Identification sensor for works buried at great depth

Abstract

A transponder for a RFID-type wireless communication and contactless identification system configured to be affixed to (or close to) structure intended to be buried, said transponder comprising: a set of antenna segments consisting of electrical wires constituting at least a first and a second antenna element (203-1, 203-2), a circuit board comprising a RFID chip and at least one tuning capacitance (202x) as well as coupling means (281) allowing the electrical coupling of said antenna segments;
characterized in that said antenna segments are arranged close to each other, at a distance of less than 3 mm and preferably less than 1 mm, so as to allow the appearance of coupling capacities (280) capable of widening the band of tolerance on the RFID resonance frequency.

Claims

1. A transponder for a RFID-type wireless communication and contactless identification system configured to be affixed to a structure intended to be buried, said transponder comprising: a set of antenna segments consisting of electrical wires constituting at least a first and a second antenna element (203-1, 203-2), a connector (281) comprising a RFID chip and at least one tuning capacitance (202x) as well as coupling means allowing the electrical coupling of said antenna segments, wherein the connector further includes: a first (284-1), second (284-2) and third input electrodes (284-3) for connecting a first end of a first (701), second (702) and third (703) antenna segments, respectively; a fourth (285-1), fifth (285-2) and sixth (285-3) output electrode for connecting a second end of said first (701), said second (702) and said third (703) antenna segment; a first circuit (286-3) for connecting the first input electrode (284-1) to the sixth output electrode (285-3) via an RFID chip; a second circuit (286-1) for connecting the second input electrode (284-2) to the fourth output electrode (285-1); and a third circuit (286-2) for connecting the third input electrode (284-3) to the fifth output electrode (285-2) via a capacitance (202x); wherein said antenna segments are arranged close to each other, at a distance of less than 3 mm and preferably less than 1 mm, so as to allow the appearance of coupling capacities capable of widening the band of tolerance on the RFID resonance frequency.

2. The transponder according to claim 1, characterized in that the antenna segments are arranged in a same plane, concentrically, and electrically connected to said connector (281), wherein two immediately adjacent antenna segments are arranged at a distance less than 3 mm, and preferably 1 mm, so as to allow the appearance of coupling capacitors capable of widening the tolerance band on the RFID resonance frequency.

3. The transponder according to claim 1, characterized in that the antenna segments have planes superimposed on each other, in which two immediately adjacent antenna segments are situated at a distance of less than 3 mm and preferably less than 1 mm allowing the appearance of coupling capacitors capable of widening the tolerance band on the RFID resonance frequency.

4. The transponder according to claim 1 characterized in that the antenna segments are arranged in order to form a twist (282) allowing the appearance of coupling capabilities that can expand the tolerance band on the RFID resonance frequency.

5. The transponder according to claim 1 characterized in that said antenna segments are grouped by two or more within the same conductor cable with two or more conductors, in order to show a linear capacitance between each of the antenna segments between 50 and 75 pF/m.

6. The transponder according to claim 1, characterized in that said first, second and third antenna segments (701, 702, 703) are integrated within the same tri-wire cable making it possible to generate a capacitance distributed between said segments of antenna.

7. The transponder according to claim 1 one of the preceding claims, characterized in that it comprises means of communication of the identity, as well as the characteristics of the buried work (date of burial, nature of the work, material, etc.).

8. The transponder according to claim 1 one of the preceding claims, characterized in that it is configured to allow the identification of a fluid distribution line (e.g., drinking water) or gas, electrical cable protection or fiber cable optical.

9. The transponder according to claim 1 one of the preceding claims, characterized in that it is adapted to be arranged in an autonomous housing fixed to the tube by clipping, welding or clamping.

