RU2819826C1 - Method for non-contact selective detection of metal objects using pulse-resonance-eddy current method (versions) - Google Patents

Abstract

FIELD: detection of current-conducting and ferromagnetic objects in magnetically permeable solid, loose or liquid media.

SUBSTANCE: method involves sequential generation of pulses of the same duration supplying the coil in the frequency range from 1 Hz to 1 kHz with filling with pulses of a given frequency in the range of values from 1 kHz to 1 MHz with frequency change in each packet of pulses and without filling, pulses of different duration without filling. Upon completion of the pulse train generation process with filling or pulses without filling, the increments in the duration of the leading edge of the current decay in the coil are measured: after generation of pulse without filling of long duration—T1, short duration—T4, increment of duration of front of decay of electric current in coil after pulse generation with filling with frequency, at which the maximum signal from the object is detected,—T2. Type of metal is determined based on the ratio (T1/T2/)T3, where T3=T4/T1.

EFFECT: high accuracy of determining the type of metals.

2 cl, 7 dwg

Description

The invention relates to the field of physics and geophysics, archeology in the field of detection of conductive and ferromagnetic objects in magnetically permeable solid, granular or liquid media, incl. in soil, road surface, concrete, sea water, clothing and other magnetically permeable environments, in underwater or air operating conditions in any climate.

A method of operation of a multi-frequency metal detector is known from the prior art (US patent No. 10989829, IPC G01V 03/10, H01F 07/06, published 04/27/2021), containing a drive coil designed to create an electromagnetic field in the product, and according to at least one detector coil for detecting fluctuations in the magnetic field. field generated by metal particles present in the product; and a multi-frequency transmitter unit comprising a transducer with a plurality of drive switches, which are driven by a drive controller in accordance with operating instructions such that the drive switches alternately pass a control current through the drive coil so that the generated the electromagnetic field had two or more frequency components.

The closest technical solution is a multi-frequency metal detector and a method for identifying a metal target (Chinese patent No. 113900148, IPC G01V 03/10, G01V 03/38, published 01/07/2022), containing a controller module, a power amplification module, a transmitting module coils, receiver coil module, low noise gain module, analog-to-digital conversion module, peripheral module.

In accordance with the method for identifying a metal target provided by the invention, the following steps are performed:

stage 1: multi-frequency transmission, namely modulation by receiving square wave signals with different frequencies and duty cycles to generate the required multi-frequency transmission signals;

stage 2: generating a control signal using a timer and controlling an analog-to-digital converter to obtain a received voltage signal with a given sampling frequency;

step 3: demodulate the collected received signals, extract the characteristic quantities of different frequencies, extract two characteristic quantities of each frequency, and combine the characteristic quantities of each frequency to create a characteristic vector;

step 4: determining the modulus of the characteristic vector, comparing the modulus with the threshold value and, when the modulus of the characteristic vector is greater than the threshold value, indicating the presence of a metal target and performing the next step; when the magnitude of the characteristic vector is less than the threshold value, indicating that the metal target is not detected, ignoring the characteristic vector and moving to the next data collection period;

step 5: calculating probability values belonging to all metal categories according to the values of all elements in the feature vector;

step 6: and selecting the maximum value of the probability values of all metal categories, where the metal category corresponding to the maximum value is the category of the detected metal, and displaying and signaling the detection result.

The disadvantage of the known solution is the analysis of only two selected characteristic quantities of each frequency and the combination of the characteristic quantities of each frequency to create a characteristic vector. In this case, many physical characteristics of the measured signal are integrated into one value. Which further requires complex digital signal processing to improve the signal-to-noise ratio and highlight the useful component of the signal. Also, the method of analyzing the frequency and amplitude of the signal is typical for balanced types of metal detectors; with a balanced operating principle, the conductivity of the soil shifts the amplitude balance of the emitting and receiving coils and reduces the sensitivity to small metal objects at the physical level, due to the increased background signal arising in the receiving coil when it is reflected from highly mineralized soil.

