KR20020090235A - Antenna for contact-free transmission/reception reading system - Google Patents

Abstract

Includes a reader designed to detect the identity of a controlled access area or an electromagnetic response signal emitted from a portable non-contact object such as an ISO type card or disposable ticket 46 as an antenna inside the access system; The electromagnetic response signal is emitted by an antenna 48 located inside the portable object in response to the receipt of the electromagnetic signal emitted by the reader antenna when the holder presents the portable object in front of the reader. The antenna comprises n winding groups 20, 22, 24 and n winding groups 20, 22, 24 are arranged in series and each winding group k-1 (k varies from 2 to n) is a winding group. It has a smaller number of windings N _k-1 than the winding number N _k on k, located off the winding group k by a larger value of the distance D _k-1 than the prescribed value, the winding in every group is wound in the same direction.

Description

Contactless transceiver system reader antenna {ANTENNA FOR CONTACT-FREE TRANSMISSION / RECEPTION READING SYSTEM}

Portable objects are used to identify holders or to access areas where access is controlled, such as public transport networks, French RATP metro networks or SNCF railway networks, and in the future standard contact-type objects There will be an increase in what is known as contactless technology as opposed to -type objects (cards or tickets).

The exchange of information between the contactless object and the reader is generally done in such a way as to generate a remote electromagnetic coupling between the first antenna mounted on the portable contactless object and the second antenna mounted on the reader. Furthermore, the contactless object is equipped with an electronic module, which is characterized by the first antenna comprising a radio-frequency (RF) part among other components and which must be provided to the reader. It contains the logical functions necessary to compile the information to be stored and transmitted and to process the received information.

In areas where controlled areas such as public transport networks are involved,

In fact, there are two groups of users: the permanent users and the occasional users. For the first group, an ISO format contactless smart card is the best solution, since the cost of manufacturing a card distributed over the total number of trips made over a long period of time will always be low for the user. It is true. However, the manufacturing cost of the card in relation to the travel cost for the second group is too expensive because such a user is a temporary user who may need to purchase a card for only one trip.

Along with the ISO format card, there is a portable ticket which is the main content of French Patent Application No. 99908802, which is smaller in size than the ISO card and the ISO card is not transferable, whereas the ticket is transferable. Of course, a small format reduces the size of the antenna surface area on the ticket and requires more operating energy than an ISO format card.

As long as the reader needs to operate on both ISO format cards and negotiable tickets, the energy supplied by the reader should be sufficient even if the ticket is disposable by a non-contact object placed in front of the reader. Conventional reader antennas constructed in multiple wound forms are sufficient for contactless objects of ISO format card size, although not sufficient for ticket sized contactless objects.

The solution to the above problem is to configure a high field inside the antenna, which increases the number of turns designed to increase the vertical component of the magnetic field emitted in as many small loop areas as possible. This will add a small loop to the antenna. Unfortunately, such antennas create an ergonomic complication, in the case of disposable tickets, the tickets must function correctly in the area of a small loop. Moreover, the vertical component of the magnetic field generated by the small loop inside the reader antenna is in the opposite direction to the magnetic field produced by the winding direction of the antenna in phase. The above structure results in a significant operational void for ISO format cards when encountering small loops.

Furthermore, the prior art card readers disclosed in EP 0.766.200 or US Pat. No. 4,922,261 do not deal with these problems; Instead, these prior arts deal with the problem of exposure between the reader's transmit and receive antennas, in order to create a phase out of phase in such a way that the mutual inductance for the other antenna is zero. phase opposition relates to aligning one of two antennas with two turns directions wound in opposite directions. Unfortunately, such a solution does not solve the problem presented unless the resulting magnetic field is uniform throughout the reader.

The present invention relates to a transmission / reception system using a reader designed to detect an electromagnetic signal emitted by a portable contactless object, the detection of the electromagnetic signal being emitted by an antenna located inside the reader. The present invention is made in such a way as to detect an electromagnetic signal emitted by a portable non-contact object by presenting a portable non-contact object on the front of the reader in response to the received electromagnetic signal. An antenna (a reader antenna of a contactless transceiver system).

Objects, configurations, and features of the present invention will be more clearly understood by the drawings described below, and the accompanying drawings show the following items.

Figure 1 shows a conventional card reader having several turns of wire that indicates the value of the vertical component of the magnetic field depending on the position of the various antennas. In the description herein, 'magnetic field' refers to a magnetic field component perpendicular to the plane of the antenna.

2 shows a card reader antenna according to the invention consisting of two winding groups.

Figure 3 shows the position of the vertical strands of the reader antenna winding according to the invention, characterized by three winding groups.

4 shows a graph showing the value of a magnetic field at any point located at a distance x away from an infinitely long metal conductor through which current flows.

