Portable metal detector including a helical coil

Abstract

The present invention relates to a portable metal detector (1) comprising: - a cylindrical support (7) made of dielectric material having a general extension direction defining an axis (X) of the metal detector (1), the cylindrical support (7) having, between a first end (9) and a second end (10) of the cylindrical support (7), a diameter (D) in a plane normal to the axis (X) of the detector; and - an inductive sensor (5) comprising a coil (8) wound helically around the cylindrical support (7) from the first end (9) to the second end (10) of the cylindrical support (7) so as to form a helix, a pitch (P) of the helix being strictly greater than the diameter (D) of the cylindrical support (7). Figure for the abstract: Fig. 4a

Description

Title of the invention: Portable metal detector comprising a helical coil Technical field

[0001] The present invention relates to the general technical field of portable metal detectors, in particular for detecting metals, for example when accessing a departure lounge in an airport or any other similar place of controlled access, but also for personal (leisure) and commercial uses. STATE OF THE ART

[0002] A portable metal detector generally comprises a handle for gripping the detector by an operator, a body comprising measuring means and processing means.

[0003] The measuring means may comprise, for example, an inductive sensor for measuring the variation in inductance caused by the metals to be detected. The inductive sensor may comprise either a single winding forming a transmitter and receiver, or a separate transmitter winding and receiver winding. The transmitter winding generates an electromagnetic field which can effectively penetrate non-metallic materials, such as soil, water, clothing, etc. The presence of a metallic body near the windings disturbs the magnetic field generated by the winding. This disturbance is detected by the processing means which send an alert command to an alarm of the detector.

[0004] The coils of the detection probe of portable detectors usually comprise flat, rectangular or circular coils so as to optimize the surface / perimeter ratio and therefore present sufficient sensitivity at several centimeters of distance from the coils, or be wound transversely around a support, which makes it possible to have a more compact detection probe but with a significant loss of sensitivity at short distances. Statement of the invention

[0005] An aim of the present application is to remedy the aforementioned drawbacks, by proposing a portable metal detector which is compact while having a suitable sensitivity and at least equivalent to that of standard portable detectors.

[0006] For this purpose, according to a first aspect, there is proposed a portable metal detector comprising: - a cylindrical support made of dielectric material having a general direction of extension defining an axis of the metal detector, the cylindrical support having, between a first end and a second end of the cylindrical support, a diameter in a plane normal to the axis of the detector; and - an inductive sensor comprising a coil wound helically around the cylindrical support from the first end to the second end of the cylindrical support so as to form a helix, a pitch of the helix being strictly greater than the diameter of the cylindrical support.

[0007] Some preferred but non-limiting features of the metal detector according to the first aspect are the following, taken individually or in combination: - the helix comprises at least one turn, preferably at least two turns; - the winding forms both a transmitting element and a receiving element of the inductive sensor; - the winding forms a transmitting element of the inductive sensor and the metal detector further comprises a receiving winding wound helically around the cylindrical support between the first end and the second end of the cylindrical support so as to form a receiving helix, a pitch of the receiving helix being strictly greater than the diameter of the cylindrical support; - the pitch of the propeller and the pitch of the receiving propeller are identical; - the propeller and the receiving propeller are angularly offset by 90° between the first end and the second end of the cylindrical support; - the propeller and the receiving propeller rotate in opposite directions around the axis of the metal detector between the first end and the second end so that the winding and the receiving winding intersect; - the propeller and the receiving propeller rotate in the same direction around the axis of the metal detector between the first and second ends; - the metal detector further comprises an additional transmitter coil wound helically around the cylindrical support between the first end and the second end of the cylindrical support so as to form an additional transmitter helix, a pitch of the additional transmitter helix being strictly greater than the diameter of the cylindrical support; - the pitch of the additional transmitting helix is ​​equal to the pitch of the helix and wherein the helix and the additional transmitting helix rotate in opposite directions around the axis of the metal detector between the first end and the second end so that the winding and the additional transmitting winding intersect; - the propeller and the additional transmitting propeller intersect at the first end at a crossing point; - the metal detector further comprises an additional receiver coil wound helically around the cylindrical support between the first end and the second end of the cylindrical support so as to form a receiver helix additional, a pitch of the additional receiving propeller being strictly greater than the diameter of the cylindrical support; - the pitch of the additional receiving helix is ​​equal to the pitch of the receiving helix and the receiving helix and the additional receiving helix rotate in opposite directions around the axis of the metal detector between the first end and the second end so that the receiving winding and the additional receiving winding intersect; - the receiving helix and the additional receiving helix intersect at the first end at an additional crossing point; - the crossing point and the additional crossing point are angularly offset by 90°; and / or - The metal detector further includes a handle connected to the cylindrical support. DESCRIPTION OF FIGURES