The use of two emitting and receiving coils complicates production, increases cost and production time, and requires highly qualified workers to adjust the balance of the coils. The sensitivity of the device in mineralized soils also decreases, since the induced reflected electromagnetic signal from the ground changes the balance between the receiving and transmitting coils, which leads to a decrease in the level of the useful signal from metal objects and reduces the detection depth. The presence of a synchronous detector introduces noise and distortion into the useful signal during polarity switching and leads to an increase in the cost of the design and a decrease in its reliability, increasing the number of electronic components.

The technical objective of the claimed invention is to exclude false signals from non-metallic electrically conductive objects from the useful signal, determine the type of metal of the object regardless of its shape and distance, and increase the sensitivity of the metal detector.

The technical result of the invention is to increase the accuracy of determining the type of metals.

The technical result is achieved in that the method for non-contact selective detection of metal objects using the pulse-resonance-eddy current method includes sequential generation of pulses of different durations feeding the coil in the frequency range from 1 Hz to 1 kHz with filling with pulses of a given frequency in the range from 1 kHz to 1 MHz, with a change in frequency in each burst of pulses and without filling, stopping the power supply to the coil after the completion of the generation process of a burst of pulses or a pulse without filling, measuring the increment in the duration of the decay front of the electric current of the self-induction pulse in the coil from the reflected signal by a metal object from the unfilled pulse T1 and increments in the duration of the decay front of the electric current of the self-induction pulse in the coil from the reflected signal by a metal object after generating a pulse with filling with the frequency at which the maximum signal from the object is detected, T2.

Also, the technical result is achieved by the fact that the method for non-contact selective detection of metal objects using the pulse-resonance-eddy current method includes sequential generation of pulses of equal duration feeding the coil in the frequency range from 1 Hz to 1 kHz with filling with pulses of a given frequency in the range from 1 kHz to 1 MHz with a change in frequency in each burst of pulses and without filling, pulses of different durations with filling with pulses of a given frequency and without filling, stopping the power supply to the coil after completing the process of generating a burst of pulses or a pulse without filling, measuring the increment in the duration of the decay front of the electric current of the self-induction pulse in the coil after generating a pulse without filling of long duration T1 and short duration T4, incrementing the duration of the decay front of the electric current of the self-induction pulse in the coil after generating a pulse with filling with the frequency at which the maximum signal from the object T2 is detected, determining the ratio of the signal level with a short-duration pulse to the level signal for a long pulse T3=T4/T1.

The method for detecting metal objects according to the present invention includes assessing the electrical conductivity, magnetic permeability and inductance of metal objects located in the coverage area of the search sensor by measuring the energy characteristics of the transient process of the entire decay front of the self-inductance pulse of the measuring inductor or part thereof, at different durations, and at different frequencies. filling the supply voltage pulses of the inductor. The decay of the front of the self-induction pulse contains included energy components that characterize metal objects located in the sensor’s coverage area and re-emitting the received electromagnetic field. The energy contribution of re-emitted signals is characterized by the added duration and amplitude of the decay of the front of the self-induction pulse. In this operating mode, background induced signals do not affect the sensitivity of the metal detector.

The invention is further illustrated by the following drawings:

Fig.1. Electrical circuit of the equivalent metal object;

Fig.2. A graph illustrating the generation of pulses of the same duration with a constant frequency and the decay front of the self-induction pulse;

Fig.3. A graph illustrating the generation of pulses of the same duration with filling with pulses of a given frequency and changing the frequency in each burst of pulses with the frequency and decay front of the self-induction pulse;

Fig.4. A graph illustrating the generation of pulses of different durations and the decay front of the self-induction pulse;

Fig. 5 A graph illustrating the sequential generation of pulses of the same duration with and without filling with high-frequency pulses and the decay front of the self-induction pulse;

Fig.6. A graph illustrating the sequential generation of pulses with and without filling with high-frequency pulses, and the generation of pulses of different durations and the decay front of the self-induction pulse;

Fig.7. An example of a graphical display of the signal level showing the type of metal.

