ITTO20090814A1 - SENSOR FOR THE ACQUISITION OF BIOELECTRIC SIGNALS FROM AN ANULAR MUSCLE, IN PARTICULAR FOR MULTI-CHANNEL SURFACE ELECTROMYOGRAPHY - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

â € œSENSOR FOR THE ACQUISITION OF BIOELECTRIC SIGNALS FROM AN RING MUSCLE, IN PARTICULAR FOR MULTICHANNEL SURFACE ELECTROMYOGRAPHYâ €

The present invention relates to a sensor for multi-channel surface electromyography for the acquisition of bioelectrical signals deriving from the activity of an annular muscle, such as the external anal sphincter muscle (EAS - External Anal Sphincter), the urethral sphincter muscle or the pelvic floor muscle complex via the vaginal canal.

As known, the muscles of the body, during their contraction, generate bioelectric signals (known as myoelectric signals) which propagate along the muscle fibers towards the tendon ends. In detail, muscles are made up of a set of muscle fibers grouped into a plurality of functional units, called motor units (UM); a single motor unit includes a motor neuron, its axon and its neuromuscular junction, and the set of muscle fibers it innervates. The motor neuron propagates the nerve impulse along the axon, from the spinal cord towards the neuromuscular junction (also known as the innervation zone), and generates an electrical action potential which subsequently propagates along the muscle fibers towards the tendons.

The resulting electrical activity generated by muscle contraction (given by the combination of action potentials that propagate along the muscle fibers of the different motor units) can be acquired on the skin, or mucosa, in correspondence with the muscle with the technique of ™ surface electromyography (sEMG - Surface Electromyography). This technique provides for the sampling of electrical signals (surface electromyographic signals) through the arrangement on the portion of skin, or mucosa, overlying the muscle or muscles of interest, of sampling sensors comprising electrodes of conductive material (for example silver); this technique clearly differs from the traditional needle electromyography technique, which instead involves inserting needles of conductive material into the muscle.

In particular, it is known to acquire electromyographic signals resulting from the contraction of a sphincter (in particular the anal sphincter), through the use of a probe having an elongated body intended to be introduced inside the orifice surrounded from the annular sphincter muscle structure, and having a plurality of electrodes suitably arranged along its external surface and adapted to be placed in correspondence with respective portions of the muscle.

The electrodes, considered in a monopolar or single differential configuration (or in other configurations of interest), supply the respective electromyographic signals to the respective processing channels of the conditioning electronics, which can be amplified, filtered and suitably processed in order to identify the arrangement of the fibers along the sphincter ring (and the portions of muscle most affected by the contraction) and the location of the innervation zones of the various motor units.

This information is of great importance in the clinical setting, for example to diagnose or monitor pathologies such as faecal or urinary incontinence, and surgical, for example to avoid damage to the innervation areas of the muscle during episiotomy, fistula surgery or hemorrhoids.

Figure 1 shows an intra-anal probe for surface electromyography of a known type, indicated as a whole with 1. This probe is described in patent application TO2004A00395, in the name of the present applicant.

The reusable intra-anal probe 1 comprises a body 3, with an elongated cylindrical shape, and provided with a first end portion 3a with a rounded hemispherical cap shape, intended to facilitate its introduction into the anal orifice. The body 3 is made of insulating, non-toxic, unalterable material and can be sterilized (for example in an autoclave and / or with chemical substances currently used in the clinical field, such as peracetic acid) for the purpose of its reuse.

The intra-anal probe 1 is provided with a plurality of pickup electrodes 4, arranged on the external cylindrical surface of the body 3, having a rectilinear shape, and arranged parallel to each other.

The pick-up electrodes 4 are grouped according to a certain number of ring structures along respective circumferences arranged around the external cylindrical surface of the body 3 (for example in a number equal to three), axially spaced between them at a fixed distance; the sampling electrodes 4 of each group (for example in a number equal to sixteen) form an array, and are angularly equidistant from each other along a respective circumference, so as to be aligned with the direction of the sphincter muscle fibers and therefore with the direction of propagation of the myoelectric signal.

In particular, the pick-up electrodes 4 are rigidly fixed to the body 3, in an immovable way, being constituted by bars of conductive material (for example silver) which, during the manufacturing phase, are inserted into the body itself by hooking to it; each pickup electrode 4 is connected to a respective electric cable (not shown) which extends inside the body 3 up to its second end portion 3b, which forms its base. The electric cables associated with the pickup electrodes 4 protrude from the second end portion 3b of the body 3 inside a multipolar electric cable 6, which ends in one or more connectors (not shown here, for example one for each array of electrodes ) intended to be connected to one or more signal inputs of the relative conditioning electronics.

