Abstract:
A housing wall for a data communications device includes a metallic and electrically conductive main body. A slotted area having a number of slots is provided in a region of the housing wall, in such a way that in a region of the slotted area the housing wall is permeable to magnetic fields for inductively coupling-in signals for wireless communication.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a housing wall for a data communications device having a metallic and electrically conductive main body, to a housing for a data communications device having a housing wall, and to a data communications device, in particular a cellular phone, equipped with a housing. 
     In principle, in the case of data communications devices, such as cellular phones or RFID readers, for example, which enable wireless data transmission on the basis of inductive coupling between the data communications device and an external device, such as an NFC device or a transponder, for example, there is the problem that such data transmission by means of inductive coupling does not function through metallic or highly electrically conductive housings, or objects, or surfaces. For this reason, data communications devices such as, for example, cellular phones having metallic housings are generally not suitable for carrying out data transmission by means of inductive coupling to an external data communications device. The reason for this is mutual induction effects on account of eddy currents that are induced in the metallic objects or surfaces of the data communications device. The alternating electromagnetic field generated by the transmitter induces eddy currents in the metallic housing of the data communications device, said eddy currents being directed in the opposite direction to their cause and thus attenuating the resulting magnetic field required for the data communication in such a way that data communication is not possible. Modern smartphones having an NFC interface therefore have a non-metallic housing or a non-metallic cover in the region of the NFC antenna, which is normally situated on the rear side of the device. 
     However, the use of metallic housings for data communications devices, in particular cellular phones, has various positive aspects and advantages compared with non-shielding plastics housings, particularly with regard to stability and thermal conductivity. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide a housing wall for a data communications device, in particular a cellular phone, which is substantially metallic and has the stability and thermal conductivity of metal, but at the same time is permeable for data transmission based on inductive coupling. 
     In the case of a housing wall of the type mentioned in the introduction, the invention achieves said object with the features of described below. 
     According to the invention, in the case of a housing wall for a data communications device comprising a metallic and electrically conductive main body, it is provided that a slotted area having a number of slots is provided in a region of the housing wall, such that in the region of the slotted area the housing wall is permeable to magnetic fields for inductively coupling in signals for wireless communication. This affords a simple possibility for providing data communication between an antenna arranged in the region of the housing wall and a data communications device, such as a transponder, for example, arranged on the opposite side, wherein at the same time the advantages of a metallic housing such as the high stability or the low susceptibility to interference, for example, continue to exist. 
     In order additionally to improve this effect, it can be provided that the slots restrict a free propagation of the eddy currents in the housing wall, said eddy currents being induced by the magnetic field generated by a coil antenna, which is located in the region of the slotted area and bears against the housing wall or lies near the housing, in such a way that wireless communication based on inductive coupling is possible between the coil antenna and a further data communications device situated on the opposite side of the housing wall. 
     In order additionally to avoid entry or passage of water or gas, it can be provided that the housing wall is closed with electrically non-conductive material in the region of the slotted area, and in particular comprises an insulating layer, which covers and closes the slots, wherein in particular the slotted area of the housing wall is impermeable to air or water. 
     Advantageous data communication through the housing wall is achieved if a coil antenna is arranged on one of its sides in the region of the slotted area. 
     In order further to prevent shielding of the magnetic field emitted by an antenna, it can be provided that the slotted area projects beyond the coil antenna. 
     Advantageous suppression of the mutual induction is achieved if the webs formed between the slots have a width of at most 3 mm. 
     An arrangement having increased mechanical stability provides for the housing wall to be constructed with at least two plies and to comprise at least a first ply and a second ply, each comprising overlapping slotted areas having slots, wherein the slots in the slotted area are arranged in a manner offset relative to one another. 
     In order at the same time to achieve a high mechanical stability and low suppression of the emitted magnetic field, it can be provided that an insulating layer is formed between the first ply and the second ply, said insulating layer spacing apart the two plies from one another and electrically insulating them from one another. 
     The mechanical stability can be improved further by virtue of the slots of the first ply and the slots of the second ply forming angles of more than 45°, in particular of more than 85°, with respect to one another. 
     The invention furthermore relates to a housing for a data communications device comprising a housing wall according to the invention and a coil antenna arranged in the interior of the housing and arranged in the region of the slotted area. 
