WO2020000014A1

WO2020000014A1 - An improved metal detector

Info

Publication number: WO2020000014A1
Application number: PCT/AU2019/000079
Authority: WO
Inventors: Philip Shane WAHRLICH
Original assignee: Minelab Electronics Pty. Limited
Priority date: 2018-06-27
Filing date: 2019-06-27
Publication date: 2020-01-02

Abstract

A method for assisting a detection of a target by a metal detector, including: determining positions of a sensor head of the metal detector with respect to a coordinate system; transmitting a transmit magnetic field using a transmitter; receiving a receive magnetic field due to the transmit magnetic field using a receiver within the sensor head when the sensor head is at a determined position and associating the receive magnetic field with the determined position; analysing the receive magnetic field to determine useful information; storing the useful information associated to the determined position; repeating the steps of determining, transmitting, receiving, analysing and storing during a use of the metal detector; presenting, using a visual display, data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following: a) a current position of the sensor head; and b) useful information associated with the current position or positions within a certain distance from the current position, or both; wherein the selection is adapted and configured to avoid or reduce cluttering of data on the visual display.

Description

AN IMPROVED METAL DETECTOR

TECHNICAL FIELD

| 0001 I The present invention relates to a metal detector.

BACKGROUND

[0002] The general forms of most metal detectors which interrogate soil are either handheld battery operated units, conveyor-mounted units, or vehicle-mounted units. Examples of handheld products include detectors used to locate gold, explosive land mines or ordnance, coins and treasure. Examples of conveyor-mounted units include fine gold detectors in ore mining operations, and examples of a vehicle-mounted unit include a unit to locate buried land mines.

[0003] These metal detectors usually, but not necessarily, consist of transmit electronics generating a repeating transmit signal cycle of a fundamental period, which is applied to an inductor, for example a transmit coil, which transmits a resulting varying magnetic field, sometimes referred to as a transmit magnetic field.

[0004] These metal detectors may also contain receive electronics that process a receive signal from a measured receive magnetic field, during one or more receive periods during the repeating transmit signal cycle, to produce an indicator output signal, the indicator output signal at least indicating the presence of at least a metal target within the influence of the transmit magnetic field.

[0005] During the processing of the receive signal, the receive signal is either sampled, or demodulated, to produce one or more target channels, the one or more target channels may be further processed to produce the indicator output signal

SUMMARY

[0006] According to one aspect of the present disclosure, there is provided a method for assisting a detection of a target by a metal detector, including: determining positions of a sensor head of the metal detector with respect to a coordinate system; transmitting a transmit magnetic field using a transmitter; receiving a receive magnetic field due to the transmit magnetic field using a receiver within the sensor head when the sensor head is at a determined position and associating the receive magnetic field with the determined position; analysing the receive magnetic field to determine useful information; storing the useful information associated to the determined position; repeating the steps of determining, transmitting, receiving, analysing and storing during a use of the metal detector; presenting, using a visual display, data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following:

a) a current position of the sensor head; and b) useful information associated with the current position or positions within a certain distance from the current position, or both;

wherein the selection is adapted and configured to avoid or reduce cluttering of data on the visual display.

[0007] In one form, one or more selected useful information is unselected when the total amount selected exceeds a predetermined number such that the unselected information is not presented as data in the visual display. In one form, one or more selected useful information is unselected when a distance between the current position of the sensor head and the associated determined position exceeds a predetermined distance. In one form, one or more selected useful information is unselected after a predetermined time after being selected. In one form, the method further includes: capturing images of environments near the sensor head; and superimposing the data on one or more captured images for display by the visual display based on the associated determined positions. In one form, the images of the soil surfaces are captured and presented to the user in real time. In one form, the receiver is within the sensor head. In one form, the useful information includes one or more of:

a) one or more identifications of one or more targets;

b) soil type; and

c) one or more information of unwanted objects.

[0008] In one form, information in relation of certain types of target is given a higher priority to be selected. In one form, the user of the metal detector determines which type(s) of target is given higher priority over the others

[0009] According to another aspect of the present disclosure, there is provided a non-transitory computer readable medium including instructions to perform the steps of claim 1.

