Metal detector implementing multi-frequency detection

Abstract

This disclosure relates to the field of metal detection technology, providing a metal detector for multi-frequency detection, comprising: a balanced coil system including: a transmitting coil assembly including a low-frequency and a second transmitting coil; a first transmitting coil driving circuit including: a first signal generator generating a magnetic field generation signal time-division multiplexed by first and second frequencies; a first resonant circuit allowing switching of resonant frequencies between the first and second frequencies; a first signal switcher providing a frequency switching signal to the first resonant circuit; and a second transmitting coil driving circuit including: a second signal generator generating a magnetic field generation signal time-division multiplexed by third and fourth frequencies; a second resonant circuit allowing switching of resonant frequencies between the third and fourth frequencies; and a second signal switcher providing a frequency switching signal to the second resonant circuit; the two signal generators operate together to form a combination of alternating magnetic fields generated by each frequency. The increased number of frequencies generating alternating magnetic fields enhances detection strength and accuracy, expanding application scenarios.

Description

Technical Field

[0001] This disclosure relates to the field of metal detection technology, and in particular to a metal detection machine that enables multi-frequency detection. Background Technology

[0002] In the production and processing of food, pharmaceuticals, and other products, metal detection and control devices have become indispensable key detection equipment at the end of the production line to ensure product quality and safety and prevent safety hazards and equipment damage caused by the ingress of metal foreign objects. Currently, most mainstream metal detection systems on the market use a balanced coil system arranged on the probe. The balanced coil system includes three coils, with the transmitting coil located in the middle and two receiving coils symmetrically arranged on both sides. The distance between the two receiving coils and the transmitting coil is strictly equal and the parameters are perfectly matched, forming a symmetrical balanced structure.

[0003] The working principle of the above-mentioned balanced coil system is as follows: the transmitting coil is provided with an alternating excitation signal by the driving circuit, which in turn generates a stable alternating electromagnetic field in the internal space of the probe. In the initial balanced state without interference from metallic foreign objects, the electromagnetic signals induced by the two symmetrically arranged receiving coils have equal amplitudes and opposite phases. After differential processing, the output signal tends to zero, achieving "balance". When the product being tested containing metallic foreign objects passes through the detection area of ​​the probe, the metallic foreign objects will generate eddy current effects in the alternating electromagnetic field, thereby disturbing the surrounding magnetic field distribution. This causes a difference in the amplitude and phase of the signals induced by the two receiving coils, disrupting the balanced state. The metallic foreign objects can be identified based on the difference in signals.

[0004] However, existing metal detectors still have many technical shortcomings in actual industrial applications, making it difficult to meet the requirements for high-precision and high-stability detection. These shortcomings are as follows:

[0005] On the one hand, metal detectors are usually deployed at the end of the production line, and their operating environment is extremely complex. Equipment such as frequency converters, high-power motors, and welding machines in industrial sites will generate a large number of high-frequency harmonics and electromagnetic interference signals. At the same time, factors such as power grid fluctuations, cable wiring interference, and poor grounding will also introduce additional interference noise, affecting the detection accuracy.

[0006] On the other hand, existing metal detectors typically use a fixed, single frequency, which cannot be adaptively adjusted according to the characteristics of the products being tested. In food testing scenarios, the types of products being tested are diverse, such as fresh meat, sauces, and high-salt foods. Different types of products, due to differences in moisture, salt content, and composition, will produce different product effects (i.e., the product's own disturbance to the magnetic field) in alternating magnetic fields of different frequencies. A single detection frequency cannot meet the optimal detection needs of various products. For some products, the product effect may be confused with the metal foreign object signal, reducing detection sensitivity. For other products, frequency mismatch may prevent the effective capture of the metal foreign object signal, ultimately resulting in insufficient overall detection accuracy and making it difficult to meet the high-precision detection requirements of diverse products. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this disclosure is to provide a metal detector that realizes multi-frequency detection and solves the problems in the related art.

[0008] This disclosure provides a metal detector for multi-frequency detection, comprising: a balanced coil system including: a transmitting coil assembly including at least one first transmitting coil and a second transmitting coil; a first receiving coil and a second receiving coil symmetrically arranged on opposite sides of the transmitting coil assembly and electromagnetically coupled to the transmitting coil assembly; a first transmitting coil driving circuit including: a first signal generator for generating a first magnetic field generating signal time-division multiplexed by a first frequency and a second frequency, the first magnetic field generating signal causing the first transmitting coil to generate a first alternating magnetic field or a second alternating magnetic field; a first resonant circuit connected to the first signal generator and the first transmitting coil, allowing switching of the resonant frequency between the first frequency and the second frequency; and a first signal switcher connected to the first resonant circuit, outputting a first switching signal aligned along a time axis with the frequency switching point in the first magnetic field generating signal, so that the first resonant circuit drives the first transmitting coil to generate a first alternating magnetic field or a second alternating magnetic field. The frequency of the magnetic field-generated signal is switched to a matching resonant frequency; the second transmitting coil driving circuit includes: a second signal generator for generating a second magnetic field-generated signal that is time-division multiplexed by a third frequency and a fourth frequency, the second magnetic field-generated signal causing the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field; a second resonant circuit connected to the second signal generator and the second transmitting coil, allowing the resonant frequency to be switched between the third frequency and the fourth frequency; a second signal switcher connected to the second resonant circuit, outputting a second switching signal aligned with the frequency switching point in the second magnetic field-generated signal along the time axis, so that the second resonant circuit switches to a matching resonant frequency as the frequency of the second magnetic field-generated signal changes; wherein, the first signal generator and the second signal generator operate together to form multiple magnetic field combinations along the time axis with the first alternating magnetic field / second alternating magnetic field and the third alternating magnetic field / fourth alternating magnetic field.

[0009] In an embodiment of the first aspect, the first transmitting coil and the second transmitting coil are configured in one of the following ways: in a partitioned coplanar arrangement; in an inner and outer coplanar arrangement; or in a coaxial inner and outer coplanar arrangement.

[0010] In an embodiment of the first aspect, the first transmitting coil driving circuit includes: a first signal amplification circuit connected between the first signal generator and the first resonant circuit, for amplifying the signal generated by the first magnetic field and outputting it to the first resonant circuit; and / or, the second transmitting coil driving circuit includes: a second signal amplification circuit connected between the second signal generator and the second resonant circuit, for amplifying the signal generated by the second magnetic field and outputting it to the second resonant circuit.

[0011] In an embodiment of the first aspect, the first signal amplification circuit and the second signal amplification circuit are implemented as a first preset amplification circuit structure. The first preset amplification circuit structure includes: a signal generation input terminal connected to a preceding signal generator, including a first half-cycle amplification circuit, a second half-cycle amplification circuit, and a push-pull output circuit; the first half-cycle amplification circuit includes: a first group of amplifiers arranged in multiple stages, connected between the signal generation input terminal and the push-pull output circuit and powered by a first voltage, for generating a first switch drive signal based on the first voltage in response to an input magnetic field generation signal; the second half-cycle amplification circuit includes: a second group of amplifiers arranged in multiple stages, connected between the signal generation input terminal and the push-pull output circuit and powered by a second voltage with the opposite polarity to the first voltage, for generating a second switch drive signal based on the second voltage in response to the input magnetic field generation signal; a push-pull circuit for generating a first half-cycle amplified signal based on the first voltage and outputting it to a subsequent resonant circuit in response to the first switch drive signal; and generating a second half-cycle amplified signal based on the second voltage and outputting it to the subsequent resonant circuit in response to the second switch drive signal.