     Furthermore, the invention relates to a data communications device, in particular a cellular phone, having a housing according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       A number of exemplary embodiments of the invention are illustrated with reference to the following figures of the drawings. 
         FIG. 1  shows a cellular phone having a metallic housing according to the prior art. 
         FIG. 2  illustrates a section through the cellular phone illustrated in  FIG. 1 . 
         FIG. 3  shows the formation of eddy currents in a fully metallic housing wall. 
         FIG. 4  shows the formation of eddy currents in one preferred housing wall according to the invention. 
         FIGS. 5 to 8  show preferred housing walls according to the invention. 
         FIGS. 9 and 10  show preferred developments of the housing wall illustrated in  FIG. 5  in cross section. 
         FIGS. 11 to 13  show preferred two-ply housing walls. 
         FIGS. 14 and 15  show a further two-ply embodiment of a housing wall in front view and in section. 
         FIG. 16  shows a further advantageous embodiment of a housing wall, in which the slotted area is used as a design element. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cellular phone having a metallic housing according to the prior art. In the present example, the cellular phone  1  comprises two housing parts  11 ,  12 , namely a trough-like housing part  11  and a flat housing part  12 , which when combined enclose and shield the electronics  14  ( FIG. 2 ) of the cellular phone. 
     Furthermore,  FIG. 1  shows an NFC antenna  13  which is connected to the electronics  14  of the mobile radio device and lies in the interior of the housing of the cellular phone  1  that is formed by the two housing parts  11 ,  12 . 
     As illustrated in  FIG. 2 , an electromagnetic field is generated by the antenna  13 . The dashed arrows  15  represent that electromagnetic field which arises without the metallic shielding of the housing wall  12 . The dotted arrows  16  show the electromagnetic field that arises as a result of eddy currents  17  induced in the housing wall  12 . As a result of the superposition of the two magnetic fields  15 ,  16 , a resulting magnetic field  18  arises which is greatly attenuated relative to the original magnetic field  15 . Therefore, the range and strength of the magnetic field and of the data transmission which is possible by means of NFC proceeding from the cellular phone  1  is significantly reduced. 
     In order to achieve the aim of a resulting magnetic field sufficient for inductive communication outside the cellular phone housing, the formation of eddy current induction can be suppressed. With materials that are currently technically available, it is not possible to reduce the electrical conductivity of the material of the device housing rear wall without at the same time also losing many (thermal) advantages of a metallic device housing rear wall. 
       FIG. 3  illustrates in greater detail the effect of the current displacement in the housing wall  12  of the cellular phone  1  illustrated in  FIGS. 1 and 2 . It should be noted that the eddy currents that form, owing to the effect of the current displacement, are concentrated along the edge of the metal surface permeated by the magnetic field. 
     Sufficient suppression of the eddy current induction can be achieved, however, if the planar structure of the metallic housing  11 ,  12 , at least in the region of the inductive antenna  13 , is fashioned such that eddy currents  17  can no longer form therein or can only form therein to a very restricted extent. The simplest way of making this possible is by means of the configuration of slots  21  in the metallic housing wall  11  in the region of the antenna  13 , as illustrated in  FIG. 4 . Said slots  21  can be arbitrarily thin; it is only necessary to attain a sufficient increase in the ohmic resistance in the transverse direction with respect to the slots, as is illustrated schematically in  FIG. 4 . 
     On account of the slots in the metal, the induced eddy currents  17  cannot propagate in an unimpeded manner ( FIGS. 3 and 4 ). Eddy current induction occurs, of course, in the individual webs  22  between the slots  21 . On account of the comparatively small web width a, current paths having through-flow in opposite senses lie close to one another and compensate one another with regard to the mutual induction effect of the eddy currents. The mutual induction effect is attenuated further by selection of a small web width a. The housing wall  12  becomes all the more permeable to the magnetic field generated by the antenna  13 , the smaller the web width a is chosen to be. 
     If that region of a metallic device housing which covers the coil antenna  13  is provided with slots  21  as shown above, the magnetic field generated by the coil antenna  13  is also no longer attenuated, or is only slightly attenuated, with the result that wireless communication by inductive coupling through the metal housing  12  is possible. 
     Since the slot width b can be made very small without reducing the desired effect, there is also the possibility of obtaining a water-tight or largely air-tight cover ( FIG. 9 ) despite the slots  21 , for example by the housing wall  12  being coated with electrically non-electrically conductive materials. In this case, an electrically non-conductive material applied to the housing wall  12  bridges the slots  21 , each having only a very small slot width b. 
