Portable metal detector including spiral winding

Abstract

The invention relates to a portable metal detector (1) comprising: a cylindrical support (7) made of a dielectric material having a general extension direction defining an axis (X) of the metal detector (1), the cylindrical support (7) has a diameter (D) in a plane normal to the axis (X) of the probe between the first end (9) and the second end (10) of the cylindrical support (7); and an inductive sensor (5) comprising a winding (8) wound around the cylindrical support (7) in a spiral manner from a first end (9) to a second end (10) of the cylindrical support (7) so as to form a spiral, the pitch (P) of which is strictly greater than the diameter (D) of the cylindrical support (7).

Description

Technical Field

[0001] The present application relates to the general technical field of portable metal detectors, in particular for use in detecting metal, for example when entering an airport terminal or any other similar controlled access location, but also for personal (leisure) use and commercial use. Background Art

[0002] A portable metal detector generally comprises a handle for an operator to hold the detector, a main body comprising a measuring device and a processing device.

[0003] The measuring device may, for example, include an inductive sensor for measuring the change in inductance caused by the metal being detected. The inductive sensor may include a single winding forming a transmitter and receiver, or separate transmitting and receiving windings. The transmitting winding generates an electromagnetic field that can effectively penetrate non-metallic materials (such as soil, water, clothing, etc.). The presence of a metal object near the winding disturbs the magnetic field generated by the winding. This disturbance is detected by the processing device, which sends an alarm command to the detector's alarm.

[0004] The windings of the detection probes of portable detectors usually consist of planar, rectangular or circular coils in order to optimize the surface / perimeter ratio and thus exhibit sufficient sensitivity at a distance of several centimeters from the windings, or the windings are wound transversely around the support, which allows for a more compact detection probe, but with a severe loss of sensitivity at short distances. Summary of the Invention

[0005] An object of the present application is to overcome the above-mentioned drawbacks by proposing a portable metal detector which is compact and at the same time has a suitable sensitivity, at least equivalent to that of a standard portable detector.

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

[0007] Portable metal detectors may include, in particular:

[0008] a cylindrical support made of dielectric material, having a general extension defining the 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;

[0009] -Inductive sensors, including:

[0010] - a transmitting winding wound helically around the cylindrical support from a first end to a second end of the cylindrical support so as to form a transmitting helix.

[0011] - a receiving winding wound in a helical manner around the cylindrical support between its first and second ends so as to form a receiving helix.

[0012] Furthermore, the pitch of the transmitting helix and the pitch of the receiving helix are strictly larger than the diameter of the cylindrical support.

[0013] Some preferred but non-limiting features of the portable metal detector described above are as follows, either individually or in combination:

[0014] - the transmitting helix and the receiving helix comprise at least one turn, preferably at least two turns;

[0015] - the pitch of the transmitting helix is the same as the pitch of the receiving helix;

[0016] - the transmitting helix and the receiving helix are angularly offset by 90° between the first and second ends of the cylindrical support;

[0017] - 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 transmitting winding and the receiving winding intersect;

[0018] - the transmitting helix and the receiving helix rotate in the same direction around the axis of the metal detector between the first end and the second end;

[0019] - the portable metal detector further comprises: an additional emitting winding, the additional emitting winding being wound helically around the cylindrical support between the first end and the second end of the cylindrical support so as to form an additional emitting helix, the pitch of the additional emitting helix being strictly greater than the diameter of the cylindrical support;

[0020] - 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 about the axis of the metal detector between the first end and the second end such that the transmitting winding and the additional transmitting winding intersect;

[0021] - the emitting helix and the additional emitting helix intersect at the level of the intersection at the first end;

[0022] - the portable metal detector further comprises: an additional receiving winding, the additional receiving winding being 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, the pitch of the additional receiving helix being strictly greater than the diameter of the cylindrical support;

[0023] - 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 about 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;

[0024] - the receiving helix and the additional receiving helix intersect at the level of the additional intersection at the first end;

[0025] - the intersection point and the additional intersection point are angularly offset by 90°;

[0026] - the portable metal detector further comprising: a handle connected to the cylindrical support; and / or