To detect metal objects and determine their type of metal or alloy, the metal detector sensor generates pulses of the same duration, and, or pulses of different durations at a constant frequency and, or a variable repetition rate. The generation of monoharmonic signal pulses is also used, containing 1 harmonic for each pulse. The metal detector coil emits a pulsed alternating electromagnetic field, causing internal alternating electrical currents to appear in metal objects located in the sensor’s coverage area, which, being shorted to the active electrical resistance of the metal of the object, are converted into a secondary alternating magnetic field re-emitted by the object.

After generation is completed, the duration of the decay front of the electric current in the inductance coil of the metal detector sensor is measured to a certain specified level.

The secondary alternating magnetic field of a metal object is converted into an electric current in the metal detector coil. Determination of the magnitude of the induced electric current by an alternating magnetic field re-emitted by a metal object occurs by measuring the duration of the decay front of the electric current in the inductance coil of the metal detector to a certain specified level, after stopping the supply of supply pulses or a pulse to it.

The larger the metal object is in the area of action of the metal detector coil, the greater the intensity of the alternating magnetic field it will re-emit, the greater the current will be induced in the inductance coil of the metal detector, and the longer the duration of the decline front of the electric current in the inductor after the cessation of the generating pulse or pulses will be recorded.

And vice versa, the smaller the metal object, the less the induced current from the reflected signal in the device coil and the shorter the duration of the decay front.

Also, the magnitude of the induced electric current in the metal detector coil from the signal re-reflected by a metal object depends on the distance of the metal object from the metal detector coil. The further away the metal object is, the less the intensity of the alternating electromagnetic field generated by the metal detector sensor affects it, and the less alternating electric current arises inside the metal object and the less the alternating magnetic field re-emitted by the metal object, and the less electric current induced in the metal detector coil from the re-emitted alternating magnetic field of a metal object and the less the duration of the decline in the electric current in the metal detector coil changes after the generation of pulses or pulses stops, the lower the signal level from the object.

And vice versa, the closer the metal object, the greater the intensity of the alternating electromagnetic field generated by the metal detector sensor affects it. and the greater the alternating electric current arises inside the metal object, and the greater the alternating magnetic field re-emitted by the metal object, and the greater the electric current induced in the metal detector coil from the re-emitted alternating magnetic field of the metal object, and the more the duration of the decline of the electric current in the metal detector coil after stopping the generation of pulses or pulses, the greater the signal level from the object.

The electrical circuit of the equivalent of a metal object is shown in Fig. 1, where Ro is the internal active electrical resistance of the metal, Lo is the inductive component determined by the shape and volume of the metal object, Mo is the magnetic permeability of the metal or alloy of the object, Co is the electrical capacitance between the metal object and the ground, characterized by the contact area of the object and the soil, the thickness and dielectric properties of the oxides covering the object and isolating it from the soil, the conductivity of the soil, G - the electrical conductivity of the soil, grounding capacity.

Electromagnetic pulses from the sensor's inductor irradiate a metal object, creating eddy currents in it. Under the influence of internal eddy currents of the object, reactive power energy is first accumulated and then released in the form of a magnetic field, which reaches the measuring inductor and induces an electric current in it, causing an increase in the duration of the decline front of the electric current in the coil when the signal generation is turned off.

The metal detector uses the following methods for identifying metal objects:

1. Method for determining the electrical conductivity of a metal object

When generating pulses (A) of the same duration with a constant frequency feeding the coil, the inductor coil of the metal detector emits an alternating electromagnetic field with the characteristics of a transient process, causing the occurrence of an electric current in a metal object located in a zone of sufficient strength of the magnetic field of the coil, near the coil.

The induced electric current with the characteristic of the transient process, closing on the active electrical resistance of the metal of the object, reproduces an alternating magnetic field with the characteristic of the transient process, which induces an alternating electric current in the coil of the metal detector, which increases the duration of the decay front of the electric current in the inductance coil of the metal detector after the cessation of pulse generation, and is determined analog-digital system as the signal level from a detected metal object.

In this mode of operation (Fig. 2), the metal detector does not determine the type of metal; the reaction to different types of metals and alloys is the same, since only the conductivity of the metal object is measured, according to the level of the re-emitted alternating magnetic field of the transient process caused by the generation of one pulse by the metal detector coil. The lower the active electrical resistance of the metal or alloy of a metal object, the greater the intensity of the magnetic field resulting from the flow of current in the electrical conductor of the object. The greater the active electrical resistance of a metal or alloy of a metal object, the lower the strength of the magnetic field resulting from the flow of current in the electrical conductor of the object.

