US 3928748 A
A heater grid and antenna for defogging a window such as the windshield of an automobile comprises a plurality of resistive conductors and bus bands for the supply of heating current thereto, at least one of said bus bands having an extension beyond its connection to said resistive conductors, by means of which the resistive conductors and bus bands may be tuned for improved radio reception in the frequency modulation band.
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Description (OCR text may contain errors)
United States Patent Sauer 1 Dec. 23, 1975 1 1 COMBINED WINDOW HEATER AND 3,409,759 11/1968 Boicey 6t a1. 219/522 ANTENNA 3,484,583 12/1969 Shaw, Jr. 219/522 1 3,484,584 12/1969 Shaw, Jr. 219/522 Inventor: Gerd Sauer, Aachen-Laurensberg, 3,636,311 1/1972 Steger 219/522 Germany 3,778,898 12/1973 Gruss eta1.... 29/611 1731 AS89199 1- 1119118919, 311351353 511332 2313151311 33111:: iii/iii Neullly-sur-seme, France 3,794,809 2/1974 Beck et al 219/203 22 Filed: May 20 974 3,813,519 5/1974 Jochim et a1. 219/522  Appl' Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or Firm-Pennie & Edmonds  Foreign Application Priority Data Oct. 31, 1973 France 7338767  ABSTRACT A heater grid and antenna for defogging a window  219/522 219/203 5 such as the windshield of an automobile comprises a 51 I t Cl 2 0 43/704 plurality of resistive conductors and bus bands for the d H 5B supply of heating current thereto, at least one of said 1 0 are 9/203 bus bands having an extension beyond its connection 144/134 343/704 338/309 to said resistive conductors, by means of which the re- 56 R f ed sistive conductors and bus bands may be tuned for iml e erences It proved radio reception in the frequency modulation UNITED STATES PATENTS b 3,366,777 1/1968 Brittan et a1 219/522 3,379,859 4/1968 Marriott 219/522 2 Clams 3 D'awmg US. Patent Dec.23, 1975 Sheet10f2 3,928,748
UiS. Patent Dec. 23, 1975 Sheet 2 of2 3,928,748
COMBINED WINDOW HEATER AND ANTENNA The present invention pertains to a heating grid for the windows of automotive vehicles which is capable of functioning as an antenna for the reception of radio signals, the resistive conductors which make up the heating grid performing as conductive elements of an antenna.
It has already been proposed to employ such grids as antennas, as for example in US. Pat. Nos. 3,484,583 and 3,484,584. According to one such prior art construction, there is disposed on an exterior surface of a windshield, comprising a single sheet of glass, a series of narrow horizontal or vertical conducting resistive strips which are fed at their two ends through bus bands with heating current, typically direct current from the storage battery of the vehicle. In another prior art proposal, the resistive conductors are disposed parallel to each other and take the form of fine wires having a diameter of 0.005 to 0.05 millimeters and these are embedded in the plastic interlayer of a three-layer safety glass, parallel to the upper and lower edges of the window. Such embodiments can be used in Windshields as well as in rear windows since they do not interfere with the drivers vision. I
The heating grids of the type hereinabove described are generally of low efficiency when employed as antennas for the reception of frequency modulated signals. The shape of the conductors imposed on them by their heating function and by the dimensions of the window customarily preculde their being tuned for optimum performance in the frequency modulation band. If it is desired to effect such tuning in windows of this type, it has been necessary to employ additional circuit elements exterior of the window. This is inconvenient and moreover does not always produce satisfactory results.
The present invention provides a window of this type with improved performance in the reception of frequency modulated radio signals without the necessity for auxiliary exterior circuit elements. This result is obtained, according to the invention, by moving the radio Wave receiving conductors toward the middle of the window outside the influence of the metal parts of the automobile body which surround the window and by extending the bus bands beyond or outside the zone of the heating grid conductors, thus making it possible to tune the system in the frequency modulation band.
In comparison with known constructions, the window of the invention possesses important advantages in that it is no longer necessary to have recourse to auxiliary, exterior circuit elements to obtain an antenna tuned to the frequencies which it is expected to receive.
Spacing of the antenna conductors so as to minimize the influence of the vehicle body reduces the capacity of the antenna. In practice, it is necessary for the antenna to have a capacity below a certain limit. That capacity should not exceed 100 picofarads. This cannot be achieved when the antenna conductors are close to the vehicle body. It is then necessary to reduce capacity of the antenna by the use of exterior circuit elements, which further reduces the level of the antenna output signal.
Moreover, the solution proposed by the invention for increasing the spacing of the antenna conductor from the vehicle bodies reduces the effect of perturbating voltages from the latter.
In one embodiment of the invention the two bus bands (e.g. low resistance conducting strips) by means of which current is fed to the heating conductors are parallel to the side edges of the window and at least one of these bus bars includes extensions along the edges of the window but outside the range of influence of the vehicle body.