[0010] According to another aspect of the present disclosure, there is provided a metal detector including: a sensor for determining positions of a sensor head of the metal detector with respect to a coordinate system; a transmitter for transmitting a transmit magnetic field; a receiver within the sensor head for receiving a receive magnetic field due to the transmit magnetic field when the sensor head is at a determined position and associating the receive magnetic field with the determined position; a processor for: analysing tire receive magnetic field to determine useful information; storing the useful information associated to the determined position; repeating the steps of determining, transmitting, receiving, analysing and storing during a use of the metal detector; a visual display for presenting data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following:

a) a current position of the sensor head; and

b) useful information associated with the current position or positions within a certain distance from the current position, or both; wherein the selection is adapted and configured to avoid or reduce cluttering of data on the visual display.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:

[0012] Figure 1 depicts one embodiment of the present disclosure; and

[ 0013] Figures 2 to 7 depict one exemplary sequence of actions following the embodiment of

Figure 1.

DESCRIPTION OF EMBODIMENTS

[0014] It is common for metal detectors to generate audio outputs to their users or operators (in this specification, a user and an operator mean the same, which is a person or a robot or an AI using a metal detector). In such cases, an amplitude-modulated or pitch-modulated audio output indicates to a user that there is a metallic object in a detection zone. A detection zone is the volume or area in close proximity to a sensor head of a metal detector where metallic targets can be expected to be detected by the metal detector. Generally, the user would have to remember locations where previous targets were detected, and mentally associate the information from those targets with region of soil where the targets were detected. For instance, generally a user would have to recall that a target may be present near to visual features on the ground which coincide with the location at which the search coil was present when an audio modulation was generated Visual features may be features of the soil surface (i.e uneven surface with pebbles, exposed soil with a bush nearby, grassy area approximate 10m from a tall tree etc.). Alternatively, rather than recalling, the user would have to manually record the locations.

|0015| Some metal detectors offer visual displays to assist their users. In particular, visual displays can be used to assist a user or operator to identify and record the location of an object in a detection zone. For example, a map shown in a visual display can be marked with locations where objects of interest were discovered. Further, a heat map or contour map shown in a visual display can be used to guide a user to cover an area of interest effectively. For example, areas that had been covered can be shaded in a selected colour so that the user will be guided by the heat map to move to areas that are unshaded in order to search regions of the environment which have not yet been interrogated. Further information associated with the interrogated regions of the environment can also be displayed. For example, areas which are suspected to contain a target of interest can be annotated with derived information associated with the target, for instance the estimated depth of the target in the ground, and properties such as a label representative of the estimated type of target. However, it was discovered that often information displayed can be cluttered, especially in environments which contain many metallic objects in close proximity or in environments which generate many anomalous signals, such as an environment with highly mineralised soils. It is not uncommon for several separate metallic objects to be near the sensor head and detected by the sensor head at one instant and there are no means of omitting information from the display once the sensor head is sufficiently far away from the target location that the target may be considered to be out of the operator's focus. In other words, the information may remain on the screen even when the information is no longer of interest to the user.

[0016] The present disclosure offers an alternative to improve the experience of a user using a metal detector. In one form, the present disclosure provides a means of selectively displaying information based on the location of the search coil. Information can therefore be omitted when the search coil is moved to a location where the information is no longer relevant or less relevant than other information which could be displayed. As a result, even when there is a large amount of information which could be displayed about a particular target location, the amount of information is managed to reduce clutter on the visual display, such as in cases where there are multiple targets in close proximity.

[ 0017] In a general form of one embodiment, there is provided a metal detector with a visual display and a position sensor. In particular, with reference to Figure 1, the metal detector is able to determine positions of a sensor head of the metal detector with respect to a coordinate system (step 1 of Figure 1).

[0018] The sensor head normally includes at least a magnetic field transmitter and a magnetic field receiver. In one form, the magnetic field transmitter and the magnetic field receiver are coils for transmitting and receiving magnetic fields. In one form, the magnetic field transmitter and the magnetic field receiver are provided by a same single coil In one form, the sensor head includes a known DD coil or a DOD coil (which consists of an O-shaped transmit coil between two mirrored D- shaped receive coils). In one form, the sensor head may include just the magnetic field receiver. In one form, the sensor head includes two separate parts, one including the transmitter, the other including the receiver.

[0019] The phrase“positions of a sensor head of the metal detector with respect to a coordinate system” generally means positions of the sensor head which can be identified and located based on a selected one or more coordinate systems. In the case where the selected coordinate system is arbitrary, the absolute positions may have no relevant meaning, and the pertinent position information may be found in comparing a position with another position in the sample coordinate system. In this context, it is synonymous to“relative positions”. A coordinate system can be of any form known to a person skilled in the art, as long as it provides a reference system to track the position of the sensor. In one form, the coordinate system is one of Earth-centered Cartesian coordinate system and Earth-centered spherical/ellipsoidal coordinate system. In one form, it is based on a satellite-based positioning system. In one form, it is based on Global Positioning System (GPS) coordinates. In another form, the coordinate system is a Cartesian coordinate system centred on the position where the device was initialised.

