Portable metal detector comprising a helical winding

Abstract

The invention relates to a portable metal detector (1) comprising: - a cylindrical support (7) made of dielectric material which has a general direction of extension that defines 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 winding (8) helically wound 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).

Description

[0001] DESCRIPTION

[0002] TITLE: Portable metal detector comprising a helical coil

[0003] TECHNICAL FIELD

[0004] This application 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 use.

[0005] STATE OF THE ART

[0006] A handheld metal detector generally comprises a handle for gripping the detector by an operator, a body comprising measuring means and processing means.

[0007] 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 that 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.

[0008] 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 allows to have a more compact detection probe but with a strong loss of sensitivity at short distance.

[0009] EXPOSED

[0010] An aim of the present application is to remedy the aforementioned drawbacks by proposing a portable metal detector which is compact while having a sensitivity which is suitable and at least equivalent to that of standard portable detectors.

[0011] For this purpose, a portable metal detector is provided in accordance with the appended claims.

[0012] The handheld metal detector may include:

[0013] - 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

[0014] - an inductive sensor comprising:

[0015] - a transmitter coil wound helically around the cylindrical support from the first end to the second end of the cylindrical support so as to form a transmitter helix; and

[0016] - a receiving coil 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.

[0017] Moreover, a pitch of the transmitting propeller and a pitch of the receiving propeller being strictly greater than the diameter of the cylindrical support.

[0018] Some preferred but non-limiting features of the handheld metal detector described above are the following, taken individually or in combination:

[0019] - the transmitting propeller and the receiving propeller comprise at least one turn, preferably at least two turns.;

[0020] - the pitch of the transmitting propeller and the pitch of the receiving propeller are identical;

[0021] - the transmitting propeller and the receiving propeller are angularly offset by 90° between the first end and the second end of the cylindrical support;

[0022] - the transmitting helix and the receiving 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 receiving winding intersect;

[0023] - the transmitting propeller and the receiving propeller rotate in the same direction around the axis of the metal detector between the first and second ends;

[0024] - the portable 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;

[0025] - the pitch of the additional transmitting helix is ​​equal to the pitch of the transmitting helix and wherein the transmitting 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 transmitting winding and the additional transmitting winding intersect;

[0026] - the transmitting helix and the additional transmitting helix intersect at the first end at a crossing point;

[0027] - the portable metal detector further comprises an additional receiving 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 receiving helix, a pitch of the additional receiving helix being strictly greater than the diameter of the cylindrical support;

[0028] - 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;

[0029] - the receiving helix and the additional receiving helix intersect at the first end at an additional crossing point;

[0030] - the crossing point and the additional crossing point are angularly offset by 90°;

[0031] - the handheld metal detector further comprises a handle connected to the cylindrical support; and / or

[0032] - the transmitter winding and the receiver winding are wound against the cylindrical support so as to be in contact with the cylindrical support.

[0033] DESCRIPTION OF FIGURES

[0034] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the attached drawings in which:

[0035] Figure 1a is a schematic front view of an exemplary body of a metal detector according to a first embodiment;

[0036] Figure 1b is a bottom view of the body of Figure 1a;

[0037] Figure 2a is a schematic front view of a first exemplary body of a metal detector according to a second embodiment;

[0038] Figure 2b is a bottom view of the body of Figure 2a;

[0039] Figure 3a is a schematic front view of a second exemplary body of a metal detector according to a third embodiment;

[0040] Figure 3b is a bottom view of the body of Figure 3a;

[0041] Figure 4a is a schematic front view of a second exemplary body of a metal detector according to a fourth embodiment;

[0042] Figure 4b is a bottom view of the body of Figure 4a;

[0043] Figure 5 schematically represents a control system suitable for use in a metal detector according to one embodiment;

[0044] Figure 6a schematically represents an example of processing means of a metal detector according to a first embodiment;

[0045] Figure 6b schematically represents an example of processing means of a metal detector according to a second embodiment;

[0046] Figure 6c schematically represents an example of processing means of a metal detector according to a third embodiment;

[0047] Figure 7 illustrates an exemplary metal object detector according to one embodiment;

[0048] Figure 8 illustrates the magnetic field generated by an example of a planar winding; and

[0049] Figure 9 illustrates the magnetic field generated by an exemplary coil forming a helix according to one embodiment.