[0008] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0009] [Fig.1a] is a schematic front view of an exemplary body of a metal detector according to a first embodiment of the invention;

[0010] [Fig.lb] is a bottom view of the body of [Fig. la];

[0011] [Fig.2a] is a schematic front view of a first example of a body of a metal detector according to a second embodiment of the invention;

[0012] [Fig.2b] is a bottom view of the body of [Fig.2a];

[0013] [Fig.3a] is a schematic front view of a second example of a body of a metal detector according to a second embodiment of the invention;

[0014] [Fig.3b] is a bottom view of the body of [Fig.3a];

[0015] [Fig.4a] is a schematic front view of a second example of a body of a metal detector according to a second embodiment of the invention;

[0016] [Fig.4b] is a bottom view of the body of [Fig.4a];

[0017] [Fig. 5] schematically represents a control system that can be used in a metal detector according to one embodiment of the invention;

[0018] [Fig.6a] schematically represents an example of processing means of a metal detector according to a first embodiment of the invention;

[0019] [Fig.6b] schematically represents an example of processing means of a metal detector according to a second embodiment of the invention;

[0020] [Fig.6c] schematically represents an example of processing means of a metal detector according to a third embodiment of the invention;

[0021] [Fig.7] illustrates an example of a metal object detector according to an embodiment of the invention;

[0022] [Fig.8] illustrates the magnetic field generated by an example of a planar winding; and

[0023] [Fig.9] illustrates the magnetic field generated by an example of a winding forming a helix according to an embodiment of the invention.

[0024] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0025] A portable metal detector 1 comprises:

[0026] - a handle 2 for gripping the detector 1 by an operator;

[0027] - a body 4 comprising an inductive sensor 5; and

[0028] - processing means 6 connected to the inductive sensor 5 and configured to detect a disturbance of the magnetic field generated by the inductive sensor 5 and deduce the presence of a metallic body.

[0029] The inductive sensor 5 comprises a cylindrical support 7 made of dielectric material and one or more coils forming an emitter 8 and / or receiver 11 wound around the cylindrical support 7.

[0030] The cylindrical support 7 has a general direction of extension defining an axis X of the metal detector 1. This axis X of the detector 1 is substantially parallel to the generatrix of the cylindrical support 7. The cylindrical support 7 is preferably symmetrical and may in particular be cylindrical of revolution (tubular) or polygonal (and preferably comprise at least five sides, for example between six and twelve sides), the axis X of the detector 1 then corresponding to an axis X of symmetry of the cylindrical support 7.

[0031] In the present application, the axial direction corresponds to the direction of the X axis of the detector 1 and a radial direction is a direction perpendicular to this X axis and passing through it. Furthermore, the circumferential (or lateral) direction corresponds to a direction perpendicular to the X axis and not passing through it.

[0032] The cylindrical support 7 has a first end 9 which is connected to the handle 2 and a second end 10, which is opposite the first end 9 along the axis X and which extends close to a free end of the detector 1. An axial length L of the cylindrical support 7 corresponds to the distance, along the axis X, between the first and the second end 10. Furthermore, the cylindrical support 7 has a diameter D, in a plane normal to the axis X, between the first and the second end 10. By diameter D, we will understand here the greatest length in the radial direction which separates two points of the object. In the case of a support cylindrical 7 polygonal, the diameter D corresponds for example to the diagonal of the polygon.

