Antenna For Use With An Audio Induction Communication System

Abstract

An antenna for use with an audio induction communication system provides a communication field of substantially uniform strength at all points within a given pick-up zone along which receiver-equipped persons are expected to travel or within which such persons are expected to stand while receiving a message through their receivers. The antenna comprises a continuous wire located in the vicinity of the pick-up zone and preferably buried beneath the surface of the earth defining the pick-up zone. The wire is disposed in a plurality of loops each of which loops includes two portions crossing the zone at two different points, such zone-crossing loop portions being arranged so as to include a spaced series of such portions located along the length of the zone and through which the exciting current passes in the same direction, those zone-crossing loop portions through which the exciting current passes in the opposite direction being closely grouped together at one end of the zone.

Description

BACKGROUND OF THE INVENTION

This invention relates to audio induction communication systems wherein audio frequency messages are transmitted to receiver-equipped persons through a magnetic communication field the strength of which varies at a frequency directly related to the frequency of the transmitted message, and deals more particularly with an antenna for use in such a system for establishing the magnetic communication field.

The antenna of this invention may be used in various different situations, but is particularly well adapted for use in cases where it is desired to provide one or more communication fields in an outdoor setting. Such a setting may, for example, be an historical site, such as an old restored village, where it is desired to provide receiver-equipped visitors with informative messages as they walk along certain paths or as they stand within a given area viewing a given building or other exhibit feature. Generally, in such a case the pick-up zone within which the communication field exists should be relatively large and of course the strength of the field should be substantially uniform throughout such zone so that the message is received at the same volume level throughout the zone. In the case of a path, for example, it may be desirable to have visitors pick up a particular message as they walk or otherwise travel along such a path for a distance of 100 or 200 feet or more, and the antenna of this invention has been found to serve this purpose very well.

SUMMARY OF THE INVENTION

This invention resides in an antenna for use with an audio induction communication system and wherein such antenna comprises a continuous wire making at least one complete circuit along a wire path arranged relative to a given four-sided area, which includes the pick-up zone within which a magnetic communication field is to be established, in such a fashion as to form a plurality of loops. The four-sided area has a base line extending across one end thereof and also has a number of other lines extending thereacross generally parallel to the base line and spaced from one another along the length of the area. Each loop of the wire path has one leg or portion extending along the base line and a second leg or portion extending along a respective one of the other lines, and the disposition of the wire along the loops is such that when a current is passed through the wire the current in passing along said second portions of said loops flows in one direction across said four-sided area and the current in passing along said first portions of said loops flows in the opposite direction across said area. Preferably, the wire makes a number of circuits along such wire path and is constituted by a flat multi-conductor cable wherein the conductors are located in a common plane, the cable preferably being arranged so that said common plane of the conductors is generally perpendicular to the plane of said four-sided area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an audio induction antenna installation using an antenna embodying this invention.

FIG. 2 is a plan view of the layout of an antenna embodying this invention and generally similar to that of FIG. 1.

FIG. 3 is a plan view of an abbreviated antenna embodying this invention and showing the manner in which the wire comprising the antenna is disposed relative to the zone within which it is desired to establish a communication field.

FIG. 4 is a fragmentary perspective view taken generally on the line 4--4 of FIG. 2.

FIG. 5 is an enlarged fragmentary perspective view showing a portion of the multi-conductor cable of FIG. 4.

FIG. 6 is a schematic diagram showing the manner in which the ends of the multi-conductor cable are connected one to another to form an antenna having one continuous path for the current flowing therethrough.

FIG. 7 is a side elevational view of the antenna of FIG. 3 showing the general nature of the magnetic communication field established thereby and as encountered by a viewer.

FIG. 8 is a schematic diagram illustrating the components of a transmitting system with which the antenna of this invention may be used.

FIG. 9 is a view similar to FIG. 6 but shows the way in which the ends of a multi-conductor cable are connected to form two parallel circuits for current supplied to the antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The antenna of this invention is one adapted to produce a magnetic communication field within a relatively large pickup zone and comprises essentially an electrical conductor or wire arranged in a large number of loops, the loops being of different sizes and with portions of different loops being dispersed throughout the pick-up zone. The antenna may be installed in various different ways depending on the nature of the pickup zone with which it is to be used, and it may be used either indoors or outdoors. Generally, it is located in a substantially horizontal plane, but this is not necessary and in some cases it may also be located in a vertical plane as, for example, by being located behind the wall of a building. In a typical installation, however, the antenna is used outdoors and is buried slightly below the surface of the ground which includes the desired pickup zone. Such an installation is shown, for example, in FIG. 1.