[0050] Throughout the figures, similar elements have identical references.

[0051] DETAILED DESCRIPTION

[0052] A handheld metal detector 1 includes:

[0053] - a handle 2 for gripping the detector 1 by an operator;

[0054] - a body 4 comprising an inductive sensor 5; and - 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 to deduce therefrom the presence of a metallic body.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 polygonal cylindrical support 7, the diameter D corresponds for example to the diagonal of the polygon.

[0059] 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.

[0060] 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 a plastic material such as polyvinyl chloride PVC, acrylonitrile butadiene styrene ABS, polycarbonate PC or a mixture thereof. It is further housed in a housing 3 which is fixed on the handle 2 of the detector 1.

[0061] The transmitter element 8 is powered by an alternating electric current and is configured to generate a magnetic field. The receiver element is configured to receive the magnetic field and detect, using 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 phase change of the signal, due for example to the eddy currents generated on the metallic body. In a first embodiment (illustrated as an example in FIGS. 1a and 1b), the same winding 8 plays the role of the transmitter element and the receiver 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 s. Each winding 8, 11 is formed from a metal wire having two ends 8a, 8b and 11a, 11b.

[0062] Each winding 8, 11 is preferably wound against the cylindrical support 7 so as to be in contact with the cylindrical support 7 over a majority of its length, preferably over its entire length, except at the level of overlaps between the metal wires of the windings.

[0063] A portable detector 1 is therefore structurally different from a fixed metal detector. Indeed, the portable metal detector 1 comprises an inductive sensor 5 equipped with a single antenna which comprises at the same time at least one transmitter element and at least one receiver element which are wound on the same support 7. Conversely, a fixed metal detector comprises two separate panels, which can be connected by a crosspiece and which together delimit a channel, each panel comprising an antenna forming either a transmitter or a receiver. The transmitter and receiver elements are therefore not housed in the same panel but in separate panels and therefore cannot, a fortiori, be wound on the same support.

[0064] 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”.

[0065] 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 winding 8 forming the receiving element (whether it is the same winding (first embodiment) or the receiving winding 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 of elongated shape.Indeed, the interaction between a metallic body and the metal detector 1 depends on the number of flux lines captured by the metallic body. However, in the case of an elongated metallic body, such as a knife, few disturbed flux lines are disturbed by the metallic 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 metallic 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 at 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 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 FIGS. 8 and 9, which illustrate the magnetic field obtained by a planar winding (FIG. 8) and a helical winding according to one embodiment (FIG. 9).It emerges from the comparison of these two diagrams that the winding forming a helix (figure 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 (figure 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.

[0066] Furthermore, the intensity of the magnetic field generated by a winding rotating on a solid form (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.

[0067] 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.

[0068] 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.

[0069] In the first embodiment (Figures 1 and 1 b), the winding forms both the transmitting element and the receiving element. The inductive sensor 5 therefore comprises a single transmitting winding

[0070] 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. Preferably, the pitch P of the transmitter helix and the pitch of the receiver helix are identical and the two helices are centered on the axis X of the detector 1.

[0071] The receiving winding 11 can in particular be wound from the first to the second end

[0072] 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.

[0073] 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.

[0074] 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

[0075] 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.

[0076] Alternatively, the transmitting helix and the receiving helix may 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 transmitting winding 8 and the receiving winding 11 intersect. For example, the transmitting helix is ​​dextral and the receiving helix is ​​sinistral (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.

