WO2023247821A1

WO2023247821A1 - Flexible circuit board for magnetic tracking

Info

Publication number: WO2023247821A1
Application number: PCT/FI2022/050468
Authority: WO
Inventors: Ilpo Valtteri HÄRKÖNEN
Original assignee: Aalto University Foundation Sr
Priority date: 2022-06-23
Filing date: 2022-06-23
Publication date: 2023-12-28

Abstract

A flexible circuit board (10) having a base film (13) is usable for a magnetic tracking system (100) comprising a sensing circuit (101), a transmitting coil (102), and a sensing coil (103) positioned at a point of interest (105) and being electrically connected to the sensing circuit for tracking the point of interest on the basis of changes in electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil. The flexible circuit board comprises a sensing coil mounting site (14) for being positioned at the point of interest (105), and a pair of conductive traces (16, 17) to electrically connect the sensing coil mounting site to a connection point (20) of the flexible circuit board, the conductive traces being formed on top of each other on the opposite sides of the flexible circuit board base film (13).

Description

FLEXIBLE CIRCUIT BOARD FOR MAGNETIC TRACKING

STATE OF THE ART

Magnetic tracking can be used to track position, orientation, and/or changes thereof of obj ects in various applications . For example, smart gloves that can detect and track finger ( s ) may be used as wearable user interface devices .

Magnetic tracking can be based on a transmitting coil generating an AC magnetic field, and a receiving or sensing coil coupled with the obj ect to be tracked for sensing the magnetic field generated by the transmitting coil . The flux of the changing magnetic field going through the sensing coil results in an AC current induced in a sensing circuit to which the sensing coil is connected . The magnetic field within the sensing coil depends on the distance of the sensing coil from the transmitting coil as well as the two coils ' mutual orientation . Therefore, the position and/or orientation of the sens ing coil can be determined on the bas is of the current induced in the sensing circuit .

In some applications , the electrical connections of the sensing coil ( s ) need be routed to pass the transmitting coil ( s ) . For example , in a smart glove , control electronics of the transmitting and receiving/sensing circuits may be positioned at the location of the back of the hand or the wrist . The transmitting coil may lie at the location of the knuckle , whereas the sensing coil may be positioned at or close to the fingertip such that the conductors connecting the sensing coil to the sensing circuit must pass the transmitting coil . Thi s kind of arrangement can result in the system generating interference from itself as the stronger magnetic field close to the transmitting coil may induce in the conductors a current which may disturb the measurement of the weaker magnetic field at the sensing coil ( s ) .

In the case of conventional conductor wires , wire twisting can be used to reduce the interference to some degree . On the other hand, twisting makes the electrical connections to the sensing coil s more complex to manufacture . In addition, to effectively decrease the interference , the twisting shall be made with high accuracy . On the other hand, the more interference there is present in the system, the larger the sensing coils have to be in order to maintain an acceptable signal-to-noise ratio . This may affect the usability of the magnetic tracking system especially in applications with limited space available for the system .

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description . This Summary is not intended to identify key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

In one aspect , a flexible circuit board having a base film is disclosed for a magnetic tracking system comprising a sensing circuit , a transmitting coil , and a sensing coil positioned at a point of interest and being electrically connected via a pair of conductors to the sensing circuit for tracking the point of interest on the basis of changes in electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil .

The flexible circuit board comprises a sensing coil mounting site for being pos itioned at the point of interest of the magnetic tracking system, and a pair of conductive traces to electrically connect the sensing coil mounting site to a connection point of the flexible circuit board .

Advantageously, the conductive traces are formed on the flexible circuit board base film so as to run parallel , preferably on top of each other on the opposite sides of the flexible .

In one embodiment, the flexible circuit board comprises at least two sens ing coil mounting sites for being positioned at the same point of interest , the at least two sensing coil mounting sites being positioned so as to enable sensing coils being mounted thereon to have their principal axes directed mutually differently upon bending of the flexible circuit board .

In one embodiment , the sensing coil mounting site has two conductor pads for a surface-mount device ( SMD) sensing coil .

In one embodiment , the flexible circuit board has an elongated portion, at least one sensing coil mounting site being located in the elongated portion to enable the point of interest of the magnetic tracking system to be coupled with a finger to track the finger .

In such embodiment , the flexible circuit board may have a plurality of elongated portions and at least one sensing coil mounting site located in each of the elongated portions to enable a plurality of points of interest to be coupled with a plurality of fingers , respectively, to track the plurality of fingers .