[0012] In an embodiment of the first aspect, the first signal amplification circuit and the second signal amplification circuit are implemented as a first preset amplification circuit structure, the first preset amplification circuit structure comprising: a first half-cycle amplification circuit, comprising: a first PNP, a first NPN, a second PNP, a second NPN, and a first diode; the base of the first PNP has a signal input terminal for generating a signal from an input magnetic field; the emitter of the first PNP is connected to the positive terminal of a power supply and the base of the first NPN via a first resistor; the collector of the first PNP is connected to the negative terminal of a power supply; the collector of the first NPN is connected to the positive terminal of a power supply and the base of the second PNP via a second resistor; the emitter of the first NPN is connected to the negative terminal of the first diode and grounded via a fourth resistor; the emitter of the second PNP is connected to the positive terminal of a power supply via a third resistor, and the collector of the second PNP is connected to the positive terminal of the first diode and the base of the second NPN; the collector of the second NPN is connected to the positive terminal of a power supply, and the emitter of the second NPN is connected to one end of a fifth resistor; the other end of the fifth resistor is grounded via a sixth resistor and a fourth resistor; the second half-cycle amplification circuit comprises: a third NPN, a third PNP, a fourth NPN, a fourth PNP, and a fourth PNP. The first NPN and the second diode; the base of the third NPN is coupled to the signal input terminal; the emitter of the third NPN is connected to the negative terminal of the power supply and the base of the third PNP via a seventh resistor; the collector of the third NPN is connected to the positive terminal of the power supply; the collector of the third PNP is connected to the negative terminal of the power supply and the base of the fourth NPN via an eighth resistor; the emitter of the third PNP is connected to the positive terminal of the second diode and the emitter of the first NPN; the emitter of the fourth NPN is connected to the negative terminal of the power supply via a ninth resistor, and the collector of the fourth NPN is connected to the negative terminal of the second diode. The circuit includes: the base of the fourth PNP; the collector of the fourth PNP is connected to the negative terminal of the power supply; the emitter of the fourth PNP is connected to one end of the tenth resistor; the other end of the tenth resistor is connected to the other end of the fifth resistor, and grounded via the sixth and fourth resistors; a push-pull output circuit, including: a first NMOS and a first PMOS, connected to the common gate and coupled to the other end of the fifth resistor; the source of the first NMOS is connected to the drain of the first PMOS and leads out a signal output terminal for outputting the amplified magnetic field generation signal; the drain of the first NMOS is connected to the positive terminal of the power supply; the source of the first PMOS is connected to the negative terminal of the power supply.

[0013] In an embodiment of the first aspect, the first resonant circuit and the second resonant circuit are implemented as including a variable capacitor unit connected in parallel with their respective transmitting coils; wherein the variable capacitor unit is implemented as including capacitive elements located in a plurality of branches in parallel, some of the branches being provided with switching elements that allow a switching signal to set a switching state to turn the branch on / off.

[0014] In an embodiment of the first aspect, the first transmitting coil driving circuit includes: a first switching signal amplification circuit connected between the first signal switcher and the first resonant circuit, for amplifying the first switching signal and outputting it to the first resonant circuit; and / or, the second transmitting coil driving circuit includes: a second switching signal amplification circuit connected between the second signal switcher and the second resonant circuit, for amplifying the second switching signal and outputting it to the second resonant circuit.

[0015] In an embodiment of the first aspect, the first switching signal amplification circuit and the second switching signal amplification circuit are implemented as a second preset amplification circuit structure, the second preset amplification circuit structure comprising: a switching signal input terminal connected to a preceding signal switcher to receive an input switching signal; a first amplifier having its input terminal connected to the switching signal input terminal and its output terminal connected to the gate of a MOS switch; wherein the MOS switch is connected in series in the branch of the resonant circuit containing the capacitor element used for switching the resonant frequency; and a second amplifier having its input terminal connected to the switching signal input terminal and its output terminal connected to the source of the MOS switch; wherein one of the first amplifier and the second amplifier is a non-inverting amplifier and the other is an inverting amplifier, to form a gate-source voltage for controlling the on / off state of the MOS switch in response to the input switching signal.

[0016] In the first aspect of the embodiment, the first switching signal amplification circuit and the second switching signal amplification circuit are implemented as a second preset amplification circuit structure, the second preset amplification circuit structure comprising: a switching signal input terminal connected to a preceding signal switcher to receive an input switching signal; an inverting amplifier comprising: a fifth NPN, a sixth NPN, a fifth PNP, and a seventh NPN; the base of the fifth NPN is connected to the switching signal input terminal via an eleventh resistor, its emitter is grounded, its collector is connected to the base of the sixth NPN and connected to the positive terminal of the power supply via a twelfth resistor; the emitter of the sixth NPN is grounded via a thirteenth resistor, its collector is connected to the base of the fifth PNP and one end of a fifteenth resistor via a fourteenth resistor, the other end of the fifteenth resistor is connected to the positive terminal of the power supply; the emitter of the fifth PNP is connected to the positive terminal of the power supply via a sixteenth resistor, its collector is connected to the base of the fifth PNP via a seventeenth resistor... A resistor is connected to the base of the seventh NPN and to the emitter of the seventh NPN via the eighteenth resistor to lead out the output terminal of the inverting amplifier; the output terminal of the inverting amplifier is connected to one end of the nineteenth resistor and the gate of a MOS switch; wherein, the MOS switch is connected in series in the branch of the resonant circuit where the capacitor element used to switch the resonant frequency is located; the non-inverting amplifier includes: an eighth NPN and a sixth PNP; the gate of the eighth NPN is connected to the switching signal input terminal via the twenty-first resistor, its collector is connected to the base of the sixth PNP via the twenty-second resistor and to the positive terminal of the power supply via the twenty-third resistor, and its emitter is grounded via the twenty-fourth resistor; the emitter of the sixth PNP is connected to the positive terminal of the power supply, and its collector is connected to the collector of the seventh NPN and the other end of the nineteenth resistor via the twentyth resistor to lead out the output terminal of the non-inverting amplifier; the output terminal of the non-inverting amplifier is connected to the source of the MOS switch.

[0017] In an embodiment of the first aspect, the first frequency and the second frequency occupy the same duration in the first magnetic field generated signal, and the third frequency and the fourth frequency occupy the same duration in the first magnetic field generated signal; and / or, the first frequency and the second frequency are both higher than the third frequency and the fourth frequency, and the signal period length of the first switching signal is 1 to 3 times the signal period length of the second switching signal; and / or, the first frequency and the second frequency are in the range of 50kHz to 200kHz, and the third frequency and the fourth frequency are in the range of 200kHz to 1000kHz.

[0018] As described above, this disclosure relates to the field of metal detection technology and provides a metal detector for multi-frequency detection, comprising: a balanced coil system including: a transmitting coil assembly including at least one first transmitting coil and a second transmitting coil; a first receiving coil and a second receiving coil symmetrically arranged; a first transmitting coil driving circuit including: a first signal generator for generating a first magnetic field generation signal time-division multiplexed by a first frequency and a second frequency, for generating two alternating magnetic fields by the first transmitting coil; a first resonant circuit allowing switching of the resonant frequency between the first frequency and the second frequency; and a first signal switcher, wherein the signal period synchronously forms a switching frequency between the first and second frequencies. The signal is switched to the resonant circuit; the second transmitting coil driving circuit includes: a second signal generator for generating a second magnetic field generation signal that is time-division multiplexed by a third frequency and a fourth frequency, for the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field; a second resonant circuit that allows switching the resonant frequency between the third frequency and the fourth frequency; and a second signal switcher that periodically generates a switching signal to switch the third / fourth frequency to the resonant circuit; wherein the first signal generator and the second signal generator operate together to make the first / second alternating magnetic field and the third / fourth alternating magnetic field form multiple magnetic field combinations along the time axis. By utilizing a transmitting coil assembly that can switch between high / low frequencies separately, the frequency and the number of alternating magnetic fields at the corresponding frequencies are increased, improving detection intensity and accuracy, and expanding application scenarios. Attached Figure Description

[0019] Figure 1 The diagram shows a structural schematic of a balanced coil system for a metal detector that implements multi-frequency detection according to an embodiment of the present disclosure.

[0020] Figure 2 The diagram shown is a schematic representation of a transmitting coil driving circuit system according to an embodiment of this disclosure.

[0021] Figure 3 The diagram shows a waveform of a time-division multiplexed magnetic field-generated signal in one embodiment of this disclosure.

[0022] Figure 4 The diagram shows a schematic of an LC resonant circuit structure according to an embodiment of the present disclosure.

[0023] Figure 5 The diagram shows a waveform comparison between the output signal on the first transmitting coil, the first switching signal, the output signal on the second transmitting coil, and the second switching signal in one embodiment of this disclosure.

[0024] Figure 6 The diagram shown is a schematic representation of the transmitting coil driving circuit system in another embodiment of this disclosure.

[0025] Figure 7The diagram shows a module schematic of a first preset amplifier circuit structure in one embodiment of this disclosure.

[0026] Figure 8 The diagram shows a schematic of the circuit principle of the first preset amplifier circuit structure in a specific embodiment of this disclosure.

[0027] Figure 9 The diagram shows a module schematic of the second preset amplifier circuit structure in one embodiment of this disclosure.

[0028] Figure 10 The diagram shows a schematic of the second preset amplifier circuit structure in a specific embodiment of this disclosure.

[0029] Figure 11 The diagram shows a flowchart of a metal detection control method according to an embodiment of this disclosure.

[0030] Figure 12 The diagram shows a schematic of a metal detection control device in one embodiment of this disclosure.