5A, 5B and 5C show the magnetic field generated by the exterior group of turns, the magnetic field generated by the inner group and the resulting magnetic field, respectively.

6 shows a magnetic field generated by a reader antenna with a single group of peripheral turns.

Figure 7 shows a graph showing the magnetic field generated by a reader antenna having several winding groups that meet the conditions presented in the present invention.

8 shows a graph showing a magnetic field generated by a reader antenna having several winding groups that do not meet the conditions presented in the present invention.

The main subject of the present invention is a reader antenna for a contactless identification or access system using either an ISO format card or a disposable ticket as a portable object. To provide.

It is another object of the present invention to ensure that the reader antenna on the contactless identification or access system has a somewhat uniform magnetic field over the entire surface of the reader.

It is an object of the present invention to provide a reader antenna within an identity control or access system into an access controlled area that includes a reader designed to detect electromagnetic response signals from a portable non-contact object such as an ISO type card or disposable ticket. For the purpose of providing, the electromagnetic response signal is emitted by an antenna located inside the portable object in response to receiving the electromagnetic signal emitted by the reader antenna when the holder of the portable object presents the portable object in front of the reader. The antenna comprises n turn groups arranged in series and each winding group (k-1) has a turn number N _k-1 which is the winding in turn group k It is smaller than the number N _k , k has various values from 2 to n, and winding group k-1 is installed at a distance D _k-1 from the winding group k, which is larger than a predetermined value. The windings in the group are wound in the same direction.

As shown in FIG. 1, the conventional antenna 10 has a plurality of turns 12, 14, and 16, and various magnetic fields are generated according to the position of the antenna 10. In this way, in the inner region of the winding, the magnetic field is positive while in the outer region of the winding it is negative. In the center part of the two windings, if one ignores the magnetic field generated by the other part of the winding, the magnetic field decreases inversely with distance and gives a positive magnetic field due to a turn strand and the same absolute value due to the other winding strand The total magnetic field is zero as a result of the negative magnetic field being added together.

Magnetic fields of varying magnitude depending on the location are very disadvantageous for the generation of electromagnetic signals emitted by the antenna. The surface of the reader in front of which the portable object is presented will generally be square (or rectangular) with one side size of 15 cm to 20 cm. If the antenna is positioned too precisely in the middle of this surface, there will be areas where the magnetic field becomes negative. However, if the winding of the antenna is on the periphery of the reader surface, the magnetic field will have a positive value over the entire reader surface (inside of the antenna), which is inversely proportional to the distance away from the winding. The same result occurs even if the magnetic field is reduced to a larger value. A dead zone exists at the center of the surface. If a portable object is presented in such an area, the portable object will not receive enough energy. Moreover, a solution using a configuration that significantly increases the number of windings to amplify the magnetic field is not effective as long as the magnetic field becomes zero as well as the surface area occupied by the windings increases.

Therefore, the method proposed by the present invention consists in the use of an antenna comprising n turn groups connected in series, where each winding group k (k varies from 1 to n-1) is a group k + Included in 1, the end of the outer turn in group k is connected to the end of the inner turn in group k + 1. The number of turns in group k has a value smaller than the number of turns in group k + 1. As a result, the windings in all winding groups are wound in the same direction, for example from group 1 to group n in the counterclockwise direction.

As an embodiment, two groups are shown in FIG. 2 where the first winding group 20 includes two squares and the second group 22 is four squares away from the other group by a distance D. FIG. It includes.

3 shows the left-hand vertical strands of three consecutive winding groups 40, 42, 44, the magnetic field produced by the winding group 40 being the winding group 40. Has a negative value outside the left region of, i.e. However, the presence of the winding group 42 surrounding the winding group 40 causes a positive magnetic field to be generated in the inner region of the winding and in particular to be formed between the group 40 and the group 42.

In general, the magnetic field induced by a 1 m wide metal wire when current I flows has a varying value in the form of a curve as shown in FIG. The magnetic field has a value of zero at the center of the wire. If we assume that the origin of abscissas is the center of the wire, the magnetic field will increase rapidly and reach a relatively constant value according to the form expressed in the equation below:

_{0 <x≤l m H 1 = K} 1 × (I / 2πl m) with respect to the.

Next, the value of H decreases according to the inverse function of the abscissa according to the following formula:

for x> l _m , H ₂ = K ₂ × (I / 2πx).

The value of the magnetic field generated by a group of N turns is:

H = 0 for x = 0

H = K ₁ × (NI / 2πl _m ) for 0 <x≤l _m

H = K ₂ × (NI / 2πx) for x> l _m .