In one embodiment , the flexible circuit board base film has a thickness of less than or equal to 0 . 2 millimetres , for example , such as less than or equal to 0 . 1 mm, for example , about 0 . 08 mm .

In another aspect , the flexible circuit board is utili zed in a magnetic tracking system comprising a sensing circuit , a transmitting coil , and a sensing coil which is positioned at a point of interest of the magnetic tracking system and electrically connected via a pair of conductors to the sensing circuit for tracking the point of interest on the basis of changes in electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil .

Advantageously, the magnetic tracking system comprises a flexible circuit board in accordance with the first aspect , the sensing coil being mounted on the sensing coil mounting site , the flexible circuit board being connected to the sens ing circuit via the connection point .

In one embodiment , the flexible circuit board is in accordance with the first embodiment of the first aspect above , the magnetic tracking system comprises at least two sensing coils mounted one on each of the at least two sensing coil mounting sites , and the f lexible circuit board is bent along a three-dimensional surface of a support body such that the sens ing coils have their principal axes mutually differently directed .

In such embodiment , the flexible circuit board may comprise three sensing coil mounting sites for the same point of interest , i . e . for being positioned at the same point of interest , wherein the magnetic tracking system comprises three sensing coils mounted one on each of the three sensing coil mounting sites . In an embodiment with two or three sensing coils mounted on the two or three sensing coil mounting sites positions at the same point of interest , the sensing coils have their principal axes directed mutually orthogonally .

In an embodiment , the f lexible circuit board is in accordance with any of the embodiments of the first aspect above with one or a plural ity of elongated portions to enable tracking one or more fingers .

In yet another aspect , the magnetic tracking system i s utili zed in a smart glove which advantageously comprises a magnetic tracking system in accordance with the previous aspect with at least one point of interest being coupled with a finger part of the glove .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings , which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention .

The drawings of the Figures are schematic and not drawn to scale .

Figure 1 illustrates a magnetic tracking system having a flexible circuit board thereof ;

Figures 2 and 3 illustrate details of the magnetic tracking system and the flexible circuit board of Figure 1 ;

Figure 4 illustrates a part of a magnetic tracking system; and Figure 5 illustrates a smart glove incorporating a magnetic tracking system .

DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings is intended as a description of a number of embodiments and is not intended to represent the only forms in which the embodiments may be constructed, implemented, or utili zed .

Fig . 1 illustrates a top view of a part of a magnetic tracking system 100 .

A "magnetic tracking system" refers to a measurement arrangement capable of measuring, or "tracking" an obj ect by utili zing a magnetic field .

The magnetic tracking system 100 comprises a flexible circuit board 10 , a sensing circuit 101 , a plurality of transmitting coils 102 , and a plurality of sensing coils 103 positioned at a plurality of points of interest 105 .

A "point of interest" refers to a specific position, region, or zone in the magnetic tracking system, which position, region, or zone is to be monitored or tracked . A point of interest may be coupled with an external obj ect to enable tracking such external obj ect .

"Tracking" refers in this specification to determining at least one of the position and the orientation of the point of interest and the actual obj ect to be tracked . Tracking may also refer to determining changes of one or both of those parameters , and thereby to movements of the point of interest and the obj ect .

Being coupled with an obj ect refers to the point of interest and consequently the sensing coil being positioned at or close to the obj ect such that the position and/or orientation of the sensing coi l and thus the point of interest represent the position and/or orientation of the obj ect itself .

For example , such external obj ect may be a finger part of a smart glove incorporating the magnetic tracking system, or the finger itself of the user of the glove when it is in use . Thereby, the magnetic tracking system may be used to track the finger part of the smart glove , or the finger of the user thereof . An example of such smart glove is illustrated in Fig . 5 .

In other embodiments , a magnetic tracking system may be arranged with its point ( s ) of interest coupled with any other obj ect ( s ) to be tracked .

The f lexible circuit board 10 may be a printed circuit board .

The flexible circuit board 10 comprises sensing coil mounting sites 14 onto which the sensing coils 103 of the magnetic tracking system are mounted .

The sens ing coil mounting sites 14 are thus positioned in the flexible circuit board so that they lie in the magnetic tracking system 100 at the points of interest 105 thereof .