In another embodiment of the invention, the bus bands are respectively parallel to the upper and lower edges of the window. The lower bus band includes extensions or elongations which serve to tune the antenna; these elongations may at their extremities ex tend upwardly parallel to the side edges of the window.
Since the antenna circuit is used to heat the windshield, the supply of current thereto requires two leads. Such leads are however a source of difficulty, especially at the high frequencies which are involved, because they increase the capacity of the antenna, because they tend to introduce perturbating voltages from the vehicle body, and because they complicate the manufacturing and assembly processes.
It is possible to mitigate these short-comings by disconnecting the leads for supply of heating current when the heating grid is to be used exclusively as an antenna. A better solution resides in locating the two terminals for feed of heater current at the same location, in accordance with one feature of the invention. To this end it is advantageous to divide one of the bus bands into two segments and thereby to divide the heating conductors into two groups which are fed in series. The terminals for supply of heating current are then connected to the two halves of this bus band on opposite sides of the break therein. The antenna signal lead to the receiver is then short-circuited, for radio frequency voltages, to the heater grid, with isolation from the heating current being provided by means of capacitors.
A substantial improvement in the antenna performance may then be obtained by disposing the conductors thereof in an asymmetric way with respect to the vehicle body. Thus it is possible to give unlike lengths to the two parts of the bus band above referred to by means of which connection is made to the radio receiver and to at least one terminal of the source of heating current. i
The invention is applicable to windows comprising a single sheet of glass onto which the conductors are applied in the form of a suspension of finely divided metallic particles with a binder in a ceramic frit, the suspension being thereafter baked in place. Alternatively the conductors may be laid down in the form of .a conductive coating, for example of tin oxide. The
invention is also advantageously applicable to laminated Windshields in which when conducting wires are disposed in the plastic interlayer between inner and outer glass sheets.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described in terms of a number of presently preferred embodiments and by reference to the accompanying drawings in which:
FIG. 1 is a combined diagrammatic and elevational view of an embodiment of the invention as applied to the windshield of a motor car;
FIG. 2 is a view similar to that of FIG. 1 but showing the application of the conducting grid to the rear window of the vehicle; and
FIG. 3 is an elevational view of a third form of combined heater and windshield antenna in accordance with the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a safety glass windshield comprising two glass sheets assembled together with an intervening layer of polyvinyl butyral in which is embedded a grid or network of conductors. This includes in particular parallel vertical conductors 2 connected to an upper bus band 3 and the lower bus band divided into two parts 4 and 5. The vertical conductors 2 may have a diameter of the order of 0.01 mm. and may have a wavy shape, being spaced one or two millimeters apart. The bus bands 3, 4 and 5 may have a width of the order of 3 to 5 mm. and may take the form of silver strips electrically connecting to the vertical wires 2. The bus bands 4 and 5 connect to leads 6 and 7 through a notch 8 formed in the edge of the sheet of glass facing the inside of the vehicle, in order to prevent penetration of humidity between the laminations of the windshield. This notch 8 extends beyond the channel-shaped rubber mounting (not shown) which supports the windshield, so that the leads 6 and 7 do not touch this mounting. Instead of passing out through a marginal notch, the conductors for supply of heating current may alternatively pass out through a hole extending through one of the glass sheets at a short distance from the edge thereof, for example as described in the copending application Ser. No. 334,611 assigned to the assignee hereof.
In the embodiment illustrated in FIG. 1, the resistance wires 2 which make up the heating grid comprise two groups of conductors, the conductors of each group being geometrically parallel to the conductors of the other group and the two groups being connected electrically in series by means of the upper bus band 3. The bus band 3 may be some five centimeters down from the upper edge of the windshield. The lower bus bands 4 and 5 may be about 8 centimeters above the lower edge of the windshield. The portions 4 and 5 of the lower bus band are extended beyond the area of the heating conductors 2 at extensions 9 and 10. The bus bands may be blackened or otherwise rendered nonreflective of light so as to diminish interference with the drivers vision.
The connections of the heater grid-antenna to the source of heating current and to the radio receiver will be described below. They are designed to connect the conductors 6 and 7 to a common antenna lead by shortcircuiting them together for AC voltages derived from the radio waves but not for the heating current. The end portions 9 and 10 of the bus band sections 4 and 5 make it possible to tune the antenna for FM reception and to correct its directional properties.
The area occupied by the resistance wires 2 need not be symmetrically disposed on the windshield. The asymmetric location represented in FIG. 1 makes it possible to concentrate the heating effect in that portion of the windshield of primary interest, in front of the driver of the vehicle. Moreover it makes it possible to improve the reception characteristics of the windshield and especially its directional properties. Such improvement in directional properties may be effected in part by adjusting the length of the extensions 9 and 10.