[0031] Figure 13 The diagram shows a schematic representation of a computer device according to an embodiment of the present disclosure. Detailed Implementation

[0032] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the information disclosed herein. This disclosure can also be implemented or applied through other different specific embodiments, and various details in this disclosure can be modified or changed according to different viewpoints and application modules without departing from the spirit of this disclosure. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this disclosure can be combined with each other.

[0033] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings, so that those skilled in the art to which this disclosure pertains can readily implement it. This disclosure may be embodied in many different forms and is not limited to the embodiments described herein.

[0034] In this disclosure, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic represented in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. Furthermore, the specific features, structures, materials, or characteristics represented may be combined in any suitable manner in any one or a group of embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples represented in this disclosure, as well as the features of those different embodiments or examples.

[0035] Furthermore, the terms "first" and "second" are used for illustrative purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the representation of this disclosure, "a set" means two or more, unless otherwise explicitly specified.

[0036] For the purpose of clarity, devices unrelated to the description are omitted, and the same or similar components throughout the specification are given the same reference numerals.

[0037] Throughout this specification, when it is said that a device is "connected" to another device, this includes not only "direct connection" but also "indirect connection" by placing other components in between. Furthermore, when it is said that a device "comprises" a certain constituent element, unless otherwise stated otherwise, this does not exclude other constituent elements, but rather implies that other constituent elements may be included.

[0038] While the terms first, second, etc., are used in some examples herein to refer to various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, first interface and second interface, etc., are used. Furthermore, as used herein, the singular forms “a,” “an,” and “the” are intended to also include the plural forms unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, step, operation, element, module, item, kind, and / or group, but do not exclude the presence, occurrence, or presence of one or more other features, steps, operations, elements, modules, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are to be interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition will only occur if the combination of elements, functions, steps, or operations is inherently mutually exclusive in some way.

[0039] The technical terms used herein are for reference only to specific embodiments and are not intended to limit the scope of this disclosure. The singular form used herein includes the plural form unless the statement explicitly indicates otherwise. The word "comprising" as used in this specification means to specify a particular characteristic, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other characteristics, regions, integers, steps, operations, elements, and / or components.

[0040] Although not explicitly defined, all terms, including technical and scientific terms used herein, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms defined in commonly used dictionaries shall be further interpreted as having a meaning consistent with the relevant technical literature and the message of the present disclosure, and shall not be over-interpreted as having an ideal or overly formulaic meaning unless otherwise defined.

[0041] In the production and processing of food, pharmaceuticals, and other products, metal detection and control devices have become indispensable key detection equipment at the end of the production line to ensure product quality and safety and prevent safety hazards and equipment damage caused by the ingress of metal foreign objects. Currently, most mainstream metal detection systems on the market use a balanced coil system arranged on the probe. The balanced coil system includes three coils, with the transmitting coil located in the middle and two receiving coils symmetrically arranged on both sides. The distance between the two receiving coils and the transmitting coil is strictly equal and the parameters are perfectly matched, forming a symmetrical balanced structure.

[0042] The working principle of the above-mentioned balanced coil system is as follows: the transmitting coil is provided with an alternating excitation signal by the driving circuit, which in turn generates a stable alternating electromagnetic field in the internal space of the probe. In the initial balanced state without interference from metallic foreign objects, the electromagnetic signals induced by the two symmetrically arranged receiving coils have equal amplitudes and opposite phases. After differential processing, the output signal tends to zero, achieving "balance". When the product being tested containing metallic foreign objects passes through the detection area of ​​the probe, the metallic foreign objects will generate eddy current effects in the alternating electromagnetic field, thereby disturbing the surrounding magnetic field distribution. This causes a difference in the amplitude and phase of the signals induced by the two receiving coils, disrupting the balanced state. The metallic foreign objects can be identified based on the difference in signals.

[0043] However, existing metal detectors still have many technical shortcomings in actual industrial applications, making it difficult to meet the requirements for high-precision and high-stability detection. These shortcomings are as follows:

[0044] On the one hand, metal detectors are usually deployed at the end of the production line, and their operating environment is extremely complex. Equipment such as frequency converters, high-power motors, and welding machines in industrial sites will generate a large number of high-frequency harmonics and electromagnetic interference signals. At the same time, factors such as power grid fluctuations, cable wiring interference, and poor grounding will also introduce additional interference noise, affecting the detection accuracy.

[0045] On the other hand, existing metal detectors typically use a fixed, single frequency, which cannot be adaptively adjusted according to the characteristics of the products being tested. In food testing scenarios, the types of products being tested are diverse, such as fresh meat, sauces, and high-salt foods. Different types of products, due to differences in moisture, salt content, and composition, will produce different product effects (i.e., the product's own disturbance to the magnetic field) in alternating magnetic fields of different frequencies. A single detection frequency cannot meet the optimal detection needs of various products. For some products, the product effect may be confused with the metal foreign object signal, reducing detection sensitivity. For other products, frequency mismatch may prevent the effective capture of the metal foreign object signal, ultimately resulting in insufficient overall detection accuracy and making it difficult to meet the high-precision detection requirements of diverse products.

[0046] In view of this, the present disclosure provides a metal detector that realizes multi-frequency detection. By increasing the number of high-frequency and low-frequency transmitting coils and cooperating with the corresponding transmitting coil driving circuits to realize their respective frequency switching, the number of frequencies of alternating magnetic fields and the corresponding combinations of alternating magnetic fields that can coexist can be effectively increased, thereby strengthening the detection intensity, improving the detection accuracy, and solving the problems in related technologies.

[0047] like Figure 1 The diagram shown is a structural schematic of a balanced coil system for a metal detector that implements multi-frequency detection in one embodiment of this disclosure.

[0048] exist Figure 1 The diagram shows the balanced coil system 100 including a transmitting coil assembly and a pair of first receiving coils 130 and second receiving coils 140.

[0049] In embodiments of this disclosure, the transmitting coil assembly may include multiple transmitting coils, each of which is driven by a magnetic field generating signal of different frequency to generate an alternating magnetic field of different frequency. As an example, in... Figure 1 The image shows multiple transmitting coils, including a first transmitting coil 110 and a second transmitting coil 120. The first transmitting coil 110 and the second transmitting coil 120 can be one of a low-frequency transmitting coil and the other of a high-frequency transmitting coil, respectively, used for generating alternating magnetic fields at low and high frequencies. For example, the first transmitting coil 110 is a low-frequency transmitting coil, and the second transmitting coil 120 is a high-frequency transmitting coil. In some embodiments, it is understood that "low frequency" and "high frequency" are relative terms and do not necessarily have to conform to proprietary industry terminology. In a wide range of applications in metal detection, the frequency range may be 1kHz to 1000kHz. However, considering applications in food, medical, and security inspection fields, the low-frequency range may be 50kHz to 200kHz, and the high-frequency range may be 200kHz to 1000kHz.

[0050] The first receiving coil 130 and the second receiving coil 140 are electromagnetically coupled to the transmitting coil assembly to obtain induced signals. According to the principle of the previously described balanced coil system 100, the induced signals generated on the first receiving coil 130 and the second receiving coil 140 are a pair of differential signals used to cancel each other out. Therefore, the first receiving coil 130 and the second receiving coil 140 must be identical coils and arranged strictly symmetrically on both sides of the transmitting coil. The transmitting coil can be implemented as a planar coil wound in a plane, in which case the first receiving coil 130 and the second receiving coil 140 are also planar coils parallel to the transmitting coil. In embodiments of this disclosure, since the transmitting coil assembly includes multiple transmitting coils, in order to make the first receiving coil 130 and the second receiving coil 140 symmetrically arranged both relative to both sides of the first transmitting coil 110 and the second transmitting coil 120, the first transmitting coil 110 and the second transmitting coil 120 can be arranged coplanarly, i.e., in the same plane.

[0051] exist Figure 1 In this embodiment, the first transmitting coil 110 and the second transmitting coil 120 may be arranged coplanarly with an inner and outer sleeve. Optionally, the first transmitting coil 110 and the second transmitting coil 120 may be coaxially arranged. The winding shapes of the first transmitting coil 110 and the second transmitting coil 120 may be the same or different.

[0052] In another embodiment, the first transmitting coil 110 and the second transmitting coil 120 may also be arranged in a coplanar manner in sections, and are not limited to the figures shown.

[0053] Therefore, it can be understood that when the transmitting coil assembly contains multiple (such as two or more) transmitting coils, as long as the transmitting coils are arranged coplanarly, such that the first receiving coil 130 and the second receiving coil 140 are symmetrically arranged on both sides relative to them, a pair of precise differential induction signals can be formed for each frequency of alternating magnetic field when no metal foreign object is detected.