The flexible circuit board 100 of Fig . 1 is basically in the form of a hand, compri sing five elongated portions 19 corresponding the fingers of a hand or f inger parts of a glove . The sensing coil mounting sites 14 lie substantially at the ends of those elongated portions corresponding the fingertips of a hand of fingertip parts of a glove . This kind of configuration may enable using the flexible circuit board 10 and the magnetic tracking system 100 e . g . in a smart glove , wherein a plurality of points of interest of the magnetic tracking system are coupled with the finger parts of the glove or with the fingers of the user of the glove .

Actually, the point ( s ) of interest 105 of the magnetic tracking system 100 of Fig . 1 are coupled with fingertip ( s ) of the hand of the user of a glove . In other embodiments , point ( s ) of interest may be coupled with other part ( s ) of the hand of the user of the glove .

In other embodiments , flexible circuit boards may be implemented with one or more elongated portions , at least one sensing coil mounting site being located in the one or more elongated portions to enable one or more points of interest to be coupled with one or more fingers .

In yet another embodiments , flexible circuit boards may be implemented with one or more elongated portions , at least one sensing coil mounting site being located in the one or more elongated portions to enable one or more points of interest to be coupled with one or more obj ects other than fingers of a hand . Then, the overall shape of the flexible circuit board may also be different from a hand .

The arrangements of the points of interest and the sensing coil mounting sites of Fig . 1 are illustrated more closely in Fig . 3 showing an enlargement of the end of the leftmost elongated portion 19 of the flexible circuit board 10 .

In the example of Figs . 1 and 3 , the flexible circuit board 10 has three sens ing coil mounting sites 14 for each point of interest 105 of the magnetic tracking system 100 . Correspondingly, the magnetic tracking system compri ses three sensing coil s 103 at each point of interest 105 .

In other embodiments , a flexible circuit board may have two , or more than three sensing coil mounting sites for being positioned at one point of interest of the magnetic tracking system . It is also possible that for one or more points of interest , the f lexible circuit board comprises only one sensing coil mounting site .

In any of such embodiments , when utili zing the flexible circuit board in a magnetic tracking system, the sensing coil mounting s ites can be positioned at the points of interest of the magnetic tracking system . Such points of interest and receiving coils mounted on the receiving coil mounting sites , in turn, may be coupled with the actual obj ects which are to be tracked .

The purpose of each of the transmitting coils 102 is to generate an AC magnetic field for the tracking . Each of the sensing coils 103 , in turn, is configured to and used to detect the magnetic field generated by one or more of the transmitting coils . The flux of the alternating magnetic field through a sensing coil induces in the sensing coil an AC current . This induced current depends on the distance between , and the mutual orientation, of the transmitting coi l and the sensing coil . When the sensing coil position and/or orientation relative to the transmitting coi l changes , the AC magnetic flux through it changes , and so does the induced AC current . The induced current can be detected by the sensing circuit 101 and converted into a signal comprising information on the position and/or orientation of the sensing coil relative to the transmitting coi l . Changes of the position and/or orientation can further be used to determine the movements of the sensing coil . In the example of Fig . 1 , there are transmitting coils positioned at different points of a transmitting module 104 . A plurality of transmitting coils , which may be positioned with their principal axis mutually differently directed may be used to generate magnetic fields in different directions . This may improve the accuracy of the motion tracking .

In the example of Fig . 1 , the transmitting module comprises three transmitting coils 102 positioned in a substantially triangular arrangement . In other embodiment , magnetic tracking systems may be implemented with one, two , or any other appropriate number of transmitting coils which may be separate elements or incorporated into one or more transmitting modules .

"Sensing circuit" refers to any kind of electrical or electronic circuit , component , or module configured to at least partially automatically detect and measure the magnetic field at the location of a sensing coil on the basis of current induced by the magnetic field in the sensing coil . That current can then be used as an indication of the position and/or orientation of the sensing coil and thus the obj ect which the point of interest is coupled with . Thereby, the sensing circuit may be used for tracking the point of interest on the basis of electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil .

A "circuit board" may refer to any appropriate sheetlike structure where one or more conductor material layers are mounted on and supported by a dielectric base fi lm or layer . By appropriate patterning of such electrically conductive layers , various circuits and contact pads may be formed on the circuit board . In the example of Figs . 1 and 3 , as further illustrated in Fig . 2 showing a cross section A-A of the leftmost elongated portion 19 , the flexible circuit board comprises two conductor material layers 11 , 12 on the opposite surfaces of the base film 13 . Although no illustrated in the cross-section of Fig . 2 , the flexible circuit board may comprise any appropriate additional layers also , such as protective layer ( s ) encapsulating the conductor material layer ( s ) and/or the base film-

The materials of the base film 13 and the conductor material layers 11 , 12 may be selected in accordance with principles as such known in the art .