[0020] There are many methods to determine positions of the sensor head of the metal detector with respect to a coordinate system. One method is to use measurements from a GPS receiver. Another method is to use dead reckoning based on measurements from an inertial measurement unit, which may use an accelerometer. Another method is to use sensors external to the metal detector which determine the positions of the metal detector relative to themselves. In one form, the coordinate system is provided by an optical positioning system. In one form, local positioning is applied without reference to the location of the Earth, but with reference to previous positions etc. Other methods may include, but are not limited to, using a camera which provides position information based on the captured images. The camera may be assisted by, or complement, another positioning means, such as a GPS or an inertial measurement unit. The camera may be provided by a mobile device, such as a smartphone, paired with the metal detector. The camera may be a video recorder. The camera may provide positions with respect to a coordinate system based on images of the ground captured by the camera, or based on environmental surroundings near the sensor head (such as vegetation on the surface of the ground, or trees nearby), or both.

[0021] With reference to Figure 1, in an operation to detect a metallic target of interest, the metal detector transmits a transmit magnetic field using a transmitter (step 3), and receives a receive magnetic field due to the transmit magnetic field using a receiver within the sensor head when the sensor head is at a determined position and associating the receive magnetic field with the determined position (step 5), analyses the receive magnetic field to determine useful information (step 7), and stores the useful information associated to the determined position (step 9).

[0022] In one form, the position sensor of the metal detector provides the determined positions then the processor of the metal detector associates receive signals received when the sensor head is at that determined position. It is possible for every receive signal there is an associated determined position. Alternatively, it is also possible to have the processor first process the receive signal, and when there is useful information extracted from the processed receive signal, request a coordinate from the position sensor to associate the position with the useful information.

[0023] With reference to Figure 1, during a typical operation, at step 11 the metal detector repeats the steps of determining, transmitting, receiving, analysing and storing as described above. By repeating the steps, the metal detector builds up a repository of information, where the information is associated with positions In other words, when given a specific position, it is possible to retrieve information associated with that specific position. It is possible to store the repository locally (within a storage within the metal detector or connected storage medium), or remotely. For a remote connection, information can be transferred between the metal detector and the remote repository using a wireless communication protocol, such as WIFI, 3G, 4G, 5G etc.

10024| The metal detector then, as part of step 13, presents, using a visual display, data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following: a) a current position of the sensor head; and b) useful information associated with the current position or positions within a certain distance from the current position, or both.

[0025] A visual display can take many forms. For example, it can be a built-in screen on the metal detector, a detachable screen on the metal detector, or even third party add-on peripherals to the metal detector, such as a mobile device (smartphone, tablet, etc) linked to the metal detector to act as the visual display.

10026] However, there may be many items of useful information associated with the current position of the sensor head and positions within a certain distance from the current position. If all this information is to be displayed in the visual display at the same time, the visual display would be cluttered with information, and the user of the metal detector would not be able to extract useful information from the cluttered visual display.

[0027] In this general fonn, the processor would consider the current position of the sensor head and useful information associated with the current position and positions within a certain distance from the current position, and make assessment regarding which of the associated information to be selected or used to present data on the visual display. The presented data can be exactly the selected information, or simply based on the selected information. In other words, the selection is adapted and configured to avoid or reduce cluttering of data on the visual display.

[0028] When there is too much selected useful information, which may cause the visual display to be cluttered with this selected useful information, some of the selected information may be unselected. Alternatively, a more stringent selection criterion can be adopted. Alternatively, priority can be given to certain information. The priority can be set by a user, or pre-set by factory. The priority may be changed by the user during operation.

[0029] For example, distance from the sensor head can be used as the first criterion to decide which information is to be unselected or not selected. In one form, information with associated position X distance away from the sensor head would not be shown. X can be 30cm, 10cm, 5cm etc.

[0030] Another criterion can be a confidence level of finding a target in a position. For example, each detection may have an associated confidence level whether there is indeed a target in a position. A stringent criterion can be that only information with associated confidence level of 80% will be shown

[0031] In relation to priority, priority can be set based on types of target. For example, the user may be more interested in coins so information representing a potential coin target will be given priority. Other types of target may be jewellery, golds nuggets etc. A lower priority may be assigned to types of unwanted objects such as ferrous objects, which in many environments are typically man made junk.