Contacts 11 and 12 of the relay 13 control energization of the heating circuit. One lead 32 for the heating current connects to ground through an inductance coil 14. A second lead 33 connects to the ungrounded side of a battery 37 through an inductance coil 15 and through a resistor 44. These coils have a negligible resistance for direct current, but block the passage of the high frequency radio signals captured by the antenna. It is possible to dimension these coils in such fashion as to make them effective in blocking the frequencies of amplitude modulated (AM) radio broadcasts (of the order of one megacycle) as well as effective to block the frequencies (of the order of one hundred megacycles) employed in the broadcast of frequency modulated (FM) signals, so as to make it possible to receive either AM or FM signals during the heating operation. Since however the heating current may amount to 15 amperes this would require for these coils such size as to make them unsuitable or excessively costly in motor vehicles. If instead their inductance is limited to 4.7 microhenries, their impedance will amount to about 3000 ohms at I00 megacycles, sufficient to make them operate effectively as filters for frequency modulation signals only, i.e. to block the passage of FM signals to ground.
The normal condition of the apparatus, indicated in FIG. 1, is with the heater circuit deenergized. Relay 13 is then deenergized, with its contacts in the position shown, in which the leads 6 and 7 are isolated for all frequencies, including DC, from the battery leads 32 and 33. The leads 6 and 7 are instead conductively shortcircuited to each other so that the entire circuit on the windshield feeds the receiver 16 with radio frequency signals through a cable, advantageously of coaxial type, having a center conductor 17. The antenna is then capable of receiving AM as well as FM signals.
When a manually operable contact 18 is closed to energize relay 13 with battery voltage so as to apply that voltage to the conductors 2 for heating purposes, the conductors 6 and 7 connect to the receiver 16 only through capacitors 19 and 20, which prevent short-circuiting of battery by the receiver lead 17. The capacity of each of these capacitors is of the order of 1000 picofarads so that their impedance does not exceed 1.6 ohms at megacycles. This is sufficiently low to constitute an effective short-circuit between the receiver and the antenna for frequency modulated signals in the frequency modulation band which is in the vicinity of 100 megacycles. The indicator lamp 21 shows that the heating circuit is energized.
FIG. 2 shows a construction according to the invention for the rear window of an automobile. It comprises a single sheet of glass on which there has been deposited by the silk screen process and subsequently baked a network of resistive conductors made up of metallic particles in enamel. The heating grid comprises the two vertical bus bands 25 and 26 between which are connected horizontal resistive conductors 27. The auxiliary conductors 28 and 29 connected to the bus band 25 serve for tuning the antenna. Their length is such that the assembly of conductors on the window consti tutes a resonant circuit. The distance from the conductors 25 and 26 to the edges of the glass is of the order of 5 centimeters.
In the embodiment illustrated in FIG. 2, the two heating current supply conductors or leads 30 and 31 are disposed at opposite sides of the window. For operation .of the heating circuit of FIG. 2 as an antenna, a
relay such as that described in connection with FIG. 1 is necessary to connect and disconnect each of these leads.
FIG. 3 represents another embodiment of the invention in which the heating circuit takes the form of two conducting areas 35 and 36 covering a large part of the window. These may take the form of thin transparent layers of a metal or of a semiconductor such as tin oxide. Or they may be made up of electrically conducting sheets interposed between the two sheets of glass as described in the German published application No. 1,704,619. The two conductors 35 and 36 are connected in series by a bus band 37. The two segments 38 and 39 of the lower bus band serve for supply of the heating current and also for tuning of the antenna. This tuning is effected as hereinabove described with the aid of extensions 40 and 41, which in the embodiment illustrated extend first horizontally beyond the limit of the conducting areas 35 and 36 and then upwardly in directions generally parallel to the side edges of the window. The conductors 42 and 43 correspond to the conductors 6 and 7 of FIG. 1 and are connected to the radio receiver as described in connection with FIG. 1.
The invention thus provides a window comprising a sheet of transparent material such as the sheet 1 of FIG. 1, usually of glass, a plurality of electrically conductive resistive heating conductors such as the conductors 2, 27, 35 and 36 of FIGS. 1, 2 and 3 supported on the sheet and spanning an area thereon smaller than the surface of said sheet, and at least two bus bands such as the bands 3, 4 and 5 of FIG. 1 supported on the sheet and connecting to the conductors, at least one of the bus bands including portions such as the portions 9 and 10 of FIG. 1, 28 and 29 of FIG. 2 and 40 and 41 ofFIG. 3 extending beyond that area.