"Flexibility" of a circuit board may refer to the capability of the circuit board to be flexed or bent , preferably reversibly, without breaking the circuit board base film or the conductor material layers thereof . The flexible circuit board may be capable of being bent , for example, with a bending radius of less than or equal to 1 cm . Such bending radius may enable utili zation of the flexible circuit board, for example , in a magnetic tracking system of a smart glove .

In the example of Figs 1 and 3 , each of the sensing coil mounting sites 14 comprises a pair of contact pads 15 for mounting a surface-mount device SMD sensing coil 103 onto the mounting site such that the contacts of the sensing coil are electrically connectable to the contact pads by a soldered j oint . The contact pads are formed in the "upper" conductor material layer 11 , i . e . that conductor material layer which is visible in the top view drawing of Fig . 1 .

In other embodiments , sensing coil mounting sites may be implemented differently . For example , a sensing coil mounting site may be configured for mounting thereon a sensing coil implemented as a through-hole component instead of an SMD coil .

For each sensing coil mounting site 14 , a pair of conductive traces 16, 17 is formed in the flexible circuit board 10 to electrically connect the sensing coil mounting site to a connection point 20 of the flexible circuit board .

In the example of Fig . 1 configured for SMD sensing coils , the contact pads 15 are formed at the sensing coil mounting site ends of the conductor traces 16 , 17 .

A "connection point" of a circuit board refers to a point via which the circuit ( s ) of the circuit bord may be electrically connect to external circuit ( s ) . It thus forms an electrical interface of the circuit board .

In the example , there flexible circuit board 10 comprises a three-branch connection part 21 with connection points 20 at the ends thereof .

The conductive traces 16 , 17 serve in the magnetic tracking system 100 as conductors forming the electrical connections between the sensing coils 103 and the sensing circuit 101 .

It is to be noted that in Fig 1 , for the sake of clarity of the illustration, the conductive traces from the sensing coil mounting sites other than those of the leftmost elongated portion of the flexible circuit board are not drawn to be visible .

As shown in Fig . 1 , the conductor traces 16 , 17 are routed such that they bypass the transmitting module 104 of the magnetic tracking system . As the magnetic f ield intensity is naturally highest at the immediate proximity of the transmitting coils 102 , current may be induced in the conductor loop formed by the conductor traces 16 , 17 , the sensing coil 103 , and the sensing circuit 101 . This may adversely interfere the measurements of the weaker magnetic field at the location of the sensing coil mounting site 14 .

As shown in Figs . 1 and 3 , one of the conductor traces

17 for each sensing coil mounting site 14 runs only a short distance on the side of the flexible circuit board 10 on which the pads 15 of the sensing coil mounting site 14 lies . It is then led through a conductive via

18 to the opposite s ide of the f lexible circuit board . Most of its length, it follows the same path as the conductor trace 16 on the upper surface of the flexible circuit board . Then, the two conductor traces thus run parallel , i . e . their longitudinal directions are the same .

In other words , as illustrated in Fig . 2 , the two conductive traces 16 , 17 are formed on top of each other on the opposite sides of the flexible circuit board base film 13 .

Being positioned "on top of each other" refers to the two conductor traces at least partially overlapping each other in the cross-section of the flexible circuit board . As illustrated in Fig . 2 , in the example of Figs . 1 to 3 , the two conductor traces have the same width and are aligned so that there is a full overlap between them . In other embodiments , two parallel conductor traces with the same or different widths may be at least partially overlapping .

In yet other embodiments , two parallel conductor traces may lie with small lateral separation between them . Then, they may lie also on the same side of the base film. For example, the centerlines of the conductor traces may lie within less than or equal to 1 mm lateral (horizontal) distance from each other.

The arrangement of the conductor traces discussed above may provide particular advantages.

First, the arrangement where the conductor traces lie on the base film fixes the positions of the two conductive traces relative to each other. Their mutual positioning thus remains unchanged even if the flexible circuit board is bent. This may improve the reliability of the tracking especially in comparison to electrical connections formed by conventional wiring.