[0027] The transmitting and receiving windings are wound against the cylindrical support so as to be in contact with it. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features, objects and advantages will appear from the following description, which is illustrative only and not restrictive, and must be read in conjunction with the accompanying drawings, in which:

[0029] Figure 1a is a schematic front view of an exemplary main body of the metal detector according to the first embodiment;

[0030] Figure 1b yes Figure 1a A bottom view of the subject;

[0031] Figure 2a is a schematic front view of a first exemplary body of a metal detector according to a second embodiment;

[0032] Figure 2b yes Figure 2a A bottom view of the subject;

[0033] Figure 3a is a schematic front view of a second exemplary body of a metal detector according to a third embodiment;

[0034] Figure 3b yes Figure 3a A bottom view of the subject;

[0035] Figure 4a is a schematic front view of a second exemplary body of a metal detector according to a fourth embodiment;

[0036] Figure 4b yes Figure 4a A bottom view of the subject;

[0037] Figure 5 schematically illustrates a control system that may be used in a metal detector according to one embodiment;

[0038] Figure 6a Schematically illustrates an exemplary processing device of a metal detector according to a first embodiment;

[0039] Figure 6b schematically illustrates an exemplary processing device of a metal detector according to a second embodiment;

[0040] Figure 6c Schematically illustrates an exemplary processing device of a metal detector according to a third embodiment;

[0041] Figure 7 An exemplary metal object detector according to one embodiment is shown;

[0042] Figure 8 shows the magnetic field generated by an exemplary planar winding; and

[0043] Figure 9 The magnetic field generated by an exemplary winding forming a helix is shown according to one embodiment.

[0044] Similar elements have the same reference numerals throughout the drawings. DETAILED DESCRIPTION

[0045] A portable metal detector 1, comprising:

[0046] A handle 2 for holding the detector 1 by an operator;

[0047] - a body 4 comprising an inductive sensor 5; and

[0048] - a processing device 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.

[0049] The inductive sensor 5 comprises a cylindrical support 7 made of dielectric material and one or more windings forming a transmitter 8 and / or a receiver 11 wound around the cylindrical support 7 .

[0050] The cylindrical support 7 has a general extension direction defining the axis X of the metal detector 1. The 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 a rotation cylinder (tubular) or polygon (and preferably comprising at least five sides, for example between six and twelve sides), in which case the axis X of the detector 1 corresponds to the axis of symmetry X of the cylindrical support 7.

[0051] In the present application, the axial direction corresponds to the direction of the axis X of the probe 1, and the radial direction is a direction perpendicular to and passing through the axis X. Furthermore, the circumferential direction (or lateral direction) corresponds to a direction perpendicular to the axis X but not passing through it.

[0052] The cylindrical support 7 has a first end 9 connected to the handle 2 and a second end 10, the first end being opposite the first end 9 along the axis X and extending near the free end of the probe 1. The axial length L of the cylindrical support 7 corresponds to the distance along the axis X between the first end and the second end 10. Furthermore, the cylindrical support 7 has a diameter D between the first and second ends 10, in a plane normal to the axis X. The diameter D here means the maximum length along the radial direction separating 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.

[0053] The diameter D and axial length L of the cylindrical support 7 are selected according to the application of the metal detector 1. For example, the diameter D of the cylindrical support 7 is at least 15 mm, for example, between 20 mm and 70 mm. The axial length L of the cylindrical support 7 is at least twice its diameter D, for example, at least 50 mm, preferably between 100 mm and 500 mm, and typically about 250 mm.

[0054] The cylindrical support 7 can be made of any suitable dielectric material that has no effect on the operation of the inductive sensor 5, for example, a plastic material such as polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), polycarbonate (PC) or a mixture thereof. It is also housed in the housing 3 fixed to the handle 2 of the detector 1.