[0054] The metal detector also includes a transmitting coil drive circuit system for providing magnetic field generation signals to multiple transmitting coils to generate alternating magnetic fields at various frequencies. In some embodiments, the magnetic field generation signal can be an alternating signal, such as a sine wave signal.

[0055] like Figure 2 The diagram shown is a schematic representation of the structure of a transmitting coil driving circuit system according to an embodiment of this disclosure.

[0056] Taking a transmitting coil assembly including a first transmitting coil 110 and a second transmitting coil 120 as an example, in Figure 2The transmitting coil driving circuit system shown in the figure includes: a first transmitting coil driving circuit 150 and a second transmitting coil driving circuit 160.

[0057] The first transmitting coil driving circuit 150 includes a first signal generator 151, a first resonant circuit 152, and a first signal switcher 153.

[0058] The first signal generator 151 is configured to generate a first magnetic field generation signal that is time-division multiplexed by a first frequency and a second frequency. The first magnetic field generation signal causes the first transmitting coil 110 to generate a first alternating magnetic field or a second alternating magnetic field. In some embodiments, different times in the first magnetic field generation signal are allocated to the first frequency and the second frequency.

[0059] For reference Figure 3 The diagram shown illustrates a waveform representation of a time-division multiplexed magnetic field signal generation method. Figure 3 In this diagram, the magnetic field generates a sinusoidal signal with two frequencies, La and Lb, multiplexed in a time-division multiplexing manner. Of course, the number of frequencies is not limited to two and can be increased as needed. As shown in the figure, the two frequencies, La and Lb, periodically alternate in duration along the time axis, and the duration occupied can be n time slots, where n≥1. For example, the durations occupied by La and Lb in each signal cycle can be the same, or they can be different in other embodiments.

[0060] Therefore, by way of example, the signal portions of the first frequency and the second frequency in the signal generated by the first magnetic field can be distributed alternately every n time slots, where n ≥ 1, and is not limited to the figure shown. Specifically, n can be determined based on the duration required for each alternating magnetic field of the two frequencies. In some embodiments, the number / length of time slots occupied by the first frequency and the second frequency can also be different, and the signal ratio can be determined based on the dominant and secondary roles of the alternating magnetic fields of the two frequencies.

[0061] In some embodiments, if it is assumed that the signal generated by the first magnetic field is a low-frequency signal, such as in the range of 50kHz to 200kHz, then the first frequency and the second frequency are different frequencies selected from 50kHz to 200kHz. For example, there may be a certain frequency difference between the first frequency and the second frequency, such as a difference of 50kHz, 100kHz, etc.

[0062] The first resonant circuit 152 is connected to the first signal generator 151 and the first transmitting coil 110, allowing the resonant frequency to be switched between a first frequency and a second frequency. The first resonant circuit 152 can be implemented based on an LC resonant circuit structure. In some embodiments, the resonant circuit structure is implemented as including a variable capacitor unit connected in parallel with each transmitting coil. The variable capacitor unit is implemented as including capacitive elements located in multiple branches connected in parallel, and some of these branches are provided with switching elements, allowing a switching signal to set a switching state to turn the branch on / off.

[0063] For example, such as Figure 4 The diagram shown is a schematic representation of an LC resonant circuit structure in one embodiment of this disclosure.

[0064] exist Figure 4 In this configuration, the transmitting coil L is used to acquire the magnetic field generation signal output from the preceding stage. As an example, L can be connected to the preceding stage via a transformer P to obtain a magnetic field generation signal that has been transformed to the desired voltage, or L can directly inject the magnetic field generation signal. The magnetic field generation signal is an alternating signal multiplexed in a time-division multiplexing manner. Optionally, the magnetic field generation signal can be a sinusoidal signal multiplexed in a time-division multiplexing manner.

[0065] The transmitting coil L is connected in parallel with capacitors C1 and C2. The branch containing C2 can be switched on or off by a switch K connected between K1 and K2.

[0066] According to the formula for calculating the resonant frequency, the resonant frequency is: Therefore, when K is on, the resonant frequency is calculated based on L and the equivalent capacitance C = C1 + C2; when K is off, the resonant frequency is calculated based on L and the equivalent capacitance C = C1.

[0067] In other words, by controlling the on / off state of K, the capacitance value in the resonant circuit can be adjusted, thereby switching the resonant frequency of the resonant circuit.

[0068] The first signal switcher 153 is connected to the first resonant circuit 152 and outputs a first switching signal aligned with the frequency switching point along the time axis of the first magnetic field generating signal, so that the first resonant circuit 152 switches to a matching resonant frequency as the frequency of the first magnetic field generating signal changes. In some embodiments, the first switching signal can be implemented as a square wave pulse signal, the rising and falling edges of which can be aligned with the frequency switching point between the signal portions of the first and second frequencies in the first magnetic field generating signal. (See reference...) Figure 5The diagram shows a waveform comparison between the output signal and the first switching signal on the first transmitting coil 110. L1 and L2 represent the first frequency and the second frequency (L can represent a low frequency). As can be seen, the first switching signal, in the form of a square wave pulse, switches the first resonant circuit 152 to a suitable resonant frequency corresponding to the current frequency portion of the first magnetic field generating signal. The output signal of the first transmitting coil 110 also presents a waveform that time-division multiplexes the first and second frequencies, thereby generating alternating first and second alternating magnetic fields. In some embodiments, the switching frequency of the first switching signal can be once every tens of milliseconds.

[0069] It is understandable that the only difference between the first transmitting coil 110 and the second transmitting coil 120 is the high or low signal frequency and the corresponding alternating magnetic field formed. Therefore, the circuit implementation of the second transmitting coil driving circuit 160 is similar to that of the first transmitting coil driving circuit 150.

[0070] The second transmitting coil driving circuit 160 includes a second signal generator 161, a second resonant circuit 162, and a second signal switcher 163.

[0071] The second signal generator 161 is used to generate a second magnetic field generation signal that is time-division multiplexed by a third frequency and a fourth frequency. This second magnetic field generation signal causes the second transmitting coil 120 to generate either a third alternating magnetic field or a fourth alternating magnetic field. In some embodiments, different times in the second magnetic field generation signal are allocated to the third and fourth frequencies. The waveform of the second magnetic field generation signal can also be referenced. Figure 3 The only difference lies in the frequency. The signal portions of the third and fourth frequencies generated by the second magnetic field can be alternately distributed every n time slots, where n ≥ 1. Specifically, n can be determined based on the duration required for each alternating magnetic field of the two frequencies. In some embodiments, the number / length of time slots occupied by the third and fourth frequencies can also be different, and the signal ratio can be determined based on the dominant and secondary roles of the two alternating magnetic fields.

[0072] In some embodiments, if it is assumed that the signal generated by the second magnetic field is a high-frequency signal, such as in the range of 200kHz to 1000kHz, then the third frequency and the fourth frequency are different frequencies selected from 200kHz to 1000kHz. For example, the third frequency and the fourth frequency may have a certain frequency difference, such as a difference of 50kHz, 100kHz, etc.

[0073] The second resonant circuit 162, connected to the second signal generator 161 and the second transmitting coil 120, allows switching the resonant frequency between the third and fourth frequencies. The second resonant circuit 162 can be implemented based on an LC resonant circuit structure, for example... Figure 4The circuit structure in it.

[0074] The second signal switcher 163 is connected to the second resonant circuit 162 and outputs a second switching signal aligned along the time axis with the frequency switching point in the second magnetic field generating signal, so that the second resonant circuit 162 switches to a matching resonant frequency as the frequency of the second magnetic field generating signal changes. In some embodiments, the second switching signal can be implemented as a square wave pulse signal, the rising and falling edges of which can be aligned with the frequency switching point between the signal portions of the third and fourth frequencies in the second magnetic field generating signal. (See reference...) Figure 5 The diagram also shows a waveform comparison of the output signal on the second transmitting coil 120 and the second switching signal. H1 and H2 represent the third and fourth frequencies (H can represent high frequencies). As can be seen, the second switching signal, in the form of a square wave pulse, switches the second resonant circuit 162 to a suitable resonant frequency corresponding to the current frequency portion of the second magnetic field generating signal. The output signal of the second transmitting coil 120 also presents a waveform that time-division multiplexes the third and fourth frequencies, thereby generating alternating third and fourth alternating magnetic fields. In some embodiments, the switching frequency of the second switching signal can be once every tens of milliseconds.