For example, if the arrays are made up of sixteen electrodes, it is possible to obtain sixteen single differential signals from each of them to be sent to the respective sixteen processing channels of the conditioning electronics (each channel performing the difference of the signals taken from two adjacent electrodes). From the analysis of these signals it is possible to evaluate the propagation of myoelectric signals along the muscle fibers, simultaneously at different depths of the muscle (in correspondence with the positions assumed by the various electrode arrays), without requiring repositioning of the probe and repetition muscle contractions.

The intra-anal probe 1 is therefore certainly advantageous for performing surface electromyographic analysis of a sphincter muscle; in particular, experimental tests carried out by the same applicant have shown how it allows to evaluate, in addition to the localization of the innervation zones of the motor units, also the localization of the tendons and interruptions of the muscle fibers following surgery.

However, the intra-anal probe 1 suffers from some problems that do not allow to take full advantage of its advantages.

In particular, the manufacturing cost of this intra-anal probe 1 is high, due, among other things, to the objective difficulties in coupling the pick-up electrodes 4 to the body 3, and the construction of the relative connection cables electric inside the same body 3. Assembly costs also increase with the number of arrays and sampling electrodes, and the intra-anal probe 1 therefore offers, due to its very structure, a limited possibility of configurability, for example in order to adapt to different muscle structures or to carry out experimental tests in different sampling conditions (in terms, for example, of a different spacing between the electrodes or between the arrays of electrodes, or of a different number of ranks).

The present invention therefore has the aim of providing a surface electromyography sensor which allows to overcome the drawbacks highlighted.

According to the present invention there is therefore provided a sensor for the acquisition of bioelectrical signals from an annular muscle, as defined in claim 1.

For a better understanding of the present invention, preferred embodiments are now described, purely by way of non-limiting example and with reference to the attached drawings, in which:

Figure 1 schematically shows an intra-anal probe for surface electromyography of a known type;

- figure 2 shows, in perspective and schematic view, a sensor for the acquisition of bioelectric signals, according to an embodiment of the present invention;

figure 3 shows a support element of the sensor of figure 2;

- figures 4a and 4b show a flexible printed circuit of the sensor of figure 3, respectively in the open and closed position following the winding around a relative axis of longitudinal symmetry;

- figure 5 is a photographic image of a portion of the sensor for the acquisition of bioelectrical signals, according to a further embodiment of the present invention;

- figure 6 shows electromyographic signal plots acquired by means of the sensor of figure 2; And

- Figures 7 and 8 show the result of processing the electromyographic signals acquired by the sensor of Figure 2.

Figure 2 indicates as a whole with 10 a sensor for picking up bioelectrical signals generated by the contraction of an annular muscle, such as an anal sphincter, a urethral sphincter or the muscle complex of the pelvic floor through the vaginal canal, according to a shape embodiment of the present invention.

In particular, the sensor 10 comprises: a support element 12, of plastic material, preferably insulating, non-toxic, unalterable and possibly sterilizable and autoclavable; and a plurality of flexible printed circuits 14, on each of which a respective plurality of pick-up electrodes 15 is formed (forming a respective array), and configured (as will be described in detail below) to be coupled, stacked the one above and inside the other, on the support element 12 in such a way that the respective arrays of pickup electrodes 15 are arranged on rings having the same diameter and equally spaced axially along the lateral surface of the same element support 12. When coupled, the support element 12 and the flexible printed circuits 14, stacked together, have the same longitudinal axis of symmetry A.

In greater detail (see also Figure 3, not to scale), the support element 12 (which can be solid or hollow) extends along the longitudinal axis of symmetry A, and in particular includes: a portion of handle 12a of cylindrical shape elongated along the longitudinal axis of symmetry A, having a first diameter d1 preferably between 6 mm and 18 mm, for example equal to 8.9 mm, and a height h1 (parallel to the axis of longitudinal symmetry A) preferably between 80 mm and 160 mm, for example equal to 100 mm; a coupling portion 12b, with an inverted truncated cone shape, having a minor base in contact, and having the same first diameter d1, as the handle portion 12a and a larger base having a second diameter d2 preferably between 10 mm and 20 mm, to for example equal to 12.7 mm, and a height h2 (along the longitudinal axis of symmetry A) preferably between 60 mm and 120 mm, for example equal to 90 mm; and a head portion 12c, consisting of a cylindrical base, having the second diameter d2 and a height h3 (along the longitudinal axis of symmetry A) preferably between 2 mm and 20 mm, for example equal to 10 mm, surmounted by a hemispherical cap.