Referring to FIG. 1, the antenna there shown is indicated at 10 and is used to provide a magnetic communication field within a pick-up zone defined by a given length of a path 12. The path 12 is one along which visitors, such as those shown at 14, 14, walk while viewing a nearby house 16. The persons 14, 14 wear headpieces containing audio induction receivers, and the antenna 10 is properly excited, as hereinafter explained, to transmit a message to the persons 14, 14 concerning the house 16 or other features visible from the pick-up zone. The antenna 10 is buried beneath the surface of the ground and extends some distance to either side of the path. In FIG. 1 the length of the antenna 10 along the path is, for convenience, shown to be relatively short. However, it need not be this short and may have a length of as much as two hundred feet or more.

FIG. 2 shows in plan view an antenna 20 embodying this invention and which is similar to the antenna 10 of FIG. 1 except for being of a longer length. In FIG. 2 the reference numeral 22 indicates a path with which the antenna 20 is used, the pickup zone being generally the portion of the path 22 located between the ends of the antenna. The antenna 20 consists of a large number of loops of a continuous wire conductor arranged along lines defining a generally four-sided area embracing the pickup zone. This four-sided area includes two sides 24 and 26 and two ends 28 and 30. Between the ends 28 and 30 are a large number of other lines 32, 32 spaced from one another along the length of the area and extending between the sides 24 and 26 parallel to the sides 28 and 30. The wire constituting the antenna may make one or more complete passes around the path of lines shown in FIG. 2. In any one such pass the wire consists of a plurality of loops and each of these loops includes one leg extending along the end 28 and another leg extending along a respective one of the lines 32, 32. Therefore, for each complete pass of the wire the end 28 has extending therealong a number of wire portions equal to the number of lines 32, 32 and 30 and each line 32 has extending therealong one wire portion. The arrows in FIG. 2 indicate the direction of current flow for one polarity of excitation and from this it will be noted that the current flowing through the end 28 flows in a direction opposite the direction in which the current flows through the lines 32, 32, and 30, the current in all of the latter lines flowing in the same direction. The input lines to the antenna 20 are indicated at 34, 34.

To better understand the manner in which the wire is disposed to form an antenna such as that shown at 20 in FIG. 2, FIG. 3 shows the manner in which the antenna 20 would be wound if it included only four lines 32, 32. In FIG. 3 the continuous conductor is indicated at 36, and from viewing this figure it will be noted that, starting from the point A, the wire first extends along the side line 24 to the common base or end line 28 and then forms a loop including a first leg or portion extending along the line 28 and another leg or portion extending along the first line 32 to the left of the line 28, the loop also including two portions extending along the side lines 24 and 26, respectively. The wire is then continued on to form another loop including one portion extending along the line 28 and another portion extending along the next line 32. This formation of loops is continued, with each loop being of a progressively larger size than the preceding one and having a portion extending along the next line 32, until reaching the end line 30. Upon reaching the point B of the end line 30 the winding of one complete pass of the wire along the wire path is complete, and if the antenna is to consist of more than one such pass, the wire may be extended from the point B to the point A and from there through the additional desired pass or passes.

Preferably, the antenna does include a large number of passes of the wire through the wire path so that each line 30 and 32 of the path includes more than one conductor. FIG. 4 is a perspective view taken generally on the line 4--4 of FIG. 2 and shows the preferred manner of constructing the antenna in the case where the continuous wire makes a large number of passes around the wire path. As shown in this figure the wire is preferably part of a flat multi-conductor cable 38, and as shown more clearly in FIG. 5 the multi-conductor cable consists of 16 conductors or wires 40, 40. In making the antenna 20 from the cable 38 the cable is disposed along the path of lines shown in FIG. 2, in the manner of FIG. 3, in one pass. Then, at the two ends of the cable the various conductors 40, 40 are connected to one another and to the input lines 34, 34 in the manner shown in FIG. 6, the lines 42, 42 in FIG. 6 indicating the connections made between the conductors 40, 40 at the ends of the cable. Therefore, it will be obvious from FIGS. 4, 5 and 6 that by merely laying one pass of the cable 38 and then connecting the conductors 40, 40 in the manner of FIG. 6 the end result is to obtain 16 series connected passes of the wire around the wire path.