[0075] Optionally, the period durations of the first switching signal and the second switching signal can be related to form the desired combination of high and low frequency alternating magnetic fields. Optionally, the period duration of the switching signal corresponding to the low frequency can be no shorter than the period duration of the switching signal corresponding to the high frequency. For example, Figure 5 The duration of the period of the first switching signal corresponding to the switching between the first and second frequencies at a low frequency can be 1.5 times the duration of the period of the second switching signal corresponding to the high frequency. Alternatively, in other embodiments, it can be 1 to 3 times, and is not limited to 1.5.

[0076] It is worth mentioning that if the two frequencies in the magnetic field generation signal occupy different durations, the ratio of low level to high level in the switching signal (equivalent to duty cycle) will also be different.

[0077] It is understandable that by having the first signal generator 151 and the second signal generator 161 operate together, the first / second alternating magnetic field and the third / fourth alternating magnetic field can form various magnetic field combinations along the time axis. For example, different combinations of low- and high-frequency alternating magnetic fields, such as the combination of the first and third alternating magnetic fields (low- and high-frequency alternating magnetic fields), the combination of the first and fourth alternating magnetic fields (low- and high-frequency alternating magnetic fields), the combination of the second and third alternating magnetic fields (low- and high-frequency alternating magnetic fields), and the combination of the second and fourth alternating magnetic fields (low- and high-frequency alternating magnetic fields), can be created.

[0078] In some embodiments, the first signal generator 151 and the second signal generator 161 can be implemented by independent signal generation circuits. The generation of the switching signals for the first signal switcher 153 and the second signal switcher 163 can also be implemented by independent signal generation circuits. Alternatively, in other embodiments, reference can be made to... Figure 6 As shown, the first signal generator 151 and the second signal generator 161 can be implemented by a host computer 170 in conjunction with a direct digital frequency synthesis (DDS) function generator to generate a first magnetic field generation signal and a second magnetic field generation signal that are time-division multiplexed at multiple frequencies, respectively. The switching signals of the first signal switcher 153 and the second signal switcher 163 can also be implemented by a host computer in conjunction with a direct digital frequency synthesis (DDS) function generator.

[0079] Back Figure 2 Considering the relatively small amplitudes of the signals output by the first signal generator and the second signal generator 161, the first transmitting coil driving circuit may include a first signal amplification circuit 154 connected between the first signal generator and the first resonant circuit, for amplifying the signal generated by the first magnetic field and outputting it to the first resonant circuit. The second transmitting coil driving circuit may include a second signal amplification circuit 164 connected between the second signal generator 161 and the second resonant circuit, for amplifying the signal generated by the second magnetic field and outputting it to the second resonant circuit.

[0080] In some embodiments, the first signal amplification circuit 154 and the second signal amplification circuit 164 are implemented as a first preset amplification circuit structure.

[0081] like Figure 7 The diagram shown is a schematic representation of a first preset amplifier circuit structure in one embodiment of this disclosure.

[0082] exist Figure 7 In the first preset amplifier circuit structure, there are: a signal input terminal 710, a first half-cycle amplifier circuit 720, a second half-cycle amplifier circuit 730, and a push-pull output circuit 740.

[0083] The first half-cycle amplifier circuit 720 includes a first group of amplifiers 721 arranged in multiple stages, connected between the signal generation input terminal 710 and the push-pull output circuit 740 and powered by a first voltage, for generating a first switching drive signal based on the first voltage in response to the input magnetic field generation signal.

[0084] The second half-cycle amplifier circuit 730 includes a second group of amplifiers 731 arranged in multiple stages, connected between the signal generation input terminal 710 and the push-pull output circuit 740 and powered by a second voltage with the opposite polarity to the first voltage, for generating a second switching drive signal based on the second voltage in response to the input magnetic field generation signal.

[0085] In some embodiments, the first group of amplifiers 721 and the second group of amplifiers 731 can be implemented based on multi-stage transistors. The multi-stage transistors may include cascaded PNP and NPN transistors, which can be connected to form multi-stage positive and negative phase amplifiers. The number of negative phase amplifiers is even, allowing the signal to be recovered into the amplified signal after two negative phase amplifications.

[0086] The push-pull circuit is configured to respond to a first switch drive signal, generate a first half-cycle amplified signal based on a first voltage, and output it to a subsequent resonant circuit; and respond to a second switch drive signal, generate a second half-cycle amplified signal based on a second voltage, and output it to a subsequent resonant circuit. In some embodiments, the push-pull circuit can be implemented based on at least one pair of NMOS and PMOS, respectively used to generate positive and negative half-cycle signals from the amplified magnetic field of an alternating (e.g., sine wave) signal.

[0087] like Figure 8 The diagram shown is a schematic diagram of the circuit principle of the first preset amplifier circuit structure in a specific embodiment of this disclosure.

[0088] In this embodiment, the first half-cycle amplifier circuit includes: a first PNP Q1, a first NPN Q2, a second PNP Q3, a second NPN Q4, and a first diode D1. The base of the first PNP Q1 has a signal input terminal for generating a signal using an input magnetic field. The emitter of the first PNP Q1 is connected to the positive terminal VCC of the power supply and the base of the first NPN Q2 via a first resistor R1. The collector of the first PNP Q1 is connected to the negative terminal VSS of the power supply. The collector of the first NPN Q2 is connected to the positive terminal VCC of the power supply and the base of the second PNP Q3 via a second resistor R2. The emitter of the first NPN Q2 is connected to the negative terminal of the first diode D1 and grounded to GND via a fourth resistor R4. The emitter of the second PNP Q3 is connected to the positive terminal VCC of the power supply via a third resistor R3, and the collector of the second PNP Q3 is connected to the positive terminal of the first diode D1 and the base of the second NPN Q4. The collector of the second NPN Q4 is connected to the positive terminal of the power supply VCC, and the emitter of the second NPN Q4 is connected to one end of the fifth resistor R5; the other end of the fifth resistor R5 is grounded to GND through the sixth resistor R6 and the fourth resistor R4.

[0089] In this system, VCC and VSS are applied with opposite positive and negative voltages, for example, if VCC is +24V, then VSS is -24V.

[0090] The second half-cycle amplifier circuit includes: a third NPN Q5, a third PNP Q6, a fourth NPN Q7, a fourth PNP Q8, and a second diode D2. The base of the third NPN Q5 is coupled to the signal input terminal; the emitter of the third NPN Q5 is connected to the negative terminal VSS of the power supply and the base of the third PNP Q6 via the seventh resistor R7; the collector of the third NPN Q5 is connected to the positive terminal VCC of the power supply; the collector of the third PNP Q6 is connected to the negative terminal VSS of the power supply and the base of the fourth NPN Q7 via the eighth resistor R8; the emitter of the third PNP Q6 is connected to the positive terminal of the second diode D2 and the emitter of the first NPN Q2; the emitter of the fourth NPN Q7 is connected to the negative terminal VSS of the power supply via the ninth resistor R9, and the collector of the fourth NPN Q7 is connected to the negative terminal of the second diode D2 and the base of the fourth PNP Q8; the collector of the fourth PNP Q8 is connected to the negative terminal VSS of the power supply, and the emitter of the fourth PNP Q8 is connected to one end of the tenth resistor R10; the other end of the tenth resistor R10 is connected to the other end of the fifth resistor R5, and grounded to GND via the sixth resistor R6 and the fourth resistor R4.

[0091] It is understandable that the first PNP Q1, the first NPN Q2, the second PNP Q3, and the second NPN Q4 constitute the four-stage amplifier circuit in the upper half-cycle, amplifying the first magnetic field generation signal in four stages. Specifically, the signals at the collector and base of Q1 are in phase, serving as the first-stage non-inverting amplifier. The signals at the base and collector of Q2 are out of phase, serving as the second-stage inverting amplifier. The signals at the collector and base of Q3 are out of phase, serving as the third-stage inverting amplifier. The signals at the base and emitter of Q4 are in phase, serving as the fourth-stage non-inverting amplifier. Similarly, the third NPN Q5, the third PNP Q6, the fourth NPN Q7, and the fourth PNP Q8 constitute the four-stage amplifier circuit in the lower half-cycle, amplifying the second magnetic field generation signal in four stages. Specifically, the signals at the base and emitter of Q5 are in phase, serving as the first-stage non-inverting amplifier. The signals at the base and collector of Q6 are out of phase, serving as the second-stage inverting amplifier. The signals at the collector and base of Q7 are out of phase, serving as the third-stage inverting amplifier. The signals at the base and emitter of Q8 are in phase, making it the fourth-stage inverting amplifier.

[0092] D1 and D2 are connected between the bases of Q4 and Q8 to eliminate the dead zone voltage caused by crossover distortion.