In particular, the coupling portion 12b of the support element 12 has an angle of conicity, or opening, Î ± (intended as an inclination between a straight line generating its lateral surface and its height), whose value is ̈ preferably between 0.2 ° and 3 °, for example equal to 0.89 °.

Each flexible printed circuit 14 (see also figures 4a-4b, not drawn to scale) is made up of a sheet of flexible plastic material, for example made of Mylarâ „¢, with a thickness t preferably between 0.05 mm and 0.20 mm, for example equal to 0.12 mm, and comprises: a connecting portion 14a having an elongated rectangular shape in plan with a length l1 preferably between 100 mm and 200 mm, for example equal to 150 mm; and a respective coupling portion 14b having in plan, when not wrapped (as described below) around the support element 12 of the sensor 10, a shape of a circular ring sector delimited by a smaller arc, in contact with the portion connection 14a, and by a larger arch, arranged diametrically opposite to the same connecting portion 14a, and having oblique sides L1, L2 (which connect the major and minor arches) with a length l2 preferably between 40 mm and 80 mm, to example equal to 55 mm. In particular, the oblique sides L1, L2 are inclined with respect to the longitudinal axis of symmetry A by the same taper angle Î ± of the coupling portion 12b of the support element 12.

The pick-up electrodes 15 are formed on the coupling portion 14b of each flexible printed circuit 14, in particular in correspondence with and along the relative major arc, for example by serigraphic or photolithographic deposition of a conductive material, such as silver. The pick-up electrodes 15 consist of rectangular pads extending in a radial direction, angularly equally spaced, with a length 13 preferably comprised between 1 mm and 10 mm, for example equal to 5 mm. The number of pickup electrodes 15 is preferably between 2 and 32, for example it is equal to 16 (13 are illustrated in figure 4a, purely by way of example).

Electrical connection tracks 16 are also made on each flexible printed circuit 14, to electrically connect each pick-up electrode 15 to a connector 18, placed at the end of the connection portion 14a longitudinally opposite the coupling portion 14b, and intended to be coupled to the air conditioning electronics (directly, or by means of a multipolar electric cable). In particular, each electrical connection track 16 has: a first portion, made on the coupling portion 14b, which connects to a respective pick-up electrode 15 and has a radial extension; a second portion, made on the connection portion 14a, which connects to the connector 18 and has a straight extension along the longitudinal axis of symmetry A; and a connecting portion, also made on the coupling portion 14b, which connects the first portion with the second portion, in proximity to the smaller arc of the coupling portion 14b.

As shown in Figure 4b, the coupling portion 14b of the flexible printed circuit 14 is configured in such a way that it can be closed and wrapped around itself around the longitudinal axis of symmetry A, to form a hollow truncated cone (open above and below in correspondence of the bases), bringing the oblique sides L1, L2 close and matching (or in any case arranging them in proximity to each other); when the coupling portion 14b is closed as a truncated cone, the connecting portion 14a of the same flexible circuit 14 protrudes at the front from the minor base of the truncated cone (defined by the closing on itself of the minor arch of the coupling portion 14b around the longitudinal axis of symmetry A). In particular, the internal diameter of the major base of this truncated cone (defined by the reclosing on itself of the major arc of the coupling portion 14b around the longitudinal axis of symmetry A) corresponds to the second diameter d2 of the major base of the portion coupling 12b of the support element 12.

During the assembly phase of the sensor 10, a first flexible printed circuit 14 is wrapped around the coupling portion 12b of the support element 12 in correspondence with, and flush with, its major base, so that the relative pick-up electrodes 15 are arranged angularly equally spaced, on a ring substantially having the second diameter d2.

The coupling between the first flexible circuit 14 and the coupling portion 12b of the support element 12 is made by means of a suitable adhesive material interposed between the internal surface of the same flexible circuit 14 (i.e. the face on which there are no arranged the pick-up electrodes 15 and the electric connection tracks 16) and the external surface of the support element 12; since these surfaces are inclined by the same taper angle Î ±, the first flexible circuit 14 is positioned entirely in contact with the lateral surface of the coupling portion 12b of the support element 12.