       FIGS. 5 to 8  show examples of slotted areas  26  which are arranged in housing walls  12  and which permit an inductive coupling through the housing wall  12 . The slots  21  are illustrated in each case only as lines. 
       FIGS. 9 and 10  illustrate preferred embodiments of the invention, showing a cross section of the housing wall  12  along the sectional edge B-B from  FIG. 5 . It is particularly advantageous here for the housing wall  12  provided with slots  21  to be filled with an insulating layer  25  comprising electrically non-conductive or magnetically impermeable material. In this case, either the webs  21  can be filled with an insulating layer  25  composed of electrically non-conductive material  25 . However, as illustrated in  FIGS. 9, 10 , it is also possible only to provide an additional insulating layer  25  comprising non-conductive material that prevents water or gases from penetrating through the housing wall  12 . 
     A metallic device housing wall  12  having slots  21  has in practice poorer mechanical properties, for example lower bending stiffness, and poorer radio engineering properties in the UHF or microwave range. This last is primarily caused by the fact that slots  21  in metal structures can act very efficiently as antennas if the length of the slots  21  is in the range of the wavelength. For the frequency bands of a few hundred MHz to a few GHz that are used by modern cellular phones  1 , this could accordingly indeed be the case, as a result of which the radio engineering properties of the cellular phones  1  are adversely impaired by the slots  21  in the device housing under certain circumstances. 
     Both of the abovementioned potential disadvantages of the slots  21  in the device housing  11 ,  12 , namely possible influences of the mechanical and radio engineering properties, can be sufficiently reduced, however, by the housing wall  12  which is under consideration or that region of the housing wall  12  which is under consideration being constructed from two plies  23 ,  24  of slotted metal electrically insulated from one another, wherein the slots  21  of the two plies  23 ,  24  are arranged in a manner offset relative to one another. In order to achieve a bending stiffness similar to that of unslotted metal, an orthogonal offset with force-locking electrically non-conductive connection, in particular adhesive bonding, proves to be expedient. This is not absolutely necessary, however, for the magnetic transparency of the housing wall  12 . 
       FIGS. 11 to 13  show examples of housing walls  12  with arrangements of two metal layers which are arranged one above the other but in a manner electrically insulated from one another and which sufficiently suppress a mutual induction effect and thus enable inductive communication through the housing wall  12 . 
       FIGS. 11 to 13  illustrate a plurality of embodiments of housing walls  12  comprising two-ply slotted areas, wherein the slots  21   a  illustrated in a dashed manner are present in the first ply  23  ( FIG. 15 ) and the slots  21   b  illustrated in a dotted manner are present in the second ply  24  ( FIG. 15 ). 
     The antenna effect caused by slots  21 , particularly in the UHF and microwave range, can also be suppressed with two plies  23 ,  24  of slotted metal layers electrically insulated from one another in an arrangement in accordance with  FIGS. 14 and 15 . 
       FIG. 14  shows such an embodiment, with  FIG. 15  showing a section C-C in  FIG. 14 . An insulating layer  25  is illustrated here, which insulates the two plies  23 ,  24  from one another and prevents liquids from penetrating through the housing wall  12 . 
     Typical antennas  13  are designed for inductive data transmission in the frequency range of between 10 kHz and 100 MHz, in particular 120-135 kHz, 13-14 MHz, 25-30 MHz. 
     The mutual induction effect is locally influenced primarily by the web widths a or slot spacings. The smaller the web widths a, the better the mutual induction effect is suppressed. In practice, web widths a having a value of at most 3 mm appear to be expedient. 
     For unrestricted operation of inductive data communication, wherein communication is possible with all transponder sizes, as would also be the case in the case of a non-metallic housing, the dimensions of the slotted area  26 , in particular the rectangular area having the size of the slotted area length d×the slotted area width c, are defined as larger than the external dimensions of the coil antenna  13 . The slotted area  26  projects beyond the coil antenna  13 . If the slotted area  26  is smaller than the external dimensions of the coil antenna  13  of the cellular phone, then communication is at least still possible with transponders whose transponder antenna is smaller than the slotted area  26 . 
     It is also possible, of course, for the slotted area  26  to be fashioned such that at the same time it also fulfills advertising or brand identity or marketing purposes ( FIG. 16 ).