[0093] The push-pull output circuit includes a first NMOS M1 and a first PMOS M2, which are connected via a common gate and coupled to the other end of the fifth resistor R5. The source of M1 is connected to the drain of the first PMOS M2 and leads out to a signal output terminal for outputting the amplified magnetic field-generated signal. The drain of M1 is connected to the positive terminal VCC of the power supply, and the source of M2 is connected to the negative terminal VSS of the power supply. The two MOS transistors in the push-pull output circuit are used to output two half-cycles of the signal, respectively.

[0094] Back Figure 2 Similarly, considering that the amplitude of the switching signal may be small, in order to make it reach a suitable amplitude for driving the subsequent switching resonant frequency switch, an amplification circuit for the switching signal can also be added between the signal switcher and the resonant circuit. Optionally, the first transmitting coil driving circuit includes a first switching signal amplification circuit 155, connected between the first signal switcher and the first resonant circuit, for amplifying the first switching signal and outputting it to the first resonant circuit. Exemplarily, the second transmitting coil driving circuit includes a second switching signal amplification circuit 165, connected between the second signal switcher and the second resonant circuit, for amplifying the second switching signal and outputting it to the second resonant circuit.

[0095] In some embodiments, the first switching signal amplification circuit 155 and the second switching signal amplification circuit 165 are implemented as a second preset amplification circuit structure.

[0096] like Figure 9 The diagram shown is a schematic representation of a second preset amplifier circuit structure in one embodiment of this disclosure.

[0097] exist Figure 9 In the second preset amplifier circuit structure, there are: a switching signal input terminal 910, a first amplifier 920, and a second amplifier 930.

[0098] The switching signal input terminal 910 is connected to the preceding signal switcher to receive the input switching signal.

[0099] The first amplifier 920 has its input terminal connected to the switching signal input terminal 910, and its output terminal connected to the gate of a MOS switch. The MOS switch is connected in series in the branch of the resonant circuit containing the capacitor element used for switching the resonant frequency.

[0100] The second amplifier 930 has its input terminal connected to the switching signal input terminal 910, and its output terminal connected to the source of the MOS switch.

[0101] In this amplifier, one of the first amplifier 920 and the second amplifier 930 is a non-inverting amplifier, and the other is an inverting amplifier, to form a gate-source voltage that controls the on / off state of the MOS switch in response to the input switching signal. It is understood that by amplifying the input switching signal in both positive and inverting directions, a bias voltage (VGS) for the MOS switch with amplified amplitude is formed, thereby improving the driving capability of the MOS switch and achieving a switching result that follows the switching signal.

[0102] like Figure 10 The diagram shown is a schematic diagram of the circuit principle of the second preset amplifier circuit structure in a specific embodiment of this disclosure.

[0103] In this example, the second preset amplifier circuit structure includes: a switching signal input terminal, an inverting amplifier, a non-inverting amplifier, and a MOS switch.

[0104] The switching signal input terminal is connected to the preceding signal switcher to receive the input switching signal.

[0105] The inverting amplifier includes: a fifth NPN Q9, a sixth NPN Q10, a fifth PNP Q11, and a seventh NPN Q12. The base of the fifth NPN Q9 is connected to the switching signal input terminal via an eleventh resistor R11, and its emitter is grounded (or can be grounded via a resistor as needed). Its collector is connected to the base of the sixth NPN Q10 and connected to the positive power supply terminal via a twelfth resistor R12. The emitter of the sixth NPN Q10 is grounded via a thirteenth resistor R13, and its collector is connected to the base of the fifth PNP Q11 and one end of a fifteenth resistor R15 via a fourteenth resistor R14. The other end of the fifteenth resistor R15 is connected to the positive power supply terminal VCC. The emitter of the fifth PNP Q11 is connected to the positive power supply terminal via a sixteenth resistor R16, and its collector is connected to the base of the seventh NPN Q12 via a seventeenth resistor R17. It is also connected to the emitter of the seventh NPN Q12 via an eighteenth resistor R18 to lead out the output terminal of the inverting amplifier. The output of the inverting amplifier is connected to one end of the nineteenth resistor R19 and the gate of a MOS switch.

[0106] The non-inverting amplifier includes an eighth NPN Q13 and a sixth PNP Q14. The gate of the eighth NPN Q13 is connected to the switching signal input terminal via a twenty-first resistor R21. Its collector is connected to the base of the sixth PNP Q14 via a twenty-second resistor R22 and to the positive terminal of the power supply via a twenty-third resistor R23. Its emitter is grounded via a twenty-fourth resistor R24. The emitter of the sixth PNP Q14 is connected to the positive terminal of the power supply. Its collector is connected to the collector of the seventh NPN Q12 and the other end of the nineteenth resistor R19 via a twenty-ninth resistor R20 to lead out the output terminal of the non-inverting amplifier. R24 can be a single resistor, or optionally, a twenty-fifth resistor R25 can be connected in series with R19, which can be varied according to requirements. The output terminal of the non-inverting amplifier is connected to the source of the MOS switch.

[0107] The MOS switch is connected in series in the branch of the resonant circuit containing the capacitor element used to switch the resonant frequency. Specifically, the two ends of the MOS switch are connected to... Figure 4 In this embodiment, K1 and K2, and switch K, are implemented as the MOS switch. The MOS switch is implemented as a pair of identical MOS transistors connected in a common-source and common-gate configuration, namely NMOS M3 and M4, with their drains connected to K1 and K2 respectively. The gate of the MOS switch is equivalent to the common-gate connection point of M3 and M4, and the source of the MOS switch is equivalent to the common-source connection point of M3 and M4. In other embodiments, the MOS switch can also be implemented as multiple pairs of identical MOS transistors connected in parallel, or it can be implemented as a single MOS transistor, and is not limited to the illustration.

[0108] It should be noted that, Figure 8 and Figure 10 The resistors in the schematic diagram can be set according to requirements; some can be set to 0 resistance (i.e., canceled), and are not limited to the diagram. Furthermore, it is understandable that... Figure 8 and Figure 10 The illustration is merely an example of a power amplifier circuit implementation and can be replaced by other circuit implementations, such as op-amp-based amplifier circuits, and is not limited to the illustration.

[0109] like Figure 11 The diagram shown illustrates a flowchart of a metal detection control method according to an embodiment of this disclosure. This metal detection control method is applied to the metal detector in the above embodiments to achieve... Figure 2 or Figure 6 The timing control of the generation of the first magnetic field generation signal, the second magnetic field generation signal, the first switching signal and the second switching signal of the first transmitting coil 110 and the second transmitting coil 120 is used to realize the superposition and combination of multiple alternating magnetic fields at high and low frequencies.

[0110] exist Figure 11The metal detection control method includes:

[0111] Step S1101: Generate a first magnetic field generation signal that is time-division multiplexed by a first frequency and a second frequency, and a second magnetic field generation signal that is time-division multiplexed by a third frequency and a fourth frequency, and output the first magnetic field generation signal to the first transmitting coil through a first resonant circuit, and output the second magnetic field generation signal to the second transmitting coil through a second resonant circuit, respectively.

[0112] Step S1102: Synchronize with the first magnetic field generation signal ground, generate a first switching signal whose signal is aligned with the frequency switching point of the first magnetic field generation signal along the time axis, and output it to the first resonant circuit to switch the first transmitting coil to generate a first alternating magnetic field or a second alternating magnetic field; and synchronize with the second magnetic field generation signal ground, generate a second switching signal whose signal is aligned with the frequency switching point of the second magnetic field generation signal along the time axis, and output it to the second resonant circuit to switch the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field, so that the first alternating magnetic field / second alternating magnetic field and the third alternating magnetic field / fourth alternating magnetic field form multiple magnetic field combinations along the time axis.

[0113] like Figure 12 The diagram shown is a schematic representation of a metal detection control device according to an embodiment of this disclosure. It should be noted that the principle and technical implementation of the metal detection control device can be referenced from the metal detection control method in previous embodiments; therefore, they will not be repeated in this embodiment.

[0114] The metal detection and control device 1200 includes:

[0115] The magnetic field signal generation module 1201 is used to generate a first magnetic field generation signal that is time-division multiplexed by a first frequency and a second frequency, and a second magnetic field generation signal that is time-division multiplexed by a third frequency and a fourth frequency, and outputs the first magnetic field generation signal to the first transmitting coil through a first resonant circuit, and outputs the second magnetic field generation signal to the second transmitting coil through a second resonant circuit, respectively.