The electrical conductivity of a metal determines the process of converting the induced alternating electric current into an alternating magnetic field and is a characteristic of the active electrical resistance (Ro) of the object. The signal level cannot serve as an accurate characteristic of the conductivity value for each type of metal or alloy, since the signal level also depends on the size and distance of the metal object from the sensor.

2. Method for determining the inductance of a metal object

The generation of pulses of the same duration feeding the coil with filling with pulses of a given frequency (packet of pulses), with a change in frequency in each train of pulses (Fig. 3.), when the metal detector sensor is moved or located above a metal object, allows one to evaluate the inductive properties of the detected metal object.

The metal detector sensor generates a group of pulses, each of the pulses of the same duration is filled with pulses of a certain frequency (pulse packet), for example, a repeating group of three pulse packets, the first pulse packet with a frequency of 30 kHz, the second with 50 kHz, and the third with 100 kHz. When generating a train of pulses with a higher frequency, the sensor emits an alternating magnetic field of this frequency acting on a metal object, and the closer the emitted frequency is to the natural resonant frequency of the metal object, the greater the amplitude the electric current will flow through the electrical resistance of the object’s conductor and the greater the level of intensity of the alternating magnetic field it will re-emit . The greater the intensity of the re-emitted magnetic field, the greater the current is induced in the coil and the longer the duration of the decay front of the electric current in the metal detector coil when generation is turned off, which is the signal level from the object. The higher the frequency of the emitted electromagnetic field of the coil, the lower the reactance of the metal object, which has inductive properties, the greater the current flows in the conductor of the metal object, the greater the magnetic field strength that arises around the object and is re-emitted by it. The closer the frequency of the electromagnetic field of the coil is to the resonant frequency of the structure of the metal object (equivalent to an oscillatory circuit), the greater the current flows in the conductor of the metal object, the greater the magnetic field strength that arises around the object and is re-emitted by it. For example, with a pulse train frequency of 30 kHz and a pulse repetition rate of 200 Hz, metal objects made of round aluminum give a reflected signal of 10 μV, and metal objects of iron of the same shape give a reflected signal of 15 μV, when located at the same distance from the measuring inductor. And with a pulse train frequency of 100 kHz and a repetition of pulses with a frequency of 200 Hz, metal objects made of round aluminum give a reflected signal of 20 μV, and metal objects made of iron of the same shape give a reflected signal of 17 μV, when located at the same distance from the measuring inductor. Based on the obtained ratios of signal levels from objects measured at different pulse filling frequencies, the type of metal and the coefficient characterizing the inductance of the object Ki are determined. So, for aluminum Ki = 20 µV/10 µV = 2, for iron Ki = 17 µV/15 µV = 1.13.

Thus, for each of the pulse trains, each filled with its own pulse frequency, the level of the re-reflected alternating magnetic field by the metal object is measured. And it is determined at what pulse filling frequency the maximum signal level from the object was recorded. The frequency of the pulse burst that is as close as possible to the natural resonant frequency of the metal object is determined. This allows you to obtain a unique signal characteristic for each type of metal and alloy. In this way, the individual unique inductive characteristic (Lo) of the metal object is determined.

The function of reducing signals from unnecessary alloys and metals is also implemented; bursts of pulses are generated that feed the coil with one frequency, at which the maximum signal level from the desired metal objects made of certain metals or alloys is observed. Thus, the signal for the desired type of metal will be greater than for other types of metals and alloys.

The inductive characteristic (Lo) of a metal object is determined not only by the type of metal or alloy, but also by the shape and volume of the object, and in itself cannot be an accurate value for determining the type of metal or alloy. And also the signal level depends on the distance of the metal object from the sensor.

3. Method for determining the magnetic permeability of a metal object

When pulses of different durations are generated when the metal detector sensor is moved or positioned above a metal object, the reflected alternating magnetic field from the object is measured for each pulse duration emitted by the coil. The ratio of the levels of the reflected signal from pulses of different durations characterizes the magnetic permeability of a metal object (Mo), how quickly and efficiently the metal of the object converts an alternating magnetic field into electric current.