FIG. 7 shows the general nature of the magnetic communication field produced by the antenna 20 when excited by an audio frequency signal. In this figure the lines 44, 44 represent the magnetic flux established by the current flowing through the wire of the antenna, the view of FIG. 7 being taken generally along the center of the path 22. From FIG. 7 it will therefore be noted that a viewer in walking down the path 22 encounters a substantially uniform magnetic field throughout the major portion of the length of the path and until approaching very close to the end 28. Therefore, the message transmitted to him is received at a substantially constant volume along such major portion of the length of the path. Magnetic fields are also established by the current flowing through the wire located along the side lines 24 and 26 of FIG. 2, and in order to prevent these fields from interfering with the field in the desired pickup zone, the side lines 24 and 26 are preferably located, as shown, a substantial distance outwardly beyond the edges of the path 22.

In a typical installation, the path 22 of FIG. 2 may be 10 feet wide and the sides 24 and 26 spaced outwardly from the edges of the path by a distance of 3 to 4 feet. Also, in such a case the length of the path may be 200 feet with the spacing between the adjacent transverse lines 32, 32 being approximately 6 inches to 1 foot. The wire should be buried below the surface of the ground by a distance sufficient to minimize the possibility of it being reached and cut by gardening or other tools that might be expected to be used in its vicinity, and generally a distance of about 6 inches or more below the ground is satisfactory. Also, it is preferred to dispose the multi-conductor cable 38 in such a fashion that the plane of the conductors is generally perpendicular to the plane of the pickup zone or path 22. That is, the cable 38 is preferably placed vertically on edge as shown in FIGS. 4 and 5 when used in an in-ground installation.

FIG. 8 shows a complete audio induction transmitting system utilizing the antenna 20 of FIG. 2. This system includes a tape deck 46 which acts as a source of a suitable program of audible informative material to be transmitted to the viewers. The output from the tape deck is amplified by a power amplifier 48 and transmitted to a line run transformer 50. The line run transformer is connected to a line run 52 which transmits the output of the line run transformer to an impedence matching transformer 54 located near and connected to the input of the antenna 20. The tape deck 46, amplifier 48, and line run transformer 50 are located at a program center from which a large number of programs may be sent to a large number of antennas at different locations, and the line run 52 may be a line of considerable length. The purpose of the line run transformer and the impedence matching transformer 54 is to provide a high impedence at the input to the impedence matching transformer 54 so as to keep the current through the line run low to reduce loss of power. In a typical case, the input impedence of a line run transformer is 4 or 8 ohms and its output impedence is around 500 ohms. The impedence matching transformer 54 in turn has an input impedence of around 500 ohms to match the output impedence of the line run transformer and has an output impedence matching the impedence of the antenna 20. The impedence of the antenna depends on the type and length of wire used to make it and is typically between 8 to 500 ohms.

If for a particular installation it is found that the impedence of the antenna is too high if it is constituted of a single continuous wire wound in a number of series connected passes around the wire path, then the wire may be arranged to form two or more parallel connected sets of passes. FIG. 9, for example, shows the manner in which the multi-conductor cable of FIG. 6 may have its conductors connected to one another at the ends of the cable and to the input lines 34, 34 to form two parallel connected sets of passes around the antenna path. That is, as shown in FIG. 9 the cable 32 includes one set a of eight conductors 40, 40 which are connected to make eight series connected passes around the antenna wire path, and it also includes a second set b of another eight conductors 40, 40 which likewise make eight series connected passes around the wire path. The two sets a and b are in turn connected in parallel to one another and to the input leads 34, 34, the antenna therefore having a substantially lower impedence than if connected in the manner of FIG. 6.