[0077] In an alternative embodiment, the inductive sensor 5 further comprises an additional transmitter winding 12 and / or 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 / or a fourth helix, or “additional receiver helix”. For example, the inductive sensor 5 further comprises an additional transmitter winding 12 and an additional receiver winding 13 (alternative illustrated by way of example in FIGS. 4a and 4b) 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 an additional transmitter helix and an additional receiver helix.

[0078] Each winding 12, 13 is formed from 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 metal objects, whatever their shape. On the other hand, the processing means 6 are more complex, as is apparent for example from FIG. 6c.

[0079] 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.

[0080] The additional transmitter winding 12 is powered by an alternating electric current and is configured to generate a magnetic field. If desired, 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°.

[0081] 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 processing means 6, disturbances of the magnetic field due to the presence of a metallic body.

[0082] 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.

[0083] The additional transmitter and receiver windings 12, 13 can 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.

[0084] The emitter winding s 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 a common starting point at the first end 9 and a common ending 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 s 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).

[0085] 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.

[0086] Furthermore, when the inductive sensor 5 comprises two receiving coils 11, 13, the receiving coils 11, 13 are wound around the cylindrical support 7 so that the receiving helix and the additional receiving helix preferably 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 receiving coil 11 and the additional receiving coil 13 intersect, preferably with an identical pitch. For example, the receiving helix is ​​dextral and the additional receiving helix is ​​sinister (or vice versa). The use of two receiving coils 11, 13 makes it possible to reduce the variation in the signal intensity when the metal object being detected is elongated.

[0087] In addition, when the inductive sensor 5 comprises two receiving windings 11, 13 and two transmitting windings 8, 12, the receiving helix and the additional receiving helix preferably 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 figure 4b).

[0088] It should 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.

[0089] Optionally, one or more helical grooves may be formed on the surface of the cylindrical support 7 in order to block the transmitter 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 (transmitter(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.

[0090] Whatever the embodiment, the metal detector 1 may comprise a power supply system 14 comprising an autonomous electrical power source 15, such as a battery or cell 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 VMICRO, 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).

[0091] The processing means 6 may comprise a microprocessor 20 such as one or more electronic cards, a memory and, where appropriate, 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, where appropriate, send instructions for generating an alarm to the alarm 21 of the metal detector 1.

[0092] By way of non-limiting example, the processing means 6 include:

[0093] - a microprocessor 20 comprising a digital frequency synthesizer DDS 22 (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 transmitter winding 8,. The digital mixer 23 is 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;

[0094] - an alarm 21 connected to the microprocessor 20 and configured to receive instructions from the microprocessor 20;

[0095] - 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;

[0096] - a first amplifier 25 configured to amplify the control signal generated by the DDS and transmit the amplified signal to the transmitter winding 8;

[0097] - 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.

[0098] The processing means 6 can 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.

[0099] Figure 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 drives the winding via impedances Z. The processing means 6 illustrated in Figure 6a can therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to Figures 1a and 1b.

[0100] Figure 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 Figure 6b can therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to Figures 2a and 2b or 3a and 3b.

[0101] Figure 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 Figure 6c may therefore be implemented in a detector comprising an inductive sensor 5 as described with reference to Figures 4a and 4b.

Claims

CLAIMS 1. 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 receiving winding (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 receiving helix; a pitch (P) of the transmitting helix and a pitch (P) of the receiving helix being strictly greater than the diameter (D) of the cylindrical support (7).

2. 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, in which 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. 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. 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 a additional transmitting propeller, a pitch of the additional transmitting propeller 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. Metal detector (1) according to one of claims 7 and 8, wherein the transmitting helix and the additional transmitting helix (12) intersect at the first end (9) at a crossing point.

10. Metal detector (1) according to one of claims 1 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. Metal detector (1) according to claim 10, 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. 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. Detector according to claims 9 and 12 taken in combination, in which the crossing point and the additional crossing point are angularly offset by 90°.

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

15. Metal detector (1) according to one of claims 1 to 14, wherein the transmitter coil (8) and the receiver coil (11) are wound against the cylindrical support (7) so as to be in contact with the cylindrical support (7).

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