The other flexible printed circuits 14 (in desired number, equal to the number of electrode arrays with which the sensor 10 will be equipped), also configured in such a way as to wrap around the longitudinal axis of symmetry A and close on themselves so as to form a hollow truncated cone shape, flexible printed circuits 14 are each arranged around another (in particular, a second flexible printed circuit is intended to wrap around the first, a third flexible printed circuit is intended to wrap around the second, and so on, descending along the coupling element 12b of the support element 12 towards the connecting element 12a), so as to form a stacked structure. The height h2 of the coupling portion 12b of the support element 12 is therefore dimensioned in such a way as to allow the coupling and stacking of the desired number of flexible printed circuits 14.

In particular, the configuration of the flexible printed circuits 14 is such that the relative arrays of pickup electrodes 15 are arranged along circumferences, which are equally spaced along the longitudinal axis of symmetry A and all have the same diameter (substantially equal to second diameter d2), so as to allow the detection of electromyographic signals under the same conditions at various muscle depths. Furthermore, the pick-up electrodes 15 of the various superimposed arrays are aligned with each other in their respective radial directions.

In this regard, it should be noted how the corresponding frusto-conical shape of the coupling portion 12b of the support element 12 and of the respective coupling portions 14b of the flexible printed circuits 14 (when wound around themselves), clearly allows for compensate for the thickness t of the superimposed flexible printed circuits, and to maintain constant the diameter of the ring along which the pick-up electrodes 15 are arranged. Furthermore, the distance D along the longitudinal axis of symmetry A between the electrode arrays pickup 15 (understood as the distance between the centers of the circumferences along which the arrays themselves extend, or, in an equivalent manner, between the centers of stacked pickup electrodes 15), which is constant along the coupling element 12, is determined by the thickness t of the flexible printed circuits 14 and by the taper angle Î ±, parameters on which it is therefore possible to act, in the design phase, to determine re the characteristics of the sensor 10; such distance D between the arrays is for example equal to 6 mm.

Figure 5 shows a photographic image of a portion of a sensor 10 equipped with seven arrays of pickup electrodes 15 (and a corresponding number of flexible printed circuits 14 coupled to the support element 12). It should be noted in particular how the reduced thickness t of the flexible circuits 14 and the reduced value of the taper angle Î ± mean that the various flexible printed circuits 14 do not protrude significantly from the body of the support element 12, therefore not causing discomfort for the patient.

Figure 6 shows an example of a plot of the surface electromyographic signals taken from the sensor 10 of figure 5 (comprising seven arrays, each formed by sixteen sampling electrodes 15), as they can be displayed following suitable processing by the ™ electronic conditioning. The trace is related to the muscular activity of an anal sphincter muscle, during a rest phase, time interval from 0 s to 10 s, followed by a phase of maximum voluntary muscle contraction (MVC - Maximum Voluntary Contraction), time interval from 10 s to 30 s, and again from a rest phase, time interval from 30 s to 35 s.

The traces refer to a single differential configuration (SD) of the pick-up electrodes 15, being the result of the difference (performed by the conditioning electronics) of the signals picked up by pairs of adjacent electrodes. The sampling electrodes 15 of the array positioned more internally with respect to the sphincter muscle are indicated by the numbers from 1 to 16, those of the outermost array by the numbers from 97 to 112; for each array, the respective sixteen pickup electrodes 15 must be imagined arranged around a circumference, with the first channel being adjacent to the sixteenth.

Figure 7 instead shows the â € œprintâ € (template) of a single motor unit, as it can be identified within the electromyographic signals by means of suitable processing, for example by decomposition of the same electromyographic signals. Again, the signals collected in a single differential configuration by the various sampling electrodes 15 of the arrays located at different depths with respect to the sphincter muscle are illustrated.

It can be noted that the amplitude of the electromyographic signals collected varies according to the sampling depth. In particular, the generation effect of the action potentials of the motor units can be observed simultaneously in the various arrays of sampling electrodes 15, while the propagating components of the signal are more attenuated for the arrays farthest from the position in which the € ™ motor unit. In this way, from the examination of the traces it is possible, for example, to trace the depth of the motor units identified within the sphincter muscle. The position of the innervation zone of the motor unit illustrated is also evident, which corresponds to the zone in which two different adjacent traces present impulses with opposite polarity.

Figure 8 also shows the result of a further processing of the electromyographic signals taken from the sensor 10 by the conditioning electronics, which provides for the generation of a map of muscle activity that allows a simple and immediate visualization of the muscle activity. ™ muscle activity.