Claims

I claim:

1. An antenna for use with an audio induction communication system for producing a communication field in the vicinity of a given pickup zone, said antenna comprising a continuous wire wound in one direction of winding to form a plurality of loops, each of said loops including a first portion which extends across said zone along one line common to all of such first portions, and each of said loops including a second portion which extends across said path along a respective one of a plurality of other lines extending across said zone, said other lines being generally parallel to said one line and spaced from one another along the length of said zone.

2. An antenna as defined in claim 1 further characterized by all of said second portions of said loops being located on the same side of said first line.

3. An antenna as defined in claim 1 for use with a generally four-sided pickup zone including two end edges and two side edges and further characterized by said one line being located along one of said end edges and said one line and said other lines extending generally perpendicular to said side edges, each of said loops including other portions extending between said first and second portions, said other portions being spaced outwardly from the adjacent side edge of said zone by a distance which is substantial in comparison to the width of said zone.

4. An antenna as defined in claim 1 further characterized by said other lines being spaced from one another along the length of said zone by spacing intervals having lengths falling within the range of 6 inches to 2 feet.

5. An antenna as defined in claim 1 for use with a generally four-sided pickup zone including two end edges and two side edges and further characterized by each of said loops including third and fourth portions extending between said first and second portions, said third and fourth portions of said loops being spaced outwardly from the adjacent side edge of said zone by a distance greater than 2 feet.

6. An antenna as defined in claim 1 further characterized by additional wire wound to form an additional plurality of loops duplicating several times over said first-mentioned plurality of loops.

7. An antenna as defined in claim 6 further characterized by all of said loops being connected in series with one another.

8. An antenna as defined in claim 6 further characterized by said loops including a first set connected in series with one another and a second set connected in series with one another, and means connecting said first and second sets in parallel to one another.

9. An antenna for use with an audio induction communication system, said antenna comprising a continuous wire disposed relative to a given four-sided area in such a fashion as to form a plurality of four-legged loops, said four-sided area having first and second end edges and first and second side edges, and each of said loops having a first leg extending generally along said first end edge of said four-sided area, a second leg extending at least partially along said first side edge from said first end edge toward said second end edge, a third leg extending from said first side edge to said second side edge, and a fourth leg extending along said second side edge from said fourth leg toward said first end edge, said third legs of said loops being spaced from one another along the length of said first and second side edges, all of said loops being wound in the same direction relative to said four-sided area so that when an electrical current is passed through said wire said current in flowing through all of said first legs of said loops moves in one direction relative to said two side edges and in flowing through all of said third legs of said loops moves in the opposite direction relative to said two side edges.

10. An antenna for an audio-induction communication system for producing a communication field in the vicinity of a given pick-up zone, said antenna comprising a continuous wire disposed in a plurality of loops each of which loops includes two portions crossing said zone at two different points, said loops therefore defining one set of zone-crossing portions through which the exciting current passes in one direction and a second set of zone-crossing portions through which the exciting current passes in the opposite direction, said first set of zone-crossing portions being spaced from one another along the length of said zone and said second set of zone-crossing portions being grouped together at one end of said zone.

11. An antenna as defined in claim 10 further characterized by said pick-up zone being close to the surface of the ground and said wire being buried in the ground.

12. An antenna for use with an audio induction communication system, said antenna involving a generally four-sided wire path having two end edges, two side edges and a plurality of lines extending between said two side edges arranged generally parallel to one another and to said end edges and spaced from one another along the length of said area as measured between said two end edges, said antenna comprising a wire making at least one pass along said wire path, such pass consisting of a plurality of loops each of which loops includes one portion extending generally along one of said one edges and another portion extending along a respective one of said plurality of lines.

13. An antenna as defined in claim 12 further characterized by said wire being disposed in a number of passes around said wire path.

14. An antenna as defined in claim 12 further characterized by said wire being part of a multi-conductor cable, said cable making one complete pass along said wire path.

15. An antenna as defined in claim 14 further characterized by said multi-conductor cable having two adjacent ends across which ends its individual conductors are connected together to form a single plurality of series connected passes around said wire path.

16. An antenna as defined in claim 14 further characterized by said multi-conductor cable having two adjacent ends across which ends its individual conductors are connected together to form a plurality of parallel connected sets of passes around said wire path.