[0032] When processing a receive signal, depending on how the receive signal is processed, for example, depending on the number and types of demodulation functions used on the receive signal, many useful types of information can be obtained. Useful information includes, but is not limited to, identifications of one or more targets, soil type, information of unwanted objects, confidence level, estimated depth of a target, estimated maximum detection depth etc

[0033] Figures 2 to 7 depict one exemplary sequence of actions. Figures 2 to 7 are exemplary screen captures of the output of the visual display of a metal detector. The metal detector is equipped with a camera pointing towards the sensor head from an elevated position. As can be seen, the sensor head of the metal detector, in this case a round sensor head 21 , is also captured by the camera. The output of the camera is fed to the visual display to be shown to the user of the metal detector.

Information and shading/colouring can be superimposed on the output of the camera to the user.

[0034] In Figure 2, a first shade 23 is added to a location where a potential target (in this case a non-ferrous target ) is detected. The user can easily identify the position of the potential target by viewing visual display. In operation, the sensor head 21 , which includes a transmitter and a receiver, transmits a magnetic field which induces eddy currents in the target The eddy currents then produce a magnetic field which is detected by the receiver as a receive magnetic field The receive magnetic field induces a receive signal in the receiver. The receive signal is then processed to identify the source of the receive signal. In this case, the receive signal is considered to be from a non-ferrous target and the location where the receive signal is detected is shaded using a first shade 23 Useful information such as the estimated depth of the target based on the receive signal, and the estimated conductivity of the target is stored.

[0035] Thereafter, the metal detector determines which of the stored information at a determined location of the sensor head 21 is most relevant. The metal detector may also assess whether there is too much information already displayed on the visual display. For example, as shown in Figure 3, the processor checks and finds that there is stored useful information associated to that determined position. The useful information is presented to the user through the visual display. In this example, three pieces of useful information of a target are shown: conductivity, ferrous/non-ferrous determination, and depth shown in table 25 on screen Of course, the stored information may be in other formats/forms and requires some processing prior to being presented on the visual display.

[0036] As shown in Figure 4, as the sensor head moves further left in this scenario, it detects a potential ferrous target. The location where the receive signal due to the potential ferrous target is detected is shaded using a second shade 27. The first shade 23 and the second shade 27 are distinguishable either through different colours or different textures. Note that when the sensor head moves further left the information in relation to the potential non-ferrous target (table 25 of Figure 3) is removed but the first shade 23 remains. This is to remove clutter on the screen so that the user has a better view and understanding of what is around the detection zone. In essence, during operation, the user can focus on the visual display itself without needing to alternate between viewing the visual display and viewing the surrounding environment directly in front of the user. Without removal of the information and with the visual display cluttered with information, the user would have to view the surrounding environment directly, and cannot rely solely on viewing the surrounding environment indirectly through the visual display. Alternating viewing the visual display and viewing the surrounding environment directly would increase the fatigueless of the user.

[0037] Thereafter, the metal detector determines which of the stored information at a determined location of the sensor head 21 is most relevant. For example, as shown in Figure 5, the processor checks and finds that there is stored useful information associated to that determined position (which is the information of the ferrous target and not of the non-ferrous target). The useful information of the ferrous target is presented to the user through the visual display In this example, three pieces of useful information of a ferrous target are shown: conductivity, ferrous/non-ferrous determination, and depth shown in table 31 on screen. Of course, the stored information may be in other formats/forms and requires some processing prior to being presented on the visual display.

[0038] When the sensor head starts to move towards the right direction again as shown in Figure 6, the sensor head moves closer to the position where the potential non-ferrous target was detected (the first shade 23). The processor checks for any useful information, retrieves information in relation to the non-ferrous target and presents the information on the visual display to the user. Information in relation to the ferrous target is not present to avoid clutter

[0039] It can be observed that in this example, the distance from the target plays an important role for the processor to decide which of the information is to be selected and shown on the visual display when there is too much information to be presented in a single visual display. Of course, there are other ways for the processor to allocate priority to one or more particular pieces of information over the rest. For example, information in relation to a non-ferrous target may be given a higher priority as it is likely that a ferrous object would be an unwanted target such as a nail, junk metal scraps etc Further, if there are two objects near to each other in a location, the processor can decide, based on a priority list, information in relation to an object takes priority over information in relation to another object, thus avoiding clutter on the screen.