The magnitude of the magnetic permeability of a metal object (Mo) is determined by the number of magnetic moments of individual atoms or molecules of the metal or alloy oriented parallel to the applied external magnetic field of a given strength and how large these moments are.

For metals and alloys with a magnetic permeability close to 1, weak orientation of the moments corresponds (almost chaos in directions, the field has practically no effect on them), and for metals and alloys with a magnetic permeability much greater than 1, high ordering and large values or a large number of individual magnetic moments.

This method allows you to accurately separate groups of ferromagnetic and non-ferromagnetic metals, but does not allow you to more accurately determine the types of metals and alloys in these groups due to their similar magnetic permeability.

If for different durations of generated pulses the reflected signal from the metal is approximately the same (Fig. 4), then a metal with high magnetic permeability is detected, for which even a short electromagnetic pulse is sufficient to saturate the internal electric current, which in the conductor is converted into a secondary magnetic field of the metal object and induces electric current in the coil of the device. Increasing the pulse duration practically does not change the level of the re-reflected magnetic field of the object, since even at a short pulse duration the maximum possible saturation current is induced in it. The greater the amplitude of the alternating current that appears in the electrical conductor of an object when it is in the alternating magnetic field of a metal detector coil, the higher its magnetic permeability (Mo).

The ratio of the signal level for a short-duration pulse to the signal level for a long-duration pulse determines the characteristics of the magnetic permeability of a metal object. When the signal levels obtained are approximately equal, a metal with high magnetic permeability is detected. This case is typical for iron with a magnetic permeability of 100.

If for different durations of the generated pulses the reflected signal from the metal varies greatly, then a metal with low magnetic permeability is detected, for which even a long electromagnetic pulse is not enough to saturate the internal electric current, which is converted into a secondary magnetic field of the metal object and induces an electric current in the device coil. Increasing the pulse duration changes the level of the re-reflected magnetic field of the object, since with a short pulse duration the minimum possible current is induced in it. With an increase in the duration of the generated pulse, there is an increase in the current arising in the electrical conductor of the object and, accordingly, an increase in the re-emitted alternating magnetic field inducing an electric current in the metal detector coil upon completion of the pulse generation and an increase in the duration of the decline front (T4) of the electric current in the coil (Figure 3). This case is typical for aluminum with a magnetic permeability equal to 1.

4. Method for determining the conductivity of a metal object

When sequentially generating trains of pulses of the same duration with filling with high-frequency pulses and without filling (Fig. 5.), for example, filling pulses with a frequency of 350 kHz with a frequency of 200 Hz, when moving or placing the metal detector sensor over a metal object, allows you to simultaneously determine the conductivity function of the metal object ( Ro) and the function of its inductance (Lo).

The increment in the duration of the decay front of the electric current in the coil after generating an unfilled pulse is determined - T1, and the increment in the duration of the decay front of the electric current in the coil after generating a pulse with filling with the frequency at which the maximum signal from the object is detected - T2. The T1/T2 ratio gives a unique value characterizing the conductivity of the metal or alloy of a metal object; the value of this ratio also depends on the shape of the metal object.

To exclude the influence of the shape of a metal object from the useful signal, for a more accurate determination of the type of metal, sequential generation of pulses of the same duration with filling with high-frequency pulses and without filling is used, and generation of pulses of different durations (Fig. 6) when the metal detector sensor is moved or located over a metal object, allows you to simultaneously determine the conductivity function of a metal object, its inductance function, and the magnetic permeability function.

The increment in the duration of the decay front of the electric current in the coil after generating an unfilled pulse is determined - T1, and the increment in the duration of the decay front of the electric current in the coil after generating a pulse with filling with the frequency at which the maximum signal from the object is detected - T2, the ratio of the signal level for a pulse of short duration to the level signal during a long pulse determines the characteristic of the magnetic permeability of a metal object - T3=T4/T1.

The ratio (T1/T2)/T3 gives a unique value characterizing the conductivity of a metal or alloy of a metal object, regardless of its shape and location in space.

