entirely) out of conductive structures. Antenna  14  may be accommodated within this type of conductive housing arrangement by forming a region that is filled with air or other suitable dielectric. Ferrite tape may also be used to prevent radio-frequency signal degradation due to the proximity of conductive device structures to the conductive loops of antenna  14 . 
     An example is shown in  FIG. 6 . Housing  12  of  FIG. 6  may be associated with a computer monitor or other device  10  having a display. Housing  12  may, as an example, be formed using aluminum, steel, metal alloys, or other metal structures. Planar metal structures for the walls of housing  12  may be about 0.05 to 1 mm thick (as an example). The front surface of housing  12  may have a hole  136  that is sized to accommodate a display such as display  16  of  FIG. 1 . Portions  138  of housing  12  may surround the central region formed by hole  136 . A recessed lip  130  may be formed around the inner periphery of housing  12 . Inner edge  140  of lip  130  may have dimensions that are able to accommodate display  16 . Outer edge  142  of lip  130  may have dimensions that accommodate a clear protective panel formed of glass or plastic. Screw holes  132  may be formed in lip  130 . Mating screws may be inserted into screw holes  132  (e.g., to hold a clear protective panel and/or a protective bezel into place on housing  12 . 
     A hole or gap  134  may be formed in the conductive surface of housing  12 . For example, a substantially rectangular hole  134  may be formed in housing  12  by removing a portion of lip  130 , as shown in  FIG. 6 . Forming hole  134  in this way allows antenna  14  to operate. Without a hole in housing  12 , the conductive walls of housing  12  and the conductive housing surface that is formed when display  16  is mounted to the front of device  10  would electromagnetically shield antenna  14  and prevent antenna  14  from communicating with device  34  over communications path  32 . 
     Hole  134  may be formed in any portion of housing  12  and may have any suitable shape. With one illustrative arrangement, housing  12  includes at least one conductive surface. The conductive surface may, for example, be formed from sheets of metal or other conductors. Some of the conductive surfaces of device  10  may be formed by one or more electrical components. For example, part of a front conductive surface may be formed from a display such as display  16 . 
     Conductive housing wall layers may be planar. For example, in a computer monitor, housing  12  may include a front surface that is partially formed from a planar display and that is partly formed from a planar conductive metal layer (e.g., an aluminum layer) that surrounds the display. In this type of arrangement, the conductive layer is planar. Hole  134  may be formed in any suitable conductive layer of housing  12 , including planar or nonplanar side walls, planar or nonplanar front and rear surfaces, radiused or otherwise curved front, side, or rear surfaces, etc. 
     If desired, some of the walls of electronic device  10  may be formed from nonconductive materials. As an example, a rear housing surface, sidewall, or front housing surface of device  10  may be formed from plastic. Antenna  14  may be mounted behind one of these surfaces. In many situations, however, it may be desirable to place antenna  14  in a portion of housing  12  where there is little or no plastic present (e.g., on a conductive front or side wall of housing  12 ). Particularly in these situations, it may be advantageous to form a hole  134  in the conductive surface of housing  12  to accommodate the antenna. 
     There is generally a finite thickness associated with the conductive walls of housing  12  to accommodate the component in the interior of device  10 . The finite thickness of the conductive walls may range from about 0.1 to 5 mm (e.g., when a conductive surface is formed from metal) to about 0.2 to 2 cm (e.g., when a conductive surface is formed from components such as an LCD display). Surfaces of housing  12  may include both relatively thin planar portions (e.g., metal wall portions) and relatively thicker planar portions (e.g., display portions) or may have substantially the same thickness throughout (e.g., a metal housing sidewall). Hole  134  may be formed in any of these housing surfaces. For example, if device  10  is a computer monitor, device  10  may have a planar front surface. The planar front surface may include a display and a conductive planar metal housing front surface surrounding the display. In this type of situation, hole  134  may be formed in the metal housing surface adjacent to the display. Hole  134  may be formed in a lip such lip  130  of housing surface  138  or in other portions of housing surface  138 . 
     A portion of lip  130  is shown in  FIG. 7 . With the illustrative arrangement of  FIG. 7 , lip  130  is recessed sufficiently to allow a clear panel of glass or plastic to be mounted to portions  138  of housing  12 . A portion of lip  130  in which dielectric-filled hole or region  134  has been formed is shown in  FIG. 8 . Hole  134  may have a length D 1  and a width D 2 . These lateral dimensions may be adjusted to accommodate antenna  14 . For example, if the longer lateral dimension of antenna  14  is 50 mm, lateral dimension D 1  of hole  134  may be about 10 mm to 60 mm (as an example). If the shorter lateral dimension of antenna  14  is 30 mm, lateral dimension D 2  of hole  134  may be about 8 mm or about 4 mm to 12 mm (as examples). These lateral dimensions are merely illustrative. 