Further, the two conductor traces running at least part, preferably most, of their length parallel enable the conductor traces to be located laterally, i.e. in the transverse direction of the traces, close to each other. This enables minimization of the size of the conductor loop formed by the pair of the conductive traces 16, 17, the sensing coil 103, and the sensing circuit 101. As the interfering current induced in the conductor loop depends on the cross-section of the conductor loop, such minimization of the conductor loop may advantageously minimize the interference. In other words, the current induced in the conductor loop by the magnetic field generated by the transmitting coil (s) 102 may remain small. Then, it is possible that it does not significantly interfere with the measurements of the current induced in the sensing coil 103 by the magnetic field at the point of interest 105 of the magnetic tracking system 100.

In the example of Fig. 1, the parallel parts of the conductor traces 16, 17 lying on top of each other at the opposite sides of the base film 13 are positioned laterally with no separation at all . Then, the distance between the two conductive traces and thus the conductor loop cross section can be very effectively minimi zed as the conductive traces are separated by the thickness of the base film 13 only .

The base film thickness may be even as low as 0 . 2 mm or less , such as 0 . 1 mm or less , for example , about 0 . 08 mm .

Also with the very low thicknesses mentioned above , the dielectric base fi lm 13 may provide a high-quality and uniform insulation layer between the opposite conductor traces 16 , 17 .

Referring back to Figs . 1 and 2 , a plurality of sensing coils 103 mounted on a plurality of sensing coil mounting sites 14 positioned at one single point of interest 105 may improve the accuracy of the tracking of that point of interest and thus the obj ect with which the point of interest is coupled .

Further, with appropriate positioning of the plurality of sensing coil mounting sites , the sensing coils mounted thereon may have their principal axes directed mutually differently . This means the principal axes lying at an angle relative to each other . This may further improve the accuracy of the tracking by ensuring that in each situation, at least one of the sensing coils produces a sufficient current signal induced by the magnetic field generated by the transmitting coil ( s ) .

A "principal axis" of a coil such as a sensing coil may refer to the magnetic axis of the coi l . Alternatively, it may refer to any axis fixed in a particular direction relative to the magnetic axis . In the examples of Figs . 1 and 3 , the principal axis 107 of each sensing coil 103 is parallel to the longitudinal direction of the sensing coil .

Such mutually different directions of the principal axis of sensing coils may be implemented, for example , by having the sensing coil mounting sites directed in different rotational positions in the plane of the flexible circuit board . This is implemented in the example of Figs . 1 and 3 by having one of the three sensing coi l mounting sites , and thus one of the receiving coils , arranged perpendicularly relative to the other two sensing coil mounting sites and the sensing coils mounted thereon . Its principal axis is thus directed orthogonally relative to that of the other two sensing coi ls . In other embodiments , the directional difference may be other than perpendicular or orthogonal .

Alternatively, or additionally, also bending of the flexible circuit board may be utilized in arranging the sensing coi ls so as to have their principal axes mutually differently directed . An example is illustrated in Fig . 4 .

The magnetic tracking system 400 of Fig . 4 and the flexible circuit board 40 thereof may be basically in accordance with any of those discussed above with reference to Figs . 1 to 3 . The magnetic tracking system further comprises a bending block 408 having a three-dimensional bending surface 409 . The part of the flexible circuit board 40 where the sensing coil mounting sites 44 lie is bent along, i . e . to follow, the bending surface 409 . The bending block thus serves as a support body for the flexible circuit board 40 .

The shape of the bending block and the dimensions thereof as well as of the point of interest of the flexible circuit board are selected so that the two sensing coils mounted on the sensing coil mounting sites with the same rotational position in the plane of the flexible circuit board are , due to the bending of the flexible circuit board, positioned with their principal axes 407 perpendicular to each other . In consequence , all the three sensing coils have their principal axes directed mutually orthogonally .

In other embodiments , bending a flexible circuit board along a support body may be implemented so as to produce some other directional difference than perpendicular or orthogonal between different sensing coil mounting sites and sensing coils mounted thereon .

In the example of Fig . 4 , the bending block comprises an alignment pin 410 and the flexible circuit board has a corresponding alignment hole 51 for facilitating the correct mutual positioning of the bending block and the flexible circuit board . In other embodiments , other arrangements may be implemented for ensuring proper mutual positioning .

Figure 5 illustrates a smart glove 5000 incorporating a magnetic tracking system which may be basical ly in accordance with any of those discussed above with reference to Figs . 1 to 4 . The one or more points of interest of the may be coupled with one or more finger portion 5001 , respectively, of the glove . More accurately, a point of interest may be coupled with a specific point or part of a finger portion, such as a point or part corresponding the fingertip of a finger of the user of the glove . Thereby, the smart glove may be used to track one or more fingertips of the glove user .