The measured signal from a metal object can be displayed both on discrete displays, in the form of rows, columns, rows of indicators, and on a graph, where the value of point N on the abscissa axis corresponds to the Nth value of the magnetic permeability signal of the metal object (Mo), and on the ordinate axis Nth value of the metal object inductance signal (Lo).

The signal graphically displays the integral characteristic of the properties of a metal object located in the electromagnetic field of the measuring inductor.

In this case, in an integrated form of Lissajous loops, the device displays the inductive properties and electrical conductivity or electromagnetic susceptibility properties of the detected metal object (FIG. 7).

The metal type index represents the direction angle of the Lissajous loop and is calculated as the partial value of the magnetic permeability signal of the metal object (Mo) and the value of the inductance signal of the metal object (Lo) (X = Mo/Lo). To graphically determine the metal type index between the extreme maximum point of the loop and the zero point, the directional vector of the Lissajous figure is determined. The angle of inclination of the Lissajous figure is determined between the directional vector and the signal axis. The sign of the inclination angle is determined from the location of the figure in the negative or positive zone of the signal. The measured inclination angle is a unique integral characteristic of the type of metal or alloy detected.

The length of the figure characterizes the area of the metal object directed parallel to the coil. Based on the shape of the figure, the unevenness of the internal composition of the object is analyzed.

The method of non-contact selective imaging of metal objects makes it possible to analyze the transient process, the decay front of the self-induction pulse of the measuring coil. The informative part of the signal in the invention is contained in the front of the transient process of the self-induction phenomenon, which is measured in the device. The invention analyzes and determines the added energy of the transient process of self-induction, re-emitted by a metal object, affecting the amplitude, duration, shape of the transient process of the inductance discharge to the resistance, which converts the self-induction current into voltage, which is amplified by the operational amplifier, and is measured by the ADC.

Carrying out the invention

Based on the method of pulsed resonance eddy current non-contact selective detection of metal objects, a selective metal detector can be implemented designed to search for metal objects in the ground, in walls and in other non-conductive environments.

Selectivity by metal type will increase the accuracy of detecting the desired object, and increase the safety of construction, archaeological and sapper work. When working with a metal detector, the operator moves the measuring inductance coil parallel to the ground at a height of 3-5 cm, scanning the space underground. The metal detector operates by constantly sequentially generating pulses of the same duration with and without filling with high-frequency pulses, and generating pulses of different durations; the formation of pulses is set programmatically by the microcontroller.

The metal detector, implemented according to the proposed method of operation, is designed for remote non-contact measurement of the conductivity and inductive properties of materials using the magnetic induction method.

A pulse-resonance eddy current metal detector itself emits an alternating electromagnetic field and measures the response electromagnetic signal re-emitted by a metal object. Based on the level of the re-emitted signal, the metal detector determines the location of metal objects in any non-conducting media (soil, walls, floors, ceilings of houses, water, sea water, rock, igneous rock, etc.).

The developed pulse-resonance eddy current metal detectors respond to all types of metals, since in the volume of metal under the influence of the electromagnetic field of the metal detector, an alternating magnetic field is converted into electric current, and depending on the metal resistivity, inductance and magnetic permeability, the electric current induced in it is converted into a secondary magnetic field, which is also detected by the metal detector sensor. The developed pulse-resonance-eddy current metal detector carries out sequential generation of pulses of the same duration with filling with high-frequency pulses and without filling, and generation of pulses of different durations; the formation of pulses is set programmatically by a microcontroller.

Thus, a pulse-resonance eddy current metal detector detects metal objects made of any metals and alloys by their conductivity, inductance and magnetic permeability, which are characterized by the re-emitted electromagnetic field of the metal object in the sensor’s coverage area. Also, when analyzing the recorded secondary field from a metal object, it is possible to fairly accurately determine the type of metal, and determine the distance of the object from the metal detector sensor.

Since the operating principle of a pulse-resonance eddy current metal detector is based on the radiation of an alternating magnetic field to induce a secondary electromagnetic field in metal objects, the range of these devices is limited by the physics of the propagation of electromagnetic waves.

