Portable metal detector with spiral winding

Abstract

The present invention relates to a portable metal detector (1), comprising a cylindrical support (7) made of an insulating material, having an extension direction defining an axis (X) of the metal detector (1), and having a diameter (D) in a plane perpendicular to the axis (X) of the metal detector (1) between a first end (9) and a second end (10) of the cylindrical support (7), and an inductive sensor (5) including a transmitter winding (8) wound helically around the cylindrical support (7) to form a helix from the first end (9) to the second end (10) of the cylindrical support (7), the pitch (P) of the helix being strictly greater than the diameter (D) of the cylindrical support (7).

Description

[Technical Field]

[0001] The present application relates to the technical field of portable metal detectors, in particular metal detectors for detecting metal in controlled access areas such as airport departure halls or for personal (leisure) and commercial use. [Background technology]

[0002] A portable metal detector typically comprises a handle for an operator to hold the detector, and a body containing measuring means and processing means.

[0003] The measuring means may, for example, comprise an inductive sensor that measures the change in inductance caused by the metal being detected. The inductive sensor may have a single winding that constitutes the transmitter and receiver, or it may have separate transmitter and receiver windings. The transmitter winding generates an electromagnetic field that effectively penetrates non-metallic materials such as soil, water, and clothing. The presence of a metal object in the vicinity of the winding disrupts the magnetic field generated by the winding. This disruption is detected by the processing means, which sends an alarm signal to the detector's alarm.

[0004] The windings of handheld detector detection probes are typically constructed from planar, rectangular, or circular coils that optimize the surface area to perimeter ratio, allowing for sufficient sensitivity at distances of a few centimeters from the winding. Alternatively, more compact detection probes can be wound laterally around a support, but this significantly reduces sensitivity at short distances. Summary of the Invention

[0005] One of the objectives of the present application is to propose a portable metal detector that is compact and has adequate sensitivity, at least equal to or greater than that of a standard portable detector, in order to overcome the above-mentioned drawbacks.

[0006] To achieve this object, a portable metal detector is proposed according to the appended claims.

[0007] Portable metal detectors, in particular, a cylindrical support made of an insulating material, the cylindrical support having an extension direction defining an axis of the metal detector, the cylindrical support having a diameter in a plane perpendicular to the axis of the metal detector between a first end and a second end of the cylindrical support; An inductive sensor, a transmitter winding spirally wound around the cylindrical support from a first end to a second end of the cylindrical support to form a transmitter helix; and an inductive sensor including a receiver winding spirally wound around the cylindrical support to form a receiver helix between a first end and a second end of the cylindrical support.

[0008] Also, the pitch of the transmitter helix and the pitch of the receiver helix are strictly greater than the diameter of the cylindrical support.

[0009] Specific preferred but non-limiting features of the portable metal detector described above, individually or in combination, are:

[0010] The transmitter helix and the receiver helix each have one or more turns, preferably two or more turns.

[0011] The pitch of the transmitting spiral and the pitch of the receiving spiral are equal.

[0012] The transmitter and receiver helices are offset at a 90° angle between the first and second ends of the cylindrical support.

[0013] The transmitter and receiver helices rotate in opposite directions about the axis of the metal detector between the first and second ends such that the transmitter and receiver windings intersect.

[0014] The transmitting helix and the receiving helix rotate in the same direction about the axis of the metal detector between the first end and the second end.

[0015] The metal detector further comprises a further transmitter winding helically wound around the cylindrical support to form a further transmitter helix between the first end and the second end of the cylindrical support, the pitch of the further transmitter helix being strictly greater than the diameter of the cylindrical support.

[0016] The pitch of the further transmitter helix is ​​equal to the pitch of the transmitter helix, and the transmitter helix and the further transmitter helix rotate in opposite directions around the axis of the metal detector between the first end and the second end so that the transmitter winding and the further transmitter winding intersect.

[0017] The transmitter helix and the further transmitter helix intersect at a first end at a crossing point.