The electromyographic signals are divided into epochs (for example of 0.5 s); for each channel and for each epoch, the average rectified value (ARV - Average Rectified Value) of the acquired signal is calculated; and the ARV values thus calculated are averaged over the various epochs in order to obtain a single numerical value (indicative of the amount of muscle activity) for each channel of each array. The numerical values thus obtained are graphically reported in the map shown in figure 8, with an intensity of color increasing as muscle activity increases. The map must again be imagined wrapped around a cylinder, in such a way that the first and sixteenth channels of each row are adjacent; furthermore, the dorsal position is indicated here with â € œDâ €, with â € œVâ € the ventral position, with â € œRâ € the right lateral position and with â € œLâ € the left lateral position of the sphincter muscle with respect to the anal canal.

The advantages of the sensor for picking up bioelectric signals made according to the teachings of the present invention emerge clearly from the previous description.

The realization of the sensor 10 is in fact extremely simplified compared to that of the traditional probes, being in fact sufficient, during the assembly phase, to couple the desired number of flexible printed circuits 14 (each of which corresponds to an array of pick-up electrodes 15) to the Support element 12. In particular, it is not necessary to hook pick-up electrodes to the support element, nor to make the relative electrical connections inside the support element itself. In fact, both the pickup electrodes 15 and the electrical connection tracks 16 are already made on the flexible printed circuits 14. The times and costs of the manufacturing process are therefore much shorter.

In particular, the assembly of the sensor 10 is modular, and the realization of sensors with a different number of arrays or sampling electrodes 15 for each array, or with a different distance between arrays or between sampling electrodes 15, does not involves substantial variations in assembly costs. It is therefore advantageous to increase the number and density of the sampling electrodes 15, for example in order to improve the resolution of the muscle activity map (see figure 8), and in general the accuracy with which it is It is possible to investigate muscle activity.

Finally, it is clear that modifications and variations may be made to what is described and illustrated herein without thereby departing from the scope of protection of the present invention, as defined in the attached claims.

In particular, the sensor 10, generally provided as a single-use sensor, can possibly be reused, after having appropriately sterilized the support element 12.

The adhesive material used to make the coupling between the support element 12 and the flexible printed circuits 14 can be constituted by a sheet of double-sided adhesive applied on the inner face of the same flexible printed circuits, so as to allow the User the assembly, starting from a common support element 12, of sensors 10 having desired characteristics (in terms for example of number of arrays of pick-up electrodes 15).

It is also evident that all the dimensions mentioned above are not limiting, but purely illustrative, and that the actual dimensions of the sensor 10 and its constituent elements will obviously depend on the size of the muscle to be investigated.

Claims (14)