The larger the metal object, the deeper it will be detected, since it will re-emit a stronger secondary field; the smaller the metal object, the smaller the depth of its detection, since the re-emitted field will be weak.

Metal detectors implemented according to the proposed method of operation have simple controls and do not require constant adjustment, quick training in working with the device, simple control of detection depth, operating range of the device, and precise determination of the boundaries of a metal object and its center are realized.

Pulse-resonance-eddy-current metal detectors record only the level of the re-reflected electromagnetic field from the detected metal object, without measuring the change in the inductance of the coil. As a result, pulse-resonance eddy current metal detectors react to objects that have conductivity, and do not respond to objects that have only inductive properties. The reaction of such metal detectors to soil that has only inductive properties is excluded at the physical level.

Further in the description the following designations of positions in the drawings are used:

1. Display

2. Keyboard

3. Current pulse generator

4. Transceiver inductor

5. Signal amplifier

6. Wireless data receiving device

7. Measuring, computing microcontroller

8. Electronic amplifier control switch

9. Analog-to-digital converter, duration meter

10. Vibration indication

11. Sound indication

12. Connector for external power supply, battery charge, headphone connection

13. Charger

14. Battery compartment

15. Stabilizer, voltage converter

The pulse-resonance-eddy current metal detector consists of a transmitting-receiving inductor coil 4, a coil power pulse generator 3, a measuring differential signal amplifier 5, electronic analog switch switches for controlling the amplifying and integrating stages of the measuring amplifier and controlling the coil power generator 8, an analog-to-digital converter of the meter duration of the decay front of the current in the coil 9, measuring and computing microcontroller 7, wireless data transmission receiving device 6, vibration indicator 10, sound indicator 11, multifunctional external power connector for charging the battery, connecting headphones, charger 13, battery compartment for storing batteries 14, voltage converter stabilizer 15. Measuring and computing microcontroller 7 controls the current pulse generator (3) powering the transmitting and receiving coil (4). The microcontroller (7) can be selected of any type and any modification, having sufficient resources and internal components to perform the tasks of controlling and measuring the metal detector, having analog inputs for signal reception, digital inputs/outputs for operating the control interface and data transmission, and a clock frequency of at least 8 MHz, reset timer, 16 bit timer. The microcontroller (7) generates a control signal that opens the electronic switch (3) for supplying power to the coil (4) in accordance with the sequential generation of pulses of the same duration with and without filling with high-frequency pulses, and the generation of pulses of different durations; the formation of pulses is set programmatically by the microcontroller. Thus, power is supplied to the coil (4) in the form of an empty pulse or a packet of high-frequency pulses or pulses of the same duration. Any electronic switch (3) can also be used, with parameters that provide control of the coil power without the appearance of parasitic noise. After completing the process of generating a power pulse to the coil (4), the controller (7) disconnects the electronic control key (3) from the power line. Then the control controller (7), using the electronic key of the amplifier (5) control switch (8), resets the electrical charge and voltage accumulated in the amplification stages during the generation of a power pulse to the coil (4). The electronic key switch (8) can be used of any type with characteristics that ensure fast latching and low transition resistance. The self-induction current arising in the coil (4) after turning off the power line is converted into voltage on the precision resistor of the measuring signal amplifier unit (5). In the amplifier block (5), differential amplification of the signal and subtraction of the DC component occurs, as well as analog filtering of high and low frequencies of the signal. Any type of operational differential amplifiers that have a sufficient input dynamic range, low intrinsic noise and high gain can be used as an amplifier (5). The prepared and amplified useful signal of the current decay front in the coil is supplied to the input of the analog-to-digital converter (ADC) (9) of the device, where it is digitized and transmitted for data processing to the measuring computing microcontroller (7). The ADC (9) can be used of any type and principle of operation, with a resolution starting from 10 bits. The microcontroller (7) determines the duration of the decay front of the current in the metal detector coil (4) from the moment the sensor (4) is disconnected from the power line (the moment the pulse generation stops) until the current in the coil (4) reaches the specified minimum threshold value (Uo). The duration of this period determines the level of additional electric current induced in the coil (4) of the metal detector by the re-reflected alternating magnetic field of the metal object.