[0018] The metal detector further comprises a further receiving winding spirally wound around the cylindrical support to form a further receiving spiral between the first end and the second end of the cylindrical support, the pitch of the further receiving spiral being strictly greater than the diameter of the cylindrical support.

[0019] The pitch of the further receiving spiral is equal to the pitch of the receiving spiral, and the receiving spiral and the further receiving spiral 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 further receiving winding intersect.

[0020] The receiver helix and the further receiver helix intersect at the first end at a further intersection point.

[0021] The intersection point and the further intersection point are offset by an angle of 90°.

[0022] The metal detector further comprises a handle connected to the cylindrical support.

[0023] The transmitter winding and the receiver winding are wound around the cylindrical support so as to be in contact with the cylindrical support.

[0024] Other features, objects and advantages will become apparent from the following description, which is purely illustrative and non-limiting, read in conjunction with the accompanying drawings, in which: [Brief explanation of the drawings]

[0025] [Figure 1a] 1 is a schematic front view of an example of a main body of a metal detector according to a first embodiment. [Figure 1b] FIG. 1b is a bottom view of the main body of FIG. 1a. [Figure 2a] FIG. 10 is a schematic front view of a first example of a main body of a metal detector according to a second embodiment. [Figure 2b] FIG. 2b is a bottom view of the main body of FIG. 2a. [Figure 3a] FIG. 10 is a schematic front view of a second example of the main body of the metal detector according to the third embodiment. [Figure 3b] FIG. 3b is a bottom view of the main body of FIG. 3a. [Figure 4a] FIG. 10 is a schematic front view of a second example of the main body of the metal detector according to the fourth embodiment. [Figure 4b] FIG. 4b is a bottom view of the main body of FIG. 4a. [Figure 5] FIG. 1 shows a schematic diagram of a control system usable in a metal detector according to a first embodiment. [Figure 6a] FIG. 2 is a diagram schematically illustrating an example of a processing means of the metal detector according to the first embodiment. [Figure 6b] FIG. 10 is a diagram schematically illustrating an example of a processing means of the metal detector according to the second embodiment. [Figure 6c] FIG. 10 is a diagram schematically illustrating an example of a processing means of a metal detector according to a third embodiment. [Figure 7] FIG. 1 illustrates an example of a metal object detector according to one embodiment. [Figure 8] FIG. 1 illustrates an example of a magnetic field generated by a planar winding. [Figure 9] FIG. 2 illustrates an example of a magnetic field generated by windings forming a spiral according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] In all figures, similar elements are given the same reference numbers.

[0027] The portable metal detector 1 is a handle 2 for an operator to hold the detector 1; a main body 4 including an inductive sensor 5; and processing means 6 connected to the inductive sensor 5 and configured to detect disturbances in the magnetic field generated by the inductive sensor 5 and to infer therefrom the presence of a metal object.

[0028] The inductive sensor 5 comprises a cylindrical support 7 made of insulating material and one or more windings wound around the cylindrical support 7 constituting a transmitter 8 and / or a receiver 11 .

[0029] The cylindrical support 7 has an extension direction which defines an axis X of the metal detector 1. This axis X of the detector 1 is approximately parallel to a generatrix of the cylindrical support 7. The cylindrical support 7 is preferably symmetrical, in particular cylindrical of revolution (tubular) or polygonal (preferably having five or more sides, for example 6 to 12 sides), and the axis X of the detector 1 corresponds to the axis of symmetry X of the cylindrical support 7.

[0030] In this application, the axial direction corresponds to the direction of the axis X of the detector 1, the radial direction is the direction perpendicular to and passing through the axis X, and the circumferential direction (or lateral direction) corresponds to the direction perpendicular to and not passing through the axis X.