[0055] The transmitting element 8 is powered by an alternating current and is configured to generate a magnetic field. The receiving element is configured to receive this magnetic field and detect, by means of the processing device 6, disturbances in the magnetic field caused by the presence of the metal body, such as a decay in the amplitude of the magnetic field or even a phase change of the signal caused, for example, by eddy currents generated on the metal body. In a first embodiment (e.g. Figure 1a and Figure 1b In the example shown in FIG, the same winding 8 acts as both a transmitting element and a receiving element. The same winding is thus configured to alternately generate a magnetic field and detect its disturbances. Figures 2a to 4b In the example shown in FIG, the inductive sensor 5 includes a first winding 8 or transmitting winding configured to form a transmitting element, and a second winding 11 or receiving winding configured to form a receiving element different from the transmitting winding 8. Each winding 8, 11 is formed by a metal wire having two ends 8a, 8b and 11a, 11b.

[0056] Each winding 8 , 11 is preferably wound against the cylindrical support 7 so as to be in contact with it over most of its length, preferably over its entire length, except for the level of overlap between the metal wires of the winding.

[0057] The portable detector 1 is therefore structurally different from a fixed metal detector. In fact, the portable metal detector 1 comprises an inductive sensor 5 equipped with a single antenna, which simultaneously comprises at least one transmitting element and at least one receiving element, which are wound around a single support 7. In contrast, a fixed metal detector comprises two different panels, which can be connected by a crosspiece and jointly define a channel, each panel comprising an antenna forming a transmitter or a receiver. The transmitting element and the receiving element are therefore not housed in the same panel, but in different panels and, therefore, cannot be wound around the same support.

[0058] Whatever the embodiment, the winding 8 forming the radiating element is wound helically around the cylindrical support 7 from a first end 9 to a second end 10 thereof so as to form a first helix, or “radiating helix”.

[0059] In order 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 continuous, but are separated by an axial distance at least equal to the diameter D of the cylindrical support 7, so that the winding 8 forming the transmitting element extends essentially axially along the cylindrical support 7, and not just orthogonally thereto. The magnetic field obtained is therefore more uniform. Therefore, 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, regardless of its position or shape. This is particularly relevant when the metal body is slender. In fact, the interaction between the metal body and the metal detector 1 depends on the number of flux lines captured by the metal body. However, in the case of a slender metal body (such as a tool), if the metal body is perpendicular to the flux lines, very few disturbed flux lines are disturbed by the metal body. Therefore, when the turns are continuous (the pitch of the helix is small compared to the diameter D of the cylindrical support 7) and when the metal body is perpendicular to the magnetic field lines, the disturbance in the magnetic field is negligible. On the other hand, when the windings forming the emitting elements 8, 12 are wound helically around the cylindrical support 7 following a pitch P greater than the diameter D of the cylindrical support 4, the turns of the emitting helix are necessarily different, so that the magnetic field changes direction continuously over the entire axial length L of the cylindrical support 7: the metal body will therefore necessarily disturb the magnetic field lines generated by the coil forming the emitting element 8, whatever its position relative to the metal detector 1. This is in particular due to the fact that Figure 8 and Figure 9 It appears in Figure 8 and Figure 9 shows a planar winding ( Figure 8 ) and spiral winding ( Figure 9 ) The magnetic field obtained. From the comparison of these two diagrams, it is clear that the winding ( Figure 9 ) generates a magnetic field whose direction changes between the ends 9, 10 of the cylindrical support 7: thus, in contrast to the substantially planar coil ( Figure 8 ) is minimized compared to the magnetic field generated by the windings 8, 11, which remains substantially perpendicular to the plane of the windings over the entire length of the cylindrical support. Thus, the interaction between the metal body and the magnetic field obtained by winding the windings 8, 11 in a helical form is independent of the orientation and shape of the metal body.

[0060] Furthermore, at smaller overall dimensions, the strength of the magnetic field generated by a winding rotating on a solid shape (here in a spiral manner on the cylindrical support 7) is much greater than the strength of the magnetic field generated by a flat coil in a plane and with the same curve length.

[0061] To generate a uniform magnetic field, each helix is preferably centered on the axis X of the probe 1 so that its center of curvature lies on the axis X of the probe 1 . Furthermore, it has a substantially regular pitch P between the first and second ends 10 of the cylindrical support 7 .