The controller (7) calculates the dependence of the object signal level on the type of pulse and its frequency. Calculates and determines the type of metal or alloy of a detected metal object. The obtained results of calculations and measurements are displayed by the microcontroller (7) on the display (1); any sign-synthesizing or graphic indicator can be used as a display.

If the specified threshold values of the signal of a metal object are exceeded, the controller (7) reproduces sound (11) and vibration indication (10), a speaker of any type and any design can be installed as a sound indicator (11), a vibration motor of any type can be installed as a vibration indicator (10) type and any design.

Control of the operation of the microcontroller (7) and setting of parameters for performing calculations is carried out from the keyboard (2); the keyboard can be made of any electronic, electromechanical switches, of any shape and size, depending on the application of the device.

The microcontroller also transmits and receives data via a wireless communication channel (6), which can be organized using any wireless technology, radio frequency, acoustic, electromagnetic, optical. Via a wireless communication channel, the controller transmits signal measurement data and receives commands from a remote display and control device, which can be any smartphone, tablet computer, desktop computer, laptop, etc. any device that has a display and a wireless communication channel coordinated with the metal detector’s communication channel.

Connector (12) provides connection to the device for headphones, an external power source, and a charger. The connector can also be made of any shape and any size with any number of contact groups and any degree of sealing, depending on the tasks and operating conditions of the device.

The device can also have a built-in charger (13) for rechargeable batteries installed in the battery compartment (14); any rechargeable batteries, as well as alkaline and salt batteries of any voltage, can be used, depending on the tactical operational requirements.

Increasing or decreasing and stabilizing the battery voltage level is carried out by a stabilizer, voltage converter (15). It can be designed as a linear voltage stabilizer of any type, or as a pulsed step-down or step-up voltage stabilizer of any type, depending on the requirements for power stability and energy consumption level.

The use of one receiving-emitting coil reduces the cost of the production process, reduces the manufacturing time of the device, increases the reliability and efficiency of the metal detector by simplifying and reducing the number of components. Since the signal is emitted and received by a single coil, no balance adjustment is required and there is no loss of depth sensitivity to metal objects in highly mineralized soil. Analysis of one signal polarity does not require the use of a synchronous detector, as for bipolar signals implemented in analogues, which reduces the cost of the design, makes it more reliable and increases the sensitivity of the device due to the absence of synchronous detector noise in the useful signal.

Pulse-resonance-eddy current metal detectors can be used:

- for searching for metal objects in the ground, in archaeology, treasure hunting, rescue operations, military mine clearance tasks,

- in the food industry to detect metal objects that have entered the food product from equipment,

- in construction for the detection of copper or aluminum conductors for the purpose of bypassing when drilling or for tasks of extracting and restoring the integrity of conductors,

- in road construction for the purpose of detecting metal objects under the road surface in order to prevent damage to the road machine when metal gets into the working tool,

- in medicine to search for bullets or fragments in the human body,

- in the laundry industry to control textile products for sharp metal objects remaining in them that could damage the mechanism of the washing machine,

- in the field of inspection of citizens and luggage for the detection of prohibited metal objects,

- in any other industry.

Claims (2)

1. A method for non-contact selective detection of metal objects using a pulse-resonance-eddy current method, including sequential generation of pulses of equal duration feeding a coil in the frequency range from 1 Hz to 1 kHz with filling with pulses of a given frequency in the range from 1 kHz to 1 MHz with a change frequencies in each packet of pulses and without filling, pulses of different durations without filling, stopping the power supply to the coil after the completion of the generation process of a packet of pulses with filling or pulses without filling, measuring the increment in the duration of the decay front of the electric current in the coil after generating a pulse without filling of long duration T1 and short duration T4, increment in the duration of the decay front of the electric current in the coil after generating a pulse with filling frequency at which the maximum signal from the object T2 is detected, determination of the type of metal based on the ratio (T1/T2/)T3, where T3=T4/T1. 2. The method according to claim 1, characterized in that a certain integral characteristic of the properties of a metal object in the form of the ratio T1/T2/T3 is displayed graphically or discretely on the display.