     A plastic or glass cover may be attached to lip  130 . A bezel may be used to cover the seam between the cover and edge  142  of lip  130 . The plastic or glass cover for device  10  is represented by planar structure  144  in the example of  FIG. 8 . 
     A top view of housing  12  in which a display such as display  16  of  FIG. 1  has been placed is shown in  FIG. 9 . As shown in  FIG. 9 , some displays  16  may have an edge portion  148  and a central portion  146 . Edge portion  148  may be covered in an external layer of metal, thereby rendering this portion of display  16  particularly conductive. Central portion  146  may not include any external metal or other external conductive portions. Nevertheless, display assemblies such as those used to form liquid crystal diode (LCD) displays contain numerous conductive components (e.g., transistors, conductive traces for addressing the transistors, conductive lines for distributing power, conductive structures for forming touch sensors, etc.). The conductive nature of the components that make up a display such as display  16  render the display conductive from the standpoint of radio-frequency signals. As a result, if a conventional antenna were to be placed directly behind a display, the conductive portions of the display would serve as electromagnetic shielding and would prevent the antenna from functioning. Similarly, it is generally not desirable to place an entire antenna directly behind a solid metal housing wall, because the conductive nature of the metal housing wall would block the radio-frequency signals from the antenna. 
     With the present invention, antenna  14  may be positioned within device  10  so that at least some of the antenna  14  overlaps with hole  134 . A portion of antenna  14  may also be located on the exterior surface of the conductive structures of device  10  such as display  16 . As a result, electromagnetic fields from antenna  14  are able to escape from within the confines of device  10 , even though most of the surfaces of device  10  might be formed of metal, conductive display structures, or other conductive structures. 
     An illustrative location for antenna  14  relative to an illustrative hole  134  in conductive housing surface  12  is shown in  FIG. 10 . Part of the outline of antenna  14  is shown as a solid line and part of the outline of antenna  14  is shown as a dashed-and-dotted line. This is because the illustrative arrangement of  FIG. 10  places the upper portion of antenna  14  in front of display  16  on the exterior surface of metal-covered edge  148  and places the lower portion of antenna  14  behind portion  138  in the interior of housing  12 . There may be small exposed gaps at either end of antenna  14  when gap  134  is sized larger than antenna  14 . Alternatively, gap  134  may be shorter, so that its length equals the longer lateral dimension of antenna  14 . 
     When the loops of antenna  14  are placed in close proximity to conductive structures without shielding, the electromagnetic fields that are produced by the loops impinge directly on the conductive structures. The conductive structures then produce losses for the antenna. Particularly when the loops of a flat antenna such as antenna  14  are placed in direct contact with conductive surfaces, the losses induced by the conductive surfaces can be significant. 
     In the illustrative arrangement of  FIG. 10 , potentially significant losses may be produced for antenna  14 , because the upper portion of antenna  14  lies on top of display  16  (e.g., on top of the outer surface of metal-encased edge  148 ) and because the lower portion of antenna  14  lies against the inner surface of the conductive wall formed by portion  138  of housing  12 . To avoid these potential losses, one or more layers of ferrite tape or other suitable ferrite structures may be interposed between the rear surface of antenna  14  and underlying display  16  and between antenna  14  and overlying housing wall portion  138 . 
     The layers of ferrite may be attached to housing  12  and antenna  14  using screws, clips, or other mechanical fasteners. With one particularly suitable arrangement, ferrite layers are attached to housing  12  and antenna  14  using adhesive. The adhesive may be part of the ferrite element (e.g., when using adhesive-backed ferrite tape) or may be applied separately. One or both sides of the ferrite layers may be coated with adhesive. Adhesive may be used by itself or in conjunction with mechanical fasteners. 
     Illustrative positions were the ferrite layers may be placed relative to conductive loops  90  of antenna  14  and the surfaces of housing  12  and display  16  are shown in  FIG. 11 . In  FIG. 11 , the rectangular outline of substrate  80  of antenna  14  is depicted by solid line  158  and dashed-and-dotted line  160 . The portion of the antenna substrate  80  that is depicted by solid line  158  lies on the exterior surface of display  16  (e.g., on top of display edge  148  and, if desired, on the exterior surface of adjacent central region  146  of display  16 ). The portion of antenna substrate  80  that is depicted by dashed-and-dotted line  160  lies adjacent to the interior surface of housing wall  138  (i.e., in the interior of device  10 ). 
