DE102023136523A1 - Metal detector for classifying conductive objects, method for classifying conductive objects with a metal detector, measuring device for detecting conductive objects in a medium - Google Patents

Abstract

A metal detector for classifying an electrically conductive object, comprising: a measuring and operating circuit (1); a primary coil (2) supplied with an alternating current to generate a primary magnetic field with a plane of symmetry (3); multiple coil pairs (4), each comprising two secondary coils (411, 412; 421, 422) with identical magnetic couplings to the primary coil (2), connected to an input (5) of the measuring and operating circuit such that voltages induced by the primary magnetic field have opposite signs; wherein a sum amplitude of a coil pair (4) is formed by an amplitude of a sum of voltages induced in the coil pair (4); wherein the measuring and operating circuit (1) detects sequences of measured values of sum amplitudes of multiple coil pairs (4) and stores them as ordered time series; wherein the measuring and operating circuit (1) transmits the ordered time series externally or processes them independently; wherein one or more coil pairs have secondary coils with a symmetrical arrangement (41) and/or an asymmetrical arrangement (42) to the plane of symmetry (3) of the primary magnetic field.

Description

The invention relates to a metal detector for classifying hidden electrically conductive objects, a method for classifying hidden electrically conductive objects with a metal detector, and further to a measuring device for detecting and classifying hidden electrically conductive objects in a medium.

A metal detector is a device for locating hidden metallic objects. It is used, for example, to locate pipelines, conductive objects in containers, especially foreign bodies in media, electrical conductors, electrically conductive objects, or objects concealed on people. In light of current events, the use of metal detectors to locate munitions such as mines, munitions, and unexploded bombs is of particular interest. Common metal detectors consist of a transmitting coil, or primary coil, which is fed with an alternating current by an electronic circuit to generate the widest possible (primary) magnetic field, as well as one or more receiving coils, or secondary coils.

The writing US10056186B2 describes a metal detector as a device for detecting electrically conductive materials that includes multiple electromagnetic coils and circuit boards. The circuit boards are positioned so that their metallic surfaces and layers reduce or eliminate the influence of the coils on the detection of electrically conductive materials.

The writing WO0225318A1 teaches a device and method for detecting electrically conductive materials, comprising a primary coil, referred to as the excitation coil, which is operated with alternating voltage, a secondary coil, referred to as the detection coil, which detects output signals, and a subtraction unit that subtracts one detected signal from the other. The invention makes it possible to eliminate a background signal and enables the detection of metal particles.

The writing US2022107439A1 teaches a device for detecting objects hidden on persons, consisting of a metal detector with at least three transducers or coils arranged around a passage, so that a combination of an induced voltage allows an inaccurate localization of the object.

The writing BG3298U1 teaches a production line for filling and dosing a product in the confectionery industry, including, among other things, a metal detector. This document describes a mechanism connected to the metal detector that is partly responsible for removing a portion of the product from the production line, for example, to prevent contamination of the product with metallic objects.

The writing CN213800188U teaches a landmine detection device mounted on an unmanned aerial vehicle. The device includes a microcontroller, a metal detector, and a GPS positioner. The device can help ensure the safety of deminers, reduce detection time, and improve the efficiency of mine clearance.

State-of-the-art metal detectors usually provide no, or at best very inaccurate, information about the type and size of a detected electrically conductive object, and they also provide, at best, inaccurate information about the object's position relative to the metal detector. A metal detector is often adapted to the search conditions, for example, by varying the properties and arrangements of the secondary coils. In particular, the sizes of the receiving coils are adapted to the distance between the object and the metal detector in order to maximize the voltage induced in the secondary coils by the secondary magnetic field. Consequently, to detect hidden electrically conductive objects at an unknown distance, it is sometimes necessary to replace the receiving coils. Furthermore, conventional metal detectors typically have only two receiving coils and can therefore generate only limited information about an object.

The invention is based on the object of providing a metal detector which can classify a detected electrically conductive object according to its type, nature and size, and determine its relative position to the metal detector.

The invention solves the problem by a measuring sensor for a metal detector according to independent claim 1.