[0031] The cylindrical support 7 has a first end 9 connected to the handle 2 and a second end 10 located opposite the first end 9 along the axis X and extending toward the free end of the detector 1. The axial length L of the cylindrical support 7 corresponds to the distance between the first end and the second end 10 along the axis X. Furthermore, the cylindrical support 7 has a diameter D between the first end and the second end 10 in a plane perpendicular to the axis X. Here, the diameter D refers to the maximum radial length between two points on the object. If the cylindrical support 7 is polygonal, the diameter D corresponds, for example, to the diagonal of the polygon.

[0032] The diameter D and axial length L of the cylindrical support 7 are selected depending on the application of the metal detector 1. For example, the diameter D of the cylindrical support 7 is 15 mm or more, for example, in the range of 20 mm to 70 mm. The axial length L of the cylindrical support 7 is at least twice the diameter D, for example, 50 mm or more, preferably in the range of 100 mm to 500 mm, and typically about 250 mm.

[0033] The cylindrical support 7 is made of a suitable insulating material that does not affect the operation of the inductive sensor 5, such as a plastic material such as polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), or a mixture thereof. The cylindrical support 7 is housed in a casing 3 that is fixed to the handle 2 of the detector 1.

[0034] The transmitter 8 is driven by an alternating current and is configured to generate a magnetic field. The receiver receives the magnetic field and, using the processing means 6, detects disturbances in the magnetic field due to the presence of a metal object, such as attenuation of the magnetic field amplitude or a change in the signal phase due to eddy currents generated in the metal object. In a first embodiment (illustrated in FIGS. 1a and 1b), the same winding 8 serves as both transmitter and receiver; that is, it is configured to alternately generate a magnetic field and detect its disturbances. In a second embodiment (illustrated in FIGS. 2a to 4b), the inductive sensor 5 includes a first winding 8 (transmitter winding) configured to form a transmitter and a second winding 11 (receive winding) different from the transmitter winding 8 and configured to form a receiver. Each winding 8, 11 is formed from a metal wire having two ends 8a, 8b and 11a, 11b.

[0035] Each winding 8, 11 is wound around the cylindrical support 7 so that it is in contact with the cylindrical support 7 over most, preferably the entire length, except for the overlapping portions of the metal wires of the windings.

[0036] The portable metal detector 1 differs structurally from the fixed metal detector. In fact, the portable metal detector 1 consists of an inductive sensor 5 with a single antenna that simultaneously includes at least one transmitter and at least one receiver, wrapped around a single support 7. On the other hand, the fixed metal detector consists of two independent panels that can be connected by a crosspiece and that together define a channel, each panel having an antenna that forms a transmitter or a receiver. Therefore, the transmitter and receiver are not housed in the same panel, but are arranged on separate panels, and therefore cannot naturally be wrapped around the same support.

[0037] In either embodiment, the winding 8 forming the transmitter is wound helically around the cylindrical support 7 from a first end 9 to a second end 10 of the cylindrical support 7 to form a first helix, or "transmitter helix."

[0038] To improve the sensitivity of the detector 1, the pitch P of the transmitting spiral is strictly greater than the diameter D of the cylindrical support 7. Therefore, the loops of the transmitting spiral are not close to each other, but are spaced apart by an axial distance equal to or greater than the diameter D of the cylindrical support 7. This ensures that the winding 8 forming the transmitter extends substantially axially along the cylindrical support 7, and not perpendicularly thereto. This results in a more uniform magnetic field. Consequently, the winding 8 forming the receiver (the same winding in the first embodiment, the receiver winding 11 in the second embodiment) is more likely to interact with the metal object, regardless of the object's position or shape. This is particularly important when the metal object has an elongated shape. Indeed, the interaction between the metal object and the metal detector 1 depends on the number of magnetic flux lines captured by the metal object. However, in the case of an elongated metal object, such as a knife, the magnetic flux lines are hardly disturbed when the metal object is perpendicular to them. Therefore, when the loops are close together (the spiral pitch is small compared to the diameter D of the cylindrical support 7), the magnetic field disturbance is negligible when the metal object is perpendicular to the magnetic flux lines. On the other hand, if the windings forming the transmitters 8, 12 are wound helically around the cylindrical support 7 with a pitch P greater than the diameter D of the cylindrical support 7, the loops of the transmitter helix will necessarily be spaced apart, causing the magnetic field to change direction continuously throughout the axial length L of the cylindrical support 7. Therefore, metal objects disrupt the magnetic flux lines generated by the coils forming the transmitter 8, regardless of their position relative to the metal detector 1. This is particularly evident from FIGS. 8 and 9, which show the magnetic field resulting from a planar winding and the magnetic field resulting from a helical winding in one embodiment. A comparison of these two figures reveals that the helical winding (FIG. 9) generates a magnetic field whose direction changes between the ends 9, 10 of the cylindrical support 7. Therefore, variations in the coupling of the magnetic field with metals (especially elongated objects) are minimized compared to the magnetic field generated by a planar winding (FIG. 8), which is generally perpendicular to the planar winding throughout the entire length of the cylindrical support 7. In this way, the interaction between the magnetic field obtained by winding the windings 8 and 11 in a spiral shape and the metal body does not depend on the orientation or shape of the metal body.