[0040] In one form, the visual display is a touch screen. This enables the user to see a target overlay and to touch the screen to bring up further information about that target. Alternatively, when there is useful information available, a small icon representing the information pops up without displaying the information. Touching the icon allows information in relation to the icon to be displayed. For example, at a location, there is information in relation to a non-ferrous coin, a small “coin” icon pops up on screen. When the icon is touched/pressed by the user, information such as the depth is displayed. This has the potential to reduce the amount required to show on screen automatically to reduce clutter.

[0041] The following includes further possible additions to the metal detector to assist the user of the metal detector: a. Indication of the location or direction to“off-screen”/nearby points of interest. For example, and arrow pointing downward at the bottom of the screen indicating a target of interest behind the user previously detected; b. Contour plot, and other types of plots for displaying information; c. Information from parallel processing of multiple detector configurations (e.g. different filters, demodulation functions, processing algorithms, etc) so that the operator can more thoroughly interrogate an area; d. Mineralisation mapping (e.g. soil magnetic response, soil phase (or ground balance adjustment required)); e. Augmented reality training simulation, where a virtual target can be put in the

environment, and the detector simulates the response to it like it was real.

[0042] Those of skill in the art would understand that information and signals may be represented using any of a variety of technologies and techniques For example, data, instructions, commands, information, signals, bits, symbols, and chips may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0043] Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

[0044] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. For a hardware implementation, processing may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. Software modules, also known as computer programs, computer codes, or instructions, may contain a number of source code or object code segments or instructions, and may reside in any computer readable medium such as a RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disk, a removable disk, a CD-ROM, a DVD-ROM or any other form of computer readable medium. In the alternative, the computer readable medium may be integral to the processor. The processor and the computer readable medium may reside in an ASIC or related device. The software codes may be stored in a memory unit and executed by a processor The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

[0045] Throughout the specification and the claims that follow, unless the context requires otherwise, the words“comprise” and“include” and variations such as“comprising” and“including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0046] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0047] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims

CLAIMS:

1. A method for assisting a detection of a target by a metal detector, including:

determining positions of a sensor head of the metal detector with respect to a coordinate system;

transmitting a transmit magnetic field using a transmitter;

receiving a receive magnetic field due to the transmit magnetic field using a receiver within the sensor head when the sensor head is at a determined position and associating the receive magnetic field with the determined position;

analysing the receive magnetic field to determine useful information;

storing the useful information associated to the determined position;

repeating the steps of determining, transmitting, receiving, analysing and storing during a use of the metal detector;

presenting, using a visual display, data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following:

a) a current position of the sensor head; and

b) useful information associated with the current position or positions within a certain distance from the current position, or both;

2. The method of claim 1, wherein one or more selected useful information is unselected when the total amount selected exceeds a predetermined number such that the unselected information is not presented as data in the visual display.

3. The method of claim 1, wherein one or more selected useful information is unselected when a distance between the current position of the sensor head and the associated determined position exceeds a predetermined distance.

4. The method of claim 1, wherein one or more selected useful information is unselected after a predetermined time after being selected.

5. The method of claim 1, further including:

capturing images of environments near the sensor head; and

superimposing the data on one or more captured images for display by the visual display based on the associated determined positions.

6. The method of claim 5, wherein the images of the soil surfaces are captured and presented to the user in real time.

7. The method of claim 1, wherein the receiver is within the sensor head.

8. The method of claim 1 , wherein the useful information includes one or more of:

a) one or more identifications of one or more targets;

b) soil type; and

c) one or more information of unwanted objects.

9. The method of claim 8, wherein information in relation to certain types of target are given a higher priority to be selected

10. The method of claim 9, wherein the user of the metal detector determines which type(s) of target is given higher priority over the others.

11 A non-transitory computer readable medium including instructions to perform the steps of claim 1

12. A metal detector including:

a sensor for determining positions of a sensor head of the metal detector with respect to a coordinate system;

a transmitter for transmitting a transmit magnetic field;

a receiver within the sensor head for receiving a receive magnetic field due to the transmit magnetic field when the sensor head is at a determined position and associating the receive magnetic field with the determined position;

a processor for:

analysing the receive magnetic field to determine useful information; storing the useful information associated to the determined position; repeating the steps of determining, transmitting, receiving, analysing and storing during a use of the metal detector;

a visual display for presenting data based on selected stored useful information to a user of the metal detector, wherein the useful information is selected based on the following:

a) a current position of the sensor head; and