[0033] The diameter D and the axial length L of the cylindrical support 7 are chosen according to the application of the metal detector 1. For example, the diameter D of the cylindrical support 7 is at least equal to 15 mm, for example between 20 mm and 70 mm. The axial length L of the cylindrical support 7 is at least twice as large as its diameter D, for example at least equal to 50 mm, preferably between 100 mm and 500 mm, typically of the order of 250 mm.

[0034] The cylindrical support 7 can be made of any suitable dielectric material which has no effect on the operation of the inductive sensor 5, for example of plastic such as polyvinyl chloride PVC, acrylonitrile butadiene styrene ABS, polycarbonate PC or a mixture thereof. It is furthermore housed in a casing 3 which is fixed on the handle 2 of the detector 1.

[0035] The emitter-forming element 8 is powered by an alternating electric current and is configured to generate a magnetic field. The receiver-forming element is configured to receive the magnetic field and detect, by means of the processing means 6, disturbances of the magnetic field due to the presence of a metallic body, for example the attenuation of the amplitude of the magnetic field, or even the change of phase of the signal, due for example to the eddy currents generated on the metallic body. In a first embodiment (illustrated by way of example in FIGS. 1a and 1b), the same winding 8 plays the role of the emitter-forming element and of the receiver-forming element. This same winding is therefore configured to alternately generate the magnetic field and detect its disturbances.In a second embodiment (illustrated as an example in FIGS. 2a to 4b), the inductive sensor 5 comprises a first winding 8, or transmitter winding, configured to form a transmitter element and a second winding 11, or receiver winding, configured to form a receiver element which is distinct from the transmitter winding 8. Each winding 8, 11 is formed from a metal wire having two ends 8a, 8b and 11a, 11b.

[0036] Whatever the embodiment, the winding 8 forming the emitting element is wound helically around the cylindrical support 7, from the first end 9 to the second end 10 of the cylindrical support 7, so as to form a first helix, or “emitting helix”.

[0037] In order to improve the sensitivity of the detector 1, a pitch P of the emitting helix is ​​strictly greater than the diameter D of the cylindrical support 7. The loops of the emitting helix are therefore not contiguous but separated by an axial distance at least equal to the diameter D of the cylindrical support 7, so that the winding 8 forming the emitting element extends substantially axially along the cylindrical support. 7, and not only orthogonally to it. The magnetic field obtained is therefore more uniform. Consequently, the coil 8 forming the receiving element (whether it is the same coil (first embodiment) or the receiving coil 11 (second embodiment) is likely to interact with the metal body, whatever its position or shape. This is particularly relevant in the case where the metal body is elongated. Indeed, the interaction between a metal body and the metal detector 1 depends on the number of flux lines captured by the metal body. However, in the case of an elongated metal body, such as a knife, few disturbed flux lines are disturbed by the metal body if it is perpendicular to the flux lines.Thus, when the turns are contiguous (the pitch of the helix is ​​small compared to the diameter D of the cylindrical support 7) and the metal body is perpendicular to the field lines, the disturbance of the magnetic field is negligible. On the other hand, when the winding forming the emitting element 8,-12 is wound helically around the cylindrical support 7 with a pitch P greater than the diameter D of the cylindrical body 4, the turns of the emitting helix are necessarily distant so that the magnetic field continuously changes direction over the entire axial length L of the cylindrical support 7: the metal body will therefore necessarily disturb the field lines generated by the coil forming the emitting element 8, whatever its position relative to the metal detector 1. This is particularly evident from Figures 8 and 9, which illustrate the magnetic field obtained by a planar winding ([Fig.8]) and a helical winding according to an embodiment of the invention ([Fig.9]). It emerges from the comparison of these two diagrams that the winding forming a helix ([Fig.9]) generates a magnetic field whose direction changes between the ends 9, 10 of the cylindrical support 7: the variation of the coupling between the magnetic field and a metallic object, in particular an elongated one, is therefore minimized, in comparison with the magnetic field substantially generated by the planar coil ([Fig.8]), which remains substantially perpendicular to the planar winding over the entire length of the cylindrical support. The interaction between the metallic body and the magnetic field obtained by winding the winding(s) 8, 11 in the form of helices is therefore independent of the orientation and shape of the metallic body.