[0116] The switching signal generation module 1202 is used to synchronize with the first magnetic field generation signal ground, generate a first switching signal whose signal is aligned with the frequency switching point of the first magnetic field generation signal along the time axis, and output it to the first resonant circuit to switch the first transmitting coil to generate a first alternating magnetic field or a second alternating magnetic field; and synchronize with the second magnetic field generation signal ground, generate a second switching signal whose signal is aligned with the frequency switching point of the second magnetic field generation signal along the time axis, and output it to the second resonant circuit to switch the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field, so that the first alternating magnetic field / second alternating magnetic field and the third alternating magnetic field / fourth alternating magnetic field form multiple magnetic field combinations along the time axis.

[0117] It should be noted that, in Figure 12 The various functional modules in the embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any combination thereof. When implemented in software, they can be implemented, in whole or in part, in the form of a computer program or instruction product. A computer program or instruction product includes one or more computer programs or instructions. When a computer program or instruction is loaded and executed on a computer, it produces, in whole or in part, the flow or function according to this disclosure. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer program or instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another.

[0118] and, Figure 12 The apparatus disclosed in the embodiments can be implemented through other modular division methods. The apparatus embodiments shown above are merely illustrative. For example, the module division is only a logical functional division, and in actual implementation, there may be other division methods. For example, a group of modules or modules may be combined or dynamically integrated into another system, or some features may be ignored or not executed. Furthermore, the shown or discussed mutual coupling, direct coupling, or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or modules may be electrical or other forms.

[0119] in addition, Figure 12 The functional modules and sub-modules in the embodiments can be dynamically integrated within a single processing unit, or each module can exist physically independently, or two or more modules can be dynamically integrated within a single unit. These dynamic units can be implemented in hardware or as software functional modules. If these dynamic units are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. This storage medium can be a read-only memory, a hard disk, or an optical disk, etc.

[0120] It should be specifically noted that the flowchart representations of the embodiments described above in this disclosure can be understood as representing a module, segment, or portion of code comprising one or more executable instructions configured to implement a specific logical function or process. Furthermore, the scope of the preferred embodiments of this disclosure includes other implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved.

[0121] For example, Figure 11 The order of the steps in the method embodiment may vary in specific scenarios and is not limited to the above representation.

[0122] like Figure 13The diagram shown is a schematic representation of the structure of a computer device according to an embodiment of this disclosure.

[0123] The computer device 1300 may be exemplified as a processing terminal, such as a server, desktop computer, laptop computer, tablet computer, smartphone, or other terminal. The computer device 1300 may be implemented as a host computer, for example... Figure 6 The host computer in the middle.

[0124] The computer device 1300 includes a bus 1301, a processor 1302, and a memory 1303. The processor 1302 and the memory 1303 can communicate via the bus 1301. The memory 1303 can store computer programs or instructions. The processor 1302 implements the method flow or function of the previous embodiments by running the computer program or instructions in the memory 1303, for example... Figure 11 .

[0125] Bus 1301 can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of representation, although only one thick line is used in the diagram, this does not indicate that there is only one bus or one type of bus.

[0126] In some embodiments, the processor 1302 may be implemented as a central processing unit (CPU), a microprocessor unit (MCU), a system-on-chip (System-on-Chip), or a field-programmable array (FPGA). The memory 1303 may include volatile memory for temporary data storage during program execution, such as random access memory (RAM).

[0127] The memory 1303 may also include non-volatile memory for data storage, such as read-only memory (ROM), flash memory, hard disk drive (HElementCount), or solid-state disk (SSD).

[0128] In some embodiments, the computer device 1300 may further include a communicator 1304. The communicator 1304 is used for communication with external devices. In specific examples, the communicator 1304 may include one or more wired and / or wireless communication circuit modules. For example, the communicator 1304 may include one or more of, such as a wired network card, a USB module, a serial interface module, etc. The wireless communication protocols followed by the wireless communication module include, for example, Nearfield communication (NFC) technology, Infrared (IR) technology, Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Time-Division Code Division Multiple Access (TD-SCDMA), Long Term Evolution (LTE), Bluetooth (BT), Global Navigation Satellite System (GNSS), etc.

[0129] This disclosure also provides a computer-readable storage medium storing a computer program or instructions, which, when run, implement the method flow or function of any of the previous embodiments.

[0130] That is, the method steps in the above embodiments are implemented as software or computer code that can be stored in a recording medium (such as CD ROM, RAM, floppy disk, hard disk or magneto-optical disk), or implemented as computer code that is originally stored in a remote recording medium or a non-transitory machine-readable medium and will be stored in a local recording medium after being downloaded via a network, so that the method represented herein can be stored in such software processing on a recording medium using a general-purpose computer, a special processor or programmable or special hardware (such as ASIC or FPGA).

[0131] This disclosure may also provide a computer program product, comprising one or more computer programs or instructions, which, when run, perform all or part of the processes or functions described in this disclosure. The computer program product includes one or more computer programs or instructions.

[0132] Computer programs or instructions can be stored in a readable storage medium or transferred from one readable storage medium to another. For example, the computer program or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The readable storage medium can be any available medium capable of access, or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; an optical medium, such as a digital video optical disc; or a semiconductor medium, such as a solid-state drive. The computer-readable storage medium can be a volatile or non-volatile storage medium, or it can include both volatile and non-volatile types of storage media.

[0133] In summary, this disclosure relates to the field of metal detection technology and provides a metal detector for multi-frequency detection, comprising: a balanced coil system including: a transmitting coil assembly including at least one first transmitting coil and a second transmitting coil; a first receiving coil and a second receiving coil symmetrically arranged; a first transmitting coil driving circuit including: a first signal generator for generating a first magnetic field generation signal time-division multiplexed by a first frequency and a second frequency, for generating two alternating magnetic fields by the first transmitting coil; a first resonant circuit allowing switching of the resonant frequency between the first frequency and the second frequency; and a first signal switcher, wherein the signal period synchronously forms a switching frequency between the first and second frequencies. The signal is switched to the resonant circuit; the second transmitting coil driving circuit includes: a second signal generator for generating a second magnetic field generation signal that is time-division multiplexed by a third frequency and a fourth frequency, for the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field; a second resonant circuit that allows switching the resonant frequency between the third frequency and the fourth frequency; and a second signal switcher that periodically generates a switching signal to switch the third / fourth frequency to the resonant circuit; wherein the first signal generator and the second signal generator operate together to make the first / second alternating magnetic field and the third / fourth alternating magnetic field form multiple magnetic field combinations along the time axis. By utilizing a transmitting coil assembly that can switch between high / low frequencies separately, the frequency and the number of alternating magnetic fields at the corresponding frequencies are increased, improving detection intensity and accuracy, and expanding application scenarios.

[0134] The above embodiments are merely illustrative of the principles and effects of this disclosure and are not intended to limit this disclosure. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this disclosure. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this disclosure should still be covered by the protection scope of this disclosure.

Claims

1. A metal detector that performs multi-frequency detection, characterized in that, include: A balanced coil system includes: a transmitting coil assembly, including at least one first transmitting coil and a second transmitting coil; a first receiving coil and a second receiving coil, symmetrically arranged on opposite sides of the transmitting coil assembly, and electromagnetically coupled to the transmitting coil assembly; A first transmitting coil driving circuit includes: a first signal generator for generating a first magnetic field generating signal that is time-division multiplexed by a first frequency and a second frequency, wherein the first magnetic field generating signal causes the first transmitting coil to generate a first alternating magnetic field or a second alternating magnetic field; a first resonant circuit connected to the first signal generator and the first transmitting coil, allowing switching of the resonant frequency between the first frequency and the second frequency; and a first signal switcher connected to the first resonant circuit, outputting a first switching signal aligned along a time axis with the frequency switching point in the first magnetic field generating signal, so that the first resonant circuit switches to a matching resonant frequency as the frequency of the first magnetic field generating signal changes. The second transmitting coil driving circuit includes: a second signal generator for generating a second magnetic field generating signal that is time-division multiplexed by a third frequency and a fourth frequency, wherein the second magnetic field generating signal causes the second transmitting coil to generate a third alternating magnetic field or a fourth alternating magnetic field; a second resonant circuit connected to the second signal generator and the second transmitting coil, allowing switching of the resonant frequency between the third frequency and the fourth frequency; and a second signal switcher connected to the second resonant circuit, outputting a second switching signal aligned along the time axis with the frequency switching point in the second magnetic field generating signal, so that the second resonant circuit switches to a matching resonant frequency as the frequency of the second magnetic field generating signal changes. The first signal generator and the second signal generator operate together to form multiple magnetic field combinations along the time axis, such that the first alternating magnetic field / second alternating magnetic field and the third alternating magnetic field / fourth alternating magnetic field.