[0062] Each spiral comprises at least one turn, preferably at least two turns. Thus, the transmitting winding 8 rotates a turn of at least 360°, preferably at least 720°, around the axis X between the first end and the second end 10 of the support, thereby minimizing the impact and disturbance on equipment placed near the metal detector 1. For example, in Figure 1a 、 Figure 2a 、 Figure 3a and Figure 4a In the figure, the helix rotates exactly two turns around the axis X.

[0063] In the first embodiment (Figs. 1 and Figure 1b ), the winding forms both the transmitting element and the receiving element. Thus, the inductive sensor 5 comprises a single transmitting winding.

[0064] In the second embodiment ( Figures 2a to 4b), the inductive sensor 5 comprises a first winding 8 (transmitting winding) forming a transmitting element, and a second winding 11 (receiving winding) forming a receiving element, which is different from the transmitting winding 8. The receiving winding 11 is now wound helically around the cylindrical support 7 between its first end 9 and its second end 10, so as to form a second helix, or "receiving helix." Furthermore, the pitch of the receiving helix is strictly greater than the diameter D of the cylindrical support 7.

[0065] Preferably, the pitch P of the transmitting helix is the same as the pitch of the receiving helix, and the two helices are centered on the axis X of the detector 1 .

[0066] The receiving winding 11 may in particular be wound from a first end 10 to a second end 10 of the cylindrical support 7. Both the transmitting winding 8 and the receiving winding 11 extend along the cylindrical support 7 over a distance equal to the axial length L of the cylindrical support 7.

[0067] The transmitting winding 8 and the receiving winding 11 can be wound around the cylindrical support 7 so that the receiving and transmitting spirals 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 level of the first end 9 of the cylindrical support 7, a plane passing through the starting points 8a, 8b of the transmitting spiral (the end points of the transmitting winding 8, at the intersection of the spirals) forms a 90° angle with a plane passing through the axis X and the starting points 11a, 11b of the end points of the receiving spiral (the end points of the receiving winding 11, at the intersection of the spirals). This angular offset between the transmitting winding 8 and the receiving winding 11 reduces the mutual inductance between the transmitting winding 8 and the receiving winding 11, so that the voltage induced by the transmitting winding 8 on the receiving winding 11 is zero, which makes it possible to amplify the receiver signal without saturating the amplification step of the processing device 6. As a result, the metal detector 1 is able to detect metal objects at a greater distance. In addition, the generated magnetic field strength is greater for the same overall dimensions.

[0068] The transmitting and receiving helices 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 the same, the angular deviation between the transmitting and receiving helices is thus 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 parallel from one end to the other of the cylindrical support 7. In this example, the transmitting and receiving helices are therefore both right-handed or both left-handed.

[0069] As a variant, the transmitting and receiving helices can 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 helices are right-handed and the receiving helices are left-handed (or vice versa). This embodiment makes it possible to minimize the coupling and mutual inductance between the transmitting winding 8 and the receiving winding 11, because the transmitting winding 8 and the receiving winding 11 do not follow each other parallel to each other along the cylindrical support 7, but intersect perpendicularly.

[0070] In a variant embodiment, the inductive sensor 5 further comprises: an additional transmitting winding 12 and / or an additional receiving winding 13, which are different from the transmitting winding 8 and the receiving winding 11, respectively, and are wound in a spiral manner 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 "additional transmitting spiral") and / or a fourth spiral (or "additional receiving spiral").

[0071] For example, the inductive sensor 5 further includes an additional transmitting winding 12 and an additional receiving winding 13 (as Figure 4a and Figure 4b ), which are wound helically around the cylindrical support 7 between its first end 9 and its second end 10 so as to form an additional transmitting helix and an additional receiving helix.

[0072] Each winding 12, 13 is formed by a metal wire having two ends 12a, 12b and 13a, 13b. This variant embodiment makes it possible to further improve the response uniformity of metal objects, regardless of their shape. On the other hand, the processing device 6 is more complex, such as from e.g. Figure 6c It can be clearly seen in.

[0073] The pitch of the additional transmitting helix and the pitch of the additional receiving helix are strictly greater than the diameter D of the cylindrical support 7 .