[0038] Furthermore, the intensity of the magnetic field generated by a winding rotating on a solid shape (here, helically on the cylindrical support 7) is much greater than the intensity of the magnetic field generated by a flat coil in a plane and having the same curvilinear length, in a smaller footprint.

[0039] In order to generate a uniform magnetic field, each helix is ​​preferably centered on the X axis of the detector 1, so that its center of curvature is located on the X axis of the detector 1. In addition, it has a substantially regular pitch P between the first and second ends 10 of the cylindrical support 7.

[0040] Each helix comprises at least one turn, preferably at least two turns. The transmitter winding 8 therefore makes one turn around the X axis of at least 360° between the first and second ends 10 of the support, preferably at least 720°, which makes it possible to minimize the influence and interference with equipment placed near the metal detector 1. For example, in Figures 1a, 2a, 3a and 4a, the helixes make exactly two turns around the X axis.

[0041] In the first embodiment (Figures 1 and 1b), the winding forms both the transmitting element and the receiving element. The inductive sensor 5 therefore comprises a single transmitting winding.

[0042] In the second embodiment (Figures 2a to 4b), the inductive sensor 5 comprises the first winding 8 (transmitter winding) forming the transmitter element and the second winding 11 (receiver winding) forming the receiver element, which is distinct from the transmitter winding 8. The receiver winding 11 is then wound helically around the cylindrical support 7 between the first end 9 and the second end 10 of the cylindrical support 7 so as to form a second helix, or “receiver helix”. In addition, the pitch of the receiver helix is ​​strictly greater than the diameter D of the cylindrical support 7.

[0043] Preferably, the pitch P of the transmitting helix and the pitch of the receiving helix are identical and the two helixes are centered on the axis X of the detector 1.

[0044] The receiver winding 11 can in particular be wound from the first to the second end 10 of the cylindrical support 7. The transmitter winding 8 and the receiver winding 11 then both extend along the cylindrical support 7, over a distance equal to the axial length L of the cylindrical support 7.

[0045] The transmitter winding 8 and the receiver winding 11 can be wound around the cylindrical support 7 so that the receiver helix and the transmitter helix are angularly offset by 90° between the first end 9 and the second end 10 of the cylindrical support 7. In other words, at the first end 9 of the cylindrical support 7, the plane passing the starting points 8a, 8b of the transmitter helix (terminals of the transmitter winding 8, at the intersection of the helices) forms an angle of 90° with the plane passing through the X axis and the starting points 11a, 11b of the end of the receiver helix (terminals of the receiver winding 11, at the intersection of the helices).This angular distance between the transmitter and receiver windings 8, 11 makes it possible to reduce the mutual inductance between the transmitter winding 8 and the receiver winding 11 so that the voltage induced by the transmitter winding 8 on the receiver winding 11 is zero, which makes it possible to amplify the reception signal without saturating the amplification stage of the processing means 6. The metal detector 1 can thus detect more distant metallic bodies. Furthermore, the intensity of the magnetic field generated is greater for the same size.

[0046] The transmitting helix and the receiving helix can rotate in the same direction around the axis X of the detector 1 between the first end 9 and the second end 10. When the pitch P of the helices is identical, the angular difference between the transmitting helix and the receiving helix is ​​therefore maintained over the entire axial length L of the cylindrical support 7 so that the transmitting winding 8 and the receiving winding 11 follow each other in parallel from one end to the other of the cylindrical support 7. In this example, the transmitting helix and the receiving helix are therefore both right-handed or both left-handed.