     Device  10  may have a dielectric member such as a plastic bezel that serves to hold display  16  in place and that serves as a cosmetic cover. Some of planer antenna  14  lies on the exterior surface of the conductive structures of device  10  under the bezel or other dielectric member and some of planar antenna  14  lies on the interior of device  10 . This arrangement allows antenna  14  to support near field communications over path  32 , while remaining concealed from view. The portion of antenna  14  that lies above the display is able to interact with device  34  using near field communications, because the dielectric member conceals the antenna from view, but does not adversely affect antenna operation. The portion of antenna  14  that lies behind the conductive housing wall is concealed from view by the housing wall. 
     The location of conductive antenna loops  90  is shown by dashed lines  156  and  154 . The outer perimeter of loops  90  is depicted by dashed lines  156 . The inner perimeter of loops  90 , which preferably surrounds trace-free region  92 , is depicted by dashed lines  154 . In the illustrative arrangement of  FIG. 11 , at least some of loop-free inner region  92  overlaps with hole  134 , which helps to provide satisfactory antenna performance. Hole  134  may be filled with air, plastic, or any other suitable dielectric material that does not interfere with the electromagnetic fields produced by antenna  14 . 
     As shown in  FIG. 11 , the area of antenna  14  (i.e., the area defined by the outermost loop  90 ) may be larger than the area of hole  134 . The area of loop-free region  92  may also be larger than the area of hole  134 . Moreover, loops  90  may not overlap hole  134 . If desired, however, antennas of different sizes may be used and some or all of loops  90  may overlap hole  134 . With one illustrative arrangement, at least some of trace-free region  92  overlaps hole  134  to ensure satisfactory communications with device  34  over wireless link  32 . Arrangements in which all of loops  90  and all of loop-free region  92  lie within the boundaries of hole  134  may be used, although this type of layout may consume a relatively large amount of surface area on housing  12  of electronic device  10  and may require a relatively large bezel or other cosmetic cover to conceal. Hole  134  may be formed within lip  130  or other such housing wall structures that are concealed from view. 
     If desired, antenna arrangements of the type shown in  FIG. 2  that do not have loop-free inner regions may be used in device  10 . When antennas of this type are used, their loops may overlap at least part of hole  134  or lie entirely within hole  134 . 
     As shown in  FIG. 11 , loops  90  lie on the exterior surface of display  16  (e.g., on conductive display edge  148 ). Accordingly, a layer of ferrite tape or other suitable magnetic shielding material may be placed between the rear (inner) surface of antenna  14  and display  16 , where shown by dotted line outline  150 . Similarly, a layer of ferrite tape or other suitable magnetic shielding material may be placed between the front (outer) surface of antenna  14  and the wall of housing  12 , where shown by dotted line outline  152 . The presence of the ferrite layers helps to prevent the adjacent conductive structures of housing  12  from excessively degrading antenna performance. 
     A cross-sectional somewhat exploded side view of the structures of  FIG. 11 , as taken along line  162  of  FIG. 11 , is shown in  FIG. 12 . As shown in  FIG. 12 , display  16  may have a region such as region  148  that is coated with a layer of conductive material such as metal. This metal and the inner portion  146  of display  16  are conductive and can interfere with the electromagnetic fields produced by the loops of conductor in antenna  14 . Ferrite layer  150  may therefore be placed on top of display  16  and metal portion  148  (i.e., between the exterior surface of display  16  and the inner surface of antenna  14 ). Ferrite layer  152  may be placed on top of antenna  14  (i.e., between exterior surface  168  of antenna  14  and interior surface  166  of housing wall  138 ). Gap  134  is preferably not blocked by ferrite. A bezel such as bezel  164  or other cosmetic dielectric cover may be used to hide the seam at junction  170  between display cover  144  and housing wall  138 . 
     Portion  172  of antenna  14  lies on the exterior side of all conductive device structures (such as display  16  in the  FIG. 12  example). Portion  174  of antenna  14  lies on the interior side of conductive housing wall  138 . Dielectric member  164  may extend sufficiently far over the edge of display  16  to hide portion  172  of antenna  14  and edge  148  from view from the exterior of device  10 . Optional transparent protective cover  144  for display  16  may be formed from dielectric, so that it does not interact with the operation of antenna  14 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20070828
Publication Date: 20110705
Grant Date: 20110705
Priority Date: 20070828
Inventors: HILL ROBERT J.
LI QINGXIANG
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q7/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q7/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/27", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/27", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/08", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 44202416