The metal detector according to the invention for classifying an electrically conductive object comprises: A measuring and operating circuit; A primary coil, configured to be supplied with an alternating current by the measuring and operating circuit and configured to generate a primary magnetic field with an axis of symmetry and/or a plane of symmetry; Several coil pairs, each comprising two secondary coils with magnetic couplings with the primary coil which are identical up to tolerances and are connected to an input of the measuring and operating circuit in such a way that voltages of the two secondary coils induced by the primary magnetic field and present at the input have opposite signs; wherein a sum amplitude of a coil pair is formed by an amplitude of a sum of voltages induced in the coil pair; wherein the measuring and operating circuit is configured to record sequences of measured values of sum amplitudes of several coil pairs and to store them as ordered time series; and wherein the measuring and operating circuit is configured to either transmit the ordered time series to an external device or to process them independently; wherein one or more coil pairs have secondary coils with a symmetrical arrangement and/or an asymmetrical arrangement to the axis of symmetry or plane of symmetry of the primary magnetic field.

wobei die magnetische Kopplung der ersten Sekundärspule mit der Primärspule und magnetische Kopplung zweiten Sekundärspule mit der Primärspule derart abgestimmt ist, dass eine Amplitude der durch das primäre Magnetfeld induzierten, am Eingang anliegenden Spannung kleiner als die - vorzugsweise kleiner als eine Hälfte der - durch den Verstärkungsfaktor geteilten Sättigungsspannung der Mess- und Betriebsschaltung ist.In one embodiment of the invention, a voltage signal applied to the input of the measuring and operating circuit is amplified by an amplification factor up to a maximum value of the saturation voltage; wherein a first secondary coil of a coil pair has a main loop and a secondary loop, wherein the secondary loop is coupled to the main loop; wherein the main loop (HS) has a magnetic coupling with the primary coil M _1,H and the second secondary coil of the coil pair has a magnetic coupling with the primary coil M ₂ , so that $\frac{M_{\mathrm{1,}H}-M_2}{M_{\mathrm{1,}H}+M_2}<0.05;$

wherein the magnetic coupling of the first secondary coil with the primary coil and the magnetic coupling of the second secondary coil with the primary coil is tuned such that an amplitude of the voltage induced by the primary magnetic field and applied to the input is smaller than - preferably smaller than one half of - the saturation voltage of the measuring and operating circuit divided by the amplification factor.

In one embodiment of the invention, the asymmetric shape of the at least two secondary coils with asymmetric arrangement is a polygon, in particular a triangle.

In one embodiment of the invention, a first coil pair with a symmetrical arrangement and a second coil pair with a symmetrical arrangement have different properties; wherein the property includes an active area, an inductance, a magnetic coupling with the primary coil, a number of turns, or a shape.

In one embodiment of the invention, the primary coil comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board.

In one embodiment of the invention, the coil pairs comprise conductor tracks on a printed circuit board, in particular are formed by conductor tracks on a printed circuit board.

In one embodiment of the invention, the metal detector is attached to an aircraft, or to a vehicle, or to a swimming device.

In one embodiment of the invention, the measuring and operating circuit independently processes the stored ordered time series; wherein the processing comprises an analysis of the stored ordered time series; wherein a classification of an electrically conductive object takes place by means of voltage amplitudes induced in the coil pairs by the primary magnetic field and the secondary magnetic field generated by induced eddy currents, with regard to a result of the analysis, with regard to at least one of the following properties: a distance between a position of the object and a reference point within the metal detector, an orthogonal projection of the position of the object onto a line defined by the direction of movement of the reference point in the metal detector, a quantity/mass of conductive material, a spatial quantity.

A method according to the invention for classifying an electrically conductive object with a metal detector according to the invention, wherein a relative movement takes place between the electrically conductive object and the metal detector, comprises at least the following steps: generating a primary magnetic field with the primary coil of the metal detector, for generating a secondary magnetic field by eddy currents induced in the electrically conductive object; detecting sequences of sum amplitudes of several coil pairs by the measuring and operating circuit, and storing the sequences as ordered time series; analyzing the ordered time series with reference data; classifying the object with regard to a result of the analysis, with regard to at least one of the following properties: a minimum distance between a position of the object and a reference point within the metal detector, a minimum distance of the position of the object to a reference point in the metal detector, an orthogonal projection of the position of the object onto a line given by the direction of movement of the reference point in the metal detector, a set, Mass, and/or type of conductive material, a spatial quantity.

A measuring device according to the invention, designed to detect electrically conductive objects in a medium, comprises: a container carrying the medium; a metal detector according to the invention.