10. A transponder for a RFID-type wireless communication and contactless identification system configured to be affixed to a structure intended to be buried, said transponder comprising: a set of antenna segments consisting of electrical wires constituting at least a first and a second antenna element (203-1, 203-2), a connector (281) comprising a RFID chip and at least one tuning capacitance (202x) as well as coupling means allowing the electrical coupling of six antenna segments (801-806), the connector further includes: a first (284-1), a second (284-2), a third (284-3), a fourth (284-4), a fifth (284-5) and a sixth input electrode (284-6) for connecting a first end of a first (801), a second (802), a third (803), a fourth (804), a fifth (805)) and a sixth (806) antenna segment, respectively; a seventh (285-1), an eighth (285-2), a ninth (285-3), a tenth (285-4), an eleventh (285-5) and a twelfth (285-6) electrode of an output for connecting a second end of said first (801), second (802), third (803), fourth (804), fifth (805) and sixth (806) antenna segments, respectively; wherein said integrated circuit comprises: a first circuit (286-7) for connecting the first input electrode (284-1) to the twelfth output electrode (285-6) via an RFID chip; a second circuit (286-1) for connecting the second input electrode (284-2) to the seventh output electrode (285-1); a third circuit (286-2) for connecting the third input electrode (284-3) to the eighth output electrode (285-2) via a capacitor (202x); a fourth circuit (286-3) for connecting the fourth input electrode (284-4) to the ninth output electrode (285-3); a fifth circuit (286-4) for connecting the fifth input electrode (284-5) to the tenth output electrode (285-4); and a sixth circuit (286-5) for connecting the sixth input electrode (284-6) to the eleventh output electrode (285-5); wherein said antenna segments are arranged close to each other, at a distance of less than 3 mm and preferably less than 1 mm, so as to allow the appearance of coupling capacities capable of widening the band of tolerance on the RFID resonance frequency.

11. The transponder according to claim 10, characterized in that said first, second and third antenna segments (801, 802, 803) are integrated within a first three-wire electrical cable and in that said fourth, fifth and sixth Antenna segments (804, 805, 806) are integrated within a second three-wire electrical cable.

Description

DESCRIPTION OF THE DRAWINGS

(1) Other characteristics, objects and advantages of the invention will appear on reading the description and the drawings below, given solely by way of non-limiting examples. In the accompanying drawings:

(2) FIG. 1 illustrates the conventional structure of a RFID transponder based on the parallel connection of an antenna, an RFID chip and a capacitor.

(3) FIG. 2 illustrates the conventional structure of an RFID transponder based on the serial connection of an antenna, an RFID chip and a capacitor.

(4) FIGS. 3 and 4 illustrate two variants of a known architecture of an RFID transponder comprising a coupler 103 for connecting the RFID chip to the resonant element.

(5) FIG. 5 illustrates the electrical diagram of an embodiment of an RFID transponder comprising an RFID chip and a plurality of antenna elements.

(6) FIG. 6a shows an embodiment of a first topology of antenna segments that are concentrically arranged.

(7) FIG. 6b shows an embodiment of a second topology consisting of a superposition of the different antenna segments along an axis perpendicular to the surface of the different antenna segments.

(8) FIG. 6c shows an embodiment of a third topology consisting in twisting together the different antenna segments so as to form a twist

(9) FIG. 7a illustrates a first embodiment of a printed circuit comprising two antenna elements consisting of three antenna segments.

(10) FIG. 7b illustrates a second embodiment of a printed circuit also having two antenna elements consisting of six antenna segments.

(11) FIG. 7c illustrates the connection of the first embodiment of the connector of FIG. 7a in which the three antenna segments are made by means of a single tri-conductor cable.

(12) FIG. 7d illustrates the connection of the second embodiment of the connector of FIG. 7b in which the six antenna segments are made by means of tri-conductor cables.

(13) FIGS. 8a, 8c, 8d show the tolerance on the tuning frequency, resulting in a difference of less than 10 cm over the maximum detection distance

(14) FIG. 8a illustrates the maximum reading distance vs. frequency curves for embodiments M1 and M2.

(15) FIG. 8c illustrates the maximum reading distance vs frequency curve for embodiment M4.

(16) FIG. 8d illustrates the maximum reading distance vs frequency curve for embodiment M3.

(17) FIG. 8b illustrates measurements of frequency offsets as a function of temperature variations.

(18) FIG. 9 illustrates the block diagram of the solution recommended by the above-mentioned patent application WO 2011157941

DESCRIPTION OF A PREFERRED EMBODIMENT

(19) We will now consider a particular embodiment of an RFID transponder for carrying out a RFID tag for a pipe or pipe which is intended to be buried underground. For instance, one may consider a High Density Polyethylene pipe, specifically designed for the construction of a pipeline for the supply of drinking water, the distribution of gas, the purification, the protection of electrical cable and optical fiber.

(20) In particular, it is possible to consider the example of a polyethylene multilayer pipe designed to realize an network of pipes under pressure and buried underground, consisting of a PE80 or PE100 high density polyethylene tube according to the EN1555 standard. More specifically, the RFID tag will be used providing information representative of the tube identification, the tube manufacturing process and also the tube location.

(21) As shown in FIG. 5, illustrating the electrical diagram of one embodiment according to the invention, the RFID transponder consists of a resonant system, which comprises an antenna 291, consisting of a serial connection of antenna elements 203-1, 203-2, . . . 203-x, capacitors 202-1, 202-2 . . . 202-x, wire in series with a conventional RFID chip 201. The RFID chip is an integrated circuit adapted for the implementation of wireless communication and contactless identification techniques referred to as Radio Frequency Identification Detection (RFID), which is well known to a person skilled in the art and, for the sake of conciseness, will not be described further.