[0039] Furthermore, the strength of the magnetic field generated by a winding rotating on a solid shape (here a coil wound helically on a cylindrical support 7) will be much greater than the strength of the magnetic field generated by a planar coil on a plane of the same curved length, despite its smaller overall dimensions.

[0040] To generate a uniform magnetic field, each spiral is centered on the X-axis of the detector 1 such that its center of curvature lies on the X-axis of the detector 1. Furthermore, a substantially regular pitch P is set between the first end 10 and the second end 10 of the cylindrical support 7.

[0041] Each spiral has at least one turn, preferably at least two turns. The transmitter winding 8 can be rotated at least 360°, preferably at least 720°, about the axis X between the first and second ends 10 of the support to minimize the effect on and interference with equipment located in the vicinity of the metal detector 1. For example, in Figures 1a, 2a, 3a and 4a the spiral has exactly two turns about the axis X.

[0042] In the first embodiment (FIGS. 1 and 1b), the winding constitutes both the transmitter and the receiver, so that the inductive sensor 5 consists of a single transmitting winding.

[0043] In a second embodiment (FIGS. 2a to 4b), the inductive sensor 5 comprises a first winding 8 (transmitter winding) constituting the transmitter and a second winding 11 (receiver winding) different from the transmitter winding 8 constituting the receiver. The receiver winding 11 is wound helically around the cylindrical support 7 between the first end 9 and the second end 10 of the cylindrical support 7 to form a second spiral or "receiver spiral", the pitch of which is strictly greater than the diameter D of the cylindrical support 7.

[0044] Preferably, the pitch P of the transmitting helix and the pitch of the receiving helix are equal and both helixes are centered on the axis X of the detector 1 .

[0045] The receiver winding 11 is wound in particular from a first end to a second end 10 of the cylindrical support 7. Both the transmitter winding 8 and the receiver winding 11 extend along the cylindrical support 7 over a distance equal to the axial length L of the cylindrical support 7.

[0046] The transmitter winding 8 and the receiver winding 11 may be wound around the cylindrical support 7 such that the receiver and transmitter helices are offset by a 90° angle between the first end 9 and the second end 10 of the cylindrical support 7. That is, at the height of the first end 9 of the cylindrical support 7, a plane passing through the start points 8a, 8b of the transmitter helices (the ends of the transmitter winding 8 at the intersections of the helices) forms a 90° angle with a plane passing through the axis X and the start points 11a, 11b of the receiver helices (the ends of the receiver winding 11 at the intersections of the helices). This angular difference between the transmitter winding 8 and the receiver winding 11 reduces the mutual inductance between them and zeros the voltage induced by the transmitter winding 8 in the receiver winding 11. This allows the received signal to be amplified without saturating the amplifier stage of the processing means 6. Therefore, the metal detector 1 can detect metal objects at a greater distance. Furthermore, the strength of the magnetic field produced is greater for the same overall dimensions.