[0074] The additional transmitting winding 12 is powered by an alternating current and is configured to generate a magnetic field. If necessary, the transmitting winding 8 and the additional transmitting winding 12 can be powered by current sources having different frequencies, or by current sources having the same frequency but phase shifted (typically by 90°).

[0075] The additional receiving winding 13 is configured to receive the magnetic field generated by the transmitting windings 8 , 12 and to detect, by means of the processing device 6 , disturbances in the magnetic field due to the presence of metallic bodies.

[0076] Preferably, the pitch P of the transmitting helix is the same as the pitch of the additional transmitting helix. Furthermore, the additional transmitting helix is also centered on the X-axis of the detector 1. Similarly, the pitch P of the receiving helix is the same as the pitch of the additional receiving helix. Furthermore, the additional receiving helix is also centered on the X-axis of the detector 1.

[0077] The additional transmitting winding 12 and the additional receiving winding 13 can in particular be wound from the first end 10 to the second end 10 of the cylindrical support 7. The windings 8, 11, 12, 13 now all extend along the cylindrical support 7 over a distance equal to the axial length L of the cylindrical support 7.

[0078] The transmitting winding 8 and the additional transmitting winding 12 can be wound around the cylindrical support 7 so that the transmitting spiral and the additional transmitting spiral share the same starting point at the first end 9 of the cylindrical support 7 and share the same arrival point at the second end 10 of the cylindrical support 7. In addition, the transmitting spiral and the additional transmitting spiral 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 transmitting winding 8 and the additional transmitting winding 12 intersect, preferably with the same pitch. For example, the transmitting spiral is right-handed and the additional transmitting spiral is left-handed (or vice versa).

[0079] When the inductive sensor 5 includes two transmitting windings 8 and 12, each transmitting winding 8 and 12 generates a magnetic field. Given the configuration of the transmitting windings (rotationally opposite and positioned at the level of ends 9 and 10), these magnetic fields are substantially perpendicular to each other. Therefore, when an elongated metal object is placed near the detector 1, there is inevitably a high coupling between the metal object and at least one of the magnetic fields.

[0080] Furthermore, when the inductive sensor 5 includes two receiving windings 11, 13, the receiving windings 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 winding 11 and the additional receiving winding 13 intersect, preferably with the same pitch. For example, the receiving helix is right-handed and the additional receiving helix is left-handed (or vice versa). The use of two receiving windings 11, 13 reduces variations in signal strength when the metal object being detected is elongated.

[0081] Furthermore, when the inductive sensor 5 comprises two receiving windings 11, 13 and two transmitting windings 8, 12, the receiving spiral and the additional receiving spiral preferably share the same starting point at the first end 9 of the cylindrical support 7 and the same arrival point at the second end 10 of the cylindrical support 7, the starting point of the transmitting spirals 8, 12 being angularly offset by 90° from the starting point of the receiving spirals 11, 13. In other words, at the level of the first end 9 of the cylindrical support 7, the plane passing through the starting point of the transmitting spiral forms an angle of 90° with the plane passing through the axis X and the starting point of the ends of the receiving spirals (see Figure 4b ).

[0082] It should be noted that in Figure 4a and Figure 4b In the figure, for the sake of simplicity, the transmitting spiral and the additional transmitting spiral on the one hand and the receiving spiral and the additional receiving spiral on the other hand are represented in a slightly offset manner in order to be able to see them.

[0083] Optionally, one or more spiral grooves may be formed on the surface of the cylindrical support 7 in order to block the transmitter windings 8, 12 and the receiver windings 11, 13 relative to the cylindrical support 7. The grooves thus extend circumferentially around the cylindrical support 7 and are preferably through-grooves. All or part of the windings (transmitters 8, 12, receivers 11, 13) are then housed in the respective grooves, which makes it possible to reduce relative movements of the windings 8, 12, 11, 13 that could potentially disturb the detection.

[0084] Regardless of the embodiment, the metal detector 1 may include a power supply system 14 comprising a self-contained power source 15 , such as a cell or battery, which may be rechargeable, configured to power the transmitter windings 8 , 12 and the processing device 6 . Figure 5 1 represents, for example, a power supply system 14, which includes a rechargeable battery 15, a battery charger 16, a controller 17, a power regulator 18, and a switch 19. The voltage V at the output of the power regulator 18 is MICRO 、V TX and V RX is transmitted to the processing device 6 ( Figures 6a to 6c ).