[0047] Alternatively, the transmitting helix and the receiving helix may rotate in opposite directions around the axis X of the detector 1 between the first end 9 and the second end 10 so that the transmitting winding 8 and the receiving winding 11 intersect. For example, the transmitting helix is ​​dextral and the receiving helix is ​​sinister (or vice versa). This embodiment makes it possible to minimize the coupling and the mutual inductance between the transmitting 8 and receiving 11 windings since the transmitting and receiving windings 8, 11 do not follow each other in parallel along the cylindrical support 7 but intersect perpendicularly.

[0048] In an alternative embodiment illustrated by way of example in Figures 4a and 4b, the inductive sensor 5 further comprises an additional transmitter winding 12 and an additional receiver winding 13, which are distinct from the transmitter winding 8 and the receiver winding 11, respectively, and which are wound helically around the cylindrical support 7 between the first end 9 and the second end 10 of the cylindrical support 7 so as to form a third helix, or “additional transmitter helix” and a fourth helix, or “additional receiver helix”. Each winding 12, 13 is formed of a metal wire having two ends 12a, 12b and 13a, 13b. This alternative embodiment makes it possible to further improve the uniformity of the response of metallic objects, whatever their shape. On the other hand, the processing means 6 are more complex, as is evident for example from [Fig.6c].

[0049] The pitch of the additional transmitting propeller and the pitch of the additional receiving propeller are strictly greater than the diameter D of the cylindrical support 7.

[0050] The additional transmitter winding 12 is powered by an alternating electric current and is configured to generate a magnetic field. Where appropriate, the transmitter winding 8 and the additional transmitter winding 12 may be powered by current sources having different frequencies or by current sources having the same frequency but which are phase-shifted, typically shifted by 90°.

[0051] The additional receiver winding 13 is configured to receive the magnetic field generated by the transmitter winding(s) 8, 12 and to detect, using the means of treatment 6, disturbances of the magnetic field due to the presence of a metallic body.

[0052] Preferably, the pitch P of the transmitting helix and the pitch of the additional transmitting helix are identical. The additional transmitting helix is ​​furthermore also centered on the X axis of the detector 1. Similarly, the pitch P of the receiving helix and the pitch of the additional receiving helix are identical. The additional receiving helix is ​​furthermore also centered on the X axis of the detector 1.

[0053] The additional transmitter and receiver windings 12, 13 may in particular be wound from the first to the second end 10 of the cylindrical support 7. The windings 8, 11, 12, 13 then all extend along the cylindrical support 7, over a distance equal to the axial length L of the cylindrical support 7.

[0054] The emitter winding 8 and the additional emitter winding 12 may be wound around the cylindrical support 7 such that the emitter helix and the additional emitter helix share the same starting point at the first end 9 and the same arrival point at the second end 10 of the cylindrical support 7. In addition, the emitter helix and the additional emitter helix preferably rotate in opposite directions around the axis X of the detector 1 between the first end 9 and the second end 10 such that the emitter winding 8 and the additional emitter winding 12 intersect, preferably with an identical pitch. For example, the emitter helix is ​​right-handed and the additional emitter helix is ​​left-handed (or vice versa).

[0055] When the inductive sensor 5 comprises two emitter windings 8, 12, each emitter winding 8, 12 generates a magnetic field. Given the configuration of the emitter windings (opposite direction of rotation and positioning at the ends 9 and 10), these magnetic fields are substantially perpendicular to each other. Consequently, when an elongated metal object is placed in proximity to the detector 1, there is necessarily a high coupling between the metal object and at least one of the magnetic fields.

[0056] Furthermore, the receiving winding 11 and the additional receiving winding 13 are wound around the cylindrical support 7 so that the receiving helix and the additional receiving helix share the same starting point at the first end 9 and the same arrival point at the second end 10 of the cylindrical support 7, the starting point of the transmitting helices 8, 12 being angularly offset by 90° from the starting point of the receiving helices 11, 13. In other words, at the first end 9 of the cylindrical support 7, the plane passing the starting points of the transmitting helices forms an angle of 90° with the plane passing through the X axis and the starting points of the end of the receiving helices (see [Fig.4b]). In addition, the receiving helix and the additional receiving helix preferably rotate in opposite directions around the X axis of the detector 1 between the first end 9 and the second end 10 so that the receiver coil 11 and the additional receiver coil 13 intersect, preferably with an identical pitch. For example, the receiver helix is ​​dextral and the additional receiver helix is ​​sinister (or vice versa). The use of two receiver coils 11, 13 makes it possible to reduce the variation in signal intensity when the metal object being detected is elongated.