The bus bands may extend substantially parallel to the side edges of the sheet as in FIG. 2, the bus band 25 including at each end an extension (the extensions 28 and 29) substantially parallel to the upper and lower edges of the sheet and outside the zone of influence of a vehicle body in which the sheet may be mounted. The bus bands may however extend substantially parallel to the upper and lower edges of the sheet, as in FIGS. 1 and 3, with the portions 40 and 41 extending substantially parallel to the side edges of the sheet. The conductors 4 and 5 of FIG. 1 may be regarded as one bus band divided into two substantially collinear parts 4 and 5 each connecting with separate ones of the heat ing conductors 2, the window further including two terminals for the leads 6 and 7 at adjacent points on those two parts, whereas the bus band 3 connects to all of the heating conductors.
The heating conductors such as those illustrated at 2 and 27 may comprise a suspension of metallic particles in a frit baked on the surface of the sheet. The bus bands and heating conductors may both comprise a suspension of metallic particles in a frit applied to a surface of the sheet by a silk screen process and baked to the sheet. The window may be of laminated construction, comprising a sheet of transparent plastic adhered to and between two sheets of glass, with the heating conductors taking the form of wires disposed in the plastic sheet. The bus bands are desirably disposed at least 5 centimeters from the edge of said sheet, and the parts such as 4 and 5 of FIG. 1 and 28 and 29 of FIG. 2 (though the latter are not so illustrated), may be of unequal length.
The invention also provides a window heating circuit comprising a sheet of transparent material, a plurality of resistive heating conductors supported on the sheet and spanning an area thereon smaller than the surface of the sheet, at least two bus bands supported on the sheet and connecting to those conductors, at least one of the bus bands extending beyond that area, two leads such as the leads 6 and 7 of FIG. 1 connecting to separate ones of the bus bands, separate capacitors such as the capacitors l9 and 20 coupling those leads to a transmission line such as a coaxial transmission line of which the center conductor is shown at 17 in FIG. 1, and switch means such as the relay 13 with its contacts 11 and 12 for connecting those leads to a source of voltage such as a battery 37.
The circuit may further include inductive means such as the coils 14 and 15 interposed between each of those leads and the voltage source. According to a further feature of the invention those inductive means possess an impedance low compared to that of the transmission line for frequencies of the order of one megacycle per second and an impedance high compared to that of the transmission line for frequencies of the order of one hundred megacycles per second. The consequence of this feature of construction is that radio signals of frequencies of the order of one hundred megacycles captured by the heating conductors are effectively delivered to the transmission line and thereby to a radio receiver despite connection of the leads to the voltage source by the switch means, whereas radio signals of frequencies of the order of one megacycle will be effectively delivered to the transmission line only when the switch means disconnect the leads to the heating conductors from the voltage source.
While the invention has been described hereinabove in terms of a number of presently preferred exemplary embodiments thereof, the invention itself is not limited thereto but rather comprehends all modifications of and departures from those embodiments properly falling within the spirit and scope of the appended claims.
1. A windshield for automotive vehicles having a combined heater grid for heating said windshield at least within an area over which it is disposed and antenna for reception of frequency modulated radio signals of a frequency of the order of megacycles, said windshield comprising a transparent substantially rectangular sheet, a plurality of electrically conductive resistive heating conductors supported on a surface of the sheet substantially parallel to one dimension thereof and spanning said area thereon smaller than but constituting a major fraction of the surface of said sheet, and three bus bands likewise supported on said sheet and extending at least in part substantially parallel to the other dimension of said sheet, two of said bus bands being in spaced apart collinear relation and together with the other bus band connecting said conductors into a two-terminal circuit comprising said bus bands and conductors, each of said collinear bus bands including a portion extending beyond said area partly substantially collinearly with said bus band from which it extends and parallel to said other dimension and partly substantially parallel to said one dimension, said portions having a length substantially of the same order of magnitude as either of said dimensions, whereby said circuit may be tuned for the reception of frequency modulated signals of frequencies of the order of 100 megacycles, all parts of said combined heater grid and 7 antenna being spaced from the edge of said sheet sufficien'tly to be outside the zone of influence of a vehicle body surrounding said sheet.
2. A window for automotive vehicles having a combined heater grid for heating said window at least within an area over which it is disposed and antenna for reception of frequency modulated radio signals of a frequency of the order of 100 megacycles, said window comprising a transparent substantially rectangular sheet, a plurality of electrically conductive resistive heating conductors supported on a surface of the sheet substantially parallel to one dimension thereof and spanning said area thereon smaller than but constituting a major fraction of the surface of said sheet, and two bus bands likewise supported on said sheet and extending at least in part substantially parallel to the 8 other dimension of said sheet, said bus bands connecting said conductors into a two-terminal circuit comprising said bus bands and conductors, one of said bus bands including portions extending beyond said area partly substantially collinearly with said bus band and parallel to said other dimension and partly substantially sheet.