[0047] The transmitter and receiver helices may rotate in the same direction about the axis X of the detector 1 between the first end 9 and the second end 10. If the helical pitch P is the same, the angular difference between the transmitter and receiver helices is maintained over the entire axial length L of the cylindrical support 7, so that the transmitter winding 8 and receiver winding 11 are arranged side-by-side in parallel across the cylindrical support 7. In this example, the transmitter and receiver helices are either both right-handed or both left-handed.

[0048] Alternatively, the transmitter and receiver helices may be counter-rotated about the axis X of the detector 1 between the first end 9 and the second end 10, such that the transmitter winding 8 and the receiver winding 11 intersect. For example, the transmitter spiral may be right-handed and the receiver spiral may be left-handed (or vice versa). In this embodiment, the transmitter winding 8 and the receiver winding 11 intersect at right angles rather than being arranged parallel to each other along the cylindrical support 7, minimizing coupling and mutual inductance between the transmitter and receiver windings 8, 11.

[0049] In one variant embodiment, the inductive sensor 5 further comprises a further transmitter winding 12 and / or a further receiver winding 13, different from the transmitter winding 8 and the receiver winding 11, respectively, which are wound spirally 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 spiral or "further transmitter spiral" and / or a fourth spiral or "further receiver spiral".

[0050] For example, the inductive sensor 5 further comprises a further transmitting winding 12 and a further receiving winding 13 (variants illustrated in Figures 4a and 4b), which are wound spirally 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 further transmitting spiral and a further receiving spiral.

[0051] Each winding 12, 13 is made of a metal wire having two ends 12a, 12b and 13a, 13b. This variant allows for a further improvement in the uniformity of the response, regardless of the shape of the metal object. On the other hand, the processing means 6 becomes more complex, as can be seen for example in Fig. 6c.

[0052] The pitch of the further transmitting spiral and the pitch of the further receiving spiral are strictly greater than the diameter D of the cylindrical support 7 .

[0053] The further transmitter winding 12 is configured to be driven with an alternating current and to generate a magnetic field. If desired, the transmitter winding 8 and the further transmitter winding 12 may be driven by current sources of different frequencies or current sources of the same frequency but out of phase (typically 90° out of phase).

[0054] A further receiver winding 13 is arranged to receive the magnetic field generated by the transmitter windings 8, 12 and to detect, by means of the processing means 6, any disturbance of the magnetic field due to the presence of a metal object.

[0055] Preferably, the pitch P of the transmitter spiral and the pitch of the further transmitter spiral are equal, and the further transmitter spiral is centered about the X axis of the detector 1. Similarly, the pitch P of the receiver spiral and the pitch of the further receiver spiral are equal, and the further receiver spiral is centered about the X axis of the detector 1.

[0056] Further transmitter and receiver windings 12, 13 are wound in particular from the first end to the second end 10 of the cylindrical support 7. Furthermore, all windings 8, 11, 12, 13 extend along the cylindrical support 7 over a distance equal to the axial length L of the cylindrical support 7.

[0057] The transmitter winding 8 and the further transmitter winding 12 may be wound around the cylindrical support 7 such that the transmitter helix and the further transmitter helix share the same starting point at a first end 9 of the cylindrical support 7 and the same ending point at a second end 10. Furthermore, the transmitter helix and the further transmitter helix may be counter-rotated about the axis X of the detector 1 between the first end 9 and the second end 10, preferably with the same pitch, such that the transmitter winding 8 and the further transmitter winding 12 intersect. For example, the transmitter helix may be right-handed and the further transmitter helix may be left-handed (or vice versa).

[0058] When the inductive sensor 5 includes two transmitter windings 8, 12, each transmitter winding 8, 12 generates a magnetic field. Due to the configuration of these transmitter windings (opposite rotation and positioned at the height of the ends 9, 10), these magnetic fields are approximately perpendicular to each other. Therefore, when an elongated metal object is placed in the vicinity of the detector 1, there is a high coupling between the metal object and at least one of the magnetic fields.