An embodiment of the measuring device according to the invention is configured to measure a measured variable of a medium in a container, further comprising a measuring sensor; wherein the measuring sensor can be acted upon by the medium and is configured to generate at least one measuring signal dependent on the measured variable.

In one embodiment of the measuring device according to the invention, the measuring device is configured to determine a dielectric value of a medium by emitting a high-frequency signal; and wherein the measured variable to be determined can be derived from the dielectric value.

In one embodiment of the measuring device according to the invention, the container is a pipe; wherein the measuring device is a flow meter configured to determine a mass flow or a volume flow of a medium flowing in the pipe.

In one embodiment of the measuring device according to the invention, the measuring device is designed to determine a fill level of a medium in a container by emitting a radar signal.

The invention has the advantage that, when different secondary coils of different shapes are moved uniformly over an object to be detected, different properties of the object, such as a spatial size or the amount of conductive material contained therein, are mapped onto the curves of the voltage amplitudes induced in the secondary coils, which forms the basis for classifying the object. The invention also has the advantage that a combination of suitable secondary coils with different winding senses makes it possible to compensate for and/or detect disruptive environmental influences, such as reflections from the ground. The invention also has the advantage that very good compensation of the primary field can be achieved, whereby an amplifier with a particularly high amplification factor of at least 1000, preferably at least 10,000, can be applied without non-linear effects occurring, which makes it possible to detect and classify smaller, less conductive, or more distant objects. The invention further has the advantage that the secondary coils can be arranged on several levels of a printed circuit board, whereby the space required for and also the total weight of the measuring sensor are particularly low, so that the measuring sensor according to the invention is well suited to be attached to small, in particular unmanned, aircraft, vehicles, and swimming craft.

• 1 zeigt eine Schaltskizze einer Ausgestaltung des erfindungsgemäßen Metalldetektors.
• 2 zeigt eine Skizze von Ausführungen der einzelnen Sekundärspulen von Spulenpaaren.
• 3 zeigt einen schematischen Querschnitt einer Ausführung der Anordnung von Primärspule und Sekundärspulen auf einer Leiterplatte.
• 4a zeigt eine Seitenansicht einer Ausgestaltung des erfindungsgemäßen Verfahrens.
• 4b zeigt eine Draufsicht auf eine Ausgestaltung des erfindungsgemäßen Verfahrens.
• 5 zeigt einen Querschnitt einer Ausgestaltung des erfindungsgemäßen Messgeräts.

The invention is explained with reference to the following figures.

• 1 shows a circuit diagram of an embodiment of the metal detector according to the invention.
• 2 shows a sketch of designs of the individual secondary coils of coil pairs.
• 3 shows a schematic cross-section of an embodiment of the arrangement of primary coil and secondary coils on a printed circuit board.
• 4a shows a side view of an embodiment of the method according to the invention.
• 4b shows a plan view of an embodiment of the method according to the invention.
• 5 shows a cross section of an embodiment of the measuring device according to the invention.

The 1 The circuit diagram shown of an embodiment of the metal detector according to the invention comprises a measuring and operating circuit 1, which is connected to a primary coil 2 with a plane of symmetry 3 and feeds this with alternating voltage, so that a primary magnetic field can be generated with a plane of symmetry that corresponds to the plane of symmetry 3 of the primary coil 2. Furthermore, the measuring and operating circuit 1 is connected via an input 5 to several coil pairs 4 consisting of a first secondary coil 411 and a second secondary coil 412 in such a way that the voltage amplitudes induced by the primary magnetic field generated by the primary coil 1 in the two secondary coils 411, 412 of a coil pair 4 have opposite signs. According to the invention, the measuring and operating circuit 1 records the sum of the amplitudes of the individual secondary coils 411, 412 of the several coil pairs 4 as sum amplitudes for processing and/or evaluation. Each coil pair 4 comprises at least one main loop HS and one secondary loop NS from a plurality of secondary loops VNS, wherein one secondary loop NS from the plurality of secondary loops VNS is coupled to the main loop HS by one or more short-circuit bridges KB. In this embodiment, the coupling of a secondary loop NS to a main loop HS can increase or decrease its magnetic coupling to the primary coil 2.