CLAIMS 1. Sensor (10) for the acquisition of bioelectrical signals from an annular muscle, comprising: a support element (12) having an elongated shape along a longitudinal axis (A); and a plurality of pickup electrodes (15) carried by said support element (12), and arranged, in groups, around said longitudinal axis (A) along respective rings placed between them at a separation distance (D) along said longitudinal axis (A), characterized in that it comprises a plurality of printed circuits (14), of flexible material, on each of which a respective of said groups of pickup electrodes (15), said printed circuits (14) is arranged being coupled to said support element (12), stacked with respect to each other around a coupling portion (12b) of said support element (12). 2. Sensor according to claim 1, wherein said coupling portion (12b) of said support element (12) has an external surface inclined by an angle of inclination (Î ±) with respect to said longitudinal axis (A), and said printed circuits (14) of said plurality have a hollow conformation with an internal surface inclined by said inclination angle (Î ±). 3. Sensor according to claim 2, wherein said coupling portion (12b) of said support element (12) has a frusto-conical shape having a larger base with a pickup diameter (d2), and in which said printed circuits (14 ) of said plurality have a respective coupling portion (14b) having a corresponding hollow frusto-conical shape with a respective major base having an internal diameter equal to said withdrawal diameter (d2) and facing towards said major base of said coupling portion (12b ) of said support element (12). Sensor according to claim 3, wherein said plurality of printed circuits (14) comprises: a first printed circuit (14) wrapped around, and in contact with, said coupling portion (12b) of said support element (12) , with said respective coupling portion (14b) having the respective major base surrounding the major base of the coupling portion (12b) of said support element (12); and at least a second printed circuit (14) wrapped around, and in contact with, said respective coupling portion (14b) of said first printed circuit (14), with the major base of the respective coupling portion (14b) surrounding the outer surface of said first printed circuit (14) at said separation distance (D) from the respective major base of said first printed circuit. 5. Sensor according to claim 3 or 4, wherein said pickup electrodes (15) of each of said groups are angularly equally spaced on an external surface of a respective of said printed circuits (14), at and along, said base greater than the respective coupling portion (14b). Sensor according to any one of claims 3-5, wherein said support element (12) further comprises a handle portion (12a) having a substantially cylindrical shape along said longitudinal axis (A); and in which said printed circuits (14) have a connection portion (14a) connected to the respective coupling portion (14b) at a smaller base thereof, and extending along said longitudinal axis (A) up to a respective electrical connector ( 18) intended for electrical connection with air conditioning electronics; on each of said printed circuits (14) there are also disposed electric connection tracks (16) extending from said pick-up electrodes (15) of the respective group to said electric connector (18). 7. Sensor according to any one of claims 3-6, wherein a length of said coupling portion (12b) of said support element (12) is a function of an overall dimension along said longitudinal axis (A) of the stacked assembly of the respective coupling portions (14b) of said printed circuits (14). 8. Sensor according to any one of claims 2-7, wherein the separation distance (D) between said rings is constant along said longitudinal axis (A), and a value of said separation distance (D) is a function of said inclination angle (Î ±) and a thickness (t) of said printed circuits (14). 9. Sensor according to any one of the preceding claims, wherein said rings define circumferences all having the same diameter, equal to said pick-up diameter (d2), and said pick-up electrodes (15) of each of said groups are angularly equally spaced along a respective of said circumferences. 10. Sensor according to any one of the preceding claims, for surface electromyography, in which said groups of sampling electrodes (15) are intended to contact respective annular portions of a mucosa overlying said muscle, at different depths, as a function of said distance of separation (D); and in which said annular muscle is one of: an external anal sphincter, a urethral sphincter and the muscle group of the pelvic floor through the vaginal canal. 11. Assembly process of a sensor (10) for the acquisition of bioelectrical signals from an annular muscle, comprising the steps of: - providing a support element (12) having an elongated shape along a longitudinal axis (A); - coupling to said support element (12) a plurality of pickup electrodes (15), arranged in groups around said longitudinal axis (A) along respective rings placed between them at a separation distance (D) along said axis longitudinal (A), characterized in that said coupling step includes: coupling to said support element (12) a plurality of printed circuits (14), of flexible material, on each of which a respective one of said groups of pickup electrodes (15), said printed circuits (14) being stacked with respect to each other around a coupling portion (12b) of said support element (12). 12. Process according to claim 11, wherein said coupling step comprises: arrange said printed circuits (14) of said plurality, each having a respective coupling portion (14b) shaped as a sector of a circular ring delimited by: a greater arc, in correspondence with and along which the electrodes of removal (15) of the respective group, from a minor arch, and from oblique sides (L1, L2) connecting said major and minor arch; and wind said printed circuits (14) around said longitudinal axis (A) and said coupling portion (12b) of said support element (12), in such a way as to arrange said oblique sides in contact with or near each other (L1, L2) and ensure that said printed circuits (14) assume, when wound, a hollow truncated cone shape. 13. Process according to claim 12, wherein said plurality of printed circuits (14) comprises a first and at least one second printed circuit, and in which said coupling portion (12b) of said support element (12) has a frusto-conical shape having a larger base with a pickup diameter (d2); said wrapping phase comprising: attach by means of an adhesive material said first printed circuit (14) around, and in contact with, said coupling portion (12b) of said support element (12) with said respective coupling portion (14b) having a larger base with internal diameter equal to said withdrawal diameter (d2) and surrounding the major base of the coupling portion (12b) of said support element (12); and fixing said at least one second printed circuit (14) around, and in contact with, said coupling portion (14b) of said first printed circuit (14), with said respective major base surrounding the external surface of said first printed circuit (14) ) at said separation distance (D) from the respective major base of said first printed circuit (14). 14. Process according to claim 12 or 13, wherein said coupling portion (12b) of said support element (12) has a frusto-conical shape having an external surface inclined by an angle of inclination (Î ±) with respect to said longitudinal axis (A), and in which said printed circuits (14) of said plurality have a coupling portion (14b) having a corresponding hollow frusto-conical shape with an inclined internal surface of said inclination angle (Î ±) and a thickness (t) ; said step of preparing comprising dimensioning said thickness (t) and said inclination angle (Î ±) as a function of a desired value of said separation distance (D).