[0059] Furthermore, when the inductive sensor 5 includes two receiver windings 11, 13, these receiver windings 11, 13 are wound around the cylindrical support 7 such that the receiver spiral and the further receiver spiral rotate in opposite directions about the axis X of the detector 1, preferably with the same pitch, between the first end 9 and the second end 10, so that the receiver winding 11 and the further receiver winding 13 cross. For example, the receiver spiral may be right-handed and the further receiver spiral may be left-handed (or vice versa). Using two receiver windings 11, 13 can reduce fluctuations in signal strength when the metal object to be detected has an elongated shape.

[0060] Furthermore, if the inductive sensor 5 comprises two receiver windings 11, 13 and two transmitter windings 8, 12, the receiver spiral and the further receiver spiral preferably share a common starting point at the first end 9 of the cylindrical support 7 and a common ending point at the second end 10, the starting points of the transmitter spirals 8, 12 preferably being rotated by 90° from the starting points of the receiver spirals 11, 13, i.e. at the height of the first end 9 of the cylindrical support 7, the plane passing through the starting points of the transmitter spirals forms an angle of 90° with the axis X and with the plane passing through the starting points of the ends of the receiver spirals (see Figure 4b).

[0061] In Figures 4a and 4b, the transmitter and further transmitter spirals and the receiver and further receiver spirals are shown slightly offset for simplicity in order to make them easier to see.

[0062] Optionally, one or more spiral grooves may be formed in the surface of the cylindrical support 7 for fixing the transmitter windings 8, 12 and receiver windings 11, 13 to the cylindrical support 7. These grooves extend in the circumferential direction of the cylindrical support 7 and are preferably open. All or part of the windings (transmitter windings 8, 12 and receiver windings 11, 13) are housed in the corresponding grooves. This makes it possible to prevent relative movement of the windings 8, 12, 11, 13, which could interfere with detection.

[0063] In either embodiment, the metal detector 1 may comprise a power supply system 14 including a self-contained power supply 15, such as a rechargeable cell or battery, configured to power the transmitting windings 8, 12 and the processing means 6. Figure 5 shows, for example, the power supply system 14 comprising the rechargeable battery 15, a battery charger 16, a controller 17, a power supply regulator 18, and a switch 19. A voltage V obtained from the output of the power supply regulator 18 MICRO , V TX , and V RX is transmitted to the processing means 6 of the inductive sensor 5 (FIGS. 6a to 6c).

[0064] The processing means 6 may include a microprocessor 20, such as one or more electronic cards, a memory, and optionally an alarm 21 (e.g. an audible and / or visual alarm). The processing means 6 is connected to the inductive sensor 5 and is configured to receive and process the signals generated by the windings constituting the receivers 11, 13 and to send commands to the alarm 21 of the metal detector 1 to generate an alarm if necessary.

[0065] By way of non-limiting example, the processing means 6 may include: A microprocessor 20 comprising a digital frequency synthesizer DDS (Direct Digital Synthesizer) 22 and a digital mixer 23 connected to the DDS. The DDS is configured to generate a control signal having a predetermined frequency that is sent to the transmitting winding 8. The digital mixer 23 is configured to receive a signal from the receiving winding 11 and detect magnetic field disturbances from the frequency of the control signal. an alarm 21 connected to the microprocessor 20 and configured to receive commands from the microprocessor 20; A control means 24, such as a button, that can be actuated by an operator and that is configured to be able to control the sensitivity of the inductive sensor 5 and / or the loudness (volume level / light intensity / color) of the alarm 21. A first amplifier 25 configured to amplify the control signal generated by the DDS and to transmit the amplified signal to the transmitter winding 8. A second amplifier 26 configured to amplify the signal received at the receiver winding 11 and to transmit the amplified signal to the digital mixer 23 via a digital-to-analog converter 27.

[0066] The processing means 6 may be accommodated in whole or in part in the housing 3 of the main body 4 and / or in the handle 2 of the metal detector 1 .