The 2 The sketches shown represent embodiments of the individual secondary coils of coil pairs (4), wherein the individual secondary coils of a coil pair have a symmetrical arrangement 41 to the plane of symmetry 3 of the primary coil and thus of the primary magnetic field, and wherein the individual secondary coils of a coil pair have an asymmetrical arrangement 42. In this embodiment, the asymmetrically arranged coils are triangular and the symmetrically arranged coils are rectangular and adjacent to one another.

The 3 1 shows a cross-section of an arrangement of coil pairs 4 according to one embodiment of the invention. Several planes are arranged on the circuit board L. Here, EP denotes one or more planes comprising the primary coil 1, ESS denotes one or more planes each comprising the coil pairs with a symmetrical arrangement 41, and ESA denotes one or more planes each comprising the coil pairs with an asymmetrical arrangement 42. In this embodiment of the invention, all coils are planar, and all planes EP, ESS, ESA, and the circuit board L are parallel to a common orientation plane.

4a shows a side view of an embodiment of the method according to the invention, wherein the metal detector 7 moves along the direction of movement 11 at speed v and emits the primary magnetic field 8, among other things, to the electrically conductive object 6, where eddy currents are induced, which in turn generate a secondary magnetic field 9. The object has a minimum distance 10 from the metal detector.

4b shows a plan view of an embodiment of the method according to the invention, wherein the electrically conductive object 6 is laterally offset with respect to the direction of movement 11, with a minimum transverse distance to the trajectory of the metal detector 7 given by an orthogonal projection (10') onto the direction of movement.

The 5 The cross-section of an embodiment of the measuring device according to the invention shown shows a medium 12 that is guided in a container 13, which can be a pipe. In this embodiment, the measuring device 15 has a sensor 14 with which it can measure a measured variable of the medium. Furthermore, the measuring device 15 comprises an embodiment of the metal detector 7 according to the invention for detecting and classifying electrically conductive objects located in the medium.

List of reference symbols

1

Measuring and operating circuit

2

primary coil

3

axis of symmetry or plane of symmetry

4

Coil pairs

41

Pair of coils consisting of symmetrically arranged secondary coils

42

Coil pair of asymmetrically arranged secondary coils

411,421

First secondary coil of a coil pair

412,422

Second secondary coil of a coil pair

5

Input for measuring and operating circuit

HS

Main loop

NS

secondary loop

VNS

Numerous sub-loops

KB

short-circuit bridge

6

Electrically conductive object

7

metal detector

8

Primary magnetic field

9

Secondary magnetic field

10

Minimum distance

10'

Orthogonal projection

11

Direction of movement of the metal detector

12

medium

13

container

14

Sensor

15

measuring device

EP

PCB levels encompassing the primary coil

ESS

Coil pairs with symmetrical arrangement comprising circuit board levels

ESA

Coil pairs with asymmetrical arrangement comprising circuit board levels

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 10056186B2 [0003]
• WO 0225318A1 [0004]
• US 2022107439A1 [0005]
• BG 3298U1 [0006]
• CN 213800188U [0007]

Claims (14)

A metal detector for classifying an electrically conductive object, comprising: • A measuring and operating circuit (1); • A primary coil (2) configured to be supplied with an alternating current by the measuring and operating circuit (1) and configured to generate a primary magnetic field with an axis of symmetry and/or a plane of symmetry (3); • Several coil pairs (4), each comprising two secondary coils (411, 412; 421, 422) with magnetic couplings to the primary coil (2) that are identical, except for tolerances, and connected to an input (5) of the measuring and operating circuit such that voltages of the two secondary coils (411, 412; 421, 422) induced by the primary magnetic field and present at the input (5) have opposite signs; • wherein a total amplitude of a coil pair (4) is formed by an amplitude of a sum of voltages induced in the coil pair (4); • wherein the measuring and operating circuit (1) is configured to record sequences of measured values of total amplitudes of several coil pairs (4) and to store them as ordered time series; • and wherein the measuring and operating circuit (1) is configured to either transmit the ordered time series to an external device or to process them independently; • wherein one or more coil pairs have secondary coils with a symmetrical arrangement (41) and/or an asymmetrical arrangement (42) to the axis of symmetry or plane of symmetry (3) of the primary magnetic field. Metal detector after Claim 1 , • wherein a voltage signal applied to the input (5) of the measuring and operating circuit (1) is amplified by an amplification factor up to a maximum value of the saturation voltage; • wherein a first secondary coil (411; 421) of a coil pair (4) has a main loop (HS) and a secondary loop (NS), wherein the secondary loop (NS) is coupled to the main loop (HS); • wherein the main loop (HS) has a magnetic coupling with the primary coil M _1,H and the second secondary coil (412; 422) of the coil pair (4) has a magnetic coupling with the primary coil M ₂ , so that $\frac{M_{\mathrm{1,}H}-M_2}{M_{\mathrm{1,}H}+M_2}<0.05;$