(22) In the embodiment illustrated in FIG. 5, each end of an antenna element is connected to either a capacitor 202-1, 202-2, . . . 202-x, or to an electrode of the RFID chip 201.

(23) In general, each antenna element is composed of one or more individualized electrical conductive wires—or antenna segments designated by the generic reference 200x (not shown in FIG. 5), each of which consists of at least one significant fraction of a loop, constituting the sensing element. A first antenna segment may be, for example, consisting of a half-loop. A second antenna segment may consist of a whole loop. A third antenna segment may consist of a loop and a half. A fourth of two loops etc.

(24) Thus, the antenna elements 203-1, . . . 203-x can achieve a variety of configurations, based on multiple combinations of antenna segments 200x.

(25) In general, each antenna segment 200x consists of an electrical wire, insulated or not, arranged within a multi-strand or single-stranded cable. The wire section may vary. Each antenna segment 200x may differ from one another within a same embodiment, both by the geometry and also by the number of loops, thus allowing great possibilities of different configurations for the RFID tag.

(26) With regard to the capacitors 202-1, 202-2, . . . 202-x shown in FIG. 5, it should be noted that these can take very different forms. In particular, a capacity 202-x is not necessarily restricted to a single element, but can be conceived as a serialization and/or parallelization of several individual capacities, forming according to the rules of art the equivalent of a unique ability. In the same way, it will be noted that the capacities 202-1, 202-2, 202-x may be of different value.

(27) The antenna segments 200x composing the antenna elements 203-1, 203-x may be arranged on a support according to different embodiments, as illustrated in FIGS. 6a, 6b and 6c.

(28) More specifically, FIG. 6a illustrates a first layout topology of the antenna segments 200x which is based on a concentric arrangement of three antenna segments 200x being electrically connected to a printed circuit board 281. In this configuration, the three antenna segments have a circular shape, arranged in the same plane, and are arranged very closely. Two immediately adjacent antenna segments are located at a distance of less than 3 mm and preferably 1 mm to allow the occurrence of coupling capacitance 280 illustrated in FIG. 6a.

(29) A second topology is illustrated in FIG. 6b where one sees the superposition of different antenna segments—e.g. three antenna segments—along an axis perpendicular to the surface of those antenna segments. As previously, the three antenna segments, are electrically coupled to the printed circuit or connector 281, and are arranged very closely, preferably at a distance of less than 1 mm, to show an appearance of coupling capacitors also represented in the FIG. 6b, by the reference 280.

(30) Finally, FIG. 6c illustrates a third topology wherein the different antenna segments 200x constituting the antenna elements 203-1 . . . 203-x are twisted together to form a twist 282 which may be overmolded to form a single sheath 283 coupled to a printed circuit or connector 281. In this configuration, it is the fact of twisting the various antenna segments constituting the antenna elements that makes it possible to show an appearance of coupling capacitors whose interest will appear, with force, in the description below.

(31) The topologies illustrated in FIGS. 6a, 6b and 6c are only illustrative examples of the multiple possibilities of arrangements which may be considered for carrying out a

(32) RFID tag according to the present invention. In general, a person skilled in the art will be able to design a combination of the various topologies illustrated above, such as for example, two distinct groups of antenna segments of 3 loops, each made according to the topology of FIG. 6c, and the two groups being by the assembled sequence following the topology of FIG. 6b.

(33) Clearly, there is no limit to the possibilities of combining the different topologies illustrated.

(34) Referring now to FIGS. 7a, 7b, 7c and 7d, there will now be more particularly described the connector 281 which allows the electrical coupling of the antenna segments to the oscillating element of the RFID transponder.

(35) Generally speaking, connector 281 is configured so as to allow the electrical coupling of the different antenna segments to each other, but also to the capacitors 202-1, 202-2, . . . 202x, as well as to the RFID chip 201, so as to implement the resonant element whose electrical diagram is shown in FIG. 5.

(36) In its simplest form, the connector may be in the form of an integrated circuit on which is located RFID chip 201, as well as the different capacitors 202-1, 202-2, . . . 202x.

(37) For the sake of simplicity, in the embodiments shown in FIGS. 7a-7d, there is provided one single capacitor 202x associated with a RFID chip, so that FIGS. 7a-7d represent, in accordance with the diagram illustrated in FIG. 5, a arrangement of two antenna elements (two disconnections in the serial connection, a first one for the RFID chip and a second one for capacitor 202x).