[0067] Figure 6a shows an embodiment in which the inductive sensor 5 only includes a single winding forming the transmitter and receiver, and preferably a first amplifier 25 drives the winding via an impedance Z. The processing means 6 shown in Figure 6a can be implemented in a detector comprising the inductive sensor 5 described with reference to Figures 1a and 1b.

[0068] Figure 6b shows an embodiment in which the inductive sensor 5 comprises a transmitter winding 8 and a receiver winding 11. The processing means 6 shown in Figure 6b can be implemented in a detector equipped with the inductive sensor 5 described with reference to Figures 2a and 2b or 3a and 3b.

[0069] Figure 6c shows 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 further amplifier 25' connected to the DDS 22 and a second further amplifier 26' connected to the digital mixer 23. The processing means 6 shown in Figure 6c can be implemented in a detector equipped with the inductive sensor 5 described with reference to Figures 4a and 4b.

Claims

1. A portable metal detector (1), a cylindrical support (7) made of insulating material, having an extension direction defining an axis (X) of the metal detector (1), and having a diameter (D) in a plane perpendicular to the axis (X) of the metal detector (1) between a first end (9) and a second end (10) of the cylindrical support (7); An inductive sensor (5), a transmitter winding (8) wound helically around the cylindrical support (7) from a first end (9) to a second end (10) of the cylindrical support (7) to form a transmitter helix; an inductive sensor (5) including a receiver winding (11) wound helically around the cylindrical support (7) between a first end (9) and a second end (10) of the cylindrical support (7) to form a receiver helix; A metal detector (1) in which the pitch (P) of the transmitting helix and the pitch (P) of the receiving helix are strictly greater than the diameter (D) of the cylindrical support (7).

2. 2. The metal detector (1) according to claim 1, wherein the transmitting helix and the receiving helix have one or more turns, preferably two or more turns.

3. 3. The metal detector (1) according to claim 1 or 2, wherein the pitch (P) of the transmitting helix and the pitch (P) of the receiving helix are equal.

4. The metal detector (1) according to any one of claims 1 to 3, wherein the transmitting helix and the receiving helix are offset at an angle of 90° between the first end (9) and the second end (10) of the cylindrical support (7).

5. The metal detector (1) according to any one of claims 1 to 4, wherein the transmitting spiral and the receiving spiral 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 receiving winding (11) intersect.

6. The metal detector (1) according to any one of claims 1 to 5, wherein the transmitting helix and the receiving helix rotate in the same direction around the axis (X) of the metal detector (1) between the first end (9) and the second end (10).

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

8. 8. The metal detector (1) of claim 7, wherein the pitch of the further transmitting helix is ​​equal to the pitch (P) of the transmitting helix, and the transmitting helix and the further 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 further transmitting winding (12) intersect.

9. 9. A metal detector (1) according to claim 7 or 8, wherein the transmitter helix and the further transmitter helix (12) intersect at the first end (9) at an intersection point.

10. A metal detector (1) according to any one of claims 1 to 9, further comprising a further receiving winding (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 a further receiving spiral, the pitch of the further receiving spiral being strictly greater than the diameter (D) of the cylindrical support (7).

11. 11. The metal detector (1) of claim 10, wherein the pitch of the further receiving spiral is equal to the pitch (P) of the receiving spiral, and the receiving spiral and the further receiving spiral rotate in opposite directions about 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 further receiving winding (13) intersect.

12. 12. A metal detector (1) according to claim 10 or 11, wherein the receiving helix (11) and the further receiving helix (13) intersect at the first end (9) at a further intersection point.

13. A metal detector (1) combining claims 9 and 12, wherein the intersection point and the further intersection point are offset by an angle of 90°.

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

15. The metal detector (1) according to any one of claims 1 to 14, wherein the transmitting winding (8) and the receiving winding (11) are wound around the cylindrical support (7) so as to be in contact with the cylindrical support (7).

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