In the example of Fig . 5 , there are bumps 5002 at the fingertip parts of the finger portions 5001 . This indicates that the ends parts of the elongated portions of the flexible circuit board having the receiving coil mounting sites may be bent along a three-dimensional bending surface of abending block . In other embodiments , bending may be arranged differently or missing .

It is obvious to a person ski lled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways . The invention and its embodiments are thus not limited to the examples described above , but they may vary within the scope of the claims .

It will be understood that the benefits and advantages described above may relate to one embodiment or example or may relate to several embodiments or examples . The embodiments and examples are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items .

The term "compris ing" i s used in thi s specification to mean including the feature ( s ) followed thereafter, without excluding the presence of one or more additional features .

Claims

1. A flexible circuit board (10) , having a base film (13) , for a magnetic tracking system (100) comprising a sensing circuit (101) , a transmitting coil (102) , and a sensing coil (103) positioned at a point of interest (105) and being electrically connected to the sensing circuit for tracking the point of interest on the basis of electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil, c h a r a c t e r i z e d in that the flexible circuit board comprises a sensing coil mounting site (14) for being positioned at the point of interest (105) , and a pair of conductive traces (16, 17) to electrically connect the sensing coil mounting site to a connection point (20) of the flexible circuit board, the conductive traces being formed on the flexible circuit board base film (13) so as to run parallel, preferably on top of each other on the opposite sides of the flexible .

2. A flexible circuit board (10) as defined in claim 1, comprising at least two sensing coil mounting sites (14) for being positioned at the point of interest (105) , the at least two sensing coil mounting sites being positioned so as to enable sensing coils (103) being mounted thereon to have their principal axes directed mutually differently upon bending of the flexible circuit board.

3. A flexible circuit board (10) as defined in claim 1 or 2, wherein the sensing coil mounting site (14) has two conductor pads (15) for a surface-mount device (SMD) sensing coil.

4. A flexible circuit board (10) as defined in any of claims 1 to 3, having an elongated portion (19) , at least one sensing coil mounting site (14) being located in the elongated portion to enable the point of interest (105) to be coupled with a finger to track the finger .

5. A flexible circuit board (10) as defined in claim 4, having a plurality of elongated portions (19) and at least one sensing coil mounting site (14) located in each of the elongated portions to enable a plurality of points of interest (105) of the magnetic tracking system (100) to be coupled with a plurality of fingers to track the plurality of fingers.

6. A flexible circuit board (10) as defined in any of claims 1 to 5, wherein the flexible circuit board base film (13) has a thickness of less than or equal to 0.2 millimetres, for example, such as less than or equal to 0.1 mm, for example, about 0.08 mm.

7. A magnetic tracking system (100) comprising a sensing circuit (101) , a transmitting coil (102) , and a sensing coil (103) positioned at a point of interest (105) and being electrically connected via a pair of conductors (16, 17) to the sensing circuit for tracking the point of interest on the basis of changes in electrical current induced in the sensing coil by the magnetic field generated by the transmitting coil, wherein the magnetic tracking system comprises a flexible circuit board (10) as defined in any of claims 1 to 6, the sensing coil (103) being mounted on the sensing coil mounting site (14) , the flexible circuit board being connected to the sensing circuit (101) via the connection point (20) .

8. A magnetic tracking system (400) as defined in claim 7, wherein the flexible circuit board (40) is as defined in claim 2, the magnetic tracking system comprises at least two sensing coils (403) mounted one on each of the at least two sensing coil mounting sites (44) , and the flexible circuit board is bent along a three-dimensional surface (409) of a support body (408) such that the sensing coils have their principal axes (407) mutually differently directed.

9. A magnetic tracking system (400) as defined in claim 8, wherein the flexible circuit board (40) comprises three sensing coil mounting sites (44) for the point of interest (405) , and the magnetic tracking system comprises three sensing coils mounted one on each of the three sensing coil mounting sites.

10. A magnetic tracking system (400) as defined in claim 8 or 9, wherein the sensing coils (403) have their principal axes (407) directed mutually orthogonally.

11. A magnetic tracking system (100, 400) as defined in any of claims 8 to 10, wherein the flexible circuit board (10, 40) is as defined in claim 4 or 5 to enable tracking one or more fingers.

12. A smart glove (5000) comprising a magnetic tracking system (100, 400) as defined in any of claims 7 to 11 with at least one point of interest (105, 405) of the magnetic tracking system being coupled with a finger part (5001) of the glove.