[0057] It will be noted that in Figures 4a and 4b, the transmitting propeller and the additional transmitting propeller on the one hand and the receiving propeller and the additional receiving propeller on the other hand are represented in a slightly offset manner for the sake of simplification in order to be able to visualize them.

[0058] Optionally, one or more helical grooves may be formed on the surface of the cylindrical support 7 in order to block the emitter winding(s) 8, 12 and the receiver winding(s) 11, 13 relative to the cylindrical support 7. The grooves therefore extend circumferentially around the cylindrical support 7 and are preferably open-ended. All or part of the windings (emitter(s) 8, 12 receiver(s) 11, 13) are then housed in a corresponding groove, which makes it possible to reduce the relative movements of the windings 8, 12, 11, 13 likely to disturb the detection.

[0059] Whatever the embodiment, the metal detector 1 may comprise a power supply system 14 comprising an autonomous electrical power source 15, such as a cell or battery which may be rechargeable, configured to power the emitter winding(s) 8, 12 and the processing means 6. [Fig. 5] represents for example a power supply system 14 comprising a rechargeable battery 15, a battery charger 16, a controller 17, a power supply regulator 18 and a switch 19. The voltages Vm1Cro, Vtx and VRX at the output of the power supply regulator 18 are transmitted to the processing means 6 of the inductive sensor 5 (FIGS. 6a to 6c).

[0060] The processing means 6 may comprise a microprocessor 20 such as one or more electronic cards, a memory and, if necessary, an alarm 21 (which may be an audible and / or visual alarm). The processing means 6 are connected to the inductive sensor 5 and are configured to receive and process signals generated by the receiver coil(s) 11, 13 and, if necessary, send instructions for generating an alarm to the alarm 21 of the metal detector 1.

[0061] By way of non-limiting example, the processing means 6 comprise:

[0062] - a microprocessor 20 comprising a DDS digital frequency synthesizer 22 (an acronym for Direct Digital Synthesis) and a digital mixer 23 connected to the DDS. The DDS is configured to generate a control signal having a determined frequency which is transmitted to the winding transmitter 8,. The digital mixer 23 configured to receive a signal from the receiver winding 11, and to deduce therefrom, from the frequency of the control signal, a disturbance of the magnetic field;

[0063] - an alarm 21 connected to the microprocessor 20 and configured to receive microprocessor instructions 20;

[0064] - control means 24, such as buttons, configured to be actuated by an operator and allow the operator to control a sensitivity of the inductive sensor 5 and / or an amplitude (sound level / light intensity / color) of the alarm 21;

[0065] - a first amplifier 25 configured to amplify the generated control signal by the DDS and transmit the amplified signal to the transmitter coil 8, ;

[0066] - a second amplifier 26 configured to amplify a signal received by the receiver coil 11, and transmit the amplified signal to the digital mixer 23 via a digital-to-analog converter 27.

[0067] The processing means 6 may be housed in whole or in part in the housing 3 of the body 4 and / or the handle 2 of the metal detector 1.

[0068] [Fig.6a] illustrates an embodiment in which the inductive sensor 5 comprises only a single winding forming a transmitter and receiver, the first amplifier 25 preferably controls the winding via impedances Z. The processing means 6 illustrated in [Fig.6a] can therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to FIGS. 1a and 1b.

[0069] [Fig.6b] illustrates an embodiment in which the inductive sensor 5 comprises a transmitter winding 8 and a receiver winding 11. The processing means 6 illustrated in [Fig.6b] can therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to FIGS. 2a and 2b or 3a and 3b.