2. The metal detector for multi-frequency detection according to claim 1, characterized in that, The first transmitting coil and the second transmitting coil are configured in one of the following ways: in a partitioned coplanar arrangement; in an inner and outer coplanar arrangement; or in a coaxial inner and outer coplanar arrangement.

3. The metal detector for multi-frequency detection according to claim 1, characterized in that, The first transmitting coil driving circuit includes: a first signal amplification circuit connected between the first signal generator and the first resonant circuit, for amplifying the signal generated by the first magnetic field and outputting it to the first resonant circuit; and / or, the second transmitting coil driving circuit includes: a second signal amplification circuit connected between the second signal generator and the second resonant circuit, for amplifying the signal generated by the second magnetic field and outputting it to the second resonant circuit.

4. The metal detector for multi-frequency detection according to claim 3, characterized in that, The first signal amplification circuit and the second signal amplification circuit are implemented as a first preset amplification circuit structure, the first preset amplification circuit structure including: The signal input terminal is connected to the preceding signal generator, which includes a first half-cycle amplifier circuit, a second half-cycle amplifier circuit, and a push-pull output circuit. The first half-cycle amplifier circuit includes: a first group of amplifiers arranged in multiple stages, connected between the signal generation input terminal and the push-pull output circuit and powered by a first voltage, for generating a first switching drive signal based on the first voltage in response to the input magnetic field generation signal; The second half-cycle amplifier circuit includes: a second group of amplifiers arranged in multiple stages, connected between the signal generation input terminal and the push-pull output circuit and powered by a second voltage with the opposite polarity to the first voltage, for generating a second switching drive signal based on the second voltage in response to the input magnetic field generation signal; A push-pull circuit is used to respond to a first switch drive signal, generate an amplified signal based on a first voltage and output it to a subsequent resonant circuit; and to respond to a second switch drive signal, generate an amplified signal based on a second voltage and output it to a subsequent resonant circuit.

5. The metal detector for multi-frequency detection according to claim 3, characterized in that, The first signal amplification circuit and the second signal amplification circuit are implemented as a first preset amplification circuit structure, the first preset amplification circuit structure including: The first half-cycle amplifier circuit includes: a first PNP, a first NPN, a second PNP, a second NPN, and a first diode; the base of the first PNP has a signal input terminal for generating a signal from an input magnetic field; the emitter of the first PNP is connected to the positive terminal of a power supply and the base of the first NPN via a first resistor; the collector of the first PNP is connected to the negative terminal of a power supply; the collector of the first NPN is connected to the positive terminal of a power supply and the base of the second PNP via a second resistor; the emitter of the first NPN is connected to the negative terminal of the first diode and grounded via a fourth resistor; the emitter of the second PNP is connected to the positive terminal of a power supply via a third resistor, and the collector of the second PNP is connected to the positive terminal of the first diode and the base of the second NPN; the collector of the second NPN is connected to the positive terminal of a power supply, and the emitter of the second NPN is connected to one end of a fifth resistor; the other end of the fifth resistor is grounded via a sixth resistor and a fourth resistor. The second half-cycle amplifier circuit includes: a third NPN, a third PNP, a fourth NPN, a fourth PNP, and a second diode; the base of the third NPN is coupled to the signal input terminal; the emitter of the third NPN is connected to the negative terminal of the power supply and the base of the third PNP via a seventh resistor; the collector of the third NPN is connected to the positive terminal of the power supply; the collector of the third PNP is connected to the negative terminal of the power supply and the base of the fourth NPN via an eighth resistor; the emitter of the third PNP is connected to the positive terminal of the second diode and the emitter of the first NPN; the emitter of the fourth NPN is connected to the negative terminal of the power supply via a ninth resistor; the collector of the fourth NPN is connected to the negative terminal of the second diode and the base of the fourth PNP; the collector of the fourth PNP is connected to the negative terminal of the power supply; the emitter of the fourth PNP is connected to one end of a tenth resistor; the other end of the tenth resistor is connected to the other end of a fifth resistor, and then grounded via a sixth resistor and a fourth resistor. The push-pull output circuit includes: a first NMOS and a first PMOS, which are connected to the common gate and coupled to the other end of the fifth resistor; the source of the first NMOS is connected to the drain of the first PMOS and leads out a signal output terminal for outputting the amplified magnetic field generation signal; the drain of the first NMOS is connected to the positive terminal of the power supply; and the source of the first PMOS is connected to the negative terminal of the power supply.

6. The metal detector for multi-frequency detection according to claim 1, characterized in that, The first and second resonant circuits are implemented as including a variable capacitor unit connected in parallel with their respective transmitting coils; wherein the variable capacitor unit is implemented as including a capacitor element located in a plurality of branches in parallel, and some of the branches are provided with a switching element that allows a switching signal to set the switching state to turn the branch on / off.

7. The metal detector for multi-frequency detection according to claim 1 or 6, characterized in that, The first transmitting coil driving circuit includes: a first switching signal amplification circuit connected between the first signal switcher and the first resonant circuit, for amplifying the first switching signal and outputting it to the first resonant circuit; and / or, the second transmitting coil driving circuit includes: a second switching signal amplification circuit connected between the second signal switcher and the second resonant circuit, for amplifying the second switching signal and outputting it to the second resonant circuit.

8. The metal detector for multi-frequency detection according to claim 7, characterized in that, The first switching signal amplification circuit and the second switching signal amplification circuit are implemented as a second preset amplification circuit structure, the second preset amplification circuit structure including: The switching signal input terminal is connected to the signal switcher in the preceding stage to receive the input switching signal; A first amplifier has its input terminal connected to the switching signal input terminal and its output terminal connected to the gate of a MOS switch; wherein the MOS switch is connected in series in the branch of the resonant circuit containing the capacitor element used to switch the resonant frequency. The second amplifier has its input terminal connected to the switching signal input terminal and its output terminal connected to the source of the MOS switch. In this amplifier, one of the first amplifier and the second amplifier is an inverting amplifier, and the other is an outverting amplifier, so as to form a gate-source voltage that controls the on / off state of the MOS switch in response to the input switching signal.

9. The metal detector for multi-frequency detection according to claim 7, characterized in that, The first switching signal amplification circuit and the second switching signal amplification circuit are implemented as a second preset amplification circuit structure, the second preset amplification circuit structure including: The switching signal input terminal is connected to the signal switcher in the preceding stage to receive the input switching signal; An inverting amplifier includes: a fifth NPN, a sixth NPN, a fifth PNP, and a seventh NPN; the base of the fifth NPN is connected to the switching signal input terminal via an eleventh resistor, its emitter is grounded, its collector is connected to the base of the sixth NPN and connected to the positive terminal of the power supply via a twelfth resistor; the emitter of the sixth NPN is grounded via a thirteenth resistor, its collector is connected to the base of the fifth PNP and one end of a fifteenth resistor via a fourteenth resistor, and the other end of the fifteenth resistor is connected to the positive terminal of the power supply; the emitter of the fifth PNP is connected to the positive terminal of the power supply via a sixteenth resistor, its collector is connected to the base of the seventh NPN via a seventeenth resistor, and connected to the emitter of the seventh NPN via an eighteenth resistor to lead out the output terminal of the inverting amplifier; the output terminal of the inverting amplifier is connected to one end of a nineteenth resistor and the gate of a MOS switch; wherein, the MOS switch is connected in series in the branch of the resonant circuit where the capacitor element used to switch the resonant frequency is located; The non-inverting amplifier includes an eighth NPN and a sixth PNP; the gate of the eighth NPN is connected to the switching signal input terminal via a twenty-first resistor, its collector is connected to the base of the sixth PNP via a twenty-second resistor and to the positive terminal of the power supply via a twenty-third resistor, and its emitter is grounded via a twenty-fourth resistor; the emitter of the sixth PNP is connected to the positive terminal of the power supply, and its collector is connected to the collector of the seventh NPN and the other end of the nineteenth resistor via a twentyth resistor to lead out the output terminal of the non-inverting amplifier; the output terminal of the non-inverting amplifier is connected to the source of the MOS switch.

10. The metal detector for multi-frequency detection according to claim 1, characterized in that, The first frequency and the second frequency occupy the same duration in the signal generated by the first magnetic field, and the third frequency and the fourth frequency occupy the same duration in the signal generated by the first magnetic field; and / or, the first frequency and the second frequency are both higher than the third frequency and the fourth frequency, and the signal period length of the first switching signal is 1 to 3 times the signal period length of the second switching signal; and / or, the first frequency and the second frequency are in the range of 50kHz to 200kHz, and the third frequency and the fourth frequency are in the range of 200kHz to 1000kHz.

Images