(38) The different antenna segments are electrically coupled via electrodes 284 and 285, which may be any number.

(39) For example, connector 281 of FIG. 7a takes the form of a printed circuit comprising a set of three input electrodes, respectively 284-1, 284-2, 284-3, and three output electrodes, 285-1, 285-2 and 285-3, for the respective coupling of three antenna segments 701, 702, 703 constituting the antenna 291.

(40) The Circuit Board/Connector Comprises:

(41) a first input electrode 284-1, a second input electrode 284-2 and a third input electrode 284-3 which allow the coupling of a first end of first segment 701, a first end of second segment 702 and a first end of third antenna segment 703, respectively; a fourth output electrode 285-1, a fifth output electrode 285-2 and a sixth output electrode 285-3 which allow the coupling of a second end of first antenna segment 701, a second end of second antenna segment 702 and a second end of third antenna segment 703, respectively.
The Printed Circuit further Comprises: a first circuit 286-3 for connecting the first input electrode 284-1 to the sixth output electrode 285-3 via an RFID chip; a second circuit 286-1 for connecting the second input electrode 284-2 to the fourth output electrode 285-1; a third circuit 286-2 for connecting the third input electrode 284-3 to the fifth output electrode 285-2 via the capacitor 202x.

(42) In a preferred embodiment which is illustrated in the diagram of FIG. 7c, the first, second and third antenna segments 701, 702, 703 are integrated within the same three-conductor electric cable making it possible to generate a capacitance distributed between said antenna segments.

(43) Referring to FIG. 7b, there will now be described a second embodiment of a printed circuit having a connector 281 configured for the coupling of six antenna segments 801, 802, 803, 804, 805 and 806.

(44) More specifically, the printed circuit comprises a first input electrode 284-1, a second input electrode 284-2, a third input electrode 284-3, a fourth input electrode 284-4, a fifth electrode 284-5 input and a sixth input electrode 284-6 for connecting a first end of a first antenna segment 801, a first end of a second antenna segment 802, a first end of a third antenna segment 803, a first end of a fourth antenna segment 804, a first end of a fifth antenna segment 805 and a first end of a sixth antenna segment 806, respectively.

(45) The printed circuit further comprises a seventh output electrode 285-1, an eighth output electrode 285-2, a ninth output electrode 285-3, a tenth output electrode 285-4, an eleventh output electrode 285-5 and a twelfth output electrode 285-6 for respectively connecting a second end of the first antenna segment 801, a second end of second antenna segment 802, a second end of third antenna segment 803, a second end of fourth antenna segment 804, a second end of fifth antenna segment 805 and a second end of sixth antenna segment 806.

(46) The Printed Circuit of FIG. 7b Comprises:

(47) a first circuit 286-7 for connecting the first input electrode 284-1 to the twelfth output electrode 285-6 via a RFID chip; a second circuit 286-1 for connecting the second input electrode 284-2 to the seventh output electrode 285-1; a third circuit 286-2 for connecting the third input electrode 284-3 to the eighth output electrode 285-2 via the capacitor 202x; a fourth circuit 286-3 for connecting the fourth input electrode 284-4 to the ninth output electrode 285-3; a fifth circuit 286-4 for connecting the fifth input electrode 284-5 to the tenth output electrode 285-4; a sixth circuit 286-5 allowing the connection of the sixth input electrode 284-6 to the eleventh output electrode 285-5.

(48) Preferably, the first, second and third antenna segments 801, 802 and 803 are integrated within a first three-conductor electrical cable and the fourth, fifth and sixth antenna segments 804, 805 and 806 are integrated in within a second three-conductor electrical cable, as illustrated in the embodiment of FIG. 7d.

(49) The arrangement of the antenna segments (200x) implemented in one of the embodiments (FIGS. 6a, 6b and 6c), or any combination thereof, causes a capacitive coupling (280) to occur between each conductor (antenna segment) (200x), more or less important according to the embodiments. The distributed capacitors (280) are created either naturally by the proximity of electrical wires, or by the effective implementation of capacitors. Moreover, the presence of an outer envelope (overmoulding) (283) can further increase the value of the distributed capacitance. It is this capacitive coupling which ensures a rather strong immunity to the dispersion stresses, as well as to the dispersive influences of the external environments.

(50) The structure of the antennas is determined so that the wires are spaced from 1 to 3 mm. In one embodiment, the wires are overmoulded 3 by 3 strands, with a component having ϵ.sub.r≅5. This gives a linear capacitance (280) between the three wires, when considered two by two, of between 50 and 75 pF/m.