• wherein the magnetic coupling of the first secondary coil (411; 421) with the primary coil and the magnetic coupling of the second secondary coil (412; 422) with the primary coil is tuned such that an amplitude of the voltage induced by the primary magnetic field and applied to the input (5) is smaller than - preferably smaller than half of - the saturation voltage of the measuring and operating circuit (1) divided by the amplification factor. Metal detector according to one of the Claims 1 or 2 , • wherein the asymmetrical shape of the at least two secondary coils (42) with asymmetrical arrangement is a polygon, in particular a triangle. Metal detector according to one of the Claims 1 until 3 , • wherein a first coil pair with a symmetrical arrangement (41) and a second coil pair with a symmetrical arrangement (41') have different properties; • wherein the property comprises an active area, an inductance, a magnetic coupling with the primary coil, a number of turns, or a shape. Metal detector according to one of the Claims 1 until 4 , • wherein the primary coil comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board. Metal detector according to one of the Claims 1 until 5 , • wherein the coil pairs (4) comprise conductor tracks on a printed circuit board, in particular are formed by conductor tracks on a printed circuit board. Metal detector according to one of the Claims 1 until 6 , • wherein the metal detector (7) is attached to an aircraft, or to a vehicle, or to a swimming device. Metal detector according to one of the Claims 1 until 7 , • wherein the measuring and operating circuit (1) independently carries out an analysis of the stored ordered time series; • wherein a classification of an electrically conductive object (6) takes place by means of voltage amplitudes induced in the coil pairs by the primary magnetic field generated by eddy currents, the secondary magnetic field, with regard to a result of the analysis, with regard to at least one of the following properties: ◯ a distance between a position of the object (6) and a reference point within the metal detector (7), ◯ an orthogonal projection (10) of the position of the object (6) onto a reference point defined by the direction of movement of the reference point in the metal detector (7) given line (11), ◯ a quantity of conductive material, ◯ a spatial quantity. Method for classifying an electrically conductive object (6) with a metal detector (7) according to one of the Claims 1 until 8 , wherein a relative movement (v) takes place between the electrically conductive object and the metal detector, comprising at least the following steps: • generating a primary magnetic field (8) with the primary coil (1) of the metal detector (7), for generating a secondary magnetic field (9) by eddy currents induced in the electrically conductive object (6); • detecting sequences of sum amplitudes of several coil pairs (4) by the measuring and operating circuit (1), and storing the sequences as ordered time series; • analyzing the ordered time series with reference data; • Classifying the object (6) with regard to a result of the analysis, with regard to at least one of the following properties: ◯ A minimum distance (10) between a position of the object (6) and a reference point within the metal detector (7), ◯ A minimum distance of the position of the object (6) to a reference point in the metal detector (7), ◯ An orthogonal projection (10') of the position of the object (6) onto a line (11) given by the direction of movement of the reference point in the metal detector (7), parallel to a plane defined by a pair of coils (4), ◯ An amount of conductive material, ◯ A spatial quantity. Measuring device, designed to detect electrically conductive objects in a medium (12), comprising: • a container (13) carrying the medium (12); • a metal detector (7) according to one of the Claims 1 until 8 . Measuring device according to Claim 8 , designed to measure a measured variable of a medium (12) in a container (13), further comprising: • a measuring sensor (14); • wherein the measuring sensor (14) can be acted upon by the medium (12) and is designed to generate at least one measuring signal dependent on the measured variable. Measuring device according to Claim 11 , • wherein the measuring device (15) is configured to determine a dielectric value of a medium (12) by emitting a high-frequency signal; and • wherein the measured variable to be determined can be derived from the dielectric value. Measuring device according to Claim 11 , • wherein the container (13) is a pipe; • wherein the measuring device (15) is a flow meter, configured to determine a mass flow or a volume flow of a medium (12) flowing in the pipe (13). Measuring device according to Claim 11 , • wherein the measuring device (15) is designed to determine a fill level of a medium (12) in a container by emitting a radar signal.