3, the value of the magnetic field generated by each of the winding groups 40, 42, which are located at regular intervals in the two groups, is represented by the curves shown in FIGS. Assume that it is located in the center of the group 42. As shown in FIG. 5A, the magnetic field H ₁ generated inside the winding group 42 is positive, while the magnetic field—H ₂ generated outside of the winding group 40 as shown in FIG. 5B is negative. Note that it has a value of.

The value H _R of the synthesized magnetic field generated by the two windings in the space between the winding groups 40 and 42 formed in the above manner is the arithmetic sum of the magnetic fields shown in FIGS. 5A and 5B. The value of the above synthetic magnetic field is represented by the following equation, as shown in Figure 5c:

H _R = H ₁ -H ₂ .

As can be seen from FIG. 5, the value of the synthesized magnetic field initially has a positive value, and then the negative value starts from the distance D ₁ ′ away from the winding group 42. If the composite magnetic field is not significantly larger than the difference between D ₁ and D ₁ ′ to be negative and is not significantly smaller than the minimum order of the antenna placed on the disposable ticket, This result is not a major topic of interest if the average value of the magnetic field received by M is maintained at a positive value and must be larger than the minimum value needed to ensure ticket operation. However, by selecting the same distance D ₁ , at which the two winding groups are separated, as D ₁ ′, the area described above can be reduced to zero, and in this way the magnetic field is always positive in the area between the two winding groups. It can have a value of. In order to be as above, the maximum absolute value of the negative magnetic field -H ₂ must be less than or equal to the minimum absolute value of the positive magnetic field + H ₁ and is approximately expressed as follows;

K ₁ × (N ₁ I / 2πl _m1 ) ≤K ₂ × (N ₂ I / 2πD ₁ ) or

K ₁ · N ₁ · D ₁ ≤ K ₂ · N ₂ · l _m1 .

As an initial approximation, if both coefficients K ₁ and K ₂ are allowed to be the same, the following results are obtained:

N ₁ · D ₁ ≦ N ₂ · l _m1 ,

Since _m1 is less than D ₁ , the inequality of the above equation is satisfied by selecting the appropriate values for N ₁ and N ₂ to have the relationship

(N ₂ / N ₁ ) ≥ (D ₁ / l _m1 ), or more generally, between two consecutive winding groups k and k-1 (k has a value between 2 and n) By choosing the right value to do, the above inequality holds:

(N _k / N _k-1 ) ≥ (D _k-1 / l _mk-1 ).

The positive magnetic field generated by the winding group 42 is added to the positive magnetic field generated by the winding group 40 inside the winding, even if in a smaller range, as long as the magnetic field gets further away from the winding 42. do. Similarly, winding 44 surrounds winding 42. As a result, the amount generated by the winding group 44 within the windings compensates for the negative magnetic field generated by the winding group 42 in the region located between the two winding groups (this is the winding group). The same is true for the negative magnetic field generated by (40)). This supplementation of the negative magnetic field is generated in this region if the positive magnetic field or at least a positive mean field is sufficient. Be sure to It should be noted that the positive magnetic field generated by the winding group 44 is added to the positive magnetic field generated by the group 42 inside the winding group 42, but becomes weaker as the distance gradually increases.

The windings of a plurality of n groups with increasing number of turns may be recursively placed on the antenna support to cover the total antenna surface area of the reader. However, there is a parameter that defines the number of winding groups n at the antenna: this parameter is the distance between the groups, ie the distance D ₁ between the first and second groups _, the second group and three These parameters are the distance D ₂ between the first group, and finally the distance D _n-1 between the n-1 and n groups. Such distance D ₁ (distance between group 40 and group 42) or D ₂ (distance between group 42 and group 44) should be optimal. As mentioned in Figure 1, the above distances should not be too small to prevent the build-up of magnetic fields near the midpoint. However, this distance should not be too large so that the positive magnetic field is high enough to compensate for the negative magnetic field generated by the winding group that is externally preceded.

There is also a determining parameter for setting the condition of the antenna structure according to the invention. The disposable ticket must receive a positive average magnetic field at all points of the reader, especially when it is present on the winding group where the generated magnetic field is zero. As a result of the above, the smallest side of the ticket antenna must be larger than the width of each winding group as shown in FIG. 3, in which the width of the antenna 48 on the ticket 46 is It is shown larger than the overall width of the widest winding group 44. The closer you get to the antenna's periphery, the more the number of windings increases, so when passing from one group to another, it is essential that the metal width of the windings decreases. To always be smaller than the minimum order of antennas on the ticket. As a result, the following inequality that applies to the embodiment shown in FIG. 2 is added:

(N ₂ / N ₁ ) ≥ (D ₁ / l _m1 )

(N ₃ / N ₂ ) ≥ (D ₂ / l _m2 ),

The following inequality must also be true:

l _m1 > l _m2 > l _m3 .