[0070] [Fig.6c] illustrates an embodiment in which the inductive sensor comprises two transmitter windings 8, 12 and two receiver windings 11, 13. In this case, the processing means 6 may comprise a first additional amplifier 25' connected to the DDS 22 and a second additional amplifier 26' connected to the digital mixer 23. The processing means 6 illustrated in [Fig.6c] may therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to FIGS. 4a and 4b.

Claims

Claims

1. A portable metal detector (1) comprising: - a cylindrical support (7) made of dielectric material having a general direction of extension defining an axis (X) of the metal detector (1), the cylindrical support (7) having, between a first end (9) and a second end (10) of the cylindrical support (7), a diameter (D) in a plane normal to the axis (X) of the detector; and - an inductive sensor (5) comprising: - a transmitter coil (8) wound helically around the cylindrical support (7) from the first end (9) to the second end (10) of the cylindrical support (7) so as to form a transmitter helix; and - a receiver coil (11) wound helically around the cylindrical support (7) between the first end (9) and the second end (10) of the cylindrical support (7) so as to form a receiver helix;a pitch (P) of the transmitting propeller and a pitch (P) of the receiving propeller being strictly greater than the diameter (D) of the cylindrical support (7).;

2. A metal detector (1) according to claim 1, wherein the transmitting helix and the receiving helix comprise at least one turn, preferably at least two turns.

3. Metal detector (1) according to one of claims 1 and 2, wherein the pitch (P) of the transmitting helix and the pitch of the receiving helix are identical.

4. Metal detector (1) according to one of claims 1 to 3, wherein the transmitting helix and the receiving helix are angularly offset by 90° between the first end (9) and the second end (10) of the cylindrical support (7).

5. A metal detector (1) according to one of claims 1 to 4, wherein the transmitting helix and the receiving helix rotate in opposite directions around the axis (X) of the metal detector (1) between the first end (9) and the second end (10) so that the winding (8) and the receiving winding (11) intersect.

6. A metal detector (1) according to one of claims 1 to 5, wherein the transmitting propeller and the receiving propeller rotate in the same direction around the axis (X) of the metal detector (1) between the first and second ends (10).

7. Metal detector (1) according to one of claims 1 to 6, further comprising an additional transmitter coil (12) wound helically around the cylindrical support (7) between the first end (9) and the second end (10) of the cylindrical support (7) so as to form an additional transmitter helix, a pitch of the additional transmitter helix being strictly greater than the diameter (D) of the cylindrical support (7).

8. A metal detector (1) according to claim 7, wherein the pitch of the additional transmitting helix is ​​equal to the pitch (P) of the transmitting helix and wherein the transmitting helix and the additional transmitting helix rotate in opposite directions around the axis (X) of the metal detector (1) between the first end (9) and the second end (10) so that the transmitting winding (8) and the additional transmitting winding (12) intersect.

9. A metal detector (1) according to either of claims 7 and 8, wherein the transmitting helix and the further transmitting helix (12) intersect at the first end (9) at a crossing point.

10. Metal detector (1) according to one of claims 7 to 9, further comprising an additional receiving coil (13) wound helically around the cylindrical support (7) between the first end (9) and the second end (10) of the cylindrical support (7) so as to form an additional receiving helix, a pitch of the additional receiving helix being strictly greater than the diameter (D) of the cylindrical support (7).

11. A metal detector (1) according to claim 11, wherein the pitch (P) of the additional receiving helix is ​​equal to the pitch of the receiving helix and the receiving helix and the additional receiving helix rotate in opposite directions around the axis (X) of the metal detector (1) between the first end (9) and the second end (10) so that the receiving winding (11) and the additional receiving winding (13) intersect.

12. A metal detector (1) according to one of claims 10 and 11, wherein the receiving helix (11) and the additional receiving helix (13) intersect at the first end (9) at an additional crossing point.

13. A detector according to claims 9 and 12 taken in combination, wherein the crossing point and the further crossing point are angularly offset by 90°.

14. A metal detector (1) according to one of claims 1 to 13, further comprising a handle (2) connected to the cylindrical support (7).

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