[0085] The processing device 6 may comprise a microprocessor 20, such as one or more electronic cards, a memory and a suitable alarm 21 (which may be an audible and / or visual alarm). The processing device 6 is connected to the inductive sensor 5 and is configured to receive and process the signals generated by the windings forming the receivers 11, 13 and, if necessary, send an instruction to the alarm 21 of the metal detector 1 for generating an alarm.

[0086] By way of non-limiting example, the processing means 6 comprise:

[0087] - a microprocessor 20 comprising a digital frequency synthesizer DDS (Direct Digital Synthesis) 22 and a digital mixer 23 connected to the DDS. The DDS is configured to generate a control signal of a determined frequency, which is transmitted to the transmitting winding 8. The digital mixer 23 is configured to receive a signal from the receiving winding 11 and to derive the disturbance in the magnetic field from the frequency of the control signal;

[0088] an alarm 21 connected to the microprocessor 20 and configured to receive instructions from the microprocessor 20 ;

[0089] a control device 24 , such as a button, configured to be actuated by an operator and allowing the operator to control the sensitivity of the inductive sensor 5 and / or the amplitude (sound level / light intensity / color) of the alarm 21 ;

[0090] a first amplifier 25 configured to amplify the control signal generated by the DDS and transmit the amplified signal to the transmitting winding 8 ;

[0091] a second amplifier 26 configured to amplify the signal received by the receiving winding 11 and to transmit the amplified signal to the digital mixer 23 via a digital-to-analog converter 27 .

[0092] The processing device 6 may be housed in all or part of the housing 3 of the main body 4 and / or in the handle 2 of the metal detector 1 .

[0093] Figure 6a An embodiment is shown in which the inductive sensor 5 comprises only a single winding forming the transmitter and the receiver, the first amplifier 25 preferably driving this winding via an impedance Z. Thus, Figure 6a The processing device 6 shown may include a Figure 1a and Figure 1b The inductive sensor 5 described is implemented in a detector.

[0094] Figure 6b An embodiment is shown in which the inductive sensor 5 comprises a transmitting winding 8 and a receiving winding 11. Thus, Figure 6b The processing device 6 shown may include a Figure 2a and Figure 2b or Figure 3a and Figure 3b The inductive sensor 5 described is implemented in a detector.

[0095] Figure 6cAn embodiment is shown in which the inductive sensor comprises two transmitting windings 8, 12 and two receiving 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. Thus, Figure 6c The processing device 6 shown may include a Figure 4a and Figure 4b The inductive sensor 5 described is implemented in a detector.

Claims

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

2. The 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. The metal detector (1) according to any one of claims 1 and 2, wherein: The pitch (P) of the transmitting helix is the same as the pitch of the receiving helix.

4. The metal detector (1) according to any 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. The metal detector (1) according to any 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. 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 and the second end (10).

7. The metal detector (1) according to any one of claims 1 to 6, further comprising: An additional transmitting winding (12) is 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 transmitting helix, the pitch of the additional transmitting helix being strictly greater than the diameter (D) of the cylindrical support (7).

8. The 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. The metal detector (1) according to any one of claims 7 and 8, wherein: The emitting helix and the additional emitting helix (12) intersect at the level of the intersection point at the first end (9).

10. The metal detector (1) according to any one of claims 1 to 9, further comprising: An additional receiving winding (13) is 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, the pitch of which is strictly greater than the diameter (D) of the cylindrical support (7).

11. The 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. The metal detector (1) according to any one of claims 10 and 11, wherein: The receiving helix (11) and the additional receiving helix (13) intersect at the level of the additional intersection at the first end (9).

13. The detector according to claim 9 in combination with claim 12, wherein: The intersection point and the additional intersection point are angularly offset by 90°.

14. The metal detector (1) according to any one of claims 1 to 13, further comprising: A handle (2) is connected to the 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 against the cylindrical support (7) so as to be in contact with the cylindrical support (7).

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