(51) Operation and Adaptation of the Resonance Frequency, Resistance to Tolerances and Variations

(52) The plurality of antenna segments 200x forms the sensing surface. This surface must be sufficient to meet the power supply requirement of RFID chip 201. The total number of loops resulting from the plurality of antenna segments is such that the voltage across RFID chip 201 is sufficient to activate it.

(53) The frequency tuning is the result, firstly, of the serialization of the inductance of the global antenna (plurality of 200x) and also the plurality of capacitors 202x when coupled in series.

(54) However, the distributed capacitors 280, although having a small impact on the resonance frequency, nevertheless play a role in the calculation of the tuning capacity.

(55) But the true role of these distributed capacitors 280 is, on one hand, to attenuate the influence of the parasitic capacitances introduced by the external environment, and, on the other hand, to allow a widening of the tolerance on the tuning frequency as evidenced by the tests which were performed.

(56) On some examples of realization, we will look at which tuning frequency range one can obtain a decrease of less than 10 cm of the maximum detection distance with respect to the maximum distance expected. One experiment relates to the embodiment made according to the teaching of the aforementioned patent applications WO2011157941 and US 2009/0027208; another test relates to an embodiment (M1) being closer to the present invention, but whose gap between the loops is voluntarily set to a larger value than recommended (10 mm), while two other embodiments (M2, M3) relate to the invention.

DESCRIPTION OF TEST ACHIEVEMENTS

(57) Tag M1: the embodiment is closed to the schematics of FIG. 7c, but with an inter loop of 10 mm (thus with a very low distributed capacity), for a surface of 702 cm2.

(58) With the implementation M1, we have:

(59) f.sub.M1,min=13.530 MHz and f.sub.M1,max=13.740 MHz, thus Δ.sub.M1=210 kHz

(60) Tag M2: this embodiment is in accordance with FIG. 7c, based on a three-wire cable, for a surface of 702 cm.sup.2, one obtains:

(61) f.sub.M2,min=13.495 MHz and f.sub.M2,max=13.825 MHz, thus Δ.sub.M2=330 kHz

(62) This represents a 50% improvement in the tolerance band between M1 and M2.

(63) Tag M4: Embodiment according to the teaching of the above-mentioned patent applications WO2011157941 and US 2009/0027208, for a surface area of 132 cm.sup.2.

(64) An estimate of the width of the tolerance band was made (FIG. 8c), and the estimate is obtained:

(65) f.sub.M4,min=13.535 MHz and f.sub.M4,max=13.810 MHz, thus Δ.sub.M4=275 kHz

(66) Tag M3: this embodiment complies with FIG. 7d, composed of two cables comprising each three wires, thus forming a total of two groups of three loops, for a surface being 63 cm.sup.2.

(67) The tolerance range could be determined, as illustrated in FIG. 8d:

(68) f.sub.M3,min=13.550 MHz and f.sub.M3,max=13.940 MHz, thus Δ.sub.M3=390 kHz

(69) This represents an increase of more than 40% of the tolerance band.

(70) In addition, in this embodiment (M3), the antenna area is 63 cm.sup.2, compared with 132 cm.sup.2 of the solution described in the aforementioned patent applications WO2011157941 and US 2009/0027208, yielding a detection distance increased by 20 cms (180 cm instead of 160 cm). In one embodiment that was described above, a reading distance of 144 cm was obtained with a surface of 19.6 cm.sup.2. From an interpolation curve (calculated from various embodiments), it could be estimated that an area of 23.25 cm2 was necessary to reach a distance of 150 cm, ie 6 times less surface than the solution recommended in the aforementioned patent applications WO2011157941 and US 2009/0027208.

(71) As can be seen, the invention therefore makes it possible to significantly increase the tolerance range of the tuning frequency, for a same difference in maximum reading distance. In addition, one obtains an increased energy efficiency, since less sensing surface is required compared to conventional tags for the same maximum detection distance. The antenna segments can also be grouped by two or more within a same conductive cable with two or more wires, in order to show a linear capacitance between each of the antenna segments of a value between 50 and 75 pF/m.

(72) It will also be possible to provide a transponder comprising a printed circuit comprising a connector (281) allowing the connection of three antenna segments 701, 702, 703.

(73) The transponder may include means of communication of the identity, as well as the characteristics of the buried work (date of burial, nature of the work, characteristics of the material, . . . ). It may be configured to allow the identification of a fluid distribution line (eg drinking water) or gas, electric cable protection or optical fiber cable.

(74) It may be adapted to be arranged in an autonomous housing fixed to the tube by clipping, welding or clamping.