While the above mentioned inequalities should always be taken into account, the more the number of windings of the outer group, for example N ₃ , increases, the more the distance the group separates from adjacent inner groups, for example D _2. It is clear that it can be.

Note that the distance d separating the two windings in each winding group should be as small as possible, which is the minimum distance delegated to the conditions of turn fabrication. More generally, such distance d is the order of magnitude less than distance D. In other words, the ratio between the distance D and the distance d should be greater than the predetermined optimal ratio. As a result, if the inter-turn width is a given value d, this means that the distance D must be greater than a predefined value.

As described above, due to the continuously formed winding groups, a magnetic field high enough for the reader can be obtained for both the card and the disposable ticket. Moreover, such an arrangement also allows a relatively uniform magnetic field to be obtained over the entire surface of the reader, where the resulting magnetic field exceeds a predetermined value within a range not exceeding a standard value applicable to a noncontact object. I never do that. These facts are demonstrated by the three embodiments illustrated in Figs. 6, 7, and 8, in which the origin of the abscissa is located in the center of the reader and the following is considered:

Disposable tickets feature a square antenna with a size of 2cm x 2cm,

The reader has a size of 20 cm x 20 cm,

The minimum magnetic field to be generated for the card is 0.8 A / m,

The minimum magnetic field for disposable tickets is 2 A / m,

The permissible value of the magnetic field is 7.5 A / m,

The current through the windings is 50 mA.

1. In the first embodiment shown in FIG. 6, the reader is characterized by a simple antenna and the antenna consists of four concentric turns formed around the reader, the metal width of the winding being 1 mm and between the windings. The inter-turn distance is 1 mm.

Note that the maximum magnetic field at the periphery is 15 A / m and the magnetic field is only 0.8 A / m near the center of the reader, which is high enough for a card reader but not high enough for disposable tickets. do.

2. In the second embodiment shown in FIG. 7, the antenna of the reader consists of three winding groups according to the device of the present invention:

-The first group of two wounds, measuring 6 cm by 6 cm, with a metal width of 0.3 cm and a width of 0.1 mm between the windings;

The second group of four windings, measuring -17 cm x 17 cm, has a metal width of 0.3 cm, and a winding width of 0.1 mm.

-The third group of six windings, measuring 20cm x 20cm, the width of the metal being 1mm and the width of the windings to be 0.1mm.

It should be noted that the minimum magnetic field is 2 A / m, which is high enough to read a disposable ticket or card, and the maximum magnetic field is 7.5 A / m, which is equivalent to the limit threshold.

3. In the third embodiment shown in FIG. 8, the antenna of the reader is similar to the second embodiment, but 0.3 mm is used for the third group of windings instead of 1 mm for the width of the metal.

Note that the magnetic field can be negative in the space between the second and third groups; This is due to the fact that the number of turns in the third group is more than that in the second group, but the metal width of the third group does not decrease.

Claims (7)

A reader capable of sensing electromagnetic response signals emitted from a non-contact portable object, such as an ISO type card or a disposable ticket, the electromagnetic response signal being a Identification of an access-controlled area emitted by an antenna located inside the portable object in response to receiving an electromagnetic signal emitted by the reader antenna when the holder presents the portable object in front of the reader; or An antenna on an access system, The antenna comprises n turn groups 20, 22, 24 and the winding groups are connected in series and each winding group k-1 has a turn number N _k-1 and N _k-1 is a value smaller than the number N _k wound on the winding group k, at the k may have a value of from 2 to n, winding group k-1 is a value greater than a predetermined value from the winding group k is provided at a position apart by D _k-1, all wound on the group antenna, characterized in that the wound in the same direction. The method according to claim 1, And the number n of winding groups corresponds to a sufficient number of winding groups for the antenna to cover the entire surface of the reader in which the portable object is presented in front. The method according to claim 2, And the number of winding groups is three (40, 42, 44). The method according to claim 1 to 3, Wherein all dimensions of the antenna located within the portable object are greater than the width of the turns forming any of the groups. The method according to claim 1 to 4, Inequality below; N _k / N _k-1 ≥D _k-1 / l _{m (k-1)} , where k is a value from 2 to n, l _mk-1 is the width of the metal forming the windings of group k-1 Represents; An antenna formed between these two consecutive turn groups k-1 and k (40, 42, 44). The method according to claim 1 to 5, Characterized in that the value of ratio D _k-1 / d is greater than the predetermined value for any value k varying from 2 to n, and d is a predefined value between two adjacent windings. antenna. The method according to claim 1 to 6, Wherein the reader is 20 cm by 20 cm and the disposable card comprises an antenna 48 having